Phytochrome, a family of photoreceptors with multiple physiological roles

Abstract. Photoperception by phytochrome is crucially important at many stages of the plant life cycle in allowing adaptation to a changing light environment. Phytochrome is encoded by a family of genes subject to differential expression in response to environmental and developmental factors. Multiple forms of phytochrome exist with, in some cases, identifiably different spectrophotometric, biochemical and physiological characteristics. This article reviews the regulation of development by phytochrome and discusses evidence from physiological studies of wild type, mutant and transgenic plants consistent with the proposal that different members of the phytochrome family have different photosensory roles. We speculate briefly on the possible evolutionary relationship between the different photosensory roles, and suggest approaches towards further elucidation of the nature of phytochrome-mediated photoperception and adaptation to the natural light environment.