Peroxidase and IAA oxidase activities in sunflower plants

M.D. GROPPA; M.L. TOMARO; M.E. FERNANDEZ

Pucón. Chile.

Congreso; VIII Congreso de la Pan-American Association for Biochemistry and Molecular Biology (PABMP).; 1996

Asociación Panamericana de Sociedades de Bioquímica y Biología Molecular

Peroxidases are hemoproteins involved in  a great variety of processes, including lignification and stress response. They are also related with plant development in a complex manner. Due to the occurrence of multiple isozymes, it is not easy to study their in vivo mechanisms of control. Indoleacetic acid (IAA) catabolism is also attributed to peroxidases, although there is still controversy on this matter. We have begun to study systematically the expression of peroxidases as a function of plant development in order to shed light on these subjects. We worked with sunflower plants processed 7, 14 and 28 days after sowing. Different parts of the plants were homogenized and the soluble extracts were studied. Peroxidase activity was found in every sample. A peptidic activator that was found in seeds associated to membranes, was not detected in plants. Nevertheless soluble plant extracts were activated up to 200% by the seeds activator. Plants samples were analized by native PAGE followed by specific peroxidase staining  When cathodic gels were performed, 4 bands were revealed in seeds but no bands were detected in plants, except in cotyledons where a band coincident with one of the 4 isoforms present in seeds appeared. Several isoforms were detected in anodic gels for all plant fractions, but no anodic bands were present in seeds. IAA oxidase activity was not detected in any of the plant fractions although we could find it in seeds. We could stablish that in plants there is a soluble factor that functions as an inhibitor of seeds IAA oxidase. This could account for the lack of IAA oxidase activity in plants. The physiological implicances of this control mechanism is apparent: once the growing process has begun IAA oxidase activity is inhibited to control auxin catabolism.