THE TARGET OF AMMONIA ACTION IN DICTYOSTELIUM

The weak base ammonia is implicated in a number of key processes in Dictyostelium development, notably aggregation and culmination. To determine its intracellular site of action, we compared its biological potency with that of other weak bases. All the bases inhibited these developmental processes effectively, but differed manyfold in potency in accordance with their activity in dissipating pH gradients, as measured by in vivo P-31 NMR with pH-sensitive phosphonate probes. These results indicate that weak bases influence development by raising the pH of an intracellular acidic compartment.