| The protected cultivation of horticultural crops has expanded rapidly in recent years in China. Meanwhile, the secondary salinization of the protected horticulture is becoming increasingly severe, and has become an obstacle to limit vegetables production. Cucumber (Cucumis sativus L.) is one of the most popular cultivation conditions, and is sensitive to salt stress. In the present study, the effectiveness of grafting on salt tolerant rootstock can increase cucumber salt tolerance. However, a few researches on grafting techniques and salinity tolerance physiology of grafted cucumber have been carried out, which were mainly focused on NaCl stress, and few studies on physiological mechanisms of grafted cucumber in response to calcium nitrate stress have been reported. In this study, we use ’Qingzhen Nol’(Cucurbita maxima×Cucurbita. moschata) a salt tolerant cultivar as rootstock, and’Jinyou No3’a major cultivar in greenhouse as scion, grafting was made to compare the differences physiological mechanisms and proteomics between self-grafted and rootstock-grafted cucumber seedlings under60mmol·L-1Ca(NO3)2or90mmol·L-1NaCl stress. The main results were as follows:1. Under hight salt concentration60mmol·L-1Ca(NO3)2or90mmol·L-1NaCl treatment, the antioxidative systems of rootstock-Seedling were inhibited to varying degrees. The biomass and SOD, POD, CAT activity of’Qingzhen No.1’ were higher than other rootstock varieties, whereas its salt injury index, plasma membrane electrolytic leakage, MDA content and O2production rate were significantly lower than others. At the same time, Enzyme activity of the various rootstock under Ca(NO3)2stress were higher then ones of rootstock under NaCl stress, but its salt injury index, plasma membrane electrolytic leakage, MDA content and O2production rate were significantly lower than ones under NaCl stress. The antioxidative ability varied with different genotypes of rootstock under salt stress.’Qingzhen No.l’was less affected by salt stress and held high resistance to salt stress; Both salt inhibited the plant growth, the oxidative damage was much heavier under NaCl stress.2. That growth and antioxidant system were inhibited in rootstock-grafted and self-grafted seedlings under either Ca(NO3)2or NaCl stress. The activities of SOD, POD and CAT in rootstock-grafted seedlings were higher than self-grafted seedlings, while the index of salt injury, relative permeability of membrane, content of MDA and the production rate of Of were significantly lower. The response of iso-osmotic Ca(NO3)2or NaCl stress in cucumber seedling was different, compared to NaCl stress, the relative permeability of membrane, the content of MDA and the production rate of O2were lower in Ca(NO3)2stress, while the activities of SOD, POD, CAT and APX were higher in Ca(NO3)2stress. It is conclude that grafting with salt-tolerant pumpkin could removal the reactive oxygen species and reduce the injury of lipid peroxidation, which was beneficial for plant growth in iso-osmotic Ca(NO3)2or NaCl stress.The activities of APX, GR, DHAR, MDAR and the content of GSH and ASA, as did the ratio of GSH/GSSG in rootstock-grafted seedlings were significantly higher than self-grafted seedlings. The isozymes expression of SOD, POD, CAT and APX were significantly induced by either Ca (NO3)2or NaCl stress,3. Compared with self-grafted seedlings, the rootstock-grafted reduced content of Na+and Cl-and inhibited the loading from root endodermis to column catheter, which could maintain much Na+, Cl-in roots to prevent transport to shoots. The selective absorption and transport to shoots of K+, Ca2+, Mg2+was enhanced by grafting with salt-tolerant pumpkin, and increased the activities of plasma membrane H+-ATPase and tonoplast H+-PPase and corresponding gene expression to enhance the salt tolerance. NaCl stress cause ion stress by accumulation of Na+and Cl-in plant, while Ca (NO3)2stress mainly affect plant growth through osmotic stress by accumulation of Cl". The damage under NaCl stress was much heavier than those of under Ca (NO3)2stress.4. The photosynthetic pigment content, net photosynthetic rate (Pn), the stomatal conductance (Gs), water use efficiency (WUE), the actual photochemical efficiency of photosystem Ⅱ (ΦPS Ⅱ), the photochemical quenching (qP), the content and activity of rubisco, the expression of key genes of carbon assimilation in leaves of both rootstock-grafted and self-grafted seedlings were higher under Ca(NO3)2stress than those of under NaCl stress. Intercellular CO2concentration (Ci) was decreased by Ca(NO3)2 treatment, while was increased by NaCl treatment. The decline of Pn in seedlings was due to the decreased of Rubisco activity under NaCl stress.The photosynthetic pigment content, Pn, Gs, Ci, WUE, ΦPS II, qP, rubisco activity and content in rootstock-grafted seedlings were more higher than that of self-grafted seedlings under iso-osmotic Ca(NO3)2or NaCl stress. And the genes of RbcL (Rubisco large subunit), RCA (Rubisco activase) and PRK(5-phosphoribulokinase) were also up-regulated while RbcS (Rubisco small subunit) was down regulated by rootstock-grafted under salt stress. We concluded that grafting with salt-tolerant pumpkin could maintain higher activity of PS Ⅱ and carbon assimilation capacity.5. We compared the high resolution two-dimensional gel electrophoresis (2-DE) protein profiles of self-grafed and rootstock-grafted, and the intensity of58protein spots varied. Of these spots, the identities of55were determined by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and liquid chromatography electro-spray ionization tandem mass spectrometry.29protein spots were up-regulated in rootstock-grafted seedlings, and14protein spots were down-regulated. The intensity of48protein spots varied under Ca(NOs)2stress. Of these spots, the identities of45were determined by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and liquid chromatography electro-spray ionization tandem mass spectrometry.31protein spots were up-regulated in rootstock-grafted seedlings, and13protein spots were down-regulated. These proteins were related to photosynthesis, metabolism, defending against stress, protein biosynthesis and energy and transpor, respectively. Other proteins were related to unknown proteins. Moreover, that the transcript accumulation patterns of majority candidate proteins were consistent with protein accumulation patterns. These results imply that rootstock-grafting mediated leaves protein different accumulation patterns under salt stress. The identified proteins may play an important role in regulating adaptation activities following exposure to NaCl or Ca(NO3)2stress. |
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