Barsch Aiko, Carvalho Helena G, Cullimore Julie V, Niehaus Karsten
Proteom und Metabolomforschung, Fakultät für Biologie, Universität Bielefeld, Postfach 100131, D-33501 Bielefeld, Germany.
J Biotechnol. 2006 Dec 15;127(1):79-83. doi: 10.1016/j.jbiotec.2006.06.007. Epub 2006 Jun 21.
In symbiotic interaction with legume plants, bacteria termed Rhizobia can fix massive amounts of atmospheric nitrogen which is primarily provided in the form of ammonium to the host plants. Therefore, legume root nodules that house the symbiotic bacteria are ideally suited to study the process of primary ammonium assimilation. Here, we present a GC-MS based metabolite profiling analysis of Medicago truncatula root nodules (induced by the bacterium Sinorhizobium meliloti) before and after inhibition of glutamine synthetase (GS) by the chemical herbicide phosphinotricine. The primary role of GS in ammonium assimilation was revealed by drastically reduced levels of glutamine in phosphinotricine treated root nodules. In comparison to previous results of increased asparagine synthetase transcript and protein abundances in GS inhibited nodules the metabolic data revealed that decreased amounts of aspartate might preclude taking advantage of this elevated enzymatic activity. A potential role of glutamate dehydrogenase in ammonium assimilation was metabolically indicated 24 and 48 h after GS inhibition. Therefore, nodule ammonium assimilation might in principle involve three interdependent metabolic pathways which are adjusted to control basic nitrogen metabolism.
在与豆科植物的共生相互作用中，被称为根瘤菌的细菌能够固定大量大气中的氮，这些氮主要以铵的形式提供给宿主植物。因此，容纳共生细菌的豆科植物根瘤非常适合用于研究初级铵同化过程。在此，我们展示了基于气相色谱-质谱联用技术的代谢物谱分析，该分析针对的是在用化学除草剂草铵膦抑制谷氨酰胺合成酶（GS）之前和之后的蒺藜苜蓿根瘤（由苜蓿中华根瘤菌诱导形成）。在草铵膦处理的根瘤中，谷氨酰胺水平大幅降低，这揭示了GS在铵同化中的主要作用。与之前在GS受抑制的根瘤中天门冬酰胺合成酶转录本和蛋白质丰度增加的结果相比，代谢数据表明，天冬氨酸含量的减少可能会妨碍利用这种升高的酶活性。在GS受抑制24小时和48小时后，从代谢角度表明了谷氨酸脱氢酶在铵同化中的潜在作用。因此，根瘤铵同化原则上可能涉及三条相互依赖的代谢途径，这些途径会进行调整以控制基本的氮代谢。
