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

Abstract 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. oxycantous were subjected to three concentrations of Cd (i.e., 0, 1, and 20 µM CdCl 2 ). 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 CdCl 2 . Results indicate that genotypic differences were more obvious in the presence of low (i.e., 1 µM) rather than high (i.e., 20 µM) CdCl 2 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 CdCl 2 addition. Furthermore, in the tolerant genotype, SOD activity was lowest in both roots and shoots with low CdCl 2 addition but highest with high CdCl 2 addition, while the opposite was found for phytochelatins. Lipid peroxidation was decreased with Cd tolerance at both CdCl 2 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.