Plants of the Gila Wilderness

Anabaena is an amazing blue-green alga, also known as a cyanobacterium. It belongs to the Eubacteria, and it is a prokaryote like all bacteria. It has a circular choromosome. It is photosynthetic and contains chlorophyll a and various other pigments involved in photosynthesis. Photosynthetic cyanobacteria are responsible for the Earth's oxygen atmosphere and they reduced the amount of carbon dioxide in the air by trapping it in undersea deposits. Cyanobacteria that evolved into intracellular symbionts (endosymbionts) likely became the first chloroplasts. Many cyanobacteria and certain other prokaryotes are the only known organisms that can change atmospheric Nitrogen into a form that can be used by other organisms. This process is known as Nitrogen fixation and it occurs in specialized oxygen-exclusion chambers along the chain of cells in Anabaena strands. These specialized cells are called heterocytes (or heterocysts) and are situated at intervals along the strands. These nitrogen-fixing heterocytes look more oval than than the other cells in the strands and are slightly different color.
Anabaena azollae is especially interesting among cyanobacterium because it can be found living in specialized chambers within the leaves of the smallest fern in the world-- Azolla. The cyanobacteria gains a stable place to live, and the fern gains a usable source of organic nitrogen in the form of ammonium ions. Because it is nitrogen rich, these minute ferns have been farmed in large quantities in certain areas of the world for use as fertilizers in large rice paddies.
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Anabaena azollae, 400x photomicrograph of strands at edge of torn Azolla mexicana leaf (note heterocysts), photo Russ Kleinman, Karen Blisard & Andy Anderson, from a scoop of Azolla originally from the Gila River (thanks Denise Friedrich!), February 16, 2011

Anabaena azollae, 400x photomicrograph of strands at edge of torn Azolla mexicana leaf (note heterocysts), photo Russ Kleinman, Karen Blisard & Andy Anderson, from a scoop of Azolla originally from the Gila River (thanks Denise Friedrich!), February 16, 2011

Anabaena azollae, 400x photomicrograph of strands at edge of torn Azolla mexicana leaf (note heterocysts), photo Russ Kleinman, Karen Blisard & Andy Anderson, from a scoop of Azolla originally from the Gila River (thanks Denise Friedrich!), February 16, 2011