A New Method for Identification of Heterocysts and Proheterocysts in Morphologically Complex Cyanobacteria

Abstract

A new light microscopic method for identifying heterocysts and proheterocysts in morphologically complex cyanobacteria was evaluated for reliability and usefulness. Mature heterocysts and proheterocysts could be distinguished readily from vegetative cells in 0.25 µm sections of fixed and embedded material after staining with toluidine blue. Examination by light and electron microscopy of the same specimens indicated that the staining reactions which served to differentiate these cell types were both reproducible and accurate. Light microscopic analysis of serial sections stained with toluidire blue greatly facilitated localization of heterocysts and proheterocysts in the complex, branching cyanobacterium, Mastigocla-dus laminosus, even when its filaments of cells were intertwined in thick mats.