Characterization of the parasitic interface between Erysiphe pisi and Pisum sativum using fluorescent probes

The constituents of the interface between a strain of Erysiphe pisiand two susceptible and five resistant lines of Pisum sativum were investigated by fluorescence microscopy after treatment with specific reagents. Fragments of epidermes were detached so that the haustoria and extrahaustorial membranes were exposed directly to the reagents. The specificities of the 23 reagents employed included α- and β-linkages in polysaccharides; constituent sugars; aldehyde, amino, sulphydryl and disulphide groups; proteins, lysine, arginine, lipid, calcium and anions; and anion transport sites.

The main conclusions are that in the susceptible cultivars the extrahaustorial membrane includes polysaccharides (β1–4 linked) with small amounts of α-glucose, α-mannose and galactose, β-linked N-acetylglucosamine (haustorial face only), protein, arginine, amino and sulphydryl groups and calcium. The extrahaustorial matrix includes varying quantities of β-linked polysaccharides. Haustorial walls contain β-linked polysaccharides including α-glucose, α-mannose, galactose and N-acetyl glucosamine (β-linked). The haustorial cytoplasm contains protein and releases fluorescein from fluorescein diacetate and 3-o-methyl fluorescein phosphate.

The main differences between the susceptible lines and the resistant lines is that the resistant line, show enhanced reactivity of terminal glucose, mannose and N-acetylglucosamine groups in the extrahaustorial membranes of some lines. The last is probably due to greater accessibility of lectin effected by rupture of extrahaustorial membranes. Constituents of extrahaustorial membranes fluorescing with 4-acetamido-4′-iso-thiocyanato-stilbene-2,2′-disulphonic acid developed ore slowly and included less cross-linked protein. Calcium was rare in the extrahaustorial membranes and host cytoplasm in resistant lines.

The results are discussed in relation to the molecular and functional properties of the interface.