Department of Agricultural Biotechnology, Agricultural University of Athens, Iera Odos 75, 11855 Athens, Greece.
J Exp Bot. 2013 Mar;64(5):1317-32. doi: 10.1093/jxb/ert015. Epub 2013 Feb 11.
Symbiotic nitrogen fixation (SNF) involves global changes in gene expression and metabolite accumulation in both rhizobia and the host plant. In order to study the metabolic changes mediated by leaf-root interaction, photosynthesis was limited in leaves by exposure of plants to darkness, and subsequently gene expression was profiled by real-time reverse transcription-PCR (RT-PCR) and metabolite levels by gas chromatography-mass spectrometry in the nodules of the model legume Lotus japonicus. Photosynthetic carbon deficiency caused by prolonged darkness affected many metabolic processes in L. japonicus nodules. Most of the metabolic genes analysed were down-regulated during the extended dark period. In addition to that, the levels of most metabolites decreased or remained unaltered, although accumulation of amino acids was observed. Reduced glycolysis and carbon fixation resulted in lower organic acid levels, especially of malate, the primary source of carbon for bacteroid metabolism and SNF. The high amino acid concentrations together with a reduction in total protein concentration indicate possible protein degradation in nodules under these conditions. Interestingly, comparisons between amino acid and protein content in various organs indicated systemic changes in response to prolonged darkness between nodulated and non-nodulated plants, rendering the nodule a source organ for both C and N under these conditions.
共生固氮（Symbiotic nitrogen fixation，SNF）涉及根瘤菌和宿主植物中基因表达和代谢物积累的全球变化。为了研究叶片-根系相互作用介导的代谢变化，通过将植物暴露在黑暗中来限制叶片的光合作用，并随后通过实时逆转录聚合酶链反应（RT-PCR）和气相色谱-质谱法在模式豆科植物百脉根的根瘤中分析基因表达和代谢物水平。长时间黑暗引起的光合碳不足会影响百脉根根瘤中的许多代谢过程。在延长的黑暗期内，大多数分析的代谢基因下调。除此之外，尽管氨基酸积累，但大多数代谢物的水平降低或保持不变。糖酵解和碳固定减少导致有机酸水平降低，特别是作为类菌体代谢和 SNF 的主要碳源的苹果酸。高氨基酸浓度以及总蛋白浓度降低表明在这些条件下根瘤中可能发生蛋白质降解。有趣的是，氨基酸和各种器官中蛋白质含量之间的比较表明，在受影响的根瘤和非根瘤植物之间，长期黑暗会导致系统性变化，使根瘤在这些条件下成为 C 和 N 的源器官。
