Azolla and Anabaena
Azolla is a free-floating water fern that floats on the water and fixes atmospheric nitrogen in association with nitrogen fixing cyanobacterium,Anabaena azollae. The symbiosis of Azolla and Anabaena is the only known association of a pterophyte with a cyanophyte. Anabaena azollaeis found in all species of the aquatic heterosporous fern. [23] [24] |
The symbiotic blue-green algae occurs extracellularly in a cavity in the leaves of Azolla. these cavities are effectively sealed and algal cells apparently cannot enter or escape from intact mature leaves. The Anabaena cells in Azolla undergo a developmental pattern of differentiation parallel to that of fern. After leaf cavities are colonized, the algal cells form heterocysts, fix nitrogen and the vegetative cells expand considerably. [25] [26] [27] |