Heterocyst formation in a blue-green alga, Cylindrospermum

Abstract

THE blue-green alga Cylindrospermum, unlike a similar alga, Anabaena, where intercalary heterocysts are present, contains only two terminal heterocysts (Fig. 1A). When either or both the heterocysts are detached, new heterocysts regenerate in time. In Anabaena cylindrica, where the heterocysts occur at regular intervals, the spacing pattern is determined by intercellular interactions, probably involving some inhibitory substance produced by the heterocyst itself. No two heterocysts are produced side by side either in Anabaena or Cylindrospermum. The inhibitory substance could be ammonia or a substance derived from ammonia¹. Here we report observations which indicate that an inhibitor controls the spacing of heterocysts.