An ultrastructural study of vesicular-arbuscular mycorhiza in Zea diploperennis
The ultrastructure of the vesicular-arbuscular mycorrhizal association formed by Glomus fasciculatus with Zea diploperennis was investigated. Intercellular hyphae were prevalent everywhere varying from young hyphae which contained a dense cytoplasm and few vacuoles to older hyphae with many small vacuoles giving a "reticulate" appearance. Penetration by the invading intracellular hypha or endophyte was accompanied by the stretching and thinning of the host cell wall and the formation of a host cell wall material, the collar, around the endophyte. The arbuscules were formed as the result of branching of the endophyte within the cortical cells. The host cell responded to the infection with an increase in host plasmalemma and cytoplasm. The host cytoplasm was never observed to be in direct contact with the arbuscular system. There was an interfacial zone between the host and the fungus consisting of host plasmalemma, the interfacial matrix and the fungal cell wall. Deterioration of the arbuscular system began from the finer branches and proceeded backwards to the point of penetration. Clumps were formed as a result of deteriorated arbuscular material and remnants of the host plasmalemma. The host cell did not undergo any significant structural changes as the fungus deteriorated.