Effect of substrate-dependent microbialy produced ethylene on plant growth

Various compounds have been identified as precursors/substrates for the synthesis of ethylene (C2H4) in soil. This study was designed to compare the efficiency of four substrates, namely L-methionine (L-MET), 2-keto-4-methylthiobutyric acid (KMBA), 1-aminocyclopropane-1-carboxylic acid (ACC), and calcium carbide (CaC2) for ethylene biosynthesis in a sandy clay loam soil by gas chromatography. The classic "triple" response in etiolated pea seedling was employed as a bioassay to demonstrate the effect of substrate-dependent microbialy produced ethylene on plant growth. Results revealed that an amendment with L-MET, KMBA, ACC (up to 0.10 g/kg soil) and CaC2 (0.20 g/kg soil) significantly stimulated ethylene biosynthesis in soil. Overall, ACC proved to be the most effective substrate for ethylene production (1434 nmol/kg soil), followed by KMBA, L-MET, and CaC2 in descending order. Results further revealed that ethylene accumulation in soil released from these substrates created a classic "triple" response in etiolated pea seedlings with different degrees of efficacy. A more obvious classic "triple" response was observed at 0.15, 0.10, and 0.20 g/kg soil of L-MET, KMBA/ACC, and CaC2, respectively. Similarly, direct exposure of etiolated pea seedlings to commercial ethylene gas also modified the growth pattern in the same way. A significant direct correlation (r = 0.86 to 0.97) between substrate-derived [C2H4] and the classic triple response in etiolated pea seedlings was observed. This study demonstrated that the presence of substrate(s) in soil may lead to increased ethylene concentration in the air of the soil, which may affect plant growth in a desired direction.     

Differential response of etiolated pea seedlings to inoculation with rhizobacteria capable of utilizing 1-aminocyclopropane-1-carboxylate or L-methionine

The majority of soil microorganisms can derive ethylene from L-methionine (L-MET), while some rhizobacteria can hydrolyze 1-aminocyclopropane-1-carboxylate (ACC) due to their ACC-deaminase activity. In this study, three strains having either ACC-deaminase activity (Pseudomonas putida biotype A, A7), or the ability to produce ethylene from L-MET (Acinetobacter calcoaceticus, M9) or both (Pseudomonas fluorescens, AM3) were used for inoculation. The highly ethylene specific bioassay of a classical "triple" response in pea seedlings was used to investigate the effect of the inoculation with the rhizobacteria in the presence of 10 mM ACC or L-MET. The exogenous application of ACC had a concentration-dependent effect on the etiolated pea seedlings in creating the classical "triple" response. The inoculation with P. putida diluted the effect of ACC, which was most likely due to its ACC-deaminase activity. Similarly, the application of Co2+ reduced the ACC-imposed effect on etiolated pea seedlings. In contrast, the inoculation of A. calcoaceticus or P. fluorescens in the presence of L-MET caused a stronger classical "triple" response in etiolated pea seedlings; most likely by producing ethylene from L-MET. This is the first study, to our knowledge, reporting on the comparative effect of rhizobacteria capable of utilizing ACC vs L-MET on etiolated pea seedlings.     

Dormancy removal in apple embryos by nitric oxide or cyanide involves modifications in ethylene biosynthetic pathway

The connection between classical phytohormone-ethylene and two signaling molecules, nitric oxide (NO) and hydrogen cyanide (HCN), was investigated in dormancy removal and germination “sensu stricto” of apple (Malus domestica Borkh.) embryos. Deep dormancy of apple embryos was removed by short-term (3–6 h) pre-treatment with NO or HCN. NO- or HCN-mediated stimulation of germination was associated with enhanced emission of ethylene by the embryos, coupled with transient increase in ROS concentration in embryos. Ethylene vapors stimulated germination of dormant apple embryos and eliminated morphological anomalies characteristic for young seedlings developed from dormant embryos. Inhibitors of ethylene receptors completely impeded beneficial effect of NO and HCN on embryo germination. NO- and HCN-induced ethylene emission by apple embryo was only slightly reduced by inhibitor of 1-aminocyclopropane-1-carboxylic acid (ACC) oxidase activity during first 4 days of germination. Short-term pre-treatment of the embryos with NO and HCN modified activity of both key enzymes of ethylene biosynthetic pathway: ACC synthase and ACC oxidase. Activity of ACC synthase declined during first 4 days of germination, while activity of ACC oxidase increased markedly at that time. Additional experiments point to non-enzymatic conversion of ACC to ethylene in the presence of ROS (H₂O₂). The results indicate that NO and HCN may alleviate dormancy of apple embryos “via” transient accumulation of ROS, leading to enhanced ethylene emission which is required to terminate germination “sensu stricto”. Therefore, ethylene seems to be a trigger factor in control of apple embryo dormancy removal and germination.     

Evidence for Involvement of the Superoxide Radical in the Conversion of 1-Aminocyclopropane-1-Carboxylic Acid to Ethylene by Pea Microsomal Membranes

Electron spin resonance (ESR) spectroscopy has provided evidencefor involvement of the superoxide anion (O₂^–) radicalin the conversion of l-aminocyclopropane-l carboxylic acid (ACC)to ethylene by microsomal membranes from etiolated pea seedlings.Formation of ethylene from ACC by the membrane system is oxygen-dependent,heat denaturable, inhibited by the radical scavenger n-propylgallate and sensitive to superoxide dismutase (SOD) and catalase.Addition of 1,2-dihydroxybenzene-3,5-disulfonic acid (Tiron)to the reaction mixture results in formation of the Tiron semiquinone(Tiron radical) ESR signal derived from O₂^–, and alsoinhibits ethylene production. The radical signal is oxygen-dependentand inhibited by SOD and catalase, but is formed both in thepresence and absence of ACC. Heat denaturation of the microsomalenzyme system completely blocks formation of the radical signal.The data collectively suggest that O₂^– generated by amembrane-bound enzyme facilitates the conversion of ACC to ethylene. (Received September 8, 1981; Accepted January 19, 1982)     

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     

{alpha}-Aminoisobutyric acid : A probable competitive inhibitor of conversion of 1-aminocyclopropane-1-carboxylic acid to ethylene

Of 16 compounds related to 1-aminocyclopropane-1-carboxylicacid (ACC), aminoisobutyric acid (AIB) inhibited the productionof endogenous ethylene in the cotyledonary segments of cocklebur(Xanthium pennsylvanicum Wallr.) seeds most strongly. AIB at4 mM inhibited the formation of ethylene by about 50%, althoughthe O₂ uptake of the segments was not affected even at 20 mM.AIB also inhibited ethylene formation in the stem segments ofetiolated pea (Pisum sativum L. cv. Alaska) seedlings. Kineticanalysis with cell free extracts from etiolated pea shoots revealedthat AIB competitively inhibits the conversion of ACC into ethylene. (Received May 26, 1980; )     

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     

Forced flowering of pineapple (<Emphasis Type="Italic">Ananas comosus</Emphasis> cv. Tainon 17) in response to cold stress,ethephon and calcium carbide with or without activated charcoal

Ethylene, a gaseous plant hormone, is responsible for the initiation of reproductive development in pineapple. Reproductive development can be forced in pineapple (Ananas comosus var. comosus) throughout the year with ethylene. Inhibition of natural flowering initiation with aviglycine [(S)-trans-2-amino-4-(2-aminoethoxy)-3-butenoic acid hydrochloride], an inhibitor of ethylene biosynthesis, provides evidence that reproductive development in response to cold stress and short daylength is also in response to ethylene production. We studied the effect of cold treatment of pineapple on ethylene production and flower induction by applying a short-term cold stress to stem apices. Shoot apices of pineapple treated with ice crystals also produced twice as much ethylene as did those of control plants and significantly more than was produced by “D” leaf basal tissue. Moreover, pineapple plants treated four times with ice crystals or ice water were induced to flower under field conditions and the forcing efficiency, as evaluated by the percentages of inflorescence emergence and fruit harvest, was comparable to forcing with calcium carbide (CaC₂) and ethephon. In another field experiment two applications of a 1.0% solution of CaC₂ or 0.15% ethephon applied at 48 h intervals was sufficient to force reproductive development of ‘Tainon 17’. Furthermore, 0.5 or 1.0% solutions of CaC₂ supplemented with 0.5% activated charcoal (AC) significantly improved the forcing effectiveness of CaC₂. This could/would make it possible to reduce the number or concentration, or both, of CaC₂ required to effect forcing in pineapple.     

Auxin-induced ethylene biosynthesis in subapical stem sections of etiolated seedlings of Pisum sativum L.

1-Aminocyclopropane-1-carboxylic acid (ACC) stimulated the production of ethylene in subapical stem sections of etiolated pea (cv. Alaska) seedlings in the presence and absence of indole-3-acetic acid (IAA). No lag period was evident following application of ACC, and the response was saturated at a concentration of 1 mM ACC. Levels of endogenous ACC paralleled the increase in ethylene production in sections treated with different concentrations of IAA and with selenoethionine or selenomethionine plus IAA. The IAA-induced formation of both ACC and ethylene was blocked by the rhizobitoxine analog aminoethoxyvinylglycine (AVG). Labelling studies with L-[U-¹⁴C]methionine showed an increase in the labelling of ethylene and ACC after treatment with IAA. IAA had no specific effect on the incorporation of label into S-methylmethionine or homoserine. The specific radioactivity of ethylene was similar to the specific radioactivity of carbon atoms 2 and 3 of ACC after treatment with IAA, indicating that all of the ethylene was derived from ACC. The activity of the ACC-forming enzyme was higher in sections incubated with IAA than in sections incubated with water alone. These results support the hypothesis that ACC is the in-vivo precursor of ethylene in etiolated pea tissue and that IAA stimulates ethylene production by increasing the activity of the ACC-forming enzyme.Abbreviations ACC 1-aminocyclopropane-1-carboxylic acid - AVG aminoethoxyvinylglycine, the aminoethoxy analog of rhizobitoxine - IAA indole-3-acetic acid - SAM S-adenosylmethionine - SMM S-methylmethionine     

Modulation of ethylene synthesis in acotyledonous soybean and wheat seedlings

The characteristics of ethylene production and ACC conversion in 8-day-old soybean seedlings were examined and a relationship between cytochrome P-450 activity and ethylene-forming enzyme (EFE) activity was found. An atmosphere containing 10% carbon monoxide (CO) significantly inhibited ethylene production and ACC conversion in control soybean seedlings, but had only a slight effect on soybean seedlings treated with uniconazole. Foliar application of triclopyr, a pyridine analogue of the phenoxy herbicides, significantly increased ethylene production and ACC conversion in control, but not in uniconazoletreated seedlings. Triclopyr treatment also resulted in a three-fold increase in extractable cytochrome P-450 of 5-day-old etiolated soybeans. At equimolar concentrations tetcyclacis was more effective than uniconazole in reducing shoot elongation and endogenous ethylene production. Although uniconazole and tetcyclacis did not inhibit ACC conversion in nonherbicide-treated soybean seedlings, they did prevent the observed increase in ACC-dependent EFE activity following triclopyr application. However, the rate of ACC conversion in etiolated soybean segments was sensitive to uniconazole, and tetcyclacis inhibited the rate of ACC conversion by 2.6-fold in etiolated soybean segments within 4 h after treatment. Microsomal membranes were isolated from 5-day-old naphthalic anhydride-treated etiolated wheat shoots as this tissue contains much higher cytochrome P-450 levels than soybean shoots. Optical difference spectroscopy demonstrated that ACC generated binding spectrum characteristic of a reverse-type-I cytochrome P-450 substrate when combined with reduced microsomes. In vitro conversion of ACC to ethylene by microsomal membranes was NADPH-dependent, inhibited by CO, and had an apparent K_m and V_max of 45 M and 0.345 nl/mg protein/h, respectively. These results suggest that cytochrome P-450-mediated monooxygenase reactions may be intimately involved in the conversion of ACC to ethylene in young soybean and wheat seedlings.     

Mechanism of Ethylene Action: Biological Activity of Deuterated Ethylene and Evidence against Isotopic Exchange and cis-trans-Isomerization

Deuterated ethylene was used to study the mechanism of ethylene action in etiolated pea seedlings (Pisum sativum L. cv. Alaska). No apparent differences were observed in the biological activity of tetradeuteroethylene (C₂D₄) and ordinary ethylene (C₂H₄) using the pea stem straight growth assay. The absence of an isotopic effect is discussed in relation to the possibility that ethylene binds to a metal or that carbon to hydrogen bonds of ethylene are broken during its mechanism of action.     

Nitric oxide,hydrogen cyanide and ethylene are required in the control of germination and undisturbed development of young apple seedlings

Reactive oxygen species (ROS) and reactive nitrogen species (RNS) are emerging as important regulators of plant development (germination, flowering, senescence), acting as secondary messengers in cooperation with classical phytohormones. Apple seeds are dormant, unless they undergo a 3 month long cold stratification. Deep dormancy of isolated apple embryos can also be broken by short pre-treatment with HCN or NO with the effect associated with enhanced ethylene synthesis. Non-dormant embryos germinate well and young seedlings grown from non-dormant embryos do not exhibit any morphological anomalies, such as asymmetric growth and greening of cotyledons. One of the aims of this work was to investigate the correlation between RNS- mediated (HCN- and NO-dependent) dormancy removal and ROS (H₂O₂ and O₂^−•) accumulation in the embryos. The beneficial effect of NO and HCN on germination of dormant apple embryos has been associated with marked increases in H₂O₂ and O₂^−• concentration in the embryos at early germination stages. We also analyzed growth of young seedlings developed from embryos pre-treatment with HCN or NO or exposed to ethylene (ethephone) and its precursor 1-aminocyclopropane-1-carboxylic acid (ACC). ACC and ethephone removed all morphological anomalies of the seedlings (asymmetric growth and greening of cotyledons) but the radicle growth was rather slight. We propose that accumulation of ROS provoked by HCN and NO pre-treatment is required for embryo germination “sensu stricto”, while ethylene is required for post-germination seedling growth.     

Effect of soil applied L-methionine on growth,nodulation and chemical composition ofAlbizia lebbeck L.

A pot experiment was conducted to evaluate the influence of an ethylene (C₂H₄) precursor, L-methionine (L-MET) added to soil on the growth, nodulation and chemical composition of a leguminous tree,Albizia lebbeck L. Benth (black ciris). L-Methionine (10^-9 to 10^-1 gkg^-1 soil) was applied as a soil drench to established uniform seedlings ofAlbizia lebbeck L. L-MET treatments had significant effects on all the plant growth parameters monitored. Plants responded positively to low to medium L-MET concentrations (10^-9 to 10^-3 gkg^-1 soil) while high levels of L-MET had either negative or no effects. An L-MET treatment of 10^-6 gkg^-1 soil was the most effective in increasing shoot height, plant girth, dry weights of shoot and roots, number and dry weight of nodules and total biomass. The chemical analysis of the plant material revealed that the highest N, P and K contents were present in plants exposed to 10^-6 gL-MET kg^-1 soil, while Ca and Mg contents were maximum with 10^-5 g L-MET kg^-1 soil. A similar trend was observed with the uptake of these elements by the plant. A significant quadratic dose-response relationship was found in all cases when each individual parameter was regressed against log [L-MET] excluding the control. Since, attempts were made to prevent any nutritional and water stress, the plant response to L-MET was most likely caused by substrate-dependent microbial production of ethylene in the rhizosphere. ei]A C Borstlap     

The effect of indole-3-Acetic acid on ethylene formation in wheat seedlings

Isoperoxidase B 1 isolated from winter wheat (Triticum aestivum L., cv. Jubilar) seedlings was shown to catalyze ethylene formation from α-keto, γ-methylmercaptobutyric acid (KMBA). In the presence of Mn²⁺, indole-3-acetic acid (IAA), andp-coumaric acid, the kinetics by isoperoxidase B 1 catalyzed conversion of KMBA into ethylene and other products was similar to that of IAA oxidation. The reaction rate was therefore controlled by IAA through its electrondonating properties. Exogenous IAA induced ethylene formation in the segments of etiolated wheat coleoptiles. IAA-induced ethylene production was enhanced by L-methionine and mitomycin C. Aminoethoxy-analogue of rhizobitoxine, ferulic acid, sodium benzoate, cycloheximide and actinomyoin D exhibited significant inhibitory effects. These data indicate that the overall reaction mechanism in coleoptile segments involves RNA and protein synthesis. The site of IAA action is not specific; 2,4-dichlorophenoxyacetic, α-naphthylacetic and indole-3-butyric acids, respectively, possessed comparable inductive effect as IAA. Indole-3-propionic acid, indole, L-tryptophan and glucobrassicin had only low inductive efficiency, and moreover indole and L-tryptophan slowed down IAA-induced ethylene formation.     

Auxin and Ethylene Control of Growth in Seedlings of Zea mays L. and Avena sativa L

The effects of applied ethylene on the growth of coleoptilesand mesocotyls of etiolated monocot seedlings (oat and maize)have been compared with those on the epicotyl of a dicot seedling(the etiolated pea). Significant inhibition of elongation by ethylene (10 µll^–1for 24 h) was found in intact seedlings of all three species,but lateral expansion growth was observed only in the pea internodeand oat mesocotyl tissue. The sensitivity of the growth of seedlingparts to ethylene is in the decreasing order pea internode,oat coleoptile and oat mesocotyl, with maize exhibiting theleast growth response. Although excised segments of mesocotyland coleoptile or pea internode all exhibit enhanced elongationgrowth in IAA solutions (10^–6–2 ? 10^–5 moll^–1), no consistent effects were found in ethylene. Ethyleneproduction in segments was significantly enhanced by applicationof auxin (IAA, 10^–5 mol l^–6 or less) in all tissuesexcept those of the eat mesocotyl. Segments of maize show a slow rate of metabolism of applied[2-¹⁴C]IAA (30 per cent converted to other metabolites within9 h) and a high capacity for polar auxin transport. Ethylene(10 µl l^–1 for 24 h) has little effect on eitherof these processes. The oat has a smaller capacity for polartransport than maize and the rate ef metabolism of auxin isas fast as in the pea (90 per cent metabolized in 6 h). Althoughethylene pretreatment does not change the rate of auxin metabolismin oat, there is a marked reduction in auxin transport. It is proposed that the insensitivity of maize seedlings toethylene is related to the supply and persistence of auxin whichcould protect the seedling against the effects of applied orendogenously produced ethylene. Although the mesocotyl of oatis sensitive to applied ethylene it may be in part protectedagainst ethylene in vivo by the absence of an auxin-enhancedethylene production system. The results are discussed in relationto a model for the auxin and ethylene control of cell growthin the pea.     

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     

Regulation of ethylene biosynthesis after short-term heat treatment in etiolated pea stems

Incubation of plant tissues at a constant elevated temperature greatly inhibits both basal and wound ethylene production. However, recovery from heat treatment is relatively rapid and is followed by stimulated ethylene production. The present investigation examines the kinetics of ethylene production after short-term heal treatment and the regulation of heat-altered ethylene production. Subapical stem segments of 7-day-old etiolated pea L. cv. Alaska) seedlings were analyzed for ethylene production, 1-aminocyclopropane-l-carboxylic acid (ACC) oxidation, and ACC and l-(malonylamino)cyclopropane-l-carboxylic acid (MACC) content after a 2-min 40°C heat pulse. The short-term heat pulse transiently inhibited ethylene production and ACC oxidation accompanied by a slight ACC accumulation within a 30-min time period. Conjugation to MACC did not appear to play an integral role in heat-regulated ethylene production. It was concluded that the major factor affecting ethylene production after heat treatment is the temporary inactivation of ACC oxidation. The possible roles of ACC synthase, ACC oxidase and lipoxygenase in regulating ethylene production after heat treatment are discussed.     

Phytochrome-controlled ethylene biosynthesis of intact etiolated bean seedlings

Intact etiolated bean (Phaseolus vulgaris L. cv. Limburgse vroege) seedlings were illuminated with red light (10.5 W·m^-2) for 10 min. After different time intervals ethylene production, and contents of 1-aminocyclopropane-1-carboxylic acid (ACC) and 1-(malonylamino)cyclopropane-1-carboxylic acid were measured. The red-light-induced decrease of ethylene production in 8-d-old intact etiolated bean seedlings was fast, strong and long-lasting ad was mediated through the phytochrome system. This effect appeared to be strictly age-dependent, as it could not be detected in plants younger than 6 d or older than 11 d.The capacity for the conversion of ACC to ethylene was not affected by red light. The inhibitory effect of the light treatment on ethylene production could be related to a reduced free-ACC content. This reduction was a consequence of a temporary non-reversible increase of ACC malonylation and a long-lasting, for a certain time reversible, inhibition of ACC synthesis. The effect of a brief irradiation with red light on the decrease of ethylene production and free-ACC content was completed after about 2 h. Reversibility by far-red, however, persisted for at least 3 h, and was lost between 3 and 6 h.Abbrevation ACC 1-aminocyclopropane-1-carboxylic acid - M-ACC 1-(malonylamino)cyclopropane-1-carboxylic acid