The global shape of an ornamental plant is one of its major aesthetic criteria. It is controled by its architecture, particularly by bud bursting and shoot elongation. Environmental factors including light have a strong impact on both processes. The management of the lighting conditions during plant culture could help to produce plants with innovative shapes, using environmentally-friendly practices. However, there is a significant lack of knowledge about the mechanisms involved in the regulation of plant development by light. In this thesis, we studied the effect of blue light on the architectural development of two varieties of rose bushes coupling morphological, histological and molecular approaches. Our results show that monochromatic blue light has a depressive effect on the photosynthetic assimilation of roses but induces in both cultivars, same meristem organogenetic activity, internodes growth and floral development than full spectrum light. On the contrary, the removal of blue raies from white light stimulates the elongation of the first order axis in one of the two studied cultivars. This stimulation results from the increase of leaf photosynthetic assimilation and internode cell elongation. This photo-control is exerted on the expression of genes involved in sugar metabolism and cell wall loosening. Our study of photoreceptor mutants in pea suggests that phytochrome B is the major photoreceptor involved in this response to blue light.
