Author manuscript presented at the 4th International Crop Science Congress, 26/09-01/10/2004, Brisbane, AU Genetic variability for pre- and post-flowering nitrogen metabolism in maize in relation to plant architecture and leaf senescence Bertrand Hirel 1 , Isabelle Quilleré 1 , Bernard Pommel 2 , Matthieu Floriot 2 , Bruno Andrieu 2 , Jean-Louis Drouet 2 , Michael Chelle 2 , Antoine Martin 1 , Marie-Hélène Valadier 1 , Xana Belastegui-Macadam 1 , Alain Fortineau 2 , Michel Chartier 2 , Christian Fournier 2 , André Gallais 3 , Jean-Louis Prioul 4 , Caroline Lelarge 4 and Thérèse Tercé-Laforgue 1 . 1 INRA. Unité de Nutrition Azotée des plantes. R.D. 10, 78026 Versailles Cedex. www.versailles.inra.fr/nap/ Email hirel@versailles.inra.fr 2 Unité Environnement et Grande Culture. INRA/INAPG. 78850 Thiverval-Grignon. Email andrieu@bcgn.grignon.inra.fr 3 UMR INRA/UPS/INAPG du Moulon à Gif-sur-Yvette. Station de Génétique Végétale, Ferme du Moulon, 91190 Gif sur Yvette. Email gallais@moulon.inra.fr 4 Equipe stress abiotique: contrainte sur les organes sources ou puits des échanges d’eau. UMR 8618 UPS/CNRS d'Orsay, IBP, Université de Paris XI, 91405 Orsay Cedex. Email Jean-louis.Prioul@ibp.u- psud.fr Abstract In this poster, we present recent developments towards a better understanding of the controls of nitrogen use efficiency in the model crop maize. In this species, a better knowledge of the regulatory mechanisms controlling the transition between nitrogen assimilation and nitrogen recycling is vital for improving nitrogen use efficiency and for reducing excessive input of fertilisers without affecting yield. Using plants grown in the field at low and high nitrogen fertilization regimes, classical physiological studies combined with gene expression profiling were developed to build up a model depicting the evolution of source/sink relationships in maize in relation to the evolution of leaf senescence. Using representative physiological markers, the genetic variability of the evolution of the source/sink relationships was also studied. In parallel, 15 N labelling experiments were performed using different maize genotypes, thus allowing the demonstration that there are genotype-dependent differences in the capacity to absorb mineral nitrogen before and after silking, as well as in the efficiency of leaf proteins remobilisation. An attempt was also made to characterize the relationships between nitrogen content and light perception during leaf senescence in three-dimensional architectural models. These models may provide a way to identify representative physiological markers that can be further used during a selection process. They could be also be used and for QTLs detection in quantitative genetics. Media summary Development of new models depicting source/sink relationships for nitrogen metabolism in relation to leaf senescence during grain filling in different maize genotypes grown at low and high fertilisation input. Key words Assimilation, genotypes, maize, nitrogen, remobilisation, senescence.