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United States Department of Agriculture

Agricultural Research Service

Atlas on Ultrastructure of Infective Juveniles of the Soybean Cyst Nematode, Heterodera glycines

 

Chapter 2—Ultrastructure of Stomatal Region of Juveniles Stage of the Soybean Cyst Nematode, Heterodera glycines

Figure Captions

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 µm.

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. Bar=1.0 µm.

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). Bar=0.25 µm.

Figure 18. Cross section of somatic muscle (Sm), showing myosin filaments (mfi) alone and interdigitated with actin filaments (afi). Bar=0.25 µm.

Figure 19. Tangential 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) surrounded 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. Bar=1.0 µm.

 

Figure 22. Lateral, 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). Cross section through dorsal (DBP) and ventral (VBP) regions of basal plate shows hemidesmosomes (hd) between the basal plates and the basal lamina (bl) of somatic muscles. Cuticle (cu) 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.

 

Figure 25. Cross section through cephalic framework just anterior to basal plate. Dorsal blade (DB) is slightly wider than three of the four sublateral blades (SlB). 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 (arrows). 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 zone (EOZ1) 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 (cu). 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. Bar=1.0 µm.

 

Figure 29. Cross section illustrating the stomatal wall and the somatic and protractor muscles slightly below cephalic framework. Inner stomatal wall (SW) shows outline of longitudinally oriented evaginations that relate to flexibility of wall during stylet movement. Stylet protractor muscles Pm2 and Pm3 (plus Pm8and Pm9, not shown), although paired anteriorly, separate and merge with each of the three stylet knob muscles posteriorly (see fig. 21). Thus, muscle elements Pm9, Pm10, Pm1, and Pm2 form the dorsal knob muscle, and Pm3, Pm4, and Pm5 plus Pm6, Pm7 (not shown), and Pm8 form the ventrosublateral stylet knob muscles. Both the somatic (Sm1, Sm2, Sm3, Sm4) 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.

 

Figure 34. Cross section 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, Pm10, Pm1, and Pm2 (none shown) combine to form dorsal stylet knob protractor muscle (Pmd). Similarly, muscle elements Pm3 to Pm5 and Pm6 to Pm8(none shown) combine to form two subventral stylet knob muscles (Pmsv1, Pmsv2). Secondary muscles (sm1 to sm4) 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 µm.

 

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 µm.

 

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 µm.

 

Figure 41. Cross section of somatic muscle cell in stomatal region, showing uniform sectors of thin actin (afi) and thick myosin (mfi) filaments 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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Last Modified: 2/6/2002