Ultrastructure of nematode-trapping fungi.

Capture cells differ ultrastructurally from vegetative cells in the nematode-trapping fungi, Dactylella drechslerii, Monacrosporium rutgeriensis and Arthrobotrys dactyloides, which capture prey by means of adhesive knobs, adhesive hyphal networks, and constricting rings, respectively. Adhesive knobs and adhesive networks contain dense inclusions not found in hyphal tips or subapical regions of the vegetative hyphae, and rough- and smooth-surfaced membranes are abundant in these trap cells. The fine structure of constricting rings differs from that of adhesive traps, and it is altered by closure. In the open configuration, there are membrane-bound inclusions, labyrinthine networks, and electron-lucent regions between the protoplasts and cell wall, all localized on the luminal side of the ring cells. After closure, these features no longer are evident and the cytoplasm of trap cells stains less densely.