A review.Phototropins, a new family of UV-A/blue light receptors of higher plants, are light-activated, autophosphorylating serine/threonine kinases that function as primary photoreceptors for phototropism, which is the directional growth of plant organs toward or away from the light.Since 1988, when light-mediated phosphorylation of phototropin was first described, significant advances have been made in our understanding of the mol. mechanisms by which light signals are processed by these photoreceptors.This chapter is aimed at giving a detailed overview and discussion of all of the relevant exptl. data that meanwhile have been brought together.It will basically follow the sequence of events leading from the initial photophysiol. and biochem. anal. of the light-induced phosphorylation reaction and its correlation with phototropism to the isolation of the phototropin gene and the subsequent characterization of the structural, biochem. and, in particular, the photochem. properties of the encoded protein.Most recent genetic evidence for the involvement of at least a second member of the phototropin family in the regulation of phototropic responses, the participation of both phototropins in chloroplast movement, another well-known blue light response of higher plants, as well as currently existing hypotheses concerning possible early events in downstream signaling are further focal points.
