Effects Of Overexpression Of StNHX1 Gene On Growth And Nitrogen Fixaton In Vegetable Soybean Under Salt Stress

Vegetable soybean[Glycine max(L.)Merr.],commonly known as 'mao dou',are favored by consumers in Asian countries such as China and Japan due to their abundant protein,amino acids and vitamins.Vegetable soybean is recognized as the world's safest green health care vegetables.Soft phospholipids contained in vegetable soybeans can improve brain memory and intelligence.Trace amounts of isoflavones can have effects on some slower diseases such as obesity,high cholesterol,and cardiovascular diseases.With the continuous expansion of domestic and international market demand,the cultivation area of vegetable soybeans has also increased.Therefore,it is of great significance to fully develop and use vegetable soybeans for the development of the vegetable industry in China.Soil salt stress is a common environmental problem in all countries of the world.Vegetable soybean is a salt sensitive plan.Salt stress is an important factor that restricts the growth of vegetable soybean and the process of nodulation and nitrogen fixation,thus seriously affecting the yield and quality of vegetable soybean.The wild eggplant StNHX1 gene encodes Na+/H+ antiporter,which plays an important role Inalleviating salt damage.NHX1 gene-encoded plant vacuolar Na+/H+ antiporter can compartmentalize Na+ accumulation in the cytoplasm of the plant under salt stress to the vacuole,reduce the Na+ content in the cytoplasm and promote the uptake of K+.By adopting sand culture,three homozygous lines(T4)preserved in our laboratory were used as experimental materials to study the difference of the growth and development,nodulation and nitrogen fixation between StNHcX1 genetically engineered vegetable soybean and non-transgenic vegetable soybean.The purpose of this study is to develop salt-tolerant vegetable soybean germplasma with effective nitrogen fixation.The main results are as follows:1.Sand culture method was used to study the effect of StNHX1 gene overexpression on the growth of vegetable soybean under salt stress.The results showed that the contents of K+and proline in leaves of transgenic plants were significantly higher than those of WT plants,the contents of Na+ and MDA were significantly lower than those of WT plants.Compared with WT plants,the net photosynthetic rate(Pn)of transgenic plants was increased significantly,the stomatal conductance(Gs)and transpiration rate(Tr)was increased,the intercellular CO2 concentration(Ci)was decreased significantly,indicating that the CO2 assimilation efficiency of the transgenic plants was higher.In addition,the relative chlorophyll content,leaf area,and relative water content of the transgenic plants were also significantly increased.The plant height,stem diameter,biomass and yield of transgenic plants were significantly higher than those of WT plants.These results indicate tihat overexpression of StNHX1 gene significantly enhanced the tolerance to salt stress of vegetable soybean under salt stress,which was beneficial to the growth and development of vegetable soybean.2.Sand culture method was used to study the effect of StNHX1 gene overexpression on the nodulation and nitrogen fixation of vegetable soybean under salt stress.The results showed that the number and dry fresh weight of nodule of the transgenic plants were significantly higher than those of the WT plants,and the leghemoglobin content,glutamine synthetase activity,total nitrogen of the plants were significantly higher than those of the WT plants.In addition,qRT-PCR showed that the relative expression levels of five key Ditrogen-fixing genes(GmENOD40a,GmENOD40b,GmLba,GmGS1?1,and GmGS1?2)in nodules of transgenic plants were significantly higher than those in WT plants.These results indicate that overexpression of StNHX1 gene significantly increased the nodulation and nitrogen fixation capacity of vegetable soybean under salt stress.