Spatial pattern of heterocysts in Anabaena sp. PCC 7120 mutant strains.

Filaments were grown with ammonium and incubated for the indicated times in the absence of combined nitrogen. Heterocyst frequency (as percentage of total cells), the mean size of vegetative cell intervals between heterocysts, and the percentage of contiguous heterocysts (interval size = 0, percentage of total intervals) were calculated (for the strains included in Figs. 2, 6 and 7 values are from the data in the figures).