Involvemtnt of Ammonia Maintenance of Cytosolic Glutamine Synthetase Activity in Pisum sativum Nodules

概要

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Regulatory mechanisms of glutamine synthetase (GS, EC 6.3.1.2) activity in pea (Pisum sativum L.) nodules were investigated by using the pea mutant E135 (sym13) that forms ineffective nodules. GS activity, and the levels of polypeptides and mRNA for cytosolic GS in nitrogenfixing effective nodules increased during plant development while those in roots remained low. In the ineffective E135 nodules, GS activity and the level of polypeptides for GS were similar to those in effective nodules at the early stages of plant development, but later GS activity and level of polypeptides were lower than those found in roots although the level of the mRNA in the ineffective nodules did not decrease, and was much higher than that in roots. GS activity in the ineffective nodules at the later stages of plant development was enhanced by treatment with ammonia although the effect was transient. The treatment with ammonia also increased the level of polypeptides, but hardly affected the level of the mRNA for GS in ineffective nodules. These results suggest that the maintenance of cytosolic GS activity in pea nodules is regulated post-transcriptionally by the effectiveness of the nodules, and that ammonia produced by nitrogen fixation is involved in the maintenance of GS activity at a post-transcriptional level.
日本植物生理学会の論文