Journal Article

Biochemical Background and Compartmentalized Functions of Cytosolic Glutamine Synthetase for Active Ammonium Assimilation in Rice Roots

Keiki Ishiyama, Eri Inoue, Mayumi Tabuchi, Tomoyuki Yamaya and Hideki Takahashi

in Plant and Cell Physiology

Published on behalf of Japanese Society of Plant Physiologists

Volume 45, issue 11, pages 1640-1647
Published in print November 2004 | ISSN: 0032-0781
Published online November 2004 | e-ISSN: 1471-9053 | DOI: http://dx.doi.org/10.1093/pcp/pch190
Biochemical Background and Compartmentalized Functions of Cytosolic Glutamine Synthetase for Active Ammonium Assimilation in Rice Roots

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Rice plants in paddy fields prefer to utilize ammonium as a major nitrogen source. Glutamine synthetase (GS) serves for assimilation of ammonium in rice root, and ameliorates the toxic effect of ammonium excess. Among the three isoenzymes of the cytosolic GS1 gene family in rice, OsGLN1;1 and OsGLN1;2 were abundantly expressed in roots. Analysis of the purified enzymes showed that OsGLN1;1 and OsGLN1;2 can be classified into high-affinity subtypes with relatively high Vmax values, as compared with the major high-affinity isoenzyme, GLN1;1, in Arabidopsis. Low-affinity forms of GS1 comparable to those in Arabidopsis (GLN1;2 and GLN1;3) were absent in rice roots. The OsGLN1;1 and OsGLN1;2 transcripts showed reciprocal responses to ammonium supply in the surface cell layers of roots. OsGLN1;1 accumulated in dermatogen, epidermis and exodermis under nitrogen-limited condition. By contrast, OsGLN1;2 was abundantly expressed in the same cell layers under nitrogen-sufficient conditions, replenishing the loss of OsGLN1;1 following ammonium treatment. Within the central cylinder of elongating zone, OsGLN1;1 and OsGLN1;2 were both induced by ammonium, which was distinguishable from the response observed in the surface cell layers. The high-capacity Gln synthetic activities of OsGLN1;1 and OsGLN1;2 facilitate active ammonium assimilation in specific cell types in rice roots.

Keywords: Keywords: Ammonium assimilation — Glutamine synthetase — Rice — Root.; Abbreviations: AMT, ammonium transporter; Gln, glutamine; Glu, glutamate; GOGAT, glutamate synthase; GS, glutamine synthetase.

Journal Article.  5814 words.  Illustrated.

Subjects: Biochemistry ; Molecular and Cell Biology ; Plant Sciences and Forestry

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