蔗糖对不同氮源培养下水稻根部氨同化相关酶活性的影响

糖、有机酸以及氨基酸影响碳-氮代谢过程中的相关酶的基因表达和活性。将蔗糖分别加入到含有相同氮素浓度的（NH4）2SO4（NH4^＋）或丙氨酸（Ala）作为氮源的营养液中培养水稻，测定幼苗根的谷氨酰胺合成酶（GS）、依赖于NADH的谷氨酸合酶（NADH-GOGAT）、磷酸烯醇式丙酮酸羧化酶（PEPC）和依赖于NADP的异柠檬酸脱氢酶（NADP-ICDH）的活性。结果显示，蔗糖诱导NH4^＋氮源中幼苗根的GS、NADH-GOGAT活性，抑制Ala氮源中幼苗根的这两种酶活性，蔗糖对PEPC和NADP-ICDH活性的影响也不同；未加蔗糖时，以Ala作为氮源的幼苗根的GS、NADH-GOGAT、PEPC和NADP-ICDH的活性明显高于以NH4^＋为氮源时的活性；生物量和蛋白质水平的变化与上述参数的变化基本一致。基于Ala碳骨架的存在，这些结果表明，碳／氮平衡是影响这些酶活性差别表达的主要原因。

Effects of Sucrose on the Activities of Enzymes Involved in Ammonium Assimilation in Roots of Rice Cultivated in Different Nitrogen Source

Sugar,organic acid and amino acids play important effects on gene expression and enzyme activities involved in carbon and nitrogen metabolism.With rice cultivating,sucrose was superinduced to the nutrient solution containing(NH_4)_2SO_4(NH~+_4) or L-Ala,which contained same nitrogen content,and then determined the activities of glutamine synthetase (GS),NADH-dependent glutamate synthase(NADH-GOGAT),phosphoenolpyruvate carboxylase(PEPC),NADP-dependent isocitrate dehydrogenase(NADP-ICDH).The results showed that sucrose induced markedly the enzyme activities of GS and NADH-GOGAT in roots of seedlings with NH~+_4 as the nitrogen source,however,inhibited them in roots of seedlings growing in L-Ala nitrogen source.Sucrose had different effects on the activity changes of PEPC and NADH-ICDH.Without sucrose supplementation,the activities of GS,NADH-GOGAT,PEPC,NADP-ICDH in the roots of rice seedlings growing in L-Ala nitrogen source were higher than that with NH~+_4 as the nitrogen source.The changes trend in biomass and protein content were coincident with the former parameters.Based on the additional carbon skeleton of Ala compared to(NH_4)_2SO_4,these resulted suggested that carbon/nitrogen balance play an important role in the different regulation of the enzyme activity.