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

Summary Ethylene production was induced in excised hypocotyl segments of etiolated mungbean seedlings in response to exogenous auxin. 1,2,3,4-¹⁴C-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.