Site,process and mechanism of active uptake of water vapour from the atmosphere in the Psocoptera

In the Psocoptera, occlusion of the anus or extended areas of the thorax and abdomen with paraffin wax does not interfere with the active uptake of water vapour from subsaturated atmospheres. However, blocking the mouth or impairing the mobility of the mouthparts with wax prevents watervapour absorption. Observations of the animals synchronized with continuous weight recordings, confirm an oral site of water-vapour uptake in this insect order, and reveal some details of the uptake mechanism. During uptake, paired lingual sclerites of the ventral hypopharyngeal surface are brought into a typical absorbing position. Water-vapour condensation proceeds onto a fluid layer covering this surface. The fluid presumably originates from a pair of dorsal labial glands. The condensed water vapour is transferred from the site of condensation to the gut entrance via a paired or branched sclerotized tubule traversing the hypopharynx. Propulsion of the fluid is achieved by a cibarial sucking pump. Below the critical equilibrium humidity the fluid layer dries up, the salivarium is closed and absorption ceases.     

Effect of phosphorus supply to the surface roots of wheat on root extension and rhizosphere chemistry in an acidic subsoil

Seedlings of two cultivars of wheat (Triticum aestivum L.) differing in tolerance to aluminium (Al) were grown using a split-root sand/soil culture technique. Each culture tube was divided horizontally into a surface (0–150 mm) compartment and a subsurface (150–250 mm) compartment separated by a root-permeable paraffin wax barrier. Thus phosphorus (P) supplied to surface roots could not percolate or diffuse into the soil in the subsurface compartment. The soil in the subsurface compartment was divided into ‘rhizosphere’ and ‘non-rhizosphere’ zones using a porous (5 μm) membrane. Root growth of both cultivars into the subsurface zone was enhanced by increased P supply to surface roots, but did not conform to known relationships between root growth and soil pH, extractable-Al, or pH, Al or P concentrations in soil solution. Concentrations of Al in soil solution in the rhizosphere were greater than those in solution in the bulk soil. Concentrations of Al reactive with pyrocatechol violet (30s-RRAI) in the rhizosphere soil solution were generally greater than those in non-rhizosphere soil. With the Al-sensitive cultivar, root dry weight and length increased as concentrations of RRAl in the rhizosphere soil solution increased. Increased concentrations of Al in rhizosphere soil solutions were not related to the presence of organic ligands in solution. The effect of P in promoting root penetration into the acidic subsurface stratum was not related to differential attainment of maturity by the plant shoots, but appeared to be related to the effect of P in enhancing the rate of root growth. Thus, suboptimal supply of P to the surface roots of a plant, even at levels sufficient to preclude development of nutritional (P) stress symptoms, may seriously reduce tolerance to Al, and hence diminish the ability of roots to penetrate into acidic subsoils.     

Transport of Salt and Water in Rabbit and Guinea Pig Gall Bladder

A simple and reproducible method has been developed for following fluid transport by an in vitro preparation of mammalian gall bladder, based upon weighing the organ at 5 minute intervals. Both guinea pig and rabbit gall bladders transport NaCl and water in isotonic proportions from lumen to serosa. In the rabbit bicarbonate stimulates transport, but there is no need for exogenous glucose. The transport rate is not affected by removal of potassium from the bathing solutions. Albumin causes a transient weight loss from the gall bladder wall, apparently by making the serosal smooth muscle fibers contract. Active NaCl transport can carry water against osmotic gradients of up to two atmospheres. Under passive conditions water may also move against its activity gradient in the presence of a permeating solute. The significance of water movement against osmotic gradients during active solute transport is discussed.     

Passive exchanges during water vapour absorption in mealworms (Tenebrio molitor): a new approach to studying the phenomenon.

The weights of single mealworms were continuously recorded at 20 degrees C during exposure to periods of constant humidity and to abrupt changes in atmospheric vapour pressure. Two exchange stages were recognized in each animal. Weight changes were either limited to slow losses, suggesting transpiration through the external cuticle, or showed more rapid humidity-dependent gains as well as losses. Rapid exchanges indicated that water was gained or lost through permeable barriers, from a fluid compartmet of significantly lower vapour pressure than the haemolymph, equivalent to about 90% R.H. Weight gains and losses during humidity changes provided evidence of a significant, passively exchanging fluid compartment located between the exchange surface and absorbing mechanism. Weight changes in faecal pellets following their elimination provide further support for a rectal site of atmospheric absorption.     

Haemolymph osmoregulation and the fate of sodium and chloride during dehydration in terrestrial isopods

Osmoregulation of the haemolymph during dehydration was investigated in a selection of temperate oniscidean isopods. Inulin tracer studies show that the haemolymph contributes approximately 69% of water losses in Porcellio scaber, significantly more than predicted from the volume of this compartment (42% of total water). Haemolymph osmolality increases linearly as a function of haemolymph dehydration but at a significantly lower rate than predicted from the change in haemolymph fluid volume. Similar results for Oniscus asellus show that both species display efficient osmoregulation until lethal dehydration. Osmoregulation is associated with significant hyporegulation of haemolymph sodium and chloride. These findings indicate that: (1) cell water is conserved at the expense of the haemolymph; and (2) haemolymph dehydration is associated with the removal of Na(+) and Cl(-) contributing to net osmoregulation. During dehydration, accumulations of both Na(+) and Cl(-) are seen in the hindgut, with significant accumulations of electrolytes also seen in the luminal fluid of the hepatopancreas. Low fluid volumes in the foregut and hindgut suggest macromolecular association as the most plausible mechanism of ion sequestration. Evidence refutes ion excretion and haemocyte sequestration as osmoregulatory mechanisms. Sequestration of Na(+) as urate salts, as shown for Periplaneta and generally assumed for other insects, is insignificant in isopods.     

Visualization of endocytosed markers in freeze-fracture studies of toad urinary bladder

Antidiuretic hormone (ADH) stimulation increases the apical membrane water permeability of granular cells in toad urinary bladder. This response correlates closely with the fusion of tubular cytoplasmic vesicles with the membrane and delivery of intramembrane particle (IMP) aggregates from the tubules (aggrephores) to the apical membrane. These aggregates are believed to be associated with the channels responsible for the water permeability increase. Removal of ADH triggers apical membrane endocytosis and disappearance of aggregates from the apical membrane. However, it has been unclear whether aggregate disappearance is due to disassembly of aggregates within the apical membrane or to their endocytic retrieval as intact structures. Using colloidal gold and horseradish peroxidase to follow endocytosis from the apical surface after ADH removal, we have directly observed in cross-fractured bladder cells the intramembrane structure of intracellular vesicles that contain these fluid-phase markers. Under these conditions, intact aggregates can be identified in the membrane of tubular endocytosed vesicles. This directly demonstrates that conditions which lower apical membrane water permeability cause the tubular aggrephores to "shuttle" intact aggregates from the apical membrane back into the cytoplasm. An additional population of vesicles with tracer are found which are spherical and display structural features of the apical membrane, as well as occasional aggregates. These vesicles may be responsible for retrieval of aggregates from the surface apical membrane.     

Production of Carbon Films for Electron Microscopy; Hydrofluoric Acid Detachment from Glass

Chemically clean microscope slides are coated as usual by vaporized carbon. The carbon film is floated off the slide by slowly lowering it at an angle of 45° into 1% HF in distilled water containing 0.025% Tween 80. This solution fills completely (forming a positive meniscus at the edges) one chamber of a double-compartment Perspex trough; the other compartment being similarly filled with the Tween solution only. A Teflon bar, laid on top of the partition keeps the solutions from mixing. After the carbon film loosens, it is floated across the central partition into the second compartment with the aid of a second Teflon bar, using both bars to guide the film on the surface of the fluid. The HF is thus washed from the film. Grids are thinly coated with 0.5% poly isobutylene in toluene (as an adhesive) and previously placed on a rectangle of filter paper supported by wire screening about 1/2 inch from the bottom of the trough. While the Tween solution is drained away through a bottom opening, the carbon film is guided to cover the grids. The filter paper bearing the grids is then removed and caused to dry slowly (about 12-16 hr) to avoid cracking or distortion of the film.     

The Mechanism of Isotonic Water Transport

The mechanism by which active solute transport causes water transport in isotonic proportions across epithelial membranes has been investigated. The principle of the experiments was to measure the osmolarity of the transported fluid when the osmolarity of the bathing solution was varied over an eightfold range by varying the NaCl concentration or by adding impermeant non-electrolytes. An in vitro preparation of rabbit gall bladder was suspended in moist oxygen without an outer bathing solution, and the pure transported fluid was collected as it dripped off the serosal surface. Under all conditions the transported fluid was found to approximate an NaCl solution isotonic to whatever bathing solution used. This finding means that the mechanism of isotonic water transport in the gall bladder is neither the double membrane effect nor co-diffusion but rather local osmosis. In other words, active NaCl transport maintains a locally high concentration of solute in some restricted space in the vicinity of the cell membrane, and water follows NaCl in response to this local osmotic gradient. An equation has been derived enabling one to calculate whether the passive water permeability of an organ is high enough to account for complete osmotic equilibration of actively transported solute. By application of this equation, water transport associated with active NaCl transport in the gall bladder cannot go through the channels for water flow under passive conditions, since these channels are grossly too impermeable. Furthermore, solute-linked water transport fails to produce the streaming potentials expected for water flow through these passive channels. Hence solute-linked water transport does not occur in the passive channels but instead involves special structures in the cell membrane, which remain to be identified.     

Effects of cyclic AMP on fluid absorption and ion transport across frog retinal pigment epithelium. Measurements in the open-circuit state

A modified version of a capacitance probe technique has been used to measure fluid transport across the isolated retinal pigment epithelium (RPE)-choroid of the bullfrog. The accuracy of this measurement is 0.5-1.0 nl/min. Experiments carried out in the absence of external osmotic or hydrostatic gradients show that the RPE-choroid transports fluid from the retinal to the choroid side of the tissue at a rate of approximately 10 nl/min (4-6 microliters/cm2 X h). Net fluid absorption (Jv) was abolished within 10 min by the mitochondrial uncoupler 2,4-dinitrophenol. It was also inhibited (70%) by the removal of bicarbonate from the bulk solutions bathing the tissue. Ouabain caused a slow decrease in Jv (no effect at 10 min, 70% at 3 h), which indicates that RPE fluid transport is not directly coupled to the activity of the Na-K pump located at the apical membrane of this epithelium. In contrast to ouabain, cyclic AMP (cAMP) produced a quick decrease in Jv (84% within 5 min). Radioisotope experiments in the open circuit show that cAMP stimulated secretory fluxes of Na and Cl, which accounted for the observed cAMP-induced decrease in Jv. The direction of net fluid absorption, the magnitudes of the net ionic fluxes in the open circuit, and the dependence of Jv on external bicarbonate concentration strongly suggest that fluid absorption is generated primarily by the active absorption of bicarbonate.     

Growth of Methanogens on a Mars Soil Simulant

Currently, the surface of Mars is probably too cold, too dry, and too oxidizing for life, as we know it, to exist. But the subsurface is another matter. Life forms that might exist below the surface could not obtain their energy from photosynthesis, but rather they would have to utilize chemical energy. Methanogens are one type of microorganism that might be able to survive below the surface of Mars. A potential habitat for existence of methanogens on Mars might be a geothermal source of hydrogen, possibly due to volcanic or hydrothermal activity, or the reaction of basalt and anaerobic water, carbon dioxide, which is abundant in the martian atmosphere, and of course, subsurface liquid water. We report here that certain methanogens can grow on a Mars soil simulant when supplied with carbon dioxide, molecular hydrogen, and varying amounts of water.     

Ultrastructure of the foregut and associated glands of Calicotyle kröyeri (Monogenea: Monopisthocotylea)

The mouth, pharynx and oesophagus of Calicotyle are lined by syncytial epithelia, and there are numerous unicellular glands associated with the oesophagus. An infolding of unmodified external tegument lines the mouth cavity and is connected by discrete cytoplasmic processes to subjacent perikarya. It contains two types of secretory body and its luminal surface is invested with a finely filamentous coating. The pharynx and oesophagus are lined by irregularly-folded epithelia that are interconnected by a septate desmosome. Membranous inclusions distinguish the pharynx epithelium and there is a well developed basal lamina for insertion of the pharyngeal muscles. The oesophagus epithelium is perforated by the openings of the oesophageal glands. These lie in the surrounding parenchyma and produce a dense, membrane-bound secretion which is conveyed by duct-like extensions of the glands to the oesophagus lumen. The ducts are supported in places by microtubules and are anchored to the oesophageal epithelium by septate desmosomes. A septate desmosome also marks the junction between the epithelium and the gut caeca.     

Linear n-compartment catenary models: Formulas to describe tracer amount in any compartment and identification of parameters from a concentration-time curve

Resolution of kinetic equations and parameter identification are discussed for n-compartment linear catenary models with elimination allowed from any compartment. For a given input, general formulas are derived to describe the tracer amount in any compartment as a function of the model parameters. Conversely, explicit procedures are given to identify the model parameters when the concentration-time curve is known in one arbitrary compartment, the tracer being injected into the same compartment. In this inverse problem, the solution is not unique: the model transfer rate constants can only be localized in a finite set of intervals.     

潜流湿地和表面流湿地的净化效果与植物生长比较

分别以砾石和土壤为填料构建成潜流人工湿地和表面流人工湿地,处以较大水力负荷的污水处理。比较了两种湿地对污水的净化效果,结果表明在较大水力负荷条件下两种湿地的净化效果都较差,但潜流湿地对各种污染物的净化能力都优于表面流湿地;土柱法测量了湿地植物的根系生物量,结果显示湿地植物地上部分长势差异不明显,但潜流湿地的根系生物量显著低于表面流湿地的根系生物量(P<0.05)。结合前期实验结果得出湿地净化效果不仅与湿地植物根系生物量有相关关系,还与其他因素有一定的相关关系。     

Nonsteady-State Three Compartment Tracer Kinetics: II. Sodium Flux Transients in the Toad Urinary Bladder in Response to Short Circuit

The theoretical approach presented in the previous paper provides an analytical method for determining the unidirectional, nonsteady-state fluxes in a three compartment system. Based on this a study was made of the sodium flux transients in the toad urinary bladder. A transient time-dependent state was generated by suddenly short-circuiting a bladder previously maintained in an open-circuited steady state. The sequence of experiments suggested by the theory provided the data required for the analysis. The results of these tracer experiments were consistent with the complex non-three compartmental structure of this tissue. As a result both of the inadequacy of the three compartment model in representing the tissue and of certain experimental difficulties, attempts at a quantitative solution were not entirely successful. Useful information was nevertheless obtained through a careful use of this model, and a qualitative analysis implied that the sodium influxes into the tissue at both of its surfaces are sensitive to changes in electrical potential while both effluxes are insensitive to this change. This suggests that both of the effluxes result from active processes while both influxes are associated with passive processes. The net transepithelial transport of sodium would then necessarily result from a more complex polarization than that proposed by Koefoed-Johnsen and Ussing.     

Osmotic properties of spermatozoa from felids producing different proportions of pleiomorphisms: influence of adding and removing cryoprotectant

The spermatozoon of felids (cats) survives cryopreservation inconsistently. Using ejaculates from three species (domestic cat [normospermic versus teratospermic], the normospermic serval and the teratospermic clouded leopard), this study (1) determined the influence of adding and removing two permeating cryoprotectants (glycerol and dimethylsulfoxide) and (2) assessed the impact of one-step versus multi-step cryoprotectant removal on sperm motility and membrane integrity. Spermatozoa were exposed in a single step to various anisotonic solutions or to 1M solutions of glycerol or dimethylsulfoxide. In both cases, sperm then were returned to near isotonic conditions in a single or multi-step with de-ionized water, Ham's F10 medium or saline. Percentage of sperm motility was measured subjectively, and plasma membrane integrity was assessed using a dual fluorescent stain and flow cytometry. Sperm motility was more sensitive to anisotonic conditions than membrane integrity. Rapid dilution into various test solutions and removal of cryoprotectant with de-ionized water reduced (P<0.01) sperm motility compared to control spermatozoa maintained in Ham's F10. Exposing sperm from all species to a 1M solution of either cryoprotectant resulted in >85% spermatozoa retaining intact membranes. However, return to isotonicity with de-ionized water in a single step or multiple steps always caused severe plasma membrane disruption. In contrast, sperm motility and membrane integrity in all species and populations remained unaffected (P>0.05) when spermatozoa were returned to isotonicity in multiple steps with Ham's F10 medium or 0.9% sodium chloride. Results demonstrate that: (1) felid spermatozoa are resistant to hypertonic stress; (2) sperm motility is more sensitive to changes in osmolality than membrane integrity; and (3) removal of cryoprotectant in multiple steps with an isotonic solution minimizes loss of sperm motility and membrane disruption in both normospermic and teratospermic males.     

On the role of calcium in the mechanism of ADH action

With an increased influx of Ca2+ in the cytoplasm, the response of cells to ADH in the urinary bladder of the frog was lowered by addition of ionophore A23187 from the side of the basolateral cell membrane, but inhibited when it was added from the apical cell membrane. The removal of calcium by EGTA from the serosal surface was accompanied by a sharp increase of osmotic permeability not only to water, but also to inulin; while when calcium was removed from the mucosal surface of the urinary bladder, osmotic permeability was not changed. After being added to the Ringer solution from the outer surface of the apical cell membrane, the inhibitors of Ca2+ channels (verapamil, Ni2+, Mn2+, Co2+) decreased the effect of ADH. These data indicate that Ca2+ applied onto the outer surface of apical plasma membrane plays an important role in the action of ADH.     

Water extrustion in the trap bladders ofUtricularia vulgaris

In the trap bladder ofUtricularia vulgaris, increase in sucrose concentrations in bladder lumen fluid decreased resetting rate. Addition of 350 mM sucrose to lumen fluid stopped the resetting. Therefore, water seems to move down the water potential gradient between the lumen and the arm cells of bifid trichomes, which are the site of inlet in the water pathway. Application of dinitrophenol, sodium azide, KCN, monoiodoacetic acid or pentachlorophenol in lumen fluid much reduced the water outflow. Temperature coefficient of bladder resettings was about 2. No effect of darkness on resetting rate was found. These facts show that the resetting requires energy supplied from respiration and there exists an active ion transport mechanism somewhere in the water pathway. No effect on the resetting was seen upon immersing the bladder in 700 mM surcose solution. In the capital cells of the pavement epithelium in its outer and middle zones, which are the site of outlet in water pathway, membrance potential and resistance were lower than those in other cells. These facts indicate that bulk flow of the cell sap from the capital cells to the outside takes place by intracellular hydrostatic pressure.     

Phase transitions in films of lung surfactant at the air-water interface.

Pulmonary surfactant maintains a putative surface-active film at the air-alveolar fluid interface and prevents lung collapse at low volumes. Porcine lung surfactant extracts (LSE) were studied in spread and adsorbed films at 23 +/- 1 degrees C using epifluorescence microscopy combined with surface balance techniques. By incorporating small amounts of fluorescent probe 1-palmitoyl-2-nitrobenzoxadiazole dodecanoyl phosphatidylcholine (NBD-PC) in LSE films the expanded (fluid) to condensed (gel-like) phase transition was studied under different compression rates and ionic conditions. Films spread from solvent and adsorbed from vesicles both showed condensed (probe-excluding) domains dispersed in a background of expanded (probe-including) phase, and the appearance of the films was similar at similar surface pressure. In quasistatically compressed LSE films the appearance of condensed domains occurred at a surface pressure (pi) of 13 mN/m. Such domains increased in size and amounts as pi was increased to 35 mN/m, and their amounts appeared to decrease to 4% upon further compression to 45 mN/m. Above pi of 45 mN/m the LSE films had the appearance of filamentous materials of finely divided dark and light regions, and such features persisted up to a pi near 68 mN/m. Some of the condensed domains had typical kidney bean shapes, and their distribution was similar to those seen previously in films of dipalmitoylphosphatidylcholine (DPPC), the major component of surfactant. Rapid cyclic compression and expansion of LSE films resulted in features that indicated a possible small (5%) loss of fluid components from such films or an increase in condensation efficiency over 10 cycles. Calcium (5 mM) in the subphase of LSE films altered the domain distribution, decreasing the size and increasing the number and total amount of condensed phase domains. Calcium also caused an increase in the value of pi at which the maximum amount of independent condensed phase domains were observed to 45 mN/m. It also induced formation of large amounts of novel, nearly circular domains containing probe above pi of 50 mN/m, these domains being different in appearance than any seen at lower pressures with calcium or higher pressures in the absence of calcium. Surfactant protein-A (SP-A) adsorbed from the subphase onto solvent-spread LSE films, and aggregated condensed domains in presence of calcium. This study indicates that spread or adsorbed lung surfactant films can undergo expanded to condensed, and possibly other, phase transitions at the air-water interface as lateral packing density increases. These phase transitions are affected by divalent cations and SP-A in the subphase, and possibly by loss of material from the surface upon cyclic compression and expansion.     

Phosphorus loss from land to water: integrating agricultural and environmental management

Phosphorus (P), an essential nutrient for crop and animal production, can accelerate freshwater eutrophication, now one of the most ubiquitous forms of water quality impairment in the developed world. Repeated outbreaks of harmful algal blooms (e.g., Cyanobacteria and Pfiesteria) have increased society's awareness of eutrophication, and the need for solutions. Agriculture is regarded as an important source of P in the environment. Specifically, the concentration of specialized farming systems has led to a transfer of P from areas of grain production to animal production. This has created regional surpluses in P inputs (mineral fertilizer and feed) over outputs (crop and animal produce), built up soil P in excess of crop needs, and increased the loss of P from land to water. Recent research has shown that this loss of P in both surface runoff and subsurface flow originates primarily from small areas within watersheds during a few storms. These areas occur where high soil P, or P application in mineral fertilizer or manure, coincide with high runoff or erosion potential. We argue that the overall goal of efforts to reduce P loss to water should involve balancing P inputs and outputs at farm and watershed levels by optimizing animal feed rations and land application of P as mineral fertilizer and manure. Also, conservation practices should be targeted to relatively small but critical watershed areas for P export.     

Time-lapse Fluorescence Imaging of Arabidopsis Root Growth with Rapid Manipulation of The Root Environment Using The RootChip

The root functions as the physical anchor of the plant and is the organ responsible for uptake of water and mineral nutrients such as nitrogen, phosphorus, sulfate and trace elements that plants acquire from the soil. If we want to develop sustainable approaches to producing high crop yield, we need to better understand how the root develops, takes up a wide spectrum of nutrients, and interacts with symbiotic and pathogenic organisms. To accomplish these goals, we need to be able to explore roots in microscopic detail over time periods ranging from minutes to days.We developed the RootChip, a polydimethylsiloxane (PDMS)- based microfluidic device, which allows us to grow and image roots from Arabidopsis seedlings while avoiding any physical stress to roots during preparation for imaging¹ (Figure 1). The device contains a bifurcated channel structure featuring micromechanical valves to guide the fluid flow from solution inlets to each of the eight observation chambers². This perfusion system allows the root microenvironment to be controlled and modified with precision and speed. The volume of the chambers is approximately 400 nl, thus requiring only minimal amounts of test solution.Here we provide a detailed protocol for studying root biology on the RootChip using imaging-based approaches with real time resolution. Roots can be analyzed over several days using time lapse microscopy. Roots can be perfused with nutrient solutions or inhibitors, and up to eight seedlings can be analyzed in parallel. This system has the potential for a wide range of applications, including analysis of root growth in the presence or absence of chemicals, fluorescence-based analysis of gene expression, and the analysis of biosensors, e.g. FRET nanosensors³.