Auxin activity of 3-methyleneoxindole in wheat

A product of the enzymatic oxidation of indole-3-acetic acid, 3-methyleneoxindole, is at least 50-fold more effective than indole-3-acetic acid in stimulating the growth of wheat (Triticum vulgare, red variety) coleoptiles. Ethylenediaminetetra-acetic acid can antagonize the growth-stimulating properties of the parent compound, indole-3-acetic acid, presumably by chelating Mn(2+), which is required for the enzymatic oxidation of indole-3-acetic acid. The growth stimulating effect of 3-methyleneoxindole, a product of the blocked reaction, on the other hand, is still evident in the presence of ethylenedia-minetetraacetic acid. In the presence of 2-mercaptoethanol, indole-3-acetic acid fails to stimulate the elongation of wheat coleoptiles. The property of binding to sulfhydryl compounds including 2-mercaptoethanol is unique to 3-methyleneoxindole among indole-3-acetic acid and its oxidation products. These findings suggest that 3-methyleneoxindole is an obligatory intermediate in indole-3-acetic acid induced elongation of wheat coleoptiles.