Effects Of The Overexpression Of CsNMAPK On Physiological And Biochemical Characteristics Of Cucumber Seedlings Under NO₃^-Stress

Cucumber （Cucumis sativus L.） is the major vegetable cultivar in plastic greenhouses inChina. However, problems with continuous cropping systems have become increasinglyserious as the greenhouse ages, for example, acidification, secondary salinisation, and animbalance of nutrients and microbial communities. A lot of studies indicated that the mainstress anion in greenhouse is NO₃^-. And many studies showed that mitogen-activated proteinkinase （MAPK） could be activated by varieties of stress conditions, and the activation ofMAPK could activate various cell responses and improve plant resistance to stress conditions.In this study, effects of over-expression of CsNMAPK on physiological and biochemicalcharacteristics of cucumber seedlings under NO₃^-stress were studied. It has importanttheoretical meaning to the creation of new salt cucumber germplasm and increase utilizationefficiency of protected cultivation.The cucumber seedlings of over-expression of CsNMAPK were obtained by multiplegenerations of selfing after ovary injection. On the basis of existing research, effects ofover-expression CsNMAPK on cucumber seedlings growth, antioxidant enzymes activity,nitroge metabolism related enzymes, and the over-expression of CsNMAPK improvingcucumber seedlings to NO₃^-salt tolerance mechanism was studied by nutrient solution cultureunder140mmol L^-1NO₃^-stress.1. After140mmol L^-1NO₃^-stress5days and10days, the over-expression transgenic lineshas lower absolute increment of plant height, higher absolute increment of leaf area than wildtype. The absolute increment of plant height and absolute increment of leaf area of T₃-54-Twas higher than T₃-61-T.2. For over-expression lines, after5days under140mmol L^-1NO₃^-stress, SOD and CATactivities were decreased in leaves and roots, while APX activity in roots was increased andthe contents of O₂^.-and H₂O₂were slightly decreased. After10days under140mmol L^-1NO₃^-stress，SOD, CAT and APX activities were decreased in leaves and roots.3. Under normal growth conditions, the NO content of T₃-54was lower than wild type,the NO content of T₃-61was higher than wild type. After140mmol L^-1NO₃^-stress5daysand10days, the over-expression transgenic lines had higher NO content than wild type,among them, T₃-54-T was slightly higher than T₃-61-T.4. After5days under140mmol L^-1NO₃^-stress, the NO₃^--N and NH4+-N content ofT₃-54-T was higher than wide tipe, T₃-61-T had lower NO₃^--N content, higher NH4+-Ncontent than wide tipe. But T₃-54-T and T₃-61-T had higher NO₃^--N and NH4+-N content than wide tipe after10days. After140mmol L^-1NO₃^-stress5days and10days, the activities ofNR of the over-expression transgenic lines was higher than wide tipe. The activities of GS,GOGAT and GDH of transgenic lines was higher than wide type after5days, while lowerafter10days.5. Twelve pBI121-CsNMAPK（+）lines were obtained by Agrobacterium-mediated. PCRresults showed that all plants were transgenic plants. Four plants were choosed fromtransgenic plants. Then the quantitative real-time PCR results showed that the mRNA levelsof CsNMAPK in transgenic plants varied but was enhanced3.43⁴2.91times compared to thecontrol plants. Southern blot showed that exogenous CsNMAPK integrated into the genomeby one copy.