The weak base ammonia inhibits aggregation and culmination of wild-typ
e amoebae of Dictyostelium discoideum. Here we have examined its effec
t on a series of 'slugger' mutants previously assigned to 10 complemen
tation 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 com
plementation groups are hypersensitive to ammonia inhibition at three
dearly recognisable morphological stages of development: aggregation,
tip formation and culmination. This finding suggests that a common amm
onia-sensitive process underlies each of these developmental events.