Chapter 7Ultrastructure of Head Region of Molting Second-Stage Juveniles of Heterodera glycines, With Emphasis on Stylet Formation
Submedial longitudinal section through lip region of Heterodera glycines
at 4 days after inoculation of 'Lee' soybean roots. Nematode is in molt between second and third stages. During molt, J2 hypodermis swells to become J3 hypodermis (J3H
). It is separated from J2 cuticle by electron-opaque granular material (EOM
). These deposits extend throughout cephalic framework. Extremely electron-opaque deposits (EOD
)present in cephalic region of infective J2appear to disintegrate during molt to combine with larger mass of granular material. Feeding plug (FP
) in host cell wall forms during initial feeding stages of J2. Bar=1.0 µm.
Figure 147. Same nematode as in fig. 146 viewed near the site of deteriorated J2 stylet shaft. Electron-opaque material (EOM) fills invaginated central anterior region of J3. Posterior to this region are arcadelike cells that contribute to development of stoma wall and stylet. Secretion-laden, arcadelike cells have integrating cell junctions. Sk, stylet knob of J2; StP, stylet primordium of J3. Bar=1.0 µm.
Figure 148.Tangential longitudinal section of a Heterodera glycines juvenile at 4 days after inoculation of 'Lee' soybeans. Hypodermal cells (HC) of J3 contain microtubules (Mt), mitochondria (Mc), and secretion granules (SG). Secretion granules appear to be deposited by microectocytosis into surrounding electron-opaque material (EOM). The most anterior cell is sharply defined by cell junctions (CJ) that separate it from adjacent posterior hypodermal cells. Portion of hypodermis extends between two stylet protractor muscles (Pm), which in turn are bordered by somatic muscles (Sm). cu, cuticle of J2. Bar=1.0 µm.
Submedial dorsoventral longitudinal section through a molting J2 of Heterodera glycines
at 4 days after inoculation of 'Lee' soybeans. Invaginated central anterior region of J2 contains a granular matrix resembling molting fluid. Matrix bounded by J2 body cuticle (cu
) and J3 hypodermis surrounds the stomatal wall (SW
), stylet cone (Sc
), and stylet shaft remnants (ShR
). Section shows portions of amphidial cuticular channels (ACC
) that enclose ciliary (ci
) processes. Two of six inner labial receptors (ILR3
) of J3 are shown at base of invaginated region filled with electron-opaque material (EOM
). Remnants of J2 inner labial receptors (ILR2
) lie adjacent to stomatal wall. Junctional complexes (jc
) unite arcadelike cells that contribute to stomatal wall, stylet cone, and stylet shaft development. Electron-translucent spherical vacuole (ETV
) represents early stage of dorsal part of tripartite stylet knob. Pm
, protractor muscle. Bar=1.0 µm.
Figure 150. Section through vacuole (ETV) of fig. 149 at a different plane, showing myofilaments of protractor muscles (Pm) that are attached (arrows) to membrane. Bar=1.0 µm.
Figure 151. Submedial section of stylet initiation zone of J3. Arcadelike cell A1 is related to the stomatal wall development, A2 to the flexible arm portion of stomatal wall, A3 to the stylet cone, and A4 to the stylet shaft. These arcadelike cells can be compared to stomatal wall and stylet components in figs. 152 and 153. Numerous secretory granules (SG) occur in arcadelike cells. Portions of electron-translucent vacuoles (ETV) within myoepithelial cells are separated from cell A4 by thickened membrane (TCM). Pm, protractor muscle; ShC, stylet shaft cell; ShR, stylet shaft residue. Bar=1.0 µm.
Median longitudinal section of anterior of molting J2, showing stomatal wall and stylet primordium of Heterodera glycines
J3. Arcadelike cells (A1
) shown in tangential sections (see fig. 151)
are now shown in direct relation to developing stages of stomatal wall (SW
), stylet cone (Sc
), and stylet shaft (Sh
). Arrows indicate narrow membrane junctions that join arcade cells. Just posterior to shaft-supporting cell (A4
) are three myoepithelial cells; two of these have vacuoles (ETV
) that will form J3 stylet knobs. A third vacuole of this same nematode is shown in fig. 150. Ac
, amphidial cilia; EOM
, electron-opaque material; HC
, hypodermal cell; ILR
, inner labial receptor; ILci
, inner labial receptor cilia; MJ
, membrane junctions of amphids. Bar=1.0 µm.
Figure 153. Stylet initial zone at slightly different level and magnification than in fig. 152. Secretion granulesespecially those adjacent to stylet cone (Sc)show direct relationship between a developing stylet and the arcadelike cell (A3). Arrows, membrane junctions; A1, A2, A3, A4, arcade cells; ShC, shaft cell; Sh, stylet shaft; SW, stomatal wall. Bar=1.0 µm.
Longitudinal oblique section through anterior of head region of a Heterodera glycines
J3 at 6 days after inoculation. Cells A1
are comparable to arcadelike cells of A1
in figs. 152 and 153. Enlarged stomatal wall, stylet components, and sensory organs are comparable to stylet primordial region and inner labial receptor zones of a molting J2 (see fig. 152)
. Former base of invaginated J2 region is now the rounded anterior head region of J3. cu
, cuticle; ILR
, inner labial receptor. Bar=1.0 µm.
Figure 155. Early stage of development of stomatal wall and stylet of a J4. Arcade cells (A1, A2, A3, A4) contain numerous secretion granules that are part of development of stomatal wall and stylet components. Bar=1.0 µm.
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