To avoid pollution by nitrogen fertilizers, nitrogen acquisition and utilization by plants should be optimized. Models are potentially efficient tools to study a priori new possible scenarios. This work reviews how models formalize nitrogen economy in plants. It appears that the formalization of the processes regulating nitrogen use in plants has remained largely empirical. This hampers models ability to simulate plant behavior in innovative scenarios. The functional-structural model developed by Bertheloot et al. (2008) demonstrates the possibility for a mechanistic modeling, based on the formalization of the turnover of the proteins of the photosynthetic apparatus. However, this model specifically addresses the distribution of nitrogen between laminae and the grains during the reproductive stage of wheat. Based on this approach, we propose here a more complete model, including the simulation of root N uptake, the dynamics of N in all plant components and the extension to the pre-flowering period, when vegetative structure is dynamic.