Heterodera glycines: eggshell ultrastructure and histochemical localization of chitinous components

Abstract

The eggshell in most nematodes consists of an outer vitelline layer, a middle chitinous and an inner lipid layer. Earlier work with eggs of Heterodera glycines suggests the presence of two chitinous layers but the vitelline layer was not observed. From our observation the outer chitin layer described in past literature is actually a vitelline layer. Histochemical analysis has demonstrated that chitin is absent from the outer envelope. Electron microscope observations of the eggshell show a waxy appearance and osmium staining consistent with that of the proteinaceous vitelline layer found in other nematodes. Lectin localization also shows that the eggshell continues to develop past fertilization with the delivery and integration of eggshell precursors. Contrary to previous reports, we propose that the ultrastructure of the eggshell H. glycines follows the common three-layer structure observed in other nematodes. Index Descriptions and Abbreviations: BSA, bovine serum albumin; egg; eggshell; electron microscopy; fine structure; hatching; Heterodera glycines; histochemical; nematode; parasite; PBS, phosphate buffered saline; RT, room temperature; SEM, scanning electron microscopy; SDS, sodium dodecyl sulfate; soybean cyst nematode; TEM, transmission electron microscopy; WGA, wheat germ agglutinin; WGA-CG, wheat germ agglutinin-colloidal gold; WGA-HRP, wheat germ agglutinin-horseradish peroxidase; vitelline