Chapter 2
Ultrastructure of Stomatal Region of Juvenile Stage of the
Soybean Cyst Nematode, Heterodera glycines 1
The soybean cyst nematode larva, like other plant-parasitic
species (Bird 1971), uses its
stylet to emerge from the egg, to penetrate the host tissue, and
to initiate and feed on a syncytium (Endo
1964). Contraction of the protractor muscles that extend from
the base of the cephalic framework to the stylet knobs thrusts
the stylet forward and through the stomatal aperture. During stylet
extension, the anterior part of the stylet, the cone, and portions
of the extended stylet shaft are guided by the stomatal wall and
the supporting cephalic framework.
A study of the ultrastructural morphology of the infective
juveniles (J2) of the soybean cyst nematode reveals an extensive
cephalic framework, stylet musculature, and a cuticular support
system that are required for host penetration and feeding. The
cephalic framework and portions of the stomatal wall have a fibrillar
matrix that merges with and supports the surface cuticle. The
flat broad base of the dorsal and ventral cephalic framework blades
imparts a bilateral orientation to the framework to which stylet
protractor and somatic muscles are attached by hemidesmosomes.
Juveniles of the soybean cyst nematode have robust stylets
that are supported by an extensive network of protractor muscles.
These muscles, in turn, are attached to the stylet, cephalic framework,
and body cuticle through a network of irregular and linearly oriented
hemidesmosomes. Protractor muscles consist of 10 muscle elements
that extend posteriorly and make lateral hemidesmosomal contacts
with the stomatal wall and adjacent somatic muscles. The 10 muscle
elements merge to form 3 distinct muscle groups that attach to
the stylet knobs. The protractor muscles are attached to the stylet
knobs by extensive hemidesmosomes. Interaction between the stylet
knobs and sarcoplasm is provided by the extensive hemidesmosomes
and interhemidesmosomal membrane evaginations that extend from
the stylet knob surface into the protractor muscle cells.
The extensive stylet protractor muscle system observed in Heterodera
glycines juveniles supports studies conducted on the mechanics
and design of tylenchid stylets (Seymour
1975). Because of the anatomical structure of the stomatal
region of its juveniles, the soybean cyst nematode is well adapted
to penetrate soybean roots and establish a feeding site that can
cause irreparable damage to the host plant.
Ultrastructure of the stomatal region of the juvenile stage
of the soybean cyst nematode is shown in figures
10–18, figures 19–21,
figures 22–24, figures
25–28, figures 29–33,
and figures 41–42.
1 Reprinted in modified form
with permission of the Helminthological Society of Washington
from Proceedings of Helminthological Society of Washington 50:43–61,
1983.
Go to Chapter 2—Figure Captions
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