Interaction Mechanism Of Selenium And Mercury In Soil-Rice System

Selenium（Se） is a trace element necessary for human and animal. Animal selenium deficiency can cause myopathy white cow, pig oozing quality mulberry heart disease and poultry, human selenium deficiency can lead to Keshan disease, Kashin-Beck disease. Studies have shown that a daily intaking of the right amount of selenium, retard aging, resistance to cardiovascular disease and cancer, enhance immunity and maintain normal endocrine system. Mercury is extremely harmful organism heavy metal pollutants, and easy to enrich in the organism. Selenium and mercury have showed a wide range of antagonism. In order to further clarify the characteristics of the interaction between selenium and mercury, and further explore the antagonism mechanism between selenium and mercury, five reaches were designed : The effects of selenium and sodium selenite in different periods of rice absorb mercury; The impact of mercury and cadmium uptake by rice spraying sodium selenite; The influenece of selenium on the content of trace elements in rice plants under stress mercury; The impact of trace selenium and mercury on the antioxidant enzymes system in rice plants; And the impact of selenium on mercury absorption of rice on the presence of iron film. The main results are as follows:（1） Through the pot experiment, studing the impact of selenium and sodium selenite on the uptake and transport of mercury（Hg） in different growth stages. The results showed that sodium selenite treatments could enhance the root fixing of mercury, processing roots mercury content and the distribution ratio of mercury in root at jointing stage, stems and leaves of mercury decreased at the same time; At booting and maturity stages, the sodium selenite treatments average mercury content of grain reduced 49% and 44.13%, selenium treatments average mercury content reduced 47.0% and 28.6%. Selenium also promoted the tranfsformation of mercury in seed.（2） Through the pot experiment, by spraying different concentrations of sodium selenite（0,0.2,1.5,5.0）mg L^-1 on rice plants to study the change of transfering cadmium and mercury. The results showed that spraying sodium selenite can significantly increase grain selenium content, spraying low concentrations(<1mg L^-1) had no effect on migration of cadmium, but significantly reduced mercury content and secondary migration coefficient（STI）. At booting and maturity stage spraying high concentration sodium selenite(5mg L^-1) could promote cadmium of stem migrate to seed, thereby shoot and grain cadmium content increased, but the mercury content and migration of rice weren’t effected. Therefore, the booting and maturity stages is critical for cadmium, mercury accumulation, the characteristics of metal cations and concentration of spraying sodium selenite effects the uptake and translocation of heavy metals.（3） Through hydroponic experiment, by providing two levels of selenium(0,2 mmol L^-1), five mercury levels(0,0.25,0.5,1.0,2.0 mg L^-1) to study the impact of trace selenium on the absorbing of mercury, N, P, K, Ca, Mg, Fe. The results show that the addition of selenium can promote the rice growth under Hg stress. With the mercury concentration, the concentration of selenium in rice plants decreased gradually. Selenium can increase N, P, K and trace element content of rice plants under stress mercury, selenium which is likely to enhance the activity of antioxidant enzyme systems in plants to improve the stability of the plasma membrane, and then influence the ion channels on the cell membrane.（4）Through hydroponic experiment to explore effects of the trace selenium on absorption of mercury and antioxidant enzyme system in rice seeding. Setting two levels of mercury concentrations(0, 0.25 mg L^-1), two levels of selenium(0, 2 mmol L^-1), a total of six treatments. The results showed that trace amounts of selenium and mercury only effect the root eraly growth. Selenium and mercury adding at the same time could significantly reduce the absorption of mercury in rice, pre-treated with selenium had no significant effect on the mercury content of the rice plants. Trace amounts of selenium can increase CAT, POD activity in riceseeding, increase the content of GSH. But it has no significant effect on SOD activity, which may be due to trace amounts of mercury and selenium did not cause severe oxidative stress on plants.（5） In this experiment, using Fe²⁺ induce generating different amounts of iron plaque（Fe0, Fe10, Fe30, Fe50, Fe70）, study the influence of selenium on absorb mercury in the presence of iron plaque, and if the selenium and mercury absorbd in iron iron plaque can be reused. The results show that iron plaque on rice has a role in promoting the growth of rice. In hydroponic conditions, iron plaque has different effects on the absorption of selenium and mercury. In the process of root absorption of selenium, iron plaque it is likely to act as a barrier to action. When the amount of iron plaque number is low（Fe0, Fe10, Fe30）, selenium can promote root absorption of mercury, otherwise（Fe50, Fe70）, selenium could inhibition the absorption of mercury. Most of the selenium and mercury adsorbed in iron plaque can be released into the nutrient solution, and reused by rice.