Study On Mechanism Of Selenium Application Inhibiting Cadmium Absorption And Alleviating Cadmium Toxicity In Winter Wheat

Cadmium（Cd）is considered to be one of the most harmful heavy metals.It is generally believed that plants are the main source of Cd for human beings.Wheat is one of the main food crops in North China.Cd contaminated wheat may cause anemia,osteoporosis,kidney damage and other diseases.Selenium（Se）is an essential trace element for human beings and animals and a beneficial element for plants.In recent years,many studies have shown that Se and Cd have antagonistic effects in plants.Therefore,the effects of Se application on Cd uptake and accumulation,subcellular distribution,chemical extraction of Cd,expression of Cd uptake and transport related genes,transcriptome analysis,antioxidant system and cell ultrastructure of winter wheat were studied by hydroponic experiment,which provided a theoretical basis for revealing the possible mechanism of Se inhibiting Cd uptake by wheat.The main results are as follows:1.Under Cd stress,Se application significantly reduced Cd content,accumulation in shoot and root,Cd migration from root to shoot and average root diameter,but increased root length,surface area and root volume of winter wheat..2.Under Cd stress,the concentration of Cd in root and shoot cell wall,soluble part and organelle of winter wheat were significantly decreased by Se application.Se application decreased the distribution of Cd in root and shoot organelles,but increased the distribution of Cd in shoot soluble components and root cell wall.Under Cd stress,the application of Se reduced the active Cd（ethanol extract Cd and deionized water extract Cd）in root and promoted the transformation of active Cd to inert Cd in roots.3.The variation characteristics of Cd accumulation in wheat root with time accorded with Michaelis equation.At the levels of Cd5 and Cd20,the Imax value of wheat root without Se application was the highest.The maximum accumulation of Cd in wheat root was decreased after adding Se.At the level of Cd5,the addition of 5 and 10 μM Se increased the affinity and actual absorption capacity of wheat root for Cd,while at the level of Cd20,the addition of Se decreased the affinity and actual absorption capacity of wheat root for Cd.4.With the increase of Cd stress,the expression of Ta Nramp5-a,Ta Nramp5-b,Ta HMA3-a,Ta HMA3-b and Ta HMA2 in winter wheat root increased significantly.Under Cd stress,Se application decreased the expression of Ta Nramp5-a,Ta Nramp5-b and Ta HMA2 in root.Under Cd stress,phenylpropanoid biosynthesis,glutathione metabolism and other secondary metabolic pathways and plant hormone signal transduction pathways in wheat have a positive response.Under Cd stress,the upregulated genes were mainly enriched in nine metabolic pathways: tyrosine metabolism,α-linolenic acid metabolism,steroid biosynthesis,fatty acid degradation,glycolysis/gluconeogenesis,phenylpropane biosynthesis,but the down regulated genes were only enriched in phenylpropane biosynthesis.5.Under Cd stress,the production rate of O₂^-· and the content of H₂O₂,MDA,NPT and PCs in wheat tissues were significantly increased.Se application increased APX activity,GSH and ASA content,NPT and PCs content in leaves,restored SOD and POD activity to control level,and decreased O₂^-· production rate,H₂O₂ Content and MDA content.6.Under Cd stress,the addition of Se increased the lignin content and mechanical strength of root cell wall at 9cm.Under Cd stress,chloroplast,mitochondria and cell wall of winter wheat tissue cells were damaged most obviously.The main manifestations were chloroplast deformation,starch grain dissolution,chloroplast matrix thinning,mitochondria swelling and disintegration,cell wall deformation,unsmooth and sediment inside.Se application alleviated the toxic effect of Cd on organelles.