Ultrastructure of Anterior Neurosensory Organs of Juveniles
of the Soybean Cyst Nematode, Heterodera glycines 2
Investigations of the ultrastructure of the juveniles of a
related genus, Meloidogyne (Baldwin
and Hirschmann 1975a, Bird 1971,
Endo and Wergin 1977, Wergin
and Endo 1976) and of various other plant (De
Grisse 1977, De Grisse
et al. 1974, Yuen 1967)
and animal (McLaren 1972, 1974,
1976; Wright 1974, 1975)
parasitic species of nematodes provided a foundation for current
study of the juveniles of the soybean cyst nematode. Likewise,
ultrastructural investigations of the nervous system of a free-living
soilborne nematode, Caenorhabditis elegans (Ward
et al. 1975, Ware et al. 1975),
provided insight into the anterior sensory system of a nematode
having structural features similar to those of some plant and
animal parasitic species. Conversely, structural differences between
microbivorous and parasitic nematodes may provide clues to the
function of certain sensory organs that relate to parasitism.
The anterior neurosensory organs of the infective juvenile
(J2) of the soybean cyst nematode consist of two amphidial receptors,
six inner and four outer labial receptors, four cephalic receptors,
and two types of accessory receeptors. Each receptor has a characteristic
number and arrangement of cilia. Seven cilia are present in the
canals of each amphidial receptor, two in each inner labial receptor,
and a single cilium in each of the outer labial and cephalic receptors.
The ciliary portions of the two types of accessory receptors
are located internally and externally to the amphidial canal.
The cilia of the inner accessory receptors have their basal regions
just below the cephalic framework, whereas the basal regions of
the cilia of the outer accessory receptors merge with the basal
regions of the amphidial canal cilia. Some of the outer accessory
receptor cilia branch as they ascend toward the cephalic framework.
Both types of accessory receptors form swollen ciliary terminals
that extend into the various sectors of the cephalic framework.
The intermembranous spaces of the inner accessory receptors are
electron-translucent, whereas spaces formed by cilia in the outer
accessory and other receptors are filled with electron-opaque
Ventral and posterior to the dendrites supporting the amphidial
canal cilia is a microvillar nerve process that extends into the
amphidial sheath cell. Each nerve process dendrite terminates
in a pair of stout cilia. The membrane of the dendrite that gives
rise to these cilia evaginates to form numerous microvilli that
characterize this nerve process.
Although observations of sensory organs were concerned with
the morphology of Heterodera glycines, they provide a foundation
for future studies of neuroresponses and neurosecretions. This
information may be used to modify the behavior of plant parasitic
nematodes such as H. glycines and would thus affect future
strategies for plant pest control in agriculture.
Ultrastructure of the anterior neurosensory organs of juveniles
of the soybean cyst nematode is shown in figure
43, figures 4447, figures
48-49, figures 50-51, figures
52-56, figures 57-58, figures
59-61, figures 62-64, and figures 65-67.
Reprinted in modified form with permission of Academic Press from
Journal of Ultrastructure Research 72:349366, 1980.
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