Blue-Green Algae (Systematic) PDF

A- Blue green algae The algae are not a group of related forms; in fact, various forms of alga are assigned to different kingdoms. Because they have no nuclei, the blue-green algae are assigned to the kingdom Monera. They are prokaryotic. Members of the three phyla Euglenophyta, Chrysophyt...

A- Blue green algae The algae are not a group of related forms; in fact, various forms of alga are assigned to different kingdoms. Because they have no nuclei, the blue-green algae are assigned to the kingdom Monera. They are prokaryotic. Members of the three phyla Euglenophyta, Chrysophyta, and Pyrrophyta are assigned to the kingdom Protista because none of the members of these phyla are multicellular. Characteristics of the Blue-green Algae Being in the kingdom Monera, blue-green algae lack membrane-enclosed nuclei. They are, thus, acellular, and closely related to bacteria. In fact, they have been given the name cyanobacteria. Monera lack not only nuclei, but also mitochondria, Golgi bodies, and plastids. The prokaryotic blue-greens can be characterized by their cell walls and their pigments. As they are in bacteria, the cell walls of blue-green algae are composed of several layers of mucoprotein and other polysaccharides including lipopolysaccharides. Cellulose, which is found in the cells of flowering plants, is mostly absent. The pigments in blue-green algae are chlorophyll a, carotenoids, phycocyanin (blue), and phycoerythrin. These organisms often are not blue-green in color; they are sometimes yellowish, red, purple, violet, or nearly black. Morphology ranges from unicellular to filamentous; many possess extensive mucilaginous sheaths. Specialized features include the ability to fix atmospheric nitrogen possession of akinetes. and the trichome. a feature of some filamentous forms in which the entire row of cells is sheathed by a common outer wall layer. Asexual reproduction predominates. involving binary fission. Multiple fission resulting in endospores and hormogonia (short. gliding trichomes). True sexual reproduction is lacking. Trichodesmium erythraeum, a reddish blue-green alga that occasionally grows in great abundance, imparts a red color to water. The Red Sea is so named for this. The pigment chlorophyll a is directly responsible for photosynthesis, the carbohydrate product of which is glycogen (the same carbohydrate produced in animal livers). The colored portion of the cell lies around the periphery, and the central part of the cell (called the incipient nucleus) contains the chromatin. Vacuoles do not occur in healthy young cells. Some forms of blue green alga produce endospores. The blue-greens are well known for their capacity to thrive in adverse conditions. Some can grow on snow and ice, while others can be found in hot springs where the temperature approaches boiling. Blue-greens can also grow in desert soils when water is present. Some forms of blue-green algae grow in nodules in the roots of Cycads in the same manner as nitrogen-fixing bacteria grow on the roots of legumes. Some blue-greens serve as significant sources of food for fish, an arrangement that sometimes results in the fish themselves becoming poisonous. (Cattle have, in fact, died from drinking blue-green infested water.) Blue-green algae sometimes grow inside amoebas, diatoms, and other algal cells. A form of Anabaena grows in the hollow leaves of Azolla, and Nostoc grows in the thallus of Anthoceros, a bryophyte. Both Anabaena and Nostoc grow in the shells of turtles and snails, the intestines of some animals, and the hair follicles of the three-toed sloth. Reproduction among the blue-greens is entirely asexual. They reproduce only by fission or a form of fragmentation into hormogonia. Sterols are important to sexual reproduction, and these compounds do not. Types of Blue-green Algae There is some confusion regarding classification of algae. Some researchers have suggested that there may be as many as 7,500 species of blue-greens. This estimate may be high, however, given the tendency of alga to take on different forms in differing environments. Oscillatoria is a common blue-green that grows in filaments. It may be found in lakes, ponds, and moist soil, where the filaments appear singly or in mats. There are approximately thirty species of Oscillatoria in North America. These blue-greens give water a putrescent odor. The formation of filaments is caused by the cells dividing transversely. The cells of the filament are essentially alike, and each cell can be regarded as an individual. Oscillatoria is capable of an undulating movement, and this is the basis of the name. The movement is so slow that patience is required to detect it. Although several theories have been offered to explain this movement, the mechanism is not definitely known. The shorter pieces are called hormogonia, and this is one method of reproduction. Nostoc sp. Nostoc is a genus of blue-green algae or cyanobacteria. They are prokaryotic and perform photosynthesis. They are found mainly in freshwater as free-living colonies or attached to rocks or at the bottom of lakes. They are also found on tree trunks. They are also found as an algal component of lichens in certain bryophytes (Anthoceros). They are capable of nitrogen-fixing and perform photosynthesis. They are also present as an endosymbiont to fungus. i.e., Nostoc colonies may be found growing symbiotically with fungi, thus forming lichens.  Nostoc forms in colonies as large as a plum. In such a colony, there are thousands of filaments embedded in a jelly like matrix. Although Nostoc does occur in soil, it is more commonly found floating in water. Both Nostoc and Anabaena are capable of using atmospheric nitrogen to make compounds that can be used by higher plants. It is reasoned that the fertility of rice paddies is maintained by the presence of these algae. In this sense, they resemble the bacteria that grow in nodules on the roots of bean-family plants. Nostoc Structure Nostoc are filamentous and unbranched. Numerous filaments are found in a gelatinous mass as a colony. The colonies may be as big as an egg. The filament consists of a chain of cells, which appear like a bead. They are called trichomes Cells are oval, spherical or cylindrical Some of the cells in the filament are differentiated, they are called heterocyst. They are sites for nitrogen fixation. Nitrogenase enzyme fixes nitrogen Each filament is covered in a mucilaginous sheath, which is a protective layer. It absorbs and retains water. The gelatinous sheath is made up of polysaccharides and also contains proteins  Colonies are of different shapes, sizes and colours. They are mostly greenish or bluish-green in colour and also have red-brown or yellow-green colour. Extracellular pigments are also found, e.g. nostocine, scytonemin. These pigments along with some amino acids protect the cells from UV radiation Each cell has a thick cell wall made up of peptidoglycan The cytoplasm of a cell is differentiated into outer coloured due to peripherally arranged chromoplast and inner clear cytoplasm Cells have various pigments. Cells contain chlorophyll (green pigment). Phycocyanin (blue) and phycoerythrin (red) are also present Inner cytoplasm contains incipient nucleus or a nuclear body, DNA is without histones. Nostoc reproduction Nostoc reproduce vegetatively or asexually by spore formation. The vegetative reproduction is by fragmentation. Small colonies can grow attached to a large colony and later form separated colonies. Hormogonia are short and free filaments. They are formed when a filament breaks. It retains the gelatinous sheath. New trichomes are developed inside the colony.  Asexual reproduction is by the formation of resting spores known as akinetes. Some of the cells become thick-walled due to accumulation of food. They can withstand unfavourable conditions for many years. Under favourable conditions, they germinate to form a new filament. Nostoc also reproduce by heterocysts. Heterocysts separate from the filament. They divide and germinate into a new filament. Ecological Importance Nostoc are important for their nitrogen-fixing ability. They are used in paddy fields and are also used to increase the nutrient value of soil They are rich in proteins and vitamin C and are used as a delicacy in various Asian countries, e.g. N. flagelliforme, N. commune, etc. N. muscorum has shown to accumulate polyhydroxy butyrate, which is a precursor of plastic. It may have useful application in the industry Cyanobacteria can convert CO2 to biofuels. Nostoc have shown to produce hydrogen They can be used for bioremediation of wastewater and degrade environmental pollutants  Various species, e.g. N. muscorum, N. commune, N. insulare, etc. extracts have shown antibacterial or antiviral activity and may be used in future to prepare drugs. Oscillatoria sp. Oscillatoria, a fresh water, blue green alga, is represented by 76 species. Species are commonly found in fresh and polluted water of ponds, pools, drains, streams, and also in damp soils and rocks. These form bluish scums on water surface or at pond-bottom. It is an un-branched filamentous alga. Filaments may be either attached or free floating and rarely occur singly. In majority of the species, they form compact tangle mass or spongy sheets. The filaments may be interwoven or arranged in parallel rows. The filaments are uniseriate each containing a single trichome the trichomes are usually naked and have a thin, poorly developed sheath. They are usually smooth but sometimes constricted at the cross walls. Each trichome is an un-branched, long, flat thread like structure made up of numerous cells. The cells are broader than in their length and show prokaryotic organization. Cell wall is made of mucopeptide. Ultrastructure of cell shows that the chromoplast contains photosynthetic lamellae or single thylakoid which often run parallel to one another. The thylakoids contain photosynthetic pigments like chlorophyll a, carotenes, xanthophyll and phycobilin (C-phycocyanin, allophycocyanin, c-phycoerythrin). Phycobilins occur in minute vesicles called phycobilisomes. The centroplasm represents the incipient nucleus called gonophore. It is represented by DNA fibrils. The cell contains many ribosomes but mitochondria, plastids, ER and Golgi bodies are absent. Reserve food material is in the form of cyanophycean starch, lipid, globules and cyanophycin. Reproduction: Fragmentation: It occurs due to accidental breakage of the filament, biting of some insects or animals. Filament divides into small pieces or fragments. Each of these fragments is capable of developing into new individual. Hormorgonia: Hormogonia or hormogones are short segments of trichome which consists few cells. Hormogones are formed due to formation of separation discs. These discs are mucilaginous, pad like and biconcave in shape. These are formed by death of one or more cells of the filament. This mucilage filled dead cells are also called necridia. Movement in Oscillatoria: The name Oscillatoria is given to this alga due to the peculiar movement shown by the. trichome. It is called ‘oscillatory movement.