The Physiological Response Of Cucumber Grafted Seedlings To NO₃^- Stress

Over fertilization and no rainout during the special environment offacility production,easy to cause the secondary salinization of greenhouse soilwhich could seriously affected the growth and decreased the yield and quality．As one of the most widely planted protected vegetable crops,cucumber(Cucumis sativus L．)is a fertilizer loving but intolerant crop with theshallow roots which has much more risks in secondary salinization．Soilsecondary salinization has already become one of main obstacles in cucumberfacility production,and the main stress anion is N0₃^-．Grafting could welldevelop the root system and plays important roles in enhancement of nutrientand water uptake．Secondly,grafting could effectively prevent the diseasesand insect pests,reduce stress damage,increase stress resistance and improveeconomic benefit．The discussion on nitrate stress mechanism of graftingcucumber has important significance on cucumber sustainable production andalso the improvements on utilization ratio of horticulture facility．We studied the physiological response of nitrate stress on the basis ofpresent foundation with hydroponics．Results are as follows:1．Grafting can significantly increase the growth of the plant,onlyself-grafted seedling decreased a little compared with scion—root seedling．N0₃^- stress significantly inhibit the seedling growth,decrease the netphotosynthetic rate,chlorophyll fluorescence rate,photosynthetic capacity,NR,GS,GOGAT activities,and also normal proceeding Of photOsynthesis andnitrogen metabolism．Indexs of grafted seedling(ZJ,YJ)were significantlyhigher than that of the scion—root seedling whether the plants were under saltstress or not．The most obvious was YJ,with the lowest inhibition degree andhigh level of each index．ZJ and YJ cucumber seedlings all could improve thephotosynthetic capacity and nitrogen metabolism enzyme activity under N0₃^- stress to reduce the damage degree and enhance the salt resistance ability,andremission effect 0f YJ is more obvious 2．N0₃^- stress caused different levels of injury on cucumber seedling,alsolowered markedly the activities of SOD,CAT,POD,APX,increased theelectrolyte permeability,also the content of MDA,Pro,soluble sugar,solubleprotein,N0₃^- and NH₄⁺．SOD,POD,CAT,APX activities．And Pro,solublesugar,soluble protein content of grafted seedling were significantly higherthan scion—root seedling．Electrolyte permeability,MDA,N0₃^- and NH₄⁺contents were significantly lower than scion-root seedling,and YJ is betterthan ZJ．It showed that grafting could reduced the membrane lipid peroxidelevel,keep complete structure of chloroplast and mitochondria,accumulatedmore osmotic adj ustment material,regulated the osmotic potential and keepwater balance,decreased the contents of N0₃^- and NH₄⁺ to relief the injury．And YG'S effect was better．3．9 days after N0₃^- stress treatment,the leaf and root contents of ZT,IPA,GA,IAA decreased significantly．with ABA content increased．Whetherunder N0₃^- stress or not,ZT,IPA,GA,IAA content of grafted seedling(ZJ,YJ)were significantly higher than scion?root seedling,and the highest contentwas YJ which suggests that grafting could regulated the endogenousphytohormones metabolism to enhance the salt resistance ability．Key words:Cucumberï¼›Grafted seedlingsï¼›Nitrate stressï¼›Antioxidantenzyme activityï¼›PhotOsynthesisï¼›Endogenous hormones content...