Activity of antioxidant enzymes in response to cadmium in Crotalaria juncea

The effects of the heavy metal Cadmium (Cd) on the growth and the activities of the antioxidant enzymes, catalase (CAT. EC 1.11.1.6), Superoxide dismutase (SOD, EC 1.15.1.1) and glutathione reductase (GR. EC 1.6.4.2) have been investigated in Crotalaria juncea seedlings. Concentrations above 0.2 mM CdCl2 were shown to inhibit strongly the growth of roots and shoots. Cd was shown to accumulate to very high concentrations in the roots, whilst in the leaves. the maximum concentration obtained following treatment with 2 mM CdCl2. was only 6% of that determined in the roots. Although CAT activity did not exhibit an, major variation in the roots following CdCl2 treatment, 2 mM CdCl2 induced a 6-fold increase in activity in the leaves when compared to the untreated control. Non-denaturing PAGE gels stained for SOD activity revealed four isoenzymes, two Mn-SOD and two Cu/ZnSOD. The results observed for SOD were different of those observed for CAT activity. since in both. leaves and roots. no significant changes in the total activity or of the four isoenzymes were observed following the treatment with CdCl2. GR activity exhibited a similar pattern of that of CAT activity. The concentration of 2 mM CdCl2 induced a small increase in activity in the roots after 48 h of exposure. whereas in leaves a 7-fold increase in GR activity was detected after 48 hr exposure to 2 mM CdCl2. The results suggest that in C. juncea the reactive oxygen species (ROS) induced by Cd, are metabolised by CAT in the peroxisomes. In the case of GR activity. the increase observed in the leaves suggest that GR is also playing a role in the detoxification of Cd-induced ROS possibly via the glutathione-ascorbate cycle.