Osmoregulation

An open reading frame encoding the ectoine biosynthesis genes was cloned from the Bacillus halodurans genome. An expression plasmid containing the operon was introduced into Escherichia coli cells, and the recombinant ectoine was quantified. The secondary structure of ectoine biosynthesis proteins were predicted and was quite similar to that of reported proteins from eubacteria.

In planta RNAi (i.e. plants engineered to synthesize active RNAi molecules) has great potential as a strategy to control insect crop pests. This study investigated the impact of RNAi against osmoregulatory genes expressed in the gut of two phloem-feeding species, the green peach aphid Myzus persicae and the potato/tomato psyllid Bactericera cockerelli. The target genes comprising candidate gut sucrase, aquaporin and sugar transporter genes were identified by mining insect genomic and transcriptomic datasets for genes orthologous to empirically-tested osmoregulatory genes of the pea aphid Acyrthosiphon pisum. Insects feeding on plants with RNAi against the target genes exhibited elevated hemolymph osmotic pressure (a predicted effect of perturbed osmotic function) and some reduction in performance, especially offspring production in M. persicae and mortality in B. cockerelli, associated with up to 50% reduction in mean expression of the target genes. The effects were particularly pro...

The dynamic changes in mRNA expression levels for vasotocin (AVT) and isotocin (IT) receptor gene levels were assessed in a time-course response study in immature male specimens of the gilthead sea bream (Sparus aurata) submitted to hyper-(55‰ salinity) and hypo-osmotic (5‰ salinity) challenges. Two different cDNAs for the AVT receptor and one for the IT receptor (V1a2-type and V2-type AVTR, and ITR, respectively) were cloned by screening an S. aurata brain cDNA library. Genes for these receptors were expressed differentially and is nearly ubiquitously in 26 of the examined tissues. In the gills, both environmental salinity challenges up-regulated AVTR V1a2-type gene expression concomitantly with mRNA expression protein activity of Na + , K + -ATPase gene expression and protein, whereas the AVTR V2-type and cystic fibrosis transmembrane conductance regulator (CFTR) mRNA levels were associated with mRNAs environmental salinity, indicating a possible connection between AVTRs and these transporters. In kidney, AVTR V1a2-type gene expression peaked rapidly and lasted only a short time (12-24 h) in response to both osmotic challenges. In contrast, AVTR V2-type mRNA levels were enhanced in specimens exposed to hyperosmotic conditions, whereas they decreased under hypoosmotic environments, suggesting an antidiuretic role related to the vasoconstriction function. In the hypothalamus, only the expression of the AVTR V2-type gene was enhanced at 7 and 14 days under both experimental conditions. In the liver, both AVTRs had increased mRNA levels, with the upregulation of their AVTR V2-type gene increasing faster than the V1a2-type. The ITR gene was not sensitive to variations of external salinity in any of the analyzed tissues. Our results demonstrate the involvement of the vasotocinergic, but not the isotocinergic, pathway as well as the hypothalamic function, in the adjustments of both osmoregulatory and metabolic processes after osmotic challenges.

This research was conducted to determine the effect of salicylic acid on the drought tolerance of three pistachio (Pistacia vera L.) rootstocks. The treatments were included three irrigation levels (Control: 100 % ETc, medium stress: 65% ETc, and severe stress: 30% ETc), three pistachio rootstocks, and three salicylic acid concentrations (0, 1, and 3 mM). The salicylic acid solution was once applied as a foliar spray, starting water stress, and irrigation treatments continued for 75 days. Results showed that P. vera ‘Badami Zarand’ was less affected by water stress treatments than the other seedling rootstocks. Among the rootstocks studied, the highest photosynthesis rate (6.55 µmol CO2 m-2 s-1) was obtained in P. vera ‘Badami Zarand’ under severe water stress (30 % ETc) and 1 mM salicylic acid application. The lowest photosynthesis rate (2.75 µmol CO2 m-2 s-1) was observed in P. vera ‘Sarakhs’ under severe water stress (30 % ETc) and 3 mM salicylic acid treatment. In addition, the highest relative water content (66.16%) and the lowest ion leakage (33.29%) were obtained in ‘Badami Zarand.’ The 1 mM salicylic acid application effectively reduced the negative effects of water stress. According to the results, P. vera ‘Badami Zarand’ showed a better response to salicylic acid under stress conditions, and the highest photosynthesis, relative leaf water content, dry weight of organs (leaves, shoots, roots), and the lowest ion leakage under drought stress belonged to this rootstock.

termination of accurate extinction coeflicients and simultaneous equations for assaying chlorophylls a and b extracted with four different solvents: verification of the concentration of chlorophyll standards by atomic absorption spectroscopy,

The article discusses advances in osmoregulation and excretion with emphasis on how multicellular animals in different osmotic environments regulate their milieu intérieur. Mechanisms of energy transformations in animal osmoregulation are dealt with in biophysical terms with respect to water and ion exchange across biological membranes and coupling of ion and water fluxes across epithelia. The discussion of functions is based on a comparative approach analyzing mechanisms that have evolved in different taxonomic groups at biochemical, cellular and tissue levels and their integration in maintaining whole body water and ion homeostasis. The focus is on recent studies of adaptations and newly discovered mechanisms of acclimatization during transitions of animals between different osmotic environments. Special attention is paid to hypotheses about the diversity of cellular organization of osmoregulatory and excretory organs such as glomerular kidneys, antennal glands, Malpighian tubules and insect gut, gills, integument and intestine, with accounts on experimental approaches and methods applied in the studies. It is demonstrated how knowledge in these areas of comparative physiology has expanded considerably during the last two decades, bridging seminal classical works with studies based on new approaches at all levels of anatomical and functional organization. A number of as yet partially unanswered questions are emphasized, some of which are about how water and solute exchange mechanisms at lower levels are integrated for regulating whole body extracellular water volume and ion homeostasis of animals in their natural habitats. C 2014 American Physiological Society.

Kidney function and the role of the cloacal complex in osmoregulation was investigated in estuarine crocodile (Crocodylus porosus) exposed to three environmental salinities: hypo-, iso-and hyperosmotic to the plasma. Plasma homeostasis was maintained over the range of salinities. Antidiuresis occurred with increased salinity. Although urine from the kidneys retained an osmotic pressure between 77% and 82% of the plasma, over 93% and 98% of plasma chloride filtered at the glomeruli was reabsorbed during passage through the kidneys under hypo-and hyperosmotic conditions, respectively, and only 64% in iso-osmotic water. The kidneys were the primary site of sodium reabsorption under hypo-and hyperosmotic conditions. Secondary processing of urine during storage in the cloaca varied with salinity. During post-renal storage of urine, the difference in urine osmotic pressure increased from Ϫ26.1 Ϯ 15.5 to 35.66 Ϯ 9.29 mOsM with increased salinity, and potassium concentration of urine increased over 3-fold in C. porosus from freshwater. The almost complete reabsorption of both sodium and chloride under hyperosmotic conditions indicates the necessity for secretory activity by the lingual salt glands. The osmoregulatory response of the kidneys and cloacal complex to environmental salinity is both plastic and complementary. comp biochem physiol 119A;3:825-831, 1998.

Dehydration (10 days at 27°C) of the Namib tenebrionid Stenocara gracilipes resulted in a rapid weight loss (17.5%), and a substantial decline in haemolymph volume (72%). Although the lipid content decreased significantly, metabolic water production was insufficient to maintain total body water (TBW). Rehydration (no food) resulted in increases in haemolymph volume, body weight (sub-normal), and TBW to normality. Haemolymph osmolality, sodium, potassium, chloride, amino acids, and sugars (trehalose and glucose), were all subject to osmoregulatory control during both dehydration and rehydration. Major osmolar effectors in this species are sodium, chloride, and amino acids, with most of the contribution to regulation of haemolymph osmolality coming from changes in the levels of these constituents. Changes in amino acid levels are not the result of interchange with soluble protein during dehydration (the possibility exists during extended rehydration, however). Despite faecal losses of sodium being low (8.2% of that removed from the haemolymph during dehydration), sodium concentrations do not return to normal during rehydration. Chloride concentrations increase supra-normally when access to water is allowed, and remain elevated throughout the rehydration period. Although faecal loss of potassium greatly exceeded the amount removed from the haemolymph (by approximately 1.8 times), haemolymph potassium levels were strongly regulated during rehydration. S. gracilipes demonstrates an exquisite capacity to regulate haemolymph osmolality under conditions of both acute water-shortage and -abundance. Together with an efficient water economy (drinking when fog-water is available, and a superb water conservation mechanism in the form of wax-bloom production), this must serve to contribute to long-term survival of this species in an otherwise harsh abode. 

The article discusses advances in osmoregulation and excretion with emphasis on how multicellular animals in different osmotic environments regulate their milieu intérieur. Mechanisms of energy transformations in animal osmoregulation are dealt with in biophysical terms with respect to water and ion exchange across biological membranes and coupling of ion and water fluxes across epithelia. The discussion of functions is based on a comparative approach analyzing mechanisms that have evolved in different taxonomic groups at biochemical, cellular and tissue levels and their integration in maintaining whole body water and ion homeostasis. The focus is on recent studies of adaptations and newly discovered mechanisms of acclimatization during transitions of animals between different osmotic environments. Special attention is paid to hypotheses about the diversity of cellular organization of osmoregulatory and excretory organs such as glomerular kidneys, antennal glands, Malpighian tubules and insect gut, gills, integument and intestine, with accounts on experimental approaches and methods applied in the studies. It is demonstrated how knowledge in these areas of comparative physiology has expanded considerably during the last two decades, bridging seminal classical works with studies based on new approaches at all levels of anatomical and functional organization. A number of as yet partially unanswered questions are emphasized, some of which are about how water and solute exchange mechanisms at lower levels are integrated for regulating whole body extracellular water volume and ion homeostasis of animals in their natural habitats. C 2014 American Physiological Society.

Hewan dalam rangka memenuhi kebutuhannya akan energy (ATP) menyelenggarakan berbagai reaksi metabolisme, akan tetapi tidak hanya menghasilkan ATP dan zat-zat yang bermanfaat lainnya melainkan juga menghasilkan zat sisa, yang tidak digunakan lagi didalam tubuh, dan harus dikeluarkan melalui sistem yang disebut dengan sistem ekskresi atau sistem pengeluaran untuk menjaga konsep homeostatis dalam tubuh.

The gastrointestinal tracts (GIT) of fish and other vertebrates are challenged with a diversity of functional demands caused by changes and differences in dietary inputs and environmental conditions. This contribution reviews how hormonal regulation plays an essential role in modulating the GIT functions of fish to match changes in functional demands. Exemplary is how hormones produced by the GIT, the associated organs (e.g., pancreas), and other sources (e.g., hypothalamus, adrenal cortex, thyroid, gonads) modulate the digestive processes (motility, secretion, and nutrient absorption) in response to dietary inputs. Hormones regulate the other GIT functions of osmoregulation (secretion and absorption of electrolytes and water), immunity, endocrine secretions, metabolism, and the elimination of toxic metabolites and environmental contaminants to match changes in environmental conditions and physiological states. Although the regulatory molecules and associated signaling pathways have been conserved during evolution of the vertebrate GIT, the specific responses often vary among fish with different feeding habits and from different environments, and can differ from those described for mammals. D

Etude génétique et génomique de la réponse à un changement de salinité chez la truite arc-en-ciel Oncorhynchus mykiss Thèse soutenue à Rennes le 17 décembre 2010 devant le jury composé de : Etude génétique et génomique de la réponse à un changement de salinité chez la truite arc-en-ciel Oncorhynchus mykiss Thèse soutenue à Rennes le 17 décembre 2010 devant le jury composé de :

Adaptations of animals to the xeric environment have been studied in various taxonomic groups and across several deserts. Despite the impressive data that have been accumulated, the focus in most of these studies is mainly on the significance of one variable at a time. Here, we attempt to integrate between responses of several physiological systems, challenged by increasing diet and water salinity and extreme temperatures, acquired in different studies of thermo and osmo-regulatory adaptations, of small rodents, to the xeric environment. Studies have shown differential thermoregulatory responses to increased dietary salinity, which were attributed to habitat and habits of the relevant species. In the thermoregulatory studies, a potential adaptive significance of low metabolic rate was demonstrated. From an evolutionary point of view, the most important adaptation is in the timing of reproduction, as it enables the transfer of genetic properties to the next generation in an unpredictable ecosystem, where reproduction might not occur every year. Results in this aspect show that increased dietary salinity, through an increase in vasopressin plasma levels, plays an important role as a regulator of the reproductive system. We assume that the amount of food existing in the habitat and the amount of reserves in the animal in the form of white adipose tissue are important for reproduction. Photoperiod affects all studied physiological responses, emphasizing the importance of pre-acclimation to seasonal characteristics. We summarize the existing data and suggest neuro-endocrine pathways, which have a central role in these adaptations by affecting thermoregulation, osmoregulation and reproduction to create the optimal response to xeric conditions. These hypotheses can be used as the basis for future studies.

Salicornia europaea and Suaeda maritima plants were exposed to salinity stress, and leaf water status, solute concentrations in the cell sap, plant growth, and levels of betaine aldehyde dehydrogenase (BADH) mRNA were measured. Salicornia europaea was able to maintain a higher tugor and relative water content at low leaf water potentials which was associated with a greater capacity for osmotic adjustment. The major osmotica in Salicornia europaea leaves was Na + and glycine betaine and these solutes were increased by salinity. A similar tendency for the Na + and glycine betaine concentration was observed in Suaeda maritima leaves but at lower concentrations Suaeda maritima plants accumulated higher levels of proline in their leaves under salt stress than Salicornia europaea. Betaine aldehyde dehydrogenase gene expression (BADH mRNA) in Salicornia europaea and Suaeda maritima leaves increased with salt stress and the expression pattern coincided with the observed betaine accumulation.

Na/K-ATPase activity and osmo-ionic regulation were examined in Litopenaeus vannamei exposed to low salinities. The hemolymph osmolality of shrimp exposed to very low salinities (0.5 ppt and 1 ppt) decreased rapidly after 6 h from 800 mOsm to 540-560 mOsm; these individuals could not survive beyond 1 day. Under exposure to 7 ppt, osmolality levels decreased rapidly to 630 and 570 mOsm after 6 h and 1 day respectively, whereas in shrimp exposed to 18 ppt, levels declined slowly from 800 mOsm to 700 mOsm after 6 h and thereafter remained stable for 7 days until the end of the experiment. Hemolymph sodium ion levels showed a pattern of change similar to that of hemolymph osmolality, with initial levels being 380 mmol/L and decreasing to 180 mmol/L under very low salinity. Changes in calcium, potassium, and magnesium ion concentrations were also investigated. Na/K-ATPase activity was 3.98 μmol ADP/mg protein/ hour in the gills of control individuals maintained at 28 ppt for the experimental duration. Levels increased in individuals exposed to 18 ppt, 7 ppt and 3 ppt for 7 days to 5.06, 6.51, and 5.81 μmol ADP/mg protein/hour, respectively. Based on the above, it is suggested that L. vannamei could not survive in low salinity (b 1 ppt) due to the loss of osmoregulatory capacity when the shrimps were transferred directly from high salinities to low salinities.

Daphnia exilis is a halophylic species that was recently found in Chile, distant from its natural range. In this study, we analyze the osmoregulatory and life-history responses to salinity exhibited by Daphnia exilis, as a first step towards understanding the ecology of this exotic species whose invasion potential has been related to its ability to tolerate saline environments. A set of laboratory experiments were carried out, in which we exposed organisms to a salinity gradient, and measured internal and environmental osmolality, assessed the effect of acclimation time and measured life-history traits that were used to perform a demographic retrospective analysis. Our results showed that (i) D. exilis exhibited a hyper-osmoconformer response, (ii) acclimation time did not exert effects on the osmoregulatory response, (iii) salinity up to 6 g L 21 did not alter the population growth rate, (iv) at 8 g L 21 population growth rate declined, mainly due to a delayed age at maturity and reduced fertility. Based on this information, we suggest that the responses to salinity exhibited by the exotic D. exilis confer an advantage over its natural enemies and may facilitate colonization through exploiting disturbed places as chemical refuges.

Red pigment-concentrating hormone (RPCH) is a member of the AKH/RPCH peptide family present mainly in crustaceans and insects. Insect AKH is responsible for metabolic functions whereas RPCH plays a major role in the aggregation of red chromatophores in crustaceans. In this study, a full-length cDNA of RPCH of the black tiger shrimp, Penaeus monodon (PmRPCH) was cloned by Rapid Amplification of cDNA Ends strategies from the eyestalk RNA. A 770 bp full-length PmRPCH cDNA harbored 279 bp of an open reading frame encoding a signal peptide of 21 amino acid residues, an 8 amino acid mature RPCH peptide, followed by 61 amino acid residues of a RPCH precursor-related peptide. The highest levels of PmRPCH mRNA expression were detected in eyestalks while lower expression was found in other nervous tissues i.e. brain, thoracic ganglia and abdominal nerve cord. Expression of PmRPCH was transiently stimulated upon hypersalinity change within 12 h suggesting its osmoregulatory function. During th...

We review digestion and osmoregulation in the avian gut, with an emphasis on the ways these different functions might interact to support or constrain each other and the ways they support the functioning of the whole animal in its natural environment. Differences between birds and other vertebrates are highlighted because these differences may make birds excellent models for study and may suggest interesting directions for future research. At a given body size birds, compared with mammals, tend to eat more food but have less small intestine and retain food in their gastrointestinal tract (GIT) for shorter periods of time, despite generally higher mass-specific energy demands. On most foods, however, they are not less efficient at digestion, which begs the question how they compensate. Intestinal tissue-specific rates of enzymatic breakdown of substrates and rates of active transport do not appear higher in birds than in mammals, nor is there a demonstrated difference in the extent to which those rates can be modulated during acclimation to different feeding regimes (e.g. diet, relative intake level). One compensation appears to be more extensive reliance on passive nutrient absorption by the paracellular pathway, because the avian species studied so far exceed the mammalian species by a factor of at least two-to threefold in this regard. Undigested residues reach the hindgut, but there is little evidence that most wild birds recover microbial metabolites of nutritional significance (essential amino acids and vitamins) by reingestion of faeces, in contrast to many hindgut fermenting mammals and possibly poultry. In birds, there is some evidence for hindgut capacity to breakdown either microbial protein or protein that escapes the small intestine intact, freeing up essential amino acids, and there is considerable evidence for an amino acid absorptive capacity in the hindgut of both avian and mammalian hindgut fermenters. Birds, unlike mammals, do not excrete hyperosmotic urine (i.e. more than five times plasma osmotic concentration). Urine is mixed with digesta rather than directly eliminated, and so the avian gut plays a relatively more important role in water and salt regulation than in mammals. Responses to dehydration and high-and low-salt loads are reviewed. Intestinal absorption of ingested water is modulated to help achieve water balance in one species studied (a nectar-feeding sunbird), the first demonstration of this in any terrestrial vertebrate. In many wild avian species the size and digestive capacity of the GIT is increased or decreased by as much as 50% in response to nutritional challenges such as hyperphagia, food restriction or fasting. The coincident impacts of these changes on osmoregulatory or immune function of the gut are poorly understood.

The aim of the paper was to determine nitrogen compounds contributing to leaf cell osmoregulation of spinach ( Spinacia oleracea ) submitted to increasing salt stress. • Sodium, free amino acids and glycine betaine contents were determined in the last fully expanded leaf of plants stressed by daily irrigation with saline water (0.17 M NaCl).

Cell solute potential and cytoplasmic viscosity in four lines of wheat (Triticum aestivum L.) and two cultivars of barley (Hordeum vulgare L.) differing in their relative salt resistance were investigated. Seedlings were grown in X-strength Hoagland solution with and without 100 mM NaCI (219 mOsm; for Hor· deum, additionally isosmolal polyethylene glycol 10,000). Solute potential ('Ir,) and cytoplasmic viscosity of leaf sheath subepidermal cells (Triticum) and solute potential of coleoptile subepidermal cells (Hor· deum) were measured by the plasmolytic method and by centrifugation, respectively. NaCI decreased 'Ir, in all lines and cultivars tested and more so in Hordeum than in Triticum. In salt resistant seedlings the difference in 'Ir, between cells from control and salt treated plants was smaller than in salt sensitive seedlings but always exceeded the lowering of 'Ir, of the growth medium by NaC!. For PEG treatment the 'Ir, decrease corresponded to the decrease of 'Ir, in the solution (osmotic adjustment). Salt resistant lines had a high cytoplasmic viscosity that increased under NaCI stress. In salt sensitive lines viscosity was low and decreased further with NaCI addition. The results confirm that the deleterious effect of salinity is not attributable to osmitic stress alone and that the cytoplasm itself is significantly different for salt resistant and salt sensitive cultivars.

The intestine is one of the major osmoregulatory organs in fish. During the salmon parr -smolt transformation, the intestine must change its functions from the freshwater (FW) role of preventing water inflow, to the seawater (SW) role of actively absorbing ions and water.

In this study we investigated the effects of the high endogenous proline level on water relations, gas exchange and antioxidant enzymatic activity in leaves of transgenic ‘Swingle’ citrumelo rootstocks transformed with the P5CSF129A gene coding for the key-enzyme for proline synthesis, under water deficit. Leaf total water, osmotic and pressure potentials, stomatal conductance, photosynthetic rates and xylem sap flow were evaluated in non-transformed control and transgenic plants during water deficit treatment. Malondialdehyde (MDA) content, catalase (CAT; EC 1.11.1.6), superoxide dismutase (SOD; EC 1.15.1.1) and ascorbate peroxidase (APX; EC 1.11.1.11) activities were quantified in leaves collected based on their total water potential, representing the following conditions: irrigated (Ψw = −1.3 MPa), moderate stress (Ψw = −2.3 to −2.5 MPa), severe stress (Ψw = −3.8 to −3.9 MPa) and recovery (24 h after re-irrigation: Ψw = −1.3 to −1.9 MPa). Osmotic adjustment was observed in transgenic plants until 11 days after withholding water, while pressure potential in non-transformed controls was close to zero after nine days of water deprivation. This superior maintenance of turgor pressure in leaves of transgenic plants led to higher stomatal conductance, photosynthetic and transpiration rates when compared to non-transgenic plants. Drought caused a significant decrease in APX and SOD activities in control plants, followed by an increase after re-watering. On the other hand, CAT was more active in control than in transgenic plants under irrigated condition and both stress levels. Our results suggest that transgenic plants were able to cope with water deficit better than non-transformed controls since the high endogenous proline level acted not only by mediating osmotic adjustment, but also by contributing to gas exchange parameters and ameliorating deleterious effects of drought-induced oxidative stress.► We report the effects of high endogenous proline on water relations, gas exchange and antioxidant enzymes in transgenic citrumelo under water deficit. ► Citrumelo plants over-expressing the P5CSF129A gene accumulated high levels of proline in the leaves. ► Transgenic plants presented higher stomatal conductance, photosynthetic and transpiration rates under water deficit. ► High proline levels increased drought tolerance by osmotic adjustment and protection against oxidative stress. ► APX, SOD and CAT activities in citrumelo leaves were modulated by high endogenous proline levels.

Hepatocyte transmembrane potential (V in) behaves as an osmometer and varies with changes in extrace|lular osmotic pressure created by altering the NaCI concentration in the external medimn (Howard, L.D. and Wondergem, R. (1987) J. Membr. Biol. 100, 53). We now have demonstrated similar effects on V m by increasing external osmolality with added sucrose and not altering ionic strength. We also have demonstrated that hyperosmotic stress-induced depolarization of V m results from changes in membrane K + conductance, gK, rather than from changes in the K ~ equilibrium potential. V m and a~ of hepatocytes in liver slices were measured by conventional and ion.sensitive microelectrodes, respectively. Cell water vols. were estimated by differences in wet and dry weights of liver slices after 10-rain incubations. Effect of hyperosmotic medium on membrane transference number for K +, t K, was measured by effects on V,, of step.changes ih external [K +]. Hepatocyte V m decreased 34, 52 and 54% when tissue was superfused with medium made hyperosmotic with added sucrose (50, 100 and 150 raM). Correspondingly, a I increased 10, 18 and 29% with this hyperosmotic stress of added sucrose. Tissue water of 2.92 + 0.10 kg Hz0 / kg dry weight in control solution decreased to 2.60 _+_ 0.05, 2.25 + 0.06 and 2.22 + 0.05 kg H zO/kg dry weight with additions to medium of 50, 100 and 150 mM sucrose,, respectively. Adding 50 mM sucrose to medium decreased t K from 0.20 + 0.01 to 0.05 + 0.01. Depolarization by 59% with hyperosmotic stress (100 mM sucrose) also occurred in Cl.free medium where C!-was substituted with gluconate. We conclude that hepatocytes shrink during hyperosi increases. The accompanying decrease in V m is opposite to that expected by an increase in motic stress, and the a K a~., and at least in part results from a concomitant decrease in gK" Changes in membrane C!-conductance most likely do not contribute to osmotic stress-induced depolarization, since equivalent decreases in V m occurred with added sucrose in cells depleted of C! -by superfusing tissue with Cl-free medium.

The Asian swamp eel Monopterus albus is normally considered a freshwater species, but can also occasionally be found in brackish water. It is an obligate air-breather with highly reduced gills, making its osmoregulation physiology interesting because the gills normally represent the primary site of osmoregulation in teleosts. Being a popular fish for human consumption, the swamp eel is cultured extensively in freshwater ponds in the Mekong Delta of Vietnam. However, very little is known about its salinity tolerance, which is becoming topical due to the increasing salt-water intrusions into tropical deltas. We therefore studied how increased salinity affects survival, growth, blood pressure, heart rate, blood osmolality and plasma ions. All eels survived prolonged exposure to 5 and 10 g L À1 , although plasma osmolality increased significantly at 10 g L À1 . Further elevation to 15 and 20 g L À1 was associated with significantly elevated mortality, with a corresponding increase in plasma osmolality and ion concentrations. Our results show that swamp eels thrive in 0-10 g L À1 with an optimum growth between 0 and 9 g L À1 , indicating that utilization of low saline brackish waters for aquaculture is possible.

Expression of the proU operon of Escherichia coli is directly proportional to the osmolarity of the growth medium. The basal level of proU transcription is very low, but a large increase is triggered by a sudden rise in the external osmolarity. This increased expression is maintained for as long as the osmotic stimulus persists. We have capitalized upon these regulatory features of the proU operon and have constructed a series of expression vectors (pOSEX) permitting osmotically controlled expression of heterologous genes governed by regulatory signals of proU. The pOSEX vectors carry the proU promoter, an upstream region required for high-level expression, and part of the first structural gene (proI/), which acts as a silencer and is necessary to maintain low-level expression in low osmolarity media. An extended multiple cloning site (MCS) positioned at the 3' end of proV' permits the cloning of heterologous genes into the pOSEX plasmids, and efficient transcription terminators derived from the rrnB operon prevent deleterious readthrough transcription into the vector portion. The properties of the pOSEX expression vectors were tested by positioning a promoterless lacZ (encoding B-galactosidase) gene from E. coli and the g&A (encoding carboxytransferase) gene from the Gram+ bacterium Acidaminococcus fermentans under the control of the proU regulatory region. Efficient, osmoregulated and finely tuned expression of both la& and g&A was achieved, and the amount of B-galactosidase and carboxytransferase synthesized were simply controlled by adjusting the osmolarity of the growth medium with various concentrations of NaCl.

Crustaceans generally act as oxy-regulators, maintaining constant oxygen uptake as oxygen partial pressures decrease, but when a critical low level is reached, ventilation and aerobic metabolism shut down. Caveadapted animals, including crustaceans, often show a reduced metabolic rate possibly owing in part to the hypoxic nature of such environments. However, metabolic rates have not been thoroughly explored in crustaceans from anchialine habitats (coastal ponds and caves), which can experience variable oxygenic regimes. Here, an atypical oxy-conforming pattern of oxygen uptake is reported in the Hawaiian anchialine atyid Halocaridina rubra, along with other unusual metabolic characteristics. Ventilatory rates are near-maximal in normoxia and did not increase appreciably as PO 2 declined, resulting in a decline in VO 2 during progressive hypoxia. Halocaridina rubra maintained in anoxic waters survived for seven days (the duration of the experiment) with no measureable oxygen uptake, suggesting a reliance on anaerobic metabolism. Supporting this, lactate dehydrogenase activity was high, even in normoxia, and oxygen debts were quickly repaid by an unusually extreme increase in oxygen uptake upon exposure to normoxia. In contrast, four related anchialine shrimp species from the Ryukyu Islands, Japan, exhibited physiological properties consistent with previously studied crustaceans. The unusual respiratory patterns found in H. rubra are discussed in the context of a trade-off in gill morphology for osmoregulatory ion transport vs. diffusion of respiratory gasses. Future focus on anchialine species may offer novel insight into the diversity of metabolic responses to hypoxia and other physiological challenges experienced by crustaceans.

Pollen tube cell volume changes rapidly in response to perturbation of the extracellular osmotic potential. This report shows that specific phospholipid signals are differentially stimulated or attenuated during osmotic perturbations. Hypo-osmotic stress induces rapid increases in phosphatidic acid (PA). This response occurs starting at the addition of 25% (v/v) water to the pollen tube cultures and peaks at 100% (v/v) water. Increased levels of PA were detected within 30 s and reached maximum by 15 to 30 min after treatment. The pollen tube apical region undergoes a 46% increase in cell volume after addition of 100% water (v/v), and there is an average 7-fold increase in PA. This PA increase appears to be generated by phospholipase D because concurrent transphosphatidylation of n-butanol results in an average 8-fold increase in phosphatidylbutanol. Hypo-osmotic stress also induces an average 2-fold decrease in phosphatidylinositol phosphate; however, there are no detectable changes...

Aquaporins and aquaglyceroporins mediate the transport of water and solutes across biological membranes. Saccharomyces cerevisiae Fps1 is an aquaglyceroporin that mediates controlled glycerol export during osmoregulation. The transport function of Fps1 is rapidly regulated by osmotic changes in an apparently unique way and distinct regions within the long N-and C-terminal extensions are needed for this regulation. In order to learn more about the mechanisms that control Fps1 we have set up a genetic screen for hyperactive Fps1 and isolated mutations in 14 distinct residues, all facing the inside of the cell. Five of the residues lie within the previously characterized N-terminal regulatory domain and two mutations are located within the approach to the first transmembrane domain. Three mutations cause truncation of the C-terminus, confirming previous studies on the importance of this region for channel control. Furthermore, the novel mutations identify two conserved residues in the channel-forming B-loop as critical for channel control. Structural modelling-based rationalization of the observed mutations supports the notion that the N-terminal regulatory domain and the B-loop could interact in channel control. Our findings provide a framework for further genetic and structural analysis to better understand the mechanism that controls Fps1 function by osmotic changes.

The use and management of suitable bedding material is a crucial part of bird welfare in intensive production systems. Litter cushions the bird from the hard floor, provides insulation and has the capacity to both absorb and facilitate evaporation of faecal, urinary and spilled water. In poultry production, an increase in water excretion rate is commonly referred to as flushing, because urine and faeces are excreted simultaneously through the cloaca, making it difficult to distinguish elevated urine output or polyuria from increased faecal water loss or diarrhoea. In today's intensive production systems even relatively minor nutritionally induced osmoregulatory perturbation can cause flushing. Whilst this increase in water excretion is often initially the result of a physiological diuresis or diarrhoea, nutritionally induced pathological change may aggravate the polyuria by compromising water recovery, or increase the severity of the diarrhoea by causing enteritis. Flushing is commonly the result of a normal physiological response to nutritionally induced water, electrolyte, pH or osmotic imbalance, but sustained imbalance frequently leads to pathological change. Similarly, diets with a high proportion of non starch polysaccharides, animal protein, saturated free fatty acids, anti-nutritional factors or toxins can cause pathological change indirectly, by inducing a detrimental shift in the composition of the intestinal microbiota (dysbacteriosis), or directly, by causing toxic damage. Inflammation of the renal or gastrointestinal lining compromises water and nutrient transfer, which increases the amount of water, mucus and non-digested nutrients in the excreta. Apart from loading the litter with water, the mucus and non-digested lipid in particular, reduce the litter's water buffering capacity and exacerbate the consequences of flushing.

Located in the midline anterior wall of the third cerebral ventricle (i.e. the lamina terminalis), the median preoptic nucleus (MnPO) receives a unique set of afferent neural inputs from fore-, mid-and hindbrain. These afferent connections enable it to receive neural signals related to several important aspects of homeostasis. Included in these afferent projections are (i) neural inputs from two adjacent circumventricular organs, the subfornical organ and organum vasculosum laminae terminalis, that respond to hypertonic-ity, circulating angiotensin II or other humoural factors, (ii) signals from cutaneous warm and cold receptors that are relayed to MnPO, respectively , via different subnuclei in the lateral parabrachial nucleus and (iii) input from the medulla associated with baroreceptor and vagal afferents. These afferent signals reach appropriate neurones within the MnPO that enable relevant neural outputs, both excitatory and inhibitory, to be activated or inhibited. The efferent neural pathways that proceed from the MnPO terminate on (i) neuroendocrine cells in the hypothalamic supraop-tic and paraventricular nuclei to regulate vasopressin release, while poly-synaptic pathways from MnPO to cortical sites may drive thirst and water intake, (ii) thermoregulatory pathways to the dorsomedial hypothalamic nucleus and medullary raph e to regulate shivering, brown adipose tissue and skin vasoconstriction, (iii) parvocellular neurones in the hypothalamic paraventricular nucleus that drive autonomic pathways influencing cardio-vascular function. As well, (iv) other efferent pathways from the MnPO to sites in the ventrolateral pre-optic nucleus, perifornical region of the lateral hypothalamic area and midbrain influence sleep mechanisms.

This experiment was conducted to evaluate the effects of osmo-priming with KNO3 on the germination traits and seedling growth of two Brassica napus L. cultivars under salinity conditions. Seeds of two spring rapeseed ('Heros' and 'Eagle') were primed with KNO3 (-1.0 MPa) for 24 hrs in continuous 30°C. Primed (P) and un-primed (NP) seeds were cultured in medium grade perlite and placed in greenhouse for 40 days. Pots were daily irrigated with nutrient solutions containing different levels of salinity (0.2, 5, 10, 15 and 20 dSm -1 ). Results showed that germination percentage of primed seeds was greater than that of un-primed seeds. Radicle length, seedling height and dry weight and leaf number of plants derived from primed seeds were higher compared with un-primed seeds. Na content of plants derived from primed seeds was higher than that of un-primed ones. In contrast, K content of priming resulted plantlets was comparatively higher compared with un-primed counterpart...

Flatfish (Pleuronectiformes) distribution in the environment is influenced by salinity, and varies among species and with developmental stage. Osmoregulatory ability likely plays an important role in defining species and developmental stage-specific distribution. Although the mechanisms of osmoregulation in adult and juvenile teleosts have been widely addressed, far less is known about their larval osmoregulatory physiology. Much of our current understanding of larval fish ion-regulation stems from studies using flatfishes, and this article reviews advances in this field, primarily from the point of view of the developing flatfishes. Addressed here are the ontogeny of salinity tolerance, the development of several important osmoregulatory tissues (the skin, gut, and gill), and the influence of the endocrine system on osmoregulation during early larval development and metamorphosis.