Plant Physiol. ( 1968) 43, 117-120
Phytochrome and Seed Germination. IV. Action of Light Sources
With Different Spectral Energy Distribution
on the Germination of Tomato Seeds'
Zohara Yaniv and Alberto L. Mancinelli
Department of Biological Sciences, Columbia University, New York, New York 10027
Received September 6, 1967.
Abstract. Germination of tomato seeds exposed to a singile, saturating irradiation from
light sources of different spectral energy distribution seems to be dependent upon the photostationary PFIt/PR ratio established by the irradiation. Germination of tomato seeds exposed
to prolonged irradiations from the same light sources does not seem to be controlled solely
by the PFR/P1 ratio induced and maintained by the irradiation.
Dark germination of tomato seeds is phytochrome controlled (7, 8, 15). It has been calculiated that the relative level -o,f PER present in the
dark-germinating seeds of tomato i,s about 40 % of
the tot-al phytochrom-e (8, 15). In the response to
short, single irradiations, a dose of red light indtcing from 25 to 40 % PiR i,s sutfficient to restore
germination of seds exposed to a sinigle, saturating
FR irradiation (8,15). The rrelative level of PFR
required to induce germination 'is not always the
same. Seeds exposed to prolonged FR irradiations
require relative levels of PFR higher than 40 %
for restoration of germination (13, 15). Changes
in 'temperature and length of imbibition also affect
the relative level of PFm required for germination
(13, 15). Aipparenit phytochrome synthesis and
phytochrome decay might be as important as the
relative level of PFR induced and maintained by the
irradiation in controlbing the germination response
of seeds exposed to prolonged inhiibitory light treatments (13, 14).
There are 2 ways of inducing different PFIt/Put
ratios. One way is to use differenit doses of R or
FR radiant energy after saturation of the system
with FR or R. Reproducibility of a given PFIm
level with a givein dose of R or FR radiant energy
is no better than 10 %, depending on the stabiliity
of the source and the type of timer used. This
meth.od can be used only for short, single irradiations. The other method is that of using sources
of different spectral energy distribution (5, 9)
establishing different photostationary PFI/Pit ratio.
Thi,s second method can be used for short and
prolonged irradiations. The action upon germination of lights of spectral distriibu:tion other than
R and FR have been stu,died previouisly (2, 3, 4, 6,
10, 11). Interpretation of the germination response
1
XVork supported in part by grant GB-3299 from the
Nationial Scic ice Fotundationi.
induced by exposure to blue and white sources is
quite difficult. It has not been completely determined yet whether the response induced is due to
phytochrome alone or to other photoreactive systems as welil.
The purpose of this paper is to present some
results relative to the action upon seed germination
of short and prolonged irradiations from sources
establlishling different relative P1m levels.
Materials and Methods
Twvo varieties of tomato seeds were used: Ace
(Seeds Specialty Research, 1964 tharvest) and
Porte (U.S.D.A., Beltsville, Maryland, 1965 harvest) .
Germination tests were ruin in Petri dishes,
con,taining a disc of filter paper (Easton-Dikeman,
grade 923) moistened with distilliled waiter. During
the dark incu-bation 'periods the dishes were enclosed in bags made wilth a double layer of heavy
bliack satin cloth (darkroom type) and kept in
incubators. The restulits reported are averages of
at least 2 replicates of 4 dishes each, each dish
containing from 50 to 70 seeds.
The light sources used were: BCJ, red incandescent (RI), 'blue, red (R), white incandescent
(WI), cool white fluorescent (CW), and far red
(FR). The BCJ source is made with BCJ lamps,
u,sed in photographic darkroom. The red ineandescent soturce can be made by filtering the light
of incandescenit l,amps through red cellophane or
red plexiglas (Rohm and Haas 2444), or by using
red coated incandescent lamps. Sipectral energy
disgtribution (SED) curves of these sources were
measured with an ISCO Miodel SR spectroradiometer and have been reported in a previous paper
(9). Rates of photochiemical conversion and photostationary Pm/Pa ratio under the above sources
have been reported before (9). Levels of Pm
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118
PLANT PHYSIOLOGY
preseinit after saturating irradiation with the sources
above are reported in table I. When intermittent,
prolonged exposures are used, the length in minutes
o,f each irradiation and of the dark interval between
successive irradiations is indicated in bracketls, for
Table I. Fraction of Phytochromne Present as PFR ilt
Soliutiont anid in Avena Seediinigs After Saturating
Ir r adiation2s M'ith Various Broad Spectrumi
Light Sou rces
%
Lighlt Souirces
C\N
BCJ
\ I
R
FR
1-2
RI
44-47
40-44
B11lu
PFr,
Seedlings
Solution
75-77
28-30
58-61
75-77
75-78
28-34
52-56
75-77
1-2
41-44
41-44
Table II. A-ctionl of a Sinigle Saturating Exposire to
thc Irradi(ationt front Differenit Light Sources upon
the Germinhation of FR Treated Seeds
Teni minute FR was applied 9 hours after sowing.
Other irradiations were given immediately after FR.
Temperature was 200.
% Germinationi
Ace
Porte
Treatmiienlt
DC
FR
83
13
76
78
70
72
75
80
FR-blut
FR-BCJ
FR-RI
F, R-WI
FR-C\V
FR-R
89
32
86
92
88
85
86
90
Table III. Action of Prolonged Irradiation WVith BCJ
Lamtps on the Germination of Tomiato Seeds
Temlperature was 200.
% Germiniation
Ace
Porte
Treatment
DC'
ld DL-lOm FR-3d D
2d DL-lOm FR-3d D
ld BCJ-3d D
ld BCJ-lOm FR-3d D
2d BCJ-3d D
2d BCJ-1Om FR-3d D
1Od BCJ
lOd BCJ-4d D
lOd BCJ-lOm R-4d D
ld cyclic BCJ(1/5)-3d D
ld cyclic BCJ(1/5)-lOm FR-3d D
4d cyclic BCJ (1/5)
4-d cyclic BCJ(1/5)-4d D
d
DDay; m = minute; D =
control.
85-90
70
89
28
8
16
89-93
78
90
90
12
58
1
0
38
85
88
13
0
911
25
dark; DC = dark
0
0
20
70
62
5
0
example (1/9); this meains that 1 m,inutte irradia tions are separated by 9 mlinutes of darkness.
Results
and Discussion
Germination of tomato seeds is inhlilited by a
short exposuire to FR anid cani be restored by a
short satuirating irradiation from R, BCJ, blue,
RI, W"TI, ancd CWV light soturces (:table II)).
Tab,les III to VIII stimmcarize the restilts obtained in the studies of the action of prolonged
expostires to light souirces of different spectral
compositlon uipon the germ,ination of tonmiato seeds.
Saituira:ting irradiabions from all the sources
ulsed inrdtice a photostationary In. level o,f about
30 % or more. A short satuirating exposuire (from
2-30 mlins) to the radliation from these sotirces can
restore the germination of FR treated seeds. These
resuilts are in agreemenlet wiith the resuilts otf previouls
wN-ork (8) in which we foundcl that a relative Pnt
level of abouit 30 % was suifficielnit for the restoriation of germincationi in tomat,o seeds, variet-. Ace.
Tl'he relative level of P11. necessary for the activatioin of germiniiation in tomato Porte see(ls hlas nlot
blecn determined, buit it seems to be lower thani ini
Ace (8).
If the only photomorph,ogen ic factor controlling
germinat.on were the relative Pin. level induiced and
maiantainedJ by irradiation, one woufl(l expect the
seeds to germinaite tinlder prolongl-ed irradiationls
from the soulrces uisedl.
This is not the case. Exposuire to prolonged
irradiations causes an inhibitioln or at least a delay
of germination (tabiles III-VIII).
Consider, for example, the actioni of prolonged
exposture to cool wvhite fluorescent (table VII)
anld red (table VIII) lighit oni germiniatioul. Germina,tion is not inhibited, it is olnfly dlelayed. Tlhese
resullts seem to be quite (lifferent from the find-ings
in Orwyopsis mitili(cec( (10) where contil'1uo1is white
light was found to be inhibitory and continuous red
stimulatory for germination. In our case w e have
no inhibition, but only delay of germinationi and
red seems to delay germmination more thani cool
white fluorescenit.
Continuouis white incandesceint (WI ) light
seems to be inhibitory for germinatioin as long as
the seeds are kept under irradiatilon; when, after
a 1prolonged period of irradialtion, seeds are moved
to (lark, germination is restored (table VI). Inhibition tinder contintiotis WI light seems to be
dlifferelnt from the inhibition indticed tinder continuious FR, since, 'after continuious FR, germination is not restored by moving seeds to darkness
(7, 13, 14).
The acition of continuous BCJ (table III) is
similar to that of WI light. Germination is inhibited while the seeds are kept tinder continuous
or cyclic BCJ irradia,tion and partially restored,
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YANIV AND MANCINELLI-PHYTOCHROME AND SEED GERMINATION.
although not as much as after continuous WI,
when seeds are returned to darkness.
The comparison between the germination responses induced by continuous bltue and red incanTable IV. Action of Prolonged Irradiation with Red
Incandescent Filamtent Lamizps on the Germination
of Tomnato Seeds
Temperature was 200.
% Germination
Porte
Ace
Treatment
89-93
85-90
DC'
78
70
1d D-lOm FR-3 D
90
89
2d D-lOm FR-3d D
89
58
1d RI-3d D
10
7
1d RI-lOm FR-3d D
92
40
2d RI-3d D
7
4
2d RI-lOm FR-3d D
0
0
lOd RI
85
31
lOd RI-4d D
91
86
1d cyclic RI (1/9) -3d D
62
37
ld cyclic RI(1/9)-lOm FR-3d D
92
37
4d cyclic RI (1/9)
90
79
1d cyclic RI(1/4)-3d D
42
ld cyclic RI(1/4)-lOm FR-3d D 17
65
17
4d cyclic RI (1/4)
d = Day; m = minute; D = dark; DC = dark
control.
Table V. Action of Prolonged Irradiation With Blue
Light o0t the Germiniation, of Tomiiato Seeds
% Germination
Porte
Ace
200
17.50 200
17.50
Treatment
89-93
85
85-90
79
DC'
78
42
65
70
ld D-lOm FR-3d D
90
83
89
85
2d D-lOm FR-3d D
90
84
90
90
ld Blue-3d D
11
74
6
60
ld Blue-lOm FR-3d D
87
93
95
2d Blue-3d D
90
81
86
87
2d Blue-1Om FR-3d D 67
88
68
13
60
4d Blue
...
...
40 ...
5d Blue
87 ...
...
...
7d Blue
=
=
dark
d = Day; m
minute; D
dark; DC
control.
Table VI. Actioni of Prolonged Irradiationt with White
Incanidescentt Light on the Germiiinationt of
Tomnato Seeds
Temperature was 200.
Treatment
4d WI'
4d WI-4d D
lOd WI
DC 4d
1 d = Day; D
% Germinatio:n
Ace
Porte
0
23
0
85-90
=
dark; DC
=
dark control.
0
88
16
89-93
IV.
'i 'St
descent (RI) irradiatio"s is quite interesting. The
blue and RI sources have different spectra!l energy
distribu,tion culrves (9), but they produte the same
photo,stationary PFI level, 40 to 45 % (table I)..
Short irradiations from either sotirce restore germination oif FR treated seeds (table ,II). While
continuio-us blue has a very lititle effect on germination (table V), continuous RI has a quiite strong
inhibitory effect (itable IV).
The interpretation of the resullts reporte(d is
quite difficult. The comparison with results reported in the 'literature (2, 3, 4, 6, 10,11) is of
little help, since the seeds used in the different
Table VII. Action of Prolonged Irradiation With
White Fluorescenit Light (CW) oit the Germintation
of Tomiiato Seeds
% Germination
Ace
Porte
Treatment
Temtperatture 200
71
80
DC, 3d'
89-93
85-90
DC, 4d
70
78
ld D-lOm FR-3d D
2d D-lOm FR-3d D
90
89
94
95
ld CW-3d D
80
79
ld CWV-lOnm FR-3d D
91
2d CWV-3d D
90
2d CW-lOm FR-3d D
88
86
0
4
3d CW
90
4d CW
74
Temiperature 15°
68
37
DC (Sd)
89
65
DC (8d)
0
0
ld D-lOm FR-3d D
ld CW-4d D
74
39
0
0
ld CW-lOm FR-4d D
(1
0
5d CW
1Od CW
90
70
0
0
5d cyclic CW(1/30)
91
10d cyclic CW(1/30)
79
d
Day; m = minute; D = dark; DC = dark
control.
Table VIII. Action of Prolontged Irradiation With Red
Light on1 the Germiniation of Tomato Seleds
Temperature was 200.
Treatment
DC, 3dM
DC, 4d
1d D-lOm FR-3d D
2d D-lOm FR-3d D
ld R-3d D
ld R-lOm FR-3d D
2d R-3d D
2d R-lOm FR-3d D
3d R
4d R
5d R
d = Day; m
control.
=
% Germination
Ace
Porte
80
71
89-93
85-90
78
70
90
89
97
90
66
57
94
92
92
88
4
4
67
31
81
90
minute; D = dark; DC = dark
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120
PLANT PHYSIOLOGY
investigations are different. The only thing that
seems qtfi;tte clear is that the relative Prit level
indtuced and maintained by continuous irradiation
is not the only photomorphogenic factor controlling
the germination response of tomato seed-s to prolonged irradiation. With the exceptioin of bluie
lighit, one can see a correlation between the photostatbionary PFI level induced by the different soturces
anld the germination after prollonged irra,diations:
the soturces inducing the lower PFR levels are those
inducing less germination. Continuous bluie, induicing a relaitive Pi: level of about 40 % hais an
effect oni germinationi very similar )to that of continuouis CXV/ and R radiations, whlich induice a Pn:
level of albouit 75 %.
The restults fotund for the actioni of continut-otus
blue make it difficuilt to give a completely satisfactory explanation to the correlaitiion fouind for
the other soturces between the PrI. levells and the
germninaition respoinses induiced by prolonged irradiations. The possibility that the screening duie to
the seed coat coulld affect the quality of light
reaching the photoreactive pigment shotuld also be
considered.
Participation of the high eniergy reaction system
(9) in the action of the prolonged irradialtions onl
the germination of tomato seeds does not seem a
good possibility because of the differences fouindl
for the action of conitinlutouis blute and continuiouls
FR (6).
Another possible explaniationi is thalt the relative
PFin level is the controlling factor under most
circumstances burt, in addition, a blue absorbing
system, perhaps that active in phototropism, also
affecs germination, possibly throuigh a totally
different mechanism.
Other factors that cotlld have ani actioni in
controlling germination under contintuotus irradiation are the rate of formation of phytochrome, the
rate of destruction of phytochrome, anid the steady
sta,te level of long lived phytochrome intermedtiates
produced (1). All these factors will1 have to be
careftully studied before a satisfactory explanation
can be foulnld.
Literature Cited
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phytocliromie transfornmation in vitro. Carniegie
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3. FLINT, L. H. AND E. D. MCALISTER. 1935. Wave
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in the germinlation of dark-germinating tomato
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