Effect of heat shock on growth and division of Stylonychia mytilus

Stylonychia mytilus cells grown at 23 degrees C exhibit an immediate arrest at G1 and S stages in the cell cycle when subjected to a heat shock of 1 h at 35 degrees C. The duration of arrest was seen to be dependent on the stage at which heat shock was given. It varied from 3 to 7 h and was synchronously accompanied by the delay in the completion of cell cycle. G2 and the early dividing stage D1 were found to be even more sensitive to heat shock than G1 and S phases. Cells divide normally when heat shock was given at the late dividing stage D2. However, the G1 stage of progeny cells was prolonged to 30 h from normal 5.5 h. These observations have been compiled from the cytological studies of normal and heat-shocked Stylonychia mytilus cells at different stages of cell cycle.