Effect of 1-Aminocyclopropane-1-Carboxylic Acid on the Production of Ethylene in Senescing Flowers of Ipomoea tricolor Cav.

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Abstract
Application of 1-aminocyclopropane-1-carboxylic acid (ACC) to rib segments excised from flowers of Ipomoea tricolor Cav. resulted in the formation of C2H4 in greater quantities than produced under natural conditions. The ability of ACC to enhance C2H4 production was independent of the physiological age of the tissue and its capacity to synthesize C2H4 without applied ACC. When ACC was fed to rib segments that had been treated with [14C]methionine, incorporation of radioactivity into C2H4 was reduced by 80%. Aminoethoxyvinylglycine and aminooxyacetic acid inhibited C2H4 production in rib segments of I. tricolor but had no effect on ACC-enhanced C2H4 production. Protoplasts obtained from flower tissue of I. tricolor did not form C2H4, even when incubated with methionine or selenomethionine. They produced C2H4 upon incubation with ACC, however. ACC-dependent C2H4 production in protoplasts was inhibited by n-propyl gallate, AgCl, CoCl2, KCN, Na2S, and NaN3. ACC-dependent C2H4 synthesis in rib segments and protoplasts was dependent on O2, the Km for O2 being 1.0 to 1.4% (v/v). These results confirm the following pathway for C2H4 biosynthesis in I. tricolor. methionine [selenomethionine] → S-adenosylmethionine [selenoadenosylmethionine] → ACC → C2H4.