In the present work we studied the role of light in the regulation of flavonoid gene expression and anthocyanin synthesis in petunia (Petunia hybrida) corollas. We found that light is required for chalcone synthase gene (chs) expression, anthocyanin synthesis, and growth of detached and attached petunia corollas. Although direct illumination induced chs expression, pigmentation, and elongation of the detached corollas, irradiation of green leaves or sepals played the main role in the attached corollas. The duration, intensity, and spectrum of the light reaction suggest that phytochrome-mediated high-irradiance reactions are involved in the regulation of corolla development. Using the photosynthesis inhibitor 3-(3,4-dichlorophenyl)-1,1-dimethylurea, we showed that photosynthesis does not significantly contribute to the leaf-mediated light responses. When sepals were removed or covered, [14C]sucrose uptake by the corolla of detached intact flowers was inhibited. The results of this study suggest that light is perceived by leaves and sepals and enhances corolla sink activity, elongation, pigmentation, and chs expression. The role of leaves and sepals in the light regulation of petunia corolla development is discussed.