N. punctiforme
•The species of Nostoc, N. punctiforme, is known to have an interesting interaction with select plants. This is because it will infect specialised gland organs located within the multiple stems and then move on to infect specific cells of this organism, meaning the cyanobiont will be held intracellularly within the plant.
•Here it will undergo a large amount of differentiation, creating the largest frequency of heterocystous cells of any known cyanobacterial group.
•Sources of fixed nitrogen and carbon will be transferred between cells within the filament. However, additionally to this, the plant will also provide the cells of N. punctiforme with large quantities of fixed carbon, in return for the fixed nitrogen needed for biosynthesis of its own cellular compounds.
•This symbiotic relationship is very beneficial for Gunnera plants, as this allows them to grow in areas of very poor nitrogen availability without the need of other nitrogen fixing bacterial such as Rhizobium.
•The species N. punctiforme is not only capable of differentiation into specialised N2 fixing heterocystous cells, but also into cells known as hormogonia.
•Hormogonia are smaller filaments of cyanobacteria, lacking in heterocysts or vegetative cells, capable of motion through gliding motility. The differentiation into hormogonia results in a losss of nitrogen fixing capability and a large reduction in photosynthetic carbon fixation.
•However, this process appears to revert back to its normal state by dedifferentiation around 72-96 hours after initiation, again reforming filaments with heterocystous and vegetative cyanobacterial cells.