A review of the genus Johnstonia Quatrefages, 1866 (Polychaeta, Maldanidae), with a description of a new species from Trinidad, West Indies

In the interests of nomenclatural stability it is proposed that Johnstonia Quatrefages. 1866 (Polychaeta, Maldanidae) be conserved relative to its senior homonym Johnstonia Quatrefages, 1849 (Polychaeta, Nereidae) and its coexistent junior homonym Johnstonia Basir, 1956 (Nematoda, Thelastomatidae). Type material of all species previously assigned to Johnstonia Quatrefages, 1866 is re-examined and a new species from Trinidad described. All three valid species ( J. clymenoides Quatrefages, 1866; J. knysna Day. 1955; J. duplicata sp. n.) are described and figured in detail. An unnamed fourth species is known only from fragments collected off West Africa, and Johnstonia gracilis Kinberg, 1867 is newly synonymised with Euclymene oerstedii (Claparède. 1863).     

Fine structure of the galeal styloconic sensilla of larval Lymantria dispar (Lepidoptera: Lymantriidae)

Lepidopteran larvae possess two pairs of styloconic sensilla located on the maxillary galea. These sensilla, namely the lateral and medial styloconic sensilla, are each comprised of a smaller cone, which is inserted into a style. They are thought to play an important role in host-plant selection and are the main organs involved in feeding. Ultrastructural examination of these sensilla of fifth instar Lymantria dispar (L.) larvae reveal that they are each approximately 70 um in length and 30 um in width. Each sensillum consists of a single sensory peg inserted into the socket of a large style. Each peg bears a slightly subapical terminal pore averaging 317 nm in lateral and 179 nm in medial sensilla. Each sensillum houses five bipolar neurons. The proximal dendritic segment of each neuron gives rise to an unbranched distal dendritic segment. Four of these dendrites terminate near the tip of the sensillum below the pore and bear ultrastructural features consistent with contact chemosensilla. The fifth distal dendrite terminates near the base of the peg and bears ultrastructural features consistent with mechanosensilla. Thus, these sensilla each bear a bimodal chemo-mechanosensory function. The distal dendrites lie within the dendritic channel and are enclosed by a dendritic sheath. The intermediate and outer sheath cells enclose a large sensillar sinus, whereas the smaller ciliary sinus is enclosed by the inner cell. The neurons are ensheathed successively by the inner, intermediate, and outer sheath cells.     

Tissue abscission and wound healing in the operculum of Pomatoceros lamarckii Quatrefages (Polychaeta: Serpulidae)

Following opercular amputation in Pomatoceros lamarckii Quatrefages, wound healing is initiated from a predetermined point on the peduncle. The events of abscission, cell migration and cuticle deposition during wound healing have been studied by light and electron microscopy. Abscission occurs at a predetermined point on the peduncle indicated by specialized epidermal cells, the easy break-point cells (EBP). Following detachment of tissues distal to the EBP cells, the resultant wound is plugged by a knot of coelomocytes which provide a substratum over which epidermal cells migrate to seal and restore the epidermis. During their migration, the epidermal cells undergo differentiation and deposit a new cuticle. Cuticle formation is initiated by the deposition of a finely filamentous matrix. The fine filaments subsequently coalesce to form thicker fibrils which become aggregated into layers of orthogonally-arranged fibril bundles. The mechanisms involved in abscission, cell migration and cuticle deposition during wound healing of the opercular filament are discussed.     

The ultrastructure of the so-called olfactory setae on the antennula ofDaphnia magna Straus (Crustacea,Cladocera)

A group of nine sensory setae is found on the tip of the antennula ofDaphnia magna in both sexes. Inside a seta four dendrites are situated, each with one receptor cilium. The receptor cilia extend through a liquor space into the exterior part of the seta. The exterior part of the liquor space is divided from the interior part by a knob-like thickening of the innermost layer of the epicuticle, the basal bead. The basal bead narrows the liquor space and the receptor cilia. The interior part of the liquor space is surrounded by five sheath cells, the exterior part by a thin cuticle. In the exterior part the receptor cilia branch partly and reach a terminal pellet on the tip of the seta. The terminal pellet is a thickened part of the epicuticle. It is permeable to several dissolved substances. It is the exterior part of the receptor that projects over the tip of the antennula and seems to be the entire seta. During the premoult the fifth sheath cell builds up the articulation of the seta, the fourth the basal bead, and the third the shaft of the seta. The first sheath cell forms the cuticular sheath. The organ seems to be a chemoreceptor, but the adequate stimulus is as yet unknown.     

Female genital system of the folding-trapdoor spider Antrodiaetus unicolor (Hentz, 1842) (Antrodiaetidae, Araneae): ultrastructural study of form and function with notes on reproductive biology of spiders

The genitalia of the female folding-trapdoor spider Antrodiaetus unicolor are characterized by two pairs of spermathecae that are arranged in a single row and connected to the roof of the bursa copulatrix. Each single spermatheca is divided into three main parts: stalk, bowl, and bulb, which are surrounded by the spermathecal gland. The epithelium of the spermathecal gland is underlain by a muscle meshwork and consists of different types of cells partly belonging to glandular cell units (Class 3 gland cells) that extend into pores in the cuticle of the stalk and bowl. Interestingly, the bulb lacks glandular pores and is characterized by a weakly sclerotized cuticle. This peculiarly structured bulb probably plays an important role in the discharge of the sperm mass. It is suggested that by contraction of the muscle layer the sperm mass may be squeezed out, when the bulb invaginates and expands into the spermathecal lumen, pushing the sperm to the uterus lumen. Each glandular unit consists of usually one or two central secretory cells that are for the most part surrounded by a connecting cell that again is surrounded by a canal cell. The canal cell, finally, is separated from the other epithelial cells (intercalary cells) located between the glandular units by several thin sheath cells that form the outer enveloping layer of the unit. The secretions are released through a cuticular duct that originates proximally between the apical part of the connecting cell and the apical microvilli of the secretory cells and runs into a pore of the spermathecal cuticle. The glandular products of the Class 3 gland cells likely contribute to the conditions allowing long-term storage of the spermatozoa in this species. Details regarding the ovary, the uterus internus, and the uterus externus are reported. Most of the secretion that composes the chorion of the egg is produced in the ovary. Glandular cell units observed in the uterus externus differ structurally from those in the spermathecae and likely play a different role. Finally, we briefly discuss our results on the female genitalia of A. unicolor in the light of knowledge about the reproductive biology of spiders.     

The role of the parenchyma sheath and PCD during the development of oil cavities in Pterodon pubescens (Leguminosae-Papilionoideae)

Pterodon pubescens cavities are constituted by lumen and uniseriated epithelium surrounded by multiseriate parenchyma sheath. We studied the development of secretory cavities, including the role of parenchyma sheath, using light and transmission electron microscopy. A Tunel assay was performed to verify whether programmed cell death (PCD) occurs during the process. The lumen is formed by schizogeny and lysigeny occur in later developmental stages of the secretory cavities. Ultrastructurally, epithelial cells in later developmental stages become dark and with sinuous walls; the protoplast becomes retracted and the cytoplasm shows low organelle definition. Degenerated cells are released toward the lumen. Our results showed that PCD occurs during later developmental stages of cavities and plays a critical role in functioning of these glands. New cells originated from the parenchyma sheath differentiate into secretory cells and replace those degenerated ones. This fact associated to PCD guarantees epithelium renovation during the secretory cycle and the maintenance of secretory activity of cavities.     

Head sensory organs of Dactylopodola baltica (Macrodasyida, Gastrotricha): a combination of transmission electron microscopical and immunocytochemical techniques

The anterior and posterior head sensory organs of Dactylopodola baltica (Macrodasyida, Gastrotricha) were investigated by transmission electron microscopy (TEM). In addition, whole individuals were labeled with phalloidin to mark F-actin and with anti-alpha-tubulin antibodies to mark microtubuli and studied with confocal laser scanning microscopy. Immunocytochemistry reveals that the large number of ciliary processes in the anterior head sensory organ contain F-actin; no signal could be detected for alpha-tubulin. Labeling with anti-alpha-tubulin antibodies revealed that the anterior and posterior head sensory organs are innervated by a common stem of nerves from the lateral nerve cords just anterior of the dorsal brain commissure. TEM studies showed that the anterior head sensory organ is composed of one sheath cell and one sensory cell with a single branching cilium that possesses a basal inflated part and regularly arranged ciliary processes. Each ciliary process contains one central microtubule. The posterior head sensory organ consists of at least one pigmented sheath cell and several probably monociliary sensory cells. Each cilium branches into irregularly arranged ciliary processes. These characters are assumed to belong to the ground pattern of the Gastrotricha.     

The fine structure of the leaf nodules of Ardisia crispa (Thunb.) A.DC. (Myrsinaceae)

The fine structure of the leaf nodules of Ardisia crispa is described. The bacterial endophyte in mature nodules is extracellular, forming a compact mass which is encompassed within a 5–6 cell thick sheath of modified mesophyll cells. Processes from these sheath cells invade the bacterial mass providing a host surface across which exchange of metabolites may take place. Considerable pleomorphism is exhibited by the bacteria, paralleling that found in other symbiotic associations in which the host can influence the morphology of the microsymbiont. The spherical, highly granate chloroplasts, rich in starch, which are characteristic of the spongy mesophyll leaf cells, are replaced, in the modified sheath cells, by a degenerate plastid form containing membrane whorls. Lipid reserves appear to replace the starch in the sheath cells. The significance of these changes is discussed.     

Two-Dimensional Electrophoretic Mapping of Proteins of Bundle Sheath and Mesophyll Cells of the C(4) Grass Digitaria sanguinalis (L.) Scop. (Crabgrass)

Two-dimensional electrophoresis was performed on proteins of bundle sheath and mesophyll cells isolated from the C₄ grass Digitaria sanguinalis (L.) Scop. Two-dimensional maps of these proteins were constructed and ribulose-1,5-biphosphate carboxylase and phosphoenolpyruvate carboxylase were identified. Of the total number of proteins found in both cell types, 36% were found only in bundle sheath cells, 17% only in mesophyll cells, and 47% in both cell types. By comparison, the distributions of 48 enzymes assayed in these cell types were 35%, 21%, and 44%, respectively.

Protein patterns were also compared with C₄ plants exhibiting different decarboxylation pathways and, in both bundle sheath and mesophyll cells, proteins were found which were unique to each species. Bundle sheath proteins of one C₄ species were found to be more like bundle sheath proteins of another C₄ species than like mesophyll proteins of the same species.

     

The fine structure of the leaf nodules of Ardisia crispa (Thunb.) A.DC. (Myrsinaceae)

The fine structure of the leaf nodules of Ardisia crispa is described. The bacterial endophyte in mature nodules is extracellular, forming a compact mass which is encompassed within a 5–6 cell thick sheath of modified mesophyll cells. Processes from these sheath cells invade the bacterial mass providing a host surface across which exchange of metabolites may take place. Considerable pleomorphism is exhibited by the bacteria, paralleling that found in other symbiotic associations in which the host can influence the morphology of the microsymbiont. The spherical, highly granate chloroplasts, rich in starch, which are characteristic of the spongy mesophyll leaf cells, are replaced, in the modified sheath cells, by a degenerate plastid form containing membrane whorls. Lipid reserves appear to replace the starch in the sheath cells. The significance of these changes is discussed.     

Coxal organs of Lithobius forficatus (Myriapoda,Chilopoda)

Summary In Lithobius forficatus each of the coxae of the four posterior trunk segments bear a pore field with several coxal pores. The surrounding single-layered epithelium is composed of four different cell types: the main epithelial cells having a fine-structural organization of transport cells with deep apical and basal folds of the cell surfaces and plasmalemma-mitochondrial complexes, junctional cells, exocrine glands, and the wall cells of the pore channel. The entire epithelium is separated from the hemolymph by an inner cellular sheath. It is assumed that the coxal organs participate in fluid uptake.     

The fine structure and possible function of the sensory setae of the penis of Balanus balanoides (L.)

The structure and innervation of the sensory setae which are present in large numbers on the penis of Balanus balanoides (L.) have been established by scanning and transmission electron microscopy. Each seta contains a small number of sensory dendrites surrounded by an extracellular supporting tube which is presumed to be secreted by the enclosing sheath cell. The dendrites, which distally extend beyond both the sheath cell and supporting tube, terminate at the tip of the seta within a pore-like invagination of the cuticle and thus are in direct contact with the environment. Proximally bundles of dendrites pass into the penis tissue where they are surrounded by several sheath cells. The supporting tube terminates at a point within the body of the penis where a series of intracellular rods arise. The ciliary character of the dendrites is evident in this region, the microtubules being organized into the (9 × 2) +2 pattern. It is deduced that the sensilla are chemosensory; their structure is compared with that of other crustacean sensilla which are presumed to be chemosensory.     

Cell specific DNA-labelling in the repairing blood-brain barrier of the insect Periplaneta americana

Summary This study uses a recently developed technique for preserving the ultrastructure of cells in the insect CNS during immunohistochemical processing for 5-bromo-2-deoxyuridine incorporation into newly synthesised DNA. The results allow us to identify the proliferating cell calsses in the regenerating blood-brain barrier. High resistance barrier cells do not label with the antibody but sheath cells clearly do. Intermediate cell types appearing during repair are identified. It is hypothesised that these cells generate matrix molecules for neural lamella repair and may represent transitional forms as invasive blood cells transdifferentiate into functional sheath cells.     

Patterns of sheath elongation, cell proliferation, and manganese(II) oxidation in Leptothrix cholodnii

Leptothrix cholodnii is a Mn(II)-oxidizing and sheath-forming member of the class β-Proteobacteria. Its sheath is a microtube-like filament that contains a chain of cells. From a chemical perspective, the sheath can be described as a supermolecule composed of a cysteine-rich polymeric glycoconjugate, called thiopeptidoglycan. However, the mechanism that controls the increase in sheath length is unknown. In this study, we attempted to detect sheath elongation through microscopic examination by using conventional reagents. Selective fluorescent labeling of preexisting or newly formed regions of the sheath was accomplished using combinations of biotin-conjugated maleimide, propionate-conjugated maleimide, and a fluorescent antibiotin antibody. Epifluorescence microscopy indicated that the sheath elongates at the terminal regions. On the bases of this observation, we assumed that the newly secreted thiopeptidoglycan molecules are integrated into the preexisting sheath at its terminal ends. Successive phase-contrast microscopy revealed that all cells proliferate at nearly the same rate regardless of their positions within the sheath. Mn(II) oxidation in microcultures was also examined with respect to cultivation time. Results suggested that the deposition of Mn oxides is notable in the aged regions. The combined data reveal the spatiotemporal relationships among sheath elongation, cell proliferation, and Mn oxide deposition in L. cholodnii.     

Three-dimensional architecture of the cell sheath and septa of Methanospirillum hungatei.

The methanogenic bacterium Methanospirillum hungatei exists as filaments which have a very unusual cell wall architecture, comprising a long cylindrical sheath within which there may be many individual cells arranged in a line. The sheath has a two-dimensional crystalline structure, and the cells are separated within the tube by septa which also have a crystalline structure. We have used computer image processing of tilted-view electron micrographs to analyze the structure in negative stains of both of these components in three dimensions. The repeating unit of the sheath consists of four approximately spherical domains ca. 2.5 nm in diameter arranged in a row. Based on observations of the type of lattice imperfections that occur, we suggest that each of the domains represents a separate polypeptide subunit and that the subunits are incorporated into the wall one by one. The septa are circular plates of remarkably constant size. They are normally found as double layers. They are hexagonally symmetrical and consist of trimerically associated subunits which interact about dimer axes to form an open network containing large pores ca. 15 nm in diameter.     

Ultrastructure and ontogeny of the hair sensilla on the funicle of Calliphora erythrocephala (Insecta,Diptera)

Summary Four envelope cells are responsible for the formation of the basiconical sensilla of Calliphora. They are the thecogen, trichogen, and tormogen cells, and envelope cell 4. In early stages of development the still subepithelial sensory cilia are completely enclosed by the innermost thecogen cell. The first formation movements are initiated by a growth thrust of the hair-forming cell into the exuvial space. The sensory cilia only begin to grow into the hair anlage when the hair-forming cell has almost reached its final length. As soon as growth is completed the trichogen cell, tormogen cell, and envelope cell 4 start to excrete cuticular material. The trichogen cell forms the perforated part of the hair shaft and the stimulus-conducting system consisting of the pore tubules. The tormogen cell is responsible for the excretion of the basal non-perforated hair shaft and sheath cell 4 forms the proximal part of the socket region. The thecogen cell only begin to produce dendritic sheath material when the sensory hair is almost complete.Approximately 7–8 days after pupation the tormogen cell degenerates, having, by this time, produced about two-thirds of the sensilla cuticle. The surrounding envelope cells incorporate cell fragments of the tormogen cell. The trichogen cell continues the secretion where the tormogen cell left off. When the secretion of cuticle is finished the sheath cells begin to withdraw towards the proximal direction and to form microvilli on the apical membrane. The resulting outer receptor lymph space is bordered by envelope cell 4 and the trichogen and thecogen cells. The tormogen cell is absent in the sensilla of the imago.Abbreviations DS dendritic sheath - E4 envelope cell 4 - Ex exuvial space - G glial cell - iD inner dendritic segment - iRL inner receptor lymph space - oRL outer receptor lymph space - oD outer dendritic segment - P pore - PT pore tubules - S sensory cell - T thecogen cell - TO tormogen cell - TR trichogen cell Part 1 of a dissertation accepted by the Faculty of Bio- and Geosciences, University of Karlsruhe     

Metabolite diffusion into bundle sheath cells from c(4) plants: relation to c(4) photosynthesis and plasmodesmatal function

The present studies provide the first measurements of the resistance to diffusive flux of metabolites between mesophyll and bundle sheath cells of C₄ plants. Species examined were Panicum miliaceum, Urochloa panicoides, Atriplex spongiosa, and Zea mays. Diffusive flux of metabolites into isolated bundle sheath cells was monitored by following their metabolic transformation. Evidence was obtained that the observed rapid fluxes occurred via functional plasmodesmata. Diffusion constants were determined from the rate of transformation of limiting concentrations of metabolites via cytosolic enzymes with high potential velocities and favorable equilibrium constants. Values on a leaf chlorophyll basis ranged between 1 and 5 micromoles per minute per milligram of chlorophyll per millimolar gradient depending on the molecular weight of the metabolite and the source of bundle sheath cells. Diffusion of metabolites into these cells was unaffected by a wide variety of compounds including respiratory inhibitors, monovalent and divalent cations, and plant hormones, but it was interrupted by treatments inducing cell plasmolysis. The molecular weight exclusion limit for permeation of compounds into bundle sheath cells was in the range of 850 to 900. These cells provide an ideal system for the quantitative study of plasmodesmatal function.     

Sensory innervation monitoring movement and position in the mandibular stylets of the aphid, Brevicoryne brassicae

The sensory innervation of the mandibular stylets of the aphid Brevicoryne brassicae (L.) has been examined by electron microscopy. Two groups of sensory neurones are present in the mandible. Each has two neurones, one with a short dendrite extending into the base of the mandible and ending in the base and another with a long microtubular process which extends 500 m? down to the distal tip of the mandible. The two neurones are enclosed by an ensheathing cell comparable to the trichogen cell enveloping the group of neurones innervating pegs and hairs. This ensheathing cell is supported by extensive electron-dense filaments to form a scolopale and is embedded in the mass of stylet-forming cells at the base of the mandible. The inner segments of the dendrites are anchored to the ensheathing cell by desmosome junctions. Desmosome junctions also bind the microtubular outer segments of the short and long dendrite to each other. There is no evidence of a dendritic sheath enclosing the distal portion of the short dendrite which ends while still in the extracellular space within the ensheathing cell. The microtubular process of the long dendrite extends down the lumen of the mandible enclosed by a close-fitting extracellular sheath which penetrates and is attached to the cuticular wall of the mandible tip. Distally this sheath is thickened on one side. Deflection of the mandible would therefore deform the dendritic membrane asymmetrically because the thin walls of the sheath would bend more than the thick walls. This would exert an unequal mechanical strain on the dendritic membrane which could result in depolarization in response to deflection in a particular direction. The arrangement of the dendrites and their sheaths within the mandible is such that deflection to the right would distort one dendrite in the same way as deflection to the left would distort the other.