RESEARCH ARTICLE Effect of Pb toxicity on leaf growth, antioxidant enzyme

Background Cuttings and seedlings of Jatropha curcas L. were exposed to different regimes of lead (Pb) stress as Pb (NO3)2 at 0 (CK), 0.5, 1, 2, 3, and 4 mM kg −1 soil. Objectives The effect of Pb treatment on the root length, tolerance index, photosynthetic pigments, photosynthetic activity, lipid peroxidation, and antioxidant enzyme was studied in a greenhouse pot experiment. Results The results showed that root lengths and tolerance index decreased with increase of Pb concentration, but tolerance index of cuttings was always lower than those of the seedlings. For cuttings, Pb treatment had a stimulating effect on chlorophyll content, carotenoid content, and superoxide dismutase (SOD) activity at low concentration and an inhibitory effect at higher concentration. For seedlings, SOD activity increased with increasing Pb concentration. In both seedlings and cuttings, Pb caused inhibition of leaf growth and photosynthesis, and induced the membrane damage which was more obvious in the cuttings. In comparison with the control, the dynamic tendency of catalase and perxidase activities in the leaves of Pb-stressed plants all ascended, and then declined. Discussion The increase in enzyme activities demonstrated that seedlings were more tolerant to Pb stress than cuttings. These results also indicate that the antioxidant system may play an important role in eliminating or alleviating the toxicity of Pb in J. curcas seedlings and cuttings. The accumulation of Pb increased in a concentration-dependent manner; however, its translocation from root to shoot was low. The cuttings accumulated significantly higher Pb in roots than seedlings