The phytochrome B encoded by the HLG locus of Nicotiana plumbaginifolia is required for detection of photoperiod: hlg mutants show altered regulation of flowering and circadian movement

Abstract

SummaryThe sensitivity of the Nicotiana plumbaginifolia wild-type and phytochrome B (hlg) mutant to photoperiod was investigated. Leaf number at bolting and rosette-leaf movement were measured under conditions of different light quality and photoperiod. Bolting in wild-type plants was slightly delayed under short days (SD), compared to plants grown under long days (LD). The hlg mutant bolted later than the wild-type under LD, but not under SD. An endogenous rhythm of rosette-leaf movement in the wildtype was present under SD, but suppressed under LD. The hlg mutant behaved indistinguishably from the wild-type under SD conditions, but the movements were not suppressed under LD in the mutants. The endogenous rhythm appeared to be entrained normally in the mutants under all the conditions investigated. It was concluded that the B-type phytochrome absent in the hlg mutant is required for the measurement of photoperiod duration in N. plumbaginifolia, but is not required for entrainment of the circadian clock.

Photocontrol of subcellular partitioning of phytochrome‐B:GFP fusion protein in tobacco seedlings

“…Here we report that expression of the same chimeric construct in the N. plumbaginifolia phyB‐deficient hlg2 mutant ( Hudson et al . 1997 ; Hudson & Smith 1998) rescued R light‐induced inhibition of hypocotyl growth of transgenic hlg2 seedlings ( Table 1). Moreover, we found that light‐dependent nuclear import of the NtphyB1:GFP in these transgenic N. plumbaginifolia lines was regulated by the LFR of phytochrome as described in N. tabacum cells by Kircher et al .…”

Shade avoidance and the regulation of leaf inclination in Arabidopsis

“…5), while far‐red light caused leaves to orient at high inclinations similar to darkness in both Arabidopsis (Vandenbussche et al . 2003) and tobacco (Hudson & Smith 1998).…”

“…In tobacco, phyB was suggested to have a role in photoperiod-dependent circadian leaf movement rather than in acute shade avoidance-related leaf movement (Hudson & Smith 1998). Cotyledons of Arabidopsis also show strong circadian movements (Millar et al 1995), and these movements are affected by phyB (Salome et al 2002).…”

“…However, regulation of leaf positioning by light is one mechanism by which rosette plants can respond to neighbouring plants competing for light. Shade avoidance‐related leaf positioning has been reported in Impatiens (Whitelam & Johnson 1982), tobacco (Hudson & Smith 1998; Pierik et al . 2004a) and Arabidopsis (Vandenbussche et al .…”

Rhythms in Plants

“…In further support of this notion, in tobacco (Nicotiana plumbaginifolia), the absence of PHYB in the hlg mutant did not prevent the normal entraining of the endogenous rhythm of growth movements of rosette leaves (although it did affect the sensitivity of bolting to photoperiod, i.e. to short vs long-day regimes, Hudson and Smith 1998).…”