Response of antioxidative enzymes to nickel and cadmium stress in hyperaccumulator plants of the genus Alyssum

The term 'phytoremediation' is used to describe the clean-up of heavy metals from contaminated soils by plants. In this study, we examined Alyssum argenteum and Alyssum maritimum for their ability to accumulate Cd²⁺. We also exemined Ni²⁺ accumulation by A. maritimum with comparison with the known Ni-hyperaccumulator A. argenteum , in a hydroponic system. Both species were tolerant to low levels of Cd²⁺, and accumulated high quantities under the experimental conditions. Only very low levels of Ni²⁺ were found in the shoot of A. maritimum , defining it as a non-hyperaccumulator. The role of the antioxidative enzyme system was investigated in relation to Ni²⁺ and Cd²⁺ stress. In both species, superoxide dismutase (SOD) activity was elevated at high Cd²⁺ concentrations, while ascorbate peroxidase (APX) activity remained unchanged and glutathione reductase (GR) activity was reduced. In the presence of Ni²⁺, A. maritimum exhibited a typical antioxidative defense mechanism, as evidenced by the elevated activities of all three enzymes tested. A. argenteum exhibited a different enzyme response pattern, with a significant reduction in SOD activity, and elevated APX and GR activities only at the highest Ni²⁺ concentration.