An Electron Microscopic Study of Glycogen and Lipid in Female Meloidogyne incognita (Root-Knot Nematode)

Abstract

Changes in glycogen and lipid throughout the life cycle were observed by electron microscopy of female Meloidogyne incognita. Infective larvae had massive deposits of lipid in the intestine and smaller amounts of lipid in the hypodermis together with some /3-glycogen. Two or 3 days after invasion of roots a-glycogen began to appear and lipid to decline. Both hypodermis and intestine continued to accumulate extensive deposits of a-glycogen during growth of 2nd-stage larvae while the massive lipid of the intestine was replaced by large vacuoles with remnants of membranes. Just prior to the 3 molts, which occur in rapid succession, hypodermal glycogen was mobilized. Immediately following the molts lipid accumulated throughout the adult female. Eggs contained large quantities of lipid together with g3-glycogen. In the premolt period, lipid declines and glycogen accumulates; at molting, glycogen declines, and during postmolt adult growth, lipid accumulates, but not glycogen. The micrographs suggest that lipid is converted to glycogen in young parasitic larvae. Root-knot nematodes (Melaidogyne spp.) are endoparasites adapted for a sessile life within plant roots. Motile 2nd-stage larvae invade growing roots, migrate to the region of differentiating vascular tissues, and induce the formation of giant cells upon which they feed. The parasite grows for a time, then stops feeding and molts 3 times in rapid succession; it resumes growth and feeding as an adult female, or leaves the root as an adult male. Females become globular and produce egg sacs with up to 1,000 or more eggs in 3 to 4 weeks in favorable hosts. Males retain the elongate shape of most nematodes. As part of a nutrition study we surveyed the occurrence of glycogen in Meloidogyne incognita (Kofoid and White, 1919) Chitwood, 1949, by transmission electron microscopy through the life cycle of developing females. Glycogen occurs in two major forms in animal cells, the alpha and beta forms of Drochmans (1962). Both configurations have been found in nematode tissues (Foor, 1972; Jennings and Colam, 1970; Watson, 1965a, b; Wright and Dick, 1972). It occurs in nematode muscle, hypodermis, intestine, and gonad. Many of the published micrographs show a close spatial relation between glycogen and lipid. Jennings and Colam (1970) suggest Received for publication 3 June 1974. * This work was supported in part by USDA C.S.R.S. Grant 316-15-57. Contribution from the Missouri Agricultural Experiment Station. Journal Series Number 7038 Approved: 30 May 1974. that a lipid-glycogen system is possible in which rough endoplasmic reticulum (rer) plays a part. Passey and Fairbairn (1957) concluded on the basis of biochemical studies that fats are converted to carbohydrates during embryonation of ascaris. Barrett et al. (1971) showed that both Panagrellus redivivus and Turbatrix aceti incorporated label from '4C-tpalmitate into glycogen. In this survey of the ultrastructure of developing females of M. incognita we place special emphasis on the occurrence of glycogen