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.     

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.     

The Involvement of Water Stress and Ethylene in Senescence of Cut Carnation Flowers

Exposing cut carnation (Dianthus caryophyllus, cv. White Sim)to short term (12 h) water stress resulted in a marked increasein the water saturation deficit (WSD) of the petals. Full recoveryoccurred upon transfer of the flowers to water in humid conditions(r.h. 85%). However, an increase in aminocyclopropane carboxylicacid (ACC) content occurred immediately upon stress. An associatedrise in ethylene production following transfer to humid conditionswas observed earlier than in the control. Exogenous ethylene,applied alone or in combination with water stress, increasedthe WSD of the petals. Continuous treatment of cut flowers with amino-oxyacetic acid(AOA), a known inhibitor of ACC synthesis, suppressed ethyleneproduction, delayed the rise in WSD which accompanied developmentand senescence and hence delayed wilting. Similar results wereobtained with short term (2 h) treatment with AOA prior to stressingthe flowers. Short term AOA treatment partially inhibited therise in WSD during the stress period. On the basis of our findings, in particular that no rise inethylene production occurred during water stress, it is suggestedthat the effect of water stress is not directly mediated byethylene. The possible modulatory effect of water stress andAOA on certain characteristics of the petal cell membrane isdiscussed.     

Effects of Promoters and Inhibitors of Ethylene and ABA on Flower Senescence of Hibiscus rosa-sinensis L.

Hibiscus rosa-sinensis L. flowers (cv La France) senesce and die over a 12-h period after opening. The aim of this study was to examine the physiological mechanisms regulating the senescence process of ephemeral hibiscus flowers. Different flower stages and floral organs were used to determine whether any interaction existed during flower senescence between endogenous abscisic acid (ABA) and the predisposition of the tissue to ethylene synthesis. This was carried out on whole flowers treated with promoters and inhibitors of ethylene and ABA synthesis or a combination of them. Treatments with 1-aminocyclopropane-1-carboxylic acid (ACC), a precursor of ethylene biosynthesis, enhanced flower senescence, whereas amino-oxyacetic acid (AOA) and fluridone, an ethylene and an ABA inhibitor, respectively, extended flower longevity. These effects were more significant when applied before anthesis. Ethylene evolution was substantially reduced in all organs from open and senescent flowers treated with fluridone and AOA. Similarly, endogenous ABA accumulation was negatively affected by AOA and fluridone treatments. Application of fluridone plus ACC reduced ethylene evolution and increased ABA content in a tissue-specific manner but did not overcome the inhibitor effect on flower longevity. AOA plus fluridone treatment slightly accelerated flower longevity compared to AOA-treated flowers. Application of ABA alone promoted senescence, suppressed ethylene production, and, when applied with fluridone, countered the fluridone-induced increase in flower longevity. Taken together, these results suggest that the senescence of hibiscus flowers is an endogenously regulated ethylene- and ABA-dependent process.     

ELECTRON MICROSCOPE STUDIES ON THE MORPHOGENESIS OF PLASTIDS. X. ULTRASTRUCTURAL CHANGES OF CHLOROPLASTS IN MORNING GLORY LEAVES EXPOSED TO ETHYLENE

Electron microscopic studies were made on chloroplasts of morning glory leaves exposed continuously to ethylene (6.5 ppm) for 5 days. The leaves gradually became tinged with yellow and finally were shed. The chloroplasts suffered severe injury when plants were exposed to ethylene, i.e., normal thylakoidal membranes collapsed resulting in the formation of macrograna, and then the plastids became filled with many plastoglobules. With such a metamorphosis of chloroplasts, a great deal of phytoferritin was produced in the stroma. Plastid degeneration in this manner was similar, to a certain extent, to that in morning glory leaves exposed to ozone and in leaves undergoing natural senescence. Ethylene exposure rapidly induces senescence of plant organelles, especially chloroplasts.     

Interrelationship between Abscisic Acid and Ethylene in the Control of Senescence Processes in Carnation Flowers

The involvement of abscisic acid (ABA) in senescence of carnationflowers, in the presence of silver ions (which inhibit ethyleneaction), and aminoethoxyvinylglycine (AVG) (an inhibitor ofethylene synthesis) was studied. ABA stimulated senescence asseen by advancement of ethylene surge, and time to the developmentof in-rolling of petal margins. ABA also increased the sensitivityof the flowers to ethylene. Silver ions did not affect the timeor extent of the ethylene surge, but prevented the appearanceof visual senescence symptoms, and lowered the sensitivity toethylene. AVG delayed the ethylene surge and lowered the maximumrate of ethylene production. Also, AVG delayed the developmentof visible senscence. In the presence of silver ions, ABA advanced the ethylene surgebut senescence symptoms did not develop. The effect of ABA onthe parameters measured was prevented by AVG. Thus it is suggestedthat ABA exerts its effect on senescence via ethylene. The possibleinvolvement of an ABA-ethylene sequence as a mediator of waterstress-promoted senescence is discussed.     

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.     

Ethylene binding changes in apple and morning glory during ripening and senescence

Ethylene binding sites were measured during fruit ripening and morning glory flower senescence. Little change in ethylene binding was noted during these developmental stages, except a slight decline during the later stages of fruit ripening or flower senescence. The concentration of ethylene required to achieve 50% saturation of the binding sites was 0.14 l/liter for both apple pulp and morning glory flowers. Ethylene binding sites were calculated to be 3.2×10^–11 moles/kg and 3.8×10^–9 moles/kg in apple and morning glory, respectively. It does not appear that changes seen in ethylene sensitivity during fruit ripening can be readily ascribed to changes in the number of ethylene binding sites in the tissue.Paper No. 11398 of the Journal Series of the North Carolina Agricultural Research Service, Raleigh, NC 27695-7601, USA.     

Ethylene Synthesis and Floral Senescence following Compatible and Incompatible Pollinations in Petunia inflata

Ethylene production and floral senescence following compatible and incompatible pollinations were studied in a self-incompatible species, Petunia inflata. Both compatible and incompatible pollinations resulted in a burst of ethylene synthesis that peaked 3 hours after pollination. P. inflata pollen was found to carry large amounts of the ethylene precursor, 1-aminocyclopropane-1-carboxylic acid (ACC). The amount of pollen-held ACC varied in different genetic backgrounds, and the magnitude of the peak correlated with the amount of ACC borne by the pollen. Aminooxyacetic acid (AOA), an inhibitor of ACC synthesis, had no inhibitory effect on this ethylene response, indicating that pollen-borne ACC was largely responsible for the early synthesis of ethylene. After compatible pollination, a second increase in ethylene synthesis began at 18 hours, and the first sign of senescence appeared at 36 hours. Upon treatment with AOA, the second phase of ethylene production was reduced by 95%, indicating that endogenous ACC synthesis was required for this phase of ethylene synthesis. AOA treatment also delayed senescence to 6 days after anthesis. After incompatible pollination, a second increase in ethylene production did not occur until 3 days, and the first sign of senescence occurred 12 hours later. Unpollinated flowers showed an increase in ethylene production 3 to 4 days after anthesis and displayed signs of senescence 1 day later. The significance of the early and late phases of pollination-induced ethylene synthesis is discussed.     

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。     

Regulation of ethylene biosynthesis in response to pollination in tomato flowers

Pollination of many flowers leads to an increase in ethylene synthesis and flower senescence. We have investigated the regulation of pollination-induced ethylene synthesis in tomato (Lycopersicon esculentum) using flowers of the dialytic (dl) mutant, in which pollination can be manipulated experimentally, with the aim of developing a model system to study tomato flower senescence. Ethylene synthesis increased rapidly in dl pistils following pollination, leading to accelerated petal senescence, and was delayed in ethylene-insensitive Never-ripe (Nr) pistils. However, Nr pistils eventually produced more ethylene than dl pistils, suggesting the presence of negative feedback regulation of ethylene synthesis following pollination. LEACS1A expression correlated well with increased ethylene production in pollinated dl pistils, and expression in Nr revealed that regulation is via an ethylene-independent mechanism. In contrast, the induction of the 1-aminocyclopropane-1-carboxylic acid oxidases, LEACO1 and LEACO3, following pollination is ethylene dependent. In addition, the expression profiles of ACS and ACO genes were determined during petal senescence and a hypothesis proposed that translocated 1-aminocyclopropane-1-carboxylic acid from the pistil may be important for regulating the initial burst of ethylene production during petal senescence. These results are discussed and differences between tomato and the ornamental species previously studied are highlighted.     

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.     

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