Biosynthesis of auxin-induced ethylene in mung bean hypocotyls

The pathway of ethylene biosynthesis in auxin-treated mung bean hypocotyls was investigated by comparing the specific radioactivities of ethylene produced and S-adenosylmethionine (SAM) in the tissue following the administration of 3,4-14C-methionine, and by analyzing the methionine metabolites. When the rate of auxin-induced ethylene production was low due to a low concentration of auxin, the specific radioactivity of ethylene released was always higher than that of SAM in the tissue. When the tissue was treated with auxin, the tissue produced and accumulated a methio-nine metabolite which was converted into ethylene more efficiently than methionine. The metabolite was identified as 1-aminocyclopropane-l-carboxylic acid (AGC) by means of paper and thin-layer chromatography, high voltage paper electrophoresis and co-crystallization. ACG formation was neither inhibited by low oxygen nor by the inhibitory protein of ethylene synthesis, but inhibited by aminoethoxyvinylglycine (AVG). ACC application to the tissue greatly reduced incorporation of 3,4-14C-methionine into ethylene. The control tissue that was not treated with auxin also converted ACC into ethylene indicating that the enzyme which converts ACC into ethylene is already present in the tissue and that auxin induced production of the enzymatic system responsible for the conversion, of methionine into ACC. Ethylene synthesis from ACC was not inhibited by AVG, abscisic acid, cycloheximide or actinomycin D, but inhibited by low oxygen and the inhibitory protein