Nostoc is a genus of cyanobacteria that commonly occurs in freshwater ponds and soils. It forms large, blue-green colonies that appear as circular balls made up of twisted filaments embedded in a gelatinous sheath. The cells lack organelles like mitochondria and Golgi bodies. They contain pigments like phycoerythrin that give them a blue color. Nostoc reproduces through colony fragmentation, the formation of hormogonia fragments from filaments, and the production of resting spores called akinetes that help the plant survive unfavorable conditions.

1. Nostoc
Cyanobacteria

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