STUDIES OF SPERMATOGENESIS IN THE HEPATICAE : II. Blepharoplast Structure in the Spermatid of Marchantia

The blepharoplast in a young, developing spermatid of Marchantia polymorpha, is a composite structure consisting of two basal bodies and a subjacent narrow band of axonemal-type tubules that we have termed the "spline." For most of its length, the spline consists of six long parallel tubules that nearly encircle the cell. The spline anterior is asymmetrically widened for about 2 µ by shorter tubules of the same kind. The lateral displacement of three long, adjacent marginal tubules by three short intervening tubules at the spline tip produces a long narrow aperture. Distally, the aperture is closed by the convergence of the displaced tubules with another trio of long tubules. Together, these form the six-membered cell-encircling portion. The expanded spline anterior has, at this stage of development, the four-layered (Vierergruppe) structure, of which the aforementioned tubules constitute the uppermost layer. The lower three strata consist of diagonal fins, elongated chambers, and fine tubules, respectively. The two flagellar bases lie close above the spline tip—one slightly anterior to the other—and diverge unequally from the spline axis. A few triplets extend proximally from the basal bodies, but do not connect with the spline. The anterior basal body is longer than the posterior one.     

FINE STRUCTURE OF THE SPERMATOZOID OF ZAMIA: THE VIERERGRUPPE

The spermatozoids of Zamia integrifolia were examined by electron microscopy in order to clarify the structure of a fibrous organelle underlying the flagellar basal bodies. The ultrastructure of this organelle was found to resemble one similar in organization occurring in Marchantia spermatozoids and termed the Vierergruppe. Therefore the term is extended to include this structure in the Zamia spermatozoid. The Vierergruppe of Zamia is interpreted as composed of an upper (distal) layer of keeled microtubules and a lower (proximal) layer of vertical fins with lateral processes that give a three-layered appearance to this component.     

La paroi cellulaire de Coelastrum (Chlorophycées)

The cell wall of Coelastrum is usually composed of three layers. The outermost layer was studied most extensively. It consists of erect tubules which often bear long bristles whose function may be to stabilize the algae in its environment. The cell wall can modify its morphology according to the environment.     

STUDIES OF SPERMATOGENESIS IN THE HEPATICAE V. BLEPHAROPLAST DEVELOPMENT IN MARCHANTIA POLYMORPHA

Coaxial centrioles and a microtubule organizing center (MTOC) constitute each centrosome in spermatid mother cells of Marchantia polymorpha. During cell division the centrosome separates at its midregion and the two centrioles undergo a planar rotation that brings them to lie somewhat staggered and nearly parallel with their proximal ends embedded in osmiophilic granular material similar in appearance to that of the MTOC. Microtubules of the multilayered structure (MLS) arise in this material below the posterior centriole and parallel to its long axis. The rotation of centrioles and the initiation of S₁ tubules below the posterior centriole determine polarity of the incipient blepharoplast. Lower MLS strata are formed under the anterior centriole by the compaction of granular, osmiophilic matrix. Formation and growth of S₂ vertical lamellae occur at the left front edge of the MLS in association with MTOC-like matrix localized near the cell membrane. The MLS enlarges to about 0.4 μm wide by 0.6 μm long and is ovoid in outline except for a short distal projection underlying the posterior centriole. Subsequently the lamellae are transformed into homogenous, osmiophilic matrix that contributes directly to the expansion of all MLS strata including microtubules. The stratum of lamellae is interpreted as a planar MTOC subject to morphogenetic control. Each of the four strata grows proximally while the tapering distal projection lengthens beneath the posterior basal body. Dense matrix above the MLS, apparently elaborated by the S₂ layer, is organized into cartwheel and triplet components of the basal bodies’ proximal extensions. Organization of triplet tubules proceeds from proximal to distal toward preexisting triplets. Osmiophilic matrix contributes to the formation of microtubule keels and osmiophilic crests and may serve as a cementing material that stabilizes the spatial relationships of blepharoplast components. After full expansion of the MLS’ lower strata, the S₂ layer is reorganized into lamellae. Flagellar growth in Marchantia is postulated to involve a process whereby subunits or their precursors are elaborated by the MLS, translocated to the distal end of the flagellum and incorporated into the axonemal tubules. When MLS microtubules elongate to form a long, narrow band, the distal half of the S₂ layer is again in the osmiophilic matrix state.     

Light and electron microscope studies on the fruiting bodies of Chondromyces crocatus

Summary The fruiting bodies of Chondromyces crocatus have been examined by both light and electron microscopy. The cysts are bounded by a discrete layer of dense slime enclosing a material of lesser density in which the closely packed resting cells are embedded. The latter, in contrast to the microcysts of other myxobacters, are not enclosed in individual slime capsules. Young resting cells commonly contain numerous mesosomes while older resting cells are characterized by what appear to be large lipid granules.The slime stalk consists largely of a system of vertical, parallel empty tubules through which the cells have migrated during fruiting body development.Supported by grant number A 1022 from the National Research Council of Canada.     

Ultrastructure of the Z organ in Xiphinema ifacolum

Bieve-Zacheo T., Zacheo G. and Lamberti F. 1985. Ultrastructure of the Z organ in Xiphinema ifacolum. International Journal for Parasitology15: 453–461. The uterus in Xiphinema ifacolum can be divided into uterus proper, a 77 μm long tube and a lemon-shaped Z organ, about 28 μm long and 18 μm wide, placed between the oviduct and the uterus proper. The Z organ consists of a thick outer muscular layer of 120 cells, arranged in 20 rings of six cells each and a thin inner epithelium layer, lining the lumen. The epithelial cell walls, lining the lumen of the Z organ are thicker than those lining the uterus proper and are strongly folded. The crests of some of these folds carry six large apophyses, all about the same size and shape, these occupy the full length of the organ, becoming thicker towards the center of the lumen. There are many tubules near the surfaces of the apophyses, the contents of which can be dissolved by treatment with pepsin and pronase, indicating that they are proteins. This material probably consists of secretions which are squeezed out of the apophyses by a passing egg and may function in the formation or hardening of the egg shell.     

Fine Structure of Body Wall Cuticle of Females of Eight Genera of Heteroderidae

Body wall cuticle of adult females of eight genera within the Heteroderidae was examined by transmission electron microscopy for comparison with previously studied species within the family. Cuticle structure was used to test some current hypotheses of phylogeny of Heteroderidae and to evaluate intrageneric variability in cuticle layering. Verutus, Rhizonema, and Meloidodera possess striated cuticle surfaces and have the simplest layering, suggesting that striations have not necessarily arisen repeatedly in Heteroderidae through convergent or parallel evolution. Atalodera and Thecavermiculatus possess similar cuticles with derived characteristics, strengthening the hypothesis that the two genera are sister groups. Similarly, the cuticle of Cactodera resembles the specialized cuticle of Globodera and Punctodera in having a basal layer (D) and a surface layer infused with electron-dense substance. Heterodera betulae has a unique cuticle in which the thickest layer (C) is infiltrated with an electron-dense matrix. Little intrageneric difference was found between cuticles of two species of Meloidodera or between two species of Atalodera. However, Atalodera ucri has a basal layer (E) not found in other Heteroderidae. The most striking intrageneric variation in cuticle structure was observed between the thin three-layered cuticle of Sarisodera africana and the much thicker four-layered cuticle of Sarisodera hydrophila; results do not support monophyly of Sarisodera.     

Histology of Polypterus senegalus fin rays revisited

The present comparative histological study of the pectoral, caudal and anal fins of the polypterid Polypterus senegalus reveals the presence of a layer of dentine identified between the superficial ganoine patches and the bony part of the lepidotrichia in the three fins. Its extent varies depending on the fins. Similarly, the ganoine layer present at the surface of the proximal lepidotrichia shows fin-dependent differences in extent and distribution. The dentine layer is crossed by a system of thin worm-like vascular canaliculi that reach the ganoine layer and even penetrate within it as in the scales. In the lepidotrichia, the dentine lays directly on bone, which differs from the scales where dentine lies on isopedine, a plywood-like structure. Another difference between scales and lepidotrichia is the presence of actinotrichia that are unmineralised, fusiform rods of elastoidine located at the tip of the fins. Ontogenesis with differentiation of actinotrichia has no equivalent in scale formation. Although structural features are shared by lepidotrichia and scales in P. senegalus, observations on the scales and lepidotrichia support the hypothesis of Schaeffer (1977) that “scales and lepidotrichia are somewhat differently shaped manifestations of the same morphogenetic system”.     

The giant sperm of a minute beetle

The mature sperm of Ptinella aptera is a helically coiled, flagellate gamete ca. 1.4 mm long—twice the length of the beetle itself. The rod-like acrosome, comprising the anterior part of the sperm, is 0.4 μm thick but is expanded as a flange around the nucleus and the base of the tail, increasing the diameter of the sperm to 2 μm. The bulk of the tail consists of a pair of bodies with a characteristic ultrastructure of longitudinal tubules beneath a lamellar cortical layer. These bodies are probably homologous with the mitochondrial derivatives of other insect sperm. The axoneme is helically coiled and is flanked by a single accessory body. One of the ‘structured bodies’ is connected to the acrosome and the other to the accessory body. The sperm move actively in the female reproductive tract. The functional significance of this behaviour and of the evolution of the large gamete itself is discussed in relation to existing hypotheses.     

Structural organization of the endoplasmic reticulum

The endoplasmic reticulum (ER) is a continuous membrane system but consists of various domains that perform different functions. Structurally distinct domains of this organelle include the nuclear envelope (NE), the rough and smooth ER, and the regions that contact other organelles. The establishment of these domains and the targeting of proteins to them are understood to varying degrees. Despite its complexity, the ER is a dynamic structure. In mitosis it must be divided between daughter cells and domains must be re-established, and even in interphase it is constantly rearranged as tubules extend along the cytoskeleton. Throughout these rearrangements the ER maintains its basic structure. How this is accomplished remains mysterious, but some insight has been gained from in vitro systems.     

The structure of the egg-shell of Porrocaecum ensicaudatum (Nematoda: Ascaridida)

Wharton D. A. 1979. The structure of the egg-shell of Porrocaecum enslcaudatum (Nematoda: Ascaridida). International Journal for Parasltology9: 127–131. The egg-shell of Porrocaecum ensicaudatum is oval with an opercular plug at either end. The shell consists of three layers: an inner lipid layer, a middle chitinous layer and an outer vitelline layer. The vitelline layer has strands of particulate material attached to its outer surface. The chitinous layer consists of 8.5 nrn fibrils which are made up of a chitin microfibril core surrounded by a protein coat. The fibrils are oriented randomly or in parallel, there being no indication of helicoidal architecture.The chitinous layer varies in thickness to form a pattern of interconnecting ridges on the surface of the egg. This pattern presumably increases the shell's structural strength.     

Competitive Ability and Efficiency in Nodule Formation of Strains of Bradyrhizobium japonicum

In the American Midwest, superior N₂-fixing inoculant strains of Bradyrhizobium japonicum consistently fail to produce the majority of nodules on the roots of field-grown soybean. Poor nodulation by inoculant strains is partly due to their inability to stay abreast of the expanding soybean root system in numbers sufficient for them to be competitive with indigenous bradyrhizobia. However, certain strains are noncompetitive even when numerical dominance is not a factor. In this study, we tested the hypothesis that the nodule occupancy achieved by strains is related to their nodule-forming efficiency. The nodulation characteristics and competitiveness of nine strains of B. japonicum were compared at both 20 and 30°C. The root tip marking technique was used, with the nodule-forming efficiency of each strain estimated from the average position of the uppermost nodule and the number of nodules formed above the root tip mark. The competitiveness of the nine strains relative to B. japonicum USDA 110 was determined by using immunofluorescence to identify nodule occupants. The strains differed significantly in competitiveness with USDA 110 and in nodulation characteristics, strains that were poor competitors usually proving to be inferior in both the average position of the uppermost root nodule and the number of nodules formed above the root tip mark. Thus, competitiveness was correlated with both the average position of the uppermost nodule (r = 0.5; P = 0.036) and the number of nodules formed above the root tip mark (r = 0.64; P = 0.005), while the position of the uppermost nodule was also correlated to the percentage of plants nodulated above the root tip mark (r = 0.81; P < 0.001) and the percentage of plants nodulated on the taproot (r = 0.67; P = 0.002).     

Cuticle Ultrastructure of Hemicycliophora arenaria,Aphelenchus avenae,Hirschmanniella gracilis and Hirschmanniella belli

Ultrathin sections of all parasitic stages of Hemicycliophora arenaria revealed two major divisions in the body covering. The outermost was a seven-layered sheath and the innermost a five-layered cuticle comprising three zones; an outer trilaminate cortex, a fibrillar matrix and a striated basal layer. The body covering of the nonparasitic males also exhibited two major divisions: the outer, a relatively thin four-layered sheath and the inner, a six-layered cuticle consisting of three zones; an outer trilaminate cortex, a two-layered matrix and a striated basal layer. The cuticles of all stages of Aphelenchus avenae were similar, consisting of five layers divisible into three zones; an outer trilaminate cortex, a fibrillar matrix and a striated basal layer. Hirschmanniella gracilis and H. belli cuticles were also similar in all stages examined, consisting of six layers divisible into three zones; an outer trilaminate cortex, a two-layered matrix and a striated basal layer.     

Bioturbational disturbance of the Cretaceous-Palaeogene (K-Pg) boundary layer: Implications for the interpretation of the K-Pg boundary impact event

Detailed field observations across and along the Cretaceous-Palaeogene (K-Pg) boundary interval in the Caravaca section, SE Spain, together with laboratory analyses reveal a well-developed lowermost Danian dark-colored trace fossil assemblage. The trace fossils range continuously from the bioturbated horizons in the dark boundary layer (lowermost Danian), to the uppermost Maastrichtian sediments. The rusty boundary layer at the base of the dark boundary layer, usually related to the K-Pg boundary impact, is traditionally considered as undisturbed. However, ichnological analysis at the Caravaca section shows that this rusty boundary layer is cross-cut vertically by Zoophycos and Chondrites, but also penetrated laterally by Chondrites, revealing an important colonization of the substrate. Stereomicroscope analysis shows sharp burrow margins of dark-colored Chondrites directly against the surrounding red sediment of the rusty layer. Colonization of unfavorable substrates by Zoophycos and Chondrites tracemakers, as that represented by the rusty boundary layer, was possible because of constructing of open, probably of actively ventilated burrows that facilitate colonization of sediments poor in oxygen and food. Significant bioturbational disturbance of the rusty layer can cause vertical and horizontal redistribution of the components related to the K-Pg boundary impact and, in consequence, to induce erroneous interpretations. A detailed ichnological analysis of the K-Pg boundary interval, with special attention to the rusty layer, reveals an essential tool to avoid misinterpretations.     

Pigments, light penetration, and photosynthetic activity in the multi-layered microbial mats of Great Sippewissett Salt Marsh, Massachusetts

The multi-layered microbial mats in the sand flats of Great Sippewissett Salt Marsh were found to have five distinct layers of phototrophic organisms. The top 1–3 mm contained oxygenic phototrophs. The lower 3–4 mm contained anoxygenic phototrophic bacteria. The uppermost gold layer contained diatoms and cyanobacteria, and chlorophyll a was the major chlorophyll. The next layer down was green and was composed of primarily filamentous cyanobacteria containing chlorophyll a. This was followed by a bright pink layer of bacteriochlorophyll b-containing purple sulfur bacteria. The lowest layer was a thin dull green layer of green sulfur bacteria containing bacteriochlorophyll c. The distribution of the chlorophylls with depth revealed that two-thirds of the total chlorophyll in the mat was composed of bacteriochlorophylls present in the anoxygenic phototrophys. The cyanobacterial layers and both purple sulfur bacterial layers had photoautotrophic activity. Light was attenuated in the uppermost layers so that less than 5% of the total radiation at the surface penetrated to the layers of anoxygenic phototrophys.     

Development,cytology, lipid storage and motility of the Malpighian tubules of the nymphal dragonfly,Aeshna cyanea (Müller) (Odonata : Aeshnidae)

The Malpighian tubules of nymphal Aeshna cyanea (Odonata : Aeshnidae) were examined by light and electron microscopy. The 1st-instar nymphs have only 3 branchless tubules. With proceeding nymphal stages, these lengthen and branch. Also, additional tubules bud from the gut and show the same pattern of growth and branching, until in the final instar up to 21 separate tufts of branched tubules are present. A serpentine trachea/tracheole and a cross-striated muscle are helically wound around each tubule in close apposition. Isolated tubules show twisting movements for several days. Contraction of the muscle is responsible for fast coiling movements, while the slow decoiling movements probably depend on elastic deformations of the accompanying trachea, the basal lamina and the tubule cells, the latter showing an elaborate cytoskeleton and multiple adhesive junctions.The tubular epithelium consists of 4 types of cells. The distal segment is composed of ion transporting cells and terminates with a short, solid tip segment of undifferentiated cells. The intermediate segment consists of lipid cells which are densely filled with triglyceride droplets, as revealed by thin layer chromatography. Lipid cells are already present in the 1st instar before the nymphs have taken up any food. In later instars, the renal lipid content varies to some extent with the nutritional state and is nearly depleted during metamorphosis. The proximal segment is the region of tubular branching and may be conceived as the collecting duct of each tuft. Its epithelium consists of mucocytes.     

Intramolecular photo-switching and intermolecular energy transfer as primary photoevents in photoreceptive processes: The case of Euglena gracilis

In this paper we report the results of measurements performed by FLIM on the photoreceptor of Euglenagracilis. This organelle consists of optically bistable proteins, characterized by two thermally stable isomeric forms: A_498, non fluorescent and B₄₆₂, fluorescent.Our data indicate that the primary photoevent of Euglena photoreception upon photon absorption consists of two contemporaneous different phenomena: an intramolecular photo-switch (i.e., A₄₉₈ becomes B₄₆₂), and a intermolecular and unidirectional Forster-type energy transfer. During the FRET process, the fluorescent B₄₆₂ form acts as donor for the non-fluorescent A₄₉₈ form of the protein nearby, which acts as acceptor. We hypothesize that in nature these phenomena follow each other with a domino progression along the orderly organized and closely packed proteins in the photoreceptor layer(s), modulating the isomeric composition of the photoreceptive protein pool. This mechanism guarantees that few photons are sufficient to produce a signal detectable by the cell.     

The ultrastructure of the heart of Oniscus asellus L. and Asellus aquaticus L. (Crustacea,Isopoda)

Summary The endocardium of Oniscus asellus L. and Asellus aquaticus L. consists of lipid cells. The epicardium consists of a layer of cells with a vesiculated cytoplasm covered by a thick extracellular fibrous sheet. The myocardium is a single layer of cells, the sarcolemma invaginates at Z disc level forming transverse tubules, and longitudinal tubules branch off from these. At the A-I level' longitudinal tubules form transverse systems, which form couplings with the sarcoplasmic reticulum. The sarcoplasmic reticulum appears as perforated sheets enveloping the myofibrils. Two types of nerve terminal are found: one is embedded in a myocardial cell process, the other lies in a myocardial cell depression. They contain clear and dense-cored synaptic vesicles.This work was supported by grants from the Norwegian Research Council for Science and the Humanities     

Axostyle structure in the termite protozoon Pyrsonympha vertens

The axostyle of Pyrsonympha vertens is a cellular organelle composed of interconnected microtubules. In living organisms the axostyle has waves which originate at the anterior end of the protozoon and traverse the length to the posterior end of the protozoon so that an average of 3–4 waves are present in the organelle at any given point in time. The part of the axostyle between the waves is straight. In sections through the middle of the straight part, the microtubules are hexagonally packed, with predominant connections between tubules in rows across the width of the axostyle, but the microtubules are rectilinearly packed through the wave. The wave appears to involve changes in orientation and arrangement of the microtubules. The general structure of the microtubules, cross-bridges and axostyle in the straight and bent portions are described and related to the wave propagation by this organelle.