To investigate the antioxidant responses of radish (Raphanus sativus L.) to cadmium (Cd) treatment, seedlings of a tolerant
variety were grown in increasing concentrations of CdCl2, ranging from 0.25–1mM, for up to 72 h in a hydroponic system. Analysis
of Cd uptake indicated that most of the Cd accumulated in the roots, but some was also translocated and accumulated in the
leaves, especially at the higher concentrations of Cd used in the experiments. Roots and leaves were analysed for catalase, glutathione
reductase and superoxide dismutase activities. Catalase and glutathione reductase activities increased considerably in the roots and
leaves after 24 h exposure to the metal, indicating a direct correlation with Cd accumulation. The analysis of native PAGE enzyme
activity staining, revealed several superoxide dismutase isoenzymes in leaves, with the two predominant isoenzymes exhibiting
increases in activity in response to Cd treatment. The results suggest that in radish, the activity of antioxidant enzymes responds to
Cd treatment. The main response may be via the activation of the ascorbate–glutathione cycle for the removal of hydrogen peroxide,
or to ensure the availability of glutathione for the synthesis of Cd-binding proteins. # 2001Elsevier Science Ltd. All rights
reserved.