Interaction of salinity and cadmium stresses on antioxidant enzymes, sodium, and cadmium accumulation in four barley genotypes

A hydroponic experiment was carried out utilizing four barley genotypes with differing salt tolerances to investigate the influence of salinity (NaCl) and cadmium (Cd) on the activities of antioxidant enzymes, sodium (Na) and Cd concentrations, and accumulation in plants. The activities of the two antioxidant enzymes, superoxide dismutase (SOD) and peroxidase (POD), were significantly increased when plants were exposed to both Na and Cd stresses for all genotypes, relative to the control. The increased enzymatic activity was more predominant with a prolonged time of stress exposure. The combined stress (NaCl+Cd) led to a further increase in POD activity, but had little effect on SOD activity. Two salt-tolerant genotypes, 'Gebeina' and 'Zhou 1,' showed a more rapid increase of POD and SOD activities than the two salt-sensitive genotypes, 'Newgoutei' and 'Quzhou' in response to the combined stress treatment. Additions of NaCl to the Cd-containing medium caused a significant reduction in both Cd concentration and accumulation. The extent of the reduction in Cd concentration was also dependent on genotypes. The salt-tolerant genotypes had lower Na concentrations than sensitive genotypes, and the effect of Cd stress on Na concentration and accumulation varied with genotypes. It may be concluded that a significant interaction exists between Na and Cd in their influence on antioxidant enzyme activity and the accumulation of each element in the plant.