Localization of three sugar residues in the interface of ectomycorrhizae synthesized between Alnus crispa and Alpova diplophloeus as demonstrated by lectin binding

Abstract

The interface established between Alnus crispa and the basidiomycete Alpova diplophloeus involves structural modifications of host cell walls and hyphal walls in the Hartig net region of the ectomycorrhizae synthesized in pouches. Indirect labelling of cell wall carbohydrates by using colloidal gold conjugated with the lectins Ulex europaeus agglutinin, wheat-germ agglutinin, and concanavalin A was applied to these mycorrhizae and to nonmycorrhizal roots. Significantly more binding of the lectins was observed in the mycorrhizal roots than in control roots. In the Hartig net region of mycorrhizal roots, the lectins bound intensely to the host cell wall, particularly the wall ingrowths, and to adjacent fungal walls, whereas in nonmycorrhizal roots, a sparse labelling was recorded in the cell wall. Possible explanations for this pattern of lectin binding include the following: the sugar residues L-fucose, mannose, and N-acetylglucosamine may be utilized in the synthesis of the elaborate epidermal wall ingrowths and N-acetylglucosamine may be utilized in the synthesis of the labyrinthine wall branchings of the fungus; the sugar residues are bound to a proteinaceous fraction in the host and hyphal walls; the sugar residues bound by the lectins may be components of defense reaction elicitors released from the host wall and hyphal wall by wall-degrading enzymes; the sugar residues may simply be the result of enzymatic degradation of walls but not involving elicitors of defense reactions.