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

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Abstract
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.
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