A functional-structural model (FSPM) is proposed to simulate carbon (C) and nitrogen (N) metabolism within the wheat plant. FSPM represent the biological processes within a realistic description of plant architecture. It is expected that this approach will strengthen our capacity to represent G*E interactions. Here culm structure is composed of a root compartment, a set of photosynthetic organs and the whole grains. A culm element consists of structural, storage (protein, starch, fructan) and mobile (sucrose amino acids and nitrate) materials. Culm elements are connected to a common pool hereafter called phloem, which allows circulation of mobile metabolites through the plant. Beside, compounds originating from roots are distributed to photosynthetic tissues according to transpiration. A key feature of the model is that C and N fluxes (syntheses, degradations, loading/unloading) in each organ depend on the local concentrations in metabolites. Activities modelled for the root are (i) uptake of nitrates (ii) synthesis of organic N and cytokinins, (iii) exudation of C and N, (iv) senescence. Activities modelled by photosynthetic organs are (i) photosynthesis (ii) synthesis of storage and mobile carbohydrates, (iii) synthesis of amino acids and protein turn-over, (iv) tissue death (v) loading of C and N into the phloem. Main activity for grain are growth and filling, driven by the metabolites in phloem. Implementation is completed for the post flowering stage. The model simulates realistic concentrations of C and N metabolites in plant organs, including grains. The model predicts the dynamics of C and N at both short-term (day/night alternation) and long-term, the latter being largely driven the drastic decrease in mobile C and N during grain filling. Work under progress extends the model to the regulation of morphogenesis during the preflowering period. Then we will use the model to investigate plant traits adapted to low-N agricultural practices.