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Mode of phytochrome B action in the photoregulation of seed germination in Arabidopsis thaliana
Author(s) -
Shinomura Tomoko,
Hanzawa Hiroko,
Schäfer Eberhard,
Furuya Masaki
Publication year - 1998
Publication title -
the plant journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.058
H-Index - 269
eISSN - 1365-313X
pISSN - 0960-7412
DOI - 10.1046/j.1365-313x.1998.00049.x
Subject(s) - germination , phytochrome , arabidopsis , arabidopsis thaliana , biology , botany , horticulture , genetics , mutant , gene , red light
Summary Arabidopsis thaliana seeds imbibed for a short duration show phytochrome B (PhyB)‐specific photo‐induction of germination. Using this system, the relationship was determined between the amount of PhyB in seeds and photon energy required for PhyB‐specific germination in two transgenic Arabidopsis lines transformed with either the Arabidopsis PhyB cDNA (ABO) or the rice PhyB cDNA (RBO). Immunochemical detection of PhyB apoprotein (PHYB) showed that the expression level of PHYB in ABO seeds was at least two times higher than that in the wild‐type seeds, but in RBO seeds the PHYB level was indistinguishable from that in wild‐type seeds. The photon fluence required for induction and photoreversible inhibition of germination was examined using the Okazaki large spectrograph. At the wavelengths of 400–710 nm, the ABO seeds required significantly less photon fluence than wild‐type seeds for induction of germination, whereas the RBO seeds required similar fluence to wild‐type seeds. A critical threshold wavelength for either induction or inhibition of germination of ABO seeds shifted towards the longer wavelengths relative to wild‐type seeds. By assuming that PhyA and PhyB are similar in their photochemical parameters, amounts of P fr at each wavelength were calculated. The photon fluence required for 50% germination was equivalent to the fluence generating a P fr /P tot ratio of 0.21–0.43 in wild‐type seeds, and of 0.035–0.056 in ABO seeds. These results indicate that PhyB‐specific seed germination is not strictly a function of the P fr /P tot ratio, but is probably a function of the absolute P fr concentration.