Ethylene biosynthesis: Methionine as an in-vivo precursor of ethylene in auxin-treated mungbean hypocotyl segments.

Ethylene production was induced in excised hypocotyl segments of etiolated mungbean seedlings in response to exogenous auxin. 1,2,3,4-(14)C-Methionine was efficiently incorporated into C2H4, although cold methionine added at substrate level did not enhance C2H4 production. Incorporation of labeled glucose into C2H4 was reduced when hypocotyl segments were incubated with cold methionine and homoserine, but the rate of labeling of CO2 was not affected. Feeding of labeled glucose to segments resulted in production of labeled methionine both in the presence and the absence of auxin, and auxin did not affect rate of methionine synthesis from glucose. The decrease in the amount of endogenous methionine during auxin treatment approximated the amount of C2H4 produced. The timecourse pattern of incorporation of radioactivity from labeled methionine into C2H4 during removal or re-addition of auxin was very similar to that of C2H4 production. The role of endogenous methionine as a C2H4 precursor is discussed.