Effects Of Cucumber Seedlings’ Growth And Magnesium Absorbing On NO₃^-Stress Under Suboptimal Temperature

Cucumber (Cucumis sativus L.) is one of the most important vegetables in China, and is widely planted in greenhouse and outside field. The low light intensity, suboptimal temperature during the winter and soil salinization in solar greenhouse of northern China had inhibited protected vegetable sustainability production, leading to cucumber seedlings growth inhibition and leaf chlorosis,which could be due to the inhibitory effect of the suboptimal temperature and NO3-stress on growth, and the antagonistic absorption of potassium and calcium ion with magnesium ion. Researches indicated that exogenous nitric oxide(NO) could improve the resistance of plants to abiotic stress. But there is few study that exogenous nitric oxide(NO) mitigates the injury of cucumber seedlings induced by magnesium deficiency. Therefore, it has important theoretical and practical significance for mitigating the chlorosis induced by Mg deficiency by investigating effects of cucumber seedlings’growth and magnesium on NO3-stress under suboptimal temperature as well as exogenous NO on alleviating the stress of magnesium deficiency of cucumber seedlings under NO3-stress.In this experiment, to select cucumber varieties more suitable for solar greenhouse cultivation during the winter in northern China, effects of low light and suboptimal temperature on growth and antioxidant enzyme activities of cucumber seedlings were firstly investigated, Then, Effects of cucumber seedlings’growth and magnesium absorbing on NO3-stress under suboptimal temperature and effects of sodium nitroprusside on alleviating the stress of magnesium deficiency of cucumber seeding under NO3-stress were inveistigated. In order to establish theoretical formelation and propose new measures for mitigating the deficiency of green of cucumber seedlings. The main results are as follows:1. After14d low light intensity and suboptimal temperature stress,’Jinyou5’’Jinyoul’’Woyou2’and’Jinyou35’grew better. Under low temperature, lower electrolyte leakage was observed in’Jinyou5’’Jinyou35’’Jinyou3’and’Jinyoul’compared with’Xintaimici’’jinyan4’ and ’zhongnong9’. Compared with ’Xintaimici’ and ’zhongnong9,’Jinyou35’’Jinyoul’’Woyou2’ and ’Jinyou5’ showed lower chlorophyll concentrations under low temperature. Low temperature resulted in higher accumulation of soluble protein and antioxidant enzyme activities in ’Jinyou5’’Jinyou35’’Jinyoul’ and ’Woyou2’ Based on the observed results, it could be concluded that the adaptability of’Jinyou5’’Jinyou35’’Jinyoul’and’Woyou2’to low light intensity and suboptimal temperature was higher than the others. They are more suitable for cultivation during the winter in solar greenhouse of northern China.2. The growth, net photosynthetic rate (Pn), transpiration rate (Tr), Fv/Fm and OPSII of cucumber seedlings were significantly inhibited by NO3-stress under suboptimal temperature compared with control treatment. The contents of magnesium of cucumber seedlings were significantly decreased compared with control treatment, above results could be attributed to the inhibitory effect of the suboptimal temperature and NO3-stress on growth, and the antagonistic action of potassium and calcium with to magnesium. The magnesium deficiency symptoms of cucumber seedlings could be partly alleviated by increasing the concentration of magnesium ion in the nutrient solution.3. The growth parameter of cucumber seedlings, the chlorophyll contents, the contents of Mg2+, net photosynthetic rate (Pn), transpiration rate (Tr), stomatal conductance (Gs), intercellular CO2concentrations (Ci), Fv/Fm and OPS II were significantly increased by applying0.1mmolⅩL-1SNP. In addition, application of SNP had significant effects on enhancing contents of soluble protein, activities of superoxidase (SOD) and peroxidase (POD), and decreasing malondialdehyde (MDA) contents and electrolytic leakage of leaves. However, no significant effects could be observed by applying ferrocyanide (SF) on above parameters.