Does Pollination Induce Corolla Abscission of Cyclamen Flowers by Promoting Ethylene Production?

Very low ethylene production rates were measured in nonpollinated Cyclamen persicum Mill flowers, and no change in production was observed during the whole life span of the flower until death. Normal senescence was accompanied by a gradual discoloration and loss of turgor followed by wilting. Pollination induced a dramatic increase in ethylene evolution, culminating in a peak 4 days after pollination, and abscission of the corolla on that day. Silver-thiosulfate, an inhibitor of ethylene action, had no effect on longevity of unpollinated flowers, but completely nullified the effect of pollination on corolla abscission. Exposing unpollinated flowers to very high ethylene concentrations (50 microliters per liter) for 48 hours did not promote corolla abscission or senescence. 1-Aminocyclopropane-1-carboxylic acid, the immediate precursor of ethylene, increased ethylene production by unpollinated flowers more than 100-fold, but did not promote corolla abscission. 1-Aminocyclopropane-1-carboxylic acid did enhance corolla abscission of pollinated flowers. It is concluded that the main effect of pollination in inducing corolla abscission of cyclamen is by rendering the tissue sensitive to ethylene, apart from the promotion of ethylene production.     

Aroma production from cut sweet pea flowers (Lathyrus odoratus): the role of ethylene

The major components of the scent of cut sweet pea flowers ( Lathyrus odoratus L. cv Royal Wedding) are (E) and (Z)-ocimene, linalool, nerol, geraniol and phenylacetaldehyde. The aroma is almost exclusively produced by the standard and wing petals, with very little emanating from the keel petals and other floral structures. Only traces of these volatiles were detected in the liquid excreted by glandular trichomes on the surface of the scented petals. Once flowers are cut for display they produce increasing amounts of ethylene which induces wilting after 48 h and petal abscission 24 h later. The rate of linalool and ocimene emission declines over the first 48 h to approximately 10% of that directly after harvest. Ethylene production is not saturating during the first 24 h of vase life and exogenous ethylene further accelerates the senescence processes and loss of fragrance. Addition of the ethylene antagonists 1-methylcyclopropene (1-MCP) and silver thiosulphate (STS) delayed wilting and abscission for several days and similarly inhibits the decline in terpenoid emission.     

Effects of Diazocyclopentadiene (DACP) and Silver Thiosulphate (STS) on Ethylene Regulated Abscission of Sweet Pea Flowers (Lathyrus odoratus L.)

The ethylene production rate of cut sweet pea flower buds increased37-fold during the first 48 h of their vase life. This increasein ethylene production was accompanied by petal wilting at 72h and abscission of the buds 24 h later. Exposure of the cutspikes to the ethylene action inhibitor diazocyclopentadiene(DACP, 170 µI 1^-1) for 18 h under fluorescent lights delayedsubsequent wilting and abscission and promoted bud opening.Silver thiosulphate (0·2 mM) was more effective thanDACP, delaying wilting for longer and preventing abscissionentirely.Copyright 1995, 1999 Academic Press Ethylene, abscission, silver thiosulphate, diazocyclopentadiene, flower senescence, wilting, sweet pea, Lathyrus odoratus L     

The Control of Flower Senescence in Petunia (Petunia hybrids)

Petunia corollas wilt and abscise between one and two weeksafter detachment when maintained in distilled water in vialsat 18 °C. The onset of wilting is brought forward substantiallyby the application of 1-aminocyclopropane-1-carboxylic acid(ACC) either to the vial solution or to the stigmatic surface.Both pollination and stigma removal also shorten the time tothe onset of wilting, colour change and to abscission. In thecase of stigma removal, the life span of the corolla is shortestwhen the treatment is made at the time of flower detachment(day 0), whereas pollination has the greatest effect if it occurson day 1. Stigma damage still has an effect on corolla senescenceeven when stigma and style are removed, as long as they havebeen left in place for a few hours after treatment. Evidencefrom several experiments shows that a 17 h period is sufficientfor the full effect to be shown, and that probably there aresome effects on the corolla even if the damaged stigma is onlyleft in position for 3–6 h. Treatments which advance corolladeath (to day 3) also advance the peak of ethylene productionby the pistil (to day 1) and the corolla (to day 2). The useof silver thiosulphate (STS) overcomes all manipulative andchemical treatments used, and greatly extends vase life. Theextension occurs even when STS application is delayed for 24h, i.e. after the peak of ethylene production by the pistiland after any senescence signal has arrived at the corolla.In this case, however, the time to first morphological changeis largely unaffected, but the STS greatly extends the timeperiod between first morphological change and corolla death.The evidence suggests that early symptoms of senescence e.g.colour change and slight loss of turgor, do not automaticallylead to corolla abscission. Petunia hybrida, abscission, ACC, STS, pollination, flower senescence, ethylene     

Roles of ethylene and 1-aminocyclopropane-1-carboxylic acid in pollination and wound-induced senescence of Petunia hybrida flowers

Normal senescence of Petunia hybrida L. (cv. Pink Cascade) was associated with a 10-fold increase in their ethylene production. Soon after pollination wounding of the stigma of detached flowers there was a burst of ethylene production by the gynoecium, which reached a maximum after 3 h. A subsequnt more gradual rise in ethylene production by the flowers was accompanied by blueing, wilting, and senescence of the corolla. Treatment with 1 μl ethylene 1⁻¹ accelerated the onset of senescence as measured first by color change and then by wilting of the corolla. These changes were further accelerated by using older flowers or higher concentrations of ethylene. Senescence was also hastened by supplying 1-aminocyclopropane-1-carboxylic acid (ACC) through the flower pedicel. Petunia pollen contained high concentrations of ACC (300 nmol g⁻¹); treatment of stigmas with ACC (1 m M ) caused a 4-fold increase in their ethylene production. Senescence, whether natural or hastened by pollination or piercing, was delayed by treating the flowers with the anionic silver thiosulfate complex.     

The Importance of the Stigma in Flower Senescence in Petunia (Petunia hybrida)

Senescence of flowers of Petunia hybrida Vilm. cv Gypsy is characterizedby colour changes, wilting and abscission. In emasculated detachedflowers the onset of these processes is hastened by any treatmentwhich reduces the vigour of the stigma. Thus pricking it, excisingsegments, or freezing with liquid nitrogen all reduce the timeto morphological changes associated with corolla senescence.Removal of the stigma has the most dramatic effect, reducinglifespan of the flower by about 50 per cent, to 3 d. This reductioncan be lessened if IAA or 2,4-D is applied to the cut surfaceof the style. In intact flowers, the style may usually be implicatedin the production of a stimulus leading to corolla abscission,but abscission will also occur in the absence of the style.Some senescence acceleration takes place not only in the completeabsence of the style, but also when the upper part of the ovaryhas been excised in addition. The speeding up of senescenceand of corolla abscission cannot be due solely to damage perse since when the corolla limb was excised, leaving only thecorolla tube, the tube abscised at about the same time as thecontrols, despite the quite extensive wounding. This also impliesthat the distal parts of the corolla do not play a major rolein the development of the abscission zone at the base of thecorolla tube. A healthy, undamaged stigma appears to be very important incorolla longevity and one of its roles may be to prevent theproduction of an abscission/wilting stimulus by some other componentof the flower. Possibly auxins in the stigma are important inthat either they are mobile and protect the abscission zoneor they create a sink for other substances which are implicatedin flower senescence. Petunia hybrida, abscission, auxins (IAA, 2,4-D), corolla, flower senescence, stigma, style, wilting     

Stamen abscission and water balance in Metrosideros flowers

Cymules (3-flowered units borne on single pedicels) were cut from inflorescences of Metrosideros collina J.R. & G. Forst. cv. Tahiti and used to test the effects of ethephon and ethylene on stamen abscission in the presence of silver thiosulphate (STS) and 1-methylcyclopropene (1-MCP), and to test the effects of holding solutions on cymule water balance and the progression of floral development. Flower bud and stamen abscission occurred in response to 0.5–5.0 and 0.1 μl l⁻¹ ethylene, respectively. Ethylene effects were partially negated by scrubbing exogenous ethylene, and more completely negated by STS (2.0 m M ). 1-MCP caused greater ethylene production and inhibited stamen abscission for only 1–2 days after treatment. Ethephon (10-10 000 mg l⁻¹) induced stamen wilting rather than abscission, an effect that was not negated by STS. Stamen wilting was negatively correlated with stamen relative water content, and the increase in stamen wilting was generally reduced by treatments that enhanced cymule mass. Stamen wilting was least using a 100 g l⁻¹ sucrose pulse or holding solutions containing 30–40 g l⁻¹ sucrose, with hydroxyquinoline citrate (200 mg l⁻¹) maintained at pH 5. Our results indicate that 1-MCP may be relatively ineffective in blocking the effects of ethylene on the abscission of organs, such as the stamens of M . collina , which are highly sensitive to this hormone.     

Ethylene Co-ordinates Petal Abscission in Red Raspberry (Rubus idaeus L.) Flowers

The time-course of flower development of Rubus idaeus L. cv.Glen Clova was studied on detached buds opened in the laboratory.After sepal and petal opening petal abscission occurred withthe petals from an individual flower being shed over 3-4 h.Abscission was accompanied by a peak in ethylene production.Treatment of flowers with aminoethoxyvinylglycine eliminatedthe peak in ethylene production but did not prevent petal abscission.However, petal loss was much slower, taking place over a periodof days rather than hours. Abscission was more effectively retardedby silver thiosulphate. Exogenous ethylene accelerated the rateof petal abscission and senescence. The increase in ethyleneproduction coincident with petal abscission appears to accelerateand co-ordinate the shedding of the separate petals on an individualflower. If ethylene is important in the induction of abscissionit would appear that the low rate of production sustained inthe presence of aminoethoxyvinylglycine must be sufficient.Copyright1993, 1999 Academic Press Rubus idaeus L., raspberry, flower, petal, abscission, ethylene     

Lack of ethylene involvement in tulip tepal abscission

The tepals of cut flowers of Tulipa hybrida cv. Golden Apeldoorn and Tulipa kaufmanniana cv. Shakespeare abscise 3–4 days after harvest. The weakening of the abscission zones is accompanied by cell wall breakdown and the separation of 3–4 rows of intact cells at the base of the tepal. During senescence, there is no ethylene climacteric and ethylene production rates remain low, between 0.07 and 0.4 nl g⁻¹ fresh weight h⁻¹. Adding 3–5 μl l⁻¹ ethylene slightly accelerated the weakening of the abscission zones but had no effect on the time of first abscission. Neither 0.5 m M silver thiosulphate nor 5 m M aminoethoxyvinylglycine delayed the time to abscission. It is concluded that tulip tepal fall does not involve primary regulation by ethylene, unlike the majority of other abscission systems that have been studied.     

Studies on flower longevity in Digitalis

The flowers of Digitalis purpurea respond to pollination by rapid corolla abscission without any loss of corolla turgor, nor any significant loss of corolla constituents, relative to the corollas of unpollinated flowers of a similar age. The corollas of unpollinated flowers too eventually abscise, 6 d after the stigma opens, however, they do so with only a minimal loss of fresh weight or corolla constituents. Pollination causes an increase in ethylene production detectable within 1 h. Increased ethylene production occurs initially only from the upper portion of the style, later from the lower portion, and lastly, between 23 and 48 h after pollination, from the ovary plus calyx. The pollination response can be induced by exogenous ethylene, the degree of weakening of the corolla abscission zone being dependent upon the concentration and duration of the exposure period and on the stage of flower development. The regulation of ethylene biosynthesis and its involvement in the control of pollination-induced corolla abscission are discussed.     

Categories of Petal Senescence and Abscission: A Re-evaluation

In a previous paper (Woltering and van Doorn, 1988, Journalof Experimental Botany39: 1605–1616) we identified threetypes of flower life cessation: by petal wilting or withering,which was either ethylene-sensitive or insensitive, and by abscissionof turgid petals, which was ethylene-sensitive. These categoriestended to be consistent within families. Here we re-examinethese relationships by testing a further 200 species, and anumber of other families. As previously, flowering shoots wereexposed to 3 ppm ethylene for 24 h at 20 °C, in darkness.Most monocotyledonous species tested showed ethylene-insensitivepetal wilting, although ethylene-sensitive wilting occurredin the Alismataceae and Commelinaceae. Petals of the dicotyledonousspecies tested were generally sensitive to ethylene, exceptfor a few groups showing wilting (Crassulaceae, Gentianaceaeand Fumariaceae, and one subfamily in both the Ericaceae andSaxifragaceae). Petal abscission was generally ethylene-sensitive,but ethylene insensitivity was found in some Tulipa cultivarsand three Saxifraga species. In most tulip cultivars tested,the petals wilted and then fell. It is concluded that (a) theresponse to ethylene is often consistent within either familiesor subfamilies; and (b) a fourth category, ethylene-insensitivepetal abscission, exists both in monocotyledons and dicotyledons.Copyright 2001 Annals of Botany Company Ethylene sensitivity, flower longevity, petal abscission, petal wilting, petal withering, petal senescence, taxonomic categories     

Ethylene sensitivity: The role of short-chain saturated fatty acids in pollination-induced senescence of Petunia hybrida flowers

Normal and pollination-induced senescence of Petunia hybrida L cv. Pink Cascade flowers is accompanied by an increase in the sensitivity of the corolla to ethylene as indicated by an acceleration in the rate of corolla bluing after exposure to exogenous ethylene. Pollination resulted in the production of short-chain saturated fatty acids ranging in chain length from C₆ to C₁₀. Following pollination, these acids are synthesized in the stylar tissue via the acetate pathway within the first 12 hours. The fatty acids are transported rapidly to the corolla where they induce an increase in ethylene sensitivity. In unpollinated flowers, these acids are produced in the corolla during the early stages of senescence. Although the levels of these fatty acids decrease rapidly during the final stages of senescence, a significant increase in ethylene sensitivity could be detected prior to the decrease. It appears that the increase in ethylene sensitivity caused by the synthesis of short-chain saturated fatty acids occurs concurrently, but independent from ethylene synthesis.     

Acceleration of membrane senescence in cut carnation flowers by treatment with ethylene

The lipid microviscosity of microsomal membranes from senescing cut carnation (Dianthus caryophyllus L. cv. White Sim) flowers rises with advancing senescence. The increase in membrane microviscosity is initiated within 3 to 4 days of cutting the flowers and coincides temporally with petal-inrolling denoting the climacteric-like rise in ethylene production. Treatment of young cut flowers with aminoethoxyvinylglycine prevented the appearance of petal-inrolling and delayed the rise in membrane microviscosity until day 9 after cutting. When freshly cut flowers or aminoethoxyvinylglycine-treated flowers were exposed to exogenous ethylene (1 microliter per liter), the microviscosity of microsomal membranes rose sharply within 24 hours, and inrolling of petals was clearly evident. Thus, treatment with ethylene accelerates membrane rigidification. Silver thiosulphate, a potent anti-ethylene agent, delayed the rise in microsomal membrane microviscosity even when the flowers were exposed to exogenous ethylene. Membrane rigidification in both naturally senescing and ethylene-treated flowers was accompanied by an increased sterol:phospholipid ratio reflecting the selective loss of membrane phospholipid that accompanies senescence. The results collectively indicate that the climacteric-like surge in ethylene production during senescence of carnation flowers facilitates physical changes in membrane lipids that presumably lead to loss of membrane function.     

An increase in ethylene sensitivity following pollination is the initial event triggering an increase in ethylene production and enhanced senescence of Phalaenopsis orchid flowers

Cut Phalaenopsis (Phalaenopsis hybrid, cv. Herbert Hager) flowers usually last about 2 weeks. Following pollination however, there is a rapid acceleration of the wilting process, which is completed within 2 days. The first event detected following pollination was an increase in ethylene sensitivity. This increased sensitivity began about 4 h after pollination and peaked 6 h later. A subsequent increase in ethylene production could only be detected 12 to 14 h after pollination. Treatment of the flowers with silver thiosulfate or 1-methylcyclopropene, both inhibitors of ethylene action, completely inhibited the pollination-induced increase in ethylene production and the enhanced senescence of the flowers. This indicates that the pollination-induced increase in ethylene production is a response to the existing ethylene. Treatment of flowers with calcium and its ionophore A23187, which increased ethylene sensitivity and protein phosphorylation, also promoted ethylene production and senescence of unpollinated flowers, EGTA, a calcium chelator, decreased the sensitivity of pollinated flowers to ethylene and delayed and decreased the pollination-induced increase in ethylene production. We suggest that the pollination-induced increase in ethylene sensitivity is the initial pollination-induced event triggering the enhancement of ethylene production, which leads to enhanced senescence of Phalaenopsis flowers.     

Lack of Control by Early Pistillate Ethylene of the Accelerated Wilting of Petunia hybrida Flowers

Well before pollen tube penetration, ethylene has begun to disseminate from pollinated styles of Petunia hybrida flowers. Previous stigmatic application of aminoethoxyvinylglycine (AVG) completely prevented this ethylene synthesis, indicating that the endogenous 1-aminocyclopropane-1-carboxylic acid (ACC) in pollen is not readily converted on the stigma. Compared to other flower parts, the capacity of the ethylene forming enzyme was largest in the stigma. When applied to the stigma, ACC caused ethylene synthesis, but did not accelerate wilting, unless high concentrations (20 nanomols) were used. Upon pollination or stigma wounding, the early ethylene evolved exclusively from the gynoecium, much later followed by the synthesis of corolla ethylene. Employing wideneck Erlenmeyer flasks, the competitive inhibitor of ethylene action, norbornadiene, was applied to entire flowers in situ, with delaying effects on wound-induced wilting. In contrast, norbornadiene treatment of styles alone, using capillaries, could not postpone wilting. Pollination with foreign pollen species did not lead to accelerated corolla wilting, notwithstanding considerable synthesis of ethylene during the first 5 hours. In situ treatment of the stigma with AVG considerably delayed wound- and pollination-induced wilting. Removal of the entire AVG-treated style 6 hours after stigma wounding still allowed for the postponement of the accelerated wilting, even at very low concentrations of AVG. It is concluded that early stylar ethylene does not play a role in the acceleration of wilting but that, much later, corolla ethylene does, induced by a mobile wilting factor from the stigma, which is ACC.     

Effect of ethylene on flower abscission: a survey

The effect of ethylene on flower abscission was investigated in monocotyledons and eudicotyledons, in about 300 species from 50 families. In all species studied except Cymbidium, flower abscission was highly sensitive to ethylene. Flower fall was not consistent among the species in any family studied. It also showed no relationship with petal senescence or abscission, nor with petal colour changes or flower closure. Results suggest that flower abscission is generally mediated by endogenous ethylene, but that some exceptional ethylene-insensitive abscission occurs in the Orchidaceae.     

Physiological Responses of Cut Rose Flowers to Exposure to Low Temperature: Changes in Membrane Permeability and Ethylene Production

Senescence of cut rose flowers (Rosa hybrida L. cv. Mercedes)at 22 °C occurred earlier in flowers previously held at2 °C for 10 d or 17 d than in freshly cut flowers. Thisadvanced senescence was observed as an earlier increase in bothethylene production rate and membrane permeability. The risein ethylene production preceded the rise in the level of ionleakage from petals, and this in turn preceded visible symptomsof petal death. Applied ethylene stimulated ion leakage andinhibitors of ethylene synthesis and action (amino-oxyaceticacid and silver thiosulphate respectively) inhibited the normalincrease in ion leakage. The maximum rate of ethylene productionof 22 °C increased markedly in petals of flowers previouslyheld at 2 °C, up to nine times the level in fresh flowers.We conclude that during exposure of rose flowers to 2 °C,in addition to senescence, processes were induced which ledto stimulated ethylene production after transferral to 22 °C.Ethylene apparently caused the subsequent advance in membranepermeability and senescence. Key words: Rose flower, Low temperature, Senescence     

Inhibition of wilting and autocatalytic ethylene production in cut carnation flowers by cis-propenylphosphonic acid

The effect of cis-propenylphosphonic acid (PPOH), a structural analoge of ethylene, on flower wilting and ethylene production was investigated using cut carnation flowers which are very sensitive to ethylene. Wilting (petal in-rolling) of the flowers was delayed by continuously immersing the stems in a 5–20 mM PPOH solution. In addition, the continuous treatment with PPOH markedly reduced autocatalytic ethylene production of the petals accompanying senescence. This reduction of autocatalytic ethylene production was considered responsible for the inhibitory effect of PPOH on flower wilting. The inhibitory activity of trans-propenylphosphonic acid (trans-PPOH), on both flower wilting and the autocatalytic ethylene production accompanying senescence was markedly lower than that of PPOH, suggesting that PPOH action is stereoselective. PPOH may be of interest as a new, water-soluble inhibitor of wilting and autocatalytic ethylene production in cut carnation flowers.     

The never ripe mutation blocks ethylene perception in tomato.

Seedlings of tomato fruit ripening mutants were screened for their ability to respond to ethylene. Ethylene induced the triple response in etiolated hypocotyls of all tomato ripening mutants tested except for one, Never ripe (Nr). Our results indicated that the lack of ripening in this mutant is caused by ethylene insensitivity. Segregation analysis indicated that Nr-associated ethylene insensitivity is a single codominant trait and is pleiotropic, blocking senescence and abscission of flowers and the epinastic response of petioles. In normal tomato flowers, petal abscission and senescence occur 4 to 5 days after the flower opens and precede fruit expansion. If fertilization does not occur, pedicel abscission occurs 5 to 8 days after petal senescence. If unfertilized, Nr flowers remained attached to the plant indefinitely, and petals remained viable and turgid more than four times longer than their normal counterparts. Fruit development in Nr plants was not preceded by petal senescence; petals and anthers remained attached until they were physically displaced by the expanding ovary. Analysis of engineered 1-aminocyclopropane-1-carboxylate (ACC) synthase-overexpressing plants indicated that they are phenotypic opposites of Nr plants. Constitutive expression of ACC synthase in tomato plants resulted in high rates of ethylene production by many tissues of the plant and induced petiole epinasty and premature senescence and abscission of flowers, usually before anthesis. There were no obvious effects on senescence in leaves of ACC synthase overexpressers, suggesting that although ethylene may be important, it is not sufficient to cause tomato leaf senescence; other signals are clearly involved.