Anabaena is a filamentous blue-green algae that can exist planktonically or attach to aquatic organisms. It is found worldwide in fresh and salt water. Cells are prokaryotic and arranged in unbranched filaments. Specialized cells called heterocysts fix nitrogen and produce spores called akinetes for reproduction. Anabaena is economically important for nitrogen fixation in soil, symbiotic relationships, and reclaiming saline soils, though it can also cause harmful algal blooms and death of animals.

1. Anabaena
cyanobacteria

2. Taxonomic position
 Kingdom : Bacteria
 Phylum : Cyanobacteria
 Class : Cyanophyceae
 Order : Nostocales
 Family : Nostocaceae
 Genus : Anabaena

3. Occurrence
• It is a filamentous blue green algae
• They are both planktonic , or make the coatings on
aquatic organisms
• Few species are entophytic and grows in cavities between
the leaves of water fern Azola and roots of Cycads
• Widespread body in fresh and salt water
• It also produces water blooms
• They have heterocyst and Akinites in their bodies

4. Plant body
The thallus is unbranched filament
Cells are joined end to end
Filaments are formed as cell grows in one
direction
Single row in a colony is called trichome
There may be one or more trichomes
These trichomes are modified into Akinites
and heterocyst
Movement has been reported by terminal
trichomes

5. Cell structure
The cell is prokaryotic
The plastids and other membranous
structures including nucleus, central vacuole,
mitochondria and Golgi apparatus are absent

6. Cell wall
The protoplast is surrounded by cell wall
made up of amino acids peptides

7. Chromoplasm
1. It contains flattened sacs, thylakoids, in which photosynthetic pigments are
located
2. These thylakoids are not segregated from cytoplasm by a membrane
3. The photosynthetic pigments are : Phycobilins ( phyccocyanine and
phycorythrin ) chlorophyll a and carotenoids
4. Phycobilins are present on the outer surface of thylakoids
5. Small spherical granules rich in carbohydrates are distributed in cytoplasm
6. These are called cyanophycin starch
7. The reserved food is stored in proteinaceous bodies called cyanophycin
granules

8. Central body
It is nuclear in nature
Nucleolus is absent
But a definite membrane is present so it is
nucleus
The nuclear material is often dispersed in the
form of network

9. Pseudovacoules
There are gas vacuoles also called
pseudovacoules
These are gas filled cavities that provide
buoyancy and helps alga to float on the
surface of water
They also reduced the intensity of light
reaching to thylakoids

10. Heterocyst
It is specialized cell that differs from
vegetative cell in stricture of wall and its
transparent content
It is produced form vegetative cell
The cell enlarges and form 3 layers in
addition to original wall
a) The granular cellular contents decrease
b) The thylakoid reorganize into concentric
rings or reticulate pattern
c) Polar nodules are also present
d) The pores are helpful in making the
connection between the heterocyst and
other cell
The heterocyst are site of nitrogen fixation
They are also responsible for converting the
vegetative cells into Akinites
Ins one species there heterocyst act as
reproductive structure

11. Akinites
They are non motile spores formed by
transformation of a vegetative cell
A vegetative cell enlarges , accumulates
cyanophycin granules and the original cell
wall become thickened
The thylakoids retain the original
arrangement
These are resistant to environmental
adversities
Helps to germinate to new filament on return
of favorable conditions
They are formed next to heterocyst

12. Reproduction
Most common methods of reproduction are
a) Vegetative reproduction ( formation of
spores) and fragmentation
b) Sexual reproduction is absent

13. Fragmentation or formation of
hormogonia
• It is a type of vegetative reproduction
• In this process the chain of cells break
into multicellular fragments
• It is due to death of cell of one or more
cell in trichomes
• The breaking takes place at heterocyst
point
• The hormogonia are motile and capable
of forming new trichomes

14. Spore formation ( Akinites )
The Akinites germinate into new filament
The protoplast of the Akinites undergoes
transverse division and moves though the
ruptured spore wall to form a new filament

15. Endospore formation
In some species Anabaena cicadae ,
The heterocyst contents divide to form small
spores called endospores, these give rose to
new filament upon germination

16. Heterocyst as reproductive
structure
• In Anabaena haleness , the heterocyst
germinates to produce new filament
• The contents of heterocyst divides into two
celled germ lings , that undergo further division
to produce four germ lings
• The wall of the heterocyst ruptures at the
equatorial region and germ lings come out and
grow into the new filament
• In some cases the protoplast of the heterocyst
divides to form a number of small endospores
• These spores are released by rupture in the
wall , secrete a thick wall and undergo a period
of rest
• Each endospore germinates into a new filament
by cell division

17. Economic importance
• Nitrogen fixation
• Increase in fertility of soil and crop yield
• Symbiotic association
• Reclamation of saline soil
• Water blooms
• Death to animal

18. Nitrogen fixation
Anabaena actively participates in nitrogen
fixation, therefore increases the fertility of
the soil

19. Increase in fertility of soil and
crop yield
Anabaena spp are grown in rice fields to
increase the fertility of the soil and promotes
yield of rice crops

20. Symbiotic association
Anabaena forms symbiotic relationship with
roots of cycads

21. Reclamation of saline soil
Anabaena is grown in saline soils where they
form thick mass on the soil surface and help
in reducing the pH of the soil and increases
the water holding capacity of the soil

22. Water blooms
Anabaena forms water blooms in storage
water and impart unpleasant smell as a result
of water becomes unfit for the humans
consumption due to presence of suspended
organic matter in it

23. Death to animal
Anabaena spp produce toxins causing deaths
of animals like horses , cattle , sheep etc.