Departamento de Bioquimica Vegetal y Biologia Molecular, Universidad de Sevilla, Sevilla, Spain.
Mol Plant Microbe Interact. 2012 Feb;25(2):211-9. doi: 10.1094/MPMI-07-11-0200.
Two photorespiratory mutants of Lotus japonicus deficient in plastid glutamine synthetase (GS(2)) were examined for their capacity to establish symbiotic association with Mesorhizobium loti bacteria. Biosynthetic glutamine synthetase (GS) activity was reduced by around 40% in crude nodule extracts from mutant plants as compared with the wild type (WT). Western blot analysis further confirmed the lack of GS(2) polypeptide in mutant nodules. The decrease in GS activity affected the nodular carbon metabolism under high CO(2) (suppressed photorespiration) conditions, although mutant plants were able to form nodules and fix atmospheric nitrogen. However, when WT and mutant plants were transferred to an ordinary air atmosphere (photorespiratory active conditions) the nodulation process and nitrogen fixation were substantially affected, particularly in mutant plants. The number and fresh weight of mutant nodules as well as acetylene reduction activity showed a strong inhibition compared with WT plants. Optical microscopy studies from mutant plant nodules revealed the anticipated senescence phenotype linked to an important reduction in starch and sucrose levels. These results show that, in Lotus japonicus, photorespiration and, particularly, GS(2) deficiency result in profound limitations in carbon metabolism that affect the nodulation process and nitrogen fixation.
两个光呼吸突变体缺乏质体谷氨酰胺合成酶（GS(2)）的豌豆被检查，以观察它们与根瘤菌建立共生关系的能力。与野生型（WT）相比，突变体植物粗结节提取物中的生物合成谷氨酰胺合成酶（GS）活性降低了约 40%。Western blot 分析进一步证实了突变体结节中缺乏 GS(2)多肽。GS 活性的降低影响了高 CO2 （抑制光呼吸）条件下的结节碳代谢，尽管突变体植物能够形成结节并固定大气氮。然而，当 WT 和突变体植物被转移到普通空气气氛（光呼吸活跃条件）时，结瘤过程和固氮受到了很大的影响，特别是在突变体植物中。与 WT 植物相比，突变体结节的数量和鲜重以及乙炔还原活性均受到强烈抑制。对突变体植物结节的光学显微镜研究显示出与淀粉和蔗糖水平重要降低相关的预期衰老表型。这些结果表明，在豌豆中，光呼吸，特别是 GS(2)缺乏会导致碳代谢的严重限制，从而影响结瘤过程和固氮。
