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.
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1 November 2001
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
Shin-ya Hagiwara,
Masayuki Takahashi,
Akihiko Yamagishi,
Yulan Zhang,
Ken Goto
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Photochemistry and Photobiology
Vol. 74 • No. 5
November 2001
Vol. 74 • No. 5
November 2001