High-irradiance responses induced by far-red light in grass seedlings of the wild type or overexpressing phytochrome A

Abstract

Abstract. The occurrence of phytochrome-mediated highirradiance responses (HIR), previously characterised largely in dicotyledonous plants, was investigated in Triticum aestivum L., Zea mays L., Lolium muhiflorumLam. and in both wild-type Oryza sativa L. and in transgenic plants overexpressing oat phytochrome A under the control of a 35S promoter. Coleoptile growth was promoted (maize, ryegrass) or inhibited (wild-type rice) by continuous far-red light (FRc). However, at equal fluences, hourly pulses of far-red light (FRp) were equally effective, indicating that the growth responses to FRc were not true HIR. In contrast, in maize and rice, FRc increased anthocyanin content in the coleoptile in a fluence-rate dependent manner. This response was a true HIR as FRp had reduced effects. In maize, anthocyanin levels were significantly higher under FRc than under continuous red light. In rice, overexpression of phytochrome A increased the inhibition of coleoptile growth and the levels of anthocyanin under FRc but not under FRp or under continuous red light. The effect of FRc was fluence-rate dependent. In light-grown rice, overexpression of phytochrome A reduced leaf-sheath length, impaired the response to supplementary far-red light, but did not affect the response to canopy shade-light. In grasses, typical HIR, i.e. fluence-rate dependent responses showing reciprocity failure, can be induced by FRc. Under FRc, overexpressed phytochrome A operates through this action mode in transgenic rice.

Isolation and Characterization of Rice Phytochrome A Mutants

“…We think that in the wild type, the FR pulse-induced reverse response mediated mainly by phyB was almost canceled by phyAmediated growth inhibition induced by the FR pulse. The results presented here clearly show that the coleoptile elongation in wild-type plants is inhibited by a FR light pulse and are consistent with the results using a single short exposure (Pjon and Furuya, 1967) or hourly pulses of FR light exposure (Casal et al, 1996). In addition, we have demonstrated that a pulse of VLF-R or FR light that inhibited the coleoptile elongation in wild-type seedlings was not effective for the inhibition of coleoptile elongation in phyA mutants (Figure 6, Seven-day-old etiolated seedlings of wild type (Nipponbare [N]) and two independent phyA mutants (osphyA-1and osphyA-2) were exposed to continuous R light (cR) or continuous FR light (cFR) for 0, 4, 12, and 24 hr (h) and harvested for RNA isolation.…”

CENL1Expression in the Rib Meristem Affects Stem Elongation and the Transition to Dormancy inPopulus

“…For example, Arabidopsis mutants lacking PHYA produce elongated hypocotyls when grown under a canopy (Johnson et al, 1994;Yanovsky et al, 1995), whereas strong overexpression reduces internode elongation in several species. This is often attributed to PHYA inhibition of GA biosynthesis in vascular tissue (Boylan and Quail, 1991;Jordan et al, 1995;Casal et al, Cell division walls are anticlinal in the tunica (cell layers 1 and 2), random in the corpus (approximate cell layers 3 to 8), and periclinal in the RM (approximate cell layers 9 to 11) and upper RZ. PZ, peripheral zone; CZ, central zone; p 0 , youngest leaf primordium; T, tunica; C, corpus.…”

The function of phytochrome A

“…At least in Arabidopsis, hypocotyl growth inhibition by FR is a HIR because it shows reciprocity failure (Mazzella et al 1997). Overexpression of oat phyA in transgenic tobacco (McCormac et al 1991), Arabidopsis (Whitelam et al 1992) and rice (Casal, Clough & Vierstra 1996), rice phyA in transgenic tobacco (Emmler et al 1995) and potato phyA in transgenic potato (Heyer et al 1995) enhances the response to continuous FR. Neither Arabidopsis nor rice phyB overexpressed in transgenic Arabidopsis appears to enhance HIR (McCormac era/.…”