Infection of potato (Solanum tuberosum L.) leaves with the fungal pathogen Phytophthora infestans caused a similar, strong and co-ordinated induction of 1,3-beta-glucanases and chitinases in compatible (plant susceptible) and incompatible (plant resistant) interactions of two selected plant cultivars with appropriate races of the fungus. The temporal and spatial patterns of 1,3-beta-glucanase induction were studied in further detail by immunohistochemical and in-situ hybridization methods. Accumulation of the protein was preceded by progressive activation of the corresponding gene, commencing near infection sites and spreading rapidly throughout the whole infected leaf as well as to adjacent, non-infected leaves. Protein and mRNA distribution patterns were nearly identical in compatible and incompatible interactions. In comparison with 1,3-beta-glucanase mRNA, phenylalanine ammonia-lyase mRNA accumulated more rapidly and remained restricted to the vicinity of fungal infection sites, in addition to its constitutive occurrence in the vascular bundles. Even more rapid than any detectable mRNA induction was the accumulation of autofluorescing material in plant cells immediately surrounding fungal structures, particularly and invariably in incompatible interactions and less frequently in compatible interactions. It is concluded that cultivar-race-specific resistance is established early in the interaction of potato leaves with P. infestans and hence the observed massive accumulation of 1,3-beta-glucanase and chitinase is presumably not involved in determining this specificity.
