Seed germination of Arabidopsis thaliana phyA/phyB double mutants is under phytochrome control.
We examined the photocontrol of seed germination in the phyA/phyB double mutants of Arabidopsis thaliana seeds. Dormant phyA/phyB seeds showed a red/far-red light (R/FR)-reversible induction of seed germination. This suggests the involvement of at least one other phytochrome, phyC, D, and/or E, in controlling seed germination. We designated this spectrally active phytochrome in phyA/phyB as phyX. The full reversibility of the R-induced germination by subsequent FR pulses, and the observation that the response is reversible by FR, even after a 3-h R treatment, indicates that this phyX response belongs to the low-fluence-response type. Thus, this phyX response is functionally related to phyB-mediated responses. However, in contrast to phyB-controlled seed germination, this phyX-mediated response needs a prolonged imbibition period and exhibits reversibility kinetics different from that needed for phyB. Furthermore, this phyX response requires a prolonged irradiation time and shows a fluence rate response dependency, showing a similarity to the high irradiance response of photomorphogenesis. Thus, phyX, with regard to its control of seed germination, is a functionally new phytochrome that shares some characteristics of both phyA- and phyB-mediated responses.
Poppe
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Institut für Biologie II, Albert-Ludwigs-Universität Freiburg, Germany.
Schäfer
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E
D017360:Arabidopsis / Q000235:genetics / Q000502:physiology* / Q000528:radiation effects; D029681:Arabidopsis Proteins; D018525:Germination / Q000235:genetics*; D008027:Light; D009154:Mutation; D010786:Photoreceptor Cells; D010834:Phytochrome / Q000235:genetics* / Q000502:physiology; D051942:Phytochrome A; D051939:Phytochrome B; D012639:Seeds; D013997:Time Factors; D014157:Transcription Factors
D029681:Arabidopsis Proteins; C497973:PHYA protein, Arabidopsis; C497952:PHYB protein, Arabidopsis; D051942:Phytochrome A; D014157:Transcription Factors; D010834:Phytochrome; D051939:Phytochrome B