Immunochemical Difference of Wound-Induced 1-Aminocyclopropane-1-carboxylate Synthase from the Auxin-Induced Enzyme

Immunochemical cross-reactivity of wound- and auxin-induced1-aminocyclopropane-1-carboxylate (ACC) synthase was examinedwith the antibody against wound-induced ACC synthase purifiedfrom mesocarp of winter squash (Cucurbita maxima Duch.). Theantibody recognized ACC synthase from wounded hypocotyls ofwinter squash and from wounded pericarp of tomato fruits, butnot the enzyme from IAA-treated hypocotyls of winter squash,tomato and mung bean. These results indicate that the primarystructure of the wound-induced enzyme is different from thatof the auxin-induced enzyme in the same species, and impliesthat there are two different genes for ACC synthase, one forwound induction and the other for auxin induction. (Received June 14, 1988; Accepted July 20, 1988)     

Wound ethylene and 1-aminocyclopropane-1-carboxylate synthase in ripening tomato fruit

Ethylene production, 1-aminocyclopropane-1-carboxylic acid (ACC) levels and ACC-synthase activity were compared in intact and wounded tomato fruits (Lycopersicon esculentum Mill.) at different ripening stages. Freshly cut and wounded pericarp discs produced relatively little ethylene and had low levels of ACC and of ACC-synthase activity. The rate of ethylene synthesis, the level of ACC and the activity of ACC synthase all increased manyfold within 2 h after wounding. The rate of wound-ethylene formation and the activity of wound-induced ACC synthase were positively correlated with the rate of ethylene production in the intact fruit. When pericarp discs were incubated overnight, wound ethylene synthesis subsided, but the activity of ACC synthase remained high, and ACC accumulated, especially in discs from ripe fruits. In freshly harvested tomato fruits, the level of ACC and the activity of ACC synthase were higher in the inside parts of the fruit than in the pericarp. When wounded pericarp tissue of green tomato fruits was treated with cycloheximide, the activity of ACC synthase declined with an apparent half life of 30–40 in. The activity of ACC synthase in cycloheximide-treated, wounded pericarp of ripening tomatoes declined more slowly.Abbreviation ACC 1-aminocyclopropane-1-carboxylic acid     

Wound-Induced Ethylene Production and 1-Aminocyclopropane-1-carboxylic Acid Synthase in Mesocarp Tissue of Winter Squash Fruit

Discs (9 mm in diameter and 2 mm in thickness) sliced from mesocarpof winter squash fruit (Cucurbita maxima Duch.) upon incubationat 24°C produced ethylene at an increasing rate after alag period of 3 h. 1-Aminocydopropane-l-carboxylic acid (ACC)synthase activity also increased at a rapid rate after lag periodof less than 3 h, reaching a peak 14 h after incubation andthen declining sharply. The rise in ACC synthase activity precededa rapid increase in ACC formation and ethylene production. Inductionof ACC synthase by wounding in sliced discs was strongly suppressedby the application of cycloheximide, actinomycin D and cordycepin,suggesting that the rise in ACC synthase activity may resultfrom de novo synthesis of protein. ACC synthase extracted from wounded tissue of winter squashmesocarp required pyridoxal phosphate for its maximum activity.The optimum pH of the reaction was 8.5. Km value for S-adenosylmethioninewas 120 µM. The reaction was markedly inhibited by aminoethoxyvinylglycinewith Ki value being 2.7 µM. (Received March 23, 1983; Accepted May 23, 1983)     

Characterization and Induction of the Activity of 1-Aminocyclopropane-1-Carboxylate Oxidase in the Wounded Mesocarp Tissue of Cucurbita maxima

1-Aminocyclopropane-1-carboxylate (ACC) oxidase (ethylene-formingenzyme) was isolated from wounded mesocarp tissue of Cucurbitamaxima (winter squash) fruit, and its enzymatic properties wereinvestigated. The enzyme required Fe²⁺ and ascorbate for itsactivity as well as ACC and O₂ as substrates. The in vitro enzymeactivity was enhanced by CO₂. The apparent K_m value for ACCwas 175 µM under atmospheric conditions. The enzyme activitywas inhibited by sulfhydryl inhibitors and divalent cationssuch as Co²⁺, Cu²⁺, and Zn²⁺. ACC oxidase activity was induced at a rapid rate by woundingin parallel with an increase in the rate of ethylene production.The exposure of excised discs of mesocarp to 2,5-norbornadiene(NBD),an inhibitor of ethylene action, strongly suppressed inductionof the enzyme, and the application of ethylene significantlyaccelerated the induction of the activity of ACC oxidase inthe wounded mesocarp tissue. These results suggests that endogenousethylene produced in response to wounding may function in promotingthe induction of ACC oxidase. (Received January 13, 1993; Accepted April 15, 1993)     

Molecular Cloning and Sequence of a Complementary DNA Encoding 1-Aminocyclopropane-l-carboxylate Synthase Induced by Tissue Wounding

1-Aminocyclopropane-l-carboxylate (ACC) synthase [EC 4.4.1.14 [EC] ]is the key enzyme regulating ethylene biosynthesis in higherplants. A complementary DNA encoding wound-induced ACC synthasefrom mesocarp of winter squash (Cucurbita maxima Duch.) fruitswas cloned, and its complete nucleotide sequence determined.The cloned cDNA contained an open reading frame of 1479 basepairs encoding a sequence of 493 amino acids. Identificationof the cDNA was accomplished by expression of active enzymein Escherichia coli harboring the cDNA and by the presence ofa partial amino acid sequence identical to that found in thepurified enzyme. A putative pyridoxal phosphate binding siteof the enzyme is suggested. Northern blot analysis showed thatthe ACC synthase gene was activated by tissue wounding, andits expression was repressed by ethylene. Genomic Southern analysisindicates the presence of at least another sequence which weaklyhybridizes with the cDNA. (Received June 26, 1990; Accepted August 7, 1990)     

Molecular Size of Wound-Induced 1-Aminocyclopropane-1-carboxylate Synthase from Cucurbita maxima Duch. and Change of Translatable mRNA of the Enzyme after Wounding

Wound-induced 1-aminocyclopropane-1-carboxylate (ACC) synthasewas purified by an immunoaffinity column from wounded mesocarpof winter squash (Cucurbita maxima Duch. cv. Ebisu) fruit, anda specific antibody was raised in rabbit. Translatable mRNAcoding for ACC synthase was barely detectable in fresh tissuebut clearly increased after wounding. The apparent molecularsize of the purified enzyme as estimated by SDS-polyacrylamidegel electrophoresis (PAGE) was about 50 kDa. However, SDS-PAGEfluorograms of in vitro translation product of ACC synthasemRNA and the in vivo labeled enzyme as well as Western blotanalysis showed that the subunit size of the enzyme was 58 kDa.The enzyme was partially degraded or processed to a 50 kDa peptideboth in vivo and in vitro. (Received December 19, 1987; Accepted June 13, 1988)     

Inactivation of 1-aminocyclopropane-1-carboxylate (ACC) oxidase

The enzyme 1-aminocyclopropane-1-carboxylate (ACC) oxidase,which catalyses the final step in the biosynthesis of ethylene,showed a non-linear time-course in vitro and activity decayedwith a half-life of around 14 min. This loss of activity wasstudied using tomato ACC oxidase purified from Escherichia coiltransformed with the cDNA clone pTOM13. Inactivation was notdue to end-product inhibition by dehydroascorbic acid or cyanide.Preincubatlon of enzyme in the combined presence of Fe²⁺ ascorbateand ACC, which together allowed catalytic turnover, resultedin almost total loss of ACC oxidase activity. Enzyme Inactivatedby catalysis could not be reactivated by passage through SephadexG-25 or by treating with combina tions of DTT and CO₂ A non-lineartime-course and inactivation in the presence of all substratesand cofactors was also shown for the enzyme assayed in vivowith melon fruit discs. Using the purified tomato enzyme a distinctascorbate-dependent inactivation was also observed, which occurredIn the absence of catalysis and was prevented, although notreversed, by catalase. This ascorbate-dependent inactivationmay thus be due to H₂O₂ attack on ACC oxidase. Key words: 1-aminocyclopropane-1-carboxylate (ACC) oxidase, catalase, catalytic inactivation, ethylene     

Induction of 1-Aminocyclopropane-1-carboxylic Acid Synthase in Wounded Mesocarp Tissue of Winter Squash Fruit and the Effects of Ethylene

1-Aminocyclopropane-1-carboxylic acid (ACC) synthase activityincreased rapidly after wounding of mesocarp tissue of wintersquash fruit (Cucurbita maxima Duch.) and reached a peak at16 h after excision and then declined sharply. The rise in ACCsynthase activity was followed by increases in the endogenousACC content and the rate of ethylene production. The activityof ethylene forming enzyme (EFE) also increased rapidly in theexcised discs of mesocarp of winter squash fruit. ACC synthase activity was strongly inhibited by aminoethoxyvinylglycinewith a Ki value of 2.1 µM. Michaelis-Menten constant ofACC synthase for S-adenosylmethionine was 13.3 µM. Ethylene suppressed the induction of ACC synthase in the woundedmesocarp tissue. The suppression by ethylene increased withthe increasing concentrations of applied ethylene and the maximumeffect was obtained at about 100 µl 1^–1 ethylene,at which point the induction was suppressed by 54%. Ethylenedid not inhibit ACC synthase activity, nor did it suppress theinduction of EFE, but rather it slightly enhanced the latter. (Received August 24, 1984; Accepted October 29, 1984)     

Properties and Partial Purification of 1-Aminocyclopropane-1-carboxylate Synthase

We studied the regulation of 1-aminocyclopropane-1-carboxylate (ACC) synthase activity in tomato (Lycopersicon esculentum Mill.) fruit tissue and attempted the purification of this enzyme. The increase of ACC synthase activity in wounded tomato pericarp was inhibited by cordycepin and cycloheximide. Density labeling studies showed a 0.75% increase in the buoyant density of ACC synthase isolated from tomato pericarp tissue that had been incubated on ²H₂O as compared to ACC synthase from H₂O-treated tissue. These data are consistent with the hypothesis that ACC synthase is synthesized de novo following wounding of tomato pericarp tissue. SDS-gel electrophoresis and fluorography showed that the pattern of incorporation of l-[³⁵S]methionine into protein changed with time after wounding of the tissue. Radioactive protein bands that were not detected 1 hour after wounding, became apparent 2 to 3 hours after wounding.     

Studies on the regulation of 1-aminocyclopropane-1-carboxylate synthase in tomato using monoclonal antibodies

A partially purified preparation of 1-aminocyclopropane-1-carboxylate (ACC) synthase (EC 4.4.1.14) from tomato (Lycopersicon esculentum (Mill.) fruit tissue was used to generate monoclonal antibodies (MAb) specific for the two different MAbs yielded a 50-kDa polypeptide as shown by sodium dodecylsulfate-polyacrylamide gel electrophoresis. An enzyme-linked immunosorbent assay (ELISA) capable of detecting <1 ng of antigen was developed. The ELISA system was used to demonstrate that two of the MAbs recognized different epitopes on the ACC-synthase protein. Wound-induced increases in ACC-synthase activity in tomato fruit tissue were correlated with changes in ELISA-detectable protein. In-vivo labeling of wounded tissue with [³⁵S]methionine followed by extraction and immunopurification in the presence of various protease inhibitors yielded one major radioactive band of 50 kDa molecular mass. Pulse labeling with [³⁵S]methionine at various times after wounding indicated that the wound-induced increase in ACC-synthase activity involved de-novo synthesis of a rapidly turning over 50-kDa polypeptide.Abbreviations ACC 1-aminocyclopropane-1-carboxylic acid - ELISA enzyme-linked immunosorbent assay - MAb monoclonal antibody - SDS-PAGE sodium dodecyl sulfate-polyacrylamide gel electrophoresis     

Turnover of 1-aminocyclopropane-1-carboxylic Acid synthase protein in wounded tomato fruit tissue

Ethylene production in plant tissues declines rapidly following induction, and this decline is due to a rapid decrease in the activity of 1-aminocyclopropane-1-carboxylic acid (ACC) synthase, a key enzyme in ethylene biosynthesis. To study the nature of the rapid turnover of ACC synthase in vivo, proteins in wounded ripening tomato (Lycopersicon esculentum) fruit discs were radiolabeled with [³⁵S]methionine, followed by a chase with nonradioactive methionine. Periodically, the radioactive ACC synthase was isolated with an immunoaffinity gel and analyzed. ACC synthase protein decayed rapidly in vivo with an apparent half-life of about 58 min. This value for protein turnover in vivo is similar to that previously reported for activity half-life in vivo and substrate-dependent enzyme inactivation in vitro. Carbonylcyanide-m-chlorophenylhydrazone and 2,4-dinitrophenol, potent uncouplers of oxidative phosphorylation, strongly inhibited the rapid decay of ACC synthase protein in the tissue. Degradation of this enzyme protein was moderately inhibited by the administration of aminooxyacetic acid, a competitive inhibitor of ACC synthase with respect to its substrate S-adenosyl-l-methionine, α,α′-dipyridyl, and phenylmethanesulfonyl fluoride or leupeptin, serine protease inhibitors. These results support the notion that the substrate S-adenosyl-l-methionine participates in the rapid inactivation of the enzyme in vivo and suggest that some ATP-dependent processes, such as the ubiquitin-requiring pathway, are involved in the degradation of ACC synthase proteins.     

Inhibition of 1-Aminocyclopropane-l-carboxylic Acid Synthase Activity by Polyamines, Their Related Compounds and Metabolites of S-adenosylmethionine

Basic amino acids, monoamines, diamines and polyamines inhibitedthe activity of 1-aminocyclopropane-1-carboxylic acid (ACC)synthase extracted from wounded mesocarp tissue of winter squashfruit (Cucurbita maxima Duch.). Among the amines tested, polyamineswere highly effective, while the synthetic triamine, 1,8-diamino-4-aminomethyloctane,was an even stronger inhibitor than the polyamine spermine.Polyamines inhibited ACC synthase activity in a non-competitivemanner, while metabolic inhibitors such as aminoethoxyvinylglycineand aminooxyacetic acid inhibited ACC synthase activity competitively,showing much lower Ki values than those of polyamines. ACC synthaseactivity was also inhibited by intermediates of the methionine-recyclingpathway, 5'-methylthioadenosine and -keto--methylthiobutyricacid and by S-adenosylhomocysteine, a product of transmethylationof S-adenosylmethionine. It appears that polyamines not only inhibit ACC synthase activitybut also suppress the induction of the enzyme. However, unlikeprevious reports, polyamines did not inhibit in vivo ethyleneforming enzyme activity in the wounded mesocarp tissue. (Received October 24, 1985; Accepted January 10, 1986)     

Inactivation of stress induced 1-aminocyclopropane carboxylate synthase in vivo differs from substrate-dependent inactivation in vitro

The activity of 1-aminocyclopropane carboxylate (ACC) synthase increased rapidly in tomato (Lycopersicon esculentum Mill.) leaf discs after vacuum infiltration, reached a maximum after about 30 minutes, and subsequently decayed with an apparent half-life of about 20 minutes. Aminoethoxyvinylglycine, a known inhibitor of ACC synthase, did not alter the apparent turnover of ACC synthase in vivo although it efficiently blocked inactivation of the enzyme by its substrate S-adenosylmethionine in vitro. Similar results were obtained, using a novel assay with permeabilized cells, for ACC synthase in tomato cell cultures treated with a fungal elicitor. The results indicate that inactivation of ACC synthase in vivo differs from substrate-dependent inactivation in vitro.     

S-adenosylmethionine-dependent inactivation and radiolabeling of 1-aminocyclopropane-1-carboxylate synthase isolated from tomato fruits

1-Aminocyclopropane-1-carboxylic acid (ACC) synthase was partially purified from the homogenate of wounded tomato (Lycoperiscon esculentum Mill.) pericarp tissue by (NH₄)₂SO₄ fractionation followed by conventional column chromatography with diethylaminoethyl-Sepharose, Sephadex G-150, Affi-Gel blue and hydroxylapatite. The partially purified ACC synthase preparation attained a specific activity of about 12,000 nmoles per hour per milligram protein. Employing this enzyme preparation, we confirmed that the ACC synthase was inactivated by its substrate, S-adenosyl-l-methionine (SAM), during its catalytic action. When the partially purified enzyme preparation was incubated with [3,4-¹⁴C]SAM and the resulting proteins were analyzed by sodium dodecyl sulfate-gel electrophoresis, only one radioactive protein band was observed. This protein was thought to be ACC synthase based on its molecular mass of 50 kD and on the fact that it was specifically bound to a monoclonal antibody against ACC synthase (AB Bleecker et al. 1986 Proc Natl Acad Sci USA 83, 7755-7759). These results suggest that the substrate SAM acts as an enzyme-activated inactivator of ACC synthase by covalently linking a fragment of SAM molecule to the active site of ACC synthase, resulting in the inactivation of the enzyme.     

The Tomato E8 Gene Influences Ethylene Biosynthesis in Fruit but Not in Flowers

We investigated the function of the tomato (Lycopersicon esculentum) E8 gene. Previous experiments in which antisense suppression of E8 was used suggested that the E8 protein has a negative effect on ethylene evolution in fruit. E8 is expressed in flowers as well as in fruit, and its expression is high in anthers. We introduced a cauliflower mosaic virus 35S-E8 gene into tomato plants and obtained plants with overexpression of E8 and plants in which E8 expression was suppressed due to co-suppression. Overexpression of E8 in unripe fruit did not affect the level of ethylene evolution during fruit ripening; however, reduction of E8 protein by cosuppression did lead to elevated levels during ripening. Levels for ethylene, 1-aminocyclopropane-1-carboxylic acid (ACC), and ACC oxidase mRNA were increased approximately 7-fold in fruit of plants with reduced E8 protein. Levels of ACC synthase 2 mRNA were increased 2.5-fold, and ACC synthase 4 mRNA was not affected. Reduction of E8 protein in anthers did not affect the accumulation of ACC or of mRNAs encoding enzymes involved in ethylene biosynthesis. Our results suggest that the product of the E8 reaction participates in feedback regulation of ethylene biosynthesis during fruit ripening.