Effect of cadmium on free amino acid, glutathione and ascorbic acid concentrations in two barley genotypes (Hordeum vulgare L.) differing in cadmium tolerance

Hydroponic experiment was carried out to study the effect of three Cd levels on glutathione (GSH), free amino acids (FAA), and ascorbic acid (ASA) concentration in the different tissues of 2 barley cultivars with different Cd tolerance. Cadmium concentration in both roots and shoots increased with external Cd level, while biomass and ASA concentration declined, and Wumaoliuling, a Cd-sensitive genotype was more affected than ZAU 3, a Cd-tolerant genotype. The effect of Cd on GSH concentration was dose- and time-dependent. In the 5 d exposure, root GSH concentration increased in 0.5 microM Cd treatment compared with control, but decreased significantly in 5 microM Cd treatment, irrespective of genotypes. However, in the 10 d exposure, GSH concentration in all plant tissues decreased with increasing Cd levels in the culture medium, and Wumaoliuling was much more affected than ZAU 3. Cadmium treatment greatly altered FAA concentration and composition in plants. The effect of Cd on glutathione (Glu) concentration in roots varied with genotypes. ZAU 3 showed a steady increase in root Glu concentration in both 0.5 and 5 microM Cd treatments, while Wumaoliuling was decreased by 38.0% in 5 microM Cd treatment, compared with the control. The results indicate that GSH and ASA are attributed to Cd tolerance in barley plants, and the relative less reduction in GSH concentration in ZAU 3 under Cd stress relative to the control may account for its higher Cd tolerance.