Arsenate toxicity: effects on oxidative stress response molecules and enzymes in red clover plants

The effects of different soil concentrations of arsenate on red clover plants (Trifolium pratense L. cv. Renova) were investigated. Red clover plants were grown in a greenhouse on a sandy soil amended with different concentrations of Na2HAsO4 (5, 10 and 50 mgAs kg(-1) soil) ora heavy metal mixture (5 mg Cd, 300mg Zn and 10mgAs kg(-1) soil), respectively. We studied the accumulation of arsenic as well as macro- and micronutrients and investigated biochemical stress responses in clover shoots caused by arsenic incorporation in clover shoots. Increases in superoxide dismutase (SOD) activity, peroxidase activity as well as decreases in chlorophyll (chl) and carotenoid concentrations correlated with increasing arsenic content in plants. The analyses of native PAGE SOD activity staining indicated one Mn-SOD and two major Cu/Zn-SOD isoenzymes in clover shoots, whose capacity increased in response to arsenate treatment. Glutathione content was reduced at the highest As concentration applied. Antioxidative polyamines (PAs) accumulated at higher doses of arsenate in the soil. Increase in SOD activity and accumulation of PAs as well as chl loss could be prevented by application of Zn and Cd together with As. The results indicate that higher doses of arsenate produce oxidative damage in clover shoots. The protective role of applying a mixture of Zn and Cd together with As is discussed. (C) 2002 Elsevier Science Ireland Ltd. All rights reserved.