A comparison of the conversion of 1-amino-2-ethylcyclopropane-1-carboxylic acid stereoisomers to 1-butene by pea epicotyls and by a cell-free system

The characteristics of the conversion of 1-aminocyclopropane-1-carboxylic acid (ACC) to ethylene by pea (Pisum sativum L.) epicotyls and by pea epicotyl enzyme are compared. Of the four stereoisomers of 1-amino-2-ethylcyclopropane-1-carboxylic acid (AEC), only (1R,2S)-AEC is preferentially converted to 1-butene in pea epicotyls. This conversion is inhibited by ACC, indicating that butene production from (1R,2S)-AEC and ethylene production from ACC are catalyzed by the same enzyme. Furthermore, pea epicotyls efficiently convert ACC to ethylene with a low K _m (66 M) for ACC and do not convert 4-methylthio-2-oxo-butanoic acid (KMB) to ethylene, thus demonstrating high specificity for its substrate. In contrast, the reported pea epicotyl enzyme which catalyzes the conversion of ACC to ethylene had a high K _m (389 mM) for ACC and readily converted KMB to ethylene. We show, moreover, that the pea enzyme catalyzes the conversion of AEC isomers to butene without stereodiscrimination. Because of its lack of stereospecificity, its low affinity for ACC and its utilization of KMB as a substrate, we conclude that the reported pea enzyme system is not related to the in-vivo ethylene-forming enzyme.Abbreviations ACC 1-Amino cyclopropane-1-carboxylic acid - AEC 1-amino-2-ethylcyclopropane-1-carboxylic acid - EFE ethylene-forming enzyme - KMB 4-methylthio-2-oxobutanoic acid     

Ethylene formation from 1-aminocyclopropane-1-carboxylic acid in homogenates of etiolated pea seedlings

Homogenates of etiolated pea (Pisum sativum L.) shoots formed ethylene upon incubation with 1-aminocyclopropane-1-carboxylic acid (ACC). In-vitro ethylene formation was not dependent upon prior treatment of the tissue with indole-3-acetic acid. When homogenates were passed through a Sephadex column, the excluded, high-molecular-weight fraction lost much of its ethylene-synthesizing capacity. This activity was largely restored when a heat-stable, low-molecular-weight factor, which was retarded on the Sephadex column, was added back to the high-molecular-weight fraction. The ethylene-synthesizing system appeared to be associated, at least in part, with the particulate fraction of the pea homogenate. Like ethylene synthesis in vivo, cell-free ethylene formation from ACC was oxygen dependent and inhibited by ethylenediamine tetraacetic acid, n-propyl gallate, cyanide, azide, CoCl₃, and incubation at 40°C. It was also inhibited by catalase. In-vitro ethylene synthesis could only be saturated at very high ACC concentrations, if at all. Ethylene production in pea homogenates, and perhaps also in intact tissue, may be the result of the action of an enzyme that needs a heat-stable cofactor and has a very low affinity for its substrate, ACC, or it may be the result of a chemical reaction between ACC and the product of an enzyme reaction. Homogenates of etiolated pea shoots also formed ethylene with 2-keto-4-mercaptomethyl butyrate (KMB) as substrate. However, the mechanism by which KMB is converted to ethylene appears to be different from that by which ACC is converted.Abbreviations ACC 1-aminocyclopropane-1-carboxylic acid - IAA indole-3-acetic acid - KMB 2-keto-4-mercaptomethyl butyrate - SAM S-adenosylmethionine     

Changes in 1-aminocyclopropane-1-carboxylic-acid content of cut carnation flowers in relation to their senescence

The rise in ethylene production accompanying the respiration climacteric and senescence of cut carnation flowers (Dianthus caryophyllus L. cv. White Sim) was associated with a 30-fold increase in the concentration of 1-aminocyclopropane-1-carboxylic acid (ACC) in the petals (initial content 0.3 nmol/g fresh weight). Pretreatment of the flowers with silver thiosulfate (STS) retarded flower senescence and prevented the increase in ACC concentration in the petals. An increase in ACC in the remaining flower parts, which appeared to precede the increase in the petals, was only partially prevented by the STS pretreatment. Addition of aminoxyacetic acid (2 mM) to the solution in which the flowers were kept completely inhibited accumulation of ACC in all flower parts.Abbreviations ACC 1-aminocyclopropane-1-carboxylic acid - AOA -aminoxyacetic acid - STS silver thiosulfate complex     

Assay for and enzymatic formation of an ethylene precursor, 1-aminocyclopropane-1-carboxylic acid

A simple and sensitive chemical assay was developed for 1-aminocyclopropane-1-carboxylic acid (ACC), a precursor of ethylene. The assay is based on the liberation of ethylene from ACC at pH 11.5 in the presence of pyridoxal phosphate, MnCl₂ and H₂O₂. This assay was used to detect ACC in extracts of tomato fruits (Lycopersicon esculentum Mill.) and to measure the activity of a soluble enzyme from tomato fruit that converted S-adenosylmethionine (SAM) to ACC. The enzyme had a K_m of 13 M for SAM, and conversion of SAM to ACC was competitively and reversibly inhibited by aminoethoxyvinylglycine (AVG), an analog of rhizobitoxine. The K_i value for AVG was 0.2 M. The level of the ACC-forming enzyme activity was positively correlated with the content of ACC and the rate of ethylene formation in wild-type tomatoes of different developmental stages. Mature fruits of the rin (non-ripening) mutant of tomato, which only produce low levels of ethylene, contained much lower levels of ACC and of the ACC-forming enzyme activity than wild-type tomato fruits of comparable age.Abbreviations ACC 1-aminocyclopropane-1-carboxylic acid - AVG ammoethoxyvinylglycine, the aminoethoxy analog of rhizobitoxine L-2-amino-4-(2-aminoethoxy)-trans-3-butenoic acid - SAM S-adenosyl-L-methionine Michigan Agricultural Experiment Station No. 8876     

Rapidly induced ethylene formation after wounding is controlled by the regulation of 1-aminocyclopropane-1-carboxylic acid synthesis

Bean leaves from Phaseolus vulgaris L. var. Pinto 111 react to mechanical wounding with the formation of ethylene. The substrate for wound ethylene is 1-aminocyclopropane-1-carboxylic acid (ACC). It is not set free by decompartmentation but is newly synthesized. ACC synthesis starts 8 to 10 min after wounding at 28°C, and 15 to 20 min after wounding at 20°C. Aminoethoxyvinylglycine (AVG), a potent inhibitor of ethylene formation from methionine via ACC, inhibits wound ethylene synthesis by about 95% when applied directly after wounding (incubations at 20°C). AVG also inhibits the accumulation of ACC in wounded tissue. AVG does not inhibit conversion of ACC to ethylene. Wound ethylene production is also inhibited by cycloheximide, n-propyl gallate, and ethylenediaminetetraacetic acid.Abbreviations ACC 1-aminocyclopropane-1-carboxylic acid - AVG ammoethoxyvinylglycine - EDTA ethylenediaminetetraacetic acid     

Effects of 1-aminocyclopropane-1-carboxylic acid and oxygen concentrations on in vivo and in vitro activity of ACC oxidase of sunflower hypocotyl segments

In vivo ethylene production by hypocotyl segments of sunflower seedlings and in vitro activity of 1-aminocyclopropane-1-carboxylic acid oxidase (formerly ethylene-forming enzyme) extacted from the same tissues increase with increasing concentrations of 1-aminocyclopropane-1-carboxylic acid (ACC) and oxygen. ACC oxidase activity follows Michaelis-Menten kinetics. The apparent Km values of the enzyme towards ACC, estimated in vivo and in vitro, are respectively 219 M and 20.6 M. Both Km values towards O₂ are similar, ca 10.6–11.4%. A decrease in concentration in one of the substrates (ACC or O₂) results in an increase in in vivo apparent Km of ACC oxidase for the other substrate. On the contrary, Km values of the enzyme towards ACC or O₂ estimated in vitro are not dependent upon the concentration of the other substrate (ACC or O₂).Abbreviations ACC 1-aminocyclopropane-1-carboxylic acid - EFE ethylene-forming enzyme - MACC malonylate 1-aminocyclopropane-1-carboxylic acid - SD standard deviation     

Metabolism of α-aminoisobutyric acid in mungbean hypocotyls in relation to metabolism of 1-aminocyclopropane-1-carboxylic acid

1-Aminocyclopropane-1-carboxylic acid (ACC) is known to be converted to ethylene and conjugated into N-malonyl-ACC in plant tissues. When -amino[1-¹⁴C]isobutyric acid (AIB), a structural analog of ACC, was administered to mungbean (Vigna radiata L.) hypocotyl segments, it was metabolized to ¹⁴CO₂ and conjugated to N-malonyl-AIB (MAIB). -Aminoisobutyric acid inhibited the conversion of ACC to ethylene and also inhibited, to a lesser extent, N-malonylation of ACC and d-amino acids. Although the malonylation of AIB was strongly inhibited by ACC as well as by d-amino acids, the metabolism of AIB to CO₂ was inhibited only by ACC but not by d-amino acids. Inhibitors of ACC conversion to ethylene such as anaerobiosis, 2,4-dinitrophenol and Co²⁺, similarly inhibited the conversion of AIB to CO₂. These results indicate that the malonyalation of AIB to MAIB is intimately related to the malonylation of ACC and d-amino acids, whereas oxidative decarboxylation of AIB is related to the oxidative degradation of ACC to ethylene.Abbreviations ACC 1-aminocyclopropane-1-carboxylic acid - AIB -aminoisobutyric acid - MACC 1-(malonylamino)-cyclopropane-1-carboxylic acid - MAIB -(malonylamino)-isobutyric acid - Mes 2-(N-morpholino)ethanesulfonic acid     

Autoinhibition of Ethylene Production in Citrus Peel Discs : SUPPRESSION OF 1-AMINOCYCLOPROPANE-1-CARBOXYLIC ACID SYNTHESIS

Wound ethylene formation induced in flavede tissue of citrus fruit (Citrus paradisi MacFad. cv. Ruby Red) by slicing was almost completely inhibited by exogenous ethylene. The inhibition lasted for at least 6 hours after removal of exogenous ethylene and was then gradually relieved. The extent of inhibition was dependent upon the concentration of ethylene (1 to 10 microliters/liter) and the duration of treatment. The increase in wound ethylene production in control discs was paralleled by an increase in 1-aminocyclopropane-1-carboxylic acid (AAC) content, whereas in ethylene-treated discs there was little increase in ACC content. Application of ACC completely restored ethylene production in ethylene-pretreated discs, indicating that the conversion of ACC to ethylene is not impaired by the presence of ethylene. Thus, autoinhibition of ethylene synthesis was exerted by reducing the availability of ACC. Ethylene treatment resulted in a decrease in extractable ACC synthase activity, but this decrease was too small to account for the marked inhibition of ACC formation. The data indicate that autoinhibition of ethylene production in citrus flavede discs results from suppression of ACC formation through repression of the synthesis of ACC synthase and inhibition of its activity.     

Abscisic acid- and ethylene-induced defoliation of Radermachera sinica L.

Radermachera sinica L. is an ornamental plant with demonstrated sensitivity to ethylene-induced leaf abscission. In this study, we examine the relationship between abscisic acid (ABA) and ethylene in initiating the abscission response. Treatment with 1 l L^\s-1 of ethylene, 1 mM 1-aminocyclopropane-1-carboxylic acid (ACC) or 1 mM ABA resulted in complete defoliation of leaf explants. Application of 0.125 mM silver thiosulfate (STS) inhibited ethylene- and ACC-induced abscission but had no effect on explants treated with ABA. The ABA-induced abscission was unaffected by treatment with aminoethoxyvinylglycine (AVG) or aminooxyacetic acid (AOA). Treatment of explants with 1 mM cobalt chloride (CoCl₂) or 2000 l L^\s-1 of norbornadiene (NBD) completely inhibited abscission in explants treated with 1 l L^\s-1 ethylene or 1 mM ACC but they were only marginally effective in blocking ABA-induced abscission despite the lower level of endogenous ethylene. ABA appeared to increase the sensitivity of explants to ethylene. However, the evidence suggests that ABA may also function independent of ethylene to induce leaf abscission in R. sinica.Abbreviations ABA abscisic acid - ACC 1-aminocyclopropane-1-carboxylic acid - AOA aminooxyacetic acid - AVG aminoethoxyvinylglycine - CoCl₂ cobalt chloride - NBD norbornadiene - STS silver thiosulfate     

The effect of plant-hormone pretreatments on ethylene production and synthesis of 1-aminocyclopropane-1-carboxylic acid in water-stressed wheat leaves

Excised wheat (Triticum aestivum L.) leaves, when subjected to drought stress, increased ethylene production as a result of an increased synthesis of 1-aminocyclopropane-1-carboxylic acid (ACC) and an increased activity of the ethyleneforming enzyme (EFE), which catalyzes the conversion of ACC to ethylene. The rise in EFE activity was maximal within 2 h after the stress period, while rehydration to relieve water stress reduced EFE activity within 3 h to levels similar to those in nonstressed tissue. Pretreatment of the leaves with benzyladenine or indole-3-acetic acid prior to water stress caused further increase in ethylene production and in endogenous ACC level. Conversely, pretreatment of wheat leaves with abscisic acid reduced ethylene production to levels produced by nonstressed leaves; this reduction in ethylene production was accompanied by a decrease in ACC content. However, none of these hormone pretreatments significantly affected the EFE level in stressed or nonstressed leaves. These data indicate that the plant hormones participate in regulation of water-stress ethylene production primarily by modulating the level of ACC.Abbreviations ABA abscisic acid - ACC 1-aminocyclopropane-1-carboxylic acid - BA N⁶-benzyladenine - EFE ethylene-forming enzyme - IAA indole-3-acetic acid     

The physiological role of lipoxygenase in ethylene formation from 1-aminocyclopropane-1-carboxylic acid in oat leaves

In order to understand the physiological significance of the in-vitro lipoxygenase (EC 1.13.11.12)-mediated ethylene-forming system (J.F. Bousquet and K.V. Thimann 1984, Proc. Natl. Acad. Sci. USA 81, 1724–1727), its characteristics were compared to those of an in-vivo ethylene-forming system. While oat (Avena sativa L.) leaves, as other plant tissues, preferentially converted only one of the 1-amino-2-ethylcyclopropane-1-carboxylic acid (AEC) isomers to 1-butene, the lipoxygenase system converted all four AEC isomers to 1-butene with nearly equal efficiencies. While the in-vivo ethylene-forming system of oat leaves was saturable with ACC with a K_m of 16 M, the lipoxygenase system was not saturated with ACC even at 10 mM. In contrast to the in-vivo results, only 10% of the ACC consumed in the lipoxygenase system was converted to ethylene, indicating that the reaction is not specific for ethylene formation. Increased ACC-dependent ethylene production in oat leaves following pretreatment with linoleic acid has been inferred as evidence of the involvement of lipoxygenase in ethylene production. We found that pretreating oat leaves with linoleic acid resulted in increased ACC uptake and thereby increased ethylene production. A similar effect was observed with oleic acid, which is not a substrate of lipoxygenase. Since linoleic acid hydroperoxide can substitute for lipoxygenase and linoleic acid in this system, it is assumed that the alkoxy radicals generated during the decomposion of linoleic acid hydroperoxide are responsible for the degradation of ACC to ethylene. Our results collectively indicate that the reported lipoxygenase system is not the in-vivo ethylene-forming enzyme.Abbreviations ACC 1-Aminocyclopropane-1-carboxylic acid - AEC 1-amino-2-ethylcyclopropane-1-carboxylic acid - Epps N-(2-hydroxyethyl)-piperazine-N-3-propanesulfonic acid - LH linoleic acid - LOOH linoleic acid hydroperoxide - pyridoxal-P pyridoxal-phosphate This work was presented at the 12th International Conference on Plant Growth Substances, Heidelberg, FRG, August 1985 (Abstract No. PO 5-52)     

Ethylene biosynthesis in Regnellidium diphyllum and Marsilea quadrifolia

The pathway of ethylene biosynthesis was examined in two lower plants, the semi-aquatic ferns Regnellidium diphyllum Lindm. and Marsilea quadrifolia L. As a positive control for the ethylene-biosynthetic pathway of higher plants, leaves of Arabidopsis thaliana (L.) Heynh. were included in each experiment. Ethylene production by Regnellidium and Marsilea was not increased by treatment of leaflets with 1-aminocyclopropane-1-carboxylic acid (ACC), the precursor of ethylene in higher plants. Similarly, ethylene production was not inhibited by application of aminoethoxyvinylglycine and -aminoisobutyric acid, inhibitors of the ethylene biosynthetic enzymes ACC synthase and ACC oxidase, respectively. However, ACC was present in both ferns, as was ACC synthase. Compared to leaves of Arabidopsis, leaflets of Regnellidium and Marsilea incorporated little [¹⁴C]ACC and [¹⁴C]methionine into [¹⁴C]ethylene. From these data, it appears that the formation of ethylene in both ferns occurs mainly, if not only, via an ACC-independent route, even though the capacity to synthesize ACC is present in these lower plants.Abbreviations ACC 1-aminocyclopropane-1-carboxylic acid - AdoMet S-adenosyl-l-methionine - AIB -aminoisobutyric acid - AVG aminoethoxyvinylglycine This research was supported by the U.S. Department of Energy through grant No. DE-FG02-91ER20021 and, in part, by a fellowship of the National Engineering and Research Council of Canada to Jacqueline Chernys.     

Apical localization of 1-aminocyclopropane-1-carboxylic acid and its conversion to ethylene in etiolated pea seedlings

The biosynthetic basis for the high rates of ethylene production by the apical region of etiolated pea (Pisum sativum L.) seedlings was investigated. The ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC) was quantified in extracts of various regions of seedlings by measuring isotopic dilution of a ²H-labelled internal standard using selected-ion-monitoring gas chromatography/mass spectrometry. The ACC levels in the apical hook and leaves were much higher than in the expanded internodes of the epicotyl. The capacity of excised tissue sections to convert exogenous ACC to ethylene was also much greater in the apical region, reflecting the distribution of soluble protein in the epicotyl.Abbreviations ACC 1-aminocyclopropane-1-carboxylic acid - FW fresh weight - GC/MS coupled gas chromatography/mass spectrometry - HPLC high-performance liquid chromatography     

The effects of 2,2′-bipyridine and other metal chelators on the conversion of 1-aminocyclopropane-1-carboxylic acid to ethylene in rice

Effects of metal chelators, 2,2-bipyridine, 8-hydroxyquinoline and 1,10-phenenthroline, on the conversion of 1-aminocyclopropane-1-carboxylic acid (ACC) to ethylene in detached leaves of light-grown rice (Oryza sativa) seedlings and detached shoots of etiolated rice seedlings were investigated. Metal chelators strongly inhibited the in vivo ACC oxidase activity in detached leaves and detached etiolated shoots. This inhibition could be partially recovered by Fe²⁺. Our results support the notion that Fe²⁺ is an essential cofactor for the conversion of ACC to ethylene in vivo.Abbreviations ACC 1-aminocyclopropane-1-carboxylic acid - BP 2,2-bypyridine - HQ 8-hydroxylquinoline - MJ methyl jasmonate - PA 1,10-phenanthroline - Put putrescine     

Ethylene synthesis and growth of tomato hypocotyls: Induction by auxin and fusicoccin and inhibition by vanadate

The effects of fusicoccin (FC) on growth and ethylene synthesis of tomato (Lycopersicon esculentum Mill.) hypocotyls were compared to those of indole-3-acetic acid (IAA). Fusicoccin promoted both growth and ethylene production maximally at <2M. Growth was stimulated to a slightly greater extent by FC as compared to IAA, while ethylene synthesis rates in response to FC were about 50% less than those induced by IAA. Cycloheximide (0.5 M) inhibited auxin-induced growth by 80% but had no effect on FC-induced growth; ethylene production was inhibited to the same extent (58%) when induced by either IAA or FC. Both IAA and FC caused tissue contents of 1-aminocyclopropane-1-carboxylic acid (ACC) and malonyl-ACC to increase, indicating that like IAA, FC induces ethylene synthesis by stimulating the formation of ACC. Orthovanadate, a potent inhibitor of proton-translocating plasma membrane ATPases, reduced both IAA- and FC-induced growth and ethylene synthesis at concentrations less than 1 mM, with ethylene synthesis being approximately 10 times more sensitive to inhibition than growth. Vanadate did not affect tissue ACC levels, slightly reduced total ACC production, and inhibited conversion of ACC to ethylene. However, significant inhibition of in vivo ethylene-forming enzyme activity required high concentrations of vanadate (1 mM) and was less effective than inhibition by cobaltous ion. The site of action of vanadate in inhibiting ethylene synthesis remains unclear, but the ion did not prevent the elevation of tissue ACC levels in response to IAA or FC. It is unlikely, therefore, that stimulation of plasma membrane H⁺-ATPase activity is required for the induction of ACC synthase by IAA and FC.     

The enzymatic malonylation of 1-aminocyclopropane-1-carboxylic acid in homogenates of mung-bean hypocotyls

Homogenates of hypocotyls of light-grown mung-bean (Vigna radiata (L.) Wilczek) seedlings catalyzed the formation of 1-(malonylamino)cyclopropane-1-carboxylic acid (MACC) from the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC) and malonyl-coenzyme A. Apparent K_m values for ACC and malonyl-CoA were found to be 0.17 mM and 0.25 mM, respectively. Free coenzyme A was an uncompetitive inhibitor with respect to malonyl-CoA (apparent K_i=0.3 mM). Only malonyl-CoA served as an effective acyl donor in the reaction. The d-enantiomers of unpolar amino acids inhibited the malonylation of ACC. Inhibition by d-phenylalanine was competitive with respect to ACC (apparent K_i=1.2 mM). d-Phenylalanine and d-alanine were malonylated by the preparation, and their malonylation was inhibited by ACC. When hypocotyl segments were administered ACC in the presence of certain unpolar d-amino acids, the malonylation of ACC was inhibited while the production of ethylene was enhanced. Thus, a close-relationship appears to exist between the malonylation of ACC and d-amino acids. The cis- as well as the trans-diastereoisomers of 2-methyl- or 2-ethyl-substituted ACC were potent inhibitors of the malonyltransferase. Treatment of hypocotyl segments with indole-3-acetic acid or CdCl₂ greatly increased their content of ACC and MACC, as well as their release of ethylene, but had little, or no, effect on their extractable ACC-malonylating activity.Abbreviations ACC 1-aminocyclopropane-1-carboxylic acid - MACC 1-(malonylamino)-cyclopropane-1-carboxylic acid Dedicated to Professor Dr. Hubert Ziegler on the occasion of his 60th birthday     

The mechanism involved in ethylene-enhanced ethylene synthesis in carnations

The plant hormone ethylene triggers and enhanced ethylene synthesis in certain ripening fruits and senescing flowers. Unlike most carnation (Dianthus caryophyllus L.) cultivars exhibiting climacteric rise in ethylene production at the onset of senescence, cv. Sandrosa does not show this phenomenon naturally. In order to understand the mechanism of autocatalytic ethylene production, we exposed carnation flowers cv. Sandrosa to ethylene which resulted in an enhanced capacity for ethylene synthesis in the petals. A short time response of one hour was measured for an increase in ACC oxidase activity, about five hours in advance of an increase in ACC synthase activity and ethylene production. The observed enhancement was dependent on the presence of exogeneous ethylene, and could be partially inhibited by prior treatment of the petals with -amanitin or cycloheximide. The results of the present study suggest that in response to ethylene, activation of an existing enzyme is taking place first. This is followed by an increase in expression of ACC oxidase and ACC synthase mRNAs.Abbreviations ACC 1-aminocyclopropane-1-carboxylic acid - DTT dithiothreitol - PMSF phenyl-methylsulfonyl fluoride - SAM S-adenosyl-L-methionine     

Rhythmicity in cotton seedlings

Ethylene production by detached cotyledons of cotton (Gossypium hirsutum L.) seedlings grown under cycles of 12 h darkness and 12 h light has been shown to be rhythmic, with a minimum and maximum 4 and 16 h, respectively after the start of the cycle (Rikin, Chalutz and Anderson, 1984, Plant Physiol. 75, 493–495). Treatment with silver ions stimulated the rhythmic ethylene production in both regular and inverted cycles (i.e. dark period changed to light period, and vice versa). The rate of the conversion of [3,4-¹⁴C]methionine into ethylene also followed the stimulation of rhythmic ethylene evolution by silver ions in both regular and inverted cycles, while treatment with aminoethoxyvinylglycine (AVG) decreased this stimulation. Conversion of exogenous 1-aminocyclopropane-1-carboxylic acid (ACC) into ethylene was not affected by silver ions, but was dependent upon the immediate light conditions, regardless of the time in the light-dark cycle, light decreasing and darkness increasing this process. It is concluded that silver ions stimulate the normal rhythmic ethylene production, and this stimulation is regulated at a step prior to the conversion of ACC into ethylene. The rhythmicity in other processes (cotyledon movement, phenylalanine ammonia-lyase activity, resistance to the herbicide 3-isopropyl-1H-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide [bentazon]) was not affected by a decrease in the rhythmic changes in ethylene production by AVG or interference in ethylene action by silver ions. Thus, these rhythmic changes were not regulated by the rhythmic changes in ethylene production.Abbreviations ABA abscisic acid - ACC 1-aminocyclopropane-1-carboxylic acid - AVG aminoethyoxyvinylglycine - PAL phenylalanine ammonia-lyase     

The ethylene action in the development of cellular slime molds: an analogy to higher plants

Summary The cellular slime moldDictyostelium mucoroides-7 (Dm 7) and its mutant (MF 1) exhibit sexual or asexual development depending upon culture conditions. During the sexual cycle macrocyst formation occurs, whereas sorocarps containing spores and stalk cells are asexually formed. As previously reported, the macrocyst formation is marked by the emergence of true zygotes, and is induced by a potent plant hormone, ethylene. The concentration of ethylene required for macrocyst induction was determined to establish the similarity of ethylene action between this organism and higher plants. Macrocysts are induced by low (1 l/l) exogenous concentrations of ethylene. Higher concentrations (10–1,000 ul/l) also gave essentially the same inductive activity. Ethionine, an analogue of methionine, was found to inhibit zygote formation during sexual development through its interference with ethylene production by Dm 7 and MF 1 cells. In fact, the inhibitory effect of ethionine was mostly nullified by the application of ethylene, S-adenosyl-L-methionine, or 1-aminocyclopropane-1-carboxylic acid. Taken together these results suggest that both the effective concentration of ethylene and the pathway of ethylene biosynthesis inD. mucoroides may be similar to those in higher plants. Ethylene was also found to be produced in various species and strains of cellular slime molds, even during the asexual process. The possible functions of ethylene in the asexual development are discussed in relation to cell aggregation and differentiation.Abbreviations SAM S-adenosyl-L-methionine - ACC 1-aminocyclopropane-1-carboxylic acid - AOA (aminooxy) acetic acid - BSS Bonner's salt solution - DAPI 4,6-diamidino-2-phenylindole     

Ethylene production and β-cyanoalanine synthase activity in carnation flowers

The relationship between ethylene production and the CN^--assimilating enzyme -cyanoalanine synthase (CAS; EC 4.4.1.9) was examined in the carnation (Dianthus caryophyllus L.) flower. In petals from cut flowers aged naturally or treated with ethylene to accelerate senescence the several hundred-fold increase in ethylene production which occurred during irreversible wilting was accompanied by a one- to twofold increase in CAS activity. The basal parts of the petal, which produced the most ethylene, had the highest CAS activity. Studies of flower parts (styles, ovaries, receptacles, petals) showed that the styles had a high level of CAS together with the ethylene-forming enzyme (EFE) system for converting 1-aminocyclopropane-1-carboxylic acid (ACC) to ethylene. The close association between CAS and EFE found in styles could also be observed in detached petals after induction by ACC or ethylene. Treatment of the cut flowers with cycloheximide reduced synthesis of CAS and EFE. The data indicate that CAS and ethylene production are associated, and are discussed in relation to the hypothesis that CN^- is formed during the conversion of ACC to ethylene.Abbreviations ACC 1-aminocyclopropane-1-carboxylic acid - AVG aminoethoxyvinylglyoine - CAS -cyanoalanine synthase - CHI cycloheximide - EFE ethylene-forming enzyme