Regulation of Auxin-induced Ethylene Production in Mung Bean Hypocotyls: Role of 1-Aminocyclopropane-1-Carboxylic Acid

Ethylene production in mung bean hypocotyls was greatly increased by treatment with 1-aminocyclopropane-1-carboxylic acid (ACC), which was utilized as the ethylene precursor. Unlike auxin-stimulated ethylene production, ACC-dependent ethylene production was not inhibited by aminoethoxyvinylglycine, which is known to inhibit the conversion of S-adenosylmethionine to ACC. While the conversion of methionine to ethylene requires induction by auxin, the conversion of methionine to S-adenosylmethionine and the conversion of ACC to ethylene do not. It is proposed that the conversion of S-adenosylmethionine to ACC is the rate-limiting step in the biosynthesis of ethylene, and that auxin stimulates ethylene production by inducing the synthesis of the enzyme involved in this reaction.     

Inhibition of auxin-induced ethylene production by salicylic acid in mung bean hypocotyls

Salicylic acid (SA), a common plant phenolic compound, influences diverse physiological and biochemical processes in plants. To gain insight into the mode of interaction between auxin, ethylene, and SA, the effect of SA on auxininduced ethylene production in mung bean hypocotyls was investigated. Auxin markedly induced ethylene production, while SA inhibited the auxin-induced ethylene synthesis in a dose-dependent manner. At 1 mM of SA, auxininduced ethylene production decreased more than 60% in hypocotyls. Results showed that the accumulation of ACC was not affected by SA during the entire period of auxin treatment, indicating that the inhibition of auxin-induced ethylene production by SA was not due to the decrease in ACC synthase activity, the rate-limiting step for ethylene biosynthesis. By contrast, SA effectively reduced not only the basal level of ACC oxidase activity but also the wound-and ethylene-induced ACC oxidase activity, the last step of ethylene production, in a dose-dependent manner. Northern and immuno blot analyses indicate that SA does not exert any inhibitory effect on the ACC oxidase gene expression, whereas it effectively inhibits both the in vivo and in vitro ACC oxidase enzyme activity, thereby abolishing auxin-induced ethylene production in mung bean hypocotyl tissue. It appears that SA inhibits ACC oxidase enzyme activity through the reversible interaction with Fe²⁺, an essential cofactor of this enzyme. These results are consistent with the notion that ethylene production is controlled by an intimate regulatory interaction between auxin and SA in mung bean hypocotyl tissue.     

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)     

Calcium stimulation of ethylene production induced by 1-aminocyclopropane-1-carboxylic acid and indole-3-acetic acid

Journal of Plant Growth Regulation - Ca2+ stimulates 1-aminocyclopropane-1-carboxylic acid (ACC)- and indole-3-acetic acid (IAA)-dependent ethylene production in mung bean hypocotyls and senescing...     

Identification and characterization of three putative genes for 1-aminocyclopropane-1-carboxylate synthase from etiolated mung bean hypocotyl segments

The polymerase chain reaction (PCR) was used to produce 3 putative clones for ACC synthase from etiolated mung bean (Vigna radiata Rwilcz cv. Berken) hypocotyls. This was accomplished by utilizing genomic DNA from mung bean and degenerate primers made from information derived from highly conserved regions of ACC synthase from different plant tissues. The total length of pMAC-1, pMAC-2 and pMAC-3 are 308, 321, and 326 bp, respectively, all of which code for 68 amino acids. The introns for pMAC-1, pMAC-2 and pMAC-3 are 92, 105, and 110 bp, respectively. The degrees of homology at the DNA level for each of these clones is ca. 80% in their coding region and ca. 50% in their respective introns. This is the first report providing evidence that there are at least 3 genes for ACC synthase in etiolated mung bean.     

桃ACC合酶基因的分离及其差异表达

利用5′/3′RACE PCR技术,从桃(Prunus persica (L.) Batsch)果实中克隆了植物乙烯生物合成的关键酶--ACC合酶的全长cDNA pacs,对pacs基因进行全序列测定表明,该基因全长1 848个碱基,编码区为1 449个碱基,5′端有177个碱基的非编码区序列,3′端有219个碱基的非编码区序列(不包括终止密码子TAA).pacs基因编码区共编码483个氨基酸,蛋白质大小为54 kD,等电点为6.43.pacs与番茄(S19677)、梅(AB031026)、番木瓜(U68216)、苹果(AB034993)等其他植物ACC合酶cDNA氨基酸序列同源性分别为65%、70%、75%、90%,并存在与这些ACC合酶氨基酸的活性位点保守序列SLSKDMGFPGFR.RT-PCR结合杂交分析表明,pacs和我们以前克隆的桃ACC合酶cDNA pacs12(AF467782)在叶片和花中基因表达模式基本一致,伤处理和IAA均能诱导叶片pacs 和pacs12基因的表达,但pacs在伤处理叶片的表达水平比pacs12高;pacs 和pacs12基因在果实表达有所不同,pacs在绿熟和成熟果实中均有表达,而pacs12在绿熟果实中基本检测不到,在成熟果实中才有表达,两者在果实中的表达水平比伤处理和IAA处理叶片和花中要低.     

Inhibition of activity of the ethylene-forming enzyme by α(p-chlorophenoxy)isobutyric acid

(p-Chlorophenoxy)isobutyric acid (PCIB) inhibited indole-3-acetic acid (IAA)-induced ethylene production in etiolated mung bean hypocotyl sections. The endogenous level of 1-aminocyclopropane-1-carboxylic acid (ACC) was not significantly affected by PCIB, indicating that PCIB exerted its effect primarily by inhibiting the activity of the ethylene-forming enzyme (EFE). This conclusion was supported by the observations that PCIB inhibited the conversion of exogenously applied ACC to ethylene. The inhibitory effect of PCIB was already evident with 0.05 mM PCIB, and it increased with time after application of the inhibitor. PCIB also significantly inhibited ethylene production in apple fruit tissues, but it only slightly reduced the level of endogenous ACC. Similar to mung bean, EFE activity in apple tissue was significantly inhibited by PCIB. The possibility that PCIB also inhibits auxin-induced ACC synthase activity is discussed.     

Stereospecific conversion of 1-aminocyclopropanecarboxylic Acid to ethylene by plant tissues : conversion of stereoisomers of 1-amino-2-ethylcyclopropanecarboxylic Acid to 1-butene

Inasmuch as the molecule of 1-aminocyclopropanecarboxylic acid (ACC) possesses reflective symmetry but lacks rotational symmetry, the two chemically alike methylene groups can be distinguished by a stereospecific enzyme. To determine whether ACC conversion to ethylene by plant tissues proceeds in a stereospecific fashion, the four stereoisomers of 1-amino-2-ethylcyclopropanecarboxylic acid (AEC) were administered to postclimacteric apple (Malus sylvestris Mill., var. Golden Delicious), excised preclimacteric cantaloupe (Cucumis melo L., var. reticulatis Naud cv. PMR-45), and etiolated mung bean (Vigna radiata L., Wilczek, var. Berken) hypocotyls. In each case (1R,2S)-AEC was the preferred substrate yielding 1-butene. In contrast, all AEC isomers were converted equally well to butene by chemical oxidation using NaOCl. Both ACC and AEC appear to be substrates for the same enzyme since both reactions are inhibited in parallel by N₂ or Co²⁺, both reactions are induced in parallel by excision, and when both substrates are present simultaneously each will act as an inhibitor with respect to the other. The aforementioned observations indicate that ACC is stereospecifically converted to ethylene. For AEC to be the most active precursor of 1-butene, the ethyl substituent should be trans to the carboxyl group and the pro-(S) methylene group should be unsubstituted. This observation leads to the suggestion that the enzyme interacts with amino, carboxyl, and pro-(S) methylene groups, a configuration corresponding to a l-amino acid. This view is consistent with the observation that the l-forms of alanine and methionine inhibit the conversion of ACC to ethylene more than the corresponding d-amino acids in the mung bean hypocotyl system.     

Biosynthesis of Auxin-Induced Ethylene. Effects of Indole-3-Acetic Acid, Benzyladenine and Abscisic Acid on Endogenous Levels of 1-Aminocyclopropane-l-Carboxylic Acid (ACC) and ACC Synthase

Auxin-induced ethylene biosynthesis and its regulatory stepsin etiolated mung bean hypocotyl segments were examined. Theendogenous content of 1-aminocyclopropane- 1-carboxylic acid(ACC), an immediate precursor of ethylene, increased correspondingto the rate of ethylene production. Benzyladenine (BA), whichis a synergistic stimulator of auxin-induced ethylene production,increased the ACC content parallel to the rate of ethylene productionin the presence of IAA, but failed to increase the ACC contentin the absence of IAA while ethylene production was significantlystimulated by BA. Abscisic acid (ABA) inhibited the formationof ACC. The ACC synthase activity in the tissue was increasedby IAA, and the increase was further promoted by the presenceof BA. Cycloheximide severely inhibited the development of auxin-inducedACC synthase. The enzymatic properties of mung bean ACC synthasewere similar to those of the tomato fruit enzyme. Aminoethoxyvinylglycine(AVG) and aminooxyacetic acid, which inhibit the ACC synthasereaction, stimulated the development of ACC synthase. The regulatorymechanisms of the growth regulators are discussed in relationto ACC formation. (Received December 3, 1980; Accepted January 22, 1981)     

Anaerobiosis and plant growth hormones induce two genes encoding 1-aminocyclopropane-1-carboxylate synthase in rice (Oryza sativa L.).

The plant hormone ethylene is believed to be responsible for the ability of rice to grow in the deepwater regions of Southeast Asia. Ethylene production is induced by hypoxia, which is caused by flooding, because of enhanced activity of 1-aminocyclopropane-1-carboxylic acid (ACC) synthase, the key enzyme in the ethylene biosynthetic pathway. We have cloned three divergent members, (OS-ACS1, OS-ACS2, and OS-ACS3), of a multigene family encoding ACC synthase in rice. OS-ACS1 resides on chromosome 3 and OS-ACS3 on chromosome 5 in the rice genome. The OS-ACS1 and OS-ACS3 genes are induced by anaerobiosis and indoleacetic acid (IAA) + benzyladenine (BA) + LiCl treatment. The anaerobic induction is differential and tissue specific; OS-ACS1 is induced in the shoots, whereas OS-ACS3 is induced in the roots. These inductions are insensitive to protein synthesis inhibitors, suggesting that they are primary responses to the inducers. All three genes are actually induced when protein synthesis is inhibited, indicating that they may be under negative control or that their mRNAs are unstable. The OS-ACS1 gene was structurally characterized, and the function of its encoded protein (M(r) = 53 112 Da, pI 8.2) was confirmed by expression experiments in Escherichia coli. The protein contains all eleven invariant amino acid residues that are conserved between aminotransferases and ACC synthases cloned from various dicotyledonous plants. The amino acid sequence shares significant identity to other ACC synthases (69-34%) and is more similar to sequences in other plant species (69% with the tomato LE-ACS3) than to other rice ACC synthases (50-44%). The data suggest that the extraordinary degree of divergence among ACC synthase isoenzymes within each species arose early in plant evolution and before the divergence of monocotyledonous and dicotyledonous plants.