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Phytochrome is a photoreceptor, a pigment that plants, and some bacteria and fungi, use to detect light. It is sensitive to light in the red and far-red region of the visible spectrum. Many flowering plants use it to regulate the time of flowering based on the length of day and night (photoperiodism) and to set circadian rhythms. It also regulates other responses including the germination of seeds (photoblasty), elongation of seedlings, the size, shape and number of leaves, the synthesis of chlorophyll, and the straightening of the epicotyl or hypocotyl hook of dicot seedlings. It is found in the leaves of most plants. Biochemically, phytochrome is a protein with a bilin chromophore. Phytochrome has been found in most plants including all higher plants; very similar molecules have been found in several bacteria. A fragment of a bacterial phytochrome now has a solved three-dimensional protein structure. Other plant photoreceptors include cryptochromes, phototropins, and UVR8, which are sensitive to light in the blue and ultra-violet regions of the spectrum. == Structure == Phytochrome consists of two identical chains (A and B). Each chain has a PAS domain and GAF domain. The PAS domain serves as a signal sensor and the GAF domain is responsible for binding to cGMP and also senses light signals. Together, these subunits form the phytochrome region, which regulates physiological changes in plants to changes in red and far red light conditions. In plants, red light changes phytochrome to its biologically active form, while far red light changes the protein to its biologically inactive form. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Phytochrome」の詳細全文を読む スポンサード リンク
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