Effects of Exogenous Organic Acids Amendment on MeHg Accumulation in Rice Seedlings

<p indent="0mm">Methylmercury (MeHg) contamination in rice is a prominent ecological and environmental challenge in mercury mining areas in China. However, the understanding of the biogeochemical mechanisms of MeHg accumulation in rice is still limited. There are a variety of organic acids in soil and plants, which can regulate the uptake and translocation of heavy metals by plants through chelation and other mechanisms. Nevertheless, it is still unclear whether these organic acids affect MeHg accumulation in rice. In this study, hydroponic experiments were conducted to examine the effects of citric acid, malic acid and oxalic acid on the uptake and translocation of MeHg in rice seedlings. The results showed that oxalic acid and citric acid treatments significantly increased the dry weight of the roots of rice seedling in comparison to the control group, but there was no significant difference after malic acid treatment, suggesting that exogenous oxalic acid and citric acid could alleviate the adverse effect of MeHg in roots of rice seedlings to a certain extent. By analyzing the activity of antioxidant enzymes in the roots of rice seedlings, it was found that the ascorbate peroxidase activity in the roots of rice seedlings could be increased after oxalic acid treatment, thereby alleviating the adverse effect of MeHg on rice seedlings. The results showed that effects of these three organic acids on the MeHg accumulation in rice seedlings were different. Oxalic acid and citric acid treatment facilitated MeHg accumulation in roots but decreased its translocation to the aerial parts of the rice seedlings. Conversely, malic acid inhibited the accumulation of MeHg in the roots of rice seedlings and its translocation to stems and leaves. To conclude, the uptake and translocation of MeHg in rice seedlings are uniquely influenced by different organic acids. These results provide some new perspectives for understanding the mechanisms of MeHg accumulation in rice through exogenous organic acids amendment.