Figure 1

Synchronization of the cell cycle in P. tricornutum. (a) Confocal images of a dark-arrested cell (upper panel) showing a single parietal chloroplast and a cell after 12 h illumination (lower panel) showing divided and translocated daughter chloroplasts. Red, autofluorescence of the chloroplast. Scale bar: 5 μm. (b) Validation of synchronization of the cell cycle of P. tricornutum by flow cytometry. DNA content (abscissa) is plotted against cell number (ordinate). After a 20-h dark period, most of the cells are blocked in G1 phase (t = 0 to 4 h), indicated by the single 2C peak. After reillumination, cells proceed synchronously with their cell cycle, going through S phase (between t = 4 and 7 h), visible as the broadening and lowering of the 2C peak, and G2-M phase (t = 8 to 12 h), indicated by the accumulation of 4C cells. (c) Histogram indicating the proportion of cells in a certain cell cycle phase and chloroplast conformation during the cell cycle. Divided chloroplasts were observed starting from 5 h after illumination, after S-phase onset.