Figure 2. Heterocyst distribution in Anabaena mutant strains.

Filaments from bubbled, ammonium-supplemented cultures of the indicated strains were washed three times with BG11₀ medium, resuspended in BG11₀ and incubated under the same culture conditions for 24, 48 or 72 h (as indicated). Cells were counted after staining with Alcian Blue. Data are the mean and standard deviation of the mean of two to six independent experiments (see Materials and Methods).