Studies on antioxidant enzymes in Canna indica plant under copper stress.

Bright red-flowered Canna indica L. plants were subjected to grow in nutrient solution supplemented with five different concentrations (0, 5, 10, 30 and 50 microM) of CuCl2 to study antioxidant defense responses of the plant. Accumulation of Cu was dose-dependent and much higher in the roots (108-191 microg g(-1) d. wt.) than in the leaves (23.36-40.43 microg g d.wt.). Total ascorbate content did not changed in both tissues, but ascorbate redox state decreased (0.570-0.640) in Cu-treated Canna roots. In contrast, both total and reduced glutathione contents increased (387-591.9 nmol g(-1) f. wt.) considerably in roots, accompanied with enhanced activities of dehydroascorbate reductase (153.3-160 nmol mg(-1) protein) and glutathione reductase (67-87.5 nmol mg(-1) protein). No significant change, however, was observed for monodehydroascorbate reductase activity in both tissues of the treated plant. The efficient scavenging of hydrogen peroxide was performed by normal (control level) activities of both ascorbate peroxidase and catalase in leaf and increased activity of only catalase in root, preventing its accumulation at toxic concentrations (despite high superoxide dismutase activity) and subsequent damage of membrane lipids by peroxidation. Together, these ensured normal dry weight of leaves and roots, indicating tolerance of Canna indica plant to Cu-induced oxidative stress.