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Journal of Cell Science, Vol 91, 109-115, Copyright © 1988 by Company of Biologists

Submitted on March 16, 1988
Accepted on June 13, 1988

Differences in Cytoplasmic pH and the Sensitivity to Acid Load Between Prespore Cells and Prestalk Cells of Dictyostelium

KEI INOUYE 1

1 Department of Botany, Faculty of Science, Kyoto UniversityKyoto 606, Japan

The relationship between cytoplasmic pH (pHi) and prestalk/prespore differentiation in the cellular slime mould Dictyostelium discoideum was investigated by: (1) comparing the pHi of prestalk and prespore cells, and (2) examining the effects on pHi of weak acids, weak bases and proton-pump inhibitors. These substances are known to affect the spore-to-stalk ratio. The pHj of dissociated slug cells was measured by microfluorometry using a pH-sensitive fluorescence dye, carboxyfluorescein.

There was a slight but significant difference in pH, between prestalk cells (7.38 ± 0.09) and prespore cells (7.49 ± 0.03), and prestalk cells were more sensitive to acid load than prespore cells. In addition, weak acids and proton-pump inhibitors, which promote prestalk differentiation, significantly lowered pHi whereas weak bases, which induce prespore differentiation, elevated pHi. However, differentiation inducing factor (DIF), an endogenous inducer of stalk differentiation, caused only a slight and transient decrease in pHi. These results suggest two alternative possibilities: (1) a small and transient decrease in pHi is sufficient to induce prestalk differentiation, or (2) there is a mediator other than pHi that links the action of DIF and the pathway choice.

Key words: cytoplasmic pH, cell differentiation, Dictyostelium discoideum, cellular slime mould

Submitted on March 16, 1988
Accepted on June 13, 1988




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© The Company of Biologists Ltd 1988