硝态氮对黄瓜子叶谷氨酰胺合成酶和谷氨酸脱氢酶活性的影响

在硝态氮存在或缺乏的条件下，测定了黄瓜(Cucumis sativus L．)种子萌发和子叶发育过程中子叶可溶性蛋白质含量以及谷氨酰胺合成酶(GS)和谷氨酸脱氢酶(NAD(H)-GDH)活性的变化。在子叶发育初期，无论外源氮存在与否，每对子叶可溶性蛋白质含量和GS、NADH—GDH、NAD^ -GDH活性随发育上升。在外源氮存在下，第4d后，可溶性蛋白质含量虽有所下降，但基本保持恒定；第6d后，GS和NADH—GDH活性逐渐降低，NAD^ -GDH却相反增高。但在无外源氮条件下，于第4d后，可溶性蛋白质水平以及GS、NADH—GDH和NAD^ -GDH活性都逐渐降低。在子叶发育的整个过程中，外源氮对GS和NAD^ -GDH活性有促进作用，尤其是在子叶发育的后期对NAD^ -GDH活性的促进更为明显。

Effect of Nitrate Nitrogen on Activities of Glutamine Synthetase and Glutamate Dehydrogenase during Development of Cucumber Cotyledon

The content of the soluble protein and the activities of glutamine synthetase and glutamate dehydrogenase were determined in the development of cucumber(Cucumis sativus L.) cotyledon at the presence or absence of nitrate. In the early days of the development, the level of the protein and the activities of GS, NADH-GDH, and (NAD~+-GDH) in each pair of cotyledons increased whether exogenous nitrogen was existent or not. After 4 days, the level of the protein was constant roughly, though it was declined little at the presence of the exogenous nitrogen. The activities of GS and NADH-GDH fell gradually, but NAD~+-GDH was raised markedly. At the absence of the exogenous nitrogen, the levels of the protein, GS, NADH-GDH, and (NAD~+-GDH) decreased gradually at the same stage. In the whole course of the development, the activities of GS and NAD~+-GDH increased by exogenous nitrogen, and NAD~+-GDH activity was promoted remarkably in the late stage of the development particularly.