Scientia Horticulturae, 21 (1983) 181--188
181
Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands
FACTORS AFFECTING THE VASE LIFE OF FRONDS OF
MAIDENHAIR FERN
DAVID W. FUJINO and MICHAEL S. REID
Department of Environmental Horticulture, University of California, Davis, CA 95616
(U.S.A.)
(Accepted for publication 1 March 1983)
ABSTRACT
Fujino, D.W. and Reid, M.S., 1983. Factors affecting the vase life of fronds of maidenhair fern. Scientia Hortic., 21: 181--188.
Cut fronds of maidenhair fern (Adiantum raddianum), which last only 3 days in
DI water, were used as a model system to study factors affecting the vase life of cut
greens. Solutions containing 25 mg 1-~ Ag+ increased vase life 5-fold. Other biocides
(8-hydroxyquinoline citrate, a quaternary a m m o n i u m compound, or 8-hydroxyquinoline
citrate + NaOCl) had little effect on vase life, while inhibitors of ethylene (C2H4) production (Co 2+, aminooxyacetic acid) increased vase life. Wound C2H, production by
the cut ends of the stipes declined during the first 2 h after cutting. The hypothesis
that this C2H4 is the cause of the brief vase life of maidenhair fern is discussed.
Keywords: aminooxyacetic acid; biocides; cobalt; ethylene; silver.
INTRODUCTION
We recently surveyed the vase life of a number of species used by commercial florists as cut foliage in floral arrangements (Fujino et al., 1981a).
Most of the materials lasted well in deionized water (DI), b u t maidenhair
fern (Adiantum raddianum cultivar 'Decorum') had a very short vase life,
which probably explains the very small commercial production of this
cut green. Its vase life was terminated by irreversible wilting of the pinnae
and collapse of the stipe, indicating poor water relations in the cut frond.
It seemed possible that it would be a good model system for examining
the factors responsible for p o o r water relations in cut shoots.
In cut flowers, poor water relations have been reported to be the result
of increased stem resistance to water flow, resulting from factors such
as poor water quality, microbial growth, solution pH, physiological plugging,
and dissolved gases in the vase solution (Halevy and Mayak, 1980). These
problems have been overcome in various cut flower crops by the use of
deionized water, bactericides, low pH vase solutions, antimetabolites and
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© 1983 Elsevier Science Publishers B.V.
182
MiUipore-filtered water, respectively (Durkin, 1979a, Halevy and Mayak,
1980). We report here the effects of such treatments on the vase life of
maidenhair fern, and the results of further experiments investigating the
cause of its short vase life.
MATERIALS AND METHODS
Mature fronds (approximately 45 cm long) were randomly harvested
from 8 maidenhair fern plants grown in 7.6-1 containers under 25% shade,
and watered as needed with half-strength Hoagland's solution (Epstein,
1972). Plants were grown at 20.0/15.5°C day/night temperature.
All fronds were recut, unless n o t e d otherwise, prior to placing in vase
solutions. Cut fronds evaluated in DI water are referred to as the control.
Vase life studies were c o n d u c t e d in 1-1 mason jars containing approximately
250 ml DI or chemical solution. Chemicals were procured from standard
chemical distributors. Millipore-filtered water was prepared as described
b y Durkin (1979b).
All vase-life evaluations were conducted at 23 +2°C and a relative humidity o f 50 + 10%, under continuous cool white fluorescent light 1.5
Wm -2 photosynthetically active radiation, measured with a LI-COR ((Lincoln, Nebraska) photoradiometer). The fluorescent lamps were General
Electric, F96T12-CW-1500.
Vase life was defined as the time between placing the fronds in the vase
and the first appearance of pinnae wilting or p h y t o t o x i c s y m p t o m s (browning or necrosis of the pinnae).
C2H4 production of the cut stipes was determined by sealing approximately 1.7 g of 0.5-cm segments cut from the base of the stipes in 5-ml
vials ventilated with a 27 ml h -1 flow of C2H4-free air. At intervals, the
C2H 4 content of 3-ml samples of air withdrawn from the vials was measured by gas chromatography (Buffer et al., 1980).
RESULTS
E f f e c t o f d i f f e r e n t vase s o l u t i o n s o n f r o n d vase life. -- There was no major
increase in the vase life of fronds held continuously in tap water, MiUipore
filtered DI, citric acid, 8-hydroxyquinoline citrate (HQC), HQC + NaOC1,
or Physan-20 over that of control fronds (Table I). Frond longevity was
increased more than 5-fold b y holding in a vase solution containing 25
mg 1-1 AgNO3 (Table I, Fig. 1); 1 mM Co 2+ more than doubled frond
vase life, b u t caused a brown discoloration of the pinnae veins.
E f f e c t o f silver and nitrate ions. - - Treatment with vase solutions containing
Ag ÷ increased mean vase life of maidenhair fronds b y over 5 times, regardless of the accompanying anion (Table II). Nitrate ion (NO~) had no detectable effect on frond longevity when combined with cations other than
Ag ÷.
183
TABLE I
T h e e f f e c t o f various vase solutions on f r o n d vase life o f maidenhair fern. F r o n d s were
held c o n t i n u o u s l y in various chemical solutions. Data are the means (± S.E.) of 3 replications per t r e a t m e n t with 3 fronds per replication
Treatment
Mean vase life
(days)
Control
Tap water
Millipore-filtered DI
8 - h y d r o x y q u i n o l i n e citrate
(250 mg 1-1)
8 - h y d r o x y q u i n o l i n e citrate + NaOC1
(50mg1-1 +4mg1-1)
Physan-20 (200 mg 1-1)
Citric acid (320 mg 1-1)
A g N O 3 (25 mg 1-1)
Co(NO3) 2 (290 mg 1-1)
•
~
~"
,,
3.2 -+ 0.1
3.2 + 0.1
3.0 ± 0.0
4.7 ± 0.3
4.3
3.2
3.2
16.3
8.2
±
±
±
±
±
0.9
0.1
0.1
2.0
I.I
~2~
Fig. 1. F r o n d o f m a i d e n h a i r fern held in (left) DI water and (right) 25 mg 1-1 AgNO3 for
15 days.
184
T A B L E II
E f f e c t o f various c h e m i c a l s o u r c e s o f silver a n d n i t r a t e ions o n t h e vase life o f m a i d e n h a i r
f r o n d s . F r o n d s were h e l d c o n t i n u o u s l y in various vase s o l u t i o n s . D a t a are t h e m e a n s
(+ S.E.) o f 2 r e p l i c a t i o n s ' p e r t r e a t m e n t w i t h 3 f r o n d s p e r r e p l i c a t i o n
Treatment
M e a n vase life
(days)
Control
A g N O 3 (25 m g I-~)
Ag~SO, (25 m g I-')
Ca(NO3) ~ (12.5 m g l-')
N H 4 N O 3 (25 m g l -I)
K N O 3 (25 m g I-I)
3.1
16.8
15.8
4.2
3.0
3.3
-+ 0.4
+ 1.7
+ 1.6
+ 0.4
+ 0.4
-+ 0.5
Effect o f silver nitrate concentration.
The vase life of fronds held in 1
or 5 mg 1-1 AgNO3 was not significantly different from that of control
fronds, whereas fronds held in 10 mg 1-1 AgNO3 lasted 5.6 days longer
than control fronds (Fig. 2). Increasing the AgNO3 concentration to 25
mg 1-1 extended frond longevity to 8 times that of control fronds. No
symptoms of phytotoxicity were noted on the pinnae at any AgNO3 concentration.
-
-
22
18
O
16
'~
14-
~,~ 12.
10~
8°
~
s.
4
d °
,'o
,'5
2'o
AoNO 3 cono (mg.I "1)
='s
~o
Fig. 2. T h e e f f e c t o f AgNO 3 c o n c e n t r a t i o n o n t h e vase life o f m a i d e n h a i r fronds. T h e r e
were 3 r e p l i c a t i o n s p e r t r e a t m e n t w i t h 3 f r o n d s p e r r e p l i c a t i o n . T h e vertical b a r shows
t h e 95% c o n f i d e n c e interval.
185
Production o f C2H4 by c u t stipe segments. -- The rate of C2H4 production by cut stipe segments fell to almost 1/10 of the initial value during
the first 2 h after cutting (Fig. 3). C2H4 production remained low over
the next several days (data n o t shown).
E f f e c t o f a m i n o o x y a c e t i c acid ( A O A ) on vase life. -- Vase solutions containing as little as 0.2 mM AOA significantly increased frond vase life,
and fronds held in 0.5 mM AOA lasted 5 days longer than the controls
(Fig. 4). Vase life at this and higher concentrations was terminated by
bronzing of the pinnae.
DISCUSSION
It appears likely that the short vase life of untreated cut maidenhair
fronds is due to their inability to maintain their water balance after placing
in DI. Vase life was normally terminated when the pinnae wilted (see Fig.
1) and the stipe collapsed. Poor water relations in cut flowers can be the
result of air embolisms (Durkin, 1981), or microbial or physiological occlusions in the vascular system (Burdett, 1970; Lineberger and Steponkus,
1976).
Air embolisms in rose stems can be effectively overcome by a number
of techniques, including acidification of the vase solution, removal of dissolved gases from the vase solutions, and recutting the stems under water
(Durkin, 1981). None of these treatments was effective in increasing the
vase life of cut maidenhair fronds, so it would appear that their poor vase
life does n o t result from the presence of air embolisms in the xylem.
The beneficial effect of vase solutions containing Ag* on the vase life
of cut flower crops has widely been assumed to be the result of the powerful biocidal activity of the ion (Aarts, 1957; Mayak et al., 1977; Halevy
and Mayak, 1980). The data reported here tend to suggest, at least for
maidenhair fern, that Ag ÷ may have an alternative role in extending vase
life. Chemicals with reported bactericidal properties, such as HQC (Larsen
and Cromarty, 1967), Physan-20, a quaternary ammonium c o m p o u n d
(Farnham et al., 1978), and a combination of HQC and NaOC1 (Durkin,
1981), had no substantial effect on frond longevity. This would strongly
suggest that AgNO3 has some other function, and that microbial growth
is n o t the factor limiting frond vase life.
The active moiety of AgNO3 in improving maidenhair frond longevity
is clearly the silver ion (Ag÷), since other nitrate salts had no effect on
frond vase life (Table II). Beyer (1976) showed that Ag ÷ is a p o t e n t inhibitor of the action of C2H4 in plants. I t might therefore be suggested
that the improved vase life of maidenhair fern in solutions containing Ag ÷ relates to inhibition of C2H4 action. Although Ag ÷ in the silver thiosulfate
complex form (STS) is known to move readily in the xylem stream (Veen
and van de Geijn, 1978), AgNO3 moves very poorly in cut stems (Kofranek
186
0
0
<0
'~
°0
l=l
i
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I
{ e A e O ) e..4.!-I e e e A ueelAI
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=1
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~=.=
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187
and Paul, 1972), presumably because of the ion's high affinity for anionic
groups in the x y l em wail. Therefore, the i m p r o v e m e n t in vase life o f cut
maidenhair fronds resulting f r om the inclusion AgNO3 in the vase solut i o n p r o b a b l y relates t o inhibition o f C2H4 action near the base o f the stipe.
It is possible t hat in the stipe o f maidenhair fern, C2H4 p r o d u c t i o n by
w o u n d e d cells at the c ut surface m a y s o m ehow stimulate the f o r m a t i o n
o f vascular occlusions, which causes early wilting of the frond. The addition o f AgNO3 t o the vase solution would inhibit this effect of C2H4, thereby maintaining water flow to the frond. T he substantial p r o d u c t i o n of
w o u n d C2I-L by c ut maidenhair stipe segments, and the m arked increase
in vase life in solutions containing AOA o r Co 2+, which inhibit C2H4 biosynthesis b y plant tissues (Lau and Yang, 1976; Fujino et ai., 1981b), are
consistent with this hypothesis. It would be interesting t o examine the
possible role o f C2H4 in o t h e r cut stems where physiological plugging has
been associated with a decline in water conduct i vi t y (Durkin and Kuc,
1966; Burdett, 1970; Marousky, 1971).
ACKNOWLEDGEMENTS
D.W. Fujino was s u p p o r t e d by a grant from the Jewel Foliage Co., San
Antonio, TX. We wish t o t hank Moggia and Son Nursery, San Francisco,
CA, f o r generously supplying plants of maidenhair fern.
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