Cytoplasmic pH at the onset of development in Dictyostelium.

Cytoplasmic pH (pHi) was measured by a pH 'null point' method in synchronous populations of Dictyostelium discoideum cells. Synchronous populations of vegetative cells with a lower pHi than asynchronous populations of vegetative cells show a clear preference for the prespore differentiation pathway when they enter development. Treatment of these cells before development with the weak base ammonia results in an increase in pHi and an abolition of the preference of the cells for the prespore pathway. On the other hand, synchronous populations of vegetative cells with the same pHi as asynchronous populations of vegetative cells resemble these last cells in that they show no preference for a certain differentiation direction when they enter development. However, both these synchronous and asynchronous populations of cells do acquire a preference for the prespore pathway when they are treated before development with the weak acid 5,5-dimethyl-2,4-oxazolidineolione (DMO), which lowers their pHi. It is concluded that changes in pHi at the onset of the developmental program lead to significant changes in the preference of the cells for the prespore differentiation pathway in Dictyostelium discoideum.