ZN PHYTOTOXICITY INDUCES OXIDATIVE STRESS IN PRIMARY LEAVES OF PHASEOLUS-VULGARIS

We studied the sequence of several metabolic reactions representative for oxidative damage and protection in primary leaves of Phaseolus vul garis (cv. Limburgse vroege) after root uptake of a toxic sublethal am ount of Zn. An immediate increase of membrane peroxidation products wa s observed as soon as Zn was assimilated by the primary leaf. This ris e could be explained by activation of the enzyme lipoxygenase (EC 1.13 .11.12). In our experimental conditions, membrane lipid peroxidation a nd K+-leakage were not directly related. Zn treatment had no effect on the capacity of catalase (EC 1.11.1.6) and superoxide dismutase (EC 1 .15.1.1), while the capacity of ascorbate peroxidase (EC 1.11.1.11) wa s increased. Zn toxicity further leads to enhanced levels of hydrogen peroxide which could not be efficiently removed by the antioxidative s ystem. Therefore, it seems that an excess of Zn can cause oxidative da mage.