Effects Of Grafting With Salt-tolerant Pumpkin Rootstock On Carbohydrate Metabolism In Cucumber Seedlings Under Ca?NO₃?₂ Stress

The secondary Stalinization of protected horticulture is becoming increasingly severe,mainly due to mismanagement in production practice of protected cultivation and over fertilization,which severely limits vegetable sustainable development.Studies have shown that soil Stalinization lead to facilities disorder characterized by accumulation of high levels of NO₃^-and Ca²⁺.Cucumber?Cucumis sativus L.?is one of the most popular cultivation vegetables.Cucumber roots are weak and sensitive to salt stress.Grafting with salt tolerant rootstock can alleviate the injuries caused by salt,which is an easy-doing,low cost and effective way.Recently,many researches on grafting techniques and salinity tolerance physiology of grafted cucumber focused on NaCl stress and the injuries of growth and yield caused by salt.And little known about how rootstock-grafting regulate carbohydrate metabolism.In the present study,we use 'Jinyou No3' a major cultivar in greenhouse as scion,and 'Qingzhen Nol'?Cucurbita maxima×Cucurbita.moschata?a salt tolerant cultivar as rootstock,the differences Since the root grafting and rootstock grafted carbohydrates difference changes mechanisms and between self-grafted and rootstock-grafted cucumber seedlings under 80 mmol-L^-1 Ca?NO₃?₂ was studied.The main results were as follows:1.The growth of self-grafted seedlings was significantly inhibited after the treatment of Ca?NO₃?₂ stress,whereas the inhibition of growth was alleviated in pumpkin rootstock-grafted seedlings.Ca?NO₃?₂ stress increased the contents of the total soluble sugar,sucrose and fructose,but decreased the starch content in rootstock-grafted leaves.However,compared with self-grafted plants,rootstock-grafted seedlings were observed with a higher content of sucrose and total soluble sugar?TSS?under salt stress.Rootstock-grafted seedlings exhibited higher activities of acid invertase?AI?,neutral invertase?NI?and phosphate sucrose synthase?SPS?of sucrose metabolism in leaves than that of self-grafted seedlings under salinity.These results suggest that the rootstock-grafting improved salt tolerance,which might play a role in elevated sucrose metabolism.2.Under Ca?NO₃?₂ stress,the activities of fructokinase?FK?,hexokinase?HK?,phosphofructokinase?PFK?and pyruvate kinase?PK?of glycolysis were maintained at a higher level in leaves of rootstock-grafted seedlings after Ca?NO₃?₂ stress.And Ca?NO₃?₂ induced the accumulation of 3-PGA and phosphoenolpyruvate in the leaves of self-grafted cucumber seedlings,inhibited the activities of phosphoenolpyruvate carboxylase?PEPC?and Enolase?ENO?.Additionally,rootstock-grafting decrease the high percentage enhancement of key enzymes gene expression in glycolysis in the scion leaves of cucumber seedlings induced by salt stress.These results indicate that the rootstocks can maintain a high level of glycolytic pathway when exposed to salt stress.3.Succinic acid and malic acid content and isocitrate dehydrogenase?IDH?,succinate dehydrogenase?SDH?and malate dehydrogenase?MDH?activities were decreased significantly in TCA of self-grafted seedlings under salt stress.However with salinity,key glycolytic enzymes?PEPC,ENO,SDH,MDH?activities and the content of the TCA cycle intermediates?citrate acid,succinic acid and malic acid?in leaves of rootstock-grafted seedlings were significantly greater than that of self-grafted seedlings.Under salt stress,the IDH,SDH and MDH isozymes of rootstock-grafted cucumber seedlings were increased.Furthermore,the ATP content in leaves of rootstock-grafted seedlings significantly higher than those of self-grafted seedlings under salt stress,and the content of ADP was opposite.These results indicate that rootstock-grafting alleviate the inhibition of glycolytic pathway and TCA cycle in leaves of cucumber seedlings induced by Ca?NO₃?₂ stress.Which could helpful of the respiratory metabolism of cucumber seedlings and maintain a high ATP synthesis level,thereby increasing the salt tolerance of cucumber seedlings.4.Under Ca?NO₃?₂ stress,Rootstock-grafting had no significant effect on the number of the bearing fruits per plant and water content.However,the skin color of rootstock-grafting cucumber is dark green,and the L/D index is minimum.But physiological characteristics of cucumber fruits showed that,compared with self-grafting cucumber,the content of titratableacid and free amino acid in rootstock-grafting were lower with salt stress.However,the content of soluble protein,soluble sugar,fructose,sucrose and glucose in rootstock-grafting cucumber were higher than that of self-grafting cucumber,and the activites of source metabolism were higher.It show rootstock-grafting may alleviate injures of cucumber fruit caused by salt stress and improving the flavor and palatability of cucumber through improving the appearance properties and nutritional characteristics.