CUPRIC STRESS INDUCES OXIDATIVE DAMAGE MARKED BY ACCUMULATION OF H2O2 AND CHANGES TO CHLOROPLAST ULTRASTRUCTURE IN PRIMARY LEAVES OF BEANS (PHASEOLUS VULGARIS L.)

The effect of copper excess (CuSO4) on lipid peroxidation, H2O2 content, and antioxidative enzyme activities was studied in primary leaves of bean seedlings. Fourteen-day-old bean seedlings were cultured in a nutrient solution containing Cu2+ at various concentrations (50 and 75 mu M) for 3 days. Excess of copper significantly increased malondialdehyde content and endogenous H2O2. This radical accumulated in the intercellular spaces of palisade mesophyll cells. In addition, cupric stress induced changes in antioxidant enzyme activities. GPX (guaiacol peroxidase, EC 1.11.1.7) activity was decreased in 50 mu M Cu-stressed leaves whereas 75 mu M of CuSO4 resulted in an increase of enzyme activity. On the contrary, CAT (catalase, EC 1.11.1.6) activity was stimulated at 50 mu M CuSO4 but unaltered at 75 mu M CuSO4. Transmission electron microscopy revealed that excess copper induced changes in the ultrastructure of chloroplasts visible in form of a deterioration in the grana structure and the accumulation and swelling of starch grains in the stroma.