Ultrastructure of posterior sternal glands of Macrotermes annandalei (Silvestri): new members of the sexual glandular set found in termites (Insecta)

In female alates of Macrotermes annandalei, two types of abdominal glands are involved in the secretion of sex pheromone. Tergal glands are found at the anterior margin of tergites 6-10 and posterior sternal glands (PSGs) are located at the anterior margin of sternites 6-7. The cytological features of both types of glands are quite similar. The fine structural organization of PSGs is studied more precisely and described for the first time. The glandular cuticle is pitted with narrow apertures corresponding to the openings of numerous subcuticular pouches. Several Class 3 glandular units open in each pouch. One canal cell and one secretory cell make an individual glandular unit. The canal cell is enlarged apically and is connected with the other canal cells to form a common pouch. Based on the structural features found in these glands, we propose a common secretory process for PSGs and tergal glands. During the physiological maturation of alates inside the nest, secretory vesicles amass in the cytoplasm of secretory cells, while large intercellular spaces collapse the cuticular pouches. At the time of dispersal flight, pouches are filled with the content of secretory vesicles while intercellular spaces are sharply reduced. After calling behavior, no secretion remains in the glands and pouches collapse again, while secretory cells are drastically reduced in size. The structure and the secretory processes of PSGs and tergal glands are compared to those of abdominal sexual glands known in termites.     

黑缘烟蟋螽丝腺结构

【目的】蟋螽是直翅目中唯一具有吐丝筑巢行为的类群。本研究旨在探讨蟋螽丝腺的结构特点。【方法】应用解剖学观察、免疫荧光、苏木精-伊红染色、PAS苏木精染色、扫描电镜和透射电镜等方法从细胞水平对黑缘烟蟋螽Capnogryllacris nigromarginata丝腺的显微与超微结构进行了观察。【结果】黑缘烟蟋螽丝腺由导管和腺泡构成。腺泡由鞘细胞延伸形成的结缔组织鞘包围。腺泡的主体有4种细胞,分别为Ⅰ型分泌细胞、Ⅱ型分泌细胞、围细胞和腔细胞。Ⅰ型和Ⅱ型分泌细胞为大的腺细胞,形状不规则。分泌细胞细胞核很大,胞质内有大量的内质网和分泌颗粒。Ⅰ型分泌细胞靠近腺泡中心,PAS-苏木精染色表明Ⅰ型分泌细胞内含糖蛋白,Ⅱ型分泌细胞在腺泡外周,位于Ⅰ型分泌细胞与围细胞或结缔组织鞘之间。腔细胞分散在分泌细胞之间,包围形成胞外运输分泌物的通道。围细胞与鞘细胞接触,具有由细胞膜内陷形成的微绒毛腔,胞质内有大量的线粒体。围细胞微绒毛腔与腔细胞包围的细胞外运输通道相连,分泌细胞分泌的颗粒聚集在分泌细胞和胞外运输通道之间的连接处,并将分泌物排出至胞外运输通道。多个腺泡的胞外运输通道汇集到由单层细胞组成的丝腺导管。单层导管细胞靠近管腔外围具有规则排列的质膜内陷和大量伸长的线粒体;靠近管腔的一侧具连续的细胞膜突起,在导管壁的表皮下紧密排列。【结论】黑缘烟蟋螽丝腺分泌细胞分为Ⅰ型分泌细胞和Ⅱ型分泌细胞。分泌物质产生及分泌过程依次经过分泌细胞、腔细胞包围的胞外通道、分支导管、总导管和唾窦。其中在腺泡细胞之间,分泌物向外运输过程中,围细胞微绒毛腔的微丝束可能对分泌物的外排提供推动力。     

Morphology and ultrastructure of a bacteria cultivation organ: the antennal glands of female European beewolves, Philanthus triangulum (Hymenoptera, Crabronidae)

Females of a solitary digger wasp, the European beewolf (Philanthus triangulum F.), cultivate symbiotic bacteria of the genus Streptomyces in specialized antennal glands. The streptomycetes are secreted in the subterranean brood cells and protect the offspring against mould fungi. We reconstructed the complex morphology of the antennal glands using 3D-visualization software, investigated the ultrastructure of the glands, and examine the role of the antennal glands as organs for the cultivation of the symbiotic bacteria. The bacteria are cultivated in five antennomeres within large reservoirs that consist of two slightly bent lobes. Each gland reservoir is bordered by a monolayered epithelium lined with a partially reinforced cuticle and when completely filled with bacteria it comprises about half of the antennomere's volume. The opening of the reservoir is covered by gelatinous appendage of the cuticle. The cells of the monolayered epithelium bordering each reservoir show basal invaginations, apical microvilli and numerous vesicles. Each reservoir is surrounded by approximately 400 class 3 gland units that are connected to the reservoir lumen through conducting canals. The class 3 gland cells contain numerous vesicles and a high density of rough endoplasmatic reticulum. In the reservoir lumen, large numbers of symbiotic Streptomyces bacteria are embedded in secretion droplets. Thus, the bacteria are apparently provided with large amounts of nutrients via the gland epithelium and the class 3 gland cell units.     

Ultrastructure of epidermal glands in neotenic reproductives of the termite Prorhinotermes simplex (Isoptera: Rhinotermitidae)

The ultrastructure of epidermal glands in neotenic reproductives of Prorhinotermes simplex is described and their development is compared among young and old neotenics of both sexes. Secretory cells forming the epidermal gland are attached to the cuticle all over the body. The glands are formed by class 1 and class 3 secretory cells and corresponding canal cells with secretory function. Class 1 cells are sandglass-like and class 3 secretory units are located among them. Class 1 cells contain predominantly tubular endoplasmic reticulum, the major part represents the smooth and the minor the rough form. Numerous electron dense granules occur in the cytoplasm, they are always disintegrated prior to be released. Class 3 secretory cells contain a large amount of vacuoles, which are always lucent in males while newly produced vacuoles are dense in females. Dense vacuoles are frequently transformed into lucent ones before being released. Canal cells are locally equipped with microvilli. The conducting canal is surrounded by an electron dense secretion of regular inner structure. The cytoplasm of the canal cell contains numerous mitochondria, rough endoplasmic reticulum and a large proportion of microtubules. The young neotenic reproductives differ from the old ones by a lower amount of secretory products. Epidermal glands probably produce substances inhibiting the occurrence of superfluous reproductives.     

Fine structure of the accessory glands of the female genital tract of the ichneumonid Pimpla turionellae (Insecta,Hymenoptera)

Summary The female accessory glands include the tubular poison gland, the paired, lemon-shaped uterus glands, and Dufour's gland, an unbranched tubular organ. They consist essentially of a single layer of epithelium cells surrounded by a basement membrane. The lumen is lined by cuticle. The proteinaceous secretion of the poison gland is released into intracellular ducts provided with microvilli, each connected to a channel lined with cuticle which leads to the central lumen of the gland. The channel is formed by special canal cells. Nerve endings are interspersed among the gland cells. The uterus gland consists of four cell types derived from a single type of precursor cell found in newly hatched wasps. Type I cells are covered by type II cells and are thus without contact to the luminal surface of the gland. They contain stacks or whorls of mitochondria and smooth cisternae in an alternating arrangement. Vesicles with a secretory product are found in cells of types II and III. Deep anastomosing infoldings of the plasmalemma, stabilized by microtubules and dense material at the branchings, are characteristic for type II cells. Most secretory vesicles are found in type III cells, the prevalent cell type which is thought to be the source of the lipoprotein secretion. Coated vesicles are present at deep infoldings of the plasmalemma. The greatly enlarged apical surface area of type IV cells and the presence of mitochondria in slender outgrowths is suggestive of an osmoregulatory function. In Dufour's gland, two cell types appear in succession, the first with a very dense cytoplasm, the second with dense inclusions and many seemingly empty vesicles of smooth endoplasmic reticulum. The secretion products, lecithin and a cholesterol ester, are thought to be formed by the second cell type. The dense inclusion might be lecithin, which reacts with osmium tetroxide. The cholesterol ester could have been washed out of the empty vesicles by the embedding procedure.     

Ultrastructural organization of the anal organs in the anal capsule of Craterostigmus tasmanianus Pocock, 1902 (Chilopoda, Craterostigmomorpha)

We describe the ultrastructural organization of the anal organs of Craterostigmus tasmanianus, which are located on the ventral side of the bivalvular anal capsule. Each part of the capsule bears four pore fields with several anal pores. The pores lead into a pore canal, which is surrounded by the single-layered epithelium of the anal organs. Each anal organ is composed of four different cell types: transporting cells of the main epithelium, junctional cells, isolated epidermal glands, and the cells forming the pore canal. The transporting cells exhibit infoldings of the outer cell membranes, forming a basal labyrinth and a poorly developed apical complex. The cells are covered by a specialized cuticle with a widened subcuticular layer. Only the cuticle of the main epithelium is covered by a mucous layer, secreted by the epidermal glands. The ultrastructural organization of the anal organ is comparable to the coxal and anal organs of other pleurostigmophoran Chilopoda. It is likely that the coxal and anal organs of the Pleurostigmophora are homologous, due to their identical ultrastructural organization. Differences concerning the location on the trunk of Pleurostigmophora are not sufficient to reject a hypothesis of homology. Anal organs are found not only in Craterostigmomorpha, but also in most adult Geophilomorpha, and in larvae and most adults of Lithobiomorpha. The anal organs of C. tasmanianus are thought to play an important role in the uptake of atmospheric water. J. Morphol.     

Sperm storage by spermatodoses in the spermatheca of Trioza alacris (Flor, 1861) hemiptera,psylloidea, triozidae: A structural and ultrastructural study

Female insects generally store sperm received during mating in specific organs of their reproductive tract, i.e., the spermathecae, which keep the sperm alive for a long time until fertilization occurs. We investigated spermatheca morphology and ultrastructure in the psylloidean insect Trioza alacris (Flor, 1861 ) in which spheroidal sperm packets that we refer to as ‘spermatodoses’ are found after mating. The ectoderm‐derived epithelium of the sac‐shaped spermatheca that has a proximal neck, consists of large secretory and flat cuticle‐forming cells. Secretory cells are characterized by a wide extracellular cavity, bordered by microvilli, in which electron‐dense secretion accumulates before discharge into the spermathecal lumen. The cuticle‐forming cells produce the cuticular intima of the organ and a peculiar specialized apical structure, through which secretion flows into the lumen. At mating, the male transfers bundles of sperm cells embedded in seminal fluid into the spermathecal neck. Sperm cells proceed towards the spermathecal sac lumen, where they are progressively compacted and surrounded with an envelope that also encloses secretions of both male and female origin. We describe the formation of these sperm containing structures and document the contribution of the female secretion to spermatodose or female‐determined spermatophore construction. We also discuss the choice of the term ‘spermatodose’ for T. alacris and suggest it be used to refer to sperm masses constructed in the female reproductive organs, at least when they involve the contribution of female secretion. © 2011 Wiley Periodicals, Inc.     

Ultrastructural investigation of a salivary gland in a centipede: structure and origin of the maxilla I-gland of Scutigera coleoptrata (Chilopoda, Notostigmophora)

The maxilla I-gland of Scutigera coleoptrata was investigated using light and electron microscopy methods. This is the first ultrastructural investigation of a salivary gland in Chilopoda. The paired gland opens via the hypopharynx into the foregut and extends up to the third trunk segment. The gland is of irregular shape and consists of numerous acini consisting of several gland units. The secretion is released into an arborescent duct system. Each acinus consists of multiple of glandular units. The units are composed of three cell types: secretory cells, a single intermediary cell, and canal cells. The pear-shaped secretory cell is invaginated distally, forming an extracellular reservoir lined with microvilli, into which the secretion is released. The intermediary cell forms a conducting canal and connects the secretory cell with the canal cell. Proximally, the intermediary cell bears microvilli, whereas the distal part is covered with a distinct cuticle. The cuticle is a continuation of the cuticle of the canal cells. This investigation shows that the structure of the glandular units of the salivary maxilla I-gland is comparable to that of the glandular units of epidermal glands. Thus, it is likely that in Chilopoda salivary glands and epidermal glands share the same ground pattern. It is likely that in compound acinar glands a multiplication of secretory and duct cells has taken place, whereas the number of intermediary cells remains constant. The increase in the number of salivary acini leads to a shifting of the secretory elements away from the epidermis, deep into the head. Comparative investigations of the different head glands provide important characters for the reconstruction of myriapod phylogeny and the relationships of Myriapoda and Hexapoda.     

Fine structure of the tegumentary glands secreting the protective "shield" in a sessile insect (Homoptera, Diaspiddae)

The tegumentary pygidial glands of Aonidiella aurantii (Homoptera, Diaspididae) produce a secretion forming the shield of these fixed parasites of plants. They are formed of seven cells: a principal unpaired secretory cell which produces an abundant glycoproteinaceous secretion; a small associated cell with a secondary reservoir for this secretion; two accessory secretory cells which have very abundant tubular extensions coming from the plasma membrane, and a flocculent secretion gathered in a large sub-cuticular space; two cells forming an enlarged part of the excretory canal, functioning like a spinneret; and finally a single cell forming the tubular duct of this complex gland. The cuticle of the secretory cells has a very special porous structure, through which the secretion passes. The final product is a ribbon formed by two hollow strands stuck together. The exact nature of this secretion is not clear. It is comparable to a silk secretion though it has its own particular characteristics.     

Ultrastructural investigation of the vesicular glands in Scutigera coleoptrata (Chilopoda,Notostigmophora)

In the notostigmophoran centipedes, two pairs of vesicular glands have evolved. These paired glands are situated in the first and second trunk segment and open via cuticular ducts in the upper part of the particular pleura. The vesicular glands of Scutigera coleoptrata were investigated using light and, for the first time, electron microscopical methods. The glands consist of wide sac‐like cavities that often appear vesicular. The epithelia of both glands are identically structured and consist of numerous glandular units. Each of these units consists of four different cells: a single secretory cell, a small intermediary cell, and one proximal and one distal canal cell. The intermediary cell forms a conducting canal and connects the secretory cell with the canal cells. Proximally, the intermediary cell bears microvilli, whereas the distal part is covered with a distinct cuticle. The cuticle is a continuation of the cuticle of the canal cells. This investigation shows that the ultrastructure of glandular units of the vesicular glands is comparable to that of the glandular units of other epidermal glands in Chilopoda and Diplopoda, although the glands look completely different in the light microscope. Thus, it is likely that the vesicular glands and epidermal glands share the same ground pattern. With regard to specific differences in the cuticular lining of the intermediary cells, a common origin of epidermal glands in Myriapoda and Hexapoda is not supported. J. Morphol. 2009. © 2008 Wiley‐Liss, Inc.     

CUTICLE DEVELOPMENT ON GLANDULAR TRICHOMES OF CANNABIS SATIVA (CANNABACEAE)

The dermal sheath of glandular trichomes of Cannabis sativa L., consisting of cuticle and a subcuticular wall, was examined by transmission electron microscopy. Cuticle thickened selectively on the outer wall of disc cells of each trichome prior to formation of the secretory cavity, whereas thickening was less evident on the dermal cells of the bract. Membraned secretory vesicles that differ in size and appearance in the secretory cavity were the source of precursors for synthesis of cuticle. Vesicle contents, released following the degradation of the vesicle membrane upon contact with the subcuticular wall, contributed to both structured and amorphous phases of cuticle development. The structured phase was represented by deposition and thickening of cuticle at the subcuticular wall-cuticle interface to form a thickened cuticle. In the amorphous phase precursors permeated the cuticle in a liquid state, as shown by fusion of cuticles and wax layers between contiguous glands, and may have contributed to growth in surface area of the expanding sheath. Disc cells are interpreted to control growth of secretory cavity by secretion of membraned vesicles into the cavity. The thickened cuticle, which increased eightfold in thickness during enlargement of the gland, provided structural strength for the extensive surface area of the dermal sheath. The gland of Cannabis in which vesicle contents contribute to the growth in thickness and surface area of the cuticle of the sheath is interpreted to represent a phylogenetically derived state as contrasted to secretory glands possessing only cuticle and lacking a complement of secretory vesicles.     

Functional anatomy of oil glands in<Emphasis Type="Italic"> Collohmannia gigantea</Emphasis> (Acari,Oribatida)

Chemical and behavioural studies indicated that the oil glands of the Oribatida represented a central organ for protection and semiochemical communication. The hitherto unknown mode of action of these glands and their microscopic anatomy have been investigated in Collohmannia gigantea by histological and SEM techniques. The paired oil glands are located dorsolaterally in the hysterosoma and mainly comprise large intima-lined and sac-like reservoirs which are surrounded by glandular tissue. The reservoirs consist of a single-layered flat epithelium and probably serve for storage of the oil gland secretion only, but not for its production. Each reservoir opens to the body outside via a single pore. Externally, the pores appear as oval-shaped rings of smooth cuticle, moderately projecting from the surface of the notogaster. The pore orifices are supplied with trapdoor-like closing mechanisms, consisting of cuticular flaps which permit reservoir opening by muscles attaching to the posterior part of the reservoir and the inner side of the notogaster. These morphological data, especially the large intima-lined reservoirs along with closing mechanisms under muscular control, are consistent with supposed biological roles of oil glands as defensive or alarm pheromonal organs.     

Translocation of small preformed vesicles is responsible for the insulin activation of glucose transport in adipose cells. Evidence from the in vitro reconstitution assay

Insulin stimulates translocation of the glucose transporter isoform 4 (Glut4) from an intracellular storage compartment to the plasma membrane in fat and skeletal muscle cells. At present, the nature of the Glut4 storage compartment is unclear. According to one model, this compartment represents a population of preformed small vesicles that fuse with the plasma membrane in response to insulin stimulation. Alternatively, Glut4 may be retained in large donor membranes, and insulin stimulates the formation of transport vesicles that deliver Glut4 to the cell surface. Finally, insulin can induce plasma membrane fusion of the preformed vesicles and, also, stimulate the formation of new vesicles. In extracts of fat and skeletal muscle cells, Glut4 is predominantly found in small insulin-sensitive 60-70 S membrane vesicles that may or may not artificially derive from large donor membranes during cell homogenization. Here, we use a cell-free reconstitution assay to demonstrate that small Glut4-containing vesicles are formed from large rapidly sedimenting donor membranes in a cytosol-, ATP-, time-, and temperature-dependent fashion and, therefore, do not represent an artifact of homogenization. Thus, small insulin-responsive vesicles represent the major form of Glut4 storage in the living adipose cell. Fusion of these vesicles with the plasma membrane may be largely responsible for the primary effect of insulin on glucose transport in fat tissue. In addition, our results suggest that insulin may also stimulate the formation of Glut4 vesicles and accelerate Glut4 recycling to the plasma membrane.     

Fine structure of the spermatheca and of the accessory glands in Orchesella villosa (Collembola, Hexapoda)

The spermatheca and the accessory glands of the collembolan Orchesella villosa are described for the first time. Both organs exhibit ultrastructural differences, according to the time of the intermolt in which the specimens were observed. A thick cuticular layer lines the epithelial cells of the accessory glands. In the reproductive phase, they are involved in secretory activity; a moderately dense secretion found in the apical cell region opens into the gland lumen. Cells with an extracellular cistern are intermingled with the secretory cells. These cells could be involved in fluid secretion, with the secretory product opening into the cistern which is filled with an electron-transparent material. After the reproductive phase, the gland lumen becomes filled with a dense secretion. The accessory gland secretion may play a protective role towards the eggs. The spermatheca is located between the accessory glands; its epithelium is lined by a thin cuticle forming spine-like projections into the lumen and consists of cells provided with an extracellular cistern. Secretory cells, similar to those seen in the accessory glands, are missing. Cells with a cistern could be involved in the production of a fluid secretion determining sperm unrolling and sperm motility.     

Ultrastructure of the epidermal maxilla II-gland of Scutigera coleoptrata (Chilopoda, Notostigmophora) and the ground pattern of epidermal gland organs in Myriapoda

The epidermal maxilla II-gland of Scutigera coleoptrata was investigated using light and electron microscopy. The glandular epithelium surrounds a spacious integumental cavity at the base of the maxilla II. The gland is formed as a compound gland organ that is composed of thousands of epidermal gland units. Each of them consists of four different cell types: a secretory cell, an accessory or intermediary cell, and a proximal and distal canal cell. The intermediary and the two canal cells form a conducting canal. Only in the most distal part of the intermediary cell is the canal lined by a cuticle. In the area of the two canal cells, the conducting canal is completely covered by a cuticle. The canal passes through the cuticle and opens into the spacious integumental cavity, which serves as a secretion reservoir. The structural organization of the epidermal maxilla II-gland was compared to that of other compound epidermal gland organs in Chilopoda and Diplopoda. All these glandular organs in Myriapoda share the same ground pattern.     

Fine structure of the urnulae of Balaustium mites (Actinotrichida: Erythraeidae) representing peculiar defense organs

The urnulae, until now the enigmatic paired dorsal protrusions on idiosoma dorsum in active postlarval forms of Balaustium mites, were studied using electron microscopy. They consist of walls made of unmodified integument, which form a cylinder covered by a roof of thin cuticle. At the posterior border of the urnula, the roof has a crescent slit. On its inner surface, a rather large muscle inserts with several tendons. The roof forms a flap under which the modified columnar epidermal cells containing numerous lipid inclusions are located. These lipids are probably secreted through pore canals of the overlying cuticle. Materials mainly originating from an extensive vesicular tissue situated underneath the columnar cells of the urnula and under the adjacent unmodified epidermis are extruded through the mentioned slit. Our results support previous studies that have suggested a function of the urnulae as defensive organs. Our study further suggests that the agent that provides the repellent effect comes mainly from the vesicular tissue, whereas the columnar cells with their lipid secretions are likely to restore the external secretion layer of the epicuticle after its destruction during the repellent release. Further structural and functional details are discussed and compared with other putative defensive secretory organs.     

Ein atlas der spaltsinnesorgane von Cupiennius salei keys. Chelicerata (Araneae)

To facilitate further physiological investigation, a survey was undertaken of all the slit sense organs to be found on the body of the spider Cupiennius salei. We counted and mapped more than 3 000 sensory slits in the cuticle about half of which are combined to small groups of up to 29 slits forming compound or lyriform organs.     

Ultrastructure of the male reproductive accessory glands in the medfly Ceratitis capitata (Diptera: Tephritidae) and preliminary characterization of their secretions

The morphology and the ultrastructure of the male accessory glands and ejaculatory duct of Ceratitis capitata were investigated. There are two types of glands in the reproductive apparatus. The first is a pair of long, mesoderm-derived tubules with binucleate, microvillate secretory cells, which contain smooth endoplasmic reticulum and, in the sexually mature males, enlarged polymorphic mitochondria. The narrow lumen of the gland is filled with dense or sometimes granulated secretion, containing lipids. The second type consists of short ectoderm-derived glands, finger-like or claviform shaped. Despite the different shape of these glands, after a cycle of maturation, their epithelial cells share a large subcuticular cavity filled with electron-transparent secretion. The ejaculatory duct, lined by cuticle, has epithelial cells with a limited involvement in secretory activity. Electrophoretic analysis of accessory gland secretion reveals different protein profiles for long tubular and short glands with bands of 16 and 10 kDa in both types of glands. We demonstrate that a large amount of accessory gland secretion is depleted from the glands after 30 min of copulation.     

The ultrastructure of a pheromone-secreting gland in the male scorpion-fly Harpobittacus Australis (Bittacidae: Mecoptera)

The eversible vesicles of the sex pheromone glands consist of three cell types, secreting the cuticle, the duct and the pheromone, respectively. Each pheromone-secreting cell has an end apparatus, bounded by microvilli and lined by a granular mass, that is penetrated by remarkable elongate filaments extending far up into the secretory duct. Vesicles containing secretion or secretion precursors abound. The possible role is discussed of the various organelles in the elaboration and transport of the pheromone.     

An ultrastructural investigation of the hypocerebral organ of the adult Euperipatoides kanangrensis (Onychophora, Peripatopsidae)

The hypocerebral organs of Euperipatoides kanangrensis are a pair of spherical vesicles located ventral to the cerebral ganglia. They develop in the embryo from the most anterior pair of ventral organs, in the antennal segment. The wall of each hypocerebral organ is a dense epithelium of elongate cells with peripheral nuclei. The cytoplasm of the cells includes numerous mitochondria, Golgi bodies and microtubules. The small lumen, located eccentrically within the organ, contains concentrically layered electron-dense material resembling cuticle.Each hypocerebral organ is enclosed by a layer of extracellular matrix continuous with that surrounding the adjacent cerebral ganglion. There are no nerve connections between ganglion and organ, but cellular connections traverse the intervening matrix and could serve as a communication pathway. The ultrastructure of the hypocerebral organs indicates that they are glands.