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Nostoc
- 2. Taxonomic position • Kingdom : bacteria • Phylum : cyanobacteria • Class: cyanophyceae • Order : nostocales • Family: nostocaceae • Genus : Nostoc
- 3. Occurrence Common in fresh water ponds The large colonies are free floating Appears as circular balls They may be attached or submerges It can also be found in soil, or moist rocks, at the bottom of lakes and springs ( fresh and salt water) , but rarely in marine habitat It can also show symbiosis , with plant tissues like in hornworts , and provide nitrogen to its host through heterocyst It may also found as a part of lichen
- 4. Plant body Colony Cell structure Cell wall Pigments Nucleoplasm Reserve food material
- 5. Colony Many twisted trichomes arrogate in a gelatinous matrix to form a ball like globular colony which ranges from greenish to bluish green in color The colony is externally bounded by a tough , firm and pellicle membrane , that provides a definite shape to this.
- 6. Cell structure It is prokaryotic type The cells are without any mitochondria , endoplasmic reticulum and Golgi apparatus It has following characteristics Cell wall, pigments, nucleoplasm
- 7. Cell wall It is made up of cellulose and it surrounds the proplast
- 8. Pigments Plastids are absent The pigments are present inside chromatoplasm The cells are blue in color due to presence of phyccocyanine ( blue pigment) Other pigments include : chlorophyll , carotene and phycorythrin
- 9. Nucleoplasm A definite nucleus is absent , And nuclear material is present as central body It lacks nucleolus
- 10. Reserve food material It is in the form of sugars , glycogens, and proteinaceous material called cyanophycin
- 11. Reproduction It reproduces by following methods A: colony fragmentation B: hormogonia formation C: Akinites D: arthrospores E: endospores
- 12. Colony fragmentation The colony breaks down in to two or more fragments accidently or due to some physiological reason. Each fragment grows into a new colony
- 13. Hormogonia It is the most common method in Nostoc The filament is broken down into many short length pieces the are called as hormogonia These fragments are formed due to development of heterocyst or death of any vegetative cell These hormogonia come out of the colony by piercing the colonial sheath Each develops its own sheath and aggregate to form a new colony
- 14. Akinites These are also called resting spores A vegetative cell enlarges and secretes a thick wall around . Then stores a large amount of food and functions as Akinites They are usually present adjacent to the heterocyst, singly or in chains They help plant during unfavorable conditions When conditions become favorable these Akinites release their contents through a pore that germinate into a new filament
- 15. Arthrospores The resting Akinites are called arthrospores
- 16. Endospores In some species like Nostoc microscopium and N. commune , heterocyst contents divide to produce endospores. These spores are released into new filaments