The effect of cadmium on growth and antioxidant responses in the safflower (Carthamus tinctorius L.) callus

Safflower (Carthamus tinctorius L.) callus cultures grown in the presence of different concentrations (0-100 mu M) of cadmium were assayed for growth, Cd accumulations, and antioxidative responses. Cadmium inhibited the growth of calli by 25% and 46% at 75 and 100 mu M Cd concentrations, respectively. Cadmium concentration in the calli increased with an increased Cd supply in the growth medium. Calli accumulated 334 mg Cd kg-1 of their dry weight at 100 mu M Cd. Cadmium induced oxidative stress, which was indicated by modulating antioxidant (glutathione and alpha-tocopherol) levels and antioxidative enzymes. The effect of Cd on glutathione (GSH) was dose-dependent. The GSH content increased up to a concentration of 75 mu M Cd and then decreased. Levels of alpha-tocopherol showed a significant increase with the increase in concentrations of Cd in the media. Antioxidant enzyme activity increased significantly up to a concentration of 75 mu M Cd. Concentrations of Cd greater than 75 mu M resulted in a decline in antioxidant enzyme activity. Increased antioxidant levels and antioxidant enzyme activity in Cd-treated calli indicate that Cd detoxification and accumulation in the safflower callus might be associated with the efficiency of these mechanisms.