Effects of cadmium and copper on antioxidant capacities, lignification and auxin degradation in leaves of pea (Pisum sativum L.) seedlings.

Twelve-day-old seedlings of pea were treated for four days by 20 and 100 microM of Cd(NO3)2 or CuSO4. In leaves, all treatments caused an increase in the lipoperoxidation product rate. However, 20 microM of Cu did not affect the growth. Moreover, except for 20 microM of Cu, the activity of unspecific peroxidases, used as stress marker, was enhanced in cell walls of metal-stressed plants. No change in the antioxidant capacities was observed in plants treated with 20 microM of metal. At this dose, the Cd-reduced growth could be associated to an elevation in the activities of IAA oxidase and of lignifying peroxidases. Increase of these latter, in concert with loss in antioxidant capacities, would be responsible for the growth diminution after exposure to 100 microM of metal. However, the activity of lignifying enzymes was not affected by 100 microM of Cu. The contribution of cell fractions to enzymatic responses to stress is emphasized.