Plant Physiol. (1972) 50, 341-346

Interrelationships of Ethylene and Abscisic Acid in the Controlof Rose Petal Senescence'

Received for publication December 6, 1971

S. MAYAK AND A. H. HALEVYThe Volcani Institute of Agricultural Research,Hebrewv University, Rehovot, Israel

ABSTRACT

The role of abscisic acid and ethylene in the senescence ofrose petals cv. Golden-Wave was examined. A rise in ethyleneevolution, followed by an increase in the level of abscisic acidwas observed. The presence of abscisic acid in rose petals wasestablished, using different chromatography systems, severalbioassays, and immunoassay. External application of ethyleneaccelerated senescence and induced a rise in endogenous ab-scisic acid-like activity. Application of abscisic acid promotedsenescence, but suppressed ethylene production. The data sug-gest that the participation of these two hormones in the con-trol of senescence is via the same pathway. The possibility ofinterrelationship between abscisic acid and ethylene was testedand experimental evidence in favor of this hypothesis is pre-sented. It was suggested that ethylene affects senescence in rosepetals by inducing an increase in abscisic acid activity, whichin turn may control ethylene evolution, via a feedback mecha-nism.

Rehovot, Israel and Department of Floriculture, The

leaves (21, 34). Applied ethylene is known to enhance yellow-ing of leaves (44) and promote degradation of protein infoliage leaves and petals (36).

Ethylene evolution has been demonstrated by a wide as-sortment of flowers (7, 15, 35). Ethylene rise was found to beassociated with the fading of orchids (3) and carnation flowers(30). The rapid development of petal senescence of Vandaflowers following pollination is a result of ethylene productioninduced by high level of auxin in the stigma spreading into thecolumn and lip, there inducing the synthesis of ethylene (10).ABA induces the development of senescence in leaf discs (39),intact leaves (14), and orchid flowers (4). Also, an increase inthe level of ABA has been correlated with senescence processesin fruits (38).

In this present work an attempt was made to evaluate thechanges in ABA-like inhibitor and ethylene production in rosepetals during senescence and to study the interrelationshipbetween these hormones in the control of rose petal senescence.

The regulation of senescence processes in rose petals bycytokinins has been reported previously (28). It has beenpointed out that other phytohormones besides cytokinins mayparticipate or interact in this regulation. Interrelationshipbetween hormones, in which one controls the level of another,exists in some plant systems. The interrelation between auxinsand ethylene was recorded in many cases. Auxins were foundto enhance ethylene evolution in many plant tissues (37) in-cluding orchids (10), carnations (41), flowers of strawberriesand blueberries (22), and undifferentiated cell cultures of roses(18). This rise in ethylene production could reduce auxin levelvia a feedback mechanism (9). ABA reduces the level ofendogenous gibberellins (42) and suppresses ethylene evolutionby tissue culture of Ruta cells (18).A rise and then a decline in ethylene evolution during pear

fruit ripening was reported (24). This increase was argued asbeing only a by-product of fruit ripening processes (6). How-ever, the concept of ethylene being a ripening hormone is nowwell established (8). Although a similar rise in ethylene evolu-tion was observed prior to abscission of bean petioles (26) andsenescence of cotton cotyledons (5), we did not find in theliterature any work demonstrating such a rise in leaf blades.On the contrary, ethylene evolution tends to decline in aging

1Contribution from the Volcani Institute of Agricultural Re-search, Bet Dagan, Israel Series No. 2006-E, 1971.

MATERIALS AND METHODS

Plant Material. Petals of rose cv. Golden Wave were used.Flowers were either allowed to develop and age on the plantor were picked at an early stage and allowed to develop in avase with deionized water.

Detection of ABA-like Inhibitor. Petals from fully openflowers were extracted twice with 80% (v/v) methanol at 4 Cfor 24 hr. The combined methanolic extract was filtered andevaporated under reduced pressure to the water phase. Afteracidification to pH 3.0 with HCI, the water phase was eitherextracted four times with ethyl acetate, or in later experiments,eight times with chloroform. (In an evaluation of partitionprocedures with different solvent systems, it was found thatmost or all ABA-like inhibitors are transferred into the chloro-form phase.) Paper and thin layer chromatography with dif-ferent solvent systems were used in studying inhibitor activity.A portion of the chloroform fraction equivalent to 2 g of freshweight was applied to 3 cm wide strips of Whatman No. 3MMpaper. Three paper strips representing three replicates weredeveloped by ascending chromatography with isopropanol-ammonium hydroxide (28 %)-water (8: 1: 1, v/v). After drying,each paper strip was cut into 10 equal zones (RF), each ofwhich was transferred to a vial 11 X 35 mm used in the wheatcoleoptile and barley endosperm bioassays. In other experi-ments, portions of the chloroform fraction were streaked onTLC2 plates coated with a 250 p. layer of Silica Gel G (Merck).The plates were developed in two different solvent systems: 1.n-propanol-n-butanol-water-ammonium hydroxide (28%) (6: 2:

2 Abbreviations: TLC: thin layer chromatography; DMSO:dimethyl sulfoxide.

341

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MAYAK AND HALEVY

FIG. 1. Histograms of wheat coleoptile assafraction developed in different chromatographchromatography, isopropanol-ammonium hydi8: 1:1 (v/v); (b) T.L.C. using benzene-ethyl50:5:2 (v/v) as solvent; c: T.L.C. using n-ammonium hydroxide (28%c): water, 6:2:1:2

2:1, v/ v). 2. benzene-ethyl acetate-acetic aThe plates were developed by ascending chidistance of 15 cm and dried at room temp(air cabinet (this was done in order to evaporminterfering with the bioassay method). The Iinto 10 equal RF zones, and the silica gelscraped, eluted with absolute methanol, andtatively onto three paper pieces (I X 3 cm)transferred to vials (11 X 35 mm as describexperiment the crude methanolic extract wolots, which were processed separately andregarded as true replications.

Bioassay. Five bioassay methods were uspresence of inhibitors. (a) Wheat straight grsay (33) (the eluate of silica gel developeding solvent served as control). (b) Wheat ewhich four Petri dishes, eight embryos in eRF zone. (c) Barley endosperm assay (12),activity was evaluated on a background of(d) Soybean callus test, the inhibitory activibeing tested according to Miller (30). Twemedia containing 0.5 mg/liter kinetin andsolidified with agar, was used to grow three ecallus. (e) Immunoassay according to Fuchsthe free hormone inhibits the inactivationteriophage (a conjugate of bacteriophage vcaused by specific antibodies against the horn

Detection by Gas Chromatography. A gliinner diameter) was prepared by pouring asilica gel 0.05 to 0.2 mm (Merck) mixed in tlethyl acetate-acetic acid (50:5:2. v/v).chloroform fraction equivalent to 100 gplaced on the silica gel column and partitisolvent. Preliminary studies showed that vauthentic ABA and plant extracts were pa column, the ABA was located in test tulcontaining 1 2-ml portions. The contents ofwas therefore combined and evaporated uisure to the water phase, which was latermethylation with diazomethane, I-u.1 portioa Packard 7400 gas chromatograph, using a1.8 m long X 3.2 mm inner diameter, packeGas-chrom Q. The column temperature wagas flow of 30 ml/min served as carrier. Adetector was used (40) with radioactive tritiL

Holding Flowers for Longevity Deteilongevity evaluations were conducted in a c

ture room (22 C ± 2) relative humidity 55 to 65%, 12 hrphotoperiod, and light intensity of 90 ft-c. The stem base wasrecut and solution of water changed every other day.

Application of Ethylene to Cut Flowers. The stenm bases ofABA cut flowers were placed in deionized water in glass compart-

_10-8 ments through which 5 ul,,` 1 ethylene or air flowed continu-"l : 0-7 ously. After 20 hr the flowers were transferred to a controlled

10-6 temperature room for longevity determination. At the end ofthe 2nd day at 22 C, some of the flowers were sampled and

1o- tested for ABA-like activity in the petals. In other experiments,the stem-base of cut flowers was held in an ethylene-releasingcompound, Ethephon (2-chloroethanephosphonic lacid) solu-

D 0.5 1.0 tion of 22.5 ,ug/ml or in deionized water tor 20 hr and thentransferred to deionized water for longevity determination.

ty of the chloroform One day later the flowers were transferred to a controlledy systems. a: Paper temperature room, and flower diameter was measured as anroxide (28%)-water, indication of flower opening. Five replic-itions of four flowersacetate-acetic acid, each were used for each treatment, and each experiment was-propanol-n-butanol- repeated three times. The content of ABA-like inhibitors inv/v) as a solvent. petals was determined for the first 5 days after treatment.

Application of ABA to Cut Flowers. Two lots of cult flowers,cid (50:5:2, v/v) one with leaves on the stem and one with leaves stripped off,romatography to a were used. The stem base of the flower was placed in solutionscrature in a forced containing 0, 100, and 500 pg/ml of ABA, dissolved in 0.1I%ate solvent residues DMSO in deionized water. Five replications of four flowersplates were divided each were used for each treatment, and each experiment wasof each plate was repeated twice. In other experiments, cut flowers with theirtransferred quanti- leaves stripped off were placed in a solution of 1 mm ABA), which were then dissolved in 0.1 % DMSO. Every day petals were sampled fored above). In each ethylene evolution measurements. Apparently, DMSO facili-asdivided into two tated the penetration and transport of ABA to the tissues. It ismay therefore be known (2, 43) that in many cases little or no response is ob-

tained with external application of ABA to intact plants. This,ed in studying the may stem from difficulties in absorption and translocation of*owth coleoptile as- the hormone. The ulse of DNISO as a solvent mav help in suchin the carrespond- cases as it does in flowers.mbryo test (29) in Ethylene Evolution Determination. Flowers were pick-ed inach, were used per a commercial greenhouse in the morning, plced immediatelyin which inhibitor in tap water, and brouLght to a controlled temperature room0.1ofMGAc (19). (22 C). There they were transferred to vases containingty Ot each RF zone deionized water, their stems were recut every day, and waternty ml of nutrient was replaced every other day. Some of the flowers wereeluate of Rs zone sampled for ethylene evolution every day during the experi-explants of soybean ment. Petals were pulled off so as to avoid bruising, the onlyet al. (17) in which damage being at their point of attachment to the flower. The.of modified bac- petals were weighed (5 g fresh weight) and placed in 100-mlvith the hormone), Erlenmeyer flasks, to which 0.2 ml of water were added, and

mone. closed with a self-sealing rubber stopper. The flasks wereass column (2.5 cm placed for 5 hr at 22 C under white fluorescent light of 250slurry of 30 g of ft-c.

he solvent benzene- Two-ml air samples were withdrawn from each flask andA portion of the injected into a Packard gas chromatograph equipped with afresh weight was flame ionization detector. Eight flasks were used for eachioned by the same treatment.xhen a mixture of Ethylene evolution was determined in green foliage leaveslartitioned on such also by the same procedure. Leaves were sampled from green-bes 27 to 35, each houlse-grown plants at four development stages: (a): young.test tubes 25 to 37 pale green colored: (b): green fully expanded leaves: (c): greennder reduced pres- m-ture leaves: (d): mature leaves showing first ft ding signs oflyophilized. After initial senescence.n was injected intoglass spiral column RESULTSd with 5% QFI onIS 205 C. Nitrogen Identificatiotn of the Inhlibitor fromii Rose Petals. The in-n electron capture hibitor extracted from rose petals was tested by the wheatim foil. coleoptile bioassay in three chromatography systems (Fig. 1).rmination. Flower In all three systems the rose inhibitor mitrated to a similar R,ontrolled tempera- of authentic ABA. The presence of the ABA-like inhibitor

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ETHYLENE AND ABA IN ROSE PETALS

was further verified by testing the activity of the variouschromatogram zones in three other bioassays; the wheat em-bryo test (Fig. 2a), inhibition ot kinetin acLion in growth ofsoybean callus (Fig. 2b), and inhibition of the GA promotionof sugar release in barley endosperm (Fig. 2c). In all theseassays an inhibition zone was found at a zone correspondingto authentic ABA. Also, the data presented in Figure 3 showedthat the rose petal inhibitor has the same retention time ina gas chromatography system as ABA. Additional identifica-tion of the rose petal inhibitor as ABA was carried out by therecently introduced immunoassay for plant hormones (16). Afull account of these results is presented elsewhere (17). ABAhas been identified earlier in stems and fruits of roses (25, 29).ABA Relation to Senescence of Rose Flowers. ABA level

was determined in cut rose flowers held in water for severaldays. The inhibitor activity was relatively low tor the first 96hr (Fig. 4, upper row) and then increased sharply. Usually mostof the flowers terminated their vase life 1 to 2 days later, theirpetals wilted or dropped upon gentle shaking. The effect ofexogenous application of ABA to cut flowers was studied withtheir base in ABA solution dissolved in 0.1% DMSO. It wasfound (Table I) that ABA enhanced flower opening and short-ened their life-span. DMSO was indispensable for ABA effect.Spraying cut or intact flowers or dipping flower buds for 15min into various concentrations of ABA (100 to 500 [kg/ml)dissolved in dilute KOH adjusted with HCI to pH 8.0 gave noresponse. Table I shows results for flowers with leaves strippedoff the stems. A similar but less pronounced effect was notedwith flower stems with leaves intact.

Ethylene in Relation to Senescence of Rose Flowers.Ethylene production by petals of cut flowers enclosed in a100-ml Erlenmeyer flask (Fig. 5) was noted by daily samplingand measuring. Two days after cutting, ethylene productionhad increased and continued to do so until flowers collapsed orlost turgidity.An interesting point is that although petals are modified

leaves, their ethylene production pattern is very different fromthat of leaves. As petals mature and senesce, ethylene evolu-tion increases, whereas in foliage leaves ethylene productiontends to decrease (Table II).

Exogenous application of ethylene or Ethephon to cutflowers (Table III) significantly decreased their longevity, andin most cases increased the incidence of petal drop, an effectresembling the results of ABA application.

Effect of Ethylene on ABA-like Inhibitor Content in Petals.ABA-like inhibitor content in petals of flowers exposed toethylene was much higher than in those held in air (Fig. 6).The change of ABA-like inhibitor content in petals was furtherstudied in flowers treated with 22.5 1-g/liter Ethephon for 20*hr (Fig. 4). There was a substantial increase in ABA level 72hr after Ethephon treatment. A similar rise in ABA was ob-served also in control plants but only after 120 hr. We havechecked ethylene evolution in the Ethephon-treated flowers 2to 5 days after treatment and found it to be 4 to 5 times higherthan in untreated flowers.

Effect of ABA on Ethylene Production by Flowers. Thestem bases of cut flowers were held in ABA solution, and theflowers were sampled daily for ethylene production (Fig. 7).While ethylene production increased in flowers held in wateror in DMSO 0.1% solution, it hardly changed in those heldfor 4 days in ABA solution.

DISCUSSION

A change in hormonal activity in parallel to a process and acorresponding response to an external application of the hor-mone suggest the participation of that hormone with the proc-ess under study. In a previous report (28) we presented data

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FIG. 2. a: Wheat embryo test of T.L. chromatogram developedin ni - propanol - n - butanol - ammonium hydroxide (28%) - water,6:2:1:2 (v/v); each RF represents a mean of four Petri dishes eachcontaining 8 embryos. b: Soybean callus test of paper chromato-gram developed in isopropanol-ammonium hydroxide (28%)-water,8:1: 1 (v/v); each RF represents a mean of four flasks each con-taining 3 soybean explants. c: Histogram showing inhibition of a-amylase activity in barley endosperm by eluates from paperchromatogram strips developed as in b, increased inhibitory activ-ity is represented by lower absorbance values than of 0.1 /iM GA3.

ABA

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RFITENTION TIME (min)FIG. 3. Gas chromatography traces: 5% QF1 on Gas-chrom Q

at 205 C and nitrogen gas flow of 30 ml/min. Top: methylatedextract of rose petals; bottom: (+) methylated ABA.

supporting the participation of cytokinins in the endogenouscontrol of senescence in rose petals. We also raised the possi-bility that this process is controlled by more than one hormone.The participation of ethylene and ABA-like inhibitor in petalsenescence is demonstrated in the present studies.A rise in ethylene evolution (Fig. 5) and in the level of ABA-

Plant Physiol. Vol. 50, 1972 343

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MAYAK AND HALEVY Plant Physiol. Vol. 50, 1972

6 J

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o TIME AFTER TREATMENTO 24 hr 48 hr 72hr 96 hr 120hrL

ETHYLENE AND ABA IN ROSE PETALS

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FIG. 6. Histograms of wheat coleoptile assay of the chloroform fraction from rose petals. The flowers were exposed to 5 ,u/liter ethylene gasfor 24 hr, and after an additional 24 hr in air they were tested for ABA-like activity. The paper chromatograms were developed in isopropanol-ammonium hydroxide (28%)-water, 8:1:1 (v/v).

rise in ABA level. To test this hypothesis we treated flowerswith ethylene gas or with the ethylene-releasing compoundEthephon and tested its effect on ABA-like inhibitor. The re-sults (Figs. 4 and 6) indicate that ethylene can trigger such anincrease. Our colleagues at the Hebrew University, Rehovot,also found ABA-like inhibitor increase following treatmentwith Ethephon in oranges (20) and in cucumber seedlings (J.Rudich, A. H. Halevy, and N. Kedar, in preparation). The levelof ethylene evolution induced in young flowers by the Ethe-phon treatment was similar to that evolved naturally by oldpetals. This strengthens the physiological significance of thisfinding.

The time lag of about 2 days from the ethylene treatmentto the observed rise in ABA-like inhibitor may suggest thatthis is not merely the release of a bound inhibitor to an activestate, but that several processes are involved.

Interrelations between hormones, by which one hormoneaffects the level of another are known; for example, ethyleneinfluenced by auxin (23, 10) or reduced after treatment withABA (13), and gibberellin influenced by ABA (42).Our data indicate an interrelationship between ethylene and

ABA. We suggest that the rise in ethylene production is asignal for ABA-synthesizing processes, which in turn causesenescence of rose petals. An increased level of ABA maycontrol the production of ethylene via the feed-back mecha-nism, as was demonstrated by the decreased production ofethylene in flowers treated with ABA. A similar mechanismwas suggested by Burg (9) to explain the interrelation betweenauxin and ethylene. Our data do not, of course, rule out thepossibility that the ABA effect is a simple inhibition of meta-bolic processes.The ABA concentration used by us (1 mM) may raise the

question of the physiological significance of our findings.However, no information on the actual endogenous level ofABA in petal tissue is available, and we do not know howmuch of the applied ABA reached the petal tissue, since diffi-culties of ABA penetration have been reported elsewhere (2,43).The role of ethylene in inducing senescence has been estab-

lished in many reports (1, 11, 26, 41). A rise in ethyleneproduction is usually associated with fruit senescence (8). Thesame occurs also in flowers (3, 10, 31) and in rose petals (Fig.5). Burg (11) has suggested that an ethylene evolution rate of3 to 5 nl/g hr approximates an internal ethylene concentrationof 1 to a few .1/1. The ethylene evolution rates of rose petals(Fig. 5) were up to 0.5 nl/g-hr, corresponding therefore to in-ternal concentrations of 0.2 to 0.5 uA/l. This concentration is

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FIG. 7. Ethylene production by cut rose flowers cv. GoldenWave treated with ABA; each point is a mean of six replications±SE.

within the reported threshold value for ethylene effect on roseflowers (7, 27).The production of ethylene by leaves is generally high in

young tissues and declines as leaves mature and senesce (21,34). Green foliage rose leaves behave similarly in this respectto other green leaves (Table II). Therefore, it is of interest tonote that although petals are modified leaves, their ethyleneproduction pattern is similar to that of fruits and not to leaves.However, if one considers the life span of petals, which ismuch shorter than that of foliage leaves, a possibility existsthat leaves go through a rise and then a decline similar to whatwas demonstrated in petioles (26). Such a rise could be missedif one samples for ethylene only a few times during the rela-tively long period during which development and aging offoliage leaves take place.Hormonal changes and their interrelationships were studied

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Plant Physiol. Vol. 50, 1972 345

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346 MAYAK AND HALEVY

in a model consisting of attached rose petals going throughsenescence processes. The contributing effect of other partsof the flower, which may play a role in the senescence proc-esses of the petals, were not considered in this study.

AcAknoiwledgmeif-The expert technical assistance of lMrs. Lea Sclditner isgrateftlly acknowlecdged. Ethephon (2-chloroethaiielplhoslplionic acid) w%vas kindlysupplied by Agan Clhemicals, Tel Aviv. Abscisic acid (RO-08-0095) is a gift ofF. Hoffmann La Roche.

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