Electron-dense Lamellae Research Articles

Gonads and gametogenesis in Chaetodactylus osmiae (Acariformes: Astigmata: Chaetodactylidae) a parasite of solitary bees

Chaetodactylus osmiae (Dufour, 1839) is a mite parasitizing the solitary bee - Osmia rufa L.- used as a commercial pollinator. In this study we present the anatomy of female and male reproductive systems of this species as well as its gonadal structure and gametogenesis at the ultrastructural level. The reproductive systems are similar to those of other Astigmata. The ovaries are paired and each contains germ-line cells – a giant nutritive ovarian cell connected via funnel-type intercellular bridges to oogonia and previtellogenic oocytes. Germinal cells are embedded in several large somatic stroma cells. Remarkable numerous protrusions of the nutritive ovarian cell penetrate into the stroma cell cytoplasm. Conspicuous ER cisterns run close and parallel to the surface of the germinal cells. Oocytes entering vitellogenesis disassociate with the nutritive cell and a vitelline envelope composed of heterogeneous material appears on their surface. When vitellogenesis is completed, the oocytes are full of lipid droplets and two types of yolk spheres; the vitelline envelope transforms into a thin and homogeneous chorion.Paired testes are located on one side of the body, whereas the opposite side is filled by a male accessory gland. In testis, germinal cells are embedded in a few somatic stroma cells. The earliest spermatogonia form a compact germarium, whereas later stages are dispersed randomly within the testis. Spermatocytes are characterized by a superficial spongy layer, formation of mitochondrial derivatives, loss of nuclear envelope and condensation of chromatin in threads. A single electron-dense lamella appears during the spermatid stage, separating chromatin threads from a large spongy body surrounded by arcuate, double-membrane bounded cisterns. In spermatids, the superficial spongy layer is absent. The testicular central cell in the germarium and structures related to meiotic division were not observed in the testes. Spermatozoa are multiform cells (approx. 4x11µm) containing electron-dense lamella (ca. 45 nm thick) surrounded by mitochondrial derivatives which separate chromatin threads 45-50 nm thick from remnants of the spongy body i.e. arcuate cistern profiles. Spermatozoa deposited in female spermatheca are more electron dense; the electron-dense lamella is deeply folded several times, whereas chromatin threads are present in the center of the spermatozoon and are either flanked by lamella folds or located more peripherally under the plasmalemma. Remnants of the spongy body are not discernible.

New Species of Saprobic Labyrinthulea (=Labyrinthulomycota) and the Erection of a gen. nov. to Resolve Molecular Polyphyly within the Aplanochytrids.

A culture of a unicellular heterotrophic eukaryote was established from pollen-baited seawater acquired from the nearshore environment in Tromsø, Norway. Light microscopy revealed the production of ectoplasmic nets and reproduction by biflagellated zoospores, as well as binary division. After culturing and subsequent nucleotide extraction, database queries of the isolate's 18S small ribosomal subunit coding region identified closest molecular affinity to Aplanochytrium haliotidis, a pathogen of abalone. Testing of phylogenetic hypotheses consistently grouped our unknown isolate and A.haliotidis among the homoplasious thraustochytrids. Transmission electron microscopy revealed complex cell walls comprised of electron-dense lamella that formed protuberances, some associated with bothrosomes. Co-culturing experiments with the marine fungus Penicillium brevicompactum revealed prolonged interactions with hyphal strands. Based on the combined information acquired from electron microscopy, life history information, and phylogenetic testing, we describe our unknown isolate as a novel species. To resolve molecular polyphyly within the aplanochytrids, we erect a gen. nov. that circumscribes our novel isolate and the former A.haliotidis within the thraustochytrids.

Spermatogenesis and sperm structure in Carpoglyphus lactis (L.) (Acari: Astigmata)

Testes, spermatogenesis and spermatozoa are described in the mite Carpoglyphus lactis (L.), the first representative of the Hemisarcoptoidea superfamily studied ultrastructurally. Paired testes are located posteriorly in the idiosoma, with germaria situated dorsolaterally. The germarium consists of a compact group of spermatogonia; no testicular central cell was found. The remainder of the gonad is occupied by germ cells in different stages of spermatogenesis, distributed separately rather than in cysts, and embedded in a few large somatic cells filling the remaining space. Spermatocytes are covered by a spongy layer, a product of the Golgi apparatus. Spermatids are anucleate. Their chromatin condenses into granular and then tubular threads. As spermiogenesis progresses, the spongy layer assembles at a single site and forms a structure termed the spongy body; mitochondria become electron dense, elongate and gather forming a bundle; a narrow ER cistern, promptly transforming into a dense lamella, appears between the mitochondria and chromatin. Mature spermatozoa are small, highly electron-dense cells interdigitating with others via superficial protrusions. They possess chromatin threads, electron-dense lamella and mitochondria, but do not have an acrosome. Our results support the monophyly of Astigmata, but do not explain the phylogenetic affinities of Hemisarcoptoidea to other superfamilies of astigmatic mites.

Sperm structure and phylogeny of Astigmata

The Astigmata, a large and variable group, is still a subject of taxonomic dispute. Particularly, their origin from ancestors of the lower oribatid mites (e.g., Malaconothroidea) seems well documented by many lines of evidence. The structure of spermatozoa has been successfully applied to phylogenetic investigations in many animal groups. The aim of our study was to provide new data on spermatozoon structure in Astigmata and to consider its appropriateness in phylogenetic studies. The study reveals information on spermatozoa in 17 species of Astigmata (11 species studied for the first time) extending our knowledge to 18 species (one species known only from the literature) representing 12 families and 7 superfamilies. Spermatozoa have the same basic structure in all species: cells are multiform and the chromatin forms thin threads embedded directly in the cytoplasm; the acrosome is absent. The cytoplasm in most species contains electron-dense lamellae, varying in both number and arrangement within the cell. In Sarcoptoidea, electron-dense tubules in contact with lamellae margins were also observed in Psoroptidae (Psoroptes equi), whereas in two representatives of Sarcoptidae (Notoedres cati and Sarcoptes scabiei), only electron-dense tubules were found. In two species, Canestrinia sellnicki (Canestrinioidea: Canestriniidae) and Scutulanyssus obscurus (Analgoidea: Pteronyssidae), neither lamellae nor tubules were present. The mitochondria in a spermatozoon are usually gathered at the cell periphery and their structure is usually modified to form so-called mitochondrial derivatives. The chromatin threads are an autapomorphy strongly supporting the monophyly of Astigmata. As spermatozoa vary considerably between species in Astigmata, we deduce that sperm structure may be useful for phylogenetic analyses within the group. Several conclusions concerning the affinities within Astigmata are presented. Spermatology seems to be unhelpful, however, in questions on the origin of Astigmata (particularly for Astigmata-Oribatida relationships), since their sperm do not possess synapomorphies with sperm of the remaining groups of Acariformes, i.e., Endeostigmata, Prostigmata, and Oribatida.

Candidates for extraocular photoreceptors in the cockroach suggest homology to the lamina and lobula organs in beetles.

Using light- and electron microscopic methods, we describe two novel putative extraocular photoreceptor organs in the optic lobes of the cockroaches Leucophaea maderae and Blaberus craniifer. The lamina organ is an elongated structure distal to the first optic chiasm, adjacent to the anterior edge of the lamina. The lobula organ is situated on the anterior distal surface of the lobula. In cross sections through the pigment-free organs, cell bodies are arranged in a closed or open circle and are interconnected by desmosomes. They send protrusions with rhabdom-like microvilli into a common, central space apparently filled with extracellular matrix. A different cell type gives rise to electron-dense lamellae, which also extend into the central space and partly join to form a common lamellar bundle. Axonal processes extend from the microvillar cells and run along the outer surface of the organs to the neighboring optic neuropils. The organs receive multiple efferent innervation from neurosecretory axons. Both organs show strong immunostaining with an antiserum against Arabidopsis cryptochrome 2 that is associated with the lamellated structure in the central lumen. The specific features of the organs suggest that they are homologous to similar organs in the optic lobe of beetles and may serve a role as extraocular photoreceptors for light entrainment of the circadian system.

Ultrastructural Pathology of a Chilean Case of Tropical Spastic Paraparesis/Human T-cell Lymphotropic Type I-associated myelopathy (TSP/HAM)

Human T-cell lymphotropic virus type I (HTLV-I), is the cause of endemic tropical spastic paraparesis (TSP) or HTLV-I-associated myelopathy (HAM). Because TSP/HAM is not a fatal disease, the neuropathology of this disease, albeit relatively well understood, is based on the examination of just a few incidental cases. Previously, we demonstrated peculiar lamellated structures, called "multilamellar bodies" (MLB). In this report, we present the ultrastructural neuropathology of a TSP/HAM case from Chile, with further detailed descriptions of MLB. It is tempting to suggest that MLB may represent specific ultrastructural markers of TSP/HAM. The pathology of the anterior and posterior horns was similar and was comprised of axonal degeneration, accompanied by extensive astrocytic gliosis. Lymphocytic infiltration, particularly observed as "cuffs" around blood vessels, was scattered among other cellular elements. Ultrastructurally, myelin sheaths were relatively well preserved, and some demyelinated but not remyelinated fibers were observed. Moreover, axons with abnormal accumulations of neurofilaments, suggestive of axonal degeneration, were detected. Several axons contained Hirano bodies. In many samples, glial processes replaced most of the remaining neuropil. In a few specimens of the anterior and posterior horns of the spinal cord, MLB were observed. These structures consisted of stacks of 30 to 40 electron-dense lamellae, which were interrupted by narrow electron-lucent spaces. All of the lamellae were immersed within an amorphous substance of intermediate density. Neurons of the dorsal root ganglia were basically normal except for increased lipofuscin accumulation. As in the spinal cord, myelinated axons were well preserved, but a few were demyelinated and surrounded by concentric arrays of Schwann cell membranes. Also, axons of the dorsal roots accumulated increased number of neurofilaments. Mast cells and Schwann cells were increased in number, the latter containing abundant pi granules and myelin fragments.

Spore Wall Development inSchizaea Pectinata(Schizaeaceae: Pteridophyta)

Abstract A blechnoid type of spore wall developed in Schizaea pectinata (L.) Sw. consisting of inner and outer exospore, inner and outer perispore. The inner exospore was initiated by the formation of electron dense lamellae from the surface of the plasma membrane around each member of the tetrad. Tetrads were enclosed within chambers in the plasmodial tapetum. The outer exospore constituted the bulk of the spore wall and accumulated, at first, in irregular patches on the inner exospore; its deposition involved the activity of the plasma membrane of the plasmodial tapetum. A reticulate pattern developed on the outer exospore as a result of a differential pattern of growth involving plasmodial tapetum activity. The heterogeneous inner perispore was firmly attached to the outer exospore and its deposition involved structures found in the sporangial loculus. The outer perispore was loosely attached to the inner perispore and its formation was associated with composite bodies, which differed from the structures involved in inner perispore development, and consisted of partially polymerised sporopollenin, phenolics and silicon particles. Only the initiation of the inner exospore involved sporal activity, the development of the other parts of the spore wall were intimately associated with the plasmodial tapetum and with bodies present in the sporangial loculus.

A lamellated striated layer in the spore wall of the smut fungus Entorrhiza (Ustilaginales)

The spore wall in the smut fungus Entorrhiza has been investigated, with particular reference to layer 3. The wall is stratified into four layers, numbered 1–4 from the outside to inside of the wall. Layer 3 has a lamellated or striated organization, depending on the type of specimen preparation used for examination. In this study, thin sectioning and freeze-etching methods were used in transmission electron microscopy. Layer 3 is approximately 50 nm thick and is the narrowest layer of the wall. Thin sections viewed at high magnification show a lamellated organization, consisting of alternate electron dense and translucent spaces. Usually between 16–20 lamellae form the layer, with a lamella having a thickness of about 1–2 nm. At high resolution, each electron dense lamella is resolved as a row of closely packed subunits, approximately 1.5 nm in diameter. The electron translucent lamellae probably represent mainly lipoidal material, which is extracted during specimen preparation. In freeze-etch preparations layer 3 is termed the “striated layer”. Fracturing exposes face views of the layer, which at low magnification has a wrinkled appearance. At high magnification, layer 3 has a structure consisting of an irregular mosaic of striations. The striations in each area of the mosaic are arranged parallel, and regularly spaced 11–13 nm apart. Each area of the mosaic is separated from an adjacent area by a small step; this represents where the plane of fracture changed to a different level within layer 3. Fracturing probably occurs in the lipoidal region of the layer, corresponding to the electron translucent lamellae seen in thin section. At high magnification, the striations are resolved into subunit-like particles, approximately 1–2 nm in diameter. Layer 3 is believed to form an impervious region in the spore wall. Layer 3 in Entorrhiza closely resembles the “partition layer” reported in spores of other Tilletiaceae. This demonstration of a common wall layer strengthens the relationship between Entorrhiza and the rest of the Tilletiaceae. Entorrhiza is the only smut that forms galls on host roots.

Formation of crystalloid inclusions in the small intestine of neonatal pigs: an immunocytochemical study using colloidal gold

Enterocytes of the small intestine in 1-day-old suckling piglets contain numerous vesicles in the apical cytoplasm and a large granule located beneath the nucleus. Within the next 3 days, these granules transform into electron-dense crystalloid inclusions. These membrane-bound inclusions are up to 10 microns in length and 1-2 microns in diameter, and they are composed of electron-dense lamellae 3.9 nm apart. Postembedding immunocytochemistry, using rabbit anti-porcine IgG and goat anti-rabbit IgG conjugated to 10 nm colloidal gold, revealed that both the granules and the crystalloid inclusions contained a high concentration of maternal IgG. Although the IgG content of the crystalloid inclusions was detected on epoxy-embedded sections, the use of LR White resin resulted in a much higher density of labelling. Quantification of the labelling density showed that the concentration of IgG in the crystalloid inclusions was approximately ten times higher than that in the lumenal colostrum and approximately three times higher than that in the granules. These observations showed that there are at least three compartments involved in the accretion of IgG in the small intestine of neonatal piglets: smaller apical endocytotic vesicles, large subnuclear granules and crystalloid inclusions. The role of these compartments in maternal immunoglobulin absorption and in the acquisition of passive immunity has yet to be explored.

Development of the echinate pollen wall inFarfugium japonicum (Compositae: Senecioneae)

Development of the echinate pollen grains inFarfugium (Compositae: Senecioneae) has been studied by a combination of transmission electron microscopy and field emission scanning electron microscopy with a freeze fractured method. The inner surface of the callose wall surrounding each microspore does not possess an echinate pattern before primexine deposition begins. The primexine formation coincides with the initiation of spines. The freeze fractured primexine shows probacula which form transverse rods. The developing exine has an inner spongy substructure. The endexine is formed by the accumulation of the electron dense lamellae with white lines after the dissolution of the callose wall. In the present study, it is confirmed that the developmental process of pollen formation revealed in the field emission scanning electron microscope is consistent with the results obtained using the transmission electron microscope.

Ultrastructural, histochemical, and freeze‐fracture evaluation of multilamellated structures in human pulmonary alveolar proteinosis

Ultrastructural, histochemical, and freeze-fracture studies of material recovered by bronchoalveolar lavage from patients with pulmonary alveolar proteinosis revealed four types (A, B, C, and D) of multilamellated structures (MS). Type A, the major component, consisted of concentric, trilaminar structures which were composed of two electron-dense layers and a central lucent layer (5.7-7.5 nm in overall width) alternating with wider (25-30 nm) electron-lucent intervening layers. Type B MS were formed by concentric lamellae with a 5-5.3-nm periodicity. Type C MS were composed of wavy, electron-dense lamellae with a 4-4.5-nm periodicity. Type D MS were conglomerated masses of intricately arranged double or triple electron-dense layers (7.5-13.5 nm wide) alternating with wider (30-40-nm) electron-lucent layers. The electron-dense lamellae of type A, type C, and type D MS were stained with ruthenium red, the Thiéry method, and concanavalin A, indicating the presence of carbohydrate components. Freeze-fracture studies revealed smooth inner and outer surfaces in type A MS, with the fracture planes passing through the central parts of the trilaminar structures; the intervening layers contained 10-nm particles, which probably are proteins. Type B MS had smooth surfaces, and type C MS had slightly particulate surfaces; while type D MS showed tubular or polygonal structures, 350 nm wide, with rows of particles 7-8 nm in diameter. It is concluded that type A and type D MS contain proteins and carbohydrates, probably in the form of glycoproteins, as well as phospholipids, and are related to tubular myelin. Type B and type C MS are considered to contain mainly phospholipids; type C MS are also considered to contain carbohydrates and to be related to lamellar bodies of type II alveolar epithelial cells.

Iron-containing granules in the syncytiotrophoblast of the human chorionic villi.

The syncytiotrophoblast of the human chorionic villi during earlier stages of gestation contains abundant granules derived from Golgi complexes. The granules often include very electron-dense lamellae in their interior, and X-ray microanalysis revealed the presence of iron in these lamellae. It is, therefore, supposed that iron particles absorbed into the syncytiotrophoblast are transported to Golgi complexes and integrated into these lamellae. No evidences that the granules are released from the cells by exocytosis have been proved. Thus, one possibility to their nature might be considered, that is they play a role in lysosomal storage of iron during earlier stages when the capillaries in the chorionic stroma are undeveloped and so have little ability to transport iron into the fetal circulation.

Fine structure of the egg shells of Habrophlebia fusca (curtis) and h. consiglioi Biancheri (Ephemeroptera : Leptophlebiidae)

The eggs of 2 mayflies, Habrophlebia fusca and H. consiglioi (Ephemeroptera : Leptophlebiidae) were observed with scanning and transmission electron microscopes. The external surface of the eggs in both species had longitudinally oriented costae. The chorion of H. fusca had different structures in its costal and intercostal zones. Three distinct layers could be recognized: an inner layer close to the vitelline coat, consisting of electron-dense lamellae perpendicular to the egg surface; an intermediate layer, consisting of loosely structured fibrillar material; and an outer highly electron-dense layer, consisting of 2 separate laminae, divided by an electron-transparent line. In the egg of H. fusca, the costal area of the chorion shows a columnar structure. The columns merge distally to create wide chambers. This organization has been observed with the SEM in H. consiglioi as well. The chambers are interconnected and communicate with the exterior through openings along the costal edges. Masses of mucus-like substance are present both in the chambers and outside the chorion; they show fibrillar material and electron-dense bodies with a paracrystalline structure.

Ultrastructure and Development of Mesozoic Pollen: Classopollis

Because of its complexity one of the most unusual fossil pollen types is the genus Classopollis. Grains of this broadly defined Mesozoic taxon range from the late Triassic into the Cretaceous (Turonian), and include forms that are spherical with a subequatorial rimula. On the proximal pole is a trilete mark, and on the distal surface a thin area in the sporoderm termed the cryptopore. Ultrastructural studies of Classopollis have been completed on grains extracted from the pollen cone Classostrobus comptonensis collected from the Lower Cretaceous Wealden beds on the Isle of Wight, England. The sporoderm consists of clearly defined nexine and sexine components, with the mature nexine composed of approximately 20 electron dense lamellae, each about 10 nm thick. The sexine consists of four (S1–4) easily recognizable layers, with the most prominent zone formed of coarse, inwardly-tapering elements. The S2 layer is uniformly thickened, except in specialized areas (e.g., trilete, rimula, cryptopore) where it becomes thin. The remaining wall layers include spinules that ornament the surface and a uniform series of small lacunae associated with the spinule bases. The presence of orbicules and a complex system of membranes associated with the grains extracted from less mature cones provides an opportunity to trace some developmental stages in Classopollis sporoderm ontogeny, and to compare these stages with those of selected extant pollen types. The functional significance of the infrastructure in Classopollis pollen is discussed.

Fine structure of the chorion and site of sperm entry in the egg of Brachydanio

AbstractThe fine structure of the chorion and the region of the unfertilized egg immediately beneath the micropylar apparatus of the zebra danio, Brachydanio rerio, were studied using Nomarski differential interference optics, and scanning and transmission electron microscopy. The chorion consisted of three distinct zones: an outer, electron‐dense zone containing pore canal plugs (zona radiata externa), a middle fibrillar zone (superficial zona radiata interna), and an inner zone of 16 horizontal electrondense lamellae alternating with 15 interlamellae of lower electron density (deep zona radiata interna). The zona radiata interna was pierced by open pore canals. The single micropylar apparatus was regionalized into a cone‐shaped vestibule and a tapered micropylar canal traversing the entire chorion. The outer diameter of the micropylar canal was 7.5–8.5 μn and the inner diameter about 2.3 μn. Since the diameter of the inner micropylar aperture was slightly larger than the size of the sperm head, the block to polyspermy in eggs of the zebra danio appears to be mechanical and guaranteed by the morphological design of the micropyle. The egg plasmalemma beneath the inner micropylar aperture was differentiated as a circular cluster of 15–20 microvilli‐like projections. The cluster of surface projections, approximately 2.1–2.5 μn in diameter under scanning, electron microscopy, was distinguishable from the microplicae covering the rest of the egg surface and identified as the sperm entry site. The cortical cytoplasm subjacent to the sperm entry site was organized as a compact, electron‐dense, and homogeneous band. The sperm entry site itself was circumscribed by an area of cytoplasm (approximately 100 μn in diameter) in which cortical granules were typically arranged as a single layer immediately beneath the plasmalemma. However, there was a complete absence of cortical granules in the cytoplasm directly below the sperm entry site. The single row arrangement contrasted with the multilayered rows of cortical granules found throughout the remainder of the egg cytoplasm. Based upon Nomarski and ultrastructural analyses, there was a significant polarity in the cortex created by the size distribution and volume density of the cortical granules layered just beneath the plasmalemma. The cortical granules in the vicinity of the sperm entry site were 2.7 to 2.8 μm in diameter and densely packed. From this region to the vegetal pole, the cortical granules appeared to progressively increase in size and become less densely packed. The polarity in granule distribution established a distinct gradient in the structural organization of the egg cortex from the site of sperm entry to the vegetal pole.

Investigations on myelination in vitro: IV. "Myelin-like" or premyelin structures in cultures of dissociated brain cells from 14--15-day-old embryonic mice.

The present study reports ultrastructural and biochemical data characteristic of myelin-related structures in 30- to 41-day-old cultures of dissociated brain cells from 14- to 15-day-old embryonic mice. Multilayered membranous material was identified and displayed an alternation of electron-lucent and electron-dense lamellae with a periodicity of 102 A. In these membranes, typical myelin constituents like basic protein, cerebrosides, sulfatides, and CNPase could be identified. Although we are still unable to distinguish if these membranes are premyelin or compact myelin, which could be partly degraded, these results indicate that cultured mouse brain cells retain, to a certain extent, potential to produce myelin-related membranes.

Fine structure of isolated and non-isolated potato tuber periderm

Cell walls of the periderm of native potato tuber (Solanum tuberosum L. cv. Primura) consist of a primary wall, a suberized secondary wall and a tertiary wall. With a mixture of pectinase and cellulase intact periderm membranes can be isolated. Isolation does not affect fine structure. It is suggested that the lignin in the middle lamellae and primary walls prevents the enzymes from digesting pectinaceous materials and cellulose. In specimens fixed with OsO4, the suberized walls appear as alternating electrondense and electron-lucent lamellae. This lamellar architecture is not altered by extraction with chloroform. Therefore, the current view that the electronlucent lamellae consist of soluble lipids (waxes) can no longer be maintained. It is argued that the lamellation is a property of the suberin itself, and the suberized wall consists of alternating layers of suberins differing in polarity. A hypothesis of suberin assembly from sub-units is advanced and the subunits are shown for the first time.

Atypical mitochondria in the lung of newts, Triturus alpestris, Laur

Mitochondria with atypical cristae were found in the pulmonary cells of laboratory-kept newts, Triturus alpestris Laur. The relative number of atypical mitochondria increased with the time spent by the animals under laboratory conditions. The atypical mitochondria are plate shaped and contain two to six parallel cristae, their membrane being regularly undulated and interconnected by electron-dense lamellae inclined at an angle of approx 45° to the plane of cristae. In some sections oblique to the plane of cristae a tetragonal pattern can be seen. Our electron microscopic observations suggest that atypical cristae do not contain helical structures observed in other atypical mitochondria and the regular, oblique striae represent sections through the electron-dense lamellae bridging both membranes of crista. The occasionally observed tetragonal pattern seems to appear as a result of optical superposition of the arrays of such lamellae from two adjacent cristae.

Septal ultrastructure in some genera of the Tremellaceae

The fine structure of hyphal septa in the Tremellaceae has shown a number of modifications of the characteristic dolipore–parenthesome type septum. These variations appear of phylogenetic importance and systems of classification have been proposed based upon septal pore structure of a limited number of species. This study reports the fine structure of additional tremellaceous genera, Basidiodendron, Exidiopsis, Sebacina, and Tremellodendron. All species examined have dome-shaped pore caps bounded by unit membrane and with an electron-dense lamella in the pore cap lumen. Pore caps appeared nonperforate in Tremellodendron and Basidiodendron, while narrow discontinuations or distinct perforations were found in Exidiopsis and Sebacina. Thus, their pore cap architecture is similar to that of Exidia and other heterobasidiomycetes with the exception of species of Tremella and members of the Filobasidiaceae. It is suggested that schemes of classification based upon the fine structure of a limited number of taxa may be premature.

Studies of the spermatogenesis in the firebug, Pyrrhocoris apterus L. (Heteroptera). I. A unique basal body-associated plaque carrying a Microtubule Organizing Center (MTOC) in spermatids

A unique basal body appendage in the form of a straight or curved plaque composed of four parallel disposed electron-dense lamellae is described for firebug spermatids. The plaque is coated by two types of amorphous materials differing in thickness, electron density, and firmness of contact with the plaque. The first type forms a ∼55-nm-thick layer aligned along one side of the plaque. Numerous microtubules were always found to remain attached to this layer. The opposite side of the plaque is accompanied by amorphous material of the second type which is in the form of a thinner and more electron-dense layer and closely resembles the material in which basal body triplets are embedded. Microtubules have never been observed connected with this layer. It is suggested that the amorphous layer emanating microtubules acts as a microtubule organizing center (MTOC), which is responsible for the initiation of the assembly of microtubules that are involved in the formation of the perinuclear manchette and circummitochondrial ring in later stages of spermatid maturation. Furthermore, it is conceivable that the formation of the ordered microtubular arrangement in firebug spermatids is mediated by a self-linkage mechanism. The lamellar plaque probably serves as a rigid element providing a stable attachment for the MTOC and preventing its dislocation.