COMPOSITION AND ORGANIZATION OF EXTRACELLULAR MATRICES AROUND GERM TUBES AND APPRESSORIA OF COLLETOTRICHUM-LINDEMUTHIANUM

The ultrastructure and composition of the extracellular matrices (ECMs ) associated with germ tubes and appressoria of Colletotrichum lindemu thianum have been examined. Flexuous fibres (fimbriae), up to 6 mu m l ong and 4-30 nm in diameter, protruded from the surface of germ tubes and appressoria. Anionic colloidal gold and lectin cytochemistry showe d that ECMs of germ tubes and appressoria contain basic proteins, alph a-D-mannose and alpha-D-galactose residues. A monoclonal antibody, UB2 6, was raised to infection structures isolated from leaves of Phaseolu s vulgar is infected with C. lindemuthianum. UB26 recognised a protein epitope on two glycoproteins (M(r) 133,000 and 146,000). Reductions i n the M(r) of these proteins after treatment with peptide-N-glycosidas e and trifluoromethane sulphonic acid suggest that they carry N- and O -linked side-chains. Immunofluorescence and EM-immunogold labelling sh owed that glycoproteins recognised by UB26 were restricted to the ECMs around germ tubes and appressoria bur fimbriae were not labelled. Unl ike appressorial germ tubes formed in vitro, intracellular infection h yphae were not labelled, suggesting that the glycoproteins recognised by UB26 are not present on fungal structures formed within host cells. Ln liquid culture, these glycoproteins were not released into the med ium, suggesting they are physically linked to the cell wall. Also, the glycoproteins were not removed from glass surfaces by ultrasonication . These results suggest that glycoproteins recognised by UB26 may be i nvolved in the adhesion of germ tubes and appressoria to substrata. Ou r results show that the ECMs of germ tubes and appressoria differ mark edly in structure and composition from those of conidia and intracellu lar hyphae, and that extracellular glycoproteins are associated with s pecific regions of the fungal cell surface.