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United States Department of Agriculture

Agricultural Research Service

Atlas on Ultrastructure of Infective Juveniles of the Soybean Cyst Nematode, Heterodera glycines

 

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.

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Last Modified: 2/6/2002