Abstract
Application of 1-aminocyclopropane-1-carboxylic acid (ACC) to rib segments excised from flowers of Ipomoea tricolor Cav. resulted in the formation of C(2)H(4) in greater quantities than produced under natural conditions. The ability of ACC to enhance C(2)H(4) production was independent of the physiological age of the tissue and its capacity to synthesize C(2)H(4) without applied ACC. When ACC was fed to rib segments that had been treated with [(14)C]methionine, incorporation of radioactivity into C(2)H(4) was reduced by 80%. Aminoethoxyvinylglycine and aminooxyacetic acid inhibited C(2)H(4) production in rib segments of I. tricolor but had no effect on ACC-enhanced C(2)H(4) production. Protoplasts obtained from flower tissue of I. tricolor did not form C(2)H(4), even when incubated with methionine or selenomethionine. They produced C(2)H(4) upon incubation with ACC, however. ACC-dependent C(2)H(4) production in protoplasts was inhibited by n-propyl gallate, AgCl, CoCl(2), KCN, Na(2)S, and NaN(3). ACC-dependent C(2)H(4) synthesis in rib segments and protoplasts was dependent on O(2), the K(m) for O(2) being 1.0 to 1.4% (v/v). These results confirm the following pathway for C(2)H(4) biosynthesis in I. tricolor. methionine [selenomethionine] --> S-adenosylmethionine [selenoadenosylmethionine] --> ACC --> C(2)H(4).