ANIONIC PEROXIDASE CATALYZED ASCORBIC-ACID AND IAA OXIDATION IN THE PRESENCE OF HYDROGEN-PEROXIDE - A DEFENSE SYSTEM AGAINST PEROXIDATIVE STRESS IN PEANUT PLANT

In vitro experiments show that anionic peroxidase has a higher affinity for both ascorbic acid and IAA and a greater V(max) than cationic peroxidase in the oxidation reaction with the presence of H2O2. The peanut hypocotyls cultured in a medium with double amount of ascorbic acid (0.4 mgl-1) and IAA (4.0 mgl-1) show an increase of 104.3% and 128.4%, respectively, in anionic isozyme compared to the control, and only an increase of 22.6% and 12.8% in cationic isozyme. Treatment of entire plants with H2O2 (7.5%, v/v) demonstrated that a higher per cent of anionic isozyme over cationic is induced. These results suggest that cytoplasm-located anionic peroxidase probably plays a key role in the defence system against peroxidative stress through the detoxification of H2O2 during the processes of peroxidation of ascorbic acid and IAA.