Alleviating Effect And Mechanism Of Exogenous Selenium On Tobacco Seedlings Under Low Temperature Stress

Low temperature is one of the common non-biological factors that affect the growth and development of tobacco.Affected by geographical factors and the time of transplanting,the harm of "falling spring cold" to tobacco seedlings is widespread in the southern tobacco areas of China.Low temperature usually causes the phenomenon of"early blooming" of tobacco seedlings,so the opening of tobacco seedings caused by chilling often occurs.This sever issue resulting in a substantial reduction in the yield and quality of transplanted tobacco seedlings,and adversely affect the sustainable development of agriculture.Therefore,exploring the effect of applying exogenous substances on the cold resistance of tobacco seedlings and the physiological and biochemical mechanisms under low temperature conditions has certain guiding significance for improving the yield and quality of crops.In order to explore the differences in the responses of sodium selenate and sodium selenite to tobacco seedling physiological and partial cold resistance genes under low temperature stress,this topic uses flue-cured tobacco K326 as the test material,and studies the exogenous addition of selenium under low temperature stress at 4℃.The effects of sodium and sodium selenite on the growth and development of flue-cured tobacco,root vitality,photosynthetic pigment,antioxidant system,osmotic adjustment substances and genes related to cold resistance.The main conclusions are as follows:1.In this experiment,due to low temperature stress,the growth indicators of tobacco seedlings were significantly inhibited,and the leaf area and root length appeared to decrease,which caused the fresh weight,dry weight and roots of the tobacco seedlings.The fresh weight and dry weight are reduced.The application of exogenous selenium effectively alleviated the pressure on the growth of tobacco seedlings,increased the leaf area and root length under low temperature stress,and also increased the accumulation of biomass.Among them,sodium selenate has a positive effect on promoting leaf area and root growth under low temperature stress,while sodium selenite has a positive effect on promoting dry matter accumulation.2.The results of the study showed that the relative conductivity,MDA content,O₂^- content,H₂O₂ content,proline content and soluble sugar content increased significantly under low temperature stress,and decreased significantly after the application of exogenous selenium,all showing 4℃ The drop rate under+Se（Ⅵ）treatment was greater than 4℃+Se（Ⅲ）treatment.Under low temperature stress,root activity,photo synthetic pigment content,AsA content,GSH content,SOD activity,POD activity and CAT activity increased,while APX activity and GR activity decreased significantly,but the application of exogenous selenium further increased the tobacco Root vitality,photosynthetic pigment content,AsA content,GSH content,SOD activity,POD activity,CAT activity,APX activity and GR activity of seedlings.Except for root vitality and carotenoid content,other index data show 4℃+Se（Ⅵ）treatment is higher than 4℃+Se（Ⅳ）treatment.3.As the detection results of the relative expression of genes related to cold tolerance in tobacco,the relative expression of NtDREB1,NtERD1OB,NtNAC and NtCDPK increased significantly under low temperature stress,while the relative expression of NtbHLH and NtLDC1 decreased significantly.Compared with low-temperature treatment,the application of different exogenous selenium significantly increased the relative expression levels of NtDREB1,NtbHLH,NtNAC,NtERD10B and NtLDCl1 all of which showed that the relative expression levels under 4℃+Se（Ⅵ）treatment were higher than 4℃+Se（Ⅳ）Treatment.The relative expression level of NtCDPK showed a significant decrease,and the relative expression level under 4℃+Se（Ⅳ）treatment was higher than that under 4℃+Se（Ⅵ）treatment.In summary,different exogenous selenium can alleviate the damage to tobacco seedlings caused by low temperature stress and significantly promote the growth of tobacco seedlings under low temperature treatment.Exogenous selenium-mediated expression of NtDREBl,NtbHLH,NtNAC,NtERD1OB,and NtLDCl are all up-regulated,indicating that both sodium selenite and sodium selenate can promote the growth and development of tobacco seedling roots and improve leaf efficiency by regulating the transcription level of cold tolerance genes.The content of photosynthetic pigment increases the activity of antioxidant enzymes,thereby reducing oxidative damage and improving the cold resistance of tobacco seedlings.Among them,compared with sodium selenite,sodium selenate can more significantly up-regulate the expression of NtDREB1,NtbHLH,NtNAC,NtERD1OB,and NtLDC1,which can promote tobacco root growth,increase leaf photosynthetic pigment content,and increase antioxidant enzyme activity.It is more effective to enhance the cold resistance of tobacco seedlings.