Phytochrome, a family of photoreceptors with multiple physiological roles

Abstract

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.

Seedling growth of fifteen Brazilian tropical tree species differing in successional status

“…Leaf area was also generally more severely affected by NS treatment than AS treatment, indicating the influence of the lower R:FR ratio of the NS treatment on leaf area. Reduced leaf development is one of the responses that may be evoked by phytochrome under conditions of reduced R:FR ratio (Smith & Whitelam 1990). Internode elongation, with accompanying increase in height, is a response that is expected to occur under conditions of natural shade, because it is a typical morphogenic response (Smith & Whitelam 1990).…”

“…Reduced leaf development is one of the responses that may be evoked by phytochrome under conditions of reduced R:FR ratio (Smith & Whitelam 1990). Internode elongation, with accompanying increase in height, is a response that is expected to occur under conditions of natural shade, because it is a typical morphogenic response (Smith & Whitelam 1990). However, internode elongation was observed only in some late-successional species and it was not accompanied by height increase.…”

The function of phytochrome A

“…The availability of phyA mutants has aided investigation of the action of phyA on diverse processes under photomorphogenic control. To illustrate the magnitude of the advances, only 7 years ago it was difficult to attribute any reasonable ecological significance to verylow-fluence responses (VLFR) and high-irradiance responses (HIR), and the sensory role of the phytochrome pool accumulated during growth in darkness was thought to be complete once de-etiolation has been initiated (Smith & Whitelam 1990). The cuiTent picture is that the photoperceptive function of phyA is rather specific (Table 1) while the set of physiological events under its influence is largely common to other phytochromes (see Whitelam & Devlin 1997, this issue).…”

Flowering Responses to Altered Expression of Phytochrome in Mutants and Transgenic Lines of Arabidopsis thaliana (L.) Heynh

“…Each of the phytochromes A, B, and C is present in both dark-and light-grown plants, although in different amounts (Somers et al, 1991). The polypeptides encoded by the PHYA, PHYB, and PHYC genes are immunologically distinct (Somers et al, 1991;Wagner et al, 1991), and it has been suggested that the different members of the phytochrome family have differing functional roles (see reviews by Smith and Whitelam, 1990;Whitelam and Harberd, 1994). Phytochrome A is light labile and appears to be most relevant to de-etiolation phenomena involving HIRs to FR (Boylan and Quail, 1991;Whitelam et al, 1992;Dehesh et al, 1993;Parks and Quail, 1993).…”