Rhizobial Purine Metabolism and Nodule Development

有充分的证据表明，根瘤菌嘌呤营养不良菌不能诱导完全的根瘤发育和共生固氮。Noel博士实验室最近的研究表明，这种共生缺陷的潜在原因是无法产生该途径中的一种中间体——核糖体-5-氨基咪唑-4-羧酰胺（AICAR）。概述的项目是进一步证实最初的观察结果，检验AICAR是感染线决定因素的假设，并更清楚地定义这一作用。实验探讨了细菌对AICAR的吸收和命运，以及AICAR直接影响植物的可能性。他们将通过显微解剖分析和蛋白质电泳分析来记录AICAR刺激下结节发育的增强。寄主根和根渗出液对细菌嘌呤和AICAR代谢的影响将主要通过示踪实验进行分析，示踪实验中标记的化合物通过高分辨率的多功能薄层色谱技术分离。在用最有可能的AICAR效应的细菌介质挑战植株后，将分析根系感染区域的代谢变化。固氮菌与豆科植物根系的共生关系的建立对农业具有极其重要的意义。这对于理解信号如何从一个生物体传递到另一个生物体也很有意义。

It is well documented that rhizobial purine auxotrophs are incapable of eliciting complete nodule development and symbiotic nitrogen fixation. Recent work in Dr. Noel's laboratory suggests that the underlying cause of the symbiotic defect is inability to produce ribosyl-5-aminoimidazole-4-carboxamide (AICAR), an intermediate in the pathway. The outlined project is to substantiate further the original observations, to test the hypothesis that AICAR is an infection-thread determinant, and to define this role more clearly. The experiments probe the uptake and fate of AICAR in the bacteria and the possibility that AICAR affects the plant directly. They will document the AICAR stimulated enhancement of nodule development by microscopic analysis of anatomy and electrophoretic analysis of proteins. The effect of host roots and root exudate on bacterial purine and AICAR metabolism will be analyzed, mainly by tracer experiments in which labelled compounds are separated by a versatile thin- layer chromatography technique of great resolving power. Metabolic changes in the infectible region of the root will be analyzed after challenging the plant with the most likely bacterial mediator of the AICAR effect. %%% The establishment of the symbiotic association between nitrogen fixing bacteria and the roots of legumes is extremely important to agriculture. It is also of interest for an understanding of how signals are passed from one organism to another.