CATALASE IS A SINK FOR H2O2 AND IS INDISPENSABLE FOR STRESS DEFENSE IN C-3 PLANTS

Hydrogen peroxide (H2O2) has been implicated in many stress conditions , Control of H2O2 levels is complex and dissection of mechanisms gener ating and relieving H2O2 stress is difficult, particularly in intact p lants, We have used transgenic tobacco with similar to 10% wild-type c atalase activity to study the role of catalase and effects of H2O2 str ess in plants, Catalase-deficient plants showed no visible disorders a t low Light, but in elevated light rapidly developed white necrotic le sions on the leaves, Lesion formation required photorespiratory activi ty since damage was prevented under elevated CO2, Accumulation of H2O2 was not detected during leaf necrosis, Alternative H2O2-scavenging me chanisms may have compensated for reduced catalase activity, as shown by increased ascorbate peroxidase and glutathione peroxidase levels, L eaf necrosis correlated with accumulation of oxidized glutathione and a 4-fold decrease in ascorbate, indicating that catalase is critical f or maintaining the redox balance during oxidative stress, Such control may not be limited to peroxisomal H2O2 production, Catalase functions as a cellular sink for H2O2, as evidenced by complementation of catal ase deficiency by exogenous catalase, and comparison of catalase-defic ient and control leaf discs in removing external H2O2. Stress analysis revealed increased susceptibility-of catalase-deficient plants to par aquat, salt and ozone, but not to chilling.