Peroxidase associated with the root surface of Phaseolus vulgaris

Abstract

The surface of bean roots demonstrates an intense peroxidase activity which was detected by hydrogen peroxide dependent formation of chromogen from chloronaphthol or dianisidine. Other peroxidase functions, oxidation of indoleacetic acid and NADPH, were catalysed by intact roots and were stimulated by Mn2+ and p-coumarate. Oxidation of NADPH involved superoxide anion [Formula: see text] and hydrogen peroxide formation. Molecular sizing chromatography of root washes demonstrated NADPH oxidase and peroxidase to be associated with higher weight components than indoleacetic acid oxidase. Root surface and root wash peroxidase displayed optimal activity between pH 7 and 8, whereas both sources of indoleacetic acid oxidase were more active at acidic pH. Native poly aery lamide gel electrophoresis of sterile root washes displayed two fast-moving anodic bands, whereas homogenates of the plant roots had several slower moving bands in addition.