Effects of inhibitor on oxidative metabolism and root tissue structure of Brassica Chinensis under the stress of Cr-Pb pollution

The soil heavy metal pollution is threatenning the quality and safety of vegetable production in Guangdong. Aiming at optimization of the application levels of silicates and humic acid, pot experiments were carried out to study the effects of silicates and humic acid on growth and physiology of Brassica Chinensis which were growing up in Cr, Pb and Cr-Pb contaminated soils, respectively. The results indicate that root cells are disintegrated under the Cr-Pb pollution. The inhibitory effect of silicates on toxicity of Cr-Pb pollution is better than that of humic acid, and 1.0 g/kg silicate has the best effect. That mass fraction of silicate could improve the growth of unpolluted Brassica Chinensis, promote the SOD activity of Brassica Chinensis polluted by Cr-Pb, alleviate the damage of membrane lipid peroxidation of root plasma membrane, enhance the buffer function of cell wall and membrane, precipitate the heavy metals in cortical cell, and reduce the amount of heavy metal ions which could entry into cells. Thus, the bioavailabilities of heavy metal ions are decreased, the toxic effects of the heavy metals on plant are alleviated. While high level silicate(2.0 g/kg) or interaction between Pb and high level silicate(above 1.5 g/kg) would inhibit the growth. Humic acid could also promote SOD and POD activities at a certain degree, but its detoxification and promoting effects on growth are not significant. These results also indicate that SOD plays a key role to alleviate the peroxide stress, not POD.