Effect of dicarboxylic acids on the peroxidase‐IAA oxidase isozymes of soybean callus

Abstract

Multiple forms of peroxidase with indole‐3‐acetic acid (IAA) oxidase activity were detected in callus cultures from soybean seeds [Glycinc max (L.) Merrill, cv. Acme] using ion‐exchange chromatography and polyacrylamide gel electrophoresis. The properties of the IAA oxidase were studied with a partially purified fraction eluted from a DEAE cellulose column. At pH 5.7. p‐coumaric acid and MnCl2 were required as cofactors and H2O2 was not able to replace them, but H2O2 eliminated the usual lag period of the reaction. Activation effects obtained with some dicarboxylic acids acting only on IAA oxidase are shown. These effects were studied at different pH values and oxalic acid was found to be the most efficient activator, particularly at pH 4.6. Activation by oxalic acid occurred even in the absence of MnCl2, but the presence of this salt produced a synergistic effect. IAA oxidase showed a sigmoidal kinetic behaviour at pH 5.7 changing to hyperbolic at pH 4.6