Antioxidant defense mechanisms in response to cadmium treatments in two safflower cultivars

By using two safflower (Carthamus tinctorius L.) cultivars, Arak2811 and Goldasht, the experiments were conducted in order to study (i) the genotypic variation in cadmium (Cd) tolerance, (ii) Cd concentrations in plants, and (iii) changes in the antioxidant defense systems in leaves, including antioxidant enzymes and nonenzymatic antioxidants. Plants were grown under controlled environmental conditions and subjected to Cd treatments (0, 25, 50, 75, and 100 μM Cd) for different time periods. Cd concentrations and cultivar-dependent response to Cd were assessed. Of the two cultivars, Goldasht showed a greater sensitivity to Cd toxicity as judged from the severity of Cd toxicity symptoms on leaves, much stronger enhancement in the MDA level, and decreases in dry matter production. Increasing Cd supply markedly reduced the shoot and root dry weights in both cultivars, but at the higher Cd concentrations and longer exposure durations, this decrease was more marked in cv. Goldasht. Plants accumulated substantial amount of Cd, especially in the roots, the highest being in the roots of cv. Arak2811 at 100 μM Cd after 4 days. Cd-induced oxidative stress as was indicated by the increase in lipid peroxidation with the increase in metal concentration and exposure duration. Under different Cd stress levels, activities of antioxidant enzymes differed in the two cultivars. The results indicated that Cd tolerance of cv. Arak2811 was related to the retention of Cd in the roots and avoiding the toxic effect by activation of the antioxidant system.