The tylenchid (Nematoda) egg shell: structure, composition and permeability

Abstract

The fine structure of egg shells of four different genera belonging to the order Tylenchida has been examined. The species examined were Meloidogyne javanica, Rotylenchulus reniformis, Tylenchulus semipenetrans and Pratylenchus minyus. They are all similar in their basic structure, being composed of vitelline membrane, chitin and lipid layers, but there is considerable variability in the thickness of these layers.We have retained the conventional nomenclature because of its convenience, but it is clear that these layers have a variety of chemical components. However, they do appear to contain the compounds from which they take their name. Thus chitin occurs in the chitin layer, and lipid in the lipid layer. The latter is removed by the technique used in isolating the shell from the egg. Chemical analysis of the hydrolysis products of these shells has revealed a high (35 %) proline content which appears to be a characteristic of those nematode egg shells which have been examined so far. These analyses and treatment with enzymes indicate that the chitin layer is a chitin-protein complex.Experiments on the permeability of eggs of M. javanica at different temperatures indicate that changes in permeability are not due to the melting of a single lipid with a distinct melting point as had been thought in the past. We have found that Arrhenius activation energies calculated from the two slopes of an Arrhenius plot were 17-8 kcal/mol and 43-0 kcal/mol respectively, the transition from one to the other taking place at 62 °C. We think that these changes are due to changes in the properties of lipoprotein membranes in the lipid layer. These membranes appear to be of paramount importance in controlling the permeability of the nematode egg shell.

The egg-shell ultrastructure of Blatticola blattae (Graeffe, 1860) (Oxyuridomorpha: Thelastomatidae)

“…It was found that nematodes from the orders Trichinellida and Rhabditida (infraorders Tylenchomorpha, Rhabditomorpha and some of Ascaridomorpha) are characterized by endogenous three-layered egg-shell structure (Waller, 1971;Bird & McClure, 1976;Solomon & Grigonis, 1976;Wharton & Jenkins, 1978;Wharton, 1979e). Meanwhile, the Ascaridomorpha species of Ascaris Linnaeus, 1758 and Heterakis Dujardin, 1845 possess additional exogenous uterine layer (Foor, 1967;Lee & Lešťan, 1971).…”

“…Abbreviations: LL -lipid layer; ChL -chitinous layer; VL -vitelline layer; IUL -internal uterine layer; EUL -external uterine layer Trichinellida) the lipid layer is much thicker and occupies up to quarter of total egg-shell thickness (Foor, 1967;Lee & Lešťan, 1971;Solomon & Grigonis, 1976;Wharton & Jenkins, 1978;Wharton, 1979e). The lipid layer in plantparasitic nematodes of the infraorder Tylenchomorpha was found thickening at the shell poles and having a series of lipoprotein membranes associated with it (Bird & McClure, 1976). The chitinous layer is often the thickest layer of the eggshell.…”

“…In Ascaridomorpha this layer is characterized by non-helicoidal architecture with randomly or parallel arranged fibrils (Foor, 1967;Lee & Lešťan, 1971;Wharton, 1979e). In Tylenchomorpha it also represents a chitin-protein non-helicoidal complex (Bird & McClure, 1976). According to Wharton, in oxyurids it consists of chitin and non-protein material (Wharton, 1980).…”

“…It is always characterized by a membrane-like appearance and, as well as the lipid layer of oxyurids, is one of the thinnest layers of an egg-shell (Wharton, 1979b, c, d). In fully formed egg-shells, with only three endogenous layers and the vitelline layer as the outer layer of the shell, this latter is thick and bears minute projections with strands of particulate material adhering to its outer surface (Bird & McClure, 1976;Wharton & Jenkins, 1978;Wharton, 1979e). The uterine layers have a complex structure and define an external relief of the nematode egg-shell (Bird & Bird, 1991).…”

Effects of Proline Content of Green Gram Varieties/Lines as Influenced by Root-Knot Nematode, Meloidogyne incognita

“…The root-knot nematodes cause measurable changes in the morphology and physiology of the host plants (Williamson and Gleason, 2003). Bird and McClure (1976), in their chemical analysis of the hydrolysis products of the egg shells of M. javanica, Rotylenchulus reinformis, Pratylenchus minyus and Tylenchulus semipenetrans have revealed a high proline content (up to 25 %) which is apparently a characteristic of nematode egg shells. Nasar et al (1980) analysed the effect of root-knot nematodes on the amino acid concentration of almond and peach root stalks and reported that the combined amino acid content of roots and leaves of bitter almond and Nemagaurd peach plants were the same in control and infested plants.…”