Instituto de Agrobiotecnología (IdAB), Universidad Pública de Navarra-CSIC-Gobierno de Navarra, Campus de Arrosadía, Mutilva Baja, Spain.
J Exp Bot. 2013 Feb;64(4):885-97. doi: 10.1093/jxb/ers367.
Although the mechanisms of nodule N(2) fixation in legumes are now well documented, some uncertainty remains on the metabolic consequences of water deficit. In most cases, little consideration is given to other organs and, therefore, the coordinated changes in metabolism in leaves, roots, and nodules are not well known. Here, the effect of water restriction on exclusively N(2)-fixing alfalfa (Medicago sativa L.) plants was investigated, and proteomic, metabolomic, and physiological analyses were carried out. It is shown that the inhibition of nitrogenase activity caused by water restriction was accompanied by concerted alterations in metabolic pathways in nodules, leaves, and roots. The data suggest that nodule metabolism and metabolic exchange between plant organs nearly reached homeostasis in asparagine synthesis and partitioning, as well as the N demand from leaves. Typically, there was (i) a stimulation of the anaplerotic pathway to sustain the provision of C skeletons for amino acid (e.g. glutamate and proline) synthesis; (ii) re-allocation of glycolytic products to alanine and serine/glycine; and (iii) subtle changes in redox metabolites suggesting the implication of a slight oxidative stress. Furthermore, water restriction caused little change in both photosynthetic efficiency and respiratory cost of N(2) fixation by nodules. In other words, the results suggest that under water stress, nodule metabolism follows a compromise between physiological imperatives (N demand, oxidative stress) and the lower input to sustain catabolism.
尽管豆科植物结节 N(2)固定的机制现在已经得到很好的证明，但在水分亏缺的代谢后果方面仍存在一些不确定性。在大多数情况下，很少考虑其他器官，因此，叶片、根系和根瘤中代谢的协调变化并不为人所知。在这里，研究了水分限制对专门进行 N(2)固定的紫花苜蓿（Medicago sativa L.）植物的影响，并进行了蛋白质组学、代谢组学和生理学分析。结果表明，水分限制引起的固氮酶活性抑制伴随着根瘤、叶片和根系中代谢途径的协同改变。数据表明，在天冬酰胺合成和分配以及叶片的氮需求方面，根瘤代谢和植物器官之间的代谢交换几乎达到了同平衡状态。通常情况下，（i）会刺激氨酰基转移酶途径，以维持为氨基酸（如谷氨酸和脯氨酸）合成提供 C 骨架；（ii）糖酵解产物再分配到丙氨酸和丝氨酸/甘氨酸；（iii）氧化还原代谢物的细微变化表明存在轻微的氧化应激。此外，水分限制对叶片光合作用效率和根瘤固氮的呼吸成本几乎没有影响。换句话说，这些结果表明，在水分胁迫下，根瘤代谢在生理需求（氮需求、氧化应激）和维持分解代谢所需的较低输入之间存在妥协。
