Effects of lead stress on anti-oxidative enzymes and stress-related hormones in seedlings of Excoecaria agallocha Linn

This study aimed to evaluate the responses of anti-oxidative enzymes and stress-related hormones in E. agallocha to different levels of Pb stresses at different exposure time. The study was carried out in greenhouse, and the pot trials were conducted to investigate the stress responses of root and leaf to Pb exposure in seedlings of E. agallocha. Pb stress posed higher toxic effects on root than leaf at day 49. At days 1, 7and 49, the activities of superoxide dismutase and peroxidases increased significantly, especially in leaves. Significant increases of malondialdehyde content were also observed at day 1 but significant increases of proline were only found at day 49 in leaf. Increases of salicylic acid and jasmonic acid were mainly observed in the leaves at day 1. E. agallocha was sensitive to Pb stress and damages, but tended to acclimate to low levels of Pb stresses by increasing and maintaining high levels of SOD and POD activities even at the later stage of exposure (day 49). Increases of endogenous SA and JA concentrations at day 1 might also involve in the plant's tolerance to Pb stress.