CADMIUM AND ZINC INDUCTION OF LIPID-PEROXIDATION AND EFFECTS ON ANTIOXIDANT ENZYME-ACTIVITIES IN BEAN (PHASEOLUS-VULGARIS L)

The relationship between Cd and Zn phytotoxicities and oxidative react ions in bean plants was studied. Ten-day-old bean (Phaseolus vulgaris L. cv. Morgan) plants treated for 96 h by 5 mu M Cd and 100 mu M Zn, s eparately, showed the same reduction of growth. In response to each me tal, lipid peroxidation was enhanced in all plant organs, and catalase (CAT) activity was decreased in both roots and leaves, but not in ste ms. However, Cd and Zn stimulated the activity of guaiacol-dependent p eroxidase only in stems, where native electrophoresis revealed, at lea st, two new anionic isozymes. The induction of one of these iso-guaiac ol peroxidase (iso-GPX) was Zn-specific. The exposure to metals did no t modify the activity of ascorbate-specific peroxidase either in roots or in stems. In leaves, where the glutathione reductase (GR) activity was assayed, increases of ascorbate peroxidase (APX) and glutathione reductase (GR) activities were recorded. These results suggest that so me antioxidant enzymes can be activated, notably in upper plant parts, in response to oxidative stress induced by Cd and Zn. (C) 1997 Elsevi er Science Ireland Ltd.