How does hornwort benefit from cyanobacteria?

The gametophyte is attached to the surface of the soil by rhizoids, tiny root-like structures. The rhizoids function mostly to hold the gametophyte to the soil and, unlike roots, have little to do with the uptake of water and nutrients. The hornwort depends upon a symbiont, Nostoc, a nitrogen-fixing cyanobacteria (blue-green algae). According to David G. Adams (2002), the cyanobacteria inhabit a mucilaginous or slime cavity within the gametophyte. But Nostoc does not end up there by chance. When the gametophyte has insufficient combined nitrogen (nitrogen in nitrate form, NO3) to carry on advertisement Hornwort (Anthoceros) --> Microscopic View of a Community of Cyanobacteria Buy Photographic Print at AllPosters.com photosynthesis, the plant 'invites' the Nostoc to enter. Nostoc has two forms: a long-filament, immobile, nitrogen-fixing heterocyst and a short-filament, mobile, infective hormogonium. When the hornwort needs nitrogen, it releases a chemical called the hormogonium- ...  more