Differential response of antioxidant enzymes to cadmium stress in tolerant and sensitive cell line of cucumber (Cucumis sativus L.).

Previously, a stable cell suspension of cucumber tolerant to 100 microM CdCl(2) was obtained (Gzyl & Gwóźdź, 2005, Plant Cell Tissue Organ Cult 80: 59-67). In this study, the relationship between the activity of antioxidant enzymes and cadmium tolerance of cucumber cells was analyzed. A cadmium-sensitive and the cadmium-tolerant cell lines were exposed to 100 microM and 200 microM CdCl(2) and the activities of superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APOX) and guaiacol peroxidase (POX) were determined. In the sensitive cell line, a decrease of total activity of SOD and POX was observed, whereas the activity of CAT and APOX significantly increased in metal-supplemented medium. By contrast, in the tolerant cells, the total activity of antioxidant enzymes decreased (SOD, CAT) or was maintained at approximately the same level (APOX, POX). Moreover, a different pattern of isoenzyme activity was observed in the tolerant and sensitive cells. These results suggest that an enhanced activity of antioxidant enzymes is not directly involved in the increased tolerance to cadmium of the selected cucumber cell line.