ULTRASTRUCTURAL-LOCALIZATION OF CELL-SURFACE SUGAR RESIDUES IN ERICOID MYCORRHIZAL FUNGI BY GOLD-LABELED LECTINS

Surface sugar residues were ultrastructurally localized in two strains of Hymenoscyphus ericae, one having a strong tendency to form ericoid mycorrhiza, the other, very little. The strains were studied both in the presence and absence of the host plant. Wheat germ agglutinin (WGA) and Concanavalin A (Con A)-colloidal gold complexes were used as cytochemical markers. N-acetylglucosamine residues were localized exclusively on septa and on the inner electron-transparent layer of longitudinal walls, confirming the presence of chitin in well defined regions of the fungal cell wall, both in the infective and in the noninfective strain. Con A-binding sites were detected on extracellular material commonly radiating from the wall of the infective strain. They were particularly abundant when the infective strain was in contact with the host, but were uncommon on the surface of the noninfective strain, whether this was in contact with the host or not. The extracellular material presumed to contain glucose and mannose residues appears to be important in establishing contact between fungus and host.