Auxin Activity of 3 - Menthyleneoxindole in Wheat Received for publication March

Abstract

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. Ethylenediaminetetraacetic acid can antagonize the growth-stimulating properties of the parent compound, indole-3-acetic acid, presumably by chelating Mn'+, which is required for the enzymatic oxidation of indole-3-acetic acid. The growth stimulating effect of 3methyleneoxindole, a product of the blocked reaction, on the other hand, is still evident in the presence of ethylenediaminetetraacetic 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. Earlier reports indicate that MeOx,' an oxidation product of IAA, is an obligatory intermediate in several auxin-mediated plant growth responses, including stimulation of the growth of pea and mung bean stem segments and promotion of protein synthesis in pea stems (6). Stimulation of growth and promotion of protein synthesis by IAA can be diminished by inhibiting the enzymatic oxidation of IAA by chlorogenic acid; MeOx, a product of this reaction can effectively bypass the block. Furthermore, in the presence of reduced compounds such as glutathione, IAA is incapable of promoting the growth of stem sections. Since IAA cannot form adducts with sulfhydryl compounds, this finding suggests that IAA is first oxidized to MeOx, a sulfhydryl reagent, before any growth can occur. It is the purpose of the experiments described in this paper to determine whether MeOx has a similar role in monocots such as wheat. MATERIALS AND METHODS Chemicals. 3-Bromooxindole-3-acetic acid was prepared by reaction of IAA with N-bromosuccinimide (3). This compound on solution in water is rapidly converted to MeOx, which was purified by chromatography in isopropanol-water (5:95). Alternately, MeOx was obtained by allowing a solution of HMO to undergo complete dehydration to MeOx at 23 C IAbbreviations: MeOx: 3-methyleneoxindole; HMO: 3-hydroxymethyloxindole. for 18 hr. HMO was prepared by photooxidation of IAA in the presence of riboflavin (1). Analytical Procedures. To determine the concentration of HMO, a sample was allowed to undergo complete dehydration to MeOx during storage overnight at room temperature. The concentration of MeOx and, therefore, that of the original

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@inproceedings{TuliAuxinAO, title={Auxin Activity of 3 - Menthyleneoxindole in Wheat Received for publication March}, author={Vinita Tuli} }