One-dimensional Pattern found in Blue-Green Algae

MANY filamentous blue-green algae, when grown in the absence of combined nitrogen, produce morphologically distinct cells (heterocysts) “often, at more or less equal intervals” along the filaments1. In the presence of combined nitrogen, heterocysts occur only rarely in the algal filaments2. Fogg therefore proposed2 that the formation of a heterocyst from a vegetative cell occurs when the concentration within the cell of a specific nitrogenous inhibitory substance, either ammonia or a simple derivative of ammonia, falls below a critical level. In accordance with this hypothesis there is evidence that the heterocyst is the site of nitrogen fixation in the algae3, but this has been challenged4. The possibility that the concentration of a simple nitrogenous compound could determine spacing of heterocysts suggested a biochemical approach to the problem and provoked this study of the pattern in Anabaena cylindrica, the organism used for most earlier studies. A heterocyst pattern emerged in filaments within 12–16 h (that is, within about two-thirds of the doubling time of the organism) of their transfer from medium containing ammonia (+N medium) to medium lacking combined nitrogen (−N medium). It therefore seemed possible that the pattern was preformed in filaments grown in +N medium. Further study has confirmed this. I have demonstrated that a visible regular pattern of presumptive heterocysts is present in filaments grown in +N medium and that this pattern corresponds to that in filaments from −N medium.