Ultrastructural localization in host tissues of a toxic glycopeptide produced by Ophiostoma ulmi, using monoclonal antibodies

Abstract

Monoclonal antibodies against a phytotoxic glycopeptide from Ophiostoma ulmi (Buism.) Nannf., the Dutch elm disease pathogen, were used in a postembedding protein A – gold labeling technique to localize this toxin in experimentally infected tissues of young elm seedlings. Significant labeling was observed over pit membranes, over the innermost wall layer (protective layer) of paratracheal parenchyma cells, and over the intercellular spaces and, adjacently, the middle lamella. Host secondary walls, cytoplasm, and various organelles, except regions of amyloplastids, were free of labeling. From day 1 to day 4 after inoculation an intensification of the labeling reaction was noted that corresponded to an increase in the disease symptoms. This specific and sensitive technique has thus proved to be highly suitable for the in situ identification of antigenic macromolecules in diseased elm tissues. The classification of the toxic glycopeptide among the group of vivotoxins is discussed.