Novel findings regarding photoinduced commitments of G1-, S- and G2-phase cells to cell-cycle transitions in darkness and dark-induced G1-, S- and G2-phase arrests in Euglena.
Effects of light and darkness on cell-cycle progression were studied in the log-linear photoautotrophic growth mode of Euglena gracilis. We found that there are light-dependent restriction points in the post-G1 phases, quite in contrast to Chlamydomonas, where a light-dependent restriction is known to exist only in the G1 phase. Thus, in E. gracilis, there are photoinduced commitments of G1-, S- and G2-phase cells that allow them to progress to the G1, S and G2 phases in darkness, and there are dark-induced G1-, S- and G2-phase arrests. In darkness, only committed cells were able to progress to the committed phases (G1, S or G2), whereas uncommitted cells were unable to undergo a cell-cycle transition. Whether or not cells were induced to commit by irradiation, they were eventually arrested somewhere in the G1, S or G2 (but not M) phase within 14 h of being transferred to darkness. We also describe the dependence of photoinduced commitment on light intensity and discuss the results as they relate to cell-cycle progression in continuous light.
Hagiwara
S
S
Division of Biological Sciences, Graduate School of Science, Hokkaido University, Sapporo, Japan.
Takahashi
M
M
Yamagishi
A
A
Zhang
Y
Y
Goto
K
K
D000818:Animals; D002453:Cell Cycle / Q000187:drug effects*; D018744:DNA, Plant / Q000378:metabolism*; D003624:Darkness; D005056:Euglena gracilis / Q000166:cytology* / Q000187:drug effects / Q000528:radiation effects; D016193:G1 Phase; D016195:G2 Phase; D008027:Light
D018744:DNA, Plant