The glands of Tamarix aphylla: a system for salt recretion or for carbon concentration?

During periods of high atmospheric humidity, twigs of Tamarix aphylla (L.) Karst. become covered by an alkaline solution. The pH of that solution fluctuates between 8.0 – 8.5 in the dark and 10.5 during the light hours. Such a solution, produced by the glands, constitutes an efficient trap for atmospheric CO₂. Upon the periodic drop in pH, much of the preabsorbed carbon may gradually be released from the solution. This enriches the immediate surroundings of the twigs with CO₂ for prolonged periods of time. The expected concentrations of CO₂, at the boundary layer between the atmosphere and the surfaces of the twigs, are over 1 000 ppm. As net photosynthesis of T. aphylla reaches maximal rates only at CO₂ concentrations of above 500 ppm, the plants may benefit from this extra source of carbon and may exploit it for maximal assimilation during the early morning hours. Thus, the "salt glands'of Tamarix , which are liable for the production of the alkaline recretum, may serve a triple purpose: (a) removal of excess salts out of the twigs, (b) provision of a cover of hygroscopic solutes that moistens the twigs and shortens the duration of transpiration, and (c) providing the plants with an environment enriched in CO₂.     

Electron microprobe analysis of intracellular electrolytes in resting and isoproterenol-stimulated exocrine glands of frog skin

Summary In the intact, in vitro frog skin, isoproterenol (ISO) stimulates and amiloride-insensitive increase in short-circuit current (SCC) that can be localized to the exocrine glands and is associated with secretion of chloride. To determine which cells in the glands respond to stimulation we measured the intracellular electrolyte concentrations of the various cell types of the mucous and seromucous glands of the skin using freeze-dried cryosections and electron microprobe analysis. In the resting state, the various cell types of the glands have intracellular electrolyte concentrations similar to the epithelial cells of the skin. Exposure to amiloride (10^–4 m) has little effect on the concentration of Na and Cl in the cells of the glands. The effect of isoproterenol has two distinct phases. Analysis of glands in tissues frozen at the peak of the SCC response (13 min after addition of isoproterenol) shows that the only significant change is an increase in Na and Ca in a group of cells at the ductal pole of the acini of both gland types. These are termed gland cells. The duct cells and cells that secrete macromolecules did not show any significant changes at this timepoint. In the gland cells, after a one-hour exposure to isoproterenol the Na concentration is at prestimulation levels while Cl drops. There is also a smaller drop in Cl in the duct and skin epithelial cells. Ouabain, which can completely block the isoproterenol SCC response, has little short-term effect on Na and Cl in the control gland but accentuates the gain of Na and drop in Cl in the isoproterenol-treated condition. Bumetanide and, to a lesser extent, furosemide, also blocks the isoproterenol SCC response and causes a further drop in Cl. The results provide indirect evidence that a major portion of the ionic component of the gland secretion is produced by a distinct group of cells separate from those producing the macromolecular component and that the mechanism of secretion involves a Na:Cl coupled transport system linked to the activity of the basolateral Na pump.     

Control of the Amiloride-Sensitive Na+ Current in Salivary Duct Cells by Extracellular Sodium

We have previously reported that intralobular salivary duct cells contain an amiloride-sensitive Na⁺ conductance (probably located in the apical membranes). Since the amiloride-sensitive Na⁺ conductances in other tight epithelia have been reported to be controlled by extracellular (luminal) Na⁺, we decided to use whole-cell patch clamp techniques to investigate whether the Na⁺ conductance in salivary duct cells is also regulated by extracellular Na⁺. Using Na⁺-free pipette solutions, we observed that the whole-cell Na⁺ conductance increased when the extracellular Na⁺ was increased, whereas the whole-cell Na⁺ permeability, as defined in the Goldman equation, decreased. The dependency of the whole-cell Na⁺ conductance on extracellular Na⁺ could be described by the Michaelis-Menten equation with a K _m of 47.3 mmol/1 and a maximum conductance (G _max) of 2.18 nS. To investigate whether this saturation of the Na⁺ conductance with increasing extracellular Na⁺ was due to a reduction in channel activity or to saturation of the single-channel current, we used fluctuation analysis of the noise generated during the onset of blockade of the Na⁺ current with 200 μmol/l 6-chloro-3,5-diaminopyrazine-2-carboxamide. Using this technique, we estimated the single channel conductance to be 4 pS when the channel was bathed symmetrically in 150 mmol/l Na⁺ solutions. We found that Na⁺ channel activity, defined as the open probability multiplied by the number of available channels, did not alter with increasing extracellular Na⁺. On the other hand, the single-channel current saturated with increasing extracellular Na⁺ and, consequently, whole-cell Na⁺ permeability declined. In other words, the decline in Na⁺ permeability in salivary duct cells with increasing extracellular Na⁺ concentration is due simply to saturation of the single-channel Na⁺ conductance rather than to inactivation of channel activity. Received: 27 July 1995/Revised: 7 December 1995     

Electron microscopic study of the mandibular glands of Kalotermes flavicollis Fabr. (Isoptera; Calotermitidae)

Summary The mandibular glands of Kalotermes were examined in different castes. They showed sexual dimorphism in the soldiers and primary reproductives. Moreover, in female soldiers and queens, mandibular gland cells contained numerous crystalline structures of mitochondrial origin. The role of these glands (secretion of saliva or pheromone) is discussed.

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Résumé Les glandes mandibulaires de Calotermes sont étudiées dans les différentes castes. Elles présentent un dimorphisme sexuel chez les soldats et les sexués. Après la mue imaginale, les cellules glandulaires ont toujours une activité sécrétrice. De plus, chez les soldats femelles et les reines, elles contiennent de nombreuses formations cristallines d'origine mitochondriale. Le rôle de ces glandes (sécrétion de salive ou de phéromone) est discuté.

     

Resin gathering in neotropical resin bugs (Insecta: Hemiptera: Reduviidae): Functional and comparative morphology

Apiomerini (Reduviidae: Harpactorinae) collect plant resins with their forelegs and use these sticky substances for prey capture or maternal care. These behaviors have not been described in detail and morphological structures involved in resin gathering, transfer, and storage remain virtually undocumented. We here describe these behaviors in Apiomerus flaviventris and document the involved structures. To place them in a comparative context, we describe and document leg and abdominal structures in 14 additional species of Apiomerini that represent all but one of the 12 recent genera in the tribe. Based on these morphological data in combination with the behavioral observations on A. flaviventris, we infer behavioral and functional hypotheses for the remaining genera within the tribe Apiomerini. Setal abdominal patches for resin storage are associated with maternal care so far only documented for species of Apiomerus. Based on the occurrence of these patches in several other genera, we propose that maternal care is widespread within the tribe. Ventral abdominal glands are widespread within female Apiomerini. We propose that their products may prevent hardening of stored resins thus providing long‐term supply for egg coating. Judging from the diverse setal types and arrangements on the front legs, we predict six different behavioral patterns of resin gathering within the tribe. J. Morphol., 2011. © 2010 Wiley‐Liss, Inc.     

Cephalic modifications in dimorphic dwarf spiders of the genus oedothorax (Erigoninae,Linyphiidae, Araneae) and their evolutionary implications

Reproductive competition among males selects for a broad variety of strategies and traits from mate guarding to nuptial food gifts. Males of many dwarf spider species possess conspicuous secondary cephalic modifications, and the few studies available suggest that these cephalic structures are connected to extensive glandular tissue. Because females were observed to contact the male head structures during mating, these traits may have evolved in the context of sexual selection. We investigated the structure, glandular equipment, and sensory equipment of the cephalic regions of several species of the dwarf spider genus Oedothorax with varying degrees of sexual dimorphism using light and electron microscopy. In one Oedothorax species, there are two male morphs that exhibit a cephalic modification (O. gibbosus gibbosus) or not (O. gibbosus tuberosus). Our study demonstrates that all males investigated produce cephalic secretions, irrespective of the morphology of their cephalic region, however, they may differ in amount of secretion and in cellular organization. In males of O. apicatus, O. gibbosus gibbosus and O. retusus the gland cells are very abundant in the area of a cephalic hump, whereas in the less conspicuous O. agrestis, and O. gibbosus tuberosus the gland cells are restricted to a small area behind the ocular region or include the ocular region as in O. fuscus. The glandular tissue consists of two gland types in O. agrestis, O. fuscus, O. gibbosus tuberosus and O. retusus and of only one type in O. apicatus and O. gibbosus gibbosus. The setae present on the head structure of all species seem to function as mechano‐ and/or chemoreceptors. The implications of our findings for the evolution of secretory head structures are discussed along with their potential for driving speciation. J. Morphol. 2011. © 2011Wiley‐Liss, Inc.     

Functional anatomy of scent glands in Paranemastoma quadripunctatum (Opiliones,Dyspnoi, Nemastomatidae)

The morphological organization and functional anatomy of prosomal defensive (scent) glands in Paranemastoma quadripunctatum, a representative of the dyspnoid harvestmen, was investigated by means of histological semithin sections, software‐based 3D‐reconstruction and scanning electron microscopy. Scent glands comprise large, hollow sacs on either side of the prosoma, each of these opening to the outside via one orifice (ozopore) immediately above coxa I. In contrast to the situation known from laniatorean, cyphophthalmid and some eupnoid Opiliones, ozopores are not exposed but hidden in a depression (atrium), formed by a dorsal integumental fold of the carapace and the dorsal parts of coxae I. Glandular sacs are connected to ozopores via a short duct which is equipped with a specific closing mechanism in its distal part: A layer of modified epidermal cells forms a kind of pad‐like tissue, surrounding the duct like a valve. Several muscles attached to the anterior parts of the glandular reservoir and to the epithelial pad may be associated with ozopore‐opening. The actual mechanism of secretion discharge seems to be highly unusual and may be hypothesized on the basis of corroborating data from behavioral observations, scent gland anatomy and secretion chemistry as follows: Enteric fluid is considered to be directed towards the ozopores via cuticular grooves in the surface of the coxapophyses of legs I. Then, the fluid is sucked into the anterior part of the scent gland reservoirs by the action of dorsal dilator muscles that widen the reservoir and produce a short‐term negative pressure. After dilution/solution of the naphthoquinone‐rich scent gland contents, a secretion‐loaded fluid is thought to be discharged with the help of transversal compressor muscles. This is the first detailed study on the functional anatomy of scent glands and the mechanisms of secretion discharge in the Dyspnoi. J. Morphol. 2011. © 2011 Wiley‐Liss, Inc.     

Peculiarities of the male urogenital apparatus of two grunt species (Teleostei, Haemulidae)

An unusual testicular structure in the white grunt, Haemulon plumieri , and the French grunt, H. flavolineatum , and a urinary exocrine gland in H. flavolineatum are described. The testes of both species are comprised predominantly of efferent ducts, with spermatogenetic tissue restricted to the gonadal periphery. The epithelial cells of the efferent ducts produce glycogen which may serve a role in the storage and nutrition of sperm. The urinary gland is a male accessory gland thought to be associated with reproduction. The gland is mesonephric in origin and the epithelial cells of the gland produce mucins which may be involved in intraspecific chemical communication.     

Sternal gland structures in males of bean flower thrips,Megalurothrips sjostedti,and Poinsettia thrips,Echinothrips americanus,in comparison with those of western flower thrips,Frankliniella occidentalis (Thysanoptera: Thripidae)

Sternal pores are important features for identification of male thrips, especially within the subfamily Thripinae. They vary in shape, size and distribution even between species of one genus. Their functional role is speculated to be that of sex- and/or aggregation pheromone production. Yet, sexual aggregations are not reported in Echinothrips americanus, known to have sternal pores, while we observed aggregations in Megalurothrips sjostedti, previously reported to lack them.We examined the sternal glands and pores of the thripine species E. americanus and M. sjostedti males, in comparison with those of Frankliniella occidentalis using light microscopy, as well as scanning and transmission electron microscopy. Pore plates of F. occidentalis were ellipsoid and medial on sternites III–VII, while in E. americanus they were distributed as multiple micro pore plates on sternites III–VIII. In M. sjostedti they appeared as an extremely small pore in front of the posterior margin of each of sternites IV–VII. Pore plate and pore plate area were distributed similarly on sternites III–VII in F. occidentalis. However, in E. americanus the total pore plate area increased significantly from sternites III to VIII. Ultrastructure of cells associated with sternal glands showed typical characteristics of gland cells that differ in size, shape and number. The function of sternal glands is further discussed on the basis of morphological comparisons with other thrips species.