[Studies on the mode of action of indole-3-acetic acid by means of heavy water].

The auxin-induced cell elongation and the formation of indoleacetyl-aspartic acid (IAAsp) of pea epicotyl sections and Agrostemma hypocotyl sections are inhibited by heavy water. The formation of IAAsp requires a specific enzyme. The lack of IAAsp in D2O-treated plant tissues may be due to an influence of D2O on the induction or on the synthesis of that enzyme. Treatment of plant sections with synthetic IAAsp has no effect on the growth of the sections in D2O. Indole-3-acetic acid (IAA) increases the incorporation of (32)P-orthophosphate into ribosomal and soluble RNA of pea epicotyl sections in H2O but not in D2O. The synthesis of ribosomal RNA is decreased by heavy water.The effects of IAA and D2O on the soluble proteins of pea sections have been studied by PAA-gel electrophoresis. D2O does not change the pattern of protein bands in comparison with the H2O-control, but prevents the probably IAA-induced alteration of the Rf-value of one protein band on the pherogram. It is assumed that the inhibition of auxin-induced reactions in the D2O-medium is due to the stabilizing effect of heavy water on allosteric proteins. The results of this work support the hypothesis that IAA acts as allosteric effector.