A mycoparasite, Piptocephalis virginiana ^ shows
a resemblance to fungal parasites of higher plants in
the fine structure of hyphae and haustoria. The morphology
and fine structure of host and parasitic fungi have been
described. The mode of penetration of the host cell,
Choanephora cucurbitarum , probably involves mechanical
forces. Although the presence
of cell wall degrading enzyme was not detected by
conventional techniques, its role in penetration can't
be ruled out. A collar around the haustorial neck is formed
as an extension of the host cell wall. No papilla was
detected although appressorixim was seen during penetration.
The young haustorium is enclosed in highly invaginating
plasmalemma of the host cell and n\imerous cisternae of
endoplasmic reticulum. Appearance of an electron—dense
sheath around the mature haustorium seems to coincide with
the disappearance of cisternae of endoplasmic reticulum
from the host cystoplasm in the vicinity of the haustorium.
The role of host cytoplasm particularly of endoplasmic
reticulum in the development of the sheath is discussed.
Extensive accumulation of spherosomes-like bodies,
containing lipids, is found in haustorium, parasite and
host hypha. Electron microscope revealed the parasiticculture spore has more lipid content than the axenic
culture spore of P. virginiana . The biochemical and
cytochemical tests also support these results.
The mature spore of C. cucurbitarum possesses a
thick three-layered cell wall, different from the hyphal
wall. Its germination is accompanied by the formation
of an elastic thin inner layer which surrounds the emerging
germ tube and the growing hypha. High resolution autoradiography
showed that H N-acetyl-glucosamine , a precursor
of chitin, was incorporated preferentially in the thin
inner layer of the spore wall and also in the cell wall of
the growing hypha. When the label was fed to the infected
cells, at different intervals after inoculation, grains
were observed on the sheath which developed around the
haustorium of P. virginiana , 30 hours after inoculation.
The significance of these results in relation to the origin
and composition of the sheath is discussed