Information of Nostoc alagae

Nostoc:Taxonomic position:

Division : Cyanophyta

Class : Cyanophyceae

Order : Nostocales

Family : Nostocaceae

Genus : Nostoc

Habitat:

Nostoc is a filamentous form of both terrestrial & aquatic habitats. The colonies may be free floating or attached 

Terrestrial sp. grows on damp soil & forms leathery or rubbery sheet, it is also common in the arctic and alpine meadows.

Aquatic sp. occur are found as free floating thalli in sunny pools ,ponds and lakes or lying at the bottom attached to submerged vegetation .some species favor running water ,especially fast flowing mountain streams .attached to stones along the stream  beds. Nostoc also occurs in symbiotic association with fungi to form lichens.

 Habit:

Nostoc filaments grow in large colonies as closely packed trichomes embedded in a firm matrix of gelatinous material.

The mucilaginous lump of colony may occur free floating or attached.

Each trichome is of varying length and is made of many bead like cells.

It is enclosed by its own mucilaginous sheath.

Thus Nostoc colonies appear as yellowish of bluish green mass of jelly. Several colonies are enclosed within a gelatinous mass forming a macroscopic compound colony.

 Morphology:

Structure of the trichome:

1) Each trichome is composed of numerous rounded or oval cells.

2) The cells are joined closely from end to end into a trichome resembling a string of beads.

3) At frequent intervals along the trichomes, colorless empty looking, barrel shaped cells called heterocysts are found 

4) Heterocysts are slightly larger and have thicker walls than other vegetative cells.

5) Heterocyst is mostly intercalary but sometimes terminal in position.

6) They occur singly but sometimes in series.

7) Each intercalary heterocyst has two polar pores through which cytoplasmic connections are maintained with adjacent cells.

8) Under certain conditions some vegetative cells may become enlarged stored with food materials and greatly thickened to become resting bodies called akinets.

9) Each cell of the trichome consists of cell wall surrounding the protoplast.

10) The protoplast can be vaguely differentiated into outer pigmented cytoplasmic region called chromoplasm.

11) The chromoplasm contains colourless granules of myxophycean or cynophycean starch and cyano granules of protein mature.

Reproduction:-

Nostoc reproduces entirely vegetatively by following methods:-

1) Colony fragmentation: - the Nostoc colony, as it gets larger breaks up into smaller pieces due to storms or other disturbances. Each of these grows up to the size of parent colony.

2) Hormogone formation: - this vegetative method is common in Nostoc. The trichome ruptures at junction of heterocyst and vegetative cell, which is the weakest link in the chain. In this way smaller segments of living cells called “Hormogonia” (sing. Hormogone) become isolate. they plip out of the enclosing gelatinous matrix and establishes new colonies by division 

3) Akinets formation (): under certain condition any cell or some of the cell of the trichome becomes enlarged and each secrets a thick, highly resistant wall around it. They get filled with reserved food materials such specially modified cells are called akinets or resting pores Akinets are well adopted to survive during unfavorable conditions like water storage or unsuitable temperature. With the return of favorable season, each akinets germinates to form a new filament of Nostoc.

4) Other methods of reproduction like heterocyst germinate or endospore formation are also found.