Cytological studies of the M-haustorium of Endocronartium harknessii: morphology and ontogeny

Abstract

M-haustoria of the endocyclic rust Endocronartium harknessii (J. P. Moore) Y. Hirat. were examined with light and transmission electron microscopy in infected seedlings of Pinus banksiana Lamb. The haustoria developed from unspecialized cells of the intercellular hyphae, each of which appeared capable of producing several haustoria. The haustoria were distinct from the intercellular hyphae in possessing a narrow septate neck region which terminated in a globose haustorial body. Periodic acid – thiocarbohydrazide – silver proteinate and periodic acid – chromic acid – phosphotungstic acid staining provided evidence of an additional wall layer in the haustorial neck not evident in the intercellular hyphae and suggested that the extra-haustorial matrix contained polysaccharides of mixed linkage as well as lipids. However, cellulase extraction and the use of gold-bound wheat-germ lectin showed that neither cellulose nor chitin, respectively, was a component of the matrix. Both the haustoria and the matrix were separated from the host cytoplasm by the extrahaustorial membrane. This membrane stained positively with periodic acid – chromic acid – phosphotungstic acid, while the noninvaginated portion of the host plasmalemma with which it was continuous usually did not. The matrix fluoresced strongly when stained with aniline blue in an apparently compatible reaction. Other stains such as analinonapthalenesulphonic acid and Calcofluor white showed evidence of protein and polysaccharide in the fungal walls. Light and transmission electron microscope observations showed that penetration pegs formed as narrow tubular evaginations of the haustorial mother cell which caused inward displacement of the host cell wall. They retained their peg-like appearance as they entered the cell lumen, but eventually their distal ends enlarged to form typical globose haustorial bodies.