HETEROCYST DIFFERENTIATION AND POLARITY IN CALOTHRIX

Abstract

When grown in a nitrogen‐free medium Calothrix brevissima West has a basal heterocyst followed by a filament of cells of decreasing size. In a nitrate medium, the alga does not form heterocysts but partial polarity, i.e. tapering of the filaments, remains. In contrast, polarity as well as heterocyst differentiation, is lost on growth in an ammonium medium and the frequent formation of false branches is observed. Following exhaustion of ammonia from the medium, differentiation of heterocysts, each with two distinct polar nodules, begins at semi‐regular intervals along the filaments. Polarity is regained following breakage of the filament adjacent to a heterocyst. The ways in which nutrient limitation and heterocyst differentiation patterns can lead to three different types of false branching in the same alga are discussed. Copyright © 1978, Wiley Blackwell. All rights reserved