Inhibitory Oxidation Products of Indole-3-Acetic Acid: 3-Hydroxymethyloxindole and 3-Methyleneoxindole as Plant Metabolites

Extracts of pea seedlings (Pisum sativum, variety Alaska) oxidize indole-3-acetic acid to a bacteriostatic compound which has been identified as 3-hydroxymethyloxindole. At physiological pH this compound is readily dehydrated to 3-methyleneoxindole, another bacteriostatic agent. The extracts of pea seedlings also contain a reduced triphosphopyridine nucleotide-linked enzyme which reduces 3-methyleneoxindole to 3-methyloxindole, a non-toxic compound. These enzymatic reactions also take place in intact seedlings; thus, a pathway of indole-3-acetic acid degradation via oxindoles appears to be pertinent to plant metabolism. The significance of such metabolism lies in the fact that a key intermediate of this pathway, 3-methyleneoxindole, is a sulfhydryl reagent capable of profound effects on metabolism and growth.