The Effect Of Iso-osmotic NaCl And Ca?NO₃?₂ Stress On Proteome,Nitrogen Metabolism And Fruit Yield And Quality Of Cucumber

Cucumber,as an important horticultural crop,is easily affected by salinization,for their roots are weak and show preference for fertilier,but no tolerance to excess fertilier.Soil salinization has been a main barrier in protected cucumber production.In the soil of greenhouse cultivation,the main cation and anion are Ca2+and NO3-,SO42-,respectively,whereas Na+ and Cl-are the main forms of ions in the seaside or inland.Previous studies are more concentrated on the simplex stress,growth and physiological phenomena apparent of soil salinization on plants,while the repots of vegetable under NaCl and Ca?NO₃?₂ stresses,and the comparative studies are few.Therefore,this experiment was desighed to compare the iso-osmotic 84 mmol·L-1NaCl and 56 mmol·L-1 Ca?NO₃?₂ on the changes and the difference of growth,protemotic,activity of enzymes of nitrogen metabolism,gene expression of enzymes of nitrogen metabolism of cucumber seedlings,and fruit yield and quality of cucumber plant during fruiting period,cultivar 'Jinchun 2'?with less salt resistance?was used to carry out our experiment via hydroponics.The main results were presented as follows:1.The results showed that both salt stress inhibited plant growth,but the damage degree that under NaCl stress exceeded Ca?NO₃?₂ stress.NaCl stress significantly decreased the soluble protein content in leaves and roots.Ca?NO₃?₂ stress significantly increased the soluble protein content in leaves and roots.The patterns of SDS-PAGE profiles of root and leaf existed greatly differences between the treatments.To determine the different effect of two salt stresses on salt-responsive proteins in cucumber?Cucumis sativus L.cv.Jinchun No.2?roots,proteomic analysis was performed using two-dimensional electrophoresis?2-DE?and mass spectrometry.The expressions of 43 protein spots corresponding to enzymes were shown to change in response to salt stress.Of these,33 spots were identified by matrix-assisted laser desorption/ionization-time of flight mass spectrometry?MALDI-TOF/TOF MS analysis?.The proteins were categorized according to functional groups,including antioxidant and defense,energy and metabolism,amino acid metabolism,protein synthesis,folding and degradation,cell wall-related proteins,signal transduction and other functional.Cucumber seedlings appeared to resist Ca?NO₃?₂ stress via the expression of proteins involved in antioxidant and defense,SAMs biosynthesis,amino acid metabolism,and protein synthesis,folding,and degradation.Cucumber seedlings appeared to resist NaCl stress via the expression of proteins involved in antioxidant and defense,protein synthesis,and cell wall.2.In NaCl,the contents of NO3-significant decreased and the contents of NH4+significant increased.However,In Ca?NO₃?₂,the contents of NO3-significant increased and the contents of NH4+ significant decreased.Activities and expression of NR,GS,GOGAT in roots and leaves of cucumber seedlings were significantly decreased by both stressed,while activities of them were higher under Ca?NO₃?₂ stress.The activity of GDH in leaf and root remarkably decreased under NaCl stress,whereas it significantly enhanced under Ca?NO₃?₂ stress.Both salt stresses caused a significantly increased in proline content in leaf and root and free proline levels were higher in Ca?NO₃?₂ than in NaCl.Hence,cucumber seedlings can promote the degradation of NH4+,activate GDH pathway,promote nitrogen metabolism and induce the synthesis of Pro under Ca?NO₃?₂ stress,thereby showed stronger growth potential with respect to iso-osmotic NaCl stress.3.Salt stress significantly inhibited the growth of cucumber fruit.Determination of the quality of cucumber fruit showed that salt stress decrease the content of antitype vitamin c,soluble protein and total soluble sugar,increased the content of free amino acid,soluble solids and titratable acid.As a whole,the damage degree that under NaCl stress exceeded Ca?NO₃?₂ stress.