Effects of heavy metals on antioxidant activities of Atriplex hortensis and A. rosea

Oxidative stress is induced by a wide range of environmental factors including heavy metals stress. Therefore, antioxidant resistance mechanisms may provide a strategy to enhance metal tolerance, and processes underlying antioxidant responses to metal stress must be clearly understood. In the present study, the effects of heavy metals generating antioxidative defense systems (i.e. superoxide dismutase, ascorbate peroxydase, glutathione reductase and catalase) were studied in the leaves of Atriplex plants grown in soil polluted with heavy metals (Cu, Ni, Pb, Zn). The results showed that exposure of plants to different levels of metal reduced the dry matter production and height of shoots. The decrease in root growth caused by toxicity of metals was more severe than the decrease in shoot growth. Atriplex plants showed gradual decrease in height following metal treatments, a 4-week exposure of A. hortensis (red) to 25, 50, 75 and 100% contaminated soil gave a respective mean values of 21.4, 12.2, 9.3 and 6.5 cm, these values were lower than 39.00 cm for the control. Of the antioxidant enzymes only superoxide dismutase (SOD) and probably ascorbate peroxidase (APX) were diminished by metal toxicity. However, the activity of catalase (CAT) and glutathione reductase (GR) was increased by metal stress. Hence, the plants of the three annual arroach species or varieties used, all showed an intermediate level of tolerance according to the imposed treatments. The antioxidative activity seems to be of fundamental importance for adaptive response of Atriplex plants against environmental stress.