Isolation by ConA binding of haustoria from different rust fungi and comparison of their surface qualities

Summary Rust haustoria isolated from infected leaf tissue strongly bind to ConA. This property was exploited to purify them by affinity chromatography on a ConA-Sepharose macrobead column. Haustoria were obtained with more than 90% purity and yields of up to 50%. Binding of haustoria to the column was partially inhibited by a ConA-specific sugar, methyl a-D-mannopyranoside. Compared to ConA,Lens culinaris agglutinin and wheat germ agglutinin were less efficient affinity ligands. Using ConA-Sepharose, rust haustoria from a variety of sources could be isolated with equal efficiency, indicating that they have similar carbohydrate surface properties. The haustoria maintained their typical shape after the isolation procedure, which suggests a rather rigid wall structure. The morphology of haustoria was characteristic both for a given species and the nuclear condition of the rust mycelium. Electron microscopy of isolated haustoria revealed an intact haustorial wall surrounded by a fibrillar layer presumably derived from the extrahaustorial matrix. The matrix thus appears to represent a layer with gel-like properties which is rich in ConA-binding carbohydrates and connected to the haustorial wall but not to the host-derived extrahaustorial membrane.