Ammonia hypersensitivity of slugger mutants of D. discoideum

The weak base ammonia inhibits aggregation and culmination of wild-type amoebae of Dictyostelium discoideum. Here we have examined its effect on a series of 'slugger' mutants previously assigned to 10 complementation groups, and so-called because they remain as slugs for extended periods. We show that the mutants accumulate normal levels of ammonia and hence may be abnormally susceptible to the ammonia they produce. In agreement with this we find that representatives of the slugger complementation groups are hypersensitive to ammonia inhibition at three clearly recognisable morphological stages of development: aggregation, tip formation and culmination. This finding suggests that a common ammonia-sensitive process underlies each of these developmental events.