Combined Effect of Zinc and Cadmium Levels on Root Antioxidative Responses in Three Different Zinc-Efficient Wheat Genotypes

This work was undertaken to investigate the effect of zinc (Zn) nutrition on root antioxidative responses to cadmium (Cd) toxicity of three wheat genotypes differing in Zn efficiency. A hydroponic experiment was carried out in which two bread wheat genotypes (Triticum aestivum L. cvs. Rushan and Cross) and one durum wheat genotype (Triticum durum L. cv. Durum) were exposed to three Zn2+ (10-11.11, 10-9.11 and 10-8.81 mu m) and two Cd2+ (10-11.21 and 10-10.2 mu m) activity levels. Durum showed the highest root sulfhydryl (-SH) groups content and activity of catalase (CAT), ascorbate peroxidase (APX), and superoxide dismutase (SOD) and the lowest root membrane permeability among the studied wheat genotypes. In Durum, Zn nutrition increased root -SH groups concentration of seedlings in Cd-free nutrient solution. In Cross, as Zn2+ activity increased from 10-11.11 to 10-9.11 mu m, root -SH groups concentration was increased while decreased with increasing Zn2+ to 10-8.81 mu m. Cadmium increased root membrane permeability at both 10-11.11 and 10-9.11 mu m Zn2+ levels. Activity of CAT and APX increased in roots of Durum plants exposed to Cd at Zn2+ = 10-9.11 mu m and thereafter decreased with increasing Zn2+ activity. In contrast, CAT and APX activity in roots of Cross and Rushan genotypes exposed to Cd decreased by increasing Zn activity to 10-9.11 mu m and then increased at Zn2+ = 10-8.81 mu m. The results showed an increase in activities of antioxidative enzymes in Cd-treated plants, although this increase was dependent on the crop genotype and Zn levels in the media.