RESPONSE OF ANTIOXIDANT ENZYMES TO EXCESS COPPER IN TOMATO (LYCOPERSICON-ESCULENTUM, MILL)

15-day-old seedlings of tomato (Lycopersicon esculentum, Mill., cv. Ib iza F-1) were treated, for 7 days, by addition of 50 mu M Cu to the nu trient medium. Under these conditions, a decrease in growth, more pron ounced in leaves and in stems than in roots, was observed, as compared to controls. Copper accumulation was markedly higher in roots as comp ared to shoots. In all plant parts, excess copper induced an increase in the rate of lipid peroxidation. Catalase (CAT) activity was not mod ified in leaves and in stems, but it was decreased in roots. The activ ity of ascorbate peroxidase (APX) was unaltered in roots and in stems, while it was diminished in leaves. However, guaiacol peroxidase (GPX) activity was increased only in roots and stems. Enhancement of this a ctivity was more important in stems than in roots. Analysis of the pro file of anionic isoenzymes of GPX revealed quantitative and qualitativ e changes in roots and stems of stressed plants. These results, togeth er, indicate that a toxic concentration of copper (50 mu M) induces ox idative stress and differential responses of antioxidant enzymes in pl ant parts. Activity level of GPX, but not APX nor CAT, increased in re sponse to damage. (C) 1997 Elsevier Science Ireland Ltd.