VOLUME1, ISSUE 1 | 2004

B. Hirel1, A. M. Limami2*
1Unité de Nutrition Azotée des Plantes, I.N.R.A., R.D. 10, 78026 Versailles Cedex France.
2U.M.R. Physiologie Moléculaire des Semences. U.F.R. Sciences, 2 Bd. Lavoisier. 49045 Angers Cedex 01
France.
*Corresponding author: anis.limami@univ-angers.fr
Abstract. The ever-increasing environmental awareness, and increased need to cut costs onfertilisers made the improvement of plant nitrogen use efficiency (NUE: fertiliser taken up bythe plants which is assimilated into organic N) of high importance for plant breeding industry.
To realise potential benefits with respect to sustained agriculture, we need to identify thephysiological, biochemical and molecular mechanisms controlling nitrate uptake, nitratepartitioning between roots and shoots, and nitrate reduction and its subsequent assimilation and transfer into organic molecules. Furthermore a better understanding of the transition between nitrogen assimilation and nitrogen recycling during leaf senescence will be vital, if improvements in crop nitrogen use efficiency are to reduce fertilisers input and improve or stabilize yield. In this paper, we describe improvement in our understanding of the molecular controls of nitrogen assimilation through the use of transgenic plants and the study of genetic variability in model and crop species. To illustrate this research program, the physiological impact of modified gene expression using either transgenic plants or different genotypes was studied using 15N labelling experiments in order to monitor the influx of nitrate or ammonia and its subsequent incorporation into amino acids. Our current knowledge and prospects for future development and application to crop improvement are discussed.
Key words: molecular controls, nitrogen assimilation, transgenic plants, genetic variability.