Intracellular chloroplast photorelocation in the moss Physcomitrella patens is mediated by phytochrome as well as by a blue-light receptor.
The light-induced intracellular relocation of chloroplasts was examined in red-light-grown protonemal cells of the moss Physcomitrella patens. When irradiated with polarized red or blue light, chloroplast distribution in the cell depended upon the direction of the electrical vector (E-vector) in both light qualities. When the E-vector was parallel to the cross-wall (i.e. perpendicular to the protonemal axis), chloroplasts accumulated along the cross-wall; however, no accumulation along the cross-wall was observed when the E-vector was perpendicular to it (i.e. parallel to the protonemal axis). When a part of the cell was irradiated with a microbeam of red or blue light, chloroplasts accumulated at or avoided the illumination point depending on the fluence rate used. Red light of 0.1-18 W m-2 and blue light of 0.01-85.5 W m-2 induced an accumulation response (low-fluence-rate response; LFR), while an avoidance response (high-fluence-rate response; HFR) was induced by red light of 60 W m-2 or higher and by blue light of 285 W m-2. The red-light-induced LFR and HFR were nullified by a simultaneous background irradiation of far-red light, whereas the blue-light-induced LFR and HFR were not affected at all by this treatment. These results show, for the first time, that dichroic phytochrome, as well as the dichroic blue-light receptor, is involved in the chloroplast relocation movement in these bryophyte cells. Further, the phytochrome-mediated responses but not the blue-light responses were revealed to be lost when red-light-grown cells were cultured under white light for 2 d.
Kadota
A
A
Department of Biological Sciences, Graduate School of Science, Tokyo Metropolitan University, Japan. kadota-akeo@c.metro-u.ac.jp
Sato
Y
Y
Wada
M
M
D019068:Bryopsida / Q000378:metabolism / Q000502:physiology* / Q000528:radiation effects / Q000648:ultrastructure; D002478:Cells, Cultured; D002736:Chloroplasts / Q000502:physiology*; D008027:Light; D045322:Photosynthetic Reaction Center Complex Proteins / Q000378:metabolism*; D010834:Phytochrome / Q000378:metabolism*
D045322:Photosynthetic Reaction Center Complex Proteins; D010834:Phytochrome