Chapter 7Ultrastructure of Head Region of Molting Second-Stage
Juveniles of Heterodera glycines, With Emphasis on Stylet
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
) in host cell wall forms during initial feeding stages
of J2. Bar=1.0 µm.
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.
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.
dorsoventral longitudinal section through a molting J2 of Heterodera
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
), 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
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.
, protractor muscle. Bar=1.0 µm.
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
indicate narrow membrane junctions that join arcade cells. Just
posterior to shaft-supporting cell (A4
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;
, membrane junctions of amphids. Bar=1.0 µm.
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.
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
. 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.
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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