Effects of sodium nitroprusside on alleviating magnesium deficiency of cucumber seedlings under NO^-₃ stress

【Objectives】Soils in the protected cultivation show serious secondary salinization, resulting in magnesium deficiency symptoms of plants. To explore effect of exogenous nitric oxide donor on alleviating magnesium deficiency under NO- 3 stress in the experiment, the effect of exogenous nitric oxide donor(sodium nitroprusside, SNP)on growth of cucumber seedlings under magnesium deficiency was studied for providing a theoretical guidance to solving the problem of chlorosis of cucumber seedlings caused by magnesium deficiency. 【Methods】The hydroponic method was used to cultivate cucumber seedlings, and seedlings with three real leaves were treated, and a basic nutrient solution was prepared according to the Yamazaki formula. The concentration of magnesium was designed as two levels, Mg2+ 2 mmol/L and Mg2+ 1 mmol/L, and the concentration of nitrate was designed as two levels, NO-3 14 mmol/L and NO-3 140 mmol/L. 0.1 mmol/L SNP was applied to decrease the stress of magnesium deficiency and NO- 3 stress on cucumber plants, and 0.1 mmol/L SF(sodium ferricyanide) was used to observe influence of the SNP reaction products. The normal concentration of magnesium and nitrate treatment was set as control. NO- 3 was provided by Ca(NO3)2·4H2O and KNO3 (1∶1), and pH was adjusted by H2SO4 to keep at 5.5-6.5. 【Results】1) The plant height, leaf area and dry matter of cucumber seedlings are significantly lower under magnesium deficiency than those in the control, and the electrolyte leakage rate, the content of MDA and soluble protein of cucumber seedling leaves are increased significantly compared with the control under magnesium deficiency. The magnesium contents of roots, stems and leaves, the Pn, Ci, Gs, Tr, Fv/Fm and ΦPSⅡ,and the activities of SOD and POD of cucumber seedling leaves are decreased obviously compared with the control under magnesium deficiency. 2) The plant height, leaf area and dry matter of cucumber seedlings, the magnesium contents of roots, stems and leaves, the Pn, Ci, Gs, Tr, Fv/Fm and ΦPSⅡ,the activities of SOD and POD of cucumber seedling leaves are significantly decreased compared with the control under NO- 3 stress, while the electrolyte leakage rate, the contents of MDA and soluble protein of cucumber seedling leaves are increased significantly. 3) Under the combined stress of magnesium deficiency and NO-3 stress, the changes of plant growth indicators and physiological indexes of plant stress are more obvious. 4) 0.1 mmol/L SNP significantly increases plant height, leaf area and dry matter of cucumber seedlings, the magnesium contents of roots, stems and leaves, the Pn, Ci, Gs, Tr, Fv/Fm and ΦPSⅡ,soluble protein content, and the activities of SOD and POD of cucumber seedlings under the magnesium deficiency, NO-3 stress or their combined stress. On the contrary, 0.1 mmol/L SF does not show such effect. 【Conclusions】The growth of cucumber seedlings is significantly inhibited, and chlorosis is observed under the magnesium deficiency and/or NO-3 stress, and adding 0.1 mmol/L SNP could mitigate the inhibition of growth of cucumber seedlings, indicating that exogenous nitric oxide could decrease the injury of cucumber seedlings induced by magnesium deficiency and/or NO-3 stress through increasing salt tolerance of cucumber seedlings and magnesium absorption.