Ultrastructural aspects of host-endophyte relationships in Arbutus unedo L. mycorrhizas

A morphological examination of white-amber mycorrhizal roots of Arbutus unedo L. has been carried out using light and electron microscopy and naturally infected tissue. This type of mycorrhiza is slightly different from the typical arbutoid type; it is characterized by a few hyphae which extend along the surface of the root without forming a true mantle. They penetrate between the epidermal cells, giving rise to the Hartig net, and invade the epidermal cells. All the hyphae have simple septa and associated Woronin bodies characteristic of ascomycetous fungi. Intracellular hyphae are surrounded by invaginated host plasmalemma and by an inter-facial material of varying thickness. No evidence of lysis or digestion of the intracellular hyphae by the plant cells has been observed, the fungal hyphae generally outliving the host epidermal cells.