Cadmium (Cd) is a non-essential heavy metal that is recognized as a major environmental pollutant. Cd enters the ecosystem chiefly as the result of human activities. Present investigation was conducted to assess the biochemical and physiological responses of rice to different concentrations of Cd. Seeds of rice were sterilized and were allowed to germinate under various Cd concentrations. Cadmium caused a gradual decrease in vigor index, root length, shoot height and amylase activity. Germination indexes of treated seeds were decreased. Root length decreased under all treatments. Cadmium uptake by seedlings increased with increasing Cd concentration and followed Michaelis-Menten kinetics. The average total amylolytic activities of rice seeds did not have a significant change in less than 4mg Cd l-1 medium compared to the control, but activity was progressively depressed with increasing concentration of Cd (6–10 mg l-1). Antioxidative responses of rice seedlings were also explored. Antioxidant enzyme activity in rice leaves generally showed no significant changes at low levels of Cd exposure. But high levels of Cd stimulated enzyme activity. These results suggested that prompt antioxidative responses might be necessary for the reduction of Cd-induced oxidative stress in roots but not in leaves.
