CALCIUM LEVELS DURING CELL CYCLE CORRELATE WITH CELL FATE OF DICTYOSTELIUM DISCOIDEUM

Levels of intracellular calcium, (Ca 2+ ) i , from different stages of cell cycle of Dictyostelium discoideum were monitored using the fluorescent Ca 2+ ‐sensitive dye, Indo 1. Combinations of Ca 2+ ‐ionophore (A23187) and Ca 2+ ‐chelator (EGTA) resulted in the inhibition of progression of cell cycle. This delay was caused due to block in G 2 /M→S phase transition of the cell cycle. Rescue of the cell cycle progression was made with 0.5m m of exogenous Ca 2+ . High (Ca 2+ ) i levels overlapped with the S‐phase, of the cell cycle. Results indicate that a high (Ca 2+ ) i level during S‐phase is not required for cell cycle progression but for cell‐type choice mechanism at the onset of starvation, and these cells tend to follow the prestalk pathway.