Differential antioxidative responses to cadmium in roots and leaves of pea(Pisum sativum L. cv. Azad)

Pea (Pisum sativum L. cv, Azad) plants exposed to 4 and 40 muM of Cd for 7 d in hydroponic culture were analysed with reference to the distribution of metal, the accumulation of biomass and the metal's effects on antioxidants and antioxidative enzymes in roots and leaves. Cd-induced a decrease in pl ant biomass. The maximum accumulation of Cd occurred in roots followed by s tems and leaves. An enhanced level of lipid peroxidation and an increased t issue concentration of hydrogen peroxide (H2O2) in both roots and leaves in dicated that Cd caused oxidative stress in pea plants. Roots and leaves of pea plants responded differently to Cd with reference to the induction of e nhanced activities of most of the enzymes monitored in the present study. T hese differential responses to Cd were further found to be associated with levels of Cd to which the plants were exposed. Cd-induced enhancement in su peroxide dismutase (SOD) activity was more at 40 muM than at 4 muM in leave s. While catalase (CAT) prominently increased in leaves both at 4 and 40 mu M Cd, ascorbate peroxidase (APX) showed maximum stimulation at 40 muM Cd in roots. Enhancement in glutathione reductase (GR) activity was also more at 40 muM than at 4 muM Cd in roots. While glutathione peroxidase (GPOX) acti vity decreased in roots and remained almost unmodified in leaves, glutathio ne S-transferase (GST) showed pronounced stimulation in both roots and leav es of pea plants exposed to 40 muM Cd. Increased activities of antioxidativ e enzymes in Cd-treated plants suggest that they have some additive functio n in the mechanism of metal tolerance in pea plants.