The cyanobacteria, also known as blue green alga is one of the primitive organisms those show very simple cell biology and are sustained in the environment till now. Once we talk about the process of reproduction in cyanobacteria, they reproduce by very simple and primitive methods of reproduction which are vegetative and asexual.
They totally lack sexual reproduction however, genetic recombination has been reported by some scientist.
Vegetative Reproduction in Cyanobacteria
Cyanobacteria, generally divide by vegetative means of reproduction which include fission, fragmentation and by the formation of homogenization.
The unicellular cyanophycean reproduce by this method called binary fission. This is the chief method of multiplication in the unicellular forms. The nuclear division, either by a mitosis or mitosis, precedes the cell division. As known, cyanobacteria is the eucaryotic cells and do not have membranes bound true nucleus. In the process of binary fission, first genetic material is replicated to make its identical copy, the newly formed genetic material and old genetic material move to two corner of cell this is followed by the process of septation, and that’s how new daughter cell come in the existence.
This mode of reproduction plays an important role in non-filamentous and filamentous colonies. Reaching a certain size, the colony breaks up into small parts. Each part / fragment is the beginning of a new colony which increases in size by repeated cell division.
The fragmentation may also occur by mechanical means. It may result from the bites of the animals feeding on trichomes or stress caused by water currents or death of certain cells.
The trichomes of filamentous genera breaks up within the gelatinous sheath into short section or segments of one-many uniform living cells. These short length cells of trichomes are called hormogonia or hormogones. The hormogones are delimited either by the formation of heterocyst or by the development of bi – concave separation disc or necridia.
Asexual Reproduction in Cyanobacteria
The members of cyanophycean reproduce by the formation of non-motile, asexual spores which are of various sorts.
These are thick walled resistant resting cells which are frequently developed singly next to a heterocyst. These spore like structure contain the entire protoplasm of the cell and have the original parent cell wall as the outer portion of the spore wall.
These are small spores formed endogenously within a vegetative cell of the unicellular or cushioned forms of chamaersiphonales which do not form hormogonia.
At the time of endospores formation the vegetative cell increase in size. The protoplast divides by the method of successive bipartition. A large number of small, uninucleated daughter protoplast are formed. Each daughter protoplast secretes a wall around it to become an endospore.
The liberated endospore germinates immediately without a resting period.
In Chamaesiphon the cell wall ruptures at the distal end of the vegetative cell. The spores are successively pinched off at the exposed end of the extruded protoplast. They are called exospores. Each exospore is surrounded by a delicate membrane.
Some non-filamentous blue – green algae such as Microcytis the cell content divide repeatedly without any cell enlargement. The successive division follow closely one upon other. number ours daughter cells are produced in each parent cell. These are called nannocytes. These nannocytes are naked protoplast. They are extremely small in size, closely packed which germinate in situ to give rise to new typical colonies.
- Hoemospores or Hormocyts
Some members of cyanobacteria like Wiestiella produces a thick walled cells in the hormogonia segment. These structures are known as hormospores which on germination give rise to new thallus.