Activation ofDictyostelium discoideum spores with guanidine and methyl derivatives of urea

A majority ofDictyostelium discoideum spores were activated with guanidine hydrochloride and tetramethylurea treatments. Dimethylurea could be utilized over a wide range of concentrations to activate spores. The minimal concentration was 2 M dimethylurea employed for 45–60 min, and the maximal concentration was 5 M dimethylurea employed for 20–30 min. Moderate overstimulation with dimethylurea resulted in an increase in the postactivation lag time, while severe overstimulation caused lysis and death of the spores. Partial spore deplasmolysis was a requirement for activation with dimethylurea at 23,5°C; deplasmolysis and activation did not occur at 0°C. The time required to produce an LD₅₀ was twice the time required for optimal activation when spores were treated with high concentrations of urea derivatives. A correlation was found for the hydrophobicity of the urea family of compounds and the molar concentration required for maximal activation with a 30-min treatment (2 M tetramethylurea, 5 M dimethylurea, and 8 M urea).