Study On The Ca（N〇₃）₂ Stress Resistance Of Cucumber Seeds And Seedlings By Inducing Exogenous BR

The study takes the composition features of protected cultivation soil as the entry point, by utilizing the experiment material, Improved Jinchun No.2, calcium nitrate Ca(NO3)2 as the salt stress reagent, and Brassinosteroid(BR) as the salt stress elicitors to conduct the experiment. The purpose of this study was to reveal the effect of BR application methods on cucumber seeds and seedlings under Ca(NO3)2(60mmol/L) stress. Treated the cucumber seedlings with different methods(0.01mg/L BR soaking seeds, 0.1mg/L BR spraying leaves and applying both of them). The plant morphology indexes, physiological indexes(Pro, Ss, MDA, POD), photosynthesis, chlorophyll fluorescence parameters and ultrastructure of leaves were measured. Explored the mechanisms of exogenous BR on induced plant salt tolerance. Provided a theoretical basis in finding an effective way to relieve the secondary salinization of soil.The main results are as follows:(1) Ca(NO3)2 stress resistance of cucumber seeds could be induced by certain concentration(0.005, 0.01, 0.05, 0.1, 0.2mg/L) BR soaking seeds. As the concentration of exogenous BR increased, the germination potential, rate, index, vigor index, and α-amylase activity of cucumber seeds under Ca(NO3)2 stress firstly raised and later reduced, and 0.01 mg/L BR can get the best result.(2) As the spraying concentration of exogenous BR(0.005, 0.01, 0.05, 0.1, 0.2mg/L) rise, firstly promoted and later inhibited the growth of cucumber seedlings. 0.1mg/L BR had the best effect on cucumber seedlings, but 0.2mg/L BR inhibited the cucumber seedlings growth.(3) Ca(NO3)2 stress resistance of cucumber seedlings can be induced by 0.01mg/L BR soaking seeds, 0.1mg/L BR spraying leaves or applying both of them, but the effects was different. In general, exogenous BR soaked with the best effect. Compared to Ca(NO3)2 stress, it could improve the height, stem diameter, number of expand leaves, leaf area, fresh weight, dry weight, the content of Pro, Ss, and MDA, POD activity, photosynthesis and chlorophyll fluorescence parameters of cucumber seedlings, and the difference reached significant level. At the same time, it could keep the number and arrangement uniformity of grana and stroma lamella, and maintain the structural of mitochondria complete. BR spraying leaves with the poorer effect. The arrangement of grana lamellae disordered and thylakoid became wrinkled after BR spraying leaves.(4) After production test, it can be found that, compared to check, exogenous BR soaking seeds(0.01mg/L) could improve the height, stem diameter, number of expand leaves, leaf area of cucumber seedlings under continuous cropping soil, and the difference reached significant level. It suggested that BR soaking seeds could alleviate the barrier of cucumber seedling growth caused by continuous cropping soil.