Different response to Cd stress in domesticated and wild safflower (Carthamus spp.)

Cadmium (Cd) can stress plants by affecting various physiological functions. Cd stress-response mechanisms were investigated in two genotypes of domesticated safflower (Carthamus tinctorius) and a population of wild safflower (Carthamus oxycantous) to explore potential differences in tolerance mechanisms of these species. A hydroponic experiment was conducted with 6-day-old safflower plants. Genotypes AC-Sterling (tolerant) and Saffire (semi-tolerant) from C. tinctorius, and Arak (sensitive) a population from C. oxycantouswere subjected to three concentrations of Cd (i.e., 0, 1, and 20 mu M CdCl2). Genotypic differences were detected in Cdtolerance index, Cd concentration in shoots and roots, Cd translocation to shoots, Cd bound to cell walls, superoxide dismutase (SOD) activity, lipid peroxidation, and phytochelatins accumulation in safflower plants upon exposure to CdCl2. Results indicate that genotypic differences were more obvious in the presence of low (i.e., 1 mu M) rather than high (i.e., 20 mu M) CdCl2 concentrations. Comparing genotypes, root and shoot Cd accumulation was highest in the semi-tolerant genotype. Cadmium translocation to shoots was increased with increasing tolerance. The percentage of Cd bound to root cell walls was higher in the tolerant genotype, but only with low CdCl2 addition. Furthermore, in the tolerant genotype, SOD activity was lowest in both roots and shoots with low CdCl2 addition but highest with high CdCl2 addition, while the opposite was found for phytochelatins. Lipid peroxidation was decreased with Cd tolerance at both CdCl2 concentrations. We conclude that safflower relies mainly on binding Cd to the cell walls and the formation of phytochelatins in root and shoot tissues, in order to handle the Cd stress, evidenced by lessening Cd-induced lipid peroxidation.