Abstract
Plants have developed flexible mechanisms to respond appropriately to environmental signals. These stimuli are transduced by largely unknown signalling pathways that are likely to be modulated by endogenous developmental signals to produce an integrated response that coordinately regulates gene expression. Light is a critical environmental signal that controls many aspects of plant development via a series of photoreceptors that are able to respond to different light wavelengths. Light is also the principal energy source for photosynthesis. The photosynthetic products are carbohydrates which are translocated in the form of sucrose from the photosynthetic (source) to non-photosynthetic (sink) organs. Consequently, the control of photoregulated genes must integrate developmental inputs with signals derived from the photoreceptors, from the photosynthetic apparatus and from metabolites such as sucrose.