Postharvest Biology and Technology 56 (2010) 77–84
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Postharvest Biology and Technology
journal homepage: www.elsevier.com/locate/postharvbio
Treatment with thidiazuron improves opening and vase life of iris flowers
Andrew J. Macnish a , Cai-Zhong Jiang b,∗ , Michael S. Reid a,∗∗
a
b
Department of Plant Sciences, University of California, One Shields Avenue, Davis, CA 95616, USA
Crops Pathology and Genetics Research Unit, USDA-ARS, One Shields Avenue, Davis, CA 95616, USA
a r t i c l e
i n f o
Article history:
Received 31 August 2009
Accepted 24 November 2009
Keywords:
Flowers
Gibberellic acid
GA3
Iris
Postharvest
Sucrose
Thidiazuron
TDZ
Vase life
a b s t r a c t
The marketability of Dutch iris (Iris × hollandica) cut flowers is limited by their short display life and
frequent failure to open fully. We tested the ability of thidiazuron (TDZ), a phenyl-urea compound with
cytokinin-like activity, to improve iris flower opening and longevity. A postharvest pulse with 0.2–1 mM
TDZ for 6–24 h at 0 or 20 ◦ C extended the vase life of flowers by up to 1.5 d relative to control (0 mM TDZ)
stems in water. TDZ treatment also stimulated growth of the pedicel and ovary by up to 2.5 cm that, in
turn, led to more complete opening of flowers. Inclusion of 1 mM gibberellic acid (GA3 ) in the TDZ pulsing
solution did not extend vase life further but did increase flower shoot elongation by an additional 1.0 cm.
Provision of 20% sucrose with the TDZ plus GA3 treatment had an additive effect, increasing vase life and
shoot growth by a further 0.8 d and 1.0 cm, respectively. Pulsing stems with this combined treatment
prior to storing flowers dry for 14 d at 0 ◦ C provided maximum flower opening and display life after
storage. Treatment with 0.5 mM TDZ stimulated a significant increase in ethylene production by flowers
during their opening.
© 2009 Elsevier B.V. All rights reserved.
1. Introduction
Dutch iris (Iris × hollandica) is a commercially important cut
flower species (Jerardo, 2007), although their marketability is limited by a short vase life of 2–5 d (Jones et al., 1994; van Doorn et
al., 2003). The failure of iris flowers to open fully after dry transport and storage is also a major postharvest problem (Mayak and
Halevy, 1971; Celikel and van Doorn, 1995a). Incomplete flower
opening results from insufficient growth of the pedicel and ovary
tissues that otherwise force the bud free of the constraining sheath
leaves (Reid and Evans, 1986). Iris flower senescence is first visualized as discoloration, wilting and inward rolling of the distal edges
of tepals (van Doorn et al., 1995). These visible signs are preceded
by protein degradation and death of mesophyll cells in tepal margins (Celikel and van Doorn, 1995b; van der Kop et al., 2003; Pak
and van Doorn, 2005).
Several treatments have been tested for their ability to improve
iris flower opening and vase life. Swart (1986) reported that treating
‘Prof. Blaauw’ iris stems with 2 mg L−1 kinetin (a cytokinin) and/or
10 mg L−1 gibberellic acid (GA3 ) for 3 d at 2 ◦ C prior to dry storage
for 1 d at 9 ◦ C reduced the negative effects of water stress. Similarly,
Celikel and van Doorn (1995a) showed that pulsing ‘Blue Magic’ iris
∗ Corresponding author. Tel.: +1 530 752 7060; fax: +1 530 752 4554.
∗∗ Corresponding author. Tel.: +1 530 754 6751; fax: +1 530 752 4554.
E-mail addresses: [email protected] (C.-Z. Jiang), [email protected]
(M.S. Reid).
0925-5214/$ – see front matter © 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.postharvbio.2009.11.011
stems with 1m M GA3 for 4 h at 20 ◦ C prior to dry storage stimulated
subsequent elongation of the flower shoot and, in turn, increased
the proportion of flowers that opened fully after storage. Lee et al.
(2005) found that spraying ‘Blue Magic’ iris with 50 mg L−1 benzyladenine (BA), a synthetic cytokinin, either alone or in combination
with 50 mg L−1 GA4+7 delayed the onset of flower senescence. The
addition of inhibitors of protein synthesis (e.g. cycloheximide) and
protease activity (e.g. diisopropyl-fluorophosphate) to vase water
can also extend iris flower longevity by 1–3 d (Jones et al., 1994;
van Doorn et al., 1995; Pak and van Doorn, 2005). However, these
compounds have limited commercial value as they inhibit flower
opening and are toxic to humans (Jones et al., 1994).
Thidiazuron (TDZ; N-phenyl-N -l,2,3-thiadiazol-5-ylurea) is a
non-metabolizable phenyl-urea compound with strong cytokininlike activity (Mok et al., 1982). TDZ is commonly used at either
high (e.g. 100 ␮M) or low (e.g. 1 ␮M) concentrations as a defoliant or for regeneration in plant tissue culture, respectively (Suttle,
1986; Huetteman and Preece, 1993). Treatment with TDZ has also
been reported to prevent leaf senescence in a range of cut flower
species including alstroemeria, chrysanthemum, lupin, phlox and
tulip (Ferrante et al., 2002, 2003; Sankhla et al., 2003, 2005). In
addition, inclusion of 5–45 ␮M TDZ in vase water was found to
reduce ethylene-mediated flower abscission and senescence on
phlox and lupin stems, respectively (Sankhla et al., 2003, 2005).
This treatment also stimulated opening of additional flower buds on
cut lupin and tuberose stems (Sankhla et al., 2003; Uthairatanakij
et al., 2007). The mode by which TDZ treatment extends flower
longevity has not been determined, although it may act by regulat-
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A.J. Macnish et al. / Postharvest Biology and Technology 56 (2010) 77–84
ing cytokinin and/or auxin activity (Murthy et al., 1998; Mok et al.,
2000).
Given the positive response of iris flowers to kinetin and BA
application, we hypothesized that a pulse treatment with the nonmetabolizable TDZ would prevent leaf yellowing and also improve
the opening and longevity of cut iris flowers. In this study, we
determined the optimal TDZ concentration, treatment time and
temperature for application. We evaluated effects of TDZ treatment
on flowers at different development stages, and its relative efficacy
compared with other growth regulators. We also tested the ability
of TDZ alone or in combination with GA3 and sucrose to improve
the opening and longevity of flowers following dry storage.
2. Materials and methods
2.1. Plant material
Iris (Iris × hollandica) ‘Discovery’ flowers were obtained from
a farm near Watsonville, California. The flowers are borne on an
emergent shoot enclosed within two green sheath leaves at the
terminal node of stems (Fig. 1A). This shoot consists of a pedicel, an inferior ovary and a short tube to which the tepals attach
(Fig. 1B). A second flower that develops on a separate shoot may
also open after the first flower closes. Unless otherwise specified,
stems were harvested at commercial maturity when 0.5 cm of the
tepal tips had emerged from the sheath leaves (Fig. 1D, stage 2). Cut
stems were transported dry and horizontally to the laboratory in an
air-conditioned (about 20 ◦ C) car within 3 h. They were randomly
assigned to treatments and re-cut to 50 cm.
2.5. Response of flowers at different development stages to TDZ
treatment
Flower stems were harvested at three stages of floral development. Flower stages 1, 2 and 3 corresponded to the distal edge of
tepals being 1 cm below, 0.5 cm above, and 2 cm above the tips of
the green sheath leaves, respectively (Fig. 1C–E). Cut stems were
treated in solutions containing deionized water (control) or 0.5 mM
TDZ for 24 h at 20 ◦ C. Stems were then maintained for vase life
evaluation as described above.
2.6. Relative activity of TDZ and other plant growth regulators
To test the relative efficacy of TDZ, BA and GA3 as pulse treatments, cut stems were placed into deionized water (control),
0.5 mM TDZ, 0.22 mM BA (provided as MaxCel 1.9% SW; Valent USA
Corp., Walnut Creek, CA, USA) and/or 1 mM GA3 for 24 h at 20 ◦ C.
Flowers were then maintained in vases for evaluation.
2.7. Effects of sucrose on the efficacy of the TDZ plus GA3
treatment
The effect of sucrose, applied as a pulse or continuously in vase
solution, on the efficacy of the TDZ plus GA3 treatment was evaluated. Cut stems were pulse-treated in deionized water (control)
or a solution of 0.5 mM TDZ plus 1 mM GA3 amended with 0, 1, 5,
10 or 20% (w/v) sucrose (ACS grade, Fisher Scientific Inc.) for 24 h
at 20 ◦ C. Since TDZ is not yet registered for use on ornamentals, we
also treated additional flowers with 1 mM GA3 plus 20% sucrose. All
stems were then transferred to vases containing deionized water,
50 mg L−1 sodium hypochlorite, and 0 or 1% (w/v) sucrose for evaluation of vase life.
2.2. TDZ and GA3 treatment preparation
A 10 mM TDZ stock solution was prepared by dissolving pure
TDZ (Supelco, Bellefonte, PA, USA) in 1 M NaOH (Molecular biology grade; Fisher Scientific Inc., Fair Lawn, NJ, USA) (Ferrante et
al., 2002). Aliquots of the TDZ stock were then diluted in deionized water (pH 7) to generate desired treatment concentrations
and neutralized to pH 7 with 1 M HCl (ACS grade, Fisher Scientific
Inc.). GA3 (90% purity; Sigma–Aldrich Inc., St. Louis, MO, USA) was
dissolved in 100% (v/v) ethanol (Sigma–Aldrich Inc.) and made up
1 mM in deionized water (Celikel and van Doorn, 1995a).
2.3. Optimal TDZ treatment concentration
The efficacy of TDZ in extending the vase life of iris flowers
was initially determined by pulse-treating stems with a range of
TDZ concentrations. Cut stems were placed into cylinders that contained deionized water and 0, 0.1, 0.2, 0.5 or 1 mM TDZ for 24 h
at 20 ◦ C. Single stems were then transferred to individual vases
containing deionized water plus 50 mg L−1 sodium hypochlorite
(provided as Clorox® Ultra, The Clorox Co., Oakland, CA, USA), an
anti-bacterial compound. Flowers in vases were maintained in a
controlled environment room at 20 ◦ C and 50% relative humidity. Cool white fluorescent bulbs provided 18 ␮mol m2 s−1 of light
(12 h d−1 ) at flower height.
2.4. Optimal TDZ treatment time
The optimal duration of the TDZ pulse treatment was determined by placing cut stems in a solution of 0.5 mM TDZ for 0, 1,
3, 6, 12 and 24 h at 20 ◦ C. Stems were then maintained in the vase
solution and controlled environment conditions described above.
2.8. Effects of TDZ, GA3 and sucrose treatment prior to dry storage
In a preliminary experiment, we found that pulsing with 0.5 mM
TDZ for 24 h was equally effective at 0 or 20 ◦ C in extending cut
iris flower longevity (data not shown). With a view to developing
commercial treatment protocols, we determined the potential of
the TDZ plus GA3 and sucrose pre-treatment at 0 ◦ C to improve
iris flower opening and longevity after dry storage. Cut stems were
pulse-treated in deionized water (control), 0.5 mM TDZ and/or
1 mM GA3 amended with 0 or 20% sucrose for 24 h at 0 ◦ C. Following pulse treatment, stems were wrapped in a sheet of polyethylene
film and placed inside a fiberboard flower box at 0 ◦ C to simulate dry
shipment and/or storage. On days 0, 3, 7 and 14 of dry storage, subsamples of stems from each pulse treatment were removed from
the boxes, re-cut to 45 cm in length, and maintained in vases.
2.9. TDZ treatment effects on flower respiration and ethylene
production
Cut flowers plus their leaf sheaths were trimmed to 10 cmlength and placed individually into 946 mL glass jars containing
50 mL of deionized water (control) or 0.5 mM TDZ for 24 h at 20 ◦ C.
Stems were then transferred to matching jars containing deionized
water and maintained under controlled environment conditions
as described above. At 8–24 h intervals during pulsing and vase
life evaluation, jars were closed with screw-on lids for 4 h. At the
end of each 4 h incubation period, a 3 mL plastic syringe was used
to sample gas from inside the jars through a silicone rubber port
inserted through each lid. The concentration of CO2 and ethylene
that accumulated inside jars was determined using a Horiba PIR2000R infrared gas analyzer (Horiba Instruments Co., Irvine, CA,
USA) and a Carle model 111gas chromatograph (Carle Instruments
Inc., Anaheim, CA, USA) fitted with a HNU P1-51 photoionization
A.J. Macnish et al. / Postharvest Biology and Technology 56 (2010) 77–84
detector (HNU Systems Inc., Newton, MA, USA), respectively. CO2
and ethylene concentrations were calibrated against known standards (Airgas Inc., Sacramento, CA, USA).
2.10. Assessments
Vase life was judged as the time from opening to senescence
(in-rolling of the flag tepal distal edge by 3 mm) of the first flower
on a stem. The angle at which flag tepals unfurled relative to the
central stem was determined on day 4 of vase life using a protractor.
The external color of flag tepals was measured using a portable
Minolta CR-200 Chroma Meter (Minolta, Osaka, Japan). Data were
79
collected 1 cm from the distal edge of tepals on day 4 of display
life and expressed as the CIE (L* , a* , b* ) color space coordinates
(McGuire, 1992). The presence or absence of a second flower on
each stem was also recorded. The length of the floral pedicel, ovary
and tube for the first and second flowers was measured at the end of
each experiment using digital calipers. The chlorophyll content of
the uppermost 1 cm of sheath leaves was determined in experiment
1 as described by Inskeep and Bloom (1985). Briefly, the sheath
leaves were removed from different subsets of stems on each day
of vase life. The distal 1 cm of leaves was excised with a razor blade
and ground in 80% acetone (100 L kg−1 , fresh weight). The resulting
homogenate was centrifuged at 5000 × g for 5 min. The absorbance
Fig. 1. Photographs of iris (Iris × hollandica) ‘Discovery’ flowers. (A) An open flower showing three erect standard tepals (st) and three horizontal flag tepals (ft). The flower
is borne on an emergent shoot enclosed within two green sheath leaves (sl) at the terminal stem (s) node. A second flower (sf) may also develop on a separate shoot within
the sheath leaves. (B) Removal of the sheath leaves reveals that the shoot is comprised of a pedicel (p), inferior ovary (o) and floral tube (t) to which the tepals attach. The
second flower bud forms within two additional sheath leaves. (C–E) Stems harvested when the distal edge of tepals was either 1 cm below (stage 1), 0.5 cm above (stage 2),
or 2 cm above (stage 3) the tips of the green sheath leaves. Scale bars represent 1 cm.
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A.J. Macnish et al. / Postharvest Biology and Technology 56 (2010) 77–84
Fig. 2. Vase life of iris ‘Discovery’ flowers in response to different TDZ treatment conditions. (A) Treatment with 0, 0.1, 0.2, 0.5 and 1 mM TDZ for 24 h at 20 ◦ C. (B) Treatment
with 0.5 mM for 0, 1, 3, 6, 12 and 24 h at 20 ◦ C. Following TDZ treatment, all flowers were maintained in deionized water at 20 ◦ C for vase life evaluation. Data (means ± S.E.M.,
n = 10) followed by different letters are significantly different at P = 0.05.
of the supernatant was determined at 664.5 and 647.0 nm using
a Beckman Coulter DU 800 spectrophotometer (Beckman Coulter
Inc., Fullerton, CA, USA). The chlorophyll content was calculated
based on the fresh weight (g kg−1 ).
2.11. Experiment design and data analysis
Data are presented from a series of single experiments conducted over an entire flowering season. Treatments common to
each experiment were included to provide replication over time.
Deionized water was used as the control in all experiments since
pulsing with NaOH plus HCl at the concentrations present in TDZ
treatments had no effect on flower longevity (data not shown).
Flowers in vases were arranged in a completely randomized block
design within the evaluation room. Depending upon the experiment, 10–20 replicate flower stems were used for each treatment.
Data were analyzed using one-way ANOVA with the generalized
linear model procedure of SAS (Version 9.1, SAS Institute Inc., Cary,
NC, USA). Where significant (P ≤ 0.05) treatment effects were determined by ANOVA, data means were separated by the LSD test at
P = 0.05.
Fig. 3. Total chlorophyll content of the uppermost 1 cm of sheath leaves on iris
‘Discovery’ flower stems after a pulse treatment in 0 or 0.1 mM TDZ for 24 h at 20 ◦ C.
Sheath leaf tissue was sampled daily from different subsets of stems during vase life
in deionized water at 20 ◦ C. The chlorophyll content was calculated based on the
fresh weight (g kg−1 ). Data are presented as means ± S.E.M. (n = 6).
3. Results
3.1. Optimal TDZ treatment concentration
In a preliminary experiment, pulsing stems with 0.01–0.1 mM
TDZ for 24 h at 20 ◦ C did not significantly extend flower longevity
(data not shown). We therefore tested higher TDZ concentrations
than those used by Ferrante et al. (2002, 2003) and Sankhla et al.
(2003, 2005). Pulsing stems with 0.2, 0.5 and 1 mM TDZ for 24 h
at 20 ◦ C extended the vase life of flowers by 0.8, 1.2 and 1.5 d
(Fig. 2A). Although pulsing with 0.1 mM TDZ did not increase flower
longevity, it did prevent yellowing (loss of chlorophyll) of sheath
leaves for the duration of vase life (Fig. 3). In contrast, the uppermost 1 cm of sheath leaves on control (0 ␮M TDZ) stems showed
visible signs of yellowing by day 4 of vase life. Treatment with 0.2,
0.5 and 1 mM TDZ resulted in a 12–21% (1.0–2.5 cm) increase in
the length of the shoot on which flowers develop (Table 1). This
increase was the result of an extension of the pedicel (by 20–51%)
and inferior ovary (by 12–21%) (Table 1). TDZ did not stimulate
growth of the short tube between the ovary and tepals. Treatment
with 0.5 and 1 mM TDZ also resulted in 10 and 40% of stems displaying a second open flower, respectively, while no second flowers
opened on stems exposed to 0, 0.1 and 0.2 mM TDZ (data not
shown). The second flower opened just as the first open flower
began to senesce.
Table 1
Length of the flower shoot and pedicel, ovary and floral tube components on cut iris ‘Discovery’ stems following the termination of vase life in deionized water at 20 ◦ C.
Flowers were pulse-treated in 0, 0.1, 0.2, 0.5 and 1 mM TDZ for 24 h at 20 ◦ C. Data (means ± S.E.M., n = 10) within each column and followed by different letters are significantly
different at P = 0.05. ‘NS’ denotes no significant difference at P = 0.05.
TDZ concentration (mM)
Flower shoot (cm)
0
0.1
0.2
0.5
1
8.2
8.9
9.2
10.7
9.9
±
±
±
±
±
0.5c
0.2bc
0.4b
0.3a
0.4ab
Pedicel (cm)
3.5
4.0
4.2
5.3
4.8
±
±
±
±
±
0.3d
0.1cd
0.2bc
0.2a
0.2ab
Ovary (cm)
3.3
3.5
3.7
4.0
3.8
±
±
±
±
±
0.2c
0.2bc
0.2b
0.1a
0.2ab
Tube (cm)NS
1.4
1.4
1.4
1.4
1.4
±
±
±
±
±
0.0
0.0
0.0
0.0
0.0
A.J. Macnish et al. / Postharvest Biology and Technology 56 (2010) 77–84
81
3.2. Optimal TDZ treatment time
The vase life of iris flowers pulsed with 0.5 mM TDZ increased
with time in the solution, reaching a plateau at 12 h (Fig. 2B). TDZ
treatment also stimulated an extension of the floral shoot and
increased opening of the second bud; 30 and 70% of the second
flowers opened on stems pulsed with TDZ for 12 and 24 h, respectively, while only 10% of control stems displayed a second open
flower (data not shown).
3.3. Response of flowers at different development stages to TDZ
treatment
The vase life of control stems harvested at floral development
stages 1, 2 and 3 was between 3.7 and 4.5 d (Fig. 4). Treatment
with 0.5 mM TDZ for 24 h at 20 ◦ C extended the vase life of flowers
harvested at all three stages of development by 1.1–1.3 d. Pulsing
with TDZ stimulated a significant increase in the number of stems
on which a second flower opened relative to control stems at each
development stage (Fig. 4). Typically, the frequency of a second
open flower was greatest for stage 2 stems and least for stage 1
flowers.
3.4. Relative activity of TDZ and other plant growth regulators
Treatment with either 0.5 mM TDZ or 0.22 mM BA for 24 h at
20 ◦ C significantly extended flower vase life (Table 2). Pulse treatment with 1 mM GA3 alone had no effect on flower longevity.
Pulsing with TDZ and/or GA3 increased flower shoot length, but
BA alone had no such effect (Table 2). Treatment with TDZ alone or
in combination with GA3 resulted in opening of a second flower on
50 and 80% of stems, respectively (Table 2). Pulsing with BA was
less effective in stimulating a second flower to open, and no second
flowers opened on control stems.
3.5. Effects of sucrose on the efficacy of the TDZ plus GA3
treatment
The addition of 10 and 20% sucrose to the TDZ plus GA3 pulse
solution increased flower longevity by an additional 0.6–0.8 d
(15–20%) (Table 3). Inclusion of 1% sucrose in vase water had a
Fig. 4. Vase life of iris ‘Discovery’ flowers after a pulse treatment in either deionized water (control), 0.5 mM TDZ and/or 1 mM GA3 for 24 h at 20 ◦ C. Flowers were
harvested at three stages of floral development; tepals being 1 cm below (stage 1),
0.5 cm above (stage 2) and 2 cm above (stage 3) the sheath leaves (see Fig. 1C–E).
Stems were maintained in deionized water at 20 ◦ C for vase life evaluation. The
frequency of a second flower to open on stems was also recorded. Vase life data
(means ± S.E.M., n = 15) followed by different letters are significantly different at
P = 0.05.
similar effect. The addition of 20% sucrose to the pulse solution or
1% sucrose to the vase solution resulted in an additional increase
in length of the flower shoot and also increased the opening of the
second flower. The length of the second open flower shoot was
Table 2
Vase life and flower shoot length of iris ‘Discovery’ flowers after a pulse treatment in water, 0.5 mM TDZ, 0.22 mM BA and/or 1 mM GA3 for 24 h at 20 ◦ C. Flowers were
maintained in deionized water at 20 ◦ C for vase life evaluation. Data (means ± S.E.M., n = 10) within each column followed by different letters are significantly different at
P = 0.05.
Pulse treatment
Vase life (d)
Control (water)
TDZ
BA
GA3
TDZ + GA3
BA + GA3
4.4
5.4
5.7
4.4
5.6
5.3
±
±
±
±
±
±
Shoot length (cm)
0.2b
0.2a
0.3a
0.3b
0.2a
0.2a
8.2
10.0
8.9
10.8
11.0
9.7
±
±
±
±
±
±
Stems with second open flower (%)
0.5c
0.2a
0.3c
0.2a
0.1a
1.1b
0
50
10
30
80
10
Table 3
Vase life and flower shoot length of cut iris ‘Discovery’ flowers following pulse treatment in either water or a solution of 0.5 mM TDZ plus 1 mM GA3 amended with 0, 1, 5, 10
or 20% sucrose for 24 h at 20 ◦ C. Flowers were maintained in deionized water with or without 1% sucrose at 20 ◦ C for vase life evaluation. Data (means ± S.E.M., n = 15) within
each column followed by different letters are significantly different at P = 0.05.
Pulse treatment
Vase solution
Vase life (d)
Water + 0% sucrose
TDZ + GA + 0% sucrose
TDZ + GA + 1% sucrose
TDZ + GA + 5% sucrose
TDZ + GA + 10% sucrose
TDZ + GA + 20% sucrose
TDZ + GA + 0% sucrose
Water
Water
Water
Water
Water
Water
1% sucrose
4.1
5.6
5.3
5.5
6.2
6.4
6.3
±
±
±
±
±
±
±
0.2c
0.2b
0.2b
0.3b
0.3a
0.1a
0.2a
Flower shoot (cm)
10.1
11.0
11.0
11.0
11.5
12.0
11.8
±
±
±
±
±
±
±
0.2c
0.2b
0.2b
0.3b
0.3ab
0.2a
0.2a
Stems with second open flower (%)
7
87
71
87
93
100
100
82
A.J. Macnish et al. / Postharvest Biology and Technology 56 (2010) 77–84
Fig. 5. Vase life, length of the flower shoot, and the maximum angle at which tepals
unfurled relative to the central stem for iris ‘Discovery’ flowers that were pre-treated
with 0.5 mM TDZ and/or 1 mM GA3 amended with 0 or 20% sucrose for 24 h at 0 ◦ C.
Stems were stored dry for 0, 3, 7 and 14 d at 0 ◦ C before placement into vases containing deionized water at 20 ◦ C. Data (means ± S.E.M., n = 16) for each storage time
followed by different letters are significantly different at P = 0.05.
similar to that of the first open flower (data not shown). Including sucrose also enhanced a pulse treatment with GA3 alone but
it was less effective than TDZ plus GA3 and sucrose in improving
flower longevity and opening (data not shown). The tepals of flowers that were treated with TDZ plus GA3 and 20% sucrose were a
darker purple color at maximum opening, as evidenced by a significantly lower L* (lightness) value (35.9 ± 1.1, n = 15), than tepals
from stems pulsed with TDZ plus GA3 and 0% sucrose (43.8 ± 1.5,
n = 15).
3.6. Effect of TDZ, GA3 and sucrose treatment prior to dry storage
Dry storage slightly increased the life of control flowers, but
flower shoot length, and opening (as measured by tepal angle)
decreased steadily as storage duration increased (Fig. 5). Treatment with 0.5 mM TDZ and/or 1 mM GA3 for 24 h at 0 ◦ C prior
to storing flowers dry for 0, 3, 7 and 14 d at 0 ◦ C resulted
in a significant increase in the vase life of flowers after storage (Fig. 5). Pulsing with a combination of TDZ plus GA3 and
20% sucrose was even more effective. Storing flowers from each
treatment for 14 d at 0 ◦ C did not significantly reduce vase life
relative to non-stored flowers. The flower shoot length on stems
pulsed with 0.5 mM TDZ plus 1 mM GA3 and 20% sucrose was
as much as 60% greater than that of the controls regardless of
the storage treatment. Flower shoot elongation resulted in more
complete flower opening as judged by an increase in tepal angle
(Fig. 5).
Fig. 6. Rates of respiration and ethylene production by cut iris ‘Discovery’ flower
stems during pulse treatment with 0 or 0.5 mM TDZ for 24 h at 20 ◦ C and subsequent
vase life in deionized water at 20 ◦ C. Data are presented as means ± S.E.M. (n = 6).
3.7. TDZ treatment effects on flower respiration and ethylene
production
Freshly cut iris flowers had a high respiration rate, which fell
rapidly during the day after harvest, and then steadily during the
remainder of vase life (Fig. 6). TDZ treatment stimulated an increase
in respiration during pulsing, but thereafter rates decreased to that
of control flowers. TDZ treatment increased ethylene production
to a peak nearly 3 times that of control flowers, at flower opening
(Fig. 6).
4. Discussion
Pulsing with 0.2–1 mM TDZ for 6–24 h at 0 ◦ C (data not shown)
or 20 ◦ C provides a simple and practical postharvest treatment for
extending the longevity of iris flowers and leaves (Figs. 2 and 3).
Our findings are consistent with previous reports that TDZ treatment, albeit at relatively lower concentrations than those used in
the present study, can inhibit leaf yellowing and delay the onset of
flower senescence in other ornamental plant species (Ferrante et
al., 2002, 2003; Sankhla et al., 2005). Our discovery that a different TDZ concentration threshold exists for inhibiting leaf and floral
senescence in iris highlights an opportunity to evaluate effects of
higher TDZ concentrations on other flower species. It has been suggested that the non-metabolizable nature of TDZ is the basis for
its remarkable effects in preventing leaf yellowing (Ferrante et al.,
2002). In iris, however, TDZ treatment was no better than BA (which
is metabolized) in extending floral life (Table 2). However, BA did
not stimulate elongation of the flower shoot that was seen in stems
pulsed with TDZ. Flower shoot growth forced the floral bud free of
the sheath leaves and facilitated complete flower opening (Table 1).
As was previously shown in ‘Blue Magic’ iris (Celikel and van
Doorn, 1995a), we found that treatment with 1 mM GA3 extended
the length of the flower shoot in ‘Discovery’ iris and thereby
A.J. Macnish et al. / Postharvest Biology and Technology 56 (2010) 77–84
improved flower opening (Table 2). GA promotes stem extension by
inducing both cell division and elongation (Jones, 1973). In the dry
storage experiment, an additive effect on flower shoot growth was
observed when GA3 was combined with TDZ and this may reflect
the effect of the cytokinin on cell division, since combining GA3 and
TDZ gave greater benefits than applying TDZ or GA3 alone (Fig. 5).
Carbohydrates such as sucrose are commonly added to cut
flower solutions to provide a readily respirable substrate and
osmoticum for maintaining flower display (Marousky, 1969;
Coorts, 1973). Tirosh et al. (1983) reported that pre-treating iris
‘Prof. Blaauw’ flowers in a solution of 2% sucrose plus 2 g L−1 citric
acid for 12 h at 20 ◦ C improved flower opening after dry storage. The
authors suggested that sucrose may have contributed to the energy
pool and/or increased the osmotic potential within cells leading to
elevated rates of water uptake. We found that provision of 20%
sucrose in the TDZ plus GA3 pulse solution further extended flower
life and opening, particularly after dry storage (Table 3; Fig. 5). Placing stems treated with TDZ plus GA3 in vase water containing 1%
sucrose also delayed the onset of flower senescence by a further
0.7 d (Table 3). Similarly, van Doorn (2004) noted that sugar in the
vase solution delayed visible symptoms of iris flower senescence by
0.5 d. The efficacy of treatment with TDZ plus GA3 and sucrose to
improve flower opening and longevity even after 14 d of dry storage
to levels greater than non-stored flowers provides an opportunity
to transport iris flowers by air and sea to more distant markets
and/or dry store stems for special holidays such as Mother’s Day.
Although the exact mode of TDZ action is not known, evidence
suggests that it can regulate endogenous cytokinin biosynthesis
and/or metabolism (Mok et al., 2000). Treatment of cut carnation
and rose flowers with the synthetic cytokinins, BA or kinetin, can
delay flower senescence by reducing rates of ethylene biosynthesis
and response (Eisinger, 1977; Mayak and Halevy, 1974). Sankhla
et al. (2003, 2005) showed that TDZ treatment could also delay
ethylene-mediated floral organ abscission and senescence in phlox
and lupin. However, it is unlikely that TDZ treatment extended
‘Discovery’ iris flower longevity by reducing ethylene sensitivity.
Firstly, we showed that treatment with 0.5 mM TDZ, a relatively
high concentration, stimulated an increase in ethylene production by flowers (Fig. 6) in line with observations by Suttle (1986).
Secondly, exposure to ethylene reportedly does not hasten floral
senescence in iris (Woltering and van Doorn, 1988).
Treatment with BA has also been reported to reduce rates of
respiration and catabolic processes associated with carnation and
chrysanthemum flower senescence (MacLean and Dedolph, 1962).
However, in the present study, TDZ stimulated an increase in respiration by iris flowers during pulsing (Fig. 6). Thus, the positive
effects of this chemical on flower longevity may be related to an
increase in metabolism. Moreover, since the TDZ-induced delay in
floral senescence was associated with a prevention of yellowing of
sheath leaves (Fig. 3), the benefits of TDZ treatment may be due to
maintenance or improved carbohydrate supply from leaves to floral organs necessary for maintaining flower metabolism (Reid et al.,
2002). Further research directed at quantifying the effects of TDZ
treatment on proteolytic enzyme and photosynthetic activity may
help to define its beneficial role in delaying iris flower senescence.
Pulsing with TDZ was also associated with an extension of ‘Discovery’ iris flower shoots (Fig. 5; Tables 1 and 2) and is consistent
with reports that it may act by mimicking auxin activity (Murthy
et al., 1998). Auxin, like GA, can rapidly elicit cell elongation in a
wide range of species (Cleland, 1995). For example, treatment with
the auxin, indole-3-acetic acid promoted elongation of tulip flower
stalks (Op den Kelder et al., 1971). The addition of GA3 to the TDZ
pulse solution enhanced ‘Discovery’ iris flower shoot elongation
by stimulating growth of the pedicel and ovary (Fig. 5). However,
provision of 10 or 20% sucrose in the TDZ plus GA3 pulse solution
had a greater stimulatory effect on growth of the ovary than the
83
pedicel. This finding concurs with observations by Nichols (1975)
that applied sugar was utilized for ovary growth in cut narcissus
flowers.
‘Discovery’ iris stems often have at least one and sometimes
two additional buds below the primary flower bud. Pulsing with
TDZ pulsing stimulated an increase in the number of stems that
developed a second open flower (Table 2; Fig. 4), a response similar
to that reported for cut lupin and tuberose flower stems (Sankhla
et al., 2003; Uthairatanakij et al., 2007). We noted that the addition
of GA3 and sucrose to the pulse solution further enhanced opening
of the second flower on iris stems. Opening of the second flower
typically coincided with senescence of the first flower, so the TDZ
treatment therefore increased the overall display life of stems.
Acknowledgements
We thank the American Floral Endowment and the USDA
Floriculture Initiative for partial funding of this study. We also
acknowledge Sireena Chieng for technical assistance with experiments.
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