Effects Of Different Degrees Of Drought On Growth And Protein Expression Of Soybean Leaves At Seedling Stage

With the change of climatic conditions,extreme weather occurs frequently and lasts for a long time.Among them,drought is the main factor limiting crop growth.Soybean has the characteristics of high oil and high protein,and is an important food crop and oil crop in China.However,drought will adversely affect soybean growth and pose a threat to China ’s food security.This experiment was carried out in the experimental station of Northeast Agricultural University in 2022,using sand culture.The experimental materials were drought-tolerant soybean variety Heinong 44(HN44)and sensitive variety Heinong 65(HN65).PEG-6000(hereinafter referred to as PEG)with concentrations of 5 %(TI),10 %(T2),15 %(T3)and 20 %(T4)was used to simulate different degrees of drought conditions for 18 days.The response characteristics of soybean leaves to different degrees of drought stress at seedling stage were explored,and the changes of morphology,relative water content,membrane lipid peroxidation,osmotic adjustment substances,antioxidant enzyme activity,key enzyme activity of carbon and nitrogen metabolism,photosynthetic characteristics and protein expression level with stress time under different degrees of drought were clarified,which provided certain theoretical basis and practical experience for drought-resistant cultivation of soybean.The main results are as follows :(1)Drought stress caused serious damage to HN44 and HN65.The plant height,leaf area,leaf dry weight gain and relative water content(RWC)of the two varieties decreased with the prolongation of stress time,and the malondialdehyde(MDA)content increased with the prolongation of stress time.The effects of different treatments from small to large were T1 < T2 < T3 < T4.HN44 showed better adaptability under different degrees of drought.(2)Drought stress changed the osmotic regulation and antioxidant capacity of HN44 and HN65.The content of osmotic adjustment substances in the two varieties increased,and the content of proline(Pro)increased with the prolongation of stress time under different degrees of drought.The content of soluble sugar(SS)increased with the prolongation of stress time under T1 and T2 treatments,and increased first and then decreased under T3 and T4 treatments,and the peak appeared on the 12 th day.The change of soluble protein(SP)content in HN44 was basically consistent with SS content,but HN65 showed an increasing trend with the prolongation of stress time under different drought degrees.The content of osmotic adjustment substances in different degrees of drought showed T1 < T2 < T3 < T4,and the increase of osmotic adjustment substances in HN44 was greater than that in HN65.Drought stress increased the activities of antioxidant enzymes in leaves of HN44 and HN65.The activities of superoxide dismutase(SOD),peroxidase(POD),catalase(CAT)and ascorbate peroxidase(APX)increased first and then decreased with the prolongation of stress time under different degrees of drought,and the higher the degree of drought,the greater the change of antioxidant enzyme activity.(3)Drought stress changed the ability of sucrose metabolism and nitrogen metabolism in HN44 and HN65 leaves.Sucrose synthase(SUS)increased first and then decreased with the prolongation of stress time under different degrees of drought,and the higher the degree of drought,the greater the decrease.The activity of sucrose phosphate synthase(SPS)showed an increasing trend under T1 treatment,while it increased first and then decreased with the prolongation of stress time under T2,T3 and T4 treatments.The higher the degree of drought,the greater the increase,and the peak appeared on the 12 th or 15 th day.The activity of nitrate reductase(NR)decreased with the prolongation of stress time under different degrees of drought,and the higher the degree of drought,the greater the decrease.The activity of glutamine synthetase(GS)increased first and then decreased with the prolongation of stress time under different degrees of drought.The peak of T1 treatment appeared on the 15 th day,and T2,T3 and T4 treatments appeared on the 12 th day.The higher the degree of drought in the early stage of stress,the higher the activity,and the later stage of stress.(4)Drought stress weakened the photosynthesis of HN44 and HN65 leaves and reduced the efficiency of light energy conversion.Under different degrees of drought,the maximum fluorescence(Fm),initial fluorescence(F0),primary light energy conversion efficiency(Fv/Fm),actual photosynthetic efficiency(Phi2),non-regulatory energy dissipation quantum yield(Phi NO)showed a decreasing trend with the prolongation of stress time,and the quantum yield of regulatory energy dissipation(Phi NPQ)showed a rising trend,and the higher the degree of drought,the greater the change.The photosynthetic capacity of HN44 decreased less than that of HN65.(5)A total of 86 differential proteins were identified in HN44,of which 48 were up-regulated and38 were down-regulated.These differential proteins are involved in energy metabolism,signal transduction,stress response and other biological processes.A total of 68 differential proteins were identified in HN65,of which 55 were up-regulated and 13 were down-regulated.These differential proteins are involved in biological processes such as stress response,substance hydrolysis,redox and energy metabolism.The way of soybean with different drought resistance to drought stress was determined.Drought stress changed the pathway of carbohydrate metabolism and the content of amino acids in soybean.