Berry Alison M, Mendoza-Herrera Alberto, Guo Ying-Yi, Hayashi Jennifer, Persson Tomas, Barabote Ravi, Demchenko Kirill, Zhang Shuxiao, Pawlowski Katharina
Department of Plant Sciences, University of California, Davis, CA 95616, USA.
Centro de Biotecnología Genómica, Instituto Politécnico Nacional, 88710 Reynosa, Tamaulipas, Mexico.
Funct Plant Biol. 2011 Sep;38(9):645-652. doi: 10.1071/FP11095.
Nitrogen-fixing root nodules are plant organs specialised for symbiotic transfer of nitrogen and carbon between microsymbiont and host. The organisation of nitrogen assimilation, storage and transport processes is partitioned at the subcellular and tissue levels, in distinctive patterns depending on the symbiotic partners. In this review, recent advances in understanding of actinorhizal nodule nitrogen assimilation are presented. New findings indicate that Frankia within nodules of Datisca glomerata (Presl.) Baill. carries out both primary nitrogen assimilation and biosynthesis of arginine, rather than exporting ammonium. Arginine is a typical storage form of nitrogen in plant tissues, but is a novel nitrogen carrier molecule in root nodule symbioses. Thus Frankia within D. glomerata nodules exhibits considerable metabolic independence. Furthermore, nitrogen reassimilation is likely to take place in the host in the uninfected nodule cortical cells of this root nodule symbiosis, before amino acid export to host sink tissues via the xylem. The role of an augmented pericycle in carbon and nitrogen exchange in root nodules deserves further attention in actinorhizal symbiosis, and further highlights the importance of a comprehensive, structure-function approach to understanding function in root nodules. Moreover, the multiple patterns of compartmentalisation in relation to nitrogen flux within root nodules demonstrate the diversity of possible functional interactions between host and microsymbiont that have evolved in the nitrogen-fixing clade.
固氮根瘤是植物器官，专门用于微共生体与宿主之间氮和碳的共生转移。氮同化、储存和运输过程的组织在亚细胞和组织水平上进行划分，其独特模式取决于共生伙伴。在本综述中，介绍了对放线菌根瘤氮同化理解的最新进展。新发现表明，在聚花 Datisca（Presl.）Baill. 的根瘤内，弗兰克氏菌进行初级氮同化和精氨酸的生物合成，而不是输出铵。精氨酸是植物组织中典型的氮储存形式，但在根瘤共生中是一种新型的氮载体分子。因此，聚花 Datisca 根瘤内的弗兰克氏菌表现出相当大的代谢独立性。此外，在这种根瘤共生的未感染根瘤皮层细胞中，宿主可能会在氨基酸通过木质部输出到宿主库组织之前进行氮再同化。在放线菌共生中，加厚的中柱鞘在根瘤碳和氮交换中的作用值得进一步关注，这进一步突出了采用全面的结构 - 功能方法来理解根瘤功能的重要性。此外，根瘤内与氮通量相关的多种区室化模式表明，在固氮进化枝中，宿主与微共生体之间可能存在的功能相互作用具有多样性。
