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(blue-green algae) a division of algae belonging to the Prokariota. As in bacteria, the nuclear material is not separated by a membrane from the remaining content of the cell. The inner layer of the cell membrane is made of peptidoglycan and is sensitive to the enzyme lysozyme. The algae are mostly blue-green in color. There are also pink and black specimens, whose coloration is linked with the presence of the pigments chlorophyll a, phycobilins (phycocyanin and phycoerythrin), and carotenoids. The algae are represented by unicellular, colonial, and multicellular (filamentous) organisms. They are usually microscopic, but sometimes they form spheres, clusters, and scales up to 10 cm in size. Some of the filamentous organisms are able to move by sliding.
The protoplast consists of an external colored layer, the chromatoplasm, and a colorless inner part, the centroplasm. The chromatoplasm contains lamellae (plates), which carry out photosynthesis; the lamellae are arranged in concentric layers along the membrane. The centroplasm contains the nuclear substance, ribosomes, storage substances (granules of volutin, grains of cyanophycin with lipoproteins), and glycoprotein-containing bodies. Planktonic species have gas vacuoles. There are no chloroplasts or mitochondria in blue-green algae. The transverse barriers of filamentous species are supplied with plasmodesmata. Some filamentous blue-green algae have heterocysts—colorless cells isolated from the vegetative cells by “corks” in the plasmodesmata.
Blue-green algae reproduce by cell division (unicellular algae) and by hormogonia, that is, pieces of the filaments (multicellular algae). In addition, reproduction is facilitated by akinetes (immobile dormant spores formed entirely of vegetative cells), endospores (several spores arising in each maternal cell), exospores (spores that break off from the outside of the cells), and nannocytes (tiny cells that appear in a mass during rapid division of the contents of the maternal cell). There is no sexual process in blue-green algae; there have, however, been cases of recombination of the inherited traits by means of transformation.
There are 150 genera of blue-green algae, comprising about 2,000 species. The USSR has 120 genera, embracing more than 1,000 species. The algae form part of the plankton and benthos of fresh waters and seas; they also live on the soil surface, in hot springs with water temperatures to 80°C, in the snow of polar regions, and in the mountains. A number of species inhabit a limestone substrate, and some blue-green algae are components of lichens and symbionts of protozoa and terrestrial plants (bryophytes and cycads). The greatest number of blue-green algae grow in fresh water, sometimes causing coloration of the water and killing the fish life. Under certain conditions large aggregates of the algae aid the formation of therapeutic mud. In some countries, including China and the Republic of Chad, some species (Nostoc and Spirulina) are used as food. There are experiments under way to grow blue-green algae on a mass scale in order to obtain fodder and food protein (Spirulina). Some species fix atmospheric nitrogen and thereby enrich the soil. Fossils of blue-green algae dating as far back as the Precambrian have been found.
REFERENCESElenkin, A. A. Sinezelenye vodorosli SSSR: Obshchaia chast’. Moscow-Leningrad, 1936.
Elenkin, A. A. Sinezelenye vodorosli SSSR: Spetsial’naia (sistematicheskaia) chast’, issues 1–2. Moscow-Leningrad, 1938–49.
Opredelitel’presnovodnykh vodoroslei SSSR, issue 2. Moscow, 1953.
IU. E. PETROV