ABSTRACT
A high frequency of morphogenetic mutants of Dictyostelium discoideum can be induced by treatment with MNNG under conditions which result in relatively low cell killing. Six temperature-sensitive growth mutants induced by this treatment were isolated by replica plating. Among these, five showed spontaneous reversion rates of 10(-4) to 10(-5). The mutagenic activity of ems, measured for the induction of both morphogenetic and temperature-sensitive mutants, was weaker than that of MNNG and UV radiation. High frequencies of morphogenetic mutants were obtained only with doses of UV irradiation that resulted in high killing of cells or spores. Caffeine, at concentrations that slightly decreased the growth rate of amoebae in axenic medium, induced morphogenetic defects and also enhanced the mutagenic effect of UV irradiation. However, all the aggregateless clones derived from caffeine treatment that were studied reverted to the wild-type phenotype after a variable number of clonal re-isolations.
