BARMICHEVA, KATHERINA M.
Komarov Botanical Institute of Russian Acad. Sci, 2 Prof. Popov St., 197376 St.-Petersburg, RUSSIA.
Endomycorrhiza of the Ericaceae is one of the most important adaptations of plants of this family to the conditions of growth on acid soils. Investigation of mycorrhizas has elucidated some structural mechanisms of this accomodation. Plants (Vaccinium myrtillus L., V. uliginosum L., V. vitis-idaea L.) were collected (May-October) in the forest of Leningrad region. The plant roots were used for the fixation and subsequent microscopic studies. The structure of short hair-like roots of all the species of Vaccinium studied here is simple. The rhizodermis is covered by thick mucilage layer. The cortex consists only of two layers, one of which is differentiated as exodermis, the other one - as endodermis. The diarch or triarch stele is surrounded by pericycle. The numerous separate fungal hyphae occupy the mucilage layer on root surface and spread between and into rhizodermal cells. In the root studied practically each rhizodermal cell was colonized by fungus; but in various cells the mycorrhizal associations were at different stages of development. Fungal symbionts found in Vaccinium roots belong to both the basidiomycetes, and the ascomycetes. With the appearance of first signs of the colonization the volume of rhizodermal cells appreciably increases, their cell walls become thickened, the exodermal cells are suberized. The fungal hypha inside rhizodermal cell is usually surrounded by invaginated plasmalemma of the host. The special contact zone is formed between the invaginated host cell plasmalemma and the fungal cell wall. The main functional phase of this mycorrhizal association is of short duration, when both partners preserve the structural integrity. Soon after this period the host cell dies, somewhat later the mycobiont also degenerates.