Effect of cadmium ions on antioxidant defense system in sunflower cotyledons

Sunflower (Helianthus annuus L.) seeds were germinated and grown in the presence of 50, 100 and 200 mu M CdCl2. The lower concentration (50 mu M) of Cd2+ ions produced slight decrease in reduced glutathione (GSH) content and overall increase (except superoxide dismutase) in antioxidant enzyme activities, and in H2O2 concentration. Chlorophyll content, lipid peroxidation and protein oxidation were not affected under 50 mu M CdCl2. GSH content was diminished under 100 and 200 mu M CdCl2, and except for superoxide dismutase, which activity remained unaltered, overall decreases in the antioxidant enzyme activities (catalase, ascorbate peroxidase, dehydroascorbate peroxidase, glutathione reductase) and in guaiacol peroxidase were observed. These Cd2+ concentrations caused a decrease in chlorophyll content as well as an increase in lipid peroxidation, protein oxidation and H2O2 concentration. All the observed effects were more evident with the highest concentration of cadmium chloride used.