Antioxidative defense system differences among four plants under combined Pb and Cd stress

The hyperaccumulative plants of Solanum nigrum and Brassica juncea, and non-hyperaccumulative plants of maize (Zea?mays) and radish (Raphanus sativus) were used to analyze the antioxidative system response to combined Pb and Cd pollution. The results show that leaf biomass for the hyperaccumulators, S. nigrum and B. junce, significantly decrease under the pollution, against a slight change in root and stem biomass under low Pb and Cd concentration. The biomass of non-hyperaccumulators, maize and radish, significantly decreases with increasing concentration of heavy metals. Hyperaccumulators’superoxide dismutase (SOD) activity increases with increasing concentration of heavy metals in the soil. While peroxidase (POD) activities for the four plants are different, response of non-hyperaccumulators’ POD activities to heavy metal stress is the same and increases with increasing heavy metal concentration. Hyperaccumulators’s malondialdehyde (MDA) content also increases with increasing heavy metal concentration. B. juncea and radish have higher GSH content than the other two plants. For the hyperaccmulators, SOD, MDA, TSTA, GSH and PC are significantly correlated with heavy metal toxicity coefficient. POD and total GSH in maize significantly correlate with heavy metal toxicity coefficient, while TAST and PC in radish significantly correlate with heavy metal toxicity coefficient. The results indicate the detoxification mechanisms are different for plants. Therefore, it is important to further research on hyperaccumulator gene control and enzyme expression for a greater insight into detoxification mechanism.