Chapter 5
Ultrastructure of Esophageal Gland Secretory Granules in Juveniles
of the Soybean Cyst Nematode, Heterodera glycines 4
The dorsal and subventral glands of plant-parasitic tylenchid
nematodes secrete granules (Baldwin
et al. 1977). These granules were observed in the root-knot
nematode Meloidogyne javanica, and Bird
(1967) stated that secretions of the subventral glands appeared
to be associated with egg hatch and host penetration. Granules
in the subventral glands disappeared within 1–3 days after
penetration, during which time there was a threefold increase
in the size of the subventral and dorsal glands. Video-enhanced
light microscopy has shown the secretion granules of cyst nematodes
to move en masse from the gland cells to the ampullae located
at the anteriad extensions of the cells (Wyss
and Zunke 1985). Once the nematode has established a feeding
site, the dorsal gland secretions move through the ampulla and
stylet into the host cell and form feeding tubes. Feeding tubes
have been reported for cyst nematodes (Wyss
et al. 1984), root-knot nematodes (Rumpenhorst
1984), and reniform nematodes (Razak
and Evans 1976, Rebois 1980).
Secretion granules in the dorsal and subventral glands of infective
juveniles are initially spheroid and electron-opaque but change
in size and density after host penetration. Their products are
apparently released during salivation and feeding. This chapter
describes changes in ultrastructural morphology of secretory granules
during early stages of cyst nematode infection, the sphincters
that control movement of secretory granules through gland cells,
and the exudation of gland products into host cells.
Ultrastructural observations of the feeding sites of soybean
cyst nematode juveniles at 3 days after inoculation of soybean
roots revealed the presence of feeding tubes in the host cell
syncytium. Feeding tubes, which were extruded from the stylet
tips, were formed by products of secretory granules that originated
in the dorsal esophageal gland and accumulated in the ampulla
of the gland extension. Granules traversing the space between
the gland cell and the ampulla were regulated in their movement
by two sets of sphincterlike muscles located anterior and posterior
to the metacorpus pump chamber. Sections through the sphincter
muscles revealed obliquely arranged fibers, which in a contracted
mode caused microtubules in the gland extension to be tightly
packed.
Ultrastructure of the esophageal gland secretory granules in
juveniles of the soybean cyst nematode is shown in figure
113, figures 114-115, figure
116, figures 117-118, figure
119, figures 120-121, figure
122, figures 123-124, and figure 125.
4 Reprinted in modified form
with permission of the Society of Nematologists from Journal of
Nematology 19:469–483, 1987.
Go to Chapter 5—Figure Captions
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