| Light is one of the major environmental signals that influence plant growth and development. Plants have evolved a sophisticated system of three major classes of photoreceptors---the red/far-red light-absorbing phytochromes, the blue/UV-A light-absorbing cryptochromes and phototropins, and the UV-B light receptors---to monitor light and regulate plant physiology and morphology.; Although the roles of light in regulating many physiological processes in higher plants have been intensively studied, comparatively little information exists about the role of light on early development such as gametophyte development and embryogenesis. Ceratopteris richardii, an increasingly popular fern model, offers unique opportunities for developmental, physiological, genetic, and molecular studies of plant photomorphogenesis.; Information is lacking about the effects of phytochrome over prolonged periods and in more developed mature gametophytes. Allowing spores to germinate and develop under different controlled light conditions has yielded more information about how phytochrome acts on cell division, expansion, morphogenesis, and plastid development of maturing gametophytes and young sporophytes. These characterizations lead to demonstrate that phytochrome and blue light sensory photoreceptors play a major role in regulating germination, the rate and direction of cell division, cell expansion, chlorophyll accumulation, archegonia development and sex determination, and early sporophyte development in Ceratopteris . By comparison with other plant responses to supplementary far-red light or to end-of-day far-red light regimes, Ceratopteris responded not only differently but in a manner opposite that of angiosperms, which indicates different mechanisms of phytochrome-regulated morphogenesis.; Until recently, very little was known about the mechanisms of phytochrome signaling in lower plants. To elucidate the signal transduction mechanisms of different phytochromes, it is essential to know the sites of their action within the cell. Furthermore, the molecular biology of Ceratopteris is largely unexplored. The addition of transgenic and pharmacological analysis techniques to Ceratopteris research would improve the range of possible experiments available.; Studying AtPhyB and CrPhy1 translocation behavior in Ceratopteris has proven suggestive for understanding evolutionary conservation of behavior between higher plant and fern phytochromes. The slow kinetics of AtPhyB:GFP translocation and lack of CrPhy1:GFP nucleocytoplasmic repartitioning in Ceratopteris cells, and their distinct localization patterns, suggest that different mechanisms or signal transduction components may be active in fern and higher plant phytochrome action. |
