Effect of heat shock on the cell cycle duration of algae-containing and algae-free ciliates Climacostomum virens

Cells of algae-containing (“green”) and alga-free (“white”) strains of the ciliate Climacostomum virens were compared for their responses towards a 1 h pulse of temperature stress. Although the upper heat shock temperature limits for the two strains were different (40–41 °C for “green”, and 37–38 °C for “white” cells), the responses to high temperature were similar. The delay in the completion of cell cycle depended on the cell cycle stage at which heat shock was given. Cells exposed to heat shocks at G1 stage or at the late dividing stage and returned back to 22 °C did not show any noticeable cell cycle lengthening. The most prominent effect was observed when the cells were heat-shock treated at the early dividing stage. In this case, heat shock resulted in up to 4 h delay of the cell cycle completion. It was found that in all experiments, when heat shock was given at different stages of division, the cell cycle duration of the progeny cells was significantly longer (42–50 h) than that of the control cells (21–25 h).