Nostoc is a genus of cyanobacteria that is commonly found in alkaline soils, moist rocks, water ponds, streams, and lakes. The body, or thallus, of Nostoc consists of many filaments made up of rounded cells arranged in a chain. The filaments are embedded in a jelly-like mass and covered by a gelatinous sheath. Cells contain a centroplasm and chromoplasm but not a true nucleus. Nostoc reproduces asexually through fragmentation of filaments, formation of hormogonia, or production of thick-walled resting cells called akinetes. It can fix atmospheric nitrogen and plays an important ecological role through photosynthesis.

1. Prepared by:
Dr. E. Gayathiri
Department of Plant Biology and Plant Biotechnology
Guru Nanak College,

2. Learning Objectives
Overview:
Introduction
Thallus Structure
Structure of a cell of
Nostoc
Reproduction in Nostoc
Importance of
Cyanobacteria

3. Kingdom: Monera.
Class: Cyanophyceae
Order: Nostocales
Family: Nostocaceae
Genus: Nostoc
It is blue-green algae.
Nostoc is common as terrestrial and subaerial cyanobacteria.
NOSTOC
Distributed in
alkaline soils
moist rocks
water ponds
streams
and lakes.
Nostoc colony is jelly-like mass.
Filaments are embedded in this mass.
The individual filament is called trichome,
unbranched and appears bead-like structure.

4. Thallus Structure
 The body of Nostoc is called thallus.
 Consists of many threads like structures,
called filament, composed of many rounded
cells
 Arranged in a chain like manner or in beaded
form.
 All the cells are similar.
 The whole filament is covered by a gelatinous
sheath
Nostoc

5. Thallus Structure
 Heterocysts: Large in size,
thick wall which perform
two functions
 1.Reproduction:
 2.Nitrogen Fixation:
Nitrogen is converted into
simpler Nitrogen
compounds
Nostoc

6. TRICHOMES
Trichomes :
 Unbranched
 Beaded.
 Spherical
shaped,
 Barrel-shaped or
cylindrical.
Nostoc
 Trichome are mostly similar in structure
 slightly large in intervals known as
heterocyst
 Heterocysts are round, light yellowish thick-
walled.
 Trichomes mostly break near heterocyst and
forms hormogonia and thus help in
fragmentation.

7. a) CHROMOPLASM
Outer colored part
along the cell wall
Each cell of is round and has outer cell
wall. The protoplasm is of two parts:
Structure of a cell of
Nostoc
a) CENTROPLASM OR CENTRAL BODY
(incipient nucleus. i.e.(Incomplete nucleus).
• Colorless part
• Contains stored food granules.
• Acts as a nucleus.
• The cell does not contain a true nucleus.

8. Sexual reproduction absentReproduction in Nostoc
Asexual reproduction
by Hormogonia or
by Fragmentation
Hormogonia are formed by
Fragmentation. Heterocyst may
form the breaking point. Each
hormogonium grows into a new
filament by repeated cell division.
by Arthrospores or by
Akinetes Formation
Takes place in unfavorable
conditions, some cells,
enlarge and covered by a
thick wall, called
kinetes or Arthrospores
or
Resting Spores.
These heterocysts are
changed into a normal
reproductive cell and
detach from the cell.
It is converted into a new
filament.
by Heterocyst

9. Sexual reproduction absentReproduction in Nostoc
Asexual reproduction
by Hormogonia or
by Fragmentation
by Arthrospores or by
Akinetes Formation
by Heterocyst

10. Nutrition in Nostoc
It is Autotroph in nature.
Cyanobacteria (Blue, Green Algae) use carbon
dioxide and release oxygen during
photosynthesis, so environment becomes fresh
and is used by aquatic animals.
They take part in Nitrogen Fixation.
Importance of
Cyanobacteria