title: fhy3-1 retains inductive responses of phytochrome A.
abstract: The fhy3 mutation of Arabidopsis impairs phytochrome A (phyA)-mediated inhibition of hypocotyl growth without affecting the levels of phyA measured spectrophotometrically or immunochemically. We investigated whether the fhy3-1 mutation has similar effects on very low fluence responses (VLFR) and high irradiance responses (HIR) of phyA. When exposed to hourly pulses of far-red light, etiolated seedlings of the wild type or of the fhy3-1 mutant showed similar inhibition of hypocotyl growth, unfolding of the cotyledons, anthocyanin synthesis, and greening upon transfer to white light. In the wild type, continuous far-red light was significantly more effective than hourly far-red pulses (at equal total fluence). In the fhy3-1 mutant, hourly pulses were as effective as continuous far-red light, i.e. the failure of reciprocity typical of HIR was not observed. Germination was similarly promoted by continuous or pulsed far-red in wild-type and fhy3-1 seeds. Thus, for hypocotyl growth, cotyledon unfolding, greening, and seed germination, the fhy3-1 mutant retains VLFR but is severely impaired in HIR. These data are consistent with the idea that VLFR and HIR involve divergent signaling pathways of phyA.
authors.affiliation: I.F.E.V.A., Facultad de Agronomía, Universidad de Buenos Aires, Avenida San Martín 4453, 1417-Buenos Aires, Argentina.
authors.forename: M J
authors.initials: MJ
authors.lastname: Yanovsky
authors.forename: G C
authors.initials: GC
authors.lastname: Whitelam
authors.forename: J J
authors.initials: JJ
authors.lastname: Casal
mesh_terms: D017360:Arabidopsis / Q000254:growth & development / Q000378:metabolism / Q000502:physiology; D029681:Arabidopsis Proteins; D002734:Chlorophyll / Q000096:biosynthesis; D009154:Mutation; D010834:Phytochrome / Q000502:physiology*; D051942:Phytochrome A; D010940:Plant Proteins / Q000235:genetics / Q000502:physiology*; D015398:Signal Transduction
chemical_list: D029681:Arabidopsis Proteins; C497973:PHYA protein, Arabidopsis; D051942:Phytochrome A; D010940:Plant Proteins; D010834:Phytochrome; D002734:Chlorophyll