An ultrastructural and cytochemical study of Anabaena sp. (Cyanophyceae) envelopes

Abstract

Abstract Cytochemical methods at the ultrastructural level were used to investigate the composition of the external envelopes of Anabaena sp. (Cyanophyceae) vegetative cells. Results indicated that the cell wall layers increased their electron opacity following fixation in presence of tannic acid. This suggested the presence of proteinaceous compounds which are normally extracted by conventional methods for electron microscopy. In the external envelopes and in the proximity of cell wall perforation, an electron-opaque unstructured material was preserved by tannic acid. There was also an acidic carbohydrate-containing sheath-like layer reactive to colloidal iron and Alcian blue. The glycocalyx had a similar composition in young vegetative cells, whereas it altered its chemical format in the later stages of cell growth and became rich in glycoprotein and polysaccharide (i.e. stained by aqueous PTA and PTA-TSC-SP).