Molecular Genetic Analysis of Constitutively Photomorphogenic Mutants of Arabidopsis

Abstract

Light is one of the most important environmental signals that profoundly influence growth and development in plants all through their life cycle. Plants have thus evolved many diverse sensory photoreceptors that scan spectral regions of the solar spectrum essential for regulating photomorphogenic development. The family of red/far-red reversible phytochromes and the blue light-sensing cryptochromes and phototropin principally absorb radiation in the visible range; the latter class also perceives biologically active UV-A radiation (see Quail et al 1995, Cashmore et al 1999, Christie et al 1999, Khurana and Poff 1999). Some morphogenic responses, e.g. cotyledon curling and anthocyanin production, are also elicited by UV-B radiation but the identity of the receptors(s) remains elusive (see Stapleton 1992, Bharti and Khurana 1997). Among these sensory pigment systems, phytochromes are the best studied class primarily because they regulate important plant processes like onset of seed germination, inhibition of stem growth, cotyledon expansion and chloroplast development, and induction of flowering. Moreover, phytochrome was the first photosensory pigment identified in the 1950s (see Sage 1992 for a historical account). The phytochrome apoprotein is encoded by a multigene family in most species examined, but all of them harbor an open-chain tetrapyrrole chromophore towards the N-terminal region.