Electron microscopy of infection of nematodes byDactylaria haptotyla

Infection of nematodes byDactylaria haptotyla, a nematode-trapping hyphomycete, was studied by electron microscopy. The cytoplasm of the adhesive knob in the fungus contained a number of electron-dense, membrane-bound vesicles, 0.2–0.5 µm in diam. The vesicles were rarely seen in the stalk cell or vegetative cell cytoplasm. When the adhesive knob came into contact with the nematode's cuticle, it secreted an adhesive which was seen in ultrathin sections between the knob and the cuticle as an amorphous mass. At the same time, electron-dense vesicles in the cytoplasm were reduced in number and many small vacuoles developed. Soon after capture of a nematode, the cell wall of the adhesive knob became obscure at the prospective site of penetration, where a vesicle, 0.7 µm in diam, was found in serial thin sections of the knob's cytoplasm. At the site facing the vesicle, the peripheral part of the nematode's cell exhibited a high electron density. The vesicle, which appeared to be derived from smaller electron-dense vesicles coalesced with each other, released its enzymic contents toward the captured nematodes before penetration by the fungus.