Márquez Antonio J, Betti Marco, García-Calderón Margarita, Pal'ove-Balang Peter, Díaz Pedro, Monza Jorge
Departamento de Bioquímica Vegetal y Biología Molecular, Facultad de Química, Universidad de Sevilla, Apartado 553, E-41080 Sevilla, Spain.
J Exp Bot. 2005 Jul;56(417):1741-9. doi: 10.1093/jxb/eri171. Epub 2005 May 23.
This paper summarizes some recent advances in the understanding of nitrate assimilation in the model legume Lotus japonicus. First, different types of experimental evidence are presented that emphasize the importance of the root in the nitrate-reducing assimilatory processes in this plant. Secondly, the main results from an ethyl methanesulphonate mutagenesis programme are presented. In this programme, chlorate-resistant and photorespiratory mutants were produced and characterized. The phenotype of one particular chlorate-resistant mutant suggested the importance of a low-affinity nitrate transport system for growth of L. japonicus plants under nitrate nutrition. The phenotype of photorespiratory mutants, affected in all forms of plastid glutamine synthetase in leaves, roots, and nodules, indicated that plastid glutamine synthetase was not required for primary nitrate assimilation nor for the symbiotic associations of the plant (nodulation, mycorrhization), provided photorespiration was suppressed. However, the phenotype of these mutants confirmed that plastid glutamine synthetase was required for the reassimilation of ammonium released by photorespiration. Finally, different aspects of the relationship between nitrate assimilation and osmotic stress in L. japonicus are also discussed, with specific reference to the biosynthesis of proline as an osmolyte.
本文总结了在模式豆科植物百脉根中对硝酸盐同化作用理解的一些最新进展。首先，展示了不同类型的实验证据，这些证据强调了根在该植物硝酸盐还原同化过程中的重要性。其次，介绍了甲磺酸乙酯诱变计划的主要结果。在该计划中，产生并鉴定了抗氯酸盐和光呼吸突变体。一个特定抗氯酸盐突变体的表型表明，低亲和力硝酸盐转运系统对硝酸盐营养条件下百脉根植物的生长很重要。光呼吸突变体在叶片、根和根瘤中所有形式的质体谷氨酰胺合成酶都受到影响，这表明只要光呼吸受到抑制，质体谷氨酰胺合成酶对于初级硝酸盐同化以及植物的共生关系（结瘤、菌根形成）都不是必需的。然而，这些突变体的表型证实，质体谷氨酰胺合成酶对于光呼吸释放的铵的再同化是必需的。最后，还讨论了百脉根中硝酸盐同化与渗透胁迫之间关系的不同方面，特别提到了作为渗透溶质的脯氨酸的生物合成。
