Effect of UV-B radiation on antioxidant defense system in sunflower cotyledons

The behavior of the antioxidant defense system was studied in sunflower cotyledons subjected to ultraviolet-B (UV-B) radiation. The two doses assayed (15.0 and 30.0 kJ m(-2)) induced oxidative damage, as evidenced by an increase in lipid peroxidation and a decrease in both chlorophyll content and superoxide dismutase activity. However, the reduced glutathione/oxidized glutathione ratio was significantly increased and ascorbate/dehydroascorbate ratio was not affected by UV-B treatments. In addition, the activity of the antioxidant enzymes catalase, glutathione dehydrogenase and guaiacol peroxidase were increased at the two doses of UV-B radiation used, while ascorbate peroxidase and glutathione reductase activities were not altered under the two irradiation treatments. These results suggest that UV-B radiation undoubtedly induces antioxidant defense system in sunflower cotyledons, allowing plant survival in spite of the oxidative stress generation. However, more research is necessary to elucidate the precise role that the antioxidant system plays under UV-B stress. (C) 2002 Elsevier Science Ireland Ltd. All rights reserved.