581.145.1:577.17
FLORAL INDUCTION,
FLORAL HORMONES AND
FLOWERING
(WITH A SUMMA RY IN DUTCH)
PROEFSCHRIFT
TER VERKRIJGING VAN DE GRAAD
VAN DOCTOR IN DE LANDBOUWWETENSCHAPPEN
OP GEZAG VAN DE RECTOR MAGNIFICUS, MR. J. M. POLAK,
HOOGLERAAR IN DE RECHTS- EN STAATSWETENSCHAPPEN
VAN DE WESTERSE GEBIEDEN,
IN HET OPENBAAR TE VERDEDIGEN
TEGEN DE BEDENKINGEN
VAN EEN COMMISSIE UIT DE SENAAT
VAN DE LANDBOUWHOGESCHOOL TE WAGENINGEN
OP WOENSDAG 24 MEI 1972 TE 16.00 UUR
DOOR
P. A.VAN DE POL
H. VEENMAN & ZONEN N.V. - WAGENINGEN - 1972
This thesis isalso publishedas MededelingenLandbouwhogeschool Wageningen 72-9(1972),
(Communications Agricultural University Wageningen, The Netherlands)
as publication No. 363of the 'Laboratorium voor Tuinbouwplantenteelt'.
Inderganzen Geschichte des Menschen ist kein
Kapitelunterrichtenderfur HerzundGeistalsdie
AnnalenseinerVerirrungen.
(F.vonSchiller)
AanEmmelien
WOORD VOORAF
Gaarne betuig ik mijn dank aan alien die aan dit proefschrift hebben meegewerkt.
In het bijzonder gaat mijn dank uit naar mijn hooggeachte promoter, Prof.
Dr. Ir.S.J. Wellensiek.Ikdank hem voorzijn leidingin deafgelopenjaren,in
het bijzonder voor de wijze waarop dezewerd gegeven: door grote vrijheid te
laten aan deeigeninitiatieven,endezeintussenterichten entestimuleren door
discussieen tot de kern van dezaak doordringende belangstelling.
Alle medewerkers van Tuinbouwplantenteelt dank ik voor de enthousiaste
wijze waarop ze hun onmisbare medewerking hebben verleend.
De Landbouwhogeschool wilik gaarnedanken voor degeboden faciliteiten.
Gaarne gebruik ik deze gelegenheid om mijn ouders te danken voor de
stabiliteit die ze mij geboden hebben in mijn jeugd vanwaar uit ik mij kon
ontwikkelen.
Mijn vrouw, Emmelien, dank ik voor de bijzondere wijze waarop ze haar
aandeel tijdens het tot stand komen van dit proefschrift heeft geleverd, vooral
door inspiratie en vertrouwen.
CONTENTS
Abbreviations, SymbolsandTerms
1. GENERAL INTRODUCTION
0
1
2. MATERIALS AND METHODS
2.1. Plant material
2.2. Growing and grafting
4
4
5
3.EXPERIMENTSWITHSOMECRASSULACEAE
7
3.1. Introduction
7
3.2. Influence of temperature on thefloweringprocess of some Crassulaceae . . .
8
3.3. The floral hormone of Bryophyllum daigremontianum
24
3.4. SD-induction of an early and a late cv. of Kalanchoe blossfeldiana
28
3.5. Graft combinations between K. blossfeldiana and B. daigremontianum . . . . 30
3.6. Conclusions
35
4. THE FLORAL HORMONE OF XANTHIUM STRUMARIUM
37
4.1. Floral hormone and floral development
37
4.2. Floralstagesatdifferent balancesbetweenvegetativeandgenerativedevelopment
as a result of grafting
42
4.3. Factors influencing the transmission of floral hormone by grafting
44
4.4. Interaction of induction and floral hormone
53
4.5. Comparison of an early, a middle and a late line
54
4.6. Conclusions
58
5. EXPERIMENTS WITH CARYOPHYLLACEAE
5.1. Introduction
5.2. Induction
5.3. Grafting-experiments
5.4. Silenearmeria
5.5. Melandriumalbum
5.6. Conclusions
60
60
60
62
65
70
74
6. GENERAL DISCUSSION
76
7. SUMMARY
82
8. SAMENVATTING: Bloei-inductie, bloeihormonen en bloei
9. ACKNOWLEDGEMENT
10. REFERENCES
84
86
87
Abbreviations,SymbolsandTerms.
= long day, 16h light and 8hdarkness.
LD
= short day, 8h light and 16h darkness.
SD
= long-day plant.
LDP
= short-day plant.
SDP
= long-short-day plant.
LSDP
= day-neutral plant.
DNP
=
continuous light.
CL
= receptor, beingthe non induced graft partner.
r
= defoliated receptor.
r= donor, beingthe induced graft partner.
d
= receptor grafted on receptor (control).
r/r
= receptor grafted on donor.
r/d
donor grafted on receptor.
d/r
= shoot of a grafted receptor r l5 regrafted on a new receptor
d/rx ->rjr2
nr
= treatment number.
= quotientofthenumberoffloweringreceptors(ina graftingexperiment) or flowering plants (in an induction experiment) on the total number of survived receptors or plants.
=
percentage
offloweringplants or shoots.
/o
=
average
number
of daysfrom the beginning of a treatment
days
until macroscopically visibleflowerbuds.
GA3
= gibberellicacid, gibberellin number 3.
°1
= temperature in °Cduring the light.
°d
= temperature in °Cduring the dark.
h
= hour.
sum
= sum of the products of temperature times hours per 24
hours.
induction
= deblocking of the synthesis offloralhormone.
floralhormone = one or more substances, usually synthesized in induced
leaves and initiating the formation of floral primordia in
the receptive meristems.
q
1. GENERAL INTRODUCTION
1.1. HISTORICAL REVIEW
Since the invention of an incandescent lamp by EDISON in 1879 many investigators showed that flowering of several horticultural plants could be
accelerated byextendingnaturaldaylengthswiththeaidoftheselamps (EVANS,
1969). The general explanation was that the growth and development were
promoted by additional light. However, TOURNOIS (1912) was the first to
demonstrate the promotive influence of short daylength on thefloweringof
hops and hemp. It was KLEBS(1913),investigating the influence of continuous
lightonthefloweringofSempervivumfunkii, whoconcluded thattheadditional
light wasacting 'catalytically and not as a nutritional factor'.
The recognition of daylength as a major flowering controlling factor dates
from GARNER and ALLARD (1920),who found the SD response of Mammoth
tobacco and Peking soybeans and introduced the terms photoperiod for daylength, photoperiodism for the responseof organismsto the relative lengthsof
light and darkness.
Experiments by GARNER and ALLARD(1925)with COSMOS and by RAZUMOV
(1931) on photoperiodic control of tuberization in potatoes suggested that it
werethe leaveswhich initially respond to daylength.
The term photoperiodic induction wasintroduced into flowering-physiology
by LUBIMENKOand SZEGLOVA (1932). KNOTT (1934) gave different daylengths
separatelytotheshootapexand totheleavesofspinach,demonstrated thatthe
leavesaretheorgansreacting todaylength,and concluded that theresponse to
a photoperiod, favourable for reproductive growth, may be the production of
some substance or stimulus, transported from the leaves to the growing-point.
In 1865 SACHS already suggested the existence of 'flower forming substances'
whichcouldmovewithin aplant(in EVANS,1969).KNOTT'Stechniquewasused
by other investigators, who found similar mechanisms in severalplants.
The definite proof of the concept of a floral hormone followed soon from
grafting-experiments, in which was shown that receptor plants under non
inductive conditions could be brought tofloweringby grafting them to donor
plantsofthe samestrain,whichhad previously been keptunder inductive daylengthconditions.ThefirstexperimentsofthiskindwerecarriedoutbyKUIJPER
and WIERSUM(1936)with Glycinemaxand almost simultaneouslybyCHAJLAKHYAN(1936b) with Perilla and Helianthus and MOSHKOV (1937)with tobacco.
CHAJLAKHYAN(1936a)postulated thataflowerhormoneregulatestheprocesses
of development. Hechristened the hypothetical substanceflorigen.Afterwards
CHOLODNY(1939)proposed the term anthesin and VAN DE SANDEBAKHUYZEN
(1947)following WENT'S nomenclature (1938) of organ-forming substances introduced thetermanthocaline. Manycasesofsuccessful transmission of floweringbygrafting followed. LANG(1965) summarized about 35cases.
Meded. Landbouwhogeschool Wageningen 72-9(1972)
1
Thenatureoffloralhormone isoften discussed. Evidencefor a moregeneral
character came from experiments in which donors of one daylength response
typecouldinducefloweringinreceptorsofadifferent responsetype.Extractsof
flowering plants have never induced reproduceable flower formation in vegetative plants. Moreover none of the efforts of chemical identification of the
floralhormone met with success. Sothe character offloralhormone can until
nowonlybestudied invivo,byinducingpartsofplantsand bygrafting experiments.
Besides floral hormones, in some plants floral inhibitors could be demonstrated. BHARGAVA(1964, 1965)even proved transmissable floral inhibitors in
Salviaoccidentalis and Perilla crispa. In the latter case a hormone-like floral
inhibitor isformed, which isdirectly translocated to the growing-tip, where it
interferes with the functioning of the floral stimulus. This inhibitor does not
interfere with the production or the translocation of the floral stimulus.
Anotherfactor whichmaydeterminefloweringistemperature,withamechanism,sometimesdiffering from photoperiodism. Theaction oflowtemperature
hasbeencalled vernalization by WHYTEand HUDSON(1933).In mostcases the
siteofperception oflowtemperature isnot separated from theplacewherethe
effect manifests itself:both are localized in a growing apex (WHYTE, 1948),or
perhaps in a meristem. For biennial Hyoscyamusniger, MELCHERS (1936)
showed that the low temperature requirement can be fulfilled by grafting a
vernalized growing-point near to a non-vernalized one.After grafting with the
short-day plant 'Maryland Mammoth' tobacco,flowerformation in cold requiringH.nigeroccurredirrespectivewhetherthedonorswerekeptinshortday
orinlongday.So,evenwhenthistobaccovarietywasnotcapableof flowering
itself,itcould stillsupply astimuluswhichcausedfloweringintheunvernalized
H. niger stocks.Therefore, MELCHERS(1939)concluded that the transmissable
stimulus in biennials (produced after a low-temperature treatment) is different
from floral hormone. To stress their specific natures he called the former
vernalin.
A second case of temperature determining flowering is induction by high
temperature. VAN DE VOOREN(1969) intensively worked out this phenomenon
for the LDP Silene armeria. Heconcludedthat high temperaturesabove 30°C.
prevent a process, which is supposed to be the rebuilding of an inhibition
('reblocking') during the dark period.
Besides photoperiodism and temperature, some chemicals, especially some
gibberellins, promote flowering. Studies about differences in behaviour of
floralhormones in different plants gave more information about the character
of the floral hormones. Until now only 3plants have been reported with the
particular property that receptors, brought intofloweringby grafting, can act
as a donor in a next grafting. These plants are Xanthium strumarium (LONA,
1946), Bryophyllum daigremontianum (ZEEVAART and LANG, 1962) and Silene
armeria (WELLENSIEK, 1966).In literature thisphenomenon iscalled: 'indirect
induction by the floral hormone' (ZEEVAART and LANG, 1962,p. 537); 'auto2
Meded. Landbouwhogeschool Wageningen 72-9(1972)
catalytical multiplication of the floral hormone' (WELLENSIEK, 1966, p. 9) or
'secondary induction' (EVANS, 1971, p. 378). Classic is the comparison of
Xanthium strumarium and Perilla crispa, worked out by ZEEVAART (1958). In
contrast to Xanthium, receptors ofPerilla, in spite of aflowering-reaction,do
notreceivedonorcapacitybygrafting. Thisraised thequestion of theexistence
of different floral hormones.
1.2. SCOPE OFTHE PRESENT EXPERIMENTS
Letusfirstdefine somefrequently usedterms.'Induction' willberestricted to
'deblocking of thesynthesis offloralhormone', indicating the process bywhich
an inhibition or blocking offlowerformation in vegetative plants is removed,
followed by synthesis offloralhormone (WELLENSIEK, 1969).'Floral hormone'
staysfor: 'oneormoresubstancesofanunknowncomposition,synthesizedusually
ininducedleaves, andinitiating theformationoffloralprimordia inthe receptive
meristems.'A choice out of the terms 'indirectinduction', 'autocatalytically
multiplyingfloralhormone' and 'secondary induction' could not be made since
until now no clear evidence about the mechanism of the synthesis of floral
hormone in non exogenously induced parts of plants could be demonstrated.
It is questionable whether floral hormone can act as an induction factor, or
whether it can multiply itself autocatalytically. Therefore, the term 'nonlocalizedsynthesis' isused, indicating that the synthesisisnot restricted to the
induced part of the plant, contrary to the clear example of Perilla crispa with
strictly 'localizedsynthesis'. The properties offloralhormones were studied by
investigation offactors influencing itssynthesis,itstransmissionanditsactivity,
and by trying new graft combinations. The central question is whether other
explanations for differences in behaviour offloralhormone can be given than
the assumption of the existence of different floral hormones. Comparison of
the plants with non-localized synthesis of floral hormone mutually and with
other plants was supposed to give useful information. Therefore, the former
plants and plants of their families, being the Compositae, Crassulaceae and
Caryophyllaceae, were chosen as experimental material.
Meded. Landbouwhogeschool Wageningen 72-9(1972)
2. M A T E R I A L A N D M E T H O D S
2.1. PLANT MATERIAL
Crassulaceae:
Bryophyllum daigremontianum (R. HAMET et PERR.) BERG., originating from
the Laboratorium voor Tuinbouwplantenteelt, Wageningen. Propagated vegetatively by means of leaf plantlets.
Bryophyllum pinnatum (LAM.) OKENkindly supplied byProf.J.T H . HACKMAN,
Enschede. Propagated vegetatively by means of cuttings.
Kalanchoe blossfeldiana cv.'Vulcan' and cv. 'Hendrik van der Dussen' were
obtained from commercial sources. The cv. 'Annette' and cv. 'Josine' were
kindly supplied byMiss L. LEFFRING, Proefstation Aalsmeer. Allthese cultivars
were propagated vegetatively by means of cuttings.
Kalanchoejongmansii, HAMET et PERRIER.
Kalanchoe manginii, HAMET et PERRIER.
Both thesespecieswere kindly supplied bytheBotanic Garden ofthe University
of Leiden. Propagation vegetatively by means of cuttings.
Compositae:
Xanthium strumarium L., from the Laboratorium voor Tuinbouwplantenteelt, Wageningen. This strain was originally obtained from D R . J. A. D.
ZEEVAART, U.S.A. Two other strains were kindly supplied by Prof. C. M A C MILLAN, U.S.A. Thenomenclature is according to SALISBURY (1969). The propagation was generative.
Rudbeckia bicolor NUTT., obtained from a commercial source and propagated generatively.
Caryophyllaceae
Chosen from a collection of 50 species, brought together by WELLENSIEK
(unpublished) and determined by Mrs. N. E. NANNENGA-BREMEKAMP of the
Herbarium Vadense, Wageningen.
Silene armeria L., originally obtained from D R . A. LANG, U.S.A. The other
species are listed in table 39(p.60-62). Thepropagation was generative.
Labiatae
Perilfa crispa (THUMB.) TANAKA. Thenomenclature isaccording to ZEEVAART
(1969b). Seeds were obtained from a commercial source and the propagation
was vegetative by cuttings.
Meded. Landbouwhogeschool Wageningen 72-9(1972)
2.2. GROWING ANDGRAFTING
Plants were grown in a greenhouse at approximately 20°C. For LD natural
day lightwassupplemented by MLL 160WPhilipslamps,givingat plantlevel
at least 1750 erg. cm - 2 , sec -1 . The generally used LD conditions were 16h
lightand 8hdark.In ordertoreducetheinfluence ofpossibletechnicaldisturbances,the LDconditions for Xanthium strumarium werekept at 20hlight and
4 h darkness. Cuttings were made in a mist propagation bench. Temperature
experiments were done in a phytotron with TL 55 Philips lamps and a light
intensity of about 35000 erg.cm -2 . sec. -1 at plant level.
The mostlyused method of grafting was an ordinary cleft graft in the stem.
Theplaceofgraftingwassurroundedbyaspongyrubberband,calledstericrepe,
madebyBeaconand JanisLTD,Southampton Row, London,W.C.I. Another
method wasacleft graft inthe rosette.In thiscasethegraft partnerswereheld
together by ordinary hair grips (curly grips). According to literature, receptor
rosettesareoften treated withGA3for stemelongation and splitgrafting inthe
stem isapplied in the elongated stem. However, the rosette-grafting technique
was developed and used in thosecaseswherethe receptor rosette could not be
elongated by GA3 without therisk of partial or completeinduction by GA3 as
such.Photo 1 showsarosettegrafting of Silenearmeria.Thegrafted plants were
kept in a plastic cabinet in a controlled LD or SD room at 20°C with TL29
PHOTO 1. Rosette-grafting d/r.
A donor shoot of Silenearmeriawas cleft grafted in a vegetative rosette of the same species.
The graft partners wereheld together byan ordinary hair grip.
Photo left: 3weeks after the grafting.
right: 7 weeks after the grafting, the receptor is flowering.
Meded. Landbouwhogeschool Wageningen 72-9(1972)
5
Philips lamps of 65W, resulting in a light intensity of about 8000erg. cm - 2 .
sec -1 , at plant level. In the plastic cabinet the air humidity was kept high by
misting twice a day with water, mixed with 1g/1 TMTD to protect the plants
against fungi. When the graft union had been established, the plants were
hardened off, and put in the LD or SDdivision of a greenhouse.
Meded. Landbouwhogeschool Wageningen 72-9(1972)
3.EXPERIMENTSWITHSOMECRASSULACEAE
3.1. INTRODUCTION
Most ofthe Crassulaceaearenatives ofMadagascar. Besidesthe ornamental
valueofKalanchoeblossfeldiana, thefamily ofthe Crassulaceae provedtobeof
great interest for research on the physiology of flowering.
ROODENBURG (1939) already noted that short days acceleratefloweringof
K. blossfeldianaand HARDER and his school (1940) confirmed that thisspecies
represents a typical short-day plant. On account of the quantitative relation
between induction and the number offlowersproduced, this plant has been
useful in numerousinvestigations into photoperiodic behaviour and the underlyingmechanisms.
DOSTAL (1949, 1950) discovered the dual daylength requirement of Bryophyllum crenatum and B. tubiflorum (= B. verticillatum). Both speciesremained
vegetativeif keptincontinuous LD or SDfor twoyears,whiletheshift LD -»
SDdid result inflowerformation. RESENDE(1952)found that B. daigremontianum,K.mocambicana, K.rotundifolia and Aloebulbillifera alsoneeded the shift
LD -»SD forflowerinduction and called this newclass of photoperiodically
sensitive plants long-short-day plants(LSDP).
Soon after gibberellicacid (GA3) was discovered asa chemical which could
inducefloweringin a number of cold-requiring plants, BUNSOW and HARDER
(1956)reported thet GA3 can substitute for the LDbut notfor theSDrequirement in two Bryophyllum species.
DOSTAL(1949, 1950)reported thatfloralhormone could betransmitted from
a donor to a receptor in B. crenatumand B. tubiflorum. ZEEVAART (1958)
extendedtheseobservationstoB.daigremontianum, and RESENDE(1959)proved
transmission offloweringbetween hybrids of different species ofBryophyllum.
CARR and MELCHERS(1954)succeeded intransmitting thefloralhormone from
induced plants of K. blossfeldiana acting as donors to non-induced receptors.
Theyalsocould provetransmission ofthefloralhormone ofSedumkamtschaticumas a donor to K. blossfeldiana as a receptor. ZEEVAART (1958) reported
positivetransmission ofthefloralhormoneofKalanchoeblossfeldianato Sedum
spectabile and S. ellacombianum and from both these long-day plants to K.
blossfeldiana.
Surveyingtheseresults,thequestionarosewhetherthefamily ofthe Crassulaceaehasoneuniversalfloralhormone,independent from thedifferences indaylength requirement and growth habit. In the present experiments factors influencing induction, production of floral hormone and reaction on floral
hormone wereinvestigated, especially temperature and somenewgraft combinations. The floral mechanisms of some Crassulaceae were compared, particularly the relations between K.blossfeldiana and B. daigremontianum.
Meded. Landbouwhogeschool Wageningen 72-9 (1972)
7
3.2 INFLUENCE OF TEMPERATURE ON THE FLOWERING OF SOME
CRASSULACEAE
3.2.1. Introduction.
HARDER and VON WITSCH (1940) found that a change of temperature per
cycle of SD during the induction of K. blossfeldiana gives a stronger floral
impulse than a constant temperature.
It were ZEEVAART and LANG (1962), who discovered that induction of B.
daigremontianum and B. crenatum by LSD as well as by GA 3 -treatments in SD,
is only possible when a day temperature of 23°C iscombined with a night temperature of 15°C or less. A night temperature of 19°C or higher prevented the
induction. So it is clear that temperature plays an important role during
induction of K. blossfeldiana, B. daigremontianum and B. crenatum.
In the presentexperimentsthe needfor thermoperiodicity during induction of
K. blossfeldiana and B. daigremontianum is compared.
HARDER and VON WITSCH (1940) and RUNGER (1959) found that in K. blossfeldiana the flowering influenced by temperature is light independent. This
means that the lowtemperature can act in the light as well asin the dark period.
The question arose whether the reaction of B. daigremontianum is similar to
K. blossfeldiana as found by HARDER and VON WITSCH, cited above.
B. daigremontianum beinga LSDPhastwo inductivereactions, onein LD and
one in SD.The influence of temperature on these two daylength reactions could
give more information about these processes.
Another important question will be: What is the influence of the external
factors on the flowering after induction and are there differences in comparison
with the inductive process? RESENDE and VIANA(1948) alreadydiscovered that
generative B. daigremontianum becomes vegetative when the induced leaves
received light of a low intensity. RESENDE (1965) reported that in LD with
warmnights theinflorescences ofB. daigremontianum tend torevert to vegetative
growth. In my first grafting-experiments the generative B. daigremontianum
donor rootstocks becamevegetative.Theseresultsshow that not only induction,
but also the induced state can be influenced by external and unknown factors.
The influence of temperature on the induced state of B. daigremontianum and
K. blossfeldiana therefore is investigated.
3.2.2. GA3 + SD-induction of B. daigremontianum.
Experiment 1. Plants grown in SD from plantlets were sprayed, at an age of
4 months, with GA 3 100 ppm once and brought to the phytotron, where they
received SD at different temperature combinations. As B. daigremontianum can
form various degrees of inflorescence development due to the level of induction
(PENNER, 1960),observations were made not only on flowering as such, but also
on floral stage, total lengths of the upper 4 internodes, total lengths of the
lateral floral shoots and the plant length. The upper 4 internodes were chosen,
because they concern a normally developed inflorescence. The data were
obtained 74days after the beginning of the GA 3 + SD-induction and hence are
8
Meded.Landbouwhogeschool Wageningen 72-9(1972)
aninstantaneousobservationof the degreeofinflorescencedevelopmentdueto
different temperaturetreatments.
Themain resultsarepresented inTable 1whichshowsthat completeinduction + realization(stage6) arepossiblewhenthesumoftheproductsoftemperaturetimeshoursper24 hoursis472orless.Asumof 504 resultedinmoderate
flowering, whereas sums of 536and higher did not have any effect. This corresponds with the conclusions of ZEEVAART and LANG (1962): induction is
possiblewhenadaytemperatureof23°C iscombinedwithanighttemperature
of 15°Cor lower, meaninga temperaturesumof 424orlower. In theirexperiments nofloweringoccurred when a day temperature of 23°C or higher was
TABLE 1. The flowering response of B. daigremontianumafter GA 3 + SD-induction and
realization at different temperature treatments.
stage = average stage of thefloweringplants, according to PENNER (1960):
stage 0. Plants completely vegetative, no axillary shoots
stage 1. Axillary shoots grown out partially
stage 2. Vegetative inflorescence: axillary shoots fully developed, but no flower buds
stage 3. Inflorescence with a few flower buds; bracts show phyllody
stage 4. No phyllody, but inflorescence with very short internodes
stage 5. Normal inflorescence
stage 6. Normal inflorescence with additional inflorescences arisingfrom theupper leaf pairs
internodes= mean sum of the lengths in cm of the upper 4 internodes
shoots = mean sum of the lengths in cm of the axillary floral shoots
* = no observiations made
Further abbreviations see p.0
number of plants per treatment: 16
nr.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
°1
13
21
17
25
13
21
17
25
13
21
17
25
4hl3+ 4h21
2hl3+ 6h21
13
21
17
25
21
25
°d
13
9
13
9
17
13
17
13
21
17
21
17
21
21
25
21
25
21
25
25
sum
312
312
344
344
376
376
408
408
440
456
472
472
472
488
504
504
536
536
568
600
%
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
0
0
0
0
Meded. Landbouwhogeschool Wageningen 72-9(1972)
days
43
37
43
37
36
37
35
30
33
43
69
oo
oo
(X)
oo
stage
6
6
6
6
6
6
6
6
6
6
6
6
6
5
5
4
0
0
0
0
inflorescence
internodes
shoots
20
•
24
*
29
37
29
43
17
18
•
22
•
33
45
26
66
27
16
2
1,5
1,5
1,5
1,5
17
0,2
0
0
0
0
combined with a night temperature of 19°C or higher, meaning a temperature
sum of 488 or higher.
Table 1 also showsthat lowtemperature,tendingto declinethe temperature
sum, works in the light as well as in the dark period. This means that the
temperature influence is light independent. It appears that thecombination of
high day temperature with low night temperature (25713°, treatment 8)gives
thebest result. Comparison oftreatments 7and 8, 17°/170and 25713°respectively,both with a temperature sum of 408, shows a betterfloralresult for the
latter.
nr. 1
7
nr. — treatment number of table 1(p. 9)
PHOTO 2. Inflorescencedevelopmentof B. daigremonlianumasaresultofGA$ + SD-induction
plusrealizationat constanttemperatures of 13, 17and21''C.
Photo: 74 days after the beginning of the inductive treatment.
Photos 2, 3and 4show the influence of different temperature conditions on
theflowering,(p.10,11,12).
Experiment 2. In contrast to experiment 1 induction and realization are
separated as well as possible. Similarly to those of experiment 1plants were
sprayed with GA3 100 ppm once and brought to the phytotron, where they
received SD at different temperature conditions for 21 days, followed by LD
21°/13°,wherethefloweringastheexpression ofinduction plusrealizationwas
observed. Hence, besides the part of the realization which already occurred
during the SD-treatment, therest took placeunder the sametemperature con10
Meded. Landbouwhogeschool Wageningen 72-9(1972)
M
* » l g » ^ « w « W » » r w « n f l W f f «T>^*.tf°i«'**i**rs*:??*.-.*?*^
treatment number of table 1 (p.9)
PHOTO 3. Inflorescencedevelopmentof B. daigremontianumasaresultofGA3 + SD-induction
plus realizationat a day temperatureof 13"C combinedwithnight temperaturesof 17,21and
25°C.
Photo: 74 days after the beginning of the inductive treatment.
ditions,sothatdifferences infloweringwillmainlybeduetotheinfluence ofthe
different temperature treatments during induction.
Table 2 shows that induction is possible when the temperature sum lies
between 312and 568,whileevensomefloweringoccurred between the sumsof
248 and 312. Comparison with experiment 1shows that induction is possible
between widermargins of temperature than induction + realization. Thissuggeststhat mainlytherealization offlowering isinfluenced bytemperature. Itis
remarkable that there are no differences between the floral stages while the
lengths of the inflorescences, measured 122days after the beginning of induction,hardly differed. Treatment 12withthetemperaturecombination of9°/21°
showsthefewest daystillvisibleflowerbuds,while 17°/17°atthesametemperature sum of 408, results in 6days later flowering.
Photo 5demonstrates the results of treatments 14and 25of table 2.(p.14)
Experiment3. RUNGER (1959) gave a SD-period of 12days with a shift of
temperature after 6 days. His results are cited in Table 3. Temperatures of
20°C or 25°C during the first period followed by 15°C or 20°C during the
second 6days are the best.
Similar to the experiment of RUNGER (1959) with Kalanchoe blossfeldiana,
Meded. Landbouwhogeschool Wageningen 72-9(1972)
11
^..„,J
nr. = treatment number of table 1 (p.9)
PHOTO4. Inflorescencedevelopmentof B. daigremontianum asaresultofGA3 + SD-induction
plus realization at a night temperature of 13"C combinedwithday temperatures of 17,21and
25°C.
Photo: 74 days after the beginning of the inductive treatment.
one change of temperature during the wholeinductive treatment of B. daigremontianum istried inthenextexperiment. Youngplants of B. daigremontianum
obtained from plantlets and grown in the SD division of a greenhouse, were
sprayed with GA3 100ppm and moved to the phytotron where they received
different cyclesofSDat temperature conditionspresented inTable 4,followed
byLD21°l/13°d.(p.14)
Treatment 1 demonstrates that 10cyclesof SDat 25CCarenot sufficient for
induction, while treatment 2 shows that induction is possible at 25°C, so the
last 4 cycles of treatment 2 are necessary for induction. Comparison of treatments 2, 6and 8shows that induction during the first 10cycles of SD occurs
optimally, in spite of a temperature of 25°C. However, during the following 4
inductive cycles 13°C is better than 25°C, while treatments 3, 4 and 9 show
that after induction a temperature of 25° acts negatively.
The conclusion is that hardly induction but rather the resulting processes
are influenced by too high a temperature. This corresponds with the results of
experiments 1and 2.
>
12
Meded.Landbouwhogeschool Wageningen 72-9(1972)
TABLE 2. Thefloweringresponse of B. daigremontianum after GA 3 + 3 weeks SD-induction
at different temperature combinations followed by LD 21°I/13°d.
nr.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
°1
9
13
9
17
13
21
9
17
25
13
21
9
17
25
13
21
9
17
25
13
21
17
25
21
25
°d
9
9
13
9
13
9
17
13
9
17
13
21
17
13
21
17
25
21
17
25
21
25
21
25
25
sum
•216
248
280
280
312
312
344
344
344
376
376
408
408
408
440
456
472
472
472
504
504
536
536
568
600
%
q
0/8
1/8
3/8
7/8
7/8
8/8
8/8
8/8
8/8
8/8
8/8
8/8
8/8
8/8
8/8
8/8
8/8
8/8
8/8
8/8
8/8
8/8
8/8
8/8
2/8
0
13
38
88
88
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
25
days
stage
inflorescence
internodes
shoots
10
44
33
45
47
44
42
44
43
45
45
43
46
43
44
42
45
41
42
42
41
42
40
40
33
0
106
50
95
90
116
96
90
97
81
83
68
72
82
82
84
69
78
84
84
70
78
94
74
38
0
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
CV)
40
42
38
34
32
31
31
35
32
30
29
35
31
31
35
34
34
35
34
36
37
36
38
42
TABLE 3. Average number of axillary shoots withflowersofK.blossfeldianaasa result of one
change of temperature after 6days during an inductive period of 12cyclesof SD(Cited from
RONGER, 1959).
Temp. in the second period of 6days
Temp. in thefirst
perioc1of 6 days
15
15
20
25
30
1,6
4,7
5,9
1,6
20
25
average number of axillary shoots withflowers
0,6
4,1
3,2
3,8
0,0
0,0
2,2
0,4
30
0,0
0,0
0,0
0,0
3.2.3. LSD-induction of B. daigremontianum.
B. daigremontianum, needing 2 daylengths for induction, will have 2 daylength dependent processes preceding the synthesis of floral hormone. It is
Meded.Landbouwhogeschool Wageningen 72-9 (1972)
13
nr.
25
nr. — treatment number of table 2(p.13)
PHOTO 5. Inflorescence development of B. daigremontianum asa result ofGA3
followed byLD 21°U13°d.
Left: SD at 25"1/25°d. Right: SD at 25°l/13°d
Photo: 74 days after the beginning of SD induction.
+ 21days SD
TABLE4. FloweringofB.daigremontianumasaresult ofGA 3 + SDtreatments,with different
cycles of SD and no or one change of temperature, followed by LD 21°l/13°d.
nr.
1
2
3
4
5
6
7
8
9
10
14
GA 3 + SD treatment
flowering
days 13°
days25°
days 13°
q
0
0
0
0
0
0
0
0
10
20
10
14
20
0
0
0
0
4
4
10
10
0
0
0/8
5/8
2/8
0/8
0/8
8/8
0/8
8/8
0/8
8/8
PO
0
10
0
10
10
o>
%
0
63
25
0
0
100
0
100
0
100
days
stage
oo
42
51
oo
0
6
6
0
0
6
0
6
0
6
PO
31
PO
31
PO
45
Meded. Landbouwhogeschool Wageningen 72-9(1972)
questionable, when the LD component is available as a precursor, whether a
separate SD component isformed or directly thefloralhormone.
The inductive circumstances of these two daylength processes could be optimal at different temperature levels. In order to investigate this, the temperaturemustbealtered inlightanddarkness,in LDaswellasinSD.Aproblemis
that with 5different temperatures 5 4 = 625combinations are possible.Therefore a choice had to be made.
Experiment4. Vegetative plants with 15 pairs of leaves, grown up in SD,
weremovedtoaphytotronwheretheyreceived 6weeksof LD followed bySD,
both at different temperature conditions. Thefloweringwas observed in SD
76days after the shift LS->SD and isdue to the influence of temperature on
induction + realization.
In Table 5,comparison oftreatments 1,2and 3showsthat at a similar SDtreatment of 21°/13°,the LD-treatments at 13721° and 13°/25° have better
effects onfloweringthan 17°/17°. Comparison of the treatments 3,4, 5and 6
shows that at the same LD-treatment of 17°/17°, the SD-treatment of21°/13°
isthe best, while SD 13°/25°doesnot givefloweringat all. Sohere is a clear
parallelism with the influence of temperature on the GA3 + SD-induction. It
isobvious that themarginal LD-induction of 17°/17°willreduce the marginal
temperature sum for SD-induction. Treatments 7, 8 and 9 show that LDinduction occursverywellat temperatures ofa sumbetween 504and 600.The
following SD-induction however isnot possible at a sum of600.
Thefloweringresults are illustrated in photo 6. (p.16)
3.2.4. Influence of temperature onthefloweringof B. daigremontianum.
The preceding experiments clearly showed the influence of temperature on
induction. However, what is the influence on the other floral processes like
inductive state and synthesis and activity offloralhormone?
TABLE 5. The flowering of B. daigremontianumas a result of LSD-induction at different
temperature combinations.
Number of plants per treatment = 5.
Annotations: internode length = average length of the upper 4 internodes
shoot length = average length of the total floral shoots.
nr.
°1
LD
°d
sum
°1
SD
°d
sum
%
days
1
2
3
4
5
6
7
8
9
13
13
17
17
17
17
25
25
25
21
25
17
17
17
17
13
25
25
376
408
408
408
408
408
504
600
600
21
21
21
17
13
13
25
25
25
13
13
13
17
21
25
13
13
25
392
392
392
408
440
504
408
408
600
100
100
100
100
80
0
100
100
0
35
40
45
47
41
oo
•
*
oo
flowering
Meded. Landbouwhogeschool Wageningen 72-9 (1972)
plant inter- shoot
length
stage lengthnode
length
6
6
6
3
4
0
6
6
0
139
135
102
93
95
79
•
•
•
51
47
24
18
17
3
•
•
•
110
118
65
22
25
0
*
•
*
15
%-7r
13/21 21/13
13/25 21/13
17/17 21/13
nr. 1
2
3
nr. — treatment number of table5
17/17 17/17
4
%-'K
17/17 13/21
17/17 13/25
6
PHOTO 6. Inflorescence development of B. daigremontianum as a resultof LSD inductionplus
realization at differenttemperaturecombinations inLD and SD.
. Photo: 76 days after the shift LD ->• SD.
Experiment 5. Flowering plants, 6weeksafter thebeginning of GA3 + SDinduction, received different temperature treatments in SD.
Table 6 shows that floral development is influenced by temperature. Treatments6and7showthatfloweringplantscanreverttothevegetativestagewhen
the temperature sum per 24hours is higher than 536.
Photo 7showsthe results.
Experiment 6. Old generative plants, 5months after GA3 + SD-induction,
received different temperature treatments in SD or in LD.
Table7,treatments 1-8, showsthat inSDatemperaturesumabove472stops
TABLE 6. Theflowering-stageofgenerative B.daigremontianumafter 2monthsof temperature
treatment in SD.
16
nr.
°l
°d
sum
stage
1
2
3
4
5
6
7
25
27
13
25
17
21
13
17
25
21
25
25
25
408
472
504
536
536
568
600
6
6
6
6
6
3
2
25
.
Meded. Landbouwhogeschool Wageningen 72-9(1972)
nr.
5
nr. —treatment number of table 6
PHOTO 7. Flowering-stagesofB. daigremontianumafter7weeksoftemperaturetreatment in SD.
Photo: 49 days after the beginning of the temperature treatment.
the flowering of old generative plants. Treatments 9-13 show that in LD a
temperature sum of 472 isalready too highfor thecontinuing of flowering.
Photo's 8and 9show theresults.
TABLE 7. Theflowering-stageof old generative plants of B. daigremontianum after 2 months
of temperature treatment in SD or LD
nr.
daylength
°1
°d
sum
stage
1
2
3
4
5
6
7
8
SD
SD
SD
SD
SD
SD
SD
SD
17°C
17
25
25
17
25
25
25
9°C
13
9
13
17
17
21
25
280
344
344
408
408
472
536
600
6
6
6
6
6
6
3
0
9
10
11
12
13
LD
LD
LD
LD
LD
25
25
25
25
25
9
13
17
21
25
472
504
536
568
600
2
2
0
0
0
Meded. Landbouwhogeschool Wageningen 72-9(1972)
17
25/25
25/21
nr:
8
7
nr. — treatment number of table 7
25/17
6
25/13
4
25/9
3
PHOTO 8. Flowering-stages of oldgenerative plants of B. daigremontianum after 2 months of
25°C duringthe lightperiod of SD, combinedwithdifferenttemperatures(25, 21, 17, 13 and
9°C) duringthedarkperiod.
Photo: 64 days after the beginning of the temperature treatment.
25/25
25/21
nr:
13
12
nr. = treatment number of table 7
25/17
11
25/13
10
25/9
9
PHOTO 9. Flowering-stages of oldgenerative plants of B. daigremontianum after 2 months of
25°C duringthe lightperiod of LD, combinedwithdifferenttemperatures(25, 21, 17, 13and
9°C) during thedarkperiod.
Photo: 64 days after the beginning of the temperature treatment.
3.2.5. Influenceof temperature on the inductive state of B. daigremontianum
studiedbygrafting.^ r,\
Astoo highatemperature sumstopsthefloweringof a generative plant,itis
questionable what happens to the inductive state, being the capacity of producing floral hormone. Also, what happens with the donor capacities?
Experiment 7. Vegetative shoots were grafted"on generative rootstocks, 7
weeks after^ the beginning of GA3 + SD-induction in 21°/13°. The grafted
plants* 7d received LD or SD at different temperature combinations and the
flowering result of the receptors was observed.
Table 8shows that transmission offloweringonly occurs during a temperature sum of 552or lower, both under LD and SD-conditions.
Photo 10shows the results of grafting at SD25°/25°and 25°/13°.
Experiment 8. The results of the preceding experiment raisethe question:is
thereaction ofthegrowing-point tofloralhormone suppressed by temperature
or are thefloralhormone and its synthesis destructed?
Young generative plants, 7weeks after the beginning of GA3 + SD-induction, received 2 or 4 weeks LD at 21°/13° or 25°/25°. After this temperature
treatment the plants were grafted in the combinations r~/d in LD 21°/13°.
Table 9shows thefloweringofthe receptors. It appears that 2weeks of LD
25°/25° is too short to destruct the donor capacity of the rootstocks. A treatment of4weeksofLD25°/25°,however, islongenough to makethe influence
of the temperature irreversible, resulting in nofloweringof the receptors.
Itisobviousthatahightemperaturesumstopstheactivityoffloralhormone,
produced before the temperature treatment, and moreover destructs the inductive state.
Experiment 9. The question arises whether re-induction is possible of the
leavesfrom whichtheinductivestatewasdestructedbyahightemperaturesum.
Plants, 8 weeksafter thebeginning ofGA3 + SD-treatment, received temperature treatments. In order to determine the inductive state,the donor capacity
was tested by grafting the combination rjd.
The receptors of grafting 1of Table 10showthat the donor capacity issuppressed by 25°/25° (treatments 2 and 3). Next the receptors were removed to
prevent induction of these shoots by GA3. The table shows that the axillary
TABLE 8. ThefloweringofreceptorshootsofB.daigremontianum,grafted ondonorrootstocks
and grown at different temperatureconditions.
flowering
nr.
daylength
1
2
3
4
5
SD
SD
SD
LD
LD
°1
25
4h13 + 4h25
25
25
25
°d
13
25
25
13
25
Meded. Landbouwhogeschool Wageningen 72-9 (1972)
sum
408
552
600
504
600
q
%
days
16/16
16/16
0/16
14/15
0/16
100
100
0
93
0
24
23
oo
22
oo
19
nr:
5
nr. — treatment number of table8
PHOTO 10. Transmission offloweringimpulseof B. daigremontianum at different temperature
conditions.
Left: LD 25°l/25°d Right: LD 25°l/13°d
Photo: 47 days after grafting in LD.
TABLE 9. Flowering of receptors of B. daigremontianum, grafted on donors which received
2 or 4 weeks of temperature treatment before grafting.
nr.
1
2
3
4
flowering
donorbefore grafting
2 weeks LD 21/13
2 weeks LD 25/25
4 weeks LD 21/13
4 weeks LD 25/25
q
%
days
10/10
10/10
9/9
0/10
100
100
100
0
28
30
29
shoots of the donors do not flower under the favourable circumstances of
25°/13° when 25°/25° preceded. So the suppressing action of 25°/25° is irreversible. When however GA3 was added to the leaves which were in an inductive state before, the axillary shoots flowered. The second grafting r2/d
confirms that re-induction by GA3 occurred.
20
Meded. Landbouwhogeschool Wageningen 72-9(1972)
TABLE 10. The flowering reaction of receptors of B. daigremontianum grafted on rootstocks
which were temperature treated and re-induced.
nr.
re-induction /d
r,/d during 31days SD
GAj+SD
temp. flowering of ri
1
2
3
25/13
25/25
25/25
q
%
days
13/16
0/16
0/16
81
0
0
27
oo
oo
SD 25/13
GAj + SD25/I3
r2/d in LD25/13
flowering of/d
floweringof ri
q
%
q
% days
0/16
16/16
0
100
0/10
5/8
0 CSD
63 34
3.2.6. SD-induction ofKalanchoe blossfeldiana.
Other Crassulaceae were tried in order to find out parallelisms withBryophyllum about theinfluence oftemperatureonthefloweringprocess.Although
a similarexperimentwasalreadydoneby RUNGER (1959),theinfluenceoftemperatureon induction ofK.blossfeldiana wastested underthe sameconditions
asB. daigremontianum.
Experiment 10. Plants of K. blossfeldiana cv. 'Van der Dussen', obtained
from cuttings,received SD-induction at different temperatureconditions.After
6 weeks the plants were moved into the LD-division of a greenhouse for the
observation of flowering.
Table 11 shows,thatthereactionon thetemperaturesumisonlyquantitative,
resultingin 100%floweringunderallcircumstances,withdifferences innumber
of days till the first openingflower.Similarly to B. daigremontianum thecombination of25°/13°isthebest,resultingin77daystillthefirst opening flower,
differing highly significantly from 25°/25°. In another experiment K.blossfeldiana cv. 'Vulcan'flowerednormally under permanent conditions of SD
25°/25°, so induction aswell as realization are possible in25°.
TABLE 11. Thefloweringof K. blossfeldiana cv.'Van der Dussen' asa result of SD-induction
at different temperature combinations.
days = average number of days till the first openingflower
Number of plants per treatment = 9.
nr.
°1
°d
sum
%
days
1
2
3
4
5
6
7
25
25
13
25
17
21
25
13
17
25
21
25
25
25
408
472
504
536
536
568
600
100
100
100
100
100
100
100
77
90
81
89
83
102
105
Meded. Landbouwhogeschool Wageningen 72-9 (1972)
21
3.2.7. Influence of temperature on thefloweringof K. blossfeldiana.
Experiment 11. Analogous to B. daigremontianumfloweringplants of K.
blossfeldiana cv. 'Van der Dussen' received different temperature treatments in
LD. A light temperature of 25CCwas combined with dark temperatures of 9,
13, 17,21and 25°C.Although therewasavariationoftemperature sums from
472to 600,no differences infloweringoccurred within 2months.
3.2.8. GA3 + SD-induction ofBryophyllumpinnatum.
Experiment12. Similar to B. daigremontianum the influence of temperature
on GA3 + SD-induction of B. pinnatum,another LSDP, was tested. Plants
obtained from cuttings were sprayed with GA3 and received SD at different
temperatures in the phytotron.
Table 12shows that only the extremely low and high temperature sums of
312(21°/9°)and 600(25°/25°)did not give 100% flowering.
TABLE 12. Thefloweringof B.pinnatum after GA 3 + SD-induction at different temperature
conditions
nr.
°d
°1
sum
flowering
%
q
21
21
25
13
21
25
21
25
25
1
2
3
4
5
6
7
8
9
9
13
13
21
17
17
21
21
25
.1
-•-
14/16
16/16
16/16
16/16
16/16
16/16
16/16
16/16
4/16
312
392
408
440
456
472
504
536
600
87
100
100
100
100
100
100
100
25
3.2.9 GA3 + SD-induction ofKalanchoejongmansii.
Experiment13. Plants grown up from cuttings in LD were moved to the
phytotron and received different inductive treatments.
Table 13 showsthatGA3-treatmentisnecessaryforinduction inSDalthough
LD-treatment preceded. It is possible that K.jongmansii is a LSDP like B.
TABLE 13. The flowering of K. jongmansii as a result of GA 3 + SD-induction at different
temperatures.
nr.
1
2
3
22
°1
25
25
25
°d
13
13
25 *>
sum
408
408
600
flowering
GA-treatment
+
+
q
%
0/16
16/16
0/16
0
100
0
Meded. Landbouwhogeschool Wageningen 72-9(1972)
treatment number of table 13
PHOTO 11. Flowering ofK. jongmansiias a resultof SD + GA3-inductionplus realizationat
different temperature conditions.
Photo: 74 days after the beginning of the inductive treatment.
daigremontianum and B.pinnatum,but that rejuvenation occurred by the cutting-procedure. More exact research on the daylength type is required. Treatments 2and 3show that induction is possible at 25°/13° and not at 25°/25°.
This issimilar to B. daigremontianum.
Photo 11illustrates the results.
3.2.10. SD-induction ofKalanchoe manginii.
Experiment14. Plants grown up from cuttings in LD were moved to the
phytotron and received SD at different temperature combinations.
Table 14shows that no GA3 is necessary for induction in SD. This means
that K.manginiiisa SDPor a LSDPwhich wasold enough at the shift LD->
SD.
Table 14alsoshowsthatinduction ispossibleat 25°/13°and not at 25°/25°.
Thisis similar to B. daigremontianum and K.jongmansii.
Photo 12showsthe results.
Meded. Landbouwhogeschool Wageningen 72-9 (1972)
23
TABLE 14. ThefloweringofK. manginii after temperature treatments in SD.
nr.
1
2
°1
25
25
°d
13
25
sum
408
600
flowering
q
%
16/16
0/16
100
0
nr:
2
nr. = treatment numberoftable 14
PHOTO 12. Floweringof K. manginiiasa result of SD inductionplusrealizationatdifferent
temperature conditions.
Photo: 74days after thebeginning ofthe SD induction.
3.3. THE FLORAL HORMONE OF BRYOPHYLLUM
DAIGREMONTIANUM
3.3.1. Indirect induction andjuvenility of B. daigremontianum.
ZEEVAART (1962) discovered that a vegetative, juvenile shoot of B. daigremontianum can be brought into flowering by grafting on a generative rootstock.
24
Meded. Landbouwhogeschool Wageningen 72-9(1972)
Hence, the apex being able to react to floral hormone, the juvenility of B.
daigremontianum must be caused by the absence of the floral hormone under
otherwise inductive circumstances. This absence of floral hormone can be
broughtaboutbytheincapability ofyoungleavestobephoto-induced orbythe
incapabilityto producethefloralhormone.Asalready mentioned(before (p.2),
ZEEVAART and LANG (1962) found that vegetative receptor rootstocks of B.
daigremontianum, broughtintofloweringbygrafting withaB. daigremontianum
donor, can act asdonors to other vegetative scionsin a nextgrafting: 'indirect
induction'.Whenajuvenileshoot,broughtintofloweringbygrafting, isableto
act as donor in a next grafting, this would mean that ajuvenile shoot can be
brought tomultiplication offloralhormone,resultingindonorcapacity.In this
casejuvenility would onlyexist of theinability to react to photo-induction.
Experiment15.From young plants, grown from plantlets, shoots were cut
off, just when the fourth pair of leaves was developed. These shoots, with the
third and fourth pairofleaves,weregrafted onGA3 + SDinduced rootstocks.
Just when the first floral bud became visible, the shoots were cut off and regrafted onvegetative defoliated rootstocks.Theapical and lateral inflorescence
of the shoots wereremoved to prevent apical dominance to thelateral budsof
the rootstock. Unfortunately, the lateral buds of the rootstocks released very
slowly and did notflower.Even whenin anext experimentthe rootstockswere
decapitated 4weeksbefore the grafting, to release the lateral buds sooner, no
flowering occurred. Thequestion wasput whether thedownward movement of
thefloralhormoneofB. daigremontianumgoesmoredifficultly thantheupward
movement.
Experiment 16. FollowingTable15,juvenileshootsr lf broughtinto flowering
by grafting on d, were regrafted on vegetative, defoliated rootstocks r2, which
weredecapitated 4weeksearlier.After 2weeks,vegetativedefoliated shoots r2
were grafted on the samejuvenile shoot. The result was a generativejuvenile
shootwithatleast2pairsofleavesasinterstockbetweenavegetative, defoliated
rootstock and a vegetative defoliated shoot.
Table 15shows thatjuvenile shoots are ableto act asdonor, so that in this
casethejuvenility isnot a matter ofnon-production offloralhormone,but an
TABLE 15. Flowering ofreceptors n of B.daigremontianumgrafted onvegetative or generative
rootstocks (grafting 1)andfloweringof receptors r 2 , grafted withrx as interstock (grafting 2).
nr.
1
grafting 1
T
•1
flowering
of ri
grafting 2
q
%
days
0/15
0
oo
Ti~ ' veg.
+
ri
r
2
+
d
+
14/15
93
27
Meded. Landbouwhogeschool Wageningen72-9(1972)
flowering
of r 2
q
%
days
0/12
0
oo
U*" veg.
r 2 "' veg.
-
-
-
0/12
0
CO
r 2 " veg.
14/14
100
38
ri'
gen.
r 2 " veg.
-
-
-
1/14
7
82
25
inability to react to photo-induction. An explanation for the poor result of
experiment 15and the poorfloweringof the rootstocks of the present experiment is,that thedownward movement of thefloralhormone of B. daigremontianum indeed proceeds very difficultly and slowly. This phenomenon is also
found in other experimentswith B.daigremontianum. Table 15 also shows that
thenumberofdaystillvisibleflowerbudisloweringrafting 1 than ingrafting2.
An explanation is that in grafting 1the donor with 6pairs of well developed
leaves contained more floral hormone than r, + generative of grafting 2 with
2pairs of small leaves.
Photo 13illustrates the results.
f
nr:
nr. • treatment number of grafting 2of table 15
PHOTO 13. 63days after the last grafting.
26
Meded. Landbouwhogeschool Wageningen 72-9(1972)
3.3.2. The result ofLD and SD induction of B. daigremontianum asstudied by a
shift of day length.
B. daigremontianum being a LSDP can be induced to flowering by LD,
followed by SD. BUNSOW and HARDER (1956) and PENNER (1960) found that
GA 3 can replace LD-treatment of B. crenatum as well as B. daigremontianum.
PENNER moreover discovered that GA 3 can induce flowering in B. crenatum in
LD, however only when the plants were at least 6 months and received SD till
no more than 5 days before the GA-treatment. PENNER supposed that B.
crenatum produces, when old enough, a substance in SD and another substance
in LD. When these substances will come together, flowering occurs. PENNER
concluded that the SD substance is produced also when no LD treatment preceded. When the plants are shifted from SD to LD, the production of the LD
substance will proceed slowly and the SD substance will be broken off by LD
before enough LD substance is made. GA 3 however can replace the LD substance. If given before the SD substance is broken off, there will be flowering.
The question arose whether B. daigremontianum, like B. crenatum, produces
a flower forming substance in SD, independent whether LD preceded or not.
Experiment 17. Plants of 1 year with 15 pairs of leaves and grown in SD
received 6weeks SDat thetemperature combinations25°/13°,25°/17°, 13°/25°,
25°/21°,21°/25°,25°/25°.Next the plants were sprayed with GA 3 100ppm and
moved to LD 21°/13°. None of the 4 plants per treatment flowered.
May be B. daigremontianum can be brought into flowering when there are
somecyclesofSDbetween GA-treatment and theshift to LD.Whenthe number
of these necessary SD-cycles is lower than the normal minimum number of 15,
necessary for SD-induction, it is obvious that SD before LD is active in B.
daigremontianum too.
Experiment 18. Vegetative plants of about 1 year with 14pairs of leaves and
grown in SD were exposed to 4 weeks SD at different temperatures. Next the
plants were sprayed with GA 3 100ppm and after 0, 1, 5, 10or 15cycles of SD
21°/13° moved to LD 21713°. Only the plants with 15cycles of inductive SD
after the GA 3 treatment flowered, independent of the preceding temperature
treatment.
The conclusion isthat no SD induction occurs inB. daigremontianum without
preceding GA 3 or LD.
3.3.3. Effect ofLD and SD as studied by grafting.
It is possible that LD-induction of B. daigremontianum results in the production of a LD substance and SD results in the production of a SD substance.
Are these substances transmissable and can they be brought together by grafting, resulting in a floral hormone?
RUNGER obtained negative results by giving different day lengths to two pairs
of leaves standing upright above each other. Nevertheless,grafting of two parts
of plants from different day lengths will be of interest.
Experiment 19. Shoots of adult SD plants were grafted on adult LD rootstocks. The graftings were placed in a LSD cabinet (described by WELLENSIEK
Meded. Landbouwhogeschool Wageningen 72-9 (1972)
27
and ELINGS, 1967),wherethe scionsreceived SD and the stocks LD.Although
the temperature conditions were favourable, being 22°/15°, none of the 10
graft combinations producedflowerswithin 3months. Neither did the reverse
graft combination LD/SD. The conclusion isthat the existence of graft transmissablesubstances,produced under LD-orunderSD-conditions,couldnotbe
demonstrated.
3.3.4. Therole ofGA3 during theproduction offloralhormone.
ZEEVAARTand LANG(1963)found that CCC,applied to B. daigremontianum
duringtheSD-treatment after theshift LD->SD,suppressestheflowerformation. As GA-treatment could nullify the CCC effect by causingflowering,
ZEEVAART and LANG concluded that CCC prevented the activity of GA, produced by the plant under LD-induction.
Thequestionswereasked:IsGAaninductionfactor forB. daigremontianum,
producing an inductive state, or is GA a permanently necessary buildingsubstance in the synthesis of floral hormone? Does afloweringplant only
continuetoflower,whentheproduction offloralhormone continues?
When GA isa precursor offloralhormone, and when continued production
offloralhormoneisacondition forcontinuedflowering,application ofCCCto
flowering plants might have a disturbing effect on the flowering.
Experiment 20. GenerativeplantsofB.daigremontianum,inducedbyGA3 +
SD, were treated with CCC by administering to the roots 100 ml 4000 ppm
solution 3 x with intervals of 5 days. During and after the treatment the
flowering-pattern wascomparedwithuntreatedcontrolplants.However,during
4 months no differences could be observed. It ispossible that the quantity of
applied CCCwasnot sufficient tonullify theamount ofapplied GA3,butsince
there are absolutely no differences with the controls, it islikelythat GA3 does
not play a role in the continuation of flowering.
3.4. SD-INDUCTION OF AN EARLY AND A LATE CV. OF K. BLOSSFELDIANA
For one cv., under certain conditions of light and temperature, a range of
inductivecyclescan begiven,resulting from aborting buds to 100% flowering.
Hence K. blossfeldiana is a SDP with a quantitative flowering-reaction after
sub-optimal SD-induction.
In experiment21the inductive ranges of an early and a late cultivar were
compared. Plants of the early cv. 'Vulcan' and the late 'Van der Dussen' were
grownupfrom cuttingsinLD.InductivetreatmentwasgivenintheSD-division
of a greenhouse. Table 16 shows that the inductive range of the early cv.
'Vulcan' lies between 7and 14cyclesof SD.
The inductive range of the late cv. 'Van der Dussen' is demonstrated in
Table 17and lies between 21 and 28 cycles of SD. So there is a difference of
about 14cyclesof SD-induction between the early and the late variety.
Photos 14and 15illustrate theseresults.
28
'
Meded. Landbouwhogeschool Wageningen 72-9 (1972)
w SD
treatment number of table16
PHOTO 14. K. blossfeldiana 'Vulcan' after 1 (left) or 2 (right) weeksof SD induction.
Photo: 92days after the beginning of the induction.
• treatment number of table17
PHOTO 15. K.blossfeldiana 'VanderDussen'after 2(left), 3 (middle)or4 (right) weeksof SD
induction.
Photo: 92 days after the beginning of the induction.
Meded. Landbouwhogeschool Wageningen 72-9(1972)
29
TABLE 16. The flowering of early K. blossfeldiana cv. 'Vulcan' after different cycles of SD.
nr.
1
2
3
4
5
6
7
8
9
1
SD-cycles
6
7
8
9
10
11
12
13
14
flowering
q
%
0/10
3/10
5/10
10/10
10/10
10/10
10/10
10/10
10/10
0
30
50
100
100
100
100
100
100
aborting
buds
stopping
flowering
continuous
flowering
3/10
5/10
10/10
10/10
5/10
-
-
-
5/10
5/10
3/10
-
5/10
7/10
10/101
Average number of days till visible bud was21.
TABLE 17. The flowering of late K. blossfeldianacv. 'Van der Dussen' after different cycles
ofSD
nr.
1
2
3
4
5
6
7
8
9
1
flowering
SD-cycles
20
21
22
23
24
25
26
27
28
q
7.
0/10
2/10
2/10
5/10
6/10
8/10
10/10
10/10
10/10
0
20
20
50
60
80
100
100
100
aborting
buds
stopping
flowering
continuous
flowering
_
-
2/10
2/10
5/10
5/10
5/10
6/10
3/10
_
-
-
1/10
3/10
4/10
7/10
10/10'
Average number of days till visible bud was33.
3.5. GRAFTCOMBINATIONS BETWEEN K. BLOSSFELDIANA
AND B. DAIGREMONTIANUM
3.5.1. Graft combinations with B. daigremontianum under different temperature
~conditions.
ZEEVAART (1958) demonstrated the identity of the floral hormones of the
Crassulaceae Kalanchoe blossfeldiana, Sedum ellacombianum and Sedum spectabile. In the present experiments graft combinations of K. blossfeldiana and B.
daigremontianum are investigated to find out the relationship between their
floral hormones. K. blossfeldiana waschosen asa plant with early and late culti30
Meded. Landboiwhogeschool Wageningen 72-9(1972)
vars, while grafting of Kalanchoe with Bryophyllum presents the combination
ofaplantwithout non localized productionoffloralhormoneandaplantwith
that property.
Experiment 22. Vegetative shoots of the early cv. 'Vulcan' and the late cv.
'Van der Dussen' of K. blossfeldiana were grafted on generative Bryophyllum
(K.r/B.d)to find out whether thefloralhormones of B. daigremontianum and
K.blossfeldiana areidenticalandtocomparethefloralreaction oftheearlyand
latecv.ofKalanchoe. ThereversecombinationB.daigremontianum receptoron
K. blossfeldiana donor-rootstock wasmade too (B.r/K.d). In order tofindout
the influence of temperature on thesegraft combinations,different conditions
weregiven during 6weeksof LD in the phytotron, followed by LD-treatment
under greenhouseconditions.
In Table 18,treatments 10, 12and 16showthat B.daigremontianum isable
to bringK.blossfeldiana intoflowering,whilethe controls 9, 11 and 15 remain
strictlyvegetative.Comparison oftreatments2, 10and 14 showsaslow floweringreaction of only theearlycultivar ofKalanchoe duringthenextgreenhouse
temperature conditions,sothat 6weeksof 25°Cin light and dark willreduce
the level of floral hormone of the B. daigremontianum donor. This would
suggestthat early K.blossfeldiana needslessfloralhormonethan late K. blossfeldianaor B. daigremontianum.
Treatments 6and 8show that neither in 25°/25°nor in 25°/13°K. blossfeldianaisabletobringB.daigremontianumintoflowering.Anexplanationforthis
might bethat the sum of temperature of LD 25°/13° of 504istoo highfor B.
daigremontianum to react to thefloralhormone of K.blossfeldiana. ZEEVAART
TABLE 18. The influence of dark temperature on the transmission of flowering-capacity of
some graft combinations of B.daigremontianum andtheearlyandlatecv. of K. blossfeldiana.
flowering
nr.
combination
°1
°d
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
fl.r/fl.r
fl.r/fl.d
fl.r/fl.r
fl.r/fl.d
B.r/tf.earlyr
fl.r/AT.early d
fl.r/AT.early r
fl.r/AT.early d
Nearly r/fl.r
AT.earlyr/fl.d
Nearly r/fl.r
Nearly r/fl.d
#.later/fl.r
tf.later/fl.d
AT.later/fl.r
AT.later/fl.d
25"C
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25°C
25
13
13
25
25
13
13
25
25
13
13
25
25
13
13
Meded. Landbouwhogeschool Wageningen 72-9(1972)
q
0/10
0/15
0/10
14/15
0/10
0/15
0/10
0/15
0/10
12/14
0/10
12/12
0/10
0/14
0/9
12/13
%
0
0
0
93
0
0
0
0
0
86
0
100
0
0
0
92
days
oo
CO
oo
21,6
(X)
oo
oo
oo
oo
74,0
oo
20,3
oo
oo
oo
20,1
3.1
(l958)also found that it isdifficult to bring B.daigremontianum into flowering
by a K. blossfeldiana donor.
Photo 16shows the results of treatments 15and 16,while photo 17clearly
demonstrates the influence of the temperatures of treatments 16and 14.
Experiment 23. Following experiment 22,vegetative shoots of B. daigremontianumwere grafted on generative rootstocks of the early cv. 'Annette' of K.
blossfeldianain LD2l°/l3 0 (fl.r,+/KA+). Asacontrol B.daigremontianum was
grafted on vegetative rootstocks of K. blossfeldiana (B.r^/K.r*). Also the
reverse combinations K./B. weremade.
Table 19,left part, treatment 2shows thatfloweringof Z?.r,+ occurred after
upward movement of the floral hormone, while in treatment 4 the downward
movement ofthefloralhormone did not result inflowering,confirming former
experiments.Thefloweringreaction oftreatment 2,however,wasveryslowand
nr:
nr.
15
16
treatment number of table18
PHOTO 16. K. blossfeldiana asreceptorgrafted on B. daigremontianum receptor (control, left)
or on B. daigremontianumdonor(right) at 2S°lll3°d in LD.
Photo: 72days from grafting.
>
32
Meded. Landbouwhogeschool Wageningen 72-9(1972)
nr:
16
14
nr. — treatment number of table 18
PHOTO 17. K. blossfeldiana as receptoron B. daigremontianum donorat 25°lll3°d (left) and
25°U25°d(right) in LD.
Photo: 66 days after grafting.
thefloralstage was moderate.
In grafting 2,thefloweringreceptors ( r ^ gen.) of treatment 2of grafting 1,
were regrafted as an interstock between vegetative, defoliated pieces of B.
daigremontianum(r 2 " veg.).Asacontrol thevegetativereceptorsoftreatment1
ofgrafting 1 (r, + veg.)weregrafted identically.Table 19,rightpart, showsthat
the generative B. daigremontianum receptors have no donor capacities.
The conclusion of this experiment is that K. blossfeldiana is hardly able to
bring B. daigremontianum intofloweringand cannot induce donor capacities
to B. daigremontianum.
3.5.2. GraftcombinationsofB.daigremontianumwithdifferentperiodsofgraftingcontact.
Experiment 24. Another approach to the problem of differences in the
amount of floral hormone between early and late cultivars of K. blossfeldiana
hasbeento graft vegetativeshootsoftheearlycv.'Vulcan'and ofthelate'Van
der Dussen' on generative B. daigremontianum rootstocks in LD 21°/13°. The
Meded. Landbouwhogeschool Wageningen 72-9(1972)
33
TABLE 19. Thefloweringof B. daigremontianumreceptors grafted with receptors ordonorsof
K. blossfeldiana in LD21°l/13°d.
nr.
grafting 1
Br,*
1
K.T*
flowei ing
grafting 2
q
%
days
stage
0/10
0
oo
0
Br,*
KA*
6/10
3
K.r*
B.r-
0/10
0
oo
0
4
KA*
B.r~
0/10
0
co
0
2
60
77
flowering
q
4
%
days
A r 2 " veg.
B.r,* veg.
B.r2~ veg.
0/10
0
oo
0/10
0
oo
B.r2~ veg.
B.r,+ gen.
B.r2~ veg.
0/6
0
oo
0/6
0
oo
K. blossfeldiana receptors were defoliated till the appearance of the first floral
bud.After different periodsofgrafting-contact thesereceptorswere sidegrafted
on vegetative rootstocks of thecv. 'Josine' of K. blossfeldiana.
Table 20 shows that the early cv. 'Vulcan' needs less grafting-contact for
flowering than the late cv. does. However, there are no differences in days till
visible flowering between early and late. Moreover no differences in floral
stages between any of thefloweringreceptors were observed.
Hence,ifashootobtainssufficientfloralhormone forflowering,the duration
till visibleflowerbuds will be equal for theearly and late cv. None of the regrafted flowering receptors was able to bring the vegetative K. blossfeldiana
'Josine'rootstocksintoflowering.Even3 monthsafter theregrafting therewere
TABLE 20. Flowering of receptors of an early and a late cultivar of K. blossfeldiana,grafted
on B.daigremontianumdonorswith different durationsofgraft contact, followed by regrafting
on vegetative K. blossfeldiana cv. 'Josine.'
nr.
1
23
4
5
6
7
8
34
cultivar
early
early
early
early
late
late
late
late
duration K.rjBA
flowering
in days
q
7d.
14 d.
21 d.
oo
7d.
14 d.
21 d.
oo
0/14
11/13
13/14
5/5
0/15
2/15
7/15
5/5
%
days
0
85
93
100
0
13
47
100
oo
27,4
22,5
24,4
oo
28,5
19,7
23,6
Meded. Landbouwhogeschool Wageningen 72-9(1972)
flowering shoots onvegetativerootstocks. Thesefloweringshootsformed vegetative lateral shoots. So B. daigremontianum was not able to bring about non
localized synthesis of floral hormone in K. blossfeldianal
3.6. CONCLUSIONS
1. SD-induction + realization of B. daigremontianum by GA3 + SD aswell
as by LSD, was only obtained when the sum of products of temperature
times hours per 24 hours did not exceed a certain value (Exp. 1and 4).
2. Lowtemperature treatment of B. daigremontianum to reduce the temperature sumisactiveinthe light-aswellasinthedark period.(Exp. 1 and4).
3. Hardly induction but rather the following realization is inhibited by too
high a temperature. (Exp. 2and3).
4. Similarcasesofqualitativeinfluenceoftemperatureoninduction + realization werefound in Kalanchoejongmansiiand K.manginii. (Exp. 13and 14).
Experiments 10and 12with K. blossfeldiana and B.pinnatum respectively,
however,showamorequantitativeinfluence oftemperature.Itislikelythat
themarginallevelofthetemperature sumfor theseplantsishigherthan for
the former Crassulaceae, and is not reached in the present experiments.
The negative results of RUNGER (1959) with K. blossfeldiana at 30°C
confirm the last supposition. (Exp. 10, 12, 13and 14).
5. Temperature sums between 392 and 600 do not prevent LD-induction of
B. daigremontianum. Itislikelythatfor LD-induction aperiodper24hours
at a temperature above 17°Cispreferable. (Exp.4).
6. FloweringofB.daigremontianumisstoppedbytoohighatemperaturesum.
The marginal level of this temperature sum depends on thefloweringcondition of the plant. Also the donor capacity of afloweringB. daigremontianumplantcouldbedestructed byhightemperature.(Exp.5,6and7).
7. It is likely that the influence of a high temperature sum on the flowering
processisadestruction offloralhormone and inductive state,both formed
before the temperature treatment. (Exp. 5,6and 8).
8. Thedestruction ofthefloralstateisirrevisiblewhenthe temperature treatment exceedsacertain duration, resultingin avegetativeplant. (Exp.8).
9. A generative plant of B. daigremontianum, which becomes vegetative by
temperature treatment can be induced again via the leaves which were in
an inductive state before. (Exp.9).
10. ThefloralstateofAT. blossfeldianacannotbeinfluenced bythe temperature
combinations which wereused. In contrary to B. daigremontianum there is
a quantitative influence oftemperature on induction whileno influence on
the realization could bedemonstrated. (Exp. 11).
11. Juvenility of B. daigremontianum means the period of development during
which the leavescannot be photo-induced bythe shift LD->SD. Juvenile
leaves,however,arecapableto reproduce thefloralhormone after grafting
with a donor. (Exp.16).
Meded. Landbouwhogeschool Wageningen 72-9(1972)
35
12. SD-induction without preceding LD-treatment could not be demonstrated
by the shift SD -»GA3 -f LD or SD ->GA3 + unsufficient SD ->LD.
(Exp. 17and18).
13. No transmissable substance after SD- or LD-induction could be demonstratedbygrafting partsofplantsfrom SDandLDoneachother.(Exp.19).
14. GA-induced,floweringplants of B. daigremontianum were not influenced
by CCC, applied to the roots. This could mean that GA3 does not play a
role in thecontinuation offlowering.(Exp.20).
15. Vegetative shoots of K. blossfeldiana can be brought into flowering by
grafting on a generative rootstock of B. daigremontianum. This suggests
identity of the floral hormones of the LSDP B. daigremontianum and the
SDP K.blossfeldiana. (Exp.22).
16. The flowering of K. caused by grafting on a B. rootstock is abundant.
Nevertheless, the floral hormone of B., a plant with the property of non
localized synthesis offloralhormone,cannot bringabout thiscapacity into
the K. receptors. Following conclusion 15it is likely that the differences
between B.and K.,concerning non localized synthesis offloralhormone is
caused by internal differences between these plants, and not by different
floralhormones. (Exp.24).
17. The graft combination B. receptor on K. donor gives a slow floweringreactionoftheB.receptorsandalowfloralstage.Asconclusion 15suggests
identityofthefloralhormonesofB.andAT.,themoderatereactionoftheB.
receptor suggests a lower level of floral hormone in afloweringK., compared with afloweringB. (Exp.23).
18. ModeratelyfloweringB. receptors,after grafting with K.,werenot able to
actasdonorsinanextgrafting. SoK.wasnotabletobringabout synthesis
offloralhormone in B. (Exp.23).
19. The early cv. 'Vulcan' of K.needs 14cycles of SD-induction less than the
late cv. 'Van der Dussen' for completeflowering.(Exp. 21). However, in
contrast to SD-induction, both cultivars flowered simultaneously, when
grafted onB.donorrootstocks.Ontheotherhand,forbecominggenerative
theearlycv.needsshorter grafting-contact withB.donorthan thelateone.
This means that the early and late cv. will have different threshold values
ofthefloralhormonefor afloweringreaction.Itislikelythattherateofthe
floral reactionisinfluenced bytheamountoffloralhormone.Therefore, the
number ofdaystillvisibleflowerbudofthelateandearlycv. canbeequal,
provided sufficientfloralhormone isavailable.(Exp.21and24).
20. When the donor capacity of B. islowered by temperature treatment, only
the earlycv.ofK.becomesgenerative,whilethe B.receptorsaswell asthe
late K. receptors remain vegetative. This result is in accordance with conclusion 19,that the early cv. of AT. needs lessfloralhormone forflowering
than the late one.(Exp.22).
36
'*
Meded. Landbouwhogeschool Wageningen 72-9 (1972)
4. T H E F L O R A L H O R M O N E O F X A N T H I U M S T R U M A R I U M
4.1. FLORAL HORMONE AND FLORAL DEVELOPMENT
4.1.1. The floral development of Xanthium strumarium.
Manyinvestigations about the flowering of Xanthium havealready been done.
SALISBURY (1969) cited about 200 papers. Still questions about the role of the
floral hormone in the transition from vegetative to generative development
remain.
Already HAMNER and BONNER (1938) concluded that the development of
floral primordia into mature flowers proceeds much more slowly in a plant
which has been induced by onelong dark period than inone givena succession
of long dark periods. They observed the terminal buds microscopically at a
certain period after the inductive treatment and characterized the magnitude of
flowering as: strictly vegetative, inflorescence primordia, flower primordia, or
macroscopical flowers and fruits. NAYLOR (1941) presented an extensive study
about the daily development of the male and female flowers as a result of
different cycles of SD induction. SALISBURY (1955, 1963) supposed that the rate
of development of the Xanthium flower (specifically the male flower at the stem
apex) seems to be primarily a function of the amount of floral hormone which
arrives at the tip. He established a series of 8arbitrary morphogenetic stages of
development of the bud. LINCOLN et al. (1956) assumed that the transverse
diameter of the staminate inflorescence at the time of dissection is a direct
function of the relative amount of the floral initiating stimulus, that has reached
the apical bud. A quantitative measure of the effectiveness of the various treatments was established by assigning numerical values to recognizable stages in
the ontogeny of the terminal staminate inflorescence. The values were raised
one unit with each 0,25 mm increase indiameter above 1 mm. SALISBURY (1969)
summarized most of the floral stage systems used for Xanthium, which have in
common that they are based on the rate of floral development.
A remaining question is whether the microscopically different floral stages
develop into permanently distinguishable plants, or only represent a difference
in the rate of development. NAYLOR (1941) already concluded that increasing
the number of inductive cycles seems to stimulate the production of carpellate
more than of staminate inflorescences. According to LINCOLN et al.(1956, 1958)
the different floral stages are due to different amounts of floral hormone, and
the continuation of flowering is caused by storage or continued synthesis of
floral hormone in the young leaves. It remains questionable whether a low level
of floral hormone, resulting in a low microscopical floral stage, means a prolonged synthesis of floral hormone at a low level.
OKUDA (1953) reported that he got deviations from normal flowering of
Xanthium canadense, when he brought plants into flowering by grafting with
some LD Compositae.
Meded. Landbouwhogeschool Wageningen 72-9 (1972)
37
Thefloweringrootstocks ofXanthiumstrumarium, asaresultofgrafting with
Calendula officinalis (VAN DE POL, 1971) were not able to serve as a donor
within 3 months after the appearance of the first floral bud. Moreover, 15
months after thegrafting these plants werestill alive,whileformation of stems
and leaveswith axillary budsoccurred incombination withgenerativedevelopment,beingtheformation ofmaleandfemaleflowers.Simularformsofdevelopment were obtained by short grafting-contact with a Xanthium donor. Completelyfloweringplants, as a result of sufficient induction or plenty graftingcontactwithadonorofXanthiumitselforofHelianlhusannuus, showgenerative
development with little or no vegetative development. When all the present
meristemshaveformedflowersandtheflowersareripening,theplantdies.
The conclusion is,that thefloralpattern of Xanthium strumarium can show
different balances of vegetative and generative development.
4.1.2. Theinflorescence ofXanthium strumarium.
Xanthium is a monoecious plant. The terminal meristem always forms a
staminatecapitulumduetoinduction,whiletheaxillaryreproductivebudsform
one pistillatefloweror an axiswith usually threeflowers.Thesefemale flowers
have an involucre. The male capitulum, originating from the top meristem,
always appears before the axillary femaleflowers.Often some buds from the
axilsoftheinvolucral bractsofthismalecapitulum form axeswithoneormore
malecapitulums.Frequently,axillarybudsfrom theleaveswillbecomebranches
with a terminal staminate capitulum and axillary pistillateflowers(SALISBURY,
1969).
The question was put: What factors are influencing the development of an
axillarybud intofemaleflowersorinto ashootwithafinalmalecapitulum and
femaleflowersin the lower axils?
Experiment 25. Plants of 5weeks from sowing in LD, at a size of about 8
nodes,weremovedto SD.After 1 weekofSDtreatment theplantsweremoved
back to LD where thefloraldevelopment was observed 4weeks later.
Table21showsthe placeand number ofthemalecapitulums and the female
flowers. It appears that thefinalmeristem alwaysforms a malecapitulum with
sometimes a second one developed from the lowest male flower bud. It is
remarkable that with one exception the 4 axils below thefinalmeristem form
femaleflowersonly.Sincetheplants had about 8nodesat thebeginning of the
SD-induction, thesehighest 4axillary buds are formed during and after induction. The axillary buds from about the sixth until the lowest bud, which were
already formed before induction, allform shootswitha malecapitulum on the
top followed by femaleflowersin the axils of small leaves.
It would be preferable to reserve the term inflorescence of Xanthiumfor a
shoot with a final male capitulum, with eventual side-capitulums, and female
flowers in the axils of the lower leaves. Remarkable is the appearence of bisexual capitulums in the transitory zone of axils 4, 5and 6 which can be described as a femaleflowerwith maleflowersin the axils of the prickles of the
involucrum.Besidesthesecases,similaronesinothermaterialwereoccasionally
38
"*
Meded.Landbouwhogeschool Wageningen 72-9 (1972)
TABLE 21. The average place and number of male capitulums and female flowers and the
average lengths of internodes and axillary shoots of X. strumariumas a result of 7 days SD
induction; n = 10.
axil number 0 = the top meristem.
axil
number
male
capitulums
female
flowers
bisexual
flowers
0
1
2
3
4
5
6
7
8
9
10
11
12
13
1,3
0
0
0
0
0,2
0,5
1,0
1,0
1,0
1,0
0,5
0,1
0,1
0
1,6
2,1
2,5
2,2
2,9
2,7
3,5
4,5
4,6
4,6
1,9
0,5
0,3
0
0
0
0
0,1
0,1
0,4
0
0
0
0
0
0
0
Total
6,7
33,9
0,6
internode
length
0,2 cm
0,2
0,3
0,4
0,8
1,5
2,0
2,5
3,0
6,0
4,0
9,0
8,0
5,0
shoot
length
0 cm
0
0
0
0
0,3
1,0
2,0
5,0
2,0
1,0
0
0
0
found directly below the final male capitulum. So it appears that bisexual
capitulums are formed at places where male as well as femaleflowerscan be
formed.TheexistenceofbisexualcapitulumsconfirmstheoldstatementofFARR
(1915),that a bur is a modified capitulum.
Table 21 also shows the lengths of the internodes and axillary shoots. It
appears that the length of the main inflorescence, being the sum of the internodesbetween axilnumbers0and 5isverysmall.Thismeanshardly anyvegetativedevelopment duringthe formation of theflowers.It isacommon phenomenon that the lengths of the axillary shoots, being inflorescences, increase in
downward direction, with exception of the lowest ones. These differences in
inflorescence can beexplained bythe general condition of the plant during the
flowerformation. The main inflorescence of this well induced plant will be
formed during a high endogenous leveloffloralhormone. Sinceno newleaves
are formed after the induction, the present leaves grow olderandthesynthesis
offloralhormonewilldiminish.Thelaterdevelopingaxillaryinflorescences will
havethedisposaloflessfloral hormone and showastrongervegetativedevelopment duringtheflowerformation, resultingin anincrease ofthe shoot lengths.
The lowest inflorescences areformed when the plant hasalmost died, and they
do not reach full development, sotheir lengthscannot becompared.
4.1.3. TheinfluenceofdifferentcyclesofSD on theappearanceofmalecapitulums
andfemale flowers.
Fromtheeffect of2or4cyclesofSDinduction, HAMNERand BONNER(1938)
concluded that the rate of development of floral primordia depends on inducMeded. Landbouwhogesehool Wageningen 72-9(1972)
39
tion. The rate ofdevelopment ofthe inflorescence asa result ofinduction is
investigated inthe next experiment.
Experiment 26. Plantsof6weeksfrom sowingin LD weretransferred toSD
andafter 1 to5daysremoved backtoLDwheretheratesofappearanceofmale
capitulums and femaleflowerswere observed.
Table 22showsthat theflowersappear sooner when morecyclesofSDpreceded.Thefemaleflowersalwaysappear later than the malecapitulums. However, thedifferences decline rapidly after longer induction.
Thedifferences between thenumbersofdaystill the appearanceofmaleand
femaleflowerbudscanbeconsidered asameasurementfor therateofdevelopment ofthe inflorescence.
TABLE 22. Number of days from beginning of SD till theappearence of male capitulums and
female flowers of X. strumarium in L D after different cycles of SDinduction; n = 10.
SD
0
1
2
3
4
5
cJ
$
oo
37d.
cv>
86d.
31
29
28
24
61
39
34
29
$ minus<J
-49d.
30
10
6
5
4.1.4. Floral stages at different balancesbetween vegetativeand generative
development.
Asmentioned before, manyfloralstagesystemswereusedtodistinguish the
rate of flower development asa result of inductive treatments. A flowering
Xanthiumplant almost never reverts tothevegetative state, even iftheplant
never receivesaninducing treatment again. Observation ofplants,which were
brought intofloweringbydifferent periods ofgrafting-contact orby grafting
withotherdonorsthanXanthium,showedthatdifferent balancedstagesbetween
vegetative and generative development occur. Arethese balances caused by
continuous synthesisoffloralhormoneatdifferent levels? Before entering into
this question, thenext classification andPhoto 18demonstrate therepresentative floral stagesofXanthium, which could be distinguished macroscopically.
Floral stages atdifferent balances between vegetative andgenerative development.
Stage0. Vegetative development.
Formation ofleaves with axillary buds andinternodes. Noorvery late branching by apical dominance.
40
*
Meded. Landbouwhogeschool Wageningen 72-9(1972)
Stage 1.Slowmalefloweringwith strongvegetative development.
Continuously growing malecapitulum at the top, with bracts which grow into
green leaves,and staycloser together than normal leaves ofavegetative shoot.
Thebudsofthemaleflowersintheaxilsofthebractsdonotdeveloporslowly.
Sometimes they form a shoot with leaves, with a male capitulum at the top.
The axillary buds below the capitulum do not develop, or very late, since the
apical dominance ofthecontinuously growingcapitulum goeson. Sothevegetative development isso strong that the plant does not surpass the formation
of thefinalmale capitulum.
Stage2. Maleandfemalefloweringwithvegetative development.
A final male capitulum withflowerswhich produce pollen. The bracts are or
are not developed. Sometimes the lowest buds of the capitulum form a male
capitulum or an axis with some male capitulums or even a femaleflower.By
thefloweringof the final capitulum the apical dominance is stopped and the
axillary budsbelowthecapitulum growoutand form shootswithleaveswitha
final male capitulum or a final female flower. The female flower is usually
surrounded by a rosette of leaves.The many newly formed axillary buds form
shootswithleavesagain,withafinalmaleorfemaleflower.Thisstageresultsin
anendlesslygrowingandfloweringbushyplantwithasmallnumber of flowers.
Stage3. Normalfloweringwithoutvegetative development.
A small final male capitulum with quickly developingflowers.The bracts are
notdeveloped. Sometimesthelowest malebudsform asecond malecapitulum.
The axillary buds below the capitulum form 1femalefloweror an axis with 3
femaleflowers,with a few small leavesor none at all.The lowest axillary buds
PHOTO 18. FloralstagesofX. strumariumatdifferentbalancesbetween vegetativeandgenerative development.
From left to right:
0 = vegetative development.
1 = slow male flowering with strong vegetative development.
2 = male and femalefloweringwith vegetative development.
3 = normal flowering without vegetative development.
Meded. Landbouwhogeschool Wageningen 72-9(1972)
41
form inflorescences, also being a small shoot with a final male capitulum and
femaleflowersin the lower axils. Since all meristems becomeflowersand no
new buds are formed, this stagemeans the end of the plant.
The stages described will be used in the following.
4.2. FLORAL STAGES ASA RESULTOFGRAFTING
4.2.1. Differentperiods of grafting-contact in the combination Xanthium d/r.
Experiment 27. Plants of 5 weeksfrom sowingin LDweregrafted abovethe
firstpair of leaveswith donor shoots,whichhad received 4weeksof SD. After
different periods of grafting-contact the donors were removed.
Table23showstheresultsat 5months after thegrafting. It appears,that the
figures about theflowering-quotient,percentage andstage,risewith increasing
duration of the grafting-contact, while the numbers of days till visible flower
bud decrease. Since during a longer graft-contact more floral hormone will
arrive in the receptor, it islikelythattherateof theflowering-reactionand the
floralstage are determined by the amount offloralhormone.
TABLE 23. Flowering of receptor rootstocks of X. strumarium after different periodsof grafting-contact of the combination d/r-.
nr.
1
2
3
4
5
6
7
duration d/r-
flowering
in days
q
%
days
stage
0
8
10
12
14
16
18
0/18
8/14
9/14
11/12
13/13
15/15
17/17
0
57
64
92
100
100
100
oo
42
36
32
32
32
31
0
1,2
1,3
1,4
2,4
2,6
3,0
4.2.2. Rudbeckia bicolor asadonorfor Xanthium strumarium.
OKUDA (1953)demonstrated transmission of flowering-impulse by approach
grafting ofadonor of Rudbeckiabicolorand areceptor ofXanthium canadense.
Although he applied permanent grafting-contact, his averagefloralpercentage
didnotexceed46%. InthenextexperimentthedonorcapacityofR. bicolorwas
tested.
Experiment28. ShootsofR. bicolor,inducedinLD,withatleast4leavesand
a just visible flower bud, were grafted on defoliated rootstocks ofXanthium
strumarium, which had an age of 5weeksfrom sowingin LD.
Table 24 shows that the control rootstocks of X. in grafting 1 remained
42
?
Meded. Landbouwhogeschool Wageningen 72-9 (1972)
strictly vegetative. The donor shoots of R. bicolor in grafting 1, treatment 2,
were only capable to bring 20%of the X. rootstocks intoflowering,although
the growing together of donors and receptors was satisfactory. Moreover, the
flowering waslateand atstage2,whilenosynthesisoffloralhormonecould be
demonstrated in grafting 2.
AsR.bicolor, like Calendulaofficinaliscan onlybringaboutlimited flowering
in X. receptors, in spite of long grafting-contact, it is likely that the level of
floralhormone of afloweringR. bicolor islow. (p.38)
TABLE 24. Flowering of receptor rootstocks of X. strumariumafter grafting with donors of
R. bicolor.Shoots of receptors in grafting 1 were tested on synthesis of floral hormone in
s *••
nr.
grafting 1
q
1
2
Xs
Xs,*
Rudbeckiad
flowering
%
days
grafting 2
0
0/15
3/15
20
64
flowering
stage
2
q
Xs,* veg.
'.
Xs2~ veg.
Xs,* gen.
'
XSi~ veg.
%
0/15
0/3
4.2.3. Thedonor capacity ofshootsfrom Xanthiumplants,flowering atstage2.
We have seen that no donor capacity could be proved of the X. rootstocks
which were brought into flowering by grafting with Calendula officinalis,
Rudbeckiabicolor orbyshort grafting-contact withgenerativeX. shoots.However,aX. plant,floweringatstage2,showsbigdifferences inthefloraldevelopment of its individual shoots. The question arose whether shoots with only a
malecapitulum contain adifferent leveloffloralhormone incomparison with
shootswith only a female top flower.
Experiment 29. In an attempt to demonstrate possible differences in levels
of floral hormone, shoots with a male capitulum and shoots with a female
flower were grafted on receptor shoots.
Table 25showsthat somemaleaswellassomefemalefloweringshootswere
able to bring aboutfloweringin the receptors. The low flowering-percentages,
themanydaystillvisibleflowerbud,andthelowfloralstagessuggestlowlevels
of floral hormone in both donor types. Comparison of combinations 2 and 3
shows a somewhat better floral reaction, when a female flowering shoot was
used asdonor.Thiscould mean that a femalefloweringshoot containsasomewhat higher level of floral hormone than a malefloweringshoot. The small
number offloweringreceptors, however, does not allow definite conclusions.
Meded. Landbouwhogeschool Wageningen 72-9(1972)
43
TABLE 25. Flowering of receptor rootstocks of X. strumariumafter grafting with male or
female flowering donor shoots.
nr.
graft
combination
1
2
3
r/r
<Jd/r
?d/r
Iflowering
q
%
days
stage
0/24
2/24
2/12
0
8
17
cv
105
60
1
1
4.3. FACTORS INFLUENCING THE TRANSMISSIONOFFLORAL HORMONE BY
GRAFTING
4.3.1. Introduction
Grafting is a radical action with many factors influencing the results. It is
likely that many unexpected and contradictory effects are caused by unknown
influences.
OKUDA (1953) concluded that some unknown factors would be responsible
for the abnormal fruits formed by grafted plants of Xanthium canadense.
HAMNER and BONNER (1938) investigated the influence of leaves and buds on
thetransmission offloweringoftwo-branched plantsof Xanthium. They found
aninverserelationshipbetweentheamountofLDleaftissueandthemagnitude
oftheflowering-responseofthereceptorbranch.Young LDleaves were found
to be favourable for theflowering-reactionof the receptor, while removal of
buds and youngleavesfrom the SD-donorshoot had a favourable influence on
the flowering of the receptor. LINCOLN et al. (1956) extended this work and
concluded that young and rapidly growing leaves and buds causean area of
carbohydratedeficit.Theyexplainedtheinfluenceonfloweringbyassumingthat
the flow of carbohydrates carries floral hormone with it.
In the present work some factors, influencing the transmission of floral
hormone bygrafting ofXanthium, werestudied. Experiment 27already showed
theinfluence oftheduration of grafting-contact onthe transmission of flowering.Shorteningthenecessaryduration ofgrafting-contact isimportant, sincein
most casestheoptimal condition of thedonor only existsfor a shorttime.
4.3.2. TheinfluenceofSD induction andLD treatmentonthe donor capacity.
Experiment 30. Xanthiumplantsatanageof4weeksfrom sowinginLDwhen
the fourth leaf wasjust developing, received different cycles of SD induction.
In aneffort to separateinduction and synthesis offloralhormone,the different
cyclesofinductivetreatment werefollowed bydifferent periods of LDat about
20°C.Topshootsfrom theseinducedplantswerecutoffandgrafted onreceptor
rootstocks with a contact of 3weeks.
Table26showsthatthebestflowering%isobtainedaftertreatment 12,where
the donor received 3weeks of SD followed by 1 week of LD. Comparing the
influences of the LD periods following the SDinduction, it isremarkable that
44
Meded. Landbouwhogeschool Wageningen 72-9 (1972)
TABLE26. Flowering of receptor rootstocks of X. strumarium after 3 weeks grafting-contact
with donors, pretreated differently.
nr.
donor pretreatment
weeks SD
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
0
2
2
2
2
3
3
3
4
4
5
weeks LD
5
0
1
2
3
4
0
1
2
3
0
1
2
0
1
0
flowering
q
%
days
0/16
3/17
5/13
4/10
1/10
0/10
5/13
11/14
4/12
0/6
4/11
8/9
1/11
6/11
7/11
3/8
0
18
39
40
10
0
39
79
33
0
36
89
9
55
64
38
cv>
55
39
54
38
c\>
24
33
31
oo
27
41
32
36
33
33
100 r %
80
60
10
GRAPH. 1. The flowering-percent-
20
ages (ordinate) of receptor rootstocks of X. strumarium after
grafting with donors, induced by
1, 2 or 3 weeks of SD, followed by
• 0 to 4 weeksof LD before grafting.
2
3
wetks of LD betwetn SD and grafting (Table 26)
Meded. Landbouwhogeschool Wageningen 72-9(1972)
45
.{always1 weekofLDhasafavourableeffect ontheflowering%.Todemonstrate
thismoreclearly,therelevant data arecomposed in Graph 1,whichalsoshows
thatmoreLDtreatmentthan oneweekhasanegativeinfluence onthe flowering
%,with theexception of2weeksLD after 1 week SD.An explanation for this
influence of LDcould perhaps bethat thedonors received morelightenergyin
LD than in SD,because the experiment was done in a greenhouse in summer.
4.3.3. Theinfluence of temperature onthesynthesis offloralhormone.
SALISBURY (1963) concluded that low night and day temperatures are unfavourable for flowering of Xanthium,whether they are given before the SD
period or after it. Heassumesthat thebest temperature conditionswill depend
stronglyonthespeciesused. SALISBURYfound for hisXanthium strainingrowth
chambers with adequate light intensities, that thefloweringresponse was still
increasing with increasing day and night temperatures up to 27°C, the highest
temperature tested. The preceding experiment 30showed that 2or 3weeks of
SDwerealmostsufficient for completeinduction,while 1 weekoffollowing LD
provedtobefavourable. Whentheeffect ofthislastweekisduetoan influence
on the synthesis of floral hormone, the question arises, what other environmental factors are ableto influence this synthesis.
Experiment 31. In order tofindout the influence of temperature on thesynthesis offloralhormone, different temperatures weregiven during oneweekin
LDor SDtoplantswhichhad received 2weeksof SD.Thetop shoots ofthese
plants were cut off after the temperature treatment and grafted on vegetative
rootstocks. After 12days of grafting-contact the donor shoots were removed.
Table 27 shows the unexpected results. It appears that the level of floral
hormone 2weeks after the beginning of induction was hardly sufficient for a
transmission offloweringwithin 12days.Only when these 2weekswere filled
up with SD,normalfloweringoccurred.
Comparison of treatments 1, 2 and 3, 4, 5 shows that instead of aflower
promoting effect of LD as found in experiment 30 a flower inhibiting effect
occurred at the higher temperatures.
TABLE 27. Flowering of receptor rootstocks of X. strumarium after 12 days of graftingcontact with donors which received 1 week of LD or SD at different temperatures after
2 weeks of ordinary SD induction.
nr.
1
2
3
4
5
6
7
8
46
temperature donor
flowering
after 2weeks of SD
q
LD 9°C
LD130
LD17"
LD21°
LD25°
SD 17°
SD 21°
SD 25°
7/19
7/19
0/20
0/20
0/20
9/10
16/18
18/18
%
37
37
0
0
0
90
89
100
Meded. Landbouwhogeschool Wageningen 72-9 (1972)
4.3.4. The influenceofthesurface-activechemicaldimethyhulfoxydeon thetransmission offloralhormone.
Several investigators concluded that at least a tissueconnection and in most
cases a vessel connection is required for transmission offloweringby grafting
(ZEEVAART 1958). Therefore the question was asked whether a surface-active
chemical could raise the membrane permeability of especially the walls of the
cellsaround the grafting-place.
Experiment 32. Vegetative rootstocks with 2 branches were grafted with a
donor shoot on one branch. During the 3weeks of grafting-contact the graft
combinationsweremistedweeklywithsolutions ofdimethylsulfoxyde (DMSO)
in order to try to promote thetransmission offloweringfrom the donor to the
receptor and eventually from the grafted branch to the ungrafted branch.
Table28doesnot showcleardifferences withthecontrols.Soaninfluence of
DMSO on thetransmission of flowering could not be demonstrated.
TABLE 28. The flowering of 2-branched receptor rootstocks of X. strumariumafter weekly
spraying with D.M.S.O. during 3weeks of grafting-contact with a donor.
nr.
1
2
3
DMSO
floweringof grafted branch
floweringof second branch
%
q
%
days
q
7.
days
0
0,1
1
24/27
25/26
27/31
89
96
88
26
25
26
24/27
25/26
22/31
89
96
71
30
29
28
4.3.5. The influence of the matureleaves of the receptor on thegrowthof the
axillaryshootsand the transmission offloweringfrom a grafted donorshoot.
HAMNER and BONNER (1938) and later LINCOLN et al. (1956) convincingly
proved that the presence of mature leaves on the receptor branch of a twobranched Xanthium plant,inhibitsthetransmission offloweringfrom thedonor
branch. In the present experiments usually a donor shoot was grafted on a
receptor rootstock andtheflowering oftheupper axillary shoot ofthereceptor
was observed. However, when the receptor rootstocks were completely defoliated at the moment of grafting with a donor shoot, the axillary shoots
developedslowlyandoften manyoftherootstocksdied.Whenthematureleaves
of the rootstocks were removed when the axillary buds were developing, less
mortalityoccurred. Moreoveritwasremarkable,thatwhenashootofXanthium
was used as a donor and the mature leaves were removed at the moment of
grafting, more rootstocks survived than when a lessor non related donor, like
Calendula officinalis orPerilla crispa, wasused.
According to these observations it is likely that a Xanthiumrootstock dies
due to a lack of substances produced in its own leaves. DE STIGTER (1956)
Meded. Landbouwhogeschool Wageningen 72-9(1972)
47
extensively studied this problem in Cucurbitaceae. The differences in mortality
betweenthegraftings ofXanthiumonXanthiumandanotherdonoronXanthium
could be explained by differences in rate of growing together of the graftingpartners and/or differences in leaf substances between the donors. Besides the
necessity ofsurvivingof therootstocks, theinfluence of defoliation on the rate
ofdevelopment oftheaxillary budswillbeofinterest for the reaction onfloral
hormone. Although not directly related to the present subject, it seems worth
whiletoinvestigatetheinfluence ofthepresenceofaleafonthedevelopmentof
thecorresponding axillary bud.
Experiment 33. Plantsof3weeksfrom sowinginLDweredecapitated above
the first pair of leaves, in order to release the axillary buds. The first pair of
leaveswasremoved at different periods after decapitation. Table 29showsthat
the growth of the axillary shoots is strongly influenced by the corresponding
leaves, especially during the first week of development. Photo's 19 and 20
clearly demonstrate this.
For grafting-experiments with a donor, this means that the point of timeof
defoliation of the receptor determines the vegetative development which interactswiththefloralhormone.
TABLE 29. The average lengths of the axillary shoots from thefirstleaf pair of X.strumarium
in mm as a result of decapitation with removal of the first leaf pair at different moments;
n = 10.
days between
decapitation and
defoliation
0
3
7
11
(X)
days between decapitation and observation
21
28
35
42
49
17
13
38
53
61
37
38
68
83
96
56
60
96
109
118
83
93
125
147
153
115
123
159
167
178
The next questions are:Does a connectionbetweenthe leaf surface and the
growth oftheaxillary budsexist?Istheinfluence ofa leaf restricted to thecorresponding bud?
Experiment 34. Plants at an ageof 3weeksfrom sowingin LD weredecapitated above the first pair of leaves, in order to release the axillary buds. The
surface of the first pair of leaves was reduced and the lengths of the axillary
shoots were measured at some intervals from 2 weeks after the decapitation.
Table 30shows the results. It is remarkable that the effects of treatments 2
and 3,in spiteoftransverseorlongitudinal halvingoftheleaves,are absolutely
equal. Comparison of treatments 1and 4 shows that the axillary bud of the
rightleafoftreatment 4isinfluenced bytheleft leaf.Comparison oftreatments
48
Meded. Landbouwhogeschool Wageningen 72-9(1972)
<
^
^^/
^*^
^ vi
^
treatments of table29
PHOTO 19. Influence of thefirstpair of leaves of X. strumariumon thegrowthof theiraxillary
shoots.
Decapitation above the first pair of leaves.
From left to right defoliation after 0, 3, 7, 11or oo days after decapitation.
The growth of the axillary shoots of the first pair of leavesand even of thecotyledons increases at longer presence of the first pair of leaves.
Photo: 28 daysafter decapitation.
PHOTO 20. Influence of thefirstpair of leaves of X. strumarium onthegrowthof theiraxillary
shoots.
Left: decapitated above the first pair of leaves and defoliated.
Right: decapitated above the first pair of leaves without defoliation.
Photo: 77days after decapitation.
Meded. Landbouwhogeschool Wageningen 72-9(1972)
49
TABLE 30. The lengths of the axillaryshoots from thefirstpair of leaves of X. strumariumin
mm as a result of decapitation with differently reduced leaf surfaces; n = 10.
—= removed completely.
+ = intact.
nr.
leaf surface
days between decapitation and observation
14
21
28
left leaf right leaf—
3
3
12
12
32
32
transversely
halved:
left leaf
right leaf
20
20
48
48
78
78
longitudinally
halved:
left leaf
right leaf
20
20
48
48
78
78
left leaf +
right leaf—
18
17
49
39
71
60
left leaf +
right leaf +
32
32
74
74
109
109
4 and 5 shows that the influence of the left leaf on the right axillary bud of
treatment 4reduced the influence of the left leaf on its own axillary bud.
Thegrowthoftheshootsoftreatment4approachesthegrowthattreatments
2and 3.Theconclusion isthat thetotalleaf surface oftheplant determinesthe
growth of the released axillary buds. Theinfluence of the leavesis transversely
translocated.
This induced the question whether also vertical translocation occurs.
Experiment 35. Plants of 5weeks from sowing in LD with the fourth leaf
justfullydeveloped,weredecapitatedabovethefourth leafinordertoreleasethe
axillary buds.The leaves were removed in different combinations as shown in
Table 31. It appears that the highest buds, which werethe soonest released by
decapitation,showthestrongestgrowth,withonlysmalldifferences betweenthe
third and the fourth, stayingclosely together.
Sothetotalleafsurfaceperplantdeterminesthegrowthoftheaxillaryshoots
in sequence ofreleasing,independent from the placeoftheleaves.
Experiment 36. Plants at an age of 5weeksfrom sowing in LDwere grafted
with donor shoots above the first pair of leaves. The donor shoots were cut
from plantswhichhad received 4weeksof SD.Theleavesofthereceptor rootstockswerecut off at 0, 3or 8days after the grafting. The donor shootswere
removed after 12days of grafting-contact.
In Table 32 comparison of treatments 1 and 2 shows that the number of
50
Meded. Landbouwhogeschool Wageningen 72-9(1972)
TABLE 31. The average lengths of the axillary shoots of X. slrumarium in mm after decapitation above the fourth leaf, with variously reduced leaves; n = 10.
Leaves: —= removed; + = present.
nr.
leaves
days between decapitation and observation
21
28
cotyledons
first pair
third
fourth
—
—
—
—
0
0
0
0
0
0
22
17
cotyledons
first pair
third
fourth
+
—
—
—
0
1
10
12
0
4
31
34
0
6
16
8
0
15
54
34
cotyledons
first pair
third
fourth
cotyledons
first pair
third
fourth
cotyledons
first pair
third
fourth
—
+
—
—
—
—
+
+
+
+
+
+
,
0
11
40
48
0
15
74
85
0
10
48
71
0
12
120
135
survivingrootstocksishigherwhentheleavesareonthereceptorforsomedays.
Thenumber ofdaystillvisibleflowerbudincreaseswithlongerpresenceofthe
receptor leaves. The number of days till visible bud of treatment 2 is hardly
higher than of treatment 1,while theflowering%of the former isbetter. The
conclusion is that it is preferable to defoliate the receptor rootstocks 3 days
after the grafting, although it isnot surewhether 3days are optimal. Presence
of the mature leaves of the receptor for a longer period inhibits the rate of
transmission of flowering.
TABLE 32. Surviving and flowering of receptor-rootstocks of X. strumariumafter 12 daysof
grafting-contact, during whichthe receptors weredefoliated at different times.
nr.
1
2
3
surviving
defoliated after
flowering
days
q
%
q
%
days
0
3
8
24/32
31/32
30/32
67
97
94
16/24
24/31
22/30
67
77
73
30
32
39
Meded. Landbouwhogeschool Wageningen 72-9 (1972)
51
Thenextquestionis:Whenthepresenceofleavesisrequiredforsomedaysin
order to release the axillary buds more rapidly, has decapitation before the
grafting the same or a better effect, because then the leavescan be removed at
the grafting and do not have a possible inhibiting influence.
Experiment37. Plantsof5weeksfrom sowinginLDweredecapitated above
thefirstpair ofleavesat different times.At 8daysafter the decapitation ofthe
firstgroup the plants were grafted with donor shoots from plants which had
received 4 weeks of SD. After 12 days of grafting-contact, the donors were
removed.
Table33showsthat, likeintheprecedingexperiment, thenumber ofdaystill
visible flower bud increases with a longer period between decapitation and
grafting, or:with a stronger growth ofthe axillary shoots.Theabsolute values
of thefiguresof theflowering-resultsof tables 32and 33cannot be compared
since the experiments were taken at different seasons.
TABLE 33. Flowering of receptor rootstocks of X. strumarium, which were decapitated at
different times, after 12days of grafting-contact.
days between
decapitation
and grafting
1
2
3
0
3
8
flowering
q
%
days
39/42
35/36
25/29
93
97
86
25
28
30
4.3.6. Theinfluence of theageof thereceptor onthetransmission of flowering.
Experiment38.Arangeofplantsatagesfrom 3to7weeksfrom sowingin LD
were grafted with donor shoots. The number of available rootstocks of the
different ageswasvariable.The rootstocks weredefoliated and thegraft places
were chosen as high as possible. The donors were cut from plants which had
received 4weeksof SD, and wereremoved after 20daysof grafting-contact.
Table 34shows that theflowering-resultisbetter, the younger the receptor.
ZEEVAART (1969a) proved that the grafting-place of Bryophyllum is important
for the rate of transmission offlowering.Young tissue in the top of the stem
proved to bebetter than the morewoody tissuein the lowerparts of the stem.
He concluded that differences in rate of growing together, due to differences
between the tissues at the grafting-places, were responsible for these results.
However, in the present experiment the graft-places were chosen in the young
tissues below the apical meristem. Therefore it is not likely that this factor
alone isresponsible for the big differences. It ispresumable that other factors,
therootsystemincluded,playarole.Forinstancetheinfluence ofadonorshoot
on a small rootstock will be of more importance than the influence on a big
rootstockonaccountoftherelativedifferences inthesizesofthegraft partners.
52
Meded. Landbouwhogeschool Wageningen 72-9(1972)
TABLE 34. Flowering of receptor rootstocks of X. strumariumof different ages at grafting
after 20days of grafting-contact.
1
2
3
4
5
receptor
age in weeks
flowering
q
3
4
5
6
7
18/18
23/24
7/9
4/11
3/7
%
100
96
78
36
43
days
17
20
26
36
38
Thenextquestion is:What istheinfluence oftheheight ofthe grafting-place?
Experiment 39. Plants of 7 weeks from sowing in LD were defoliated and
grafted withdonorshootsatdifferent heights.Thedonorshootswerecut from
plantswhichhadreceived4weeksof SD.After 20daysofgrafting-contact the
donors wereremoved.
In table 35it is remarkable that relativelyfewof the rootstocks whichwere
grafted abovethecotyledonssurvived.Evidentlyreferring to experiment 33on
p. 48, the slow development of the axillary buds of the cotyledons will be
responsiblefor this.Furthermore,asfar astherootstocks survived,the flowering-results are variable and no clear influence of the grafting-place could be
demonstrated.
TABLE 35. Surviving and flowering of receptor rootstocks of X. strumariumafter 20 days of
grafting-contact with the graft places at different heights.
nr.
1
2
3
4
5
graft-place
above:
cotyledons
first leaf pair
third leaf
fourth leaf
fifth leaf
flowering
surviving
rootstocks
q
%
q
%
days
8/18
15/18
13/18
13/18
13/18
44
83
72
72
72
6/8
8/15
8/13
5/13
6/13
75
53
61
38
46
33
36
31
32
29
4.4. INTERACTIONOFINDUCTIONANDFLORAL HORMONE
Asdiscussed before, thematureleavesofareceptorinhibit thetransmission
offloweringfrom a donor (exp. 36, p. 50).This inhibiting action can be explainedbythesupplyingofthereceptorbudswithassimilates,which interferes
with theflowof assimilateswithfloralhormonefrom thedonor. Moreover, it
Meded. Landbouwhogeschool Wageningen 72-9 (1972)
53
is possible, that the mature leaves are a sink offloralhormone, or even form
inhibiting substances.
The question arose: Can the inhibiting activity of mature receptor leavesbe
diminished by limited induction, hardly sufficient for afloweringreaction as
such? It is clear, that the inhibiting influence due to assimilate synthesis will
remain. Experimental evidenceisavailable that 1 cycleof SDgiven to awhole
plant givesa slowflowering-reaction,while 1 SDgivento areducednumber of
leaves hardly yields any flowering.
A next question is whether the floral hormone from a grafted donor will
cooperate withfloralhormone, synthesized by the receptor leaves. A problem
willbetolettheaction ofbothtypesoffloralhormonecoincideatthereceptive
meristem.
Experiment 40. Plants of 5weeks from sowing in LD received 0, 1, 2 or 3
cyclesof SDand weregrafted oneweeklater above thefirstpair ofleaveswith
a donor shoot which had received 4 weeks of SD. The rootstocks were not
defoliated. Thedonor shootswereremoved after 12daysof grafting-contact.
The results are presented in Table 36. Comparing the effects of SD alone
(treatments 1,2, 3,4)and of grafting alone (treatment 5)with their combined
effects (treatment6,7,8),showsthatthereisaninteractionbetweentheresultof
induction and 12 daysofgrafting-contact. Comparison oftreatments 2,5 and6
showsthat the result of 1 SD given to the relatively oldfirstpair ofleavescan
onlybedemonstrated intreatment 6.Thismeans,thattheinteraction technique
might be useful in order to demonstrate induction-effects which cannot be
observed assuch.
TABLE 36. The flowering of receptor rootstocks of X. strumariumwhich were exposed to 0,
1,2or 3cycles of SD-induction, not followed ('0') orfollowed bygrafting with donor shoots,
grafting-contact 12days ('12 d.').
nr.
SD
grafting d/r +
flowering
q
1
2
3
4
5
6
0
1
2
3
0
1
0
0
0
0
12d.
12d.
12d.
12d.
0/9
0/9
2/9
7/9
4/9
6/9
7/9
8/8
%
0
0
22
78
44
67
78
100
days
oo
oo
21
16
28
23
23
18
stage
0
0
1
1
1,4
2,1
2,4
3,0
4.5. COMPARISONOFANEARLY, A MIDDLEAND A LATELINE
4.5.1. Material
Precedingexperimentsshowed that theusedlineofX.strumarium, for which
•?•
54
Meded. Landbouwhogeschool Wageningen 72-9 (1972)
the critical dark period could befixedto 8.33 h., only needs one cycle of SD
(8 h. light/16 h. dark) to become just generative, while 3 cycles of SD are
already sufficient for anormalflowering-result.Inthisconnection theusedline
isnot alwayssuitable for experiments with sub-optimal induction, for example
interaction experiments.A laterfloweringline ofX. strumarium would then be
preferable. MCMILLAN (1970, 1971)has collected lines of X. strumarium with
different critical dark periods. Seeds of lines with critical dark periods of 8.00
and 11.00 were obtained from him. Considering that our own line with a
critical dark period of 8.33 liesbetween 8.00 and 11.00, the 3lines werecalled
early,middleand late.Sincethenumbersof seed oftheearlyand latelinewere
limited, only some preliminary experiments could bedone.
4.5.2. SD induction ofmiddle andlate.
Experiment 41. Plants of middle and late, 5weeksfrom sowingin LD,were
moved to SDandwithintervalsofoneweekweremoved back to LD.Table37
shows that the middle line isoptimally induced after 1 week of SD treatment.
However, the latelinedoesnot show aweakflowering-responsebefore2weeks
of SD.Although 3and 4weeksofSDgiveplantsfloweringnormally(stage3),
theflowering-quotientremains incomplete. Only continuous SD results in a
complete flowering.
Photo21showsthedifferences betweentreatments2and7with 1 weekofSD.
TABLE 37. Thefloweringof a middle and a late line of X. strumariumafter different numbers
of SD-treatment during increasing numbers of weeks.
nr.
1
2
3
4
5
6
7
8
9
10
11
line
SD
flowering
in weeks
q
7.
days
stage
middle
middle
middle
middle
middle
0
1
2
3
4
0/6
6/6
6/6
6/6
6/6
0
100
100
100
100
oo
18
18
18
18
0
3
3
3
3
late
late
late
late
late
late
0
1
2
3
4
oo
0/6
0/6
3/6
2/6
3/6
6/6
0
0
50
33
50
100
oo
oo
30
21
21
30
0
0
1
3
3
3
Meded.Landbouwhogeschool Wageningen 72-9(1972)
55
nr:
2
nr. — treatment number of table37
PHOTO 21. Theflowering-responseto1weekofSD ofamiddleandalatelineofX. strumarium.
Left: middle - generative.
Right: late - vegetative.
Photo: 5weeks from the beginning of induction.
4.5.3. Grafting ofearly, middle andlate.
Theevidenceofinterspecies grafts (VAN DE POL, 1971)and the results of the
present experiment 22 on an early and a late cv. of Kalancho'e blossfeldiana
(p. 31)induced the questions whether differences in the level offloralhormone
between early, middle and late lines of X. strumarium exist and influence their
flowering and non localized synthesis offloralhormone.
Experiment 42. Plants of the 3 lines, 5 weeks from sowing in LD, were
decapitated above the first pair of leaves and grafted 2 days later with donor
shoots of the middle line from plants which had received 5weeks of SD. The
receptors were defoliated. The donors were removed after different periods of
grafting-contact.
Table 38 shows, that 10days of grafting-contact are enough for an optimal
floralstage of the early line;the middle line needs 14days, while the late one
requires morethan 20days. Shoots of thefloweringreceptors werecut off and
grafted onvegetativerootstocks,inordertotesttheirdonorcapacity.It appears
that only the optimallyfloweringreceptors of treatments 2, 8, 9 and 16were
ableto act completely asadonor, asfar asthetest goes.Theconclusion isthat
longer grafting-contact isnecessary for aflowering-reactionand non localized
synthesis of floral hormone, as the receptor needs more SD induction.
Photo22showsthedifferences betweenthe3lines,2monthsafterthegrafting.
56
Meded. Landbouwhogeschool Wageningen 72-9(1972)
TABLE 38. Flowering of receptor rootstocks of anearly,middleand latelineofX.strumarium
after different periods of grafting-contact with middle donors in the combinations d/r!~.
Shoots of ri were tested on synthesisof floral hormone in ri/r 2 .
r, = receptor rootstocktype.
contact = duration of grafting-contact of d/r! - , in days.
r,/r 2 = next grafting of rLon middle r 2 .
nr.
rt
contact
q
%
days stage
early
early
early
early
0
10
12
14
0/5
5/5
3/3
1/1
0
100
100
100
CO
5
6
7
8
9
10
middle
middle
middle
middle
middle
middle
0
10
12
14
16
18
0/5
2/4
5/5
4/4
4/4
3/3
0
50
100
100
100
100
CO
11
12
13
14
15
16
late
late
late
late
late
late
0
10
14
17
20
co
0/5
0/5
3/4
5/5
5/5
4/4
0
0
75
100
100
100
CO
1
2
3
4
floweringr2 ofr,/rj [
floweringr t
Meded. Landbouwhogeschool Wageningen 72-9(1972)
21
18
17
23
28
23
27
30
CO
33
31
31
29
days ! stage
q
7.
0
3
3
3
0/5
5/5
0
100
CO
65
0
3
-
-
-
-
0
2
2
3
3
3
0/5
0/2
1/5
4/4
3/3
0
0
20
100
100
CO
82
74
74
0
0
2
2
3
-
-
-
-
0
0
2
2
2
3
0/5
0/5
0/3
0/5
0/5
4/4
0
0
0
0
0
100
CO
0
0
0
0
0
2
CO
CO
CO
CO
CO
76
57
treatment number of table38
PHOTO 22. Floweringof 3linesofX. strumarium asreceptorsafter 10daysofgrafting-contact.
Left: early line, normal flowering, stage3.
Middle: middle line, only maleflowering,stage2.
Right: late line, noflowering,stage 0.
Note the differences in internode lengths between the lines.
Photo: 2 months after the grafting.
4.6. CONCLUSIONS
21. Xanthium strumarium can showdifferent balances between vegetative and
generativedevelopment(4.1.1.).
22. Meristems, which were formed before complete induction, form a shoot
with a final male capitulum and female flowers in the lower axils. It is
preferabletoreservetheterminflorescenceofXanthiumforsucha flowering
shoot. (Exp.25).
23. Bisexual capitulums were found at placeswhere a male capitulum aswell
as a femaleflowercould beformed. (Exp.25).
24. Four floral stages at balances of vegetative and generative development
weredistinguished:0 = vegetative;
1 = male only + strongvegetativedevelopment;
2 = maleand female withvegetativedevelopment;
58
Meded. Landbouwhogeschool Wageningen 72-9(1972)
3 = male and female with little or no vegetative development, (p. 40).
25. Differences between the numbers of days till the appearance of maleand
female flower buds are a function of the number of inductive cycles and
can be considered as a measurement for the rate of development of the
inflorescence. (Exp.26).
26. Grafting-experiments showed that it islikely that the different balancesof
vegetative and generative development implicate different, constant levels
offloralhormone. (Exp.27,28and29).
27. Rudbeckia bicolor can only bring about limitedfloweringin Xanthium, in
spiteoflonggrafting-contact. Thefewfloweringreceptorswerenot ableto
actasdonorinanextgrafting. Itislikelythattheleveloffloralhormoneof
Rudbeckia islowin contrast to Helianthus annuus or Xanthium (Exp.28).
28. Only some shoots of plants of Xanthiumin stage 2 wereabletotransmit
flowering by grafting. (Exp.29).
29. Theduration of grafting-contact of d/r determines the continuous levelof
the balance between vegetative and generative development. It is possible
that continuous synthesisoffloralhormone in Xanthium canbeinitiated at
different levels.(Exp.27).
30. LD treatment of the donor after SD and before grafting proved to beimportant for the donor condition; 1week LD after the SD-induction was
optimal in the present experiment. (Exp.30).
31. No influence ofthesurface activechemical dimethylsulfoxyde (DMSO) on
thetransmission offloweringcould bedemonstrated (Exp.32).
32. Thegrowth of axillary shoots wasstronglyinfluenced bythetotal leaf surfaceperplant,especiallyduringthefirstweekofdevelopment.(Exp.33, 34
and 35).
33. Defoliation of the receptor stimulated the rate of the flowering-response.
However,itispreferable todefoliate somedaysafter thegrafting toprevent
dying of the rootstocks by too slow a development of the axillary buds.
(Exp.36).
34. Decapitation before thegrafting had the sameinfluence on thereleasingof
the buds and growth of the axillary shoots as delaying of defoliation after
the grafting. (Exp.37).
35. Three weeks old receptor rootstocks proved to be better than older ones
for transmission offlowering.(Exp.38).
36. No clear influence of the height of the grafting-place on the transmission
offloweringcould be demonstrated. (Exp.39).
37. Interaction between induction of the receptors and transmission of flowering by grafting could bedemonstrated. (Exp.40).
38. A late line needed more than 1week of SD for anyflowering-reactionin
contrast to a middle line with a completeflowering-reactionalready after
1weekof SD.(Exp.41).
39. Longergrafting-contact wasnecessaryfor aflowering-reactionandfor non
localized synthesis of floral hormone, as the receptor needed more SD
induction. (Exp.42).
Meded. Landbouwhogeschool Wageningen 72-9 (1972)
59
5. EXPERIMENTS WITH CARYOPHYLLACEAE
5.1. INTRODUCTION
WELLENSIEK(1966)demonstrated the great persistence of the floral hormone
ofSilenearmeriamd mentionedaspossiblemechanismautocatalyticalmultiplication of thefloralhormone.In the present experimentsother Caryophyllaceae
were tried in order to study whether a transmissable floral hormone could be
demonstrated andwhether graft combinationswith S. armeriacould givemore
information about the nature of the persistence of the floral hormone.
5.2. INDUCTION
Experiment 43. Agroupof 16 Caryophyllaceaewasselectedfrom acollection
of 50 species, brought together by WELLENSIEK (unpublished). After about 8
weeksfrom sowinginSD, theconditionsforflowerinductionwereinvestigated.
The plants received:permanent SD or LD,and in somecases 3 x GA3sprays
100p.p.m., or 16 weeks2°Cin SDfollowed byordinary SDor LD.
Table 39summarizes the results. It appears that most of these Caryophyllaceaearequalitative LDP.Inspecies 1andinspecies 14for 9%, therequirement
of LD for induction could bereplaced by GA3. Species4can beconsidered as
an LDPwith requirement for lowtemperature or GA3. Species 2and 15have
lowtemperature requirement and then are DNP, while species 3looks like the
sametypebut withthepossibility ofreplacing low temperatureby GA3.
TABLE 39. Flowering of caryophyllous species after SD,LD, GA 3 or 2°C treatment.
+ = applied; —= not applied.
nr.
species
1 Silene cucubalis WIBEL
2 Silene italica PERS.
SD
+
_
—
+
GA 3
_
—
2°C
—
—
+
+
+
—
—
+
—
+
—
+
—
_
—
—
—
+
—
+
—
—
—
60
LD
+
+
+
+
—
—
+
+
flowering
induction
q
%
by
0/20
20/20
20/20
4/20
0
100
100
20
LD
SD + GA 3
2° + SD
0/15
0/15
0/15
0/15
15/15
15/15
0
0
0
0
100
100
2° + LD
2° + SD
Meded. Landbouwhogeschool Wageningen 72-9 (1972)
species
SD
LD
GA 3
2°C
flowering
q
3 Silene nutans L.
4 Silene otites S.M.
5 SilenegallicaKOCH
6 Silene nocturna L.
7 Silene bosniaca BECK
8 Silene maritima WITH.
%
induction
by
+
+
+
+
+
+
-
+
+
-
+
+
0/15
0/15
4/15
14/15
7/15
10/15
0
0
27
93
47
67
+
+
+
+
+
-
+
+
-
+
+
0/15
7/15
0/15
15/15
15/15
3/15
0
47
0
100
100
20
+
-
-
-
0/15
15/15
0
100
LD
+
- + - -
-
0/15
15/15
0
100
LD
-
0/22
22/22
0
100
LD
2/13
13/13
15
100
SD
LD
0/13
13/13
0
100
LD
0/13
13/13
0
100
LD
0/22
22/22
0
100
LD
+
+
-
+
GA 3 + SD
GA 3 + LD
2° + LD
2° + SD
LD
GA 3 + LD
2°C + LD
2°C + SD
9 Silene annulata
HORT. ex FENZL
+
+
10 Silene brachypetala
HORT. ex FSNZL
11 Silene quinquevulnera L.
+
-
+
-
-
+
-
+
+
-
+
0/22
22/22
0
100
LD
+
-
+
0/22
21/22
0
95
LD
+
+
+
+
0/22
22/22
2/22
20/22
0
100
9
90
12 Silene echinosperma
Boiss. et HELDER
13 Silenealba (MILLER)
E. H. L. KRAUSE
14 Melandrium album
(MILL.) GARCKE
+
+
Meded. Landbouwhogeschool Wageningen 72-9(1972)
LD
GA 3 + SD
2°C + SD
61
nr.
SD
species
LD
GA 3
flowering
2°C
induction
by
q
%
0
0
0
100
100
2° + SD
2° + LD
100
100
SD
LD
15 Melandrium rubrum
+
—
—
—
+
—
—
+
+
0/22
0/22
0/22
22/22
22/22
+
—
—
-
—
—
22/22
22/22
+
(WEIG.) GARCKE
—
+
+
16 Dianthus sinensis
c.v. 'Bravo'
—
—
—
—
+
+
—
—
—
It is likely that flowering responses between 0 and 100% are caused by
genetic differences in the unselected material, as will be demonstrated for
Melandrium album on p.70.
5.3. GRAFTING-EXPERIMENTS
Experiment 44. Themostpromisingspeciesoftheavailable Caryophyllaceae
were selected and tried in grafting-experiments. For the graft combination r/d
alwaysa splitgrafting inthe stemwasmade,whilefor thereverse combination
d/r mostlyasplit-grafting intherosettewasmade,asdescribed in'Methods',p.
5.
Moreover, it is possible that for many plants an interaction exists between
GA3 and other inductive factors.
Table40showsa summary ofthegraft combinations withat least2months
of grafting-contact. The control graftings of the combinations without transmission offloweringare not mentioned; all are negative. It isremarkable that
most of the graft combinations did not show any transmission of flowering.
Besidescombinations33 and34withthealreadyknowncaseofS.armeria, only
apart ofthereceptorsoftreatments 16,19 and20flowered.Althoughthenumbers of thefloweringplants are small, the strictly vegetative controls of combinations 15and 18allow the provisional conclusion that afloweringplant of
S. echinospermacontains atransmissablefloralhormone whichisableto bring
vegetative shoots of both S. echinosperma and 5*.armeria in the combination
r/d intoflowering.Moreover, 2rootstocks of S. armeria reacted on downward
movement of floral hormone from donor shoots of S. echinosperma (nr. 20).
The successful combinations of treatments 16 and 19 are demonstrated in
photo's 23and 24.
Thepromisinggraft combinationswithS.echinosperma,treatments15,16and
17, were planned to be repeated in experiment45. However, all the plants,
'A
62
Meded. Landbouwhogeschool Wageningen 72-9(1972)
TABLE 40. Flowering response of some Caryophyllaceae receptors after at least 2 months of
grafting-contact with donors of the same family,
s = cleft grafting in the stem,
r = cleft grafting in the rosette.
nr.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
combination
grafting-
flowering
method
q
s
r
0/20
0/20
0/20
0/20
0/6
0/6
0/5
0/8
0/7
0/8
0/9
0/9
0/12
0/10
0/12
7/10
0/11
0/12
5/12
2/10
0/50
0/31
0/28
0/10
0/30
0/14
0/7
0/9
0/6
0/3
0/12
0/51
48/55
71/75
S. cucubalis r / S. cucubalis d
S. cucubalis d/ S. cucubalis x
S. armeriar / S. cucubalis d
S. cucubalis d / S. armeriar
S. nutansr / S. nutansd
S. nutansd / S.nutansr
5. nutansr / S. armeria d
5. otites r / S. otites d
S. otites d / 5.otites r
S. armeriad/ 5.otites r
S. armeriar / S.gallicad
S.gallicar / S. armeria d
S. armeriax/ S. nocturna d
5. nocturna d / 5.armeriar
5. echinosperma x/ S. echinosperma r
S. echinosperma r / S. echinosperma d
S.echinosperma d1 S. echinospermar
5. armeriar / 5.armeriar
5. armeriax/ S. echinosperma d
5. echinosperma d / 5.armeriar
Af. a/iu/Hr / Af. a/bumd
Af. a/6wmd / A/.a/6«m r
Af. a/i«m r / S.armeriad
5. armeriad/ M.albumr
5. armeriar / M.aftum d
Af. a/5wmd / S.armeriar
A/,albumx1 S. cucubalis d
5. cucubalis d/ Af. a/6«m r
Af. rubrumd/ 5.armeria x
S. armeriax/ D.sinensis d
Z>. sinensis d / 5.armeria x
S. armeriax/ 5.armeriar
5. armeriar / 5.armeria d
5. armeriad/ 5.armeriar
s
r
s
r
s
s
r
r
s
s
s
s
s
s
s
s
s
s
s
r
s
r
s
r
s
r
s
s
s
r
s
r
%
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
70
0
0
42
20
0
0
0
0
0
0
0
0
0
0
0
0
87
95
grown in SDbecame generative before the grafting. SoS. echinosperma, which
reactedinexperiments43and 44asaqualitative LDP,behaved nowasa DNP,
althoughthesameseedlotwasused.Apossibleexplanation forthisunexpected
reaction is that experiments 43 and 44 were done in winter with low light
intensity, while experiment 45 was done in summer. Since S. echinosperma
seemsto beofinterest for research onthefloralhormone, especially incombination with S. armeria,more research into the inductive circumstances is
Meded. Landbouwhogeschool Wageningen 72-9(1972)
63
nr:
15
nr. — treatment number of table40
PHOTO 23. S. echinospermaaftergraftingona vegetative rootstock (R/R, notflowering)oron
agenerative rootstock (RID, flowering).
Photo: 75 days after the grafting.
M»£e!*»M^«Mmt&Jl
treatment number of table40
PHOTO 24. S. armeriaaftergraftingonvegetativeS. armeria (RjR, inrosette) orongenerative
S. echinosperma (RID, weakfloweringshootsfrom the rosette).
Photo: 81days after grafting.
64
Meded. Landbouwhogeschool Wageningen 72-9(1972)
wanted. Selection for a late line might be a solution for the problem of undesired flowering.
Theflowering-responseof S. armeriadue to grafting with a donor of S.
echinosperma (treatment 19of table 40),was slow and weak, as could be seen
in photo 24.So it wasno surprise that these old, weakfloweringshoots of S.
armeria were not able to act as a donor in a next grafting on vegetative rootstocks of S,armeria.
5.4. SlLENE ARMERIA
5.4.1. Themechanism ofGA3 inflowerformation.
Experiment 46. Thedonor activity ofplantswhichwerebrought into floweringby GA3 in SDwasdemonstrated preliminary by WELLENSIEK (1966).This
problem could be extensively studied since WELLENSIEK (1970b) selected lines
of S. armeria, like N 4 , which can be brought intofloweringby GA3 in SD.
Another line, L,, could not be brought intofloweringby GA3. In order to
investigate whether floral hormone was present in GA-treated plants of N 4 ,
flowering shoots were cut off and grafted via the rosettegrafting method on
vegetative rosette plants of Lj.
Table 41showstheresults.Although somefloweringcontrol plants in treatment 1occurred, probably due to a technical error, thefiguresof treatment 2
convincingly demonstrate, that a GA3 treated N 4 is a good donor for Lx. So
GA3 induces the synthesis of afloralhormone in N 4 .
TABLE 41. Flowering of receptor rootstocks of the late line Li of S. armeria after rosettegrafting with L x r (control) or with donors of the GA3-induced line N 4 of S. armeria.
nr.
combination
flowering
%
1
2
L,r/L,r
N*d/L,r
3/21
17/18
14
94
days
94
60
5.4.2. Theinfluenceoftherootsandthe lowerpartoftherosetteontheinhibition
forflowering of theshoots ofa vegetativeplant.
Asmentioned before, severallinesofS. armeriawereselected.Someofthem
could notbeinducedtofloweringbyGA3,for exampleL t . GA3 appliedto L,,
gave stem elongation, and when the influence of GA3 had been finished, the
plants formed again a rosette,but now on a stem.When cut off and placed on
smallbottleswithwater,mostoftheserosetteselongated and evenfloweredfor
about 30%, although they were always under non-inductive circumstances.
Since the rosettes with roots remained vegetative, even although the lower
Meded. LandbouvhogeschoolWageningen 72-9(1972)
65
leaveswereremoved, thequestionsarose:Doesan inhibitinginfluence exist on
flowering, arisingfrom the roots, and isthereinteraction between an inductive
treatment and removal ofthe roots?
Experiment47. Plants of the line L ls 8 weeks from sowing in SD, were
misted 3times weekly with GA3-100p.p.m. The plants elongated and 5weeks
after thelast GA3-treatment,whentheactivity ofGA3haddimished androsettesonstemshadbeenformed, 0or2cyclesofCLweregiven.Thenextdaythe
rosettes were not or werecutoff and placed onwater.The results are presented
in table 42. Comparison of treatments 1and 3 shows the generally observed
phenomenon of somefloweringunder non inductive circumstances as a result
of removal of the roots. The limited reaction can perhaps be explained by assuming geneticaldifferences for the inhibiting influence of the roots. Comparison of treatments 2 and 4 shows that the small number of flowering plants
induced by 2cyclesof CLcan be increased by removal of the roots. The relatively large numbers of daystill visibleflowerbud points to slow development
on water. The conclusion is that interaction between CL and removal of the
roots might be possible. However, the small numbers do not allow definite
conclusions.
TABLE 42. The flowering of rosettes of S. armeria'Li' after 0 or 2cycles of CL, not followed
or followed by removal of the roots, or: with roots (+)and without roots (—) respectively.
CL
1
2
3
4
0
2
0
2
roots
+
+
—
—
flowering
q
%
days
0/9
2/12
3/12
5/10
0
17
25
50
cv>
40
53
55
WELLENSIEK (1967) demonstrated that GA3 is a partial induction factor for
the line L t . This means, that the inductive influence of GA3 can only be demonstrated in an interaction experiment. In order to investigate an eventual
interaction between GA3 and removal of the roots, the next experiment was
done.
Experiment 48. Plants of 8 weeks from sowing in SD received 3 weekly
GA 3^treatments. Directly after the last GA3 misting, the shoots were not or
werecut off and placed onwater or on one of 3concentrations of GA3. Table
43shows the results. Comparison of treatments 1 and 2showsthat also in this
experiment removal of the roots resulted in a partialflowering-reaction.
Although GA3wasapplieduntiltheremovaloftheroots,nocomplete flowering
appeared. Comparison of treatments 2, 3, 4 and 5 shows that GA3 in the
absorption medium had noinfluence ontheflowering-reaction.The conclusion
66
Meded. Landbouwhogeschool Wageningen 72-9 (1972)
TABLE 43. Flowering-reaction of S. armeria 'LV after misting with GA 3 , not followed or
followed by removal of the roots, or: with roots ( + ) and without roots (—) respectively and
placing of the shoots on water or one of 3concentrations of GA 3 .
nr.
1
2
3
4
5
roots
+
—
—
—
—
medium
_
water
GA 3 50 p.p.m.
GA3100 p.p.m.
GA3200 p.p.m.
flowering
q
%
0/10
19/49
3/10
3/10
3/10
0
39
30
30
30
is, that no interaction between GA3 and removal of the roots could be demonstrated.
5.4.3. Thefloralhormones of Silenearmeria andPerilla crispa.
In 1. 'General Introduction', it has already been mentioned thatXanthium
strumarium,BryophyllumdaigremontianumandSilenearmeriahavetheproperty
of non-localized synthesis of floral hormone, contrary to Perilla crispa with
strictlylocalizedsynthesis.However, ZEEVAART(1958)convincinglyprovedthat
induced leavesofP.crispapossesaverypersistent synthesis offloralhormone,
sincetheywereabletotransmitfloweringinaseriesofsuccessivegraftings.The
question was put: Are the differences between the former group and P. crispa
causedbydifferences betweenthefloralhormonesorbydifferences betweenthe
endogenous conditionsof the plants.Inthelatter casethefloralhormones can
beidentical,butthereactions of the plants aredifferent.This would meanthat
P. crispa forms afloralhormone after SD induction only.In order toinvestigate the reaction ofS. armeria on thefloralhormone ofP. crispa, a graftingexperiment wasdone.
Experiment 49. Plants of S. armeria 'L x ' were stem-elongated by GA3.
When the activity of GA3 had stopped, the shoots werecut off and grafted on
generative rootstocks of P. crispawhich had received 3 weeks of SD. The
flowersof the P. crispa rootstocks were regularly removed, while the newly
formed leavesremainedsincetheywereinducedbythepermanentSDconditions
and wereconsidered asnewsourcesoffloralhormonesynthesis.However, after
5 weeks the rootstocks began to die, while the receptor shoots were still in a
good condition. According to the method of WELLENSIEK (1970a) the shoots
were cut off and regrafted on vegetative rootstocks of S. armeria ' L / . When
thesegraft combinationshadgrowntogether,theywerehardenedoffandplaced
in the SDdivision of a greenhouse.
Inthecontrolgrafts S.armeriax\P. crispartheshootsofS. armeriahadtobe
exposed to SD, theP. crispa rootstocks to LD, since otherwise theywould be
induced to flower bud formation by photoperiodic action. These conditions
could be achieved in the 'daylength cabinet', described by WELLENSIEK and
Meded. Landbouwhogeschool Wageningen 72-9(1972)
67
ELINGS (1967). However, the shoots of S. armeria could not be supplied with
sufficient water and wilted.
Another control wasthe grafting of 5*. armeriaix shoots on vegetative rootstocksr t ofthesamespecies,followed byregrafting ther t shoots on vegetative
rootstocks r2 after 5weeks.
Table 44showsthat the shoots of the control treatment with only graftingcontact with S. armeria remained strictly vegetative, while treatment 2 shows
that the 5weeksofgrafting-contact withP.crispaingrafting 1 resulted in71 %
floweringingrafting 2.Thenumber ofdaystillvisibleflowerbud demonstrates,
that theflowering-reactionof the receptors was very slow. Still all generative
receptors reached the stage of completeflowering,about 5months from grafting1. However,therootstockswereoldonthatmomentandshowedhardlyany
development.May be due to thiscondition of the rootstocks, no transmission
offloweringfrom the generative receptors r t to the vegetative rootstocks r2
could be observed.
Photo 25 demonstrates the flowering of S. armeriaafter grafting with P.
crispa.
TABLE 44. Flowering of shoots of 5. armeria'IV after 5weeks of grafting-contact with rootstocks of vegetative S. armeria 'IV, or generative Perilla crispa,followed by regrafting on
vegetative rootstocks of S. armeria 'IV.
days = average number of days till visible flower bud from the date of grafting 1.
nr.
1
2
grafting 1
flowering
grafting 2
q
%
days
S. armeriar t
5. armeriart
S. armeriaTt
S. armeriar2
0/10
0/10
0
0
CS3
S. armeriar!
P. crispad
S. armeriart
S. armeriar 2
10/14
0/14
71
0
92
<x>
CO
5.4.4. Graftcombinations between S. armeria, B. daigremontianum andX.strumarium.
WELLENSIEK (1970a) clearly demonstrated transmission of flowering from
X. strumarium to S. armeria,although numerous attempts with the reverse
combination completely failed (personal communication). He points to the
possibility of identity of the floral hormones of these plants, which have the
property of non-localized synthesis of floral hormone in common. Another
plant withthisproperty isB. daigremontianum.
The question arose: Is there identity between the floral hormones of S.
armeria,B. daigremontianum and X. strumarium! Many graft combinations
were made between X. strumarium receptors and donors and B. daigremontianumdonorsandreceptors,however,withoutflowering-reactionofthereceptors.
68
Meded. Landbouwhogeschool Wageningen 72-9(1972)
Kt'r
nr: 1
grafting 1
nr. = treatment number of table44
grafting 2
PHOTO 25. Transmission of flowering from a generative rootstock of P. crispa to a grafted
vegetative shootof S. armeria.
Grafting 1: left: S. armeriaTiJS. armeriar t (control), right: S. armeriaTt/P.crispad.
Photo: 4 weeks from grafting 1.
Grafting 2: shoots regrafted after 5weeks of grafting contact in grafting 1.
Left: S. armeriar J S . armeriar2 (rj = control-shoot of grafting 1).
Right: S. armeriarJS. armeriar 2 (rx had 5weeks of grafting-contact with P.crispa).
Photo: 12weeks from regrafting on r».
Experiment50. Thegraft combination ofS.armeriar/B.daigremontianum d
seemed to bepromising.After 5weeksofgrafting-contact the shootswerestill
alive. However, neither shoots kept on B. daigremontianum nor shoots, regrafted on vegetativerootstocks of S. armeria, showed any flowering-reaction.
5.4.5. Theinfluenceofthesurface-activechemicaldimethylsulfoxydeonthetransmission offloralhormone.
Experiment 51. Plants of S. armeria ' L , \ 8weeksfrom sowingin SD,were
grafted withdonorshootsofL t ,whichwerecutfrom plantswhichhadreceived
3 weeks of LD. The grafting-method was split grafting in the rosette. Before
andafter thegrafting aseriesofDMSOtreatmentswasapplied.Althoughhigh
amountsofDMSOweregiven,notoxiceffect couldbeobserved.
Table45showsthat 3 weeksofdonor-contactofd/r istooshortfor theslow
downwardtransmissionoffloralhormonetoobtaingoodflowering.DMSOdid
not improvethistransmission at all.
5.4.6. Inoculation experiments with sapfromfloweringplants.
Certainpropertiesoffloralhormoneshowsimilaritywith somevirusses. For
instance:transmission by grafting and the eventual capacity of autocatalytical
multiplication of the floral hormones of some plants (WELLENSIEK, 1966). A
remarkable property ofvirussesistransmission byinoculation.
Meded. Landbouwhogeschool Wageningen 72-9(1972)
69
TABLE 45. Flowering of rootstocks of S. armeria'Li* after 3 weeks of grafting-contact with
a donor, while different mistings with dimethylsulfoxyde (DMSO) were applied.
nr.
combination
DMSO
in%
1
2
3
4
5
6
7
8
9
10
d/r
d/r
r/r
d/r
r/r
d/r
d/r
d/r
d/r
d/r
0
5
5
5
1
1
0
1
0
1
flowering
misting
r, 3d. before grafting
r, 4 h. before grafting
d/r, 2 x a day
r/r, 2 x a day
d, daily
d, daily
d, daily
r, daily
r, daily
q
%
days
6/24
3/17
0/21
4/23
0/21
2/18
1/16
0/16
2/16
1/18
25
18
0
17
0
11
6
0
12
6
40
43
cv>
36
CV)
38
69
CS3
68
69
Experiment 52. Inoculation techniques,usedinvirology,weretried totransmitfloweringfromfloweringplants of S. armeriato vegetative ones. However,
none of thesetreatments resulted infloweringof the receptors.The conclusion
is,that thefloralhormone of S. armeria immediatelylosesitspersistence,once
outside the plant.
5.5. MELANDRIUMALBUM
5.5.1. Introduction.
In experiment 43of 5.2. M.album provedto be a qualitative LDP in which
low temperature treatment of 2°C could replace the LD action. Moreover,
induction by mistingwith GA3 waseffective for some plants. The general impression was that M. albumcould be a Caryophyllaceae, like S. armeria, of
interest for theresearch oftheflowering-process.However,inexperiment 44of
5.3.notransmissionoffloweringbygrafting couldbedemonstrated. Inthenext
experiments someselections are described and the existence of a transmissable
floralhormone wasstudied intensively.
5.5.2. Induction experiments.
Experiment 53. Plantsof8 weeksfrom sowinginSDreceived 1, 2or3 weeks
of LD and were moved back to SD. The earliestfloweringmale and female
plants of the group of 1 week LD were selected and placed in LD where they
werecrossed and yielded the seedsof the line early I. Similarly the crossingof
the latestfloweringplantsofthegroup,whichreceived 3weeksof LD, resulted
in the linelate I.
Bothlines, earlyI andlate I, weremisted withGA3 100p.p.m. Allthe plants
reacted with stem elongation.
Table46showsthat theplantsofthelineearlyI reacted to GA3with flower70
Meded. Landbouwhogeschool Wageningen 72-9(1972)
TABLE 46. Flowering of M.albumlines early I and late I after misting GA 3 100 p.p.m.
weekly, varying times, in SD.
nr.
line
GAj
flowering
%
q
1
2
3
4
5
6
early I
early I
early I
early I
late I
late I
0 x
1X
2 x
3 x
0 x
3 x
0/60
3/72
58/78
60/63
0/60
0/60
0
4
74
95
0
0
ingbetteratincreasingamountsofGA3,whilelateIdidnotreacttothehighest
amount of GA3 at all.Thefloweringplants of treatment 2,being 2males and
one female, were crossed and yielded the seeds of the line early II, which was
used in the following experiments, where the uniformity of the new selection
early II and the inheritance of the sensitivity for GA3-induction were studied.
Experiment 54. The lines early II and late I were inbred and crossed. The
seedsofthe newgenerationsofearlyIIandlateIand oftheirhybrid weresown
in SD.From 8weeksafter sowing the plants weretreated with GA3.
Table 47 shows that early II flowered uniformly after one treatment with
GA3. Late I did notflowerat all after 4 weekly treatments with GA3, while
under theseconditions the Fj, early x late,floweredfor 46%.Theconclusion
isthat theFt ofearly Xlate,concerningtheflowering-reactionafter treatment
with GA3, lies between the rapidlyfloweringearly II and the non flowering
late I.
Photo 26illustrates theseresults.
Experiment 55. ThelinesearlyII,lateIandtheir Fi weresownin LD. After
varying numbers of weeks of LD the plants were moved back to SD. The
TABLE 47. Flowering of 2 lines of M. album and their F! after misting GA 3 100 p.p.m.
weekly,varying times, in SD.
nr.
line
flowering
GA 3
q
1
2
3
4
5
6
7
8
early II
early II
late I
late I
late I
early x late
early x late
early x late
0 x
1X
0 x
1X
4 x
0 x
1X
4 x
Meded. Landbouwhogeschool Wageningen 72-9 (1972)
0/25
25/25
0/25
0/25
0/25
0/25
0/25
11/24
%
days
0
100
0
0
0
0
0
46
cv>
18
oo
C\3
OO
<X>
oo
33
71
wtMWIMtqBMnwW'o^^r^v*^' **'vf**~
treatment number of table47
PHOTO 26. Flowering-response of an early (E) and a late (L) line and their Fi (E XL) of
M. albumafter 1 misting withGA3 100 p.p.m.
Only E (left) flowered. Thestem elongation of E x L (right) after theGA 3 treatment was
stronger than of L.
Photo: 44 days after the GA 3 treatment.
flowering-results are presented in table 48.Comparison of treatments 2, 7and
12showsthatwithin 5weeksfrom sowingonlyearlyIIcanbeinducedfor 35%.
Treatments 3,8and 13 showthat thenumbersofLD,necessaryfor a floweringreaction of F t , are intermediate between early II and late I. Moreover, comparison of the treatments with 95%floweringshows that Fi with 7 weeks,
treatment 14,liesbetween earlywith6weeks,treatment 3,and lateI with more
than 8weeks,treatment 10.
Experiment56. Plants of 8 weeks from sowing in SD received varying
numbersofcyclesofLDinordertoinvestigatetheminimumnumber ofLD for
a 100percentfloweringin SDofthelinesearlyII,lateI and their F t .
Table 49 shows that 7 or less cycles of LD are sufficient for 100 percent
flowering ofearly II,whilelate I needsmore than 13cyclesand the Fxflowers
completelyafter thistreatment.TheFx isvariable,buttendstobeintermediate.
72
Meded. Landbouwhogeschool Wageningen 72-9(1972)
TABLE 48. Flowering of 2 lines of M. album and their Ft in SD after varying numbers of
weeks in LD from sowing.
nr.
LD in weeks
line
flowering
%
q
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
early II
early II
early II
early II
early II
late I
late I
late I
late I
late I
Fx
F,
F,
F,
F,
4
5
6
7
8
4
5
6
7
8
4
5
6
7
8
0/20
7/20
19/20
19/20
19/20
0/20
0/20
0/20
19/24
19/24
0/20
0/20
8/20
19/20
20/20
0
35
95
95
95
0
0
0
79
79
0
0
40
95
100
TABLE49. Flowering of 2 lines of M. album and their Ft after growing in SD for 8weeks,
followed by varying numbers of cycles of LD.
nr.
line
LD cycles
flowering
q
1
2
3
4
5
6
7
8
9
10
11
12
early II
early II
early II
early II
late I
late I
late I
late I
F,
F,
F,
F,
7
9
11
13
7
9
11
13
7
9
11
13
5/5
5/5
5/5
5/5
1/5
0/5
3/5
1/5
1/5
3/5
3/5
5/5
%
100
100
100
100
20
0
60
20
20
60
60
100
days
15
14
12
12
42
(X)
40
41
45
26
24
20
5.5.3 Grafting-experiments.
The preceding experiments showed,that the line late I cannot beinduced to
flowering by GA3-treatment, although stem elongation takes place.
Experiment57. Rootstocks and shoots ofthesevegetativeelongated rosettes
weregrafted, bymeansofanordinarycleft graft, withshootsand rootstocksof
flowering plants respectively. Although many variations within the graft
technique and material used were tried, never a transmission of flowering was
Meded. Landbouwhogeschool Wageningen 72-9(1972)
73
observed. Evenwhentheearly linewasused asa receptor, by meansoftherosette grafting without GA3 treatment, nofloweringof the receptor appeared.
Thegeneralphenomenon wasthatthedonors,whichwereinducedinLD,becamevegetativeunderthefollowing,non-inductiveSDcircumstances.Thisinduced
thequestion whether diminishing ofthedonor capacity by SDwas responsible
for the non transmission offloralhormone to the receptor.
In a next experiment graft combinations ofa latereceptor shoot on an early
donor rootstock and the reverse were sprayed with GA3 in SD. Bythis treatment the late receptors remained vegetative, while the early donors could be
permanently induced and keptflowering.Different treatments were tried, like
theuseofyoungvegetative,just induced donors ordonorsalreadyfloweringat
the moment of grafting. Also the removal of donor buds and flowers and
receptorleaveswasvaried.However,nofloweringofthereceptorsoccurred.The
impossibility to demonstrate atransmissablefloralhormone ofM. album could
not be explained. It was asked whether graft combinations of M. album with
the related Silene armeria could give more information. Maybe the very
persistentfloralhormone of S. armeria could bring M. album intofloweringor
perhaps a receptor of S. armeria was more sensitive to react to the eventual
floralhormone of M. album than M. album itself.
All possible combinations of S. armeria as receptor or donor and M.album
asreceptor or donor weretried. However, in spiteof good growingtogether of
all thesegraft combinations, none of the receptors showed anyfloweringreaction.
5.6. CONCLUSIONS
40. Theinductivecircumstances of 16Caryophyllaceae wereinvestigated. They
provedtobeDNPorLDPwithinsomecasesarequirementoflowtemperature or reaction on GA3.
No SD response was found. In2species the requirement of LD could be
replaced by GA3.
Since the inductive treatments wereabundant, it is likely thatfloweringresponsesbetween 0and 100%arecausedbygeneticdifferences. (Exp.43).
41. Out of 34graft combinations besides the well known case of S.armeria,
only S. echinosperma gave transmission of flowering, while moreover
5. echinosperma could bring S. armeria into flowering. This suggests
identity between theirfloralhormones. In general, transmission of flowering by grafting was an exception rather than a rule. (Exp.44).
42. DonorcapacityofthelineN 4 ofS.armeria,broughtintofloweringbyGA3,
demonstrated that GA3 actslikeanother induction factor viathesynthesis
offloralhormone. (Exp.46).
43. Shoots cut from vegetative, GA3-elongated plants of S. armeria ' L i \
floweredfor about 30%, when placed on water under non inductive circumstances. This points to the possibility of aflowerinhibiting influence
74
Meded. Landbouwhogeschool Wageningen 72-9(1972)
arising from the roots. CL and removal of the roots had some promotive
effect, but the combination of GA3 + removal of the roots had not. It is
possible that genetic variability is responsible for the limited floweringreaction after removal of the roots. (Exp. 47and 48).
44. S.armeriacouldbebroughtintofloweringbygrafting ontheSDP.P. crispa
Although theflowering-reactionof S. armeriawasveryslowandthe floweringreceptorswerenot ableto act asdonor,thepossibilityexistsofidentity
of the floral hormones of S. armeria and P. crispa. (Exp.49).
45. No transmission of flowering between the graft combinations of Silene
armeria and Bryophyllum daigremontium could be demonstrated. (Exp.
50).
46. No influence of thesurface activechemicaldimethylsulfoxyde (DMSO) on
thetransmission offloweringbygrafting couldbedemonstrated. (Exp.51.)
47. Transmission of flowering by inoculation of S. armeriawith sap from
flowering plants of this speciescould not be demonstrated. (Exp.52).
48. M. albumis a qualitative LDP. Two lines could be selected, early II and
late I, of which early II could be induced tofloweringby 1treatment of
GA3, while lateI remained vegetative after 4treatments.(Exp.54).
49. The F t of early II X late I was intermediate concerning the response to
GA3-induction. (Exp.54).
50. Even in extended experiments transmission of flowering could not be
demonstrated by grafting of M. album with M. album and M. album with
S. armeria in all possible combinations. (Exp.57).
Meded. Landbouwhogeschool Wageningen 72-9 (1972)
75
6. GENERAL DISCUSSION
6.1. T H E FLOWERING-PROCESS
Thefloweringofplantsispreceded bythe change ofthe active growing-points
from the vegetative to the generative stage. In most plants this change will be
dueto anendogenoussignal,beingtheresultofachain ofprocesses,called the
floral chainin the following discussion. This floral chain is often called the
induction offlowering(EVANS, 1969). Another concept is to reserve the term
induction for the initial stages of the floral chain, resulting after complete
induction in the inductive state.
There are plants in which induction occurs without any specific exogenous
signal after the completion of eventualjuvenility. Other plants, however, need
such a signal, for example thermo-induction, photo-induction or chemoinduction.
In several plants theexistence ofafloralhormone could beproved. In those
cases induction can be considered as the deblocking of the synthesis offloral
hormone. The term deblocking implicates the hypothesis that no synthesis of
floralhormone occursbefore induction. However, when induction would be a
raiseofthelevelofalreadypresentfloralhormone,thetermaccelerationwould
be better. The floral chain of plants with a floral hormone can be roughly
divided in: induction and realization, the latter subdivided in transport and
action offloralhormoneasinitiation offlowerbudsinthereceptivemeristems.
Thispresentationwillbetoosimple,andmoreprocessesbetweeninductionand
visiblefloweringmayoccur.However,theabsenceofmoreconcreteknowledge
mayjustify theuseofasimplescheme.Studyofseparatefactors influencing the
individual processesofthefloralchainmaygivemoreinformation. Mostofthe
preceding experiments were done with that purpose and some of their results
justify a further discussion.
6.2. THE INFLUENCEOFTEMPERATURE ONTHE FLORALCHAIN
OF SOMECRASSULACEAE
In the case of Bryophyllumdaigremontianumnofloweringoccurred after the
shift LD -»SDorafter GA3 + SDwhentheaveragetemperatureper24hours
wasabout 23°Cor higher (exp. 1).Differentiation of theinfluence of temperature on the individual processes of thefloralchain resulted in the conclusions
that not the LD induction was influenced by the investigated temperatures
(exp.4),whilecomparison ofexperiments 1 up to andincluding9demonstrates
thatnot theSDinduction,buttheresultinginductivestateandthealreadysynthesizedfloralhormone aredestructed bytoo higha temperature.
Because both the inductive state and the floral hormone are destructed by
76
Meded.Larulbouwhogeschool Wageningen 72-9 (1972)
toohighatemperature, itmightbepossiblethatfor acontinued inductivestate
under non inductive circumstances the presence of floral hormone is required
for itsowncontinued synthesislikeinachainreaction mechanism.Inthiscase,
destruction of the inductive state is only indirectly influenced by temperature.
Experiment9demonstrated thattemperaturetreatment,whenlongenough,can
destruct theinductivestatecompletelywhilerenewed induction ofthe formerly
induced leaves is possible. This points to the hypothesis that high temperature
causes a reblocking of induced leaves.
Since normalfloweringoccurs when the temperature during induction was
at a level,destructive forfloralhormone,it isnot likelythat synthesis offloral
hormone takes placebefore the stage of complete induction.
Theconclusion ofexperiment 1 wasthat theinhibitory action of temperature
is determined by a sum of the products of temperatures times hours per 24
hours. This means that moderate temperature, in light as well as in darkness,
can nullify the influence of high temperature. No further data are available to
explain this phenomenon.
RUNGER (1959) demonstrated that the related Kalanchoe blossfeldiana has
a requirement for thermoperiodicity during the SD induction, which could be
fullfilled by thecombination of2temperatures per 24hours or by dividing the
SD induction into 2 periods with different temperatures. The hypothesis of
RUNGER was that 2processes with different temperature optima are necessary
for complete induction. Experiment 10 confirmed these results about the influence oftemperature duringinduction, whileinexperiment 11 noinfluence of
temperatureonthecontinuedfloweringcouldbedemonstrated. Experiments12,
13and 14showed that also the floral chain of the Crassulaceae Bryophyllum
pinnatum, Kalanchoejongmansii and K. manginii is temperature sensitive.
The general conclusion is that temperature influences somewhere thefloral
chain of the investigated Crassulaceae, whilethe cases of B. daigremontianum
and K. blossfeldiana demonstrate that in individual species different processes
of thefloralchain may be influenced.
6.3. FLORALHORMONE
Transmission offlowering- read: of the impulse to flowering - between
graft-partners of different photoperiodic response types or even of different
families, suggests a moreuniversalfloralhormone.This could beconfirmed by
the next new graft combinations:
SDP K. blossfeldiana r/LSDP B. daigremontianum d (exp.22)
DNP H. annuus d/SDP X. strumarium r
j nr n F P n i 10711
DNP C.officinalis d/SDP X. strumarium r \ vvAN DETOLi*/ ) .
LDP Caryophyllaceae S. armeria r/SDPLabiatae P. crispa d (exp.49).
It was questionable whether the LSDP B. daigremontianum synthesized 2
components of floral hormone, one in LD and one in SD, as supposed by
PENNER (1960). The negative result after the shift SD + GA3->LD demonMeded. Landbouwhogeschool Wageningen 72-9(1972)
77
strates that no SD induction occurs before LD induction (exp. 17).ZEEVAART
(1967)demonstrated that although thelevel ofendogenous GA of a plant kept
inSDisquitelowcomparedtoaplantinLD,itwillbetheshift LD ->SDthat
increasestheendogenousleveloncemore.ZEEVAARTandLANG(1963)discovered
suppression offloralinitiation byCCC,whenapplied duringtheSD treatment
after the shift LD -»SD. Their conclusion wasthat B. daigremontianum needs
ahighGAlevelfor production offloralhormoneinSD.Anexplanation forthe
negativeresultsoftheexperimentsinwhichaLD-andaSDpartofaplantwere
connected (RUNGER, I960,and exp. 19)mightbethat inthe LD part ofa plant
the GA level is still too low to be active in the SD part when transported.
LD + GA3.
RUNGER did not obtainfloweringin thecombination
—
Difficult
downward movement of GA3could be an explanation for thisnegative result.
SD
It isa pitythatthereversecombination . _ > , - , . — w a s not made.
LD + GA3
Theconclusionfor B.daigremontianumisthatthereareno2daylengthcomponents of thefloralhormone, but that one leaf needs both daylengths in the
sequence LD + SDfor complete induction. Applied GA3 in SDmust then be
considered as an induction factor, which replaces the requirement for LD, as
wasdemonstrated by ZEEVAARTand LANG(1962).
Experiment 46alsodemonstrated that GA3 in S. armeriainduces to thesynthesis offloralhormone, like other induction factors.
6.4. TRANSPORT OFFLORALHORMONE
All experiments, in which the influence of the duration of grafting-contact
on the transmission of flowering was tested, demonstrate that a minimal
period isnecessary (EVANS, 1969).The reason willbethat a graft combination
without sufficient growingtogether ofthepartnerswillnot givea translocation
of intactfloralhormone. Thenegative results offloralhormone extraction and
inoculation experiments with S. armeria(exp. 52) would suggest that even
persistentfloralhormonesaredirectlyinactivated outsidetheplant.Theconclusionisthatfloralhormonecanonlyremainactiveduringthetransport from the
leavestothemeristems,whentheplantcanprotectitagainstdestructingexternal influences.
Inmanycasesit could bedemonstrated that translocation offloralhormone
willaccompanytheflowofcarbohydrates. LINCOLNet al. (1956) demonstrated
with-X.strumarium that factors influencing thetranslocation of carbohydrates,
for instance the creation of a carbohydrate-deficient condition, will also influence thetransportoffloralhormone.Theyconcludedthataninverserelationship exists between the amount of LD leaf tissue of a receptor shoot and the
magnitude of theflowering-response.A unit area of LD leaf tissue would be
abletonegateadefinitequantityofhormone.Experiment 36demonstrated that
defoliation of a grafted receptor stimulated the rate of the flowering-response.
78
Meded. Landbouwhogeschool Wageningen 72-9 (1972)-
Anexplanation for theinhibitingaction ofLDleavesisthattheyform asinkof
floralhormone. Experiments 33,34and 35demonstrated that the presence of
receptor leaves has a strong influence on the growth of axillary shoots. When
defoliation means a lowering of the vegetative development, it might beeasier
for thefloralhormone to promote the generative development.
Grafting-experiments demonstrated that many factors can influence the
transmission of floral hormone. Experiment 16 demonstrated that the floral
hormoneofB.daigremontianumprefersupwardmovement. RESENDEand VIANA
(1948) discovered that inverted generative plants of B. daigremontianum could
flower from the root pole,whileusually the basic budsform vegetativeshoots.
ThismeansthatthemovementofthefloralhormoneofB.daigremontianum has
a negative geotrophism.
Experiment 38 demonstrated that young receptor rootstocks of X.strumarium can react much more easily tofloralhormone than old ones.In thiscase
the age ofthe receptor tissuemay influence thetransport offloralhormone.
6.5. FLORAL HORMONEAND FLORALINITIATION
Thetermfloralinitiation isusedfor thechangeofa meristemfrom thevegetativetothegenerativestage. EVANS(1969p.457)prefers thetermevocationfor
this process,adopted from embryology. However, to myopinion initiation indicates the processsatisfactorily andhas theadvantageof being generallyused.
In literature many negative flowering-reactions in interspecies graftingexperiments were explained by assuming the existence of different floral hormones. In this reasoningflowerdevelopment of the meristems of one type of
plant could only be initiated by one specific type of floral hormone. Like
different keys belong to different locks, different floral hormones implicate
different types of meristems. However, comparison of the cases of K.blossfeldianaearly and late (exp.24)and X. strumarium early,middle and late(exp.
42) demonstrates that early lines need less floral hormone for afloweringreactionthan thelateones.Thiscould mean that thethreshold valuesforfloral
hormone ofthemeristemswillbelowerfortheearlylinesthanforthelateones.
It remainsunanswered whya lowrequirement for induction and alowrequirement for floral hormone are combined. Moreover, the question cannot be
answered whether the endogenous level offloralhormone of afloweringearly
plant remains lower than of afloweringlate plant.
The good donor capacity of B. daigremontianum towards K. blossfeldiana
(exp. 22) in contrast to the donor capacity of K. blossfeldiana for B. daigremontianum (exp.23)suggestsa lowerleveloffloralhormoneinK. blossfeldiana
thaninB.daigremontianum. Experiment29showed thatamoderately flowering
plant ofX. strumarium withalowleveloffloralhormoneisnot abletoactasa
donor.Sotheinabilityofsomeplantstotransmitfloweringbygrafting iscaused
bytoolowaleveloffloralhormone.Theinfluenceoftemperatureonthe floweringof Crassulaceaeand thefactors influencing thetransmission offloweringof
Meded. Landbouwhogeschool Wageningen 72-9(1972)
79
Xanthiumdemonstrated that many factors can influence the transmission of
flowering.
Experiment 44demonstrated that aflowering-reactionafter grafting avegetative and a generative part of a plant isan exception rather than a rule. The
caseofM. album(exp.57)showedthatinspiteofmanyefforts theexistenceofa
graft-transmissable floral hormone could not be proved. However, it is not
necessary to assume that plants without demonstrable transmission of floweringdonothaveafloralhormone,becausemanynegative resultscanbeascribed
to factors, mentioned intheforegoing, and to other stillunknown factors.
6.6 FLORAL HORMONE AND FLOWERDEVELOPMENT
TUKEYetal. (1954)define thefunction offloralhormoneas: 'initiation ofthe
formation offloralprimordia, orpromotion oftheirdevelopment.' Experiment
21 demonstrated that after marginal induction theflowerbuds of K. blossfeldiana abort, while the plant revertsto the vegetativestate. The explanation is
that marginal induction resultsin synthesis of a small,disappearing amount of
floralhormone, whilethe presence of sufficient floral hormone isnecessary for
flower initiation aswell as forflowerdevelopment.
RUNGER (1959)demonstratedthat the number offlowersof K. blossfeldiana
dependsontheinductivetreatment.Inthiscasetheconclusionmightbethatthe
level of floral hormone, which will depend on the inductive treatment, determines the number of flowers. This could also be observed in X.strumarium
where the level offloralhormone determined the level of the balance between
vegetative and generativedevelopment (exp.27,28and29).
6.7. FLORAL HORMONEAND CONTINUEDFLOWERING
An important question in the physiology offloweringis:Why does a plant
stopflowering?InthecaseofB.daigremontianumdestruction offloralhormone
by too high a temperature is the cause of the reversion of the meristematic
development from generative to vegetative. This is an indication that the
presenceoffloralhormone isacondition for continuedflowering.Thisconclusionisconfirmed bytheflowering^patternofB.daigremontianumunder optimal
temperature conditions. In this case the lateral buds, releasing in downward
direction,form inflorescences until theinduced leavesbecomeold and willstop
synthesis of floral hormone. Then the later releasing lateral meristems form
vegetative shoots.
Itisremarkablethatthe3known plantswithnon localized synthesisof floral
hormone willcontinue toflowerunder non inductive but otherwise favourable
circumstances. It isunknown whether in other plants withcontinued flowering
under non inductive circumstances non localized synthesis of floral hormone
occurs.
80
Meded. Landbouwhogeschool Wageningen 72-9 (1972)
Theterm 'non localizedsynthesisoffloralhormone' wasalready mentioned in
the introduction, p. 3. As early as 1938 HAMMERand BONNERcalled 'indirect
induction' the continuous flowering of a receptor of X. strumarium due to
contact with a donor. ZEEVAART and LANG (1962) reserved this term for the
phenomenon that shoots of some plants, brought intofloweringby grafting,
can act as a donor in a next grafting. EVANS (1971) called this 'secondary
induction'. Itislikelythattheseauthorsmeanttoindicatethatfloralhormoneas
such can act asan induction factor. In order to distinguish thisform ofinduction from the normal exogenous induction, they used the terms indirector
secondary. The term endogenous induction would indicate more clearly what
processismeant, distinguishing itfrom exogenous induction. ZEEVAART(1969)
found that only generative plants of B. daigremontianum with leavescan act as
a donor in a grafting experiment. So here only the leaf can act as source of
floral hormone. However, no arguments are available to decide whether the
multiplication offloralhormone in non exogenously induced tissue occurs via
trueinduction orviaautocatalytical multiplication (WELLENSIEK, 1966).Therefore, the term non-localizedsynthesis offloralhormone ispreferred, indicating
the contrast to themechanism with strictly localizedsynthesis inP. crispa.
Although thefloweringof K.blossfeldiana, caused by grafting on B. daigremontianum,wasabundant,nosynthesisoffloralhormoneintheK.blossfeldiana
receptors could be demonstrated (exp.24).It istherefore likely that the differencesbetween B.daigremontianum and K. blossfeldiana, concerningthephenomenon of localized synthesis of floral hormone, are caused by differences in
internal conditions between these plants and not by different floral hormones.
AlsothecaseofS.armeria,brought intofloweringbyP.crispa(exp.49),points
to this explanation.
6.8. GENERALCONCLUSION
Thefunctions offloralhormoneintheflowering-processcanbeflowerinitiation, promotion offlowerdevelopment and continuation of flowering.
Sincedifferences inflowering-reactionscanbeexplainedbydifferent levelsof
thefloralhormone and/or by differences in internal conditions of the plant in
whichthefloralhormone hasto act after formation or arrival,theexistenceof
oneuniversalfloralhormone remainspossible.
Meded. Landbouwhogeschool Wageningen 72-9(1972)
81
7. SUMMARY
The factors, influencing the synthesis and action of floral hormones, and
possible differences between floral hormones in different plants were studied.
The experimental results are summarized in the conclusions 1-20, on pages
35-36 ^Crassulaceae"); 21-39 on pages 58-59 ('Xanthium strumarium) and
40-50 on pages 74-75 ('Caryophyllaceae').
General conclusions are as follows:
1. The processes leading toflowerformation of plants withafloralhormone
can be roughly divided in induction and realization, the latter subdivided
in synthesis, transport and action offloralhormone as initiation of flower
buds in the receptive meristems. These processes are called the 'floral
chain'.
2. In the long-short-day plant Bryophyllum daigremontianum neither the LD,
nor the SDinduction wereinfluenced qualitatively bytemperature,but the
resulting inductive state and the already synthesized floral hormone were
destructed by too high a temperature.
3. In the short-day plant Kalanchoe blossfeldianatheinductionwasinfluenced
bytemperature,sothat inindividualspeciesdifferent processesofthe floral
chain may be influenced.
4. In the LSDP B. daigremontianum no 2 separate components of thefloral
hormone are formed.
5. Thetransmission offloralhormonebygrafting isinfluenced bythedirection
of movement of the hormone in B.daigremontianum and by the age of the
receptor in the SDP Xanthiumstrumarium.Presence of the leaves in X.
strumariumstronglystimulatesthegrowthoftheaxillaryshootsand reduces
theflowering-reaction,while defoliation of receptors promotes the transmission of flowering.
6. In K.blossfeldiana and X. strumarium early lines need less floral hormone
for aflowering-reactionthan late ones.The former havea lower threshold
value of the hormone.
7. The good donor capacity of B. daigremontianum towards K. blossfeldiana
in contrast to the reverse combination suggests a lower level of floral
hormone in K. blossfeldiana than in B. daigremontianum.
8. AlsoinX.strumariumdifferent levelsoffloralhormone,correspondingwith
different floral stagesanddifferent donor capacities,couldbedistinguished.
9. The factors influencing thefloweringof a receptor, grafted with a donor,
mentioned sub 5, 6, 7and 8, make it questionable to assume that plants
without demonstrable transmission offloweringdo not have a floral hormone,whilenegativeresultsofinterspeciesgraftings need not becaused by
differences infloralhormones. New successful combinations between graft
partners ofdifferent photoperiodic response typessuggest amore universal
floralhormone.
82
Meded. Landbouwhogeschool Wageningen 72-9(1972)
10. The action of floral hormone is not restricted to floral initiation. In K.
bhssfeldiana the presence of sufficient floral hormone is also necessary for
flowerdevelopment, while in K. bhssfeldianaand in X. strumarium the
number offlowersdepend on the leveloffloralhormone. In B. daigremontianum the presence offloralhormone isa condition for continued flowering.
11. Theterm 'non-localized synthesisoffloralhormone'wasintroduced for the
phenomenon that receptors of some species brought into flowering by
grafting, can act asadonor inanext grafting. It islikelythat the difference
between B. daigremontianum and K. bhssfeldiana concerning localized
synthesis offloralhormone iscaused by differences in internal conditions
between theseplantsratherthan bydifferentfloralhormones.Alsothecase
of Silenearmeria, brought intofloweringby Perilla crispa, suggests this
explanation.
12. Sincedifferences inflowering-reactionscan beexplained bydifferent levels
offloralhormone and/or bydifferences ininternal conditions of theplants
in whichthefloralhormonehasto act,theexistenceofoneuniversalfloral
hormone remains possible.
Meded.Landbouwhogeschool Wageningen 72-9 (1972)
83
8. SAMENVATTING
BLOE1-INDUCTIE, BLOEIHORMONEN EN BLOEI
Faktoren, diedesyntheseen dewerkingvan bloeihormonen bei'nvloedenen
mogelijkeverschillen tussen bloeihormonen vanverschillendeplantenwerden
onderzocht.
Dealgemene conclusieszijn alsvolgt:
1. De processen dieleiden tot bloemknopvorming van planten met eenbloeihormoon kunnen globaal worden verdeeld in inductie en realisatie, het
laatste onderverdeeld in synthese, transport en werking van het bloeihormoon. Deze werking van het bloeihormoon bestaat uit bloei-initiatie in
ontvankelijke meristemen. Deze processen worden de 'bloeiketen' genoemd. Velevan de hier vermelde proeven werden gedaan om de invloed
van verschillendefaktoren opdeafzonderlijke processenvan debloeiketen
te onderzoeken.
2. IndeIang-korte-dagplantBryophyllumdaigremontianumwerddeLDnoch
de KD inductie kwalitatief beinvloed door temperatuur, terwijl de resulterende geinduceerde toestand en het reeds gesynthetiseerde bloeihormoon
werden vernietigd door een te hoge temperatuur.
3. In de korte-dag plant Kalanchoe blossfeldiana werd de inductie beinvloed
door de temperatuur, waaruit blijkt dat in aparte plantesoorten verschillende processen van de bloeiketen kunnen worden beinvloed.
4. IndeLKDPB.daigremontianumkonden geen2verschillendecomponenten
van het bloeihormoon worden aangetoond.
5. Deoverdrachtvanbloeihormoon doorentingwordtbijB. daigremontianum
bei'nvloed door detransportrichting, terwijl bij de KDP Xanthium strumarium deleeftijd vandereceptorvanbelangis.Deaanwezigheid vandebladeren van X. strumarium bevordert degroei van de okselscheuten sterk en
beperkt daardoor de bloeireaktie, aangezien ontbladering van receptors
overdracht van bloeihormoon bevordert.
6. Vroege lijnen van K. blossfeldiana en X. strumarium hebben minder bloeihormoon nodig voor een bloei-reactie dan late lijnen. De eersten hebben
een lageredrempelwaarde voor het bloeihormoon.
7. De tegenstelling tussen de goede donoreigenschappen van B. daigremontianumvoor K. blossfeldiana en de omgekeerde combinatie wijst op een
lager bloeihormoon-niveau in K. blossfeldiana dan in B. daigremontianum.
8.jOok in X. strumariumkonden verschillende bloeihormoon-niveaux, met
verschillendebloeistadiaenverschillendedonorcapaciteiten,worden onderscheiden.
9. Uit 5,6,7en 8blijkt dat velefaktoren debloeivan eenreceptor, geent op
een donor, kunnen beinvloeden.Daarom ishet devraag of planten, waarvan geen bloeihormoon door enting kan worden aangetoond, geen bloeihormoon hebben, terwijl negatieve resultaten bij enting van verschillende
soorten niet toegeschreven behoeven teworden aan verschillende bloeihor84
Meded. Landbouwhogeschool Wageningen 72-9(1972)
monen. Nieuwe, succesvolle combinaties tussen entpartners met verschillen in daglengtebehoefte wijzen op een meer algemeen bloeihormoon.
10. De werking van het bloeihormoon is niet beperkt tot bloei-initiatie. In
AT. blossfeldianaisbovendiendeaanwezigheid vanvoldoendebloeihormoon
nodig voor bloemontwikkeling, terwijl in K.blossfeldiana en in X.strumariumhet aantal bloemen afhangt van het bloeihormoon-niveau.InB.daigremontianum isde aanwezigheid van bloeihormoon een voorwaarde voor
voortgezette bloei.
11. De term 'niet-gelokaliseerde synthese van bloeihormoon' werd ingevoerd
voorhet verschijnsel datreceptorsvan enkelesoorten,dieinbloei gebracht
zijn door enting, in een volgende enting donor kunnen zijn. Het is waarschijnlijk dat deverschillen tussen B. daigremontianum en K. blossfeldiana,
betreffende gelokaliseerde synthese van het bloeihormoon, veroorzaakt
worden door inwendigemilieuverschillen tussen dezeplanten inplaatsvan
door verschillende bloeihormonen. Ook de bloeioverdracht tussen Perilla
crispa en Silenearmeria wijst op deze veronderstelling.
12. Aangezien verschillen in bloei-reactiesverklaard kunnen worden door verschillen in bloeihormoon-niveaux en/of door verschillen in inwendige milieu's van de planten waarin het bloeihormoon gaat werken, blijft het
bestaan van een algemeen bloeihormoon mogelijk.
Meded. Landbouwhogeschool Wageningen 72-9 (1972)
85
9. ACKNOWLEDGEMENT
I am greatly indebted to thestaff of the'Laboratorium voorTuinbouwplantenteelt' for their enthousiastic cooperation.
I am particularly grateful to Prof. Dr. Ir. S. J. Wellensiek for his interest,
adviseand encouragement during thecourse of the investigations and thepreparation of the manuscript.
86
Meded. Landbouwhogeschool Wageningen 72-9(1972)
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Curriculumvitae.
Geboren teAmerongen 11april1943
EindexamenH.B.S.-B1960
StudieLandbouwhogeschoolWageningen,richtingTuinbouwplantenteelt
Ingenieursexamen 1968
Promotie-assistentbijdeafdelingTuinbouwplantenteelt