Control of sporulation in a blue-green alga

Abstract

Sporulation of the blue-green alga Anabaena cylindrica Lemm. generally ensues adjacent to heterocysts, in strings of from one to several cells. As a preliminary to an attempt to test whether heterocysts help to initiate sporulation of cells adjacent to them, environmental conditions conducive to rapid, sure sporulation adjacent to heterocysts were established. These conditions included the absence of phosphate from the medium, presence of alanyl-glycine or alanyl-alanine as a buffer, inclusion of sodium acetate and of a relatively high concentration of calcium ion, exposure to an optimal light intensity, and use of an adequate amount of inoculum. Evidence is presented in support of the hypothesis that sporulation of a vegetative cell near a heterocyst is dependent upon two processes: (1) abatement of a sporulation-inhibiting influence which acts on the vegetative cell, and (2) a sequential process commencing adjacent to the heterocyst.