The Alleviating Effect And Mechanism Of Selenium With Different Valencv On Tobacco Seedlings Under Salt Stress

In order to explore the effects of exogenous addition of sodium selenite and sodium selenate on physiological characteristics and gene expression of tobacco seedlings under salt stress.Using Hoagland nutrient solution,the salt-sensitive tobacco variety Yunyan 87 was used as the test material to study the growth,photosynthetic characteristics,osmotic adjustment ability,antioxidant system and genes of tobacco seedlings by adding sodium selenite and sodium selenate under salt stress.The effect of expression,and the analysis of the expression of related genes reveals the physiological mechanism of different valence selenium alleviating the salt stress of tobacco,which provides a theoretical basis for the application of selenium fertilizer in the future to improve the salt tolerance of tobacco.The main conclusions are as follows:(1)Under salt stress(150 mmol/L NaCl),the dry weight and leaf area of tobacco seedlings decreased significantly,and the root lengthy root surface area,root diameter,root volume and root vigor of the roots decreased significantly.After the application of exogenous selenium,the root vigor,root length,root surface area,root diameter and root volume of tobacco seedlings under salt stress increased significantly,and at the same time,the dry matter accumulation and leaf area of tobacco seedlings were increased,and the growth of tobacco seedlings under salt stress was significantly improved.Biomass and root growth.Sodium selenate has a better effect on promoting root elongation and root vitality,and sodium selenite has a better effect on promoting root thickness.(2)Salt stress reduced the stomatal conductance,transpiration rate,net photosynthetic rate and chlorophyll content of tobacco seedlings.After applying exogenous selenium,the photosynthetic characteristics of tobacco seedlings under salt stress were significantly improved.Compared with salt stress,the stomatal conductance and net photosynthetic rate were significantly increased,the chlorophyll content was significantly increased,and the effect of dilute sodium was good.(3)Compared with the control,the reactive oxygen species(H2O2 and O2-)content,malondialdehyde(MDA)content,relative conductivity,AsA content and GSH content of tobacco seedlings under salt stress increased significantly,SOD,POD,CAT,APX and GR activity decreased significantly.After applying exogenous selenium,active oxygen content,malondialdehyde content and relative conductivity decreased significantly,antioxidant enzyme activity and GSH content increased significantly,selenium alleviated the oxidative stress caused by salt stress,and sodium selenate had a better alleviation effect.(4)The osmotic stress caused by salt stress is mainly manifested as:the content of K+and Ca2+in the leaves of tobacco seedlings decreased significantly under salt stress,and the soluble sugar,free proline,Na+/K+and Na+/Ca2+increased significantly.The application of exogenous selenium can effectively alleviate osmotic stress.The contents of K+,Ca2+,soluble sugar and free proline are significantly increased,and Na+/K+and Na+/Ca2+are significantly reduced.Sodium selenite has a better effect on increasing the content of osmotic adjustment substances,and sodium selenate has a better effect on increasing ion content.(5)Fluorescence quantification of the relative expression of salt-tolerant genes in tobacco,the results showed:Compared with the control,the relative expression of NtAREB under salt stress was significantly reduced by 46.30%,and the relative expression of NtROS2a and NtLEA5 were increased by 1.63 times and respectively 4.09 times.The application of exogenous selenium significantly increased the relative expression levels of NtAREB,NtNAC2,NtCDPK12 and NtROS2a under salt stress.Among them,the relative expression levels of NtAREB and NtROS2a under NaCl+Se(Ⅳ)treatment were significantly higher than those under NaCl+Se(Ⅵ)treatment,NtNAC2 and NtCDPK12 The relative expression of NtLEA5 was the highest under NaCl+Se(Ⅵ)treatment;however,NaCl+Se(Ⅳ)and NaCl+Se(Ⅵ)treatments significantly reduced the relative expression of NtLEA5.In short,salt stress inhibited the growth and development of tobacco seedlings.Exogenous addition of sodium selenite and sodium selenate can significantly improve the salt resistance of tobacco seedlings.Under salt stress,selenate up-regulates the expression of NtNAC2 and NtCDPK12,thereby increasing the antioxidant enzyme activity and net photosynthetic rate of tobacco seedlings.It plays a role in maintaining the integrity of cell membranes,protecting cell structure,and regulating ion balance to alleviate salt stress.And selenite,by up-regulating the expression levels of NtAREB and NtROS2a,plays a role in promoting root thickness,removing active oxygen,and promoting the synthesis of osmotic regulators to resist salt stress.