The Effect And Mechanism Of Selenium Mediated Reduction On Arsenic Stress In Rice Seedlings

Arsenic(As)is one of the heavy metal elements,can be widely founded in nature,has been caused seriously damage to the human's health.In recent years,because of the excessive exploitation and smelting of arsenic-containing minerals and the extensive use of arsenic-containing pesticides,the soil has been contaminated with arsenic.The effective absorption of arsenic by rice then enriched into human's body through the food chain,which poses a potential threat to human's health.Selenium(Se)is a necessary nutrient element for human,and it has been found that selenium can antagonize the absorption of heavy metals in rice.Sulfur(S)and Se are the same family elements,which play an important role in the metabolism of arsenic and selenium in plants.In this paper,the interaction of different concentrations of Se[0-10?mol/L Se(IV)] and As[0-25?mol/L As(III)] on the plant growth,the absorption and transfer of As and Se as well as antioxidant system in rice seedling were studied by applying a solution culture method,aiming to screening out the suitable Se concentration to alleviate the As stress in rice.On this basis,further research on the effect of different S supply levels(1.25mmol/L,0.25mmol/L)on the interaction of Se and As on rice seedling growth,As and Se accumulation and species,antioxidant system and thols content were done,in order to investigate the mechanism of interaction of Se and As and the influence of different S levels in rice,which provided scientific basis for rational using of Se and S fertilizer to achieve the effect of reducing arsenic and enriching selenium in agricultural production.The main results were as follows:1.Low As doses(5?mol/L)had no significant effect on the growth of rice seedlings,and the high As doses(25?mol/L)inhibited the plant growth,reduced the fresh weight and the SPAD value of leaves of rice seedlings.Under no As or low As treatment condition(?5?mol/L),the low Se levels(?5?mol/L)promoted the rice growth,increased the fresh weight of the ground and the root.But under the high As doses(25?mol/L)condition,only adding the high Se doses(10?mol/L)promoted therice growth.2.Se inhibited the absorption and transfer of As in rice seedlings,and reduced the content of As in roots and shoots.As treatment inhibited the transfer of Se to the shoots and reduced the content of Se in shoots.Low As doses(5?mol/L)significantly increased the content of Se in the roots of rice which was 1.2-1.8 times times that of CK treatment,while the high As doses(25?mol/L)reduced the Se content of rice roots which was only 63.2%-74.1% that of CK.3.Low As level treatment had no significant effect on the activity of antioxidant enzymes and the content of MDA in rice seedlings,while the high As doses stress significantly increased activity of SOD and POD and the content of MDA(P<0.05)in the roots and leaves of rice seedlings.Selenium treatment significantly increased the activity of GSH-Px in rice seedlings,and ameliorated the oxidative stress caused by As stress,resulting in significant reduction in MDA content in the root and leaf of rice seedlings treated high level As treatment.4.As treatment induced the formation of phytochelatins in rice seedling.The content of GSH and NPT in rice leaves and roots is positively correlated with their content of As.Under low As treatment condition,adding Se into solution reduced the GSH content of leaves and the content of NPT and PCs of root.Under high As treatment condition,with the increase of Se levels in solution,the content of GSH in leaves and roots of rice increased first and then decreasedand reached the maximum value at 5?mol/L Se level,while the content of the NPT and PCs in root decreased at first then increased and reached the maximum value was at 10?mol/L Se level.5.Compared with the low S level(0.25mmol/L),the high S level(1.25mmol/L)promoted the uptake of arsenic by rice seedlings.The content of As on the shoot and root of rice seedlings at the high S level were about 1.2 times times and 1.38-1.51 times that of low S treatment,respectively.The inhibitory effect of Se on the uptake of arsenic by rice seedlings was independent of S levels.However,the inhibitory effect of As on the content of Se in seedling was stronger at high S levels than at lowS level.Under the high S level and the low S level condition,arsenic reduced the content of Se of shoot by 62.3% and 21.3%,respectively.6.Organic selenium(SeCys and SeMet)is the dominant component in the upper part of rice seedlings,accounting for about 80%.The organic selenium and inorganic selenium in the roots are about 42%-63% and 37%-58%,respectively.Increasing sulfur levels in solution increased the percentage of organic selenium in rice seedlings.Arsenic treatment increased the percentage of organic selenium in the roots.In addtion,the percentage of SeMet in rice roots and shoots was increased,but the SeCys percentage was decreased by arsenic treatment.7.High S treatment promoted the synthesis of thois compounds in the roots of rice seedlings by As stress.The contents of GSH?NPT and the GSH/GSSG ratio at high S level were 1.16-1.34 times,1.14-1.54 times and 1.09-2.17 times of those treated with low S treatment,respectively.Under the As stress condition,the effect of Se on the thols content was related to the S level: 10?mol/L Se enhanced the content of GSH and reduced GSH/GSSG ratio of root at high S level;while Se treatment had no effect on the content of GSH,and increased GSH/GSSG ratio and reduced the content of NPT in root at the low S level.8.Under the condition of no As and high As treatment,the high S level promoted the growth of rice seedling,such as imcreasing the activity of antioxidant enzymes,decreasing the content of MDA and improving the height and biomass of plant.The S and Se has the interactive effects on the content of MDA.Compared with at high S level,adding Se into solution at the low S level had better effect on alleviating the oxidative stress and reducing MDA content of rice seedlings.