The Mechanism Of Selenium Absorption,Transformation And Regulation In Rice

Rice?Oryza sativa L.?is one of the major food crops in the world and plays an important role in supplementing various nutrients required by the human body.Selenium?Se?is an essential micronutrient for animals and humans,and it is also a beneficial element for plant growth and development.Most of soils in the world lack in selenium,which result in selenium deficiency in agricultural products and thus affect human health seriously.The production of Se-rich agricultural products is an important way to supply selenium for the human body.However,the safety threshold of human selenium intake?60-400?g/day?is relatively narrow.Thus,how to regulate selenium content in reasonable range is a valuable research issue.In this study,selenium content regulation in Se-rich rice was taken as the pointcut.A series of experiments with different reagents were employed to clarify the mechanisms of selenium absorption and distribution in rice,which aims to provide theoretical support and scientific methods for the production of safe Se-rich rice.The main results are as follows:1. The effects of exogenous selenium on Se absorption,distribution and speciation dynamic in different growth stages and young panicle differentiation stages of rice were studied by pot experiment.The result showed that organic Se including Se Cys and Se Met were the main selenium speciation in rice.Under 0.5-20mg/kg Se treatment,Se Cys and Se Met accounted for 9.0%-22.1%and 71.3%-77.8%in the young spike?pollen mother cell meiosis stage?,61.4%-75.6%and 9.9%-18.4%in brown rice,while their relative content decreased with the increase of selenium level.Under 10-20mg/kg high Se treatment,the inorganic Se,mainly Se?IV??13.7%-17.9%?and Se?VI??6.4%-10.3%?,appeared in brown rice.It is predicted that high Se treatment may cause damage to human health.According to the results of this study,<2.5 mg/kg soil selenium supplementation can be used as a safe dose for Se-rich rice production.2. Effects of soil addition of exogenous selenium?0.5-20 mg/kg?on nutrient absorption,antioxidant enzyme activity,growth and yield of rice were studied.The result showed that low level of Se??5 mg/kg?promoted rice growth,the rice height increased by 6.0%-19.9%and the rice yield increased by 6.1%-30.4%compared with the control.The appropriate Se?1.25-5mg/kg?application increased the CAT and GSH-Px activity,which increased by 104%-151%and 104%-121%compared with the control.What's more,the appropriate Se application increased the Fe,Zn,Cu and Mo content in rice shoots.3. The effects of exogenous Se on the transformation of soil Se forms and microorganism were analyzed.With the increase of Se treatment,the percentage of Fe-Mn oxide-bound Se decreased,while the organic-sulfide binding Se increased.The appropriate application of Se?1.25-5mg/kg?can increase the number and diversity of soil microorganisms,and rice rhizosphere microorganisms mainly exist in proteobacteria?41.21%-43.29%?,chloroflexi?13.43%-13.96%?,bacteroides?8.98%-9.89%?,acidobacteria?6.67%-9.23%?,firmicutes?3.85%-4.80%?,actinobacteria?3.67%-4.11%?and cyanobacteria?1.91%-3.09%?.4. The effects and mechanism of NO on the resistance to Se stress in rice were studied by hydroponic experiment.The result showed that NO increased the resistance of rice seedlings to Se stress and reduce the toxicity of high Se.Compared with high Se treatment,the addition of NO decreased the Se content in rice roots by 10%,and down-regulated the gene expression of Os PT2,Os SAMS1,Os SBP1 in root and Os PT2,Os CS,Os SBP1 in shoot,while the rice height and root length increased by 6.0%and20.9%,the net photosynthetic rate increased by 138%,the activity of SOD,POD,CAT increased by 292.0%,36.5%,207.3%.5. The effects of foliar spraying of sodium selenite combined with different nutrient elements on selenium and nutrient absorption in rice were studied by field experiment.The result showed that the plant height and yield of rice increased with the application of Se and ammonium fertilizer.The Se+?NH₄?₂SO₄and Se+NH₄NO₃treatment had the best effects,the plant height increased by 13.2%and 7.1%,and the yield increased by 18.9%and 2.6%,respectively.The Se content of brown rice was increased in all macroelement fertilizer treatments.The Se+NH₄NO₃ treatment had the best effect,and the Se content of brown rice increased 4.7 times than the single Se treatment.The Se content of brown rice was increased in all microelement fertilizer treatments.The Se+Chelated-Fe treatment had the best effect,and the Se content of brown rice increased 5.4 times than the single Se treatment.6. A hydroponic experiment was carried out to study the effects of several plant hormones on selenium uptake in rice.The result showed that all the hormones?IAA,GA₃,ETH,ABA,BL,SA?reduced the selenium content in roots and shoots of rice seedlings under high selenium stress.Under the premise of promoting rice growth,the IAA?1?M?,GA₃?0.1-1.0?M?,ETH?0.1-0.5mg/L?,ABA?0.1mg/L?treatment had a better effect,the root Se content of which decreased by 4.0%,3.0%-8.1%,1.3%-6.7%,19.0%,and the shoot Se content decreased by 13.4%,16.8%-30.4%,17.0%-30.1%,42.4%.7. The effects and mechanism of Me JA on alleviating Se toxicity of rice were studied by hydroponic experiment.The result showed that the lower concentration of Me JA treatment?0.1-1.0?M?increased the ability of rice to resist Se stress.Compared with the single Se treatment,the SOD,POD,CAT activity of Me JA treatment?0.1-1.0?M?increased by 38.6%-48.7%,34.1%-40.1%,251.0%-268.6%,and the MDA,H₂O₂content decreased by 14.3%-25.7%,15.2%-16.7%,respectively.The Me JA treatment?0.1-1.0?M?also down-regulated the gene expression of Os PT2,Os NIP2;1 in roots and Os PT2,Os NIP2;1,Os SBP1,Os CS in shoots,and decreased the absorption and accumulation of Se in rice.