title: Reappraisal of nitrogen use efficiency in rice overexpressing glutamine synthetase1.
abstract: Cytosolic glutamine synthetase (GS1) is responsible for the primary assimilation of ammonia, and a role in nitrogen (N) remobilization is implicated from its vascular localization and enhanced expression during senescence. This paper tested the hypothesis that overexpression (OX) of GS1 in rice improves utilization N use efficiency (UtE = spikelet yield/shoot N content). Three GS1 OX lines were identified using activity assays and quantitative polymerase chain reaction. Physiological analysis of the OX lines, as well as azygous and wild-type (Wt) controls, was conducted with mature plants after growth under varying nitrate conditions (non-limiting N, limiting N, transfer from non-limiting N to limiting N at panicle emergence) and growth environments (growth chamber vs greenhouse). Overall, OX lines did not differ from azygous controls in vegetative yield or shoot N content. In two of the three growth trials (i.e. the growth chamber trials) harvest index, N harvest index (spikelet N content/shoot N content) and UtE were generally enhanced in the OX lines relative to their azygous controls. These characteristics were highly correlated with percent spikelets filled and spikelet number. Thus, N partitioning in rice during grain filling could be altered by GS1 OX, resulting in improved UtE. Unfortunately, GS OX did not result in more efficient use of N under limiting N than under non-limiting N, and is therefore unlikely to result in the use of less N under field conditions. Transformation effects significantly hindered the productivity of the OX lines, but backcrossing to the Wt should overcome this.
authors.affiliation: Department of Plant Agriculture, University of Guelph, Guelph, ON N1G 2W1, Canada.
authors.forename: Elizabeth K
authors.initials: EK
authors.lastname: Brauer
authors.forename: Amanda
authors.initials: A
authors.lastname: Rochon
authors.forename: Yong-Mei
authors.initials: YM
authors.lastname: Bi
authors.forename: Gale G
authors.initials: GG
authors.lastname: Bozzo
authors.forename: Steven J
authors.initials: SJ
authors.lastname: Rothstein
authors.forename: Barry J
authors.initials: BJ
authors.lastname: Shelp
mesh_terms: D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D005974:Glutamate-Ammonia Ligase / Q000235:genetics / Q000378:metabolism*; D016254:Mutagenesis, Insertional / Q000187:drug effects; D009584:Nitrogen / Q000378:metabolism* / Q000494:pharmacology; D012275:Oryza / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D018520:Plant Shoots / Q000187:drug effects / Q000378:metabolism; D030821:Plants, Genetically Modified
chemical_list: D010940:Plant Proteins; D005974:Glutamate-Ammonia Ligase; D009584:Nitrogen