Role of ethylene in the senescence of isolated hibiscus petals

Senescence of petals isolated from flowers of Hibiscus rosa-sinensis L. (cv Pink Versicolor) was associated with increased ethylene production. Exposure to ethylene (10 microliters per liter) accelerated the onset of senescence, as indicated by petal in-rolling, and stimulated ethylene production. Senescence was also hastened by basal application of 1-aminocyclopropane-1-carboxylic acid (ACC). Aminooxyacetic acid, an inhibitor of ethylene biosynthesis, effectively inhibited ethylene production by petals and delayed petal in-rolling. In marked contrast to these results with mature petals, immature petals isolated from flowers the day before flower opening did not respond to ethylene in terms of an increase in ethylene production or petal in-rolling. Furthermore, treatment with silver thiosulfate the day before flower opening effectively prevented petal senescence, while silver thiosulfate treatment on the morning of flower opening was ineffective. Application of ACC to both immature and mature petals greatly stimulated ethylene production indicating the presence of an active ethylene-forming enzyme in both tissues. Immature petals contained less free ACC than mature, presenescent petals and appeared to possess a more active system for converting ACC into its conjugated form. Thus, while the nature of the lack of responsiveness of immature petals to ethylene is unknown, ethylene production in hibiscus petals appears to be regulated by the control over ACC availability.     

Ethylene-induced gene expression in carnation petals : relationship to autocatalytic ethylene production and senescence

Exposure of carnation (Dianthus caryophyllus L.) flowers to ethylene evokes the developmental program of petal senescence. The temporal relationship of several aspects of this developmental program following treatment with ethylene was investigated. Exposure of mature, presenescent flowers to 7.5 microliters per liter ethylene for at least 6 hours induced petal in-rolling and premature senescence. Autocatalytic ethylene production was induced in petals following treatment with ethylene for 12 or more hours. A number of changes in mRNA populations were noted in response to ethylene, as determined by in vitro translation of petal polyadenylated RNA. At least 6 mRNAs accumulated following ethylene exposure. The molecular weights of their in vitro translation products were 81, 58, 42, 38, 35, and 25 kilodaltons. Significant increases in abundance of most mRNAs were observed 3 hours following ethylene exposure. Ethylene exposure resulted in decreased abundance of another group of mRNAs. Treatment of flowers with competitive inhibitors of ethylene action largely prevented the induction of these ethylene responses in petals. An increase in flower age was accompanied by an increase in the capacity for ethylene to induce petal in-rolling, autocatalytic ethylene production, and changes in mRNA populations suggesting that these responses are regulated by both sensitivity to ethylene and ethylene concentration. These results indicate that changes in petal physiology resulting from exposure to ethylene may be the result of rapid changes in gene expression.     

Role of the gynoecium in natural senescence of carnation (Dianthus caryophyllus L.) flowers

Although the role of the gynoecium in natural senescence of the carnation flower has long been suggested, it has remained a matter of dispute because petal senescence in the cut carnation flower was not delayed by the removal of gynoecium. In this study, the gynoecium was snapped off by hand, in contrast to previous investigations where removal was achieved by forceps or scissors. The removal of the gynoecium by hand prevented the onset of ethylene production and prolonged the vase life of the flower, demonstrating a decisive role of the gynoecium in controlling natural senescence of the carnation flower. Abscisic acid (ABA) and indole-3-acetic acid (IAA), which induced ethylene production and accelerated petal senescence in carnation flowers, did not stimulate ethylene production in the flowers with gynoecia removed (-Gyn flowers). Application of 1-aminocyclopropane-1-carboxylate (ACC), the ethylene precursor, induced substantial ethylene production and petal wilting in the flowers with gynoecia left intact, but was less effective at stimulating ethylene production in the -Gyn flowers and negligible petal in-rolling was observed. Exogenous ethylene induced autocatalytic production of the gas and petal wilting in the -Gyn flowers. These results indicated that ethylene generated in the gynoecium triggers the onset of ethylene production in the petals of carnation during natural 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.     

Reversible inhibition of ethylene action and interruption of petal senescence in carnation flowers by norbornadiene

The inhibitory effects of the cyclic olefin 2,5-norbornadiene (NBD) on ethylene action were tested in carnation (Dianthus caryophyllus L. cv White Sim) flowers. Treatment of flowers at anthesis with ethylene in the presence of 500 microliters per liter NBD increased the concentration of ethylene required to elicit a response (petal senescence), indicating that NBD behaves as a competitive inhibitor of ethylene action. Transfer of flowers producing autocatalytic ethylene and exhibiting evidence of senescence (petal in-rolling) to an atmosphere of NBD resulted in a rapid reduction in ethylene production, petal 1-aminocyclopropane-1-carboxylic acid synthase activity, 1-aminocyclopropane-1-carboxylic acid content, and ethylene forming enzyme activity. Removal of NBD resulted in recovery of ethylene biosynthesis. These results support the autocatalytic regulation of ethylene production during the climacteric stage of petal senescence and suggest that continued perception of ethylene is required for maintenance of ethylene biosynthesis. The inhibition of ethylene action by NBD after the flowers had reached the climacteric peak was associated with interruption of petal senescence as evidenced by reversal of senescence symptoms. This result is in contrast to the widely held belief that the rate of petal senescence is fixed and irreversible once petals enter into the ethylene climacteric.     

1-aminocyclopropane-l-carboxylic acid (ACC)—The transmitted stimulus in pollinated flowers?

Ethylene production and senescence of petals of pollinated carnation flowers were not prevented by removal of the ethylene produced by the gynoecium, suggesting that these events are a response to movement from the gynoecium of some stimulus other than ethylene gas. Application of 1-aminocyclopropane-1-carboxylic acid (ACC) to the stigmas caused an initial increase in gynoecium and petal ethylene production similar to that reported for pollinated flowers. This response was not seen in flowers whose stigmas were treated with indoleacetic acid (IAA). When [2-¹⁴C]ACC was applied to the stigmas of carnation flowers, radioactive ethylene was produced both by the gynoecia and by the petals. The possibility that ACC, transported from the stigmas to the petals, is responsible for the postpollination changes in carnation flowers is discussed.     

Comparison between Ultraviolet Irradiation and Ethylene Effects on Senescence Parameters in Carnation Flowers

The effects of ethylene and ultraviolet (UV) irradiation on parameters of senescence in carnation (Dianthus caryophyllus L. cv White Sim) flowers were characterized and compared.

UV irradiation (λ_max = 254 nanometers), at fluences above 18 kilojoules per square meter, induced petal in-rolling, similar to that which occurred during natural senescence or after ethylene treatment. Increase in the UV dose from 36 to 54 kilojoules per square meter increased the rate of in-rolling to a maximum. Petal in-rolling was accompanied by increased electrolyte leakage, whether it occurred during natural senescence or was induced by UV irradiation or ethylene.

Sucrose uptake by cells, membrane ATPase activity, and membrane lipid fluidity all decreased after UV treatment. These parameters were shown earlier to decline during natural or ethylene-induced senescence.

UV irradiation induced ethylene production by the petals only during the period of irradiation. However, silver thiosulfate treatment, which blocks ethylene action, showed that the irradiation effects were not due to the ethylene evolved.

On the basis of the above results, we concluded that both ethylene and UV irradiation promote a sequence of reactions in the tissue similar to those of natural senescence. However, UV irradiation initiates a reaction which is independent of that which ethylene initiates.

     

Sites of ethylene production in the pollinated and unpollinated senescing carnation (Dianthus caryophyllus) inflorescence

Production of endogenous ethylene from the styles, ovary and petals of pollinated and unpollinated flowers of Dianthus caryophyllus L. was measured. The rate of ethylene production of cut, unpollinated flowers aged in water at 18°C was low until the onset of petal wilting, when a rapid surge of ethylene occurred in all tissues. The flower ethylene production was evolved mostly from the styles and petals. The bases of petals from unpollinated, senescing flowers evolved ethylene faster and sometimes earlier than the upper parts. Treatment of cut flowers with propylene, an ethylene analogue, accelerated wilting of flower petals and promoted endogenous ethylene production in all flower tissues. Pollination of intact flowers also promoted endogenous ethylene production and caused accelerated petal wilting within 2–3 days from pollination. Although the data are consistent with the hypothesis that ethylene forms a link between pollination of the style and petal wilting, in the unpollinated flower the style and petals can evolve a surge of ethylene independently of each other, about the time when the petals irreversibly wilt. The results are discussed in relation to the role of ethylene in flower senescence.     

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     

Temperature-dependent stomatal movement in tulip petals controls water transpiration during flower opening and closing

Temperature‐dependent tulip petal opening and closing movement was previously suggested to be regulated by reversible phosphorylation of a plasma membrane aquaporin ( Azad et al., 2004a ). Stomatal apertures of petals were investigated during petal opening at 20°C and closing at 5°C. In completely open petals, the proportion of open stomata in outer and inner surfaces of the same petal was 27 ± 6% and 65 ± 3%, respectively. During the course of petal closing, stomatal apertures in both surfaces reversed, and in completely closed petals, the proportion of open stomata in outer and inner surfaces of the same petal was 74 ± 3% and 29 ± 6%, respectively, indicating an inverse relationship between stomatal aperture in outer and inner surfaces of the petal during petal opening and closing. Both petal opening and stomatal closure in the outer surface of the petal was inhibited by a Ca²⁺ channel blocker and a Ca²⁺ chelator, whereas the inner surface stomata remained unaffected. On the other hand, sodium nitroprusside, a nitric oxide donor, had no effect on stomatal aperture of the outer surface but influenced the inner surface stomatal aperture during petal opening and closing, suggesting different signalling pathways for regulation of temperature‐dependent stomatal changes in the two surfaces of tulip petals. Stomata were found to be differentially distributed in the bottom, middle and upper parts of tulip petals. During petal closing, water transpiration was observed by measuring the loss of ³H₂O. Transpiration of ³H₂O by petals was fivefold greater in the first 10 min than that found after 30 min, and the transpiration rate was shown to be associated with stomatal distribution and aperture. Thus, the stomata of outer and inner surfaces of the petal are involved in the accumulation and transpiration of water during petal opening.     

香石竹花瓣对乙烯的敏感性与蛋白质合成

基因转录抑制剂α-amanitin和蛋白质合成抑制剂cycloheximide完全抑制了香石竹(Dianthuscaryophyllus L.cvs.White Sim and Sandrosa)花瓣对乙烯反应的症状,包括花瓣卷曲和细胞膜离子渗漏增加。观察到花中蛋白质合成能力随着花的衰老而降低,花对乙烯的敏感性随花的衰老而增加。但是用乙烯合成抑制剂aminooxyacetic acid(AOA)预处理切花,则改变了花对乙烯敏感性的变化趋势。常用的香石竹品种D.caryophyllus L.cv.White Sim花经AOA处理后,对乙烯的敏感性随着花的衰老而下降。这些结果揭示花对乙烯的敏感性可能受蛋白质合成能力影响。     

Synergistic effect of 1-aminocyclopropane-1-carboxylic acid and ethylene during senescence of isolated carnation petals

The effects of ethylene (C₂H₄), (2-chloroethyl)phosphonic acid (ethefon) and 1-aminocyclopropane-1-carboxylic acid (ACC) on senescence of isolated intact petals and of upper petal parts of carnation flowers ( Dianthus caryophyllus L. cv. White Sim) were investigated.
Isolated upper petal parts did not respond to treatment with ethefon or ACC. These tissues did, however, show severe wilting in intact petals that were treated with ethefon or ACC. When isolated upper petal parts were simultaneously treated with ACC and ethefon or ACC and ethylene, a marked synergistic effect on senescence was found. Treatment of isolated petals with radiolabeled ACC led to the accumulation of radiolabeled ACC and N-malonyl-ACC (MACC) in the upper parts. The formation of ethylene and the malonylation of ACC were inhibited by pretreatment of the flower with the inhibitor of ethylene action, silver thiosulphate (STS), which indicates that both were induced by endogenously produced ethylene. Treatment of isolated upper parts with ACC slightly increased their ethylene production. However, when these petal parts were simultaneously treated with ethylene and ACC, the conversion of ACC to ethylene was markedly stimulated.
The results indicate that, in intact petals, ethylene may be translocated from the basal to the upper part where it stimulates the activity of the ethylene-forming enzyme (EFE), thereby making the tissue receptive to ACC.
In addition, it was found that upon incubation of petal portions in radiolabeled ACC, both the petal tissue and the incubation solutions produced radiolabeled carbon dioxide. This was shown to be due to microorganisms that were able to metabolize the carbon atoms in the 2 and 3 position of ACC into carbon dioxide.     

Relationship between petal abscission and programmed cell death in <Emphasis Type="Italic">Prunus yedoensis</Emphasis> and <Emphasis Type="Italic">Delphinium belladonna</Emphasis>

Depending on the species, the end of flower life span is characterized by petal wilting or by abscission of petals that are still fully turgid. Wilting at the end of petal life is due to programmed cell death (PCD). It is not known whether the abscission of turgid petals is preceded by PCD. We studied some parameters that indicate PCD: chromatin condensation, a decrease in nuclear diameter, DNA fragmentation, and DNA content per nucleus, using Prunus yedoensis and Delphinium belladonna which both show abscission of turgid petals at the end of floral life. No DNA degradation, no chromatin condensation, and no change in nuclear volume was observed in P. yedoensis petals, prior to abscission. In abscising D. belladonna petals, in contrast, considerable DNA degradation was found, chromatin was condensed and the nuclear volume considerably reduced. Following abscission, the nuclear area in both species drastically increased, and the chromatin became unevenly distributed. Similar chromatin changes were observed after dehydration (24 h at 60°C) of petals severed at the time of flower opening, and in dehydrated petals of Ipomoea nil and Petunia hybrida, severed at the time of flower opening. In these flowers the petal life span is terminated by wilting rather than abscission. It is concluded that the abscission of turgid petals in D. belladonna was preceded by a number of PCD indicators, whereas no such evidence for PCD was found at the time of P. yedoensis petal abscission. Dehydration of the petal cells, after abscission, was associated with a remarkable nuclear morphology which was also found in younger petals subjected to dehydration. This nuclear morphology has apparently not been described previously, for any organism.     

Galactose metabolism in cell walls of opening and senescing petunia petals

Galactose was the major non-cellulosic neutral sugar present in the cell walls of ‘Mitchell’ petunia (Petunia axillaris × P. axillaris × P. hybrida) flower petals. Over the 24 h period associated with flower opening, there was a doubling of the galactose content of polymers strongly associated with cellulose and insoluble in strong alkali (‘residual’ fraction). By two days after flower opening, the galactose content of both the residual fraction and a Na₂CO₃-soluble pectin-rich cell wall fraction had sharply decreased, and continued to decline as flowers began to wilt. In contrast, amounts of other neutral sugars showed little change over this time, and depolymerisation of pectins and hemicelluloses was barely detectable throughout petal development. Size exclusion chromatography of Na₂CO₃-soluble pectins showed that there was a loss of neutral sugar relative to uronic acid content, consistent with a substantial loss of galactose from rhamnogalacturonan-I-type pectin. β-Galactosidase activity (EC 3.2.1.23) increased at bud opening, and remained high through to petal senescence. Two cDNAs encoding β-galactosidase were isolated from a mixed stage petal library. Both deduced proteins are β-galactosidases of Glycosyl Hydrolase Family 35, possessing lectin-like sugar-binding domains at their carboxyl terminus. PhBGAL1 was expressed at relatively high levels only during flower opening, while PhBGAL2 mRNA accumulation occurred at lower levels in mature and senescent petals. The data suggest that metabolism of cell wall-associated polymeric galactose is the major feature of both the opening and senescence of ‘Mitchell’ petunia flower petals.     

Molecular cloning and characterization of senescence-related genes from carnation flower petals

The senescence of carnation (Dianthus caryophyllus L.) flower petals is associated with increased production of ethylene which plays an important role in regulating this developmental event. Three senescence-related cDNA clones were isolated from a cDNA library prepared from mRNA isolated from senescing petals. These cDNAs are representative of two classes of mRNAs which increase in abundance in senescing petal tissue. The mRNA for one class is present at low levels during the early stages of development and begins to accumulate in mature petals prior to the increase in ethylene production. The accumulation of this mRNA is reduced, but not eliminated, in petals treated with aminooxyacetic acid, an inhibitor of ethylene biosynthesis, or silver thiosulfate, an ethylene action inhibitor. In contrast, expression of the second class of mRNAs appears to be highly regulated by ethylene. These mRNAs are not detectable prior to the rise in ethylene production and increase in abundance in parallel with the ethylene climacteric. Furthermore, expression of these mRNAs is significantly inhibited by both aminooxyacetic acid and silver thiosulfate. Expression of these mRNAs in vegetative and floral organs was limited to floral tissue, and predominantly to senescing petals.