Lectin and Antibody Labelling of Surface Components of Spores of Phytophthora cinnamomi

Abstract

Molecules on the surface of zoospores and cysts of soilborne fungi such as Phytophthora cinnamomi are important mediators in the early stages of infection of host plants. Surface components of P. cinnamomi cells have been analysed ultrastructurally and at the molecular level using lectins and monoclonal antibodies, with a view to localising and characterising molecules involved in the infection process.

Staining with ruthenium red and the lectin, concanavalin A, indicates the presence of a glycocalyx over the surface of the zoospores. Localised antibody binding also reveals that the zoospore surface is subdivided into at least three distinct molecular domains.

During encystment, the spectrum of molecules on the cell surface changes dramatically with the secretion of material which is rich in N-acetyl-D-galactosamine and which bonds the cells to any adjacent structure. lmmunolabelling shows that this material is stored in small peripheral vesicles and is secreted 1-3 min after encystment is induced. Encystment can be triggered by the binding of a monoclonal antibody to the flagella, suggesting that specific receptors may be localised there.

Surface components on the fungal cells display a variety of taxonomic specificities including those for species and genus. Monoclonal antibodies which bind to these components promise to be valuable tools for diagnostic use.