Induction of phytochelatin and responses of antioxidants under cadmium stress in safflower (Carthamus tinctorius) seedlings

We investigated the role of antioxidant compounds (e.g., alpha-tocopherol, phytochelatins, glutathione, and other non-protein thiols) in the cadmium (Cd) tolerance of safflower (Carthamus tinctorius L. cv. Arak2811) seedlings exposed to different concentrations of Cd (0-100 mu M) for a week. A concentration- and tissue- dependent response to Cd was observed. Increasing Cd supply markedly reduced the dry weight of roots. Plants accumulated a substantial amount of Cd, especially in the roots. Levels of alpha-tocopherol showed a significant increase with an increase in the concentration of Cd in leaves. Upon Cd exposure, alpha-tocopherol levels followed a similar pattern in the root tissue with no significant change as compared to the control. Cadmium exposure caused a significant increase in non-protein thiols and phytochelatin levels in roots, whereas non-protein thiols and phytochelatin levels were not affected in leaves. The glutathione content in leaves significantly increased with increasing Cd concentrations, whereas in roots glutathione contents increased up to a concentration of 50 mu M Cd and then decreased. The results indicate that the non-protein thiol and phytochelatin biosynthesis induction in roots and enhanced level of alpha-tocopherol and glutathione in leaves may be involved in Cd tolerance and hyperaccumulation in safflower.