| In recent years,the problems of soil secondary salinization and nutrient imbalance have become more and more serious.The main anions in greenhouse soil are nitrate ions,and the cations are mainly potassium and calcium ions.The accumulation of nitrate in the soil destroyed the ion balance and affected the plant growth seriously.Melatonin is an effective to improve the ability of plants to resist abiotic stresses.It can alleviate the harm of plants under abiotic stresses.Nitric Oxide is a plant signaling molecule that regulates a variety of physiological processes during plant growth and development and plays an important role in responding to external stresses.In this study,cucumber（Cucumis sativus L）variety"Jinyou 1"was used to study the effects of melatonin and nitric oxide on the plant morphology of cucumber seedlings under 75 mmol·L-1 nitrate stress.Plant morphology of cucumber seedlings;the effects of photosynthetic performance and oxidation resistance,as well as the alleviation effect of exogenous melatonin and nitric oxide interaction on cucumber seedlings and their root morphology.The main findings are as follows:1.Exogenous addition of 2μmol·L-1 melatonin or 100μmol·L-1 sodium nitroprusside can alleviate the growth inhibition of cucumber seedlings by nitrate stress,reduce the degree of membrane lipid peroxidation,and increase the osmotic adjustment substances flavonoids and soluble total sugar in leaves content,increase the net photosynthetic rate,leaf area,plant height,stem thickness,and promote the accumulation of biomass.2.Exogenous melatonin reduces the content of reactive oxygen in the leaves of cucumber seedlings under salt stress,increases the chlorophyll content,enhances the photochemical activity of the PSII reaction center,and promotes the absorption rate of N,P,K,Ca,Mg and Fe in cucumber seedling root under salt stress,and promoted the growth of cucumber seedling.3.Exogenous melatonin increased root volume,root length,root surface area,lateral root number and total root tip number of cucumber seedlings,which promoted root growth and development under nitrate stress,it affects the root morphology of cucumber seedlings by changes NO content in downstream signal.4.Exogenous MT will up-regulate the expression of NO synthase gene in the roots of cucumber seedlings under salt stress,increase the endogenous NO content,and it is positively correlated with the content of melatonin.Expression of ABA-degrading enzyme gene,and promote ABA content.Also up-regulate the expression of Cs AUX1,promote IAA transport,last increase the ratio of IAA and ABA content and induce the up-regulation of adventitious root specific expression genes Cs ARL,Cs GH3.5.Finaly promote root growth and increase root absorption of elements,alleviate the growth inhibition of cucumber seedlings.. |
