Chapter 9

Ultrastructure of Intestine of Second- and Third-Stage Juveniles of the Soybean Cyst Nematode, Heterodera glycines ⁸

The intestinal epithelium of many nematode species forms microvilli that project into the lumen (Munn and Greenwood 1984). Many animal-parasitic species of nematodes have regularly arranged, closely packed microvilli that constitute the surface of the intestinal epithelium (Wright 1963, Sheffield 1964, Bruce 1966, Munn and Greenwood 1984). Microvilli of Meloidogyne hapla, a plant-parasitic species, are similar to those of animal-parasitic species (Ibrahim 1971). However, in other plant-parasitic species, the microvilli are blunt in the anterior intestine but greatly attenuated in the midintestinal regions (Shepherd and Clark 1976). The anterior intestinal lumen of the infective J2 of Heterodera glycines has minimal membrane projections that might be termed microvilli (Endo 1984). Except for a brief description of microvilli (Wisse and Daems 1968) in the J2 Globodera rostochiensis, there is little information available on the morphology and ultrastructure of microvilli among cyst nematodes.

This chapter describes the ultrastructure of the esophago-intestinal valve and the microvillilike membrane folds associated with the lumen formed by the intestinal epithelium of infective, advanced second-stage, and third-stage juveniles of H. glycines. The intestine of juvenile stages of H. glycines consists of large epithelial cells filled with lipid droplets, glycogen rosettes, mitochondria, endoplasmic reticulum, and ribosomes. The esophago-intestinal valve consists of cells that are laterally attached with distinct junctional complexes. Apical boundaries of the cells have apposed membranes that separate during food ingestion. Cell surfaces of the intestinal epithelium that line the lumen have membrane folds, many of which resemble microvilli, but they lack central actin filament cores. The intestinal lining has a sculptured enteric coating. Membrane folds are sparse in the intestine of infective juveniles but extensive in parasitic juveniles. The structure of the intestino-rectal valve is similar to that of the esophago-intestinal valve in that junctional complexes attach the lateral membranes of apposed cells making up the valve. Muscle fibers are associated with the intestino-rectal valve but not with the esophago-intestinal valve.

Ultrastructure of the intestine of second- and third-stage juveniles of the soybean cyst nematode is shown in figures 179–185, figures 186-188, figures 189-190, figures 191-192, figures 193-195, figures 196-198, figures 199-202, figures 203-204, figure 205, figure 206, figures 207-208, figures 209-210, figure 211, figure 212, and figures 213-215.

⁸ Reprinted in modified form with permission of the Helminthological Society of Washington from Proceedings of Helminthological Society of Washington 55:117–131, 1988.

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