|The akinete is the long cell between the two vegative cells. |
It is filled with spores for long term survival.
Heterocysts and akinetes are unique type of cells formed by cyanobacteria (order Nostocales and Stigonematales).
Heterocysts are almost as big as vegetative cells, and have a different colour. They are specialized biological nitrogen-fixing cells. This means that they reduce denitrogen to ammonium, a feature that helps cyanobacteria in the process of biosynthesis. Biosynthesis plays an essential role in the metabolism and structure of the cell. They have a multi-layered cell wall, with on both sides distinctively polar plugs to transport nitrogen to the vegative cells.
Heterocysts are also a main supplier of 'new' nitrogen to the aquatic environment. They lack the process of photosynthesis and therefore contain no oxygen.
If there is already a lot of nitrogen in the water, like the by-products of fertilizers, this enables heterocystous species for not taking the effort to produce heterocysts. Why use precious energy to produce heterocyst then? Instead of producing heterocysts, they will use all their energy for growth and reproduction at enormous speed.
|Clear heterocyst (A) , granular akinete (B) |
and vegetative cells (the rest of the string)
in Anabaena flos-aquae. Olympus IX 70, DP72 and
cellSens Standard at 300x magnification oil.
Photograph: Marta Demarteau/GWL
Akinetes, on the other hand, are remarkably large cells with an abnormal cell shape (elips or rectangle with rounded edges) and with a distinctively different function. They have an extra thick, layered cell wall. Akinetes are key for hibernation and to overcome unfavorable external conditions. They store reserve substances and are able to improve growth of cyanobacteria.
In Autumn, when the vegetative cells of akinete-forming cyanobacteria die, the akinete is able to survive in a rest stage. When the conditions are favorable again in Spring and Summer, the akinetes become active and produce new vegetative cells. Akinetes are therefore specialist cells with ultimate survival strategies!
Overall, I am surprised by the complexity of the cells of cyanobacteria - these small organisms that we mostly can't see with the naked eye. Only when they bloom, we can see a big flab of drifting cyanobacteria on the surface. And this is just a start in the world of cell biology, blue greens and chemistry! A start in my quest to understand the World...
|Cyanobacteria are adapted to various environments.|
Some species are so sophisticated that they
can survive in fresh, salt and brackish waters.