MANIPULATING THE PATHWAY OF AMMONIA ASSIMILATION IN TRANSGENIC NON-LEGUMES AND LEGUMES

In this paper we discuss the ways in which our understanding of the na ture of the molecular controls of nitrogen assimilation has been incre ased by the use of non-leguminous and leguminous plants with genetical ly-altered capacities for ammonia assimilation Using tobacco or Lotus as model plants, Glutamine synthetase(GS) and glutamate synthase (GOGA T) activities have been altered by stimulating or inhibiting in an org an- or tissue-specific manner the expression of the corresponding gene s. In a few selected examples, the physiological impact of these genet ic manipulations has been studied on plants grown under different nitr ogen regimes. The use of such genetically modified plants will allow u s to better understand the molecular control of this metabolic pathway . It is also potentially of great importance in agriculture if such in terval and stable modifications are beneficial in terms of nitrogen us e efficiency, thus avoiding an excessive utilization of fertilizers or herbicides (GS inhibitors). Our current knowledge and prospects for f uture development are explored.