Effects of Exogenous Nitric Oxide on Seed Germination, Seedling Growth and Physiological Characteristics of Cucumber Under Osmotic Pressure

【Objective】The objective of this study was to investigate the effects of exogenous nitric oxide on seed germination,seedling growth,and physiological characteristics in osmotically stressed cucumber(Cucumis sativus L.).【Method】We used 25 % PEG-6000 to produce the osmotic pressure,under which the effects of sodium nitroprusside(SNP),an exogenous nitric oxide donor,were measured on seed germination,seedling growth,oxidative damage to leaves,and protective enzyme activities in cucumber.We carried out the aforementioned experiments at two concentrations of SNP: 0.1 and 0.5 mmol.L-1.【Result】The damage to cucumber caused by the osmotic stress of 25 % PEG-6000 was significantly reduced in the presence of 0.1 mmol.L-1 of SNP.Specifically,the seed germination rate,germination index,and vigor index increased by 0.24-fold,0.86-fold,and 3.01-fold,respectively;plant height,root length,and dry weight increased by 1.15-fold,2.17-fold,and 1.16-fold,respectively;proline content and enzyme activities of SOD,POD,CAT,and APX in leaves increased by 50.99 %,42.39 %,66.58 %,79.03 %,and 116.39 %,respectively;the level of malondialdehyde(MDA) in leaves decreased by 80.50 %.When the concentration of SNP was increased to 0.5 mmol.L-1,we observed a diminishing stimulative effect on cucumber seed germination and seedling growth.The oxidative damage to leaves sustained and the protective enzyme activities decreased when treated with 0.5 mmol.L-1 of SNP.【Conclusion】Based on data reported here,we conclude that SNP elicits a dose-dependent effect on the physiology of osmotically stressed cucumber.A lower concentration of SNP at 0.1 mmol.L-1 significantly stimulates cucumber seed germination and seedling growth,alleviates oxidative damage to leaves and increases the activity of SOD.A higher concentration of SNP at 0.5 mmol.L-1 is less effective in promoting germination,growth,and damage repair.The higher concentration of SNP also suppresses the activity of SOD.