Response of antioxidant enzymes to excess copper in tomato (Lycopersicon esculentum, Mill.)

15-day-old seedlings of tomato (Lycopersicon esculentum, Mill., cv. Ibiza F1) were treated, for 7 days, by addition of 50 μM Cu to the nutrient medium. Under these conditions, a decrease in growth, more~ pronounced in leaves and in stems than in roots was observed, as compared to controls. Copper accumulation was markedly higher, in roots as compared to shoots. In all plant parts, excess copper induced an increase in the rate of lipid peroxidation. Catalase (CAT) activity was not modified in leaves and in stems, but it was decreased in roots. The activity 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 activity was more important in stems than in roots. Analysis of the profile of anionic isoenzymes of GPX revealed quantitative and qualitative changes in roots and stems of stressed plants. These results together indicate that a toxic concentration of copper (50 μM) induces oxidative stress and differential responses of antioxidant enzymes in plant parts. Activity level of GPX, but not APX nor CAT, increased in response to damage.