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Title: OVER-EXPRESSION OF CYTOSOLIC GLUTAMINE SYNTHETASE INCREASES PHOTOSYNTHESIS AND GROWTH AT LOW NITROGEN CONCENTRATIONS

Author
item FUENTES, SARA - FIJACION NITROGENO MEXICO
item ALLEN, DAMIAN
item ORTIZ-LOPEZ, ADRIANA - FORMER ARS URBANA
item HERNANDEZ, GEORGINA - FIJACION NITROGENO MEXICO

Submitted to: Journal of Experimental Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/26/2001
Publication Date: N/A
Citation: N/A

Interpretive Summary: Nitrogen, which is a major limiting nutrient for plant growth, is assimilated as ammonium by the concerted action of the enzymes glutamine synthetase and glutamate synthase. Glutamine synthetase catalyzes the critical incorporation of inorganic ammonium into the amino acid glutamine. Two groups of glutamine synthetase enzymes, located in the cytosol and in the chloroplast, have been identified in plants. The genetically modified tobacco plants made much more of this critical enzymes in their leaves. Under optimum nitrogen fetilization there was no effect of glutamine syynthetase over-expression on photosynthesis or growth. However, under nitrogen starvation they had 70 percent higher shoot and 100 percent greater root dry weight as well as 50 percent more leaf area than low nitrogen controls. We demonstrated that manipulation of glutamine synthetase activity has the potential to maintain crop photosynthetic productivity while reducing nitrogen fertilization and the concomitant pollution. This outcome will be of interest to those involved in developing more sustainable agricultural cropping systems.

Technical Abstract: Nitrogen, which is a major limiting nutrient for plant growth, is assimilated as ammonium by the concerted action of glutamine synthetase (GS) and glutamate synthase (GOGAT). GS catalyzes the critical incorporation of inorganic ammonium into the amino acid glutamine. Two types of GS isozymes, located in the cytosol (GS1) and in the chloroplast (GS2) have been identified in plants. Tabacco (Nicotiana tabacum) transformants, over-expressing GS1 driven by the constitutive CaMV 35S promoter were analyzed. GS in leaves of GS-5 and GS-8 plants was up-regulated, at the level of RNA and proteins. These transgenic plants had six times higher leaf GS activity than controls. Under optimum nitrogen fertilization conditions there was no effect of GS over-expression on photosynthesis or growth. However, under nitrogen starvation the GS transgenics had ca. 70 percent higher shoot and ca. 100 percent greater root dry weight as well as 50 percent more leaf area than low nitrogen controls. This was achieved by the maintenance of photosynthesis at rates indistinguishable from plants under high nitrogen, while photosynthesis in control plants was inhibited by 40-50 percent by nitrogen deprivation. We demonstrate that manipulation of glutamine synthetase activity has potentia potential to maintain crop photosynthetic productivity while reducing nitrogen fertilization and concomitant pollution. Potential implications is pertinent to enhancing nitrogen use efficiency in crops and researchers investigating improved sustainability of crop production practices.