Antioxidant enzymes responses to cadmium in radish tissues

To investigate the antioxidant responses of radish (Raphanus sativus L.) to cadmium (Cd) treatment, seedlings of a tolerant variety were grown in incr easing concentrations of CdCl2, ranging from 0.25-1 mM, for up to 72 h in a hydroponic system. Analysis of Cd uptake indicated that most of the Cd acc umulated in the roots, but some was also translocated and accumulated in th e leaves, especially at the higher concentrations of Cd used in the experim ents. Roots and leaves were analysed for catalase, glutathione reductase an d superoxide dismutase activities. Catalase and glutathione reductase activ ities increased considerably in the roots and leaves after 24 h exposure to the metal, indicating a direct correlation with Cd accumulation. The analy sis of native PAGE enzyme activity staining, revealed several superoxide di smutase isoenzymes in leaves, with the two predominant isoenzymes exhibitin g increases in activity in response to Cd treatment. The results suggest th at in radish, the activity of antioxidant enzymes responds to Cd treatment. The main response may be via the activation of the ascorbate-glutathione c ycle for the removal of hydrogen peroxide, or to ensure the availability of glutathione for the synthesis of Cd-binding proteins. (C) 2001 Elsevier Sc ience Ltd. All rights reserved.