Nostoc is a colonial prokaryotic
cynophycean or BGA , found in both aquatic and terrestrial habitats. The plants
may be found free floating or attached to the solid substratum. Nostoc forms
shining mucilaginous colonies, popularly known as moon spit or star jelly.
plant body is simple, unbranched and filamentous. A trichome enclosed in a
sheath is called filament . All the vegetative cells of the trichome are
similar in structure which may be spherical , barrel shaped or cylindrical. At
intervals it bears large thick walled cells called heterocyst which joins the
typical cell of the Nostoc posses cell wall, cell membrane and
protoplast. Cell wall is covered on the outside by mucilaginous sheath. Plasma
membrane is selectively permeablein nature and surrounds the protoplast .
Protoplast is differentiated into cytoplasm and nuclear body (genophore).
is commonly differentiated into outer colored chromoplasma and colorless
centroplasm. The color of chromoplasm is due to the presence of photosysthetic
thyllakoids. To the membrane of thyllakoids are attached the minute vesicles
known as phycobilisome which posses three pigments: phycocyanin (blue) and
phycoerythrin (red). The major cytoplasmic organelles like are present. Nuclear
body consist of double strand of naked DNA which lies variously in the
reproduction is absent and it reproduces vegetatively by means of fragmentation
. Asexaully it reproduces by spoire like hormogones, akinets and heterocyst.
The hormogones are short segments of trichome comes out from the old colonies
and forms the heterocyst at one or both ends and later forms mucilage and
develops the young colony. Akinets are thick walled restiong spore, which after
death and decay of parental filament, germinates and produce new colony.
Heterocyst is large and thick walled cells which in fact fix the atmospheric
nitrogen but some times it helps in reproduction by forming hormogones and
endospores. The endospore are formed by the cleavage of protoplast of
heterocyst whcih on germination gives rise to the new colony of Nostoc.
1.Colonies of Nostoc
are rich in nitrogen substance and are edible in nature.
2.Nostoc increases the fertility of soil by fixing
3.The blue green algae add organic matter to the
soil and increase fertility.
4.Cyanobacteria perform the oxygenic photosynthesis
and they are the chief producers of the biosphere.
5.Some blue green algae are used as antibiotics.
6.Species of Cyanobacteria can grow on the walls
and roof of building during rainy seasons causing discoloration , corrosion and
7.Some of the blue green algae are poisonous to
fish and domesticated animals.
8.The thick blooms caused by some blue green algae
bring about depletion of oxygen resulting in large scale death of fish and
other aquatic animals.