Chapter 2Ultrastructure of Stomatal Region of Juveniles
Stage of the Soybean Cyst Nematode, Heterodera glycines
Figure 10. Lateral longitudinal
section through anterior region of a Heterodera glycines
J2. Cephalic framework (CF), stomatal wall (SW),
and protractor muscles (Pm) provide support, guidance,
and contraction required for stylet (St) protraction. Arrows,
membrane junctions of tissue related to stylet shaft; EOZ1,
particulate electron-opaque zone; EOZ2, filamentous
electron-opaque zone; EL, esophageal lumen; H, hypodermis;
PmS, protractor muscle sarcoplasm; sm, secondary
muscle (see fig. 15); Sm,
somatic muscle. Bar=1.0 µm.
Figure 11. Nematode salivation
and food ingestion occur through stylet lumen (SL), which
has a ventrally located subterminal aperture (SA). Bar=1.0
Figure 12. Longitudinal
section of stylet (St) showing invagination of stomatal
wall (SW) during stylet projection. Bar=1.0 µm.
Figure 13. Enlarged view
of anteriad shaft region of stylet (St), showing fold of
invaginated stomatal wall (SW) during stylet projection.
Figure 14. Longitudinal
section of juvenile nematode showing hypodermis (H) and
hemidesmosomes (hd) that interact with the striated basal
layer of cuticle (bcu) and the basal lamina (bl)
of somatic muscle. Bar=1.0 µm.
Figure 15. Oblique view
of secondary muscle (sm) attachment to esophageal lumen
wall (LW). EL, esophageal lumen. Bar=0.5 µm.
Figure 16. Cross section
of a nematode with linear orientation of hemidesmosomes (hd),
showing interaction between the cuticle and the basal lamina (bl)
of somatic muscle (Sm), with hypodermis as an intermediary.
bcu, basal layer of cuticle; ccu, cortical layer
of cuticle; mcu, median layer of cuticle. Bar=1.0 µm.
Figure 17. Cross section
of stylet protractor muscle (Pm), showing thick myosin
filaments (mfi) surrounded by thinner actin filaments (afi).
Figure 18. Cross section
of somatic muscle (Sm), showing myosin filaments (mfi)
alone and interdigitated with actin filaments (afi). Bar=0.25
section through a dorsoventral part of cephalic framework, showing
interfacing of the fibrillar matrix (fm
) of framework with
the cuticular surface (cs
). Also seen is relationship of
(1) the cuticularized stomatal aperture (sa
by apertures of the inner labial receptors (ILR
) and (2)
portions of an amphidial canal (AC
). Bar=1.0 µm.
Figure 20. Submedian longitudinal
section through cephalic framework, showing portion of anterior
part of stomatal wall and portions of two sublateral blades (SlB)
of cephalic framework. Narrow lateral base of cephalic framework
(bp) lies adjacent to striated basal layer (bcu)
of nematode cuticle. Bar=1.0 µm.
Figure 21. Section through
a dorsal or ventral sector of cephalic framework, showing a relatively
thick blade (CFB) that is continuous with basal plate (bp).
Hemidesmosomes (hd) provide contact points for bundles
of filaments that traverse the hypodermis and lie between the
basal plate of cephalic framework and the subjacent termini of
somatic (Sm) and protractor muscles. bl, basal lamina.
slightly submedian section through cephalic framework, showing
the fibrillar stomatal wall (SW
) with an electron-opaque
particulate zone (EOZ1
) and the centrally located
electron-opaque filamentous zone (EOZ2
section through dorsal (DBP
) and ventral (VBP
of basal plate shows hemidesmosomes (hd
) between the basal
plates and the basal lamina (bl
) of somatic muscles. Cuticle
) that covers basal plate is especially thin at last
head annulation. Bar=1.0 µm.
Figure 23. Submedian section
of cephalic framework. The two portions of sublateral framework
blades (SlB) illustrate the curved basal region of these
blades through which accessory cilia traverse. Both inner (IAci)
and outer (OAci) accessory receptor cilia are shown in
their transition from the lateral to the ventral and dorsal positions
within the cephalic framework. Bar=1.0 µm.
Figure 24. Lateral section,
slightly into somatic musculature, shows sublateral framework
blades (SlB) as they extend outward and merge with basal
plate (bp). Note interface (If) between the framework
and the anterior cuticle (cu). Note also distinct junction
(j) of the base of cuticle with the terminus of striated
basal layer of cuticle (bcu). Bar=1.0 µm.
through cephalic framework just anterior to basal plate. Dorsal
) is slightly wider than three of the four sublateral
). Although cephalic framework is highly compartmentalized
anterior to this section, interaction between dorsal and lateral
sectors is provided by curved basal region of sublateral blades
). Stylet (St
) is shown in cross section
with the anteriorly oriented lumen aperture (SLA
) and the
terminal part of sinus (Si
). An electron-opaque particulate
) lies in fibrillar region of stomatal
wall. Highly electron-opaque cylinder of closely packed radial
filaments of stomatal wall (EOZ2
) has an irregular
margin that interacts with outer layer of stomatal wall. Internal
surface appears trilaminar. Tangential section through cephalic
framework blades shows interface (If
) between the fibrillar
component of framework (CF
) and the outer head cuticle
). Bar=1.0 µm.
Figure 26. Enlargement
of electron-opaque zone of stomatal wall similar to that shown
in fig. 25, showing radially oriented fibrils. Bar=0.1 µm.
Figure 27. In cross section,
stomatal wall fibrils appear as closely packed tubules, which
may account for flexible and expandable nature of stomatal wall
during stylet projection. Bar=0.05 µm.
Figure 28. Cross section
of nematode illustrating hemidesmosomes and bundles of filaments
that traverse the hypodermis. This section is between the basal
plate (bp) and the most anterior portions of protractor
and somatic muscles that are associated with cephalic framework.
Section through trough of first body annulation (arrows)
shows the fibrillar cuticular zone of basal plate and its junction
with striated basal layer of cuticle. Tangential and cross-sectional
views of hemidesmosomes (hd) show highly electron-opaque
irregular pattern of this junctional complex that lies between
the cephalic framework and the basal lamina of muscles. Note the
broad dorsal muscle attachment (DmA) area versus the narrow
lateral (lmA) areas. Posterior to its ventrally located
aperture, the stylet lumen (SL) is circular in cross section
and the sinus (Si) is crescent-shaped. At this level, the
stomatal wall (SW) support is reduced to flanged portions
of the dorsally and ventrally extended cephalic framework blades
(CFB). EOZ1, particulate electron-opaque
zone; EOZ2, filamentous electron-opaque zone.
illustrating the stomatal wall and the somatic and protractor
muscles slightly below cephalic framework. Inner stomatal wall
) shows outline of longitudinally oriented evaginations
that relate to flexibility of wall during stylet movement. Stylet
protractor muscles Pm2
, not shown),
although paired anteriorly, separate and merge with each of the
three stylet knob muscles posteriorly (see
. Thus, muscle elements Pm9
, and Pm2
form the dorsal
knob muscle, and Pm3
(not shown), and Pm8
form the ventrosublateral
stylet knob muscles. Both the somatic (Sm1
and protractor muscles show an increase in girth as they extend
posteriorly. Thin myofilaments occur throughout protractor muscles
at this level of sectioning. Cone portion of stylet (St
has a flattened sinus and a tubular support for stylet lumen (SL
which is embedded in cone matrix. Bar=1.0 µm.
Figure 30. Cross section
through widest part of stomatal wall (see
fig.10) with two electron-opaque inner layers surrounded by
fibrillar matrix that is continuous with cephalic framework. Hemidesmosomes
(hd) provide contact between the stomatal wall (SW)
and the centripetal surfaces of protractor muscles through bundles
of filaments of intermediate hypodermis. Hemidesmosomes (hd)
between stylet protractor (Pm) and adjacent somatic muscles
(Sm) may provide stability for stylet protraction. Most
hemidesmosomes between stomatal wall and protractor muscles appear
similar to those found between somatic muscles and cuticle (cu),
where a linear orientation appears predominant. Compared to protractor
muscles in fig. 29, those in fig. 30 show enlargement centripetally
to make contact with outer surface of stomatal wall. Stylet cone
(c) is thinner and encloses a triradiate extension of stylet
shaft (Shx). Stylet lumen and surrounding tubular support
are centrally located. H, hypodermis. Bar=1.0 µm.
Figure 31. Cross section
through posteriorly extended thin stomatal wall near its attachment
to stylet shaft (see fig. 10). Stomatal
wall (SW) separation from stylet protractor muscles is
recognized by the absence of hemidesmosomes and the space formed
between these components. Concurrently, general hemidesmosomal
attachments between the stylet protractor muscles and the somatic
muscles are greatly reduced. Terminus of a different set of somatic
muscles (Sma) appears in extreme dorsal position.
Secondary muscles (sm1, sm2)
are shown between dorso- and ventrosublateral protractor muscles.
Cone (c) portion of the stylet is reduced to thin outer
cone that is supported by extensions of shaft (Shx). Flexibility
of this thin portion of stomatal wall is illustrated in figs.
12 and 13. Sm, somatic muscle. Bar=1.0 µm.
Figure 32. Cross section
through retracted stylet shows a stylet shaft (Ss) with
relatively uniform electron-translucent matrix and a moderately
electron-opaque region surrounding the stylet lumen. Wall of hypodermis
that extends posteriorly from the juncture of stomatal wall and
stylet is appressed to stylet shaft (see
fig. 33). Electron-opaque deposits occur between stylet shaft
surface and hypodermal membrane. sm1, sm2,
secondary muscles. Arrow indicates identical site shown enlarged
in fig. 33. Bar=1.0 µm.
Figure 33. Arrow indicates
enlarged site of fig. 32. Bar=0.1 µm.
through stylet protractor muscles slightly anterior to stylet
knobs. Membrane junctions show tripartite muscle arrangement of
once bilaterally symmetrical stylet protractor muscles (10 muscle
elements). Muscle elements Pm9
, and Pm2
combine to form dorsal stylet knob protractor muscle (Pmd
Similarly, muscle elements Pm3
combine to form two subventral stylet knob muscles (Pmsv1
). Secondary muscles (sm1
) appear as discrete elements. Bar=1.0 µm.
Figure 35. Cross section
through a tripartite stylet base. Stylet knobs make anterior and
lateral contact with surrounding myofilaments of protractor muscles
via electron-opaque hemidesmosomal plates (hp). Outer supporting
membrane of stylet knobs evaginates into surrounding muscle cells
(see figs. 35, 36) to form extensive
membrane surface network between stylet and supporting muscle
cells. Arrows of figs 35 and 36 point to identical sites. Bar=1.0
Figure 36. Enlargement
of a sector of a stylet knob in fig. 35 shows extensive membrane
surface network between stylet and supporting muscles. Arrow shows
site identical site to that in fig. 35. Bar=0.1 µm.
Figure 37. Section slightly
posterior to stylet knobs, showing esophageal lumen (EL),
lumen wall, and supporting membranes. Secondary muscles (sm1
to sm4) converge toward lumen wall. Electron-opaque
material accumulates on outer surface of cisternaelike spaces
formed from interhemidesmosomal membrane evaginations that originate
from stylet knob surfaces (see figs.
10, 35, 36). Section through
dorsal knob reveals plateletlike units of hemidesmosomes (arrows)
with spaces formed by evaginated stylet knob membranes. These
membrane-supported cisternal spaces extend into noncontractile
part of stylet protractor muscles (see
fig. 10). Bar=1.0 µm.
Figure 38. Cross section
into noncontractile part of protractor muscle, showing stylet
knob, associated cisternae, and electron-opaque accumulations.
Ventral and subdorsal secondary muscles (sm1
to sm4) make terminal attachments to wall of
esophageal lumen (EL). Bar=1.0 µm.
Figure 39. Slightly
oblique section of esophagus just below stylet, showing firm attachment
of secondary muscles to wall of esophageal lumen. The two dorsosublateral
muscle elements (sm1, sm4)
merge at attachment zone. The ventrosublateral secondary muscles
(sm2 and sm3) lie adjacent
to each other and extend centripetally to form a similar junction
with the lumen wall with each muscle retaining its identity. A
longitudinal view of this junction is shown in fig. 15. Bar=1.0
Figure 40. Section through
protractor muscle sarcoplasm showing esophageal lumen (EL)
with its supporting wall and associated esophageal cells. These
cells are characterized by an abundance of mitochondria (Mc)
that are integral parts of stylet protractor muscles. Bar=1.0
of somatic muscle cell in stomatal region, showing uniform sectors
of thin actin (afi
) and thick myosin (mfi
or as sectors of interdigitating filaments consisting of thick
filaments surrounded by thin filaments. Bar=1.0 µm.
Figure 42. Longitudinal
section of an obliquely striated somatic muscle, showing a broad
band of thin actin filaments (afi) adjacent to interdigitated
thin and thick myosin filaments (mfi) in contractile region
of muscle unit. Bar=1.0 µm.
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