College of Horticulture, Nanjing Agricultural University, Weigang 1, Nanjing 210095, Jiangsu Province, China.
J Plant Physiol. 2011 Jul 15;168(11):1217-25. doi: 10.1016/j.jplph.2011.01.022. Epub 2011 Apr 1.
We investigated the effects of short-term root-zone hypoxic stress and exogenous calcium application or deficiency in an anoxic nutrient solution on nitrogen metabolism in the roots of the muskmelon cultivar Xiyu No. 1. Seedlings grown in the nutrient solution under hypoxic stress for 6d displayed significantly reduced plant growth and soluble protein concentrations. However, NO₃⁻ uptake rate and activities of nitrate reductase and glutamate synthase were significantly increased. We also found higher amounts of nitrate, ammonium, amino acids, heat-stable proteins, polyamines, H₂O₂, as well as higher polyamine oxidase activity in the roots. In comparison to the reactions seen under hypoxic stress, exogenous calcium application led to a marked increase in plant weights, photosynthesis parameters, NO₃⁻ uptake rate and contents of nitrate, ammonium, amino acids (e.g., glutamic acid, proline, glycine, cystine, γ-aminobutyric acid), soluble and heat-stable proteins, free spermine, and insoluble bound polyamines. Meanwhile, exogenous calcium application resulted in significantly increased activities for nitrate reductase, glutamine synthetase, and glutamate synthase but decreased activities for diamine and polyamine oxidase, as well as lower H₂O₂ content in roots during exposure to hypoxia. However, calcium deficiency in the nutrient solution decreased plant weight, photosynthesis parameters, NO₃⁻ reduction, amino acids (e.g., alanine, aspartic acid, glutamic acid, γ-aminobutyric acid), protein, all polyamines except for free putrescine, and the activities of glutamate synthase and glutamine synthetase. Additionally, there was an increase in the NO₃⁻ uptake rate, polyamine oxidase activity and H₂O₂ contents under hypoxia-Ca. Simultaneously, exogenous calcium had little effect on nitrate absorption and transformation, photosynthetic parameters, and plant growth under normoxic conditions. These results suggest that calcium confers short-term hypoxia tolerance in muskmelon, most likely by promoting nitrate uptake and accelerating its transformation into amino acids, heat-stable proteins or polyamines, as well as by decreasing polyamine degradation in muskmelon seedlings.
我们研究了短期根区缺氧胁迫以及外源钙应用或缺乏对缺氧营养液中亚西瓜品种 Xiyu No.1 根系氮代谢的影响。在缺氧胁迫下生长 6 天的幼苗表现出明显的生长和可溶性蛋白浓度降低，但硝酸根吸收速率和硝酸还原酶和谷氨酸合酶的活性显著增加。我们还发现根中硝酸盐、铵盐、氨基酸、热稳定蛋白、多胺、H₂O₂含量以及多胺氧化酶活性更高。与缺氧应激下的反应相比，外源钙的应用导致植物重量、光合作用参数、NO₃⁻吸收速率和硝酸盐、铵盐、氨基酸（如谷氨酸、脯氨酸、甘氨酸、胱氨酸、γ-氨基丁酸）含量明显增加，可溶性和热稳定蛋白、游离腐胺和不溶性结合多胺含量增加。同时，外源钙的应用导致硝酸还原酶、谷氨酰胺合酶和谷氨酸合酶的活性显著增加，而二胺和多胺氧化酶的活性降低，以及根中 H₂O₂含量降低，在缺氧暴露下。然而，营养液中的钙缺乏会降低植物重量、光合作用参数、NO₃⁻还原、氨基酸（如丙氨酸、天冬氨酸、谷氨酸、γ-氨基丁酸）、蛋白质、除游离腐胺外的所有多胺以及谷氨酸合酶和谷氨酰胺合酶的活性。此外，在缺氧条件下，NO₃⁻吸收速率、多胺氧化酶活性和 H₂O₂含量增加。同时，外源钙对正常条件下的硝酸盐吸收和转化、光合作用参数和植物生长几乎没有影响。这些结果表明，钙赋予了西瓜短期缺氧耐受性，这可能是通过促进硝酸盐的吸收并加速其转化为氨基酸、热稳定蛋白或多胺，以及减少西瓜幼苗中多胺的降解来实现的。
