Osmoregulatory Ability Research Articles

The Physiological Mechanism of Exogenous Melatonin on Improving Seed Germination and the Seedling Growth of Red Clover (Trifolium pretense L.) under Salt Stress.

Salt stress can affect various physiological processes in plants, ultimately hindering their growth and development. Melatonin (MT) can effectively resist multiple abiotic stresses, improving plant stress resistance. To analyze the mechanism of exogenous MT to enhance salt tolerance in red clover, we conducted a comprehensive study to examine the influence of exogenous MT on various parameters, including seed germination indices, seedling morphological traits, and physiological and photosynthetic indicators, using four distinct red clover varieties (H1, H2, H3, and H4). This investigation was performed under various salt stress conditions with differing pH values, specifically utilizing NaCl, Na2SO4, NaHCO3, and Na2CO3 as the salt stressors. The results showed that MT solution immersion significantly improved the germination indicators of red clover seeds under salt stress. The foliar spraying of 50 μM and 25 μM MT solution significantly increased SOD activity (21-127%), POD activity, soluble sugar content, proline content (22-117%), chlorophyll content (2-66%), and the net photosynthetic rate. It reduced the MDA content (14-55%) and intercellular CO2 concentration of red clover seedlings under salt stress. Gray correlation analysis and the Mantel test further verified that MT is a key factor in enhancing seed germination and seedling growth of red clover under salt stress; the most significant improvement was observed for NaHCO3 stress. MT is demonstrated to improve the salt tolerance of red clover through a variety of mechanisms, including an increase in antioxidant enzyme activity, osmoregulation ability, and cell membrane stability. Additionally, it improves photosynthetic efficiency and plant architecture, promoting energy production, growth, and optimal resource allocation. These mechanisms function synergistically, enabling red clover to sustain normal growth and development under salt stress.

Investigating the effects of pelagic trawling on the welfare of Atlantic herring (Clupea harengus)

The effects of pelagic trawling on the health and welfare of Atlantic herring (Clupea harengus L.) were investigated on a refrigerated seawater vessel operating in the North Sea. A total of 495 Atlantic herring (Clupea harengus L.) were sampled during five hauls from two fishing trips in September 2021 and 2022. For assessments of consciousness and mortality, a Reflex Action Mortality Predictor test (i.e. RAMP-test) was used on herring collected following trawling and pumping. Inspections for external and internal damage or wounds were performed via morphological welfare indicators and analyses of photos and radiographs. In addition, blood samples were taken and analysed for haematological indicators of stress. Following trawling and pumping, only 5% of the investigated herring showed signs of external wounds associated with the morphological indicators of welfare, and no internal damage was observed in the radiographic inspections. However, 96% of the assessed herring scored 0 on all three reflexes included in the RAMP-test and were therefore judged dead. On average, herring lost 95% of their scales, while 95% of herring had a very high degree of ruptured red blood cells (i.e. haemolysis). Extensive scale loss results in a deterioration of the skin's protective barrier function, which in turn impairs the osmoregulatory capacity of the herring. This was evident by elevated levels of plasma osmolality and circulating chloride concentrations, which could also likely explain the high occurrence of haemolysis in captured herring. Extended trawling time and larger catch size proved to be two important factors to consider, as the former led to increased plasma levels of osmolality, whereas the latter was associated with elevated plasma levels of lactate and cortisol. In conclusion, the high mortality appears to be influenced by a combination of factors such as severe stress, loss of osmoregulatory ability, crowding density within the trawl, and extended trawling times. This study provides important information on the welfare of wild Atlantic herring caught using pelagic trawls and highlights areas where improvements can be made to safeguard the welfare of fish captured in pelagic fisheries in the future.

Osmoregulation in Alligatoroidea: shifting the paradigm untethers biogeographic questions

ABSTRACT A pervasive maxim in herpetology is that alligators (Alligatoridae) are poor salinity regulators relative to their taxonomic kin, crocodiles (Crocodylidae), evidenced by the purported lack of osmoregulatory abilities of modern Alligator and caimans, which has led to the assumption that freshwater obligation is synapomorphic across the clade, to include extinct members of Alligatoridae, or even Alligatoroidea. Presented here is a brief review of osmoregulation and the fossil record of alligatoroids and a suggestion that salt-tolerance may have been more widespread in the group than is widely assumed, based upon the observations that 1) modern alligatorids are increasingly reported from brackish and marine environs and possess osmoregulatory abilities attained through different regulatory pathways than their crocodile counterparts, and 2) fossil members of the group are routinely (or exclusively) found in or near marine depositional settings, suggesting plausibility that earlier members of the clade were more ocean-going than their extant descendants. Starting with fewer assumptions about the osmoregulatory abilities of extinct taxa may help solve continuing problems in eusuchian biogeography, namely, the dispersals of alligatoroids into Europe and Asia, and multiple dispersal events to and from pre-Interchange South America. Secondary loss of salinity tolerance in Alligator may be adaptive in continental habitats.

Effect of Cold Plasma on the Germination and Seedling Growth of Durum Wheat Genotypes

Cold atmospheric pressure plasma (CAP) has attracted increased interest in recent years for possible biomedical, environmental and agricultural applications. A wide range of cold plasma treatment effects is observed in agricultural applications, like effects on the seed germination and seedling growth, but more systematic investigations are needed. The aim of this study was to identify the most appropriate combinations of the plasma source and duration of treatment positively affecting seed germination. In addition, the effect of cold plasma on the seedling growth and osmotic stress tolerance was studied. The seeds of three Bulgarian durum wheat cultivars were treated with cold plasma in twelve variants. The results obtained were processed statistically via two-way ANOVA. The treatment of seeds with a plasma torch for 20 s and the treatment with underwater diaphragm discharge for 5 min when the seeds were placed in both cameras in two different positions (relative to the electrodes between which the plasma is supplied, “+” and “−”) have the greatest positive effect on the all traits related to germination. The analysis of variance reveals that the variation in germination energy, shoot length and root length after the cold plasma treatment of seeds is mainly due to the interaction between the genotype and treatment variant and to a small degree due to the genotype. The treatment of seeds with cold plasma improves the osmoregulation ability of cells and therefore increases the drought resistance of genotypes.

Clonal integration of stress signal induces morphological and physiological response of root within clonal network.

Clonal integration of defense or stress signal induced systemic resistance in leaf of interconnected ramets. However, similar effects of stress signal in root are poorly understood within clonal network. Clonal fragments of Centella asiaticas with first-young, second-mature, third-old and fourth-oldest ramets were used to investigate transportation or sharing of stress signal among interconnected ramets suffering from low water availability. Compared with control, oxidative stress in root of the first-young, second-mature and third-old ramets was significantly alleviated by exogenous ABA application to the fourth-oldest ramets as well as enhancement of antioxidant enzyme (SOD, POD, CAT and APX) activities and osmoregulation ability. Surface area and volume in root of the first-young ramets were significantly increased and total length in root of the third-old ramets was significantly decreased. POD activity in root of the fourth-oldest and third-old ramets was significantly enhanced by exogenous ABA application to the first-young ramets. Meanwhile, total length and surface area in root of the fourth-oldest and third-old ramets were significantly decreased. Ratio of belowground to aboveground biomass in the whole clonal fragments was significantly increased by exogenous ABA application to the fourth-oldest or first-young ramets. It is suggested that transportation or sharing of stress signal may induce systemic resistance in root of interconnected ramets. Specially, transportation or sharing of stress signal against phloem flow was observed in the experiment. Possible explanation is that rapid recovery of foliar photosynthesis in first-young ramets subjected to exogenous ABA application can partially reverse phloem flow within clonal network. Thus, our experiment provides insight into ecological implication on clonal integration of stress signal.

Salinity change evokes stress and immune responses in Atlantic salmon with microalgae showing limited potential for dietary mitigation.

Smoltification was found to impact both immune and stress responses of farmed Atlantic salmon (Salmo salar), but little is known about how salinity change affects salmon months after completed smoltification. Here, we examined (1) the effect of salinity change from brackish water to seawater on the stress and immune responses in Atlantic salmon and (2) evaluated if functional diets enriched with microalgae can mitigate stress- and immune-related changes. Groups of Atlantic salmon were fed for 8weeks with different microalgae-enriched diets in brackish water and were then transferred into seawater. Samples of the head kidney, gill, liver and plasma were taken before seawater transfer (SWT), 20h after SWT, and 2weeks after SWT for gene-expression analysis, plasma biochemistry and protein quantification. The salmon showed full osmoregulatory ability upon transfer to seawater reflected by high nkaα1b levels in the gill and tight plasma ion regulation. In the gill, one-third of 44 investigated genes were reduced at either 20h or 2weeks in seawater, including genes involved in cytokine signaling (il1b) and antiviral defense (isg15, rsad2, ifit5). In contrast, an acute response after 20h in SW was apparent in the head kidney reflected by increased plasma stress indicators and induced expression of genes involved in acute-phase response (drtp1), antimicrobial defense (camp) and stress response (hspa5). However, after 2weeks in seawater, the expression of antiviral genes (isg15, rsad2, znfx1) was reduced in the head kidney. Few genes (camp, clra, c1ql2) in the gill were downregulated by a diet with 8% inclusion of Athrospira platensis. The results of the present study indicate that salinity change months after smoltification evokes molecular stress- and immune responses in Atlantic salmon. However, microalgae-enriched functional diets seem to have only limited potential to mitigate the related changes.

Salinity tolerance in Clarias gariepinus (Burchell, 1822): insight on blood parameter variations and gill histological changes.

This study was designed to evaluate the tolerance of Clarias gariepinus juveniles to a gradual and abrupt increase in salinity over time. To this effect, C. gariepinus juveniles were exposed to three salinity incremental protocols namely 1g L-1day-1, 5g L-1day-1, and 10g L-1day-1. Changes in the hematological parameters and the gill histology of fish were analyzed to determine the impact of osmotic stress on the health status of the fish and its osmoregulatory ability. The result obtained showed that juveniles of C. gariepinus can tolerate salinity stress up to 14g L-1. At 15g L-1 and beyond, all samples died regardless of gradual (i.e., 1g L-1day-1 administered for 15days) or abrupt salinity exposure (i.e., 5g L-1day-1 administered for three days and 10g L-1day-1 administered for two days). Interestingly, more than 90% of the fish survived a direct 10g L-1 exposure for 24h without prior acclimation. The hematological parameters accessed in the fish exposed to 10g L-1 (either gradually or abruptly) showed a significant increase in the white blood cells and a decrease in the red blood cells, packed cell volume, hemoglobin concentration, and all derived blood parameters. The results of the serum biochemistry show a lower total protein and albumin in the salinity-treated fish compared to the control group. However, the serum glucose and the plasma electrolytes (i.e., K+, Na+, and Cl-) were higher in the former group than in the latter. Aside from the stress response expressed in the blood parameters, severe gill degenerations were seen in the histological micrograph obtained for the salinity-treated fish, while the control had a near-normal gill architecture. It was concluded that C. gariepinus could tolerate salinity exposure of 10g L-1day-1 (administered gradually or abruptly) and below without killing the fish within 24h.

Heterogeneous saline water irrigation improves stomatal and nonstomatal restrictions to decrease yield reduction threshold in cherry tomato

Research on the response of tomato to homogeneous and heterogeneous salinity is essential for facility agriculture development in saline land. In this study, cherry tomatoes were irrigated with homogeneous or heterogeneous saline water in root zones by double root grafting. With irrigated fresh water (0/0) as a control, two homogeneous saline water irrigation treatments (S/S: 50/50, 100/100 mmol·L−1 NaCl) and two heterogeneous saline water irrigation treatments (0/S: 0/100, 0/200 mmol·L−1 NaCl) were used to analyze cherry tomato growth, photosynthesis, and osmoregulation under homogeneous and heterogeneous saline water irrigation. The results showed that the yields for the heterogeneous irrigation treatments with 0/100 and 0/200 mmol·L−1 NaCl were 1.2 and 3.1 times greater than those for the homogeneous treatments with 50/50 and 100/100 mmol·L−1 NaCl, respectively. The inhibitory effects of salinity on cherry tomato aboveground growth and stomatal restriction were alleviated by heterogeneous irrigation, which promoted photosynthesis and maintained a stable total root content compared with homogeneous salinity. In addition, the Na+ and Cl− contents in leaves under heterogeneous salinity were significantly reduced and high K+ and K+/Na+ levels as well as strong osmoregulation ability were maintained. In conclusion, the growth of and physiological damage to cherry tomato caused by salinity and the yield reduction threshold significantly improved under heterogeneous salinity. This could provide a theoretical basis for the adaptive cultivation of cherry tomato in saline land. We believe heterogeneous saline water irrigation, an irrigation technique for declining yield reduction thresholds in cherry tomato by improving stomatal and non-stomatal limitations, which could be consider to apply to tomato production in salt-affected land.

A key evolutionary step determining osmoregulatory ability for freshwater colonisation in early life stage of fish.

Colonisation of freshwater habitats by marine animals is a remarkable evolutionary event that has enriched biodiversity in freshwater ecosystems. The acquisition of the tolerance to hypotonic stress during the early life stages is presumed to be essential for their successful freshwater colonisation, but very little empirical evidence has been obtained to support this idea. This study aimed to comprehend the evolutionary changes of osmoregulatory mechanisms that enhance the larval freshwater tolerance in amphidromous fishes, which typically spend their larval period in marine (ancestral) habitats and the rest of life history stages in freshwater (derived) habitats. We compared the life history patterns and changes in larval survivorship and gene expression depending on salinity among three congeneric marine-originated amphidromous goby species (Gymnogobius), which had been suggested to differ in their larval dependence on freshwater habitats. An otolith microchemical analysis and laboratory-rearing experiment confirmed the presence of freshwater residents only in G. urotaenia and higher larval survivorship of this species in the freshwater condition than the obligate amphidromous G. petschiliensis and G. opperiens. Larval whole-body transcriptome analysis revealed that G. urotaenia from both amphidromous and freshwater-resident populations exhibited the greatest differences in expression levels of several osmoregulatory genes, including aqp3, which is critical for water discharge from their body during early fish development. The present results consistently support the importance of enhanced freshwater tolerance and osmoregulatory plasticity in larval fish to establish freshwater forms, and further identified key candidate genes for larval freshwater adaptation and colonisation in the goby group.

The osmotic stress of Vallisneria natans (Lour.) Hara leaves originating from the disruption of calcium and potassium homeostasis caused by MC-LR

Aquatic plants are potentially impacted by microcystins (MCs) in lakes experiencing harmful algal blooms. However, how these plants respond, and possibly adapt to osmotic stress caused by MCs is unclear. Vallisneria natans is a pioneer taxon with a global distribution in eutrophic lakes. In this study, we investigated the effect of MC-LR on morphological structure, water retention, osmoregulatory ability, and homeostasis of calcium (Ca2+) and potassium (K+) ions in V. natans leaves. Results showed that the morphological changes caused by MC-LR included increased volumes of epidermal and mesophyll cells, changes in their lignification level, and the degradation of chloroplast structure and dissolution of starch granules. The increased moisture content and water potential with MC-LR concentration were consistent with the occurrence of osmotic stress, and the decreased osmotic potential implied the activation of osmoregulation. Soluble sugar and free amino acid concentrations increased at MC-LR treatments ≥10 μg/L, while inorganic ion K+ content increased in all MC-LR treatments. Although instantaneous K+inflow and Ca2+outflow occurred at 10 μg/L and 100 μg/L MC-LR, respectively, ≥1 μg/L MC-LR resulted in continuous K+ inflow and Ca2+ outflow within 24 h. Moreover, plasma membrane hyperpolarization was caused by MC-LR, especially at 1 and 10 μg/L. We suggest that Ca2+ efflux served as a signal molecule from the cytoplasmic matrix via Ca2+-ATPase, and the uptake of K+ was activated passively through transporters in response to MC-LR-induced plasma membrane hyperpolarization. Therefore, the uptake of K+ was a part of the response but not an adaptation to MC-LR stress, and is considered the cause for the uptake of water in leaves. Ca2+ and K+ homeostasis of V. natans leaves was disrupted by MC-LR concentrations as low as 1 μg/L, suggesting that aquatic plants in most eutrophic lakes may experience negative impacts such as Ca2+ loss, impacts to cell water balance, and alteration in cellular morphology, due to osmotic stress caused by MC-LR.

Salinity effects on expression and localization of aquaporin 3 in gills of the euryhaline milkfish (Chanos chanos).

Milkfish (Chanos chanos) are important euryhaline fish in Southeast Asian countries that can tolerate a wide range of salinity changes. Previous studies have revealed that milkfish have strong ion regulation and survival abilities under osmotic stress. In addition to ion regulation, water homeostasis in euryhaline teleosts is important during environmental salinity shifts. Aquaporins (AQP) are vital water channels in fish, and different AQPs can transport water influx or outflux from the body. AQP3 is one of the AQP channels, and the function of AQP3 in the gills of euryhaline milkfish is still unknown. The aim of this study was to investigate the expression and localization of AQP3 in the gills of euryhaline milkfish to contribute to our understanding of the physiological role and localization of AQP3 in fish. The AQP3 sequence was found in the milkfish next-generation sequencing (NGS) database and is mainly distributed in the gills of freshwater (FW)-acclimated milkfish. Under hypoosmotic and hyperosmotic stress, the osmolality of milkfish immediately shifted, similar to the aqp3 gene expression. Moreover, the abundance of AQP3 protein significantly decreased 3 h after transferring milkfish from FW to seawater (SW). However, there was no change within 7 days when the milkfish experienced hypoosmotic stress. Moreover, double immunofluorescence staining of milkfish gills showed that AQP3 colocalized with Na+ /K+ ATPase at the basolateral membrane of ionocytes. These results combined indicate that milkfish have a strong osmoregulation ability under acute osmotic stress because of the quick shift in the gene and protein expression of AQP3 in their gills.

Integrative transcriptomic and metabolomic analysis reveals the effects of a sudden drop in salinity on osmoregulation, metabolism, anti-oxidation, and immunity in Eriocheir sinensis megalopa and juvenile stages

Eriocheir sinensis has a special habit of migrating from marine to freshwater during its larval developmental stage. Salinity is an important environmental factor affecting the survival rate and growth performance of its larvae. Currently, the molecular mechanisms involved in the adaptation of E. sinensis larvae to a hyposaline environment remain unclear. Therefore, in this study, we designed an acute hyposaline stress experiment and sequenced the transcriptome and metabolome of the treated samples. After screening and annotation, 3323 and 2874 differentially expressed genes and 273 and 334 differentially expressed metabolites were identified by analysis of the transcriptomic data and metabolomic data at the megalopa and juvenile stages, respectively. Subsequently, a combined analysis of pathways was performed by co-mapping differentially expressed genes and differentially expressed metabolites into a KEGG database. Furthermore, the analysis results showed that 92 and 115 shared KEGG pathways were identified at the megalopa and juvenile stages, respectively. These shared pathways were mainly related to energy metabolism, osmotic pressure regulation, antioxidants, and immunity. The results showed that megalopa and juvenile had similar response mechanisms for adjusting to extremely hyposaline environments. The sudden drop in salinity may have impaired the osmoregulation ability and disturbed the energy metabolism of E. sinensis larvae. The glucose and TCA cycle processes were inhibited, and the cholesterol and glycine metabolisms were significantly changed. In addition, the sudden drop in salinity may cause oxidative stress in the larvae, accelerate the synthesis and consumption of glutathione, damage mitochondrial function, and induce cell apoptosis. Therefore, this study provides key information for understanding hyposaline tolerance mechanisms in E. sinensis larvae.

Metabolomic Analysis of the Response of Haloxylon ammodendron and Haloxylon persicum to Drought.

Haloxylon ammodendron and Haloxylon persicum, as typical desert plants in arid areas, show strong drought tolerance and environmental adaptability and are therefore ideal model plants for studying the molecular mechanisms of drought tolerance. A metabolomic analysis of H. ammodendron and H. persicum in their natural environment is lacking, and their metabolic response to drought therefore remains unclear. To elucidate the response of H. ammodendron and H. persicum to drought at the metabolic level, a non-targeted metabolomics analysis was carried out herein. Under a dry environment, H. ammodendron exhibited 296 and 252 differentially expressed metabolites (DEMs) in the positive and negative ion modes, respectively, whereas 452 and 354 DEMs were identified in the positive and negative ion modes in H. persicum, respectively. The results indicated that H. ammodendron responds to drought by increasing the content of organic nitrogen compounds and lignans, neolignans, and related compounds, and reducing the content of alkaloids and derivatives. By contrast, H. persicum adapts to the dry environment by increasing the content of organic acids and their derivatives and reducing the content of lignans, neolignans, and related compounds. In addition, H. ammodendron and H. persicum improved their osmoregulation ability, reactive oxygen species detoxification ability, and cell membrane stability by regulating the key metabolic pathways and anabolism of associated metabolites. This is the first metabolomics report on the response of H. ammodendron and H. persicum to drought in their natural environment, providing a foundation for the further study of their regulatory mechanisms under drought stress.

Is salt the solution? Interactions between trace-metal uptake and salinity in the freshwater crabPotamonautes warreniCalman, 1918 (Decapoda: Brachyura: Potamonautidae)

AbstractCrustaceans inhabiting freshwater are more vulnerable to increased loading with dissolved trace metals than those from more saline conditions for both physicochemical and physiological reasons. Potamonautes warreni (Calman, 1918) is a true freshwater crab inhabiting rivers in proximity to mining activities in South Africa. In order to assess whether the uptake of zinc (Zn2+) and cadmium (Cd2+) were associated with Na+- and Ca2+-uptake routes, individuals of P. warreni were acclimated to different Na+ or Ca2+ concentrations before measuring trace-metal uptake into the haemolymph and tissues in an intermediate freshwater. Cd2+ uptake into the haemolymph was elevated following acclimation to ‘Na+ replete’ conditions, when compared with ‘Na+ deplete’ conditions, indicating that a physiological response to the acclimation salinity had influenced Cd2+ uptake. Zn2+ uptake by the whole body was elevated in P. warreni individuals from the ‘Na+ replete’ group when compared with crabs acclimated to Na+ free water. A general change in permeability may have occurred and indeed, the apparent water permeability (water efflux) of P. warreni was increased in elevated Na+ and Ca2+ concentrations compared with that in softer water. A comparison of the osmoregulatory ability between P. warreni and the catadromous crab Eriocheir sinensisH. Milne Edwards, 1853 highlighted the greater permeability of the latter. Lower Zn2+ and Cd2+ uptake rates were measured in P. warreni in comparison to those measured in E. sinensis by other authors, indicating that the more well adapted a species is to life in freshwater, the less susceptible they will be to metal uptake. Future investigations to understand further the mechanisms influencing Zn2+ and Cd2+ uptake are required to understand the role that salinity can play in protecting a species from trace-metals released into the environment.

Does the loss of diadromy imply the loss of salinity tolerance? A gene expression study with replicate nondiadromous populations of Galaxias maculatus.

The recurrent colonization of freshwater habitats and subsequent loss of diadromy is a major ecological transition that has been reported in many ancestrally diadromous fishes. Such residency is often accompanied by a loss of tolerance to seawater. The amphidromous Galaxias maculatus has repeatedly colonized freshwater streams with evidence that freshwater-resident populations exhibit stark differences in their tolerance to higher salinities. Here, we used transcriptomics to gain insight into the mechanisms contributing to reduced tolerance to higher salinities in freshwater resident populations. We conducted an acute salinity challenge (0ppt to 23-25 ppt) and measured osmoregulatory ability (muscle water content) over 48 h in three populations: diadromous, saltwater intolerant resident (Toltén), and saltwater tolerant resident (Valdivia). RNA sequencing of the gills identified genes that were differentially expressed in association with the salinity change and associated with the loss of saltwater tolerance in the Toltén population. Key genes associated with saltwater acclimation were characterized in diadromous G. maculatus individuals, some of which were also expressed in the saltwater tolerant resident population (Valdivia). We found that some of these "saltwater acclimation" genes, including the cystic fibrosis transmembrane conductance regulator gene (CFTR), were not significantly upregulated in the saltwater intolerant resident population (Toltén), suggesting a potential mechanism for the loss of tolerance to higher salinities. As the suite of differentially expressed genes in the diadromous-resident comparison differed between freshwater populations, we hypothesize that diadromy loss results in unique evolutionary trajectories due to drift, so the loss of diadromy does not necessarily lead to a loss in upper salinity tolerance.

Effects of low salinity stress on osmoregulation and gill transcriptome in different populations of mud crab Scylla paramamosain

Animals living in estuaries suffer from rapid and continuous salinity fluctuations, while the global warming and extreme precipitation aggravate this situation. Osmoregulation is important for estuarine animals adapt to salinity fluctuations. The present study investigated the effects of low salinity stress on osmoregulation and gill transcriptome in two populations of mud crab from Hangzhou Bay and Zhangzhou Bay of China, respectively. Crabs were transferred from salinity 25 ppt to 5 ppt for 96 h. Edematous swelling in gill filaments was caused by low salinity stress and was more serious in Zhangzhou Bay population. Gill Na+/K+-ATPase activity increased (p < 0.01) in both populations under the low salinity stress and was significantly higher (p < 0.01) in Hangzhou Bay population than in Zhangzhou Bay population. According to transcriptome analysis, there were 191 genes differentially expressed under the low salinity stress in gill tissue of both populations. Several ion transport and energy metabolism related pathways, as well as the arginine and proline metabolism pathway, were enriched by these genes. On the other hand, 272 genes were identified to differentially express between two populations under the low salinity stress, but not under the control salinity. The enrichment analysis showed that these genes were mainly related to ion transport, energy metabolism, osmolytes metabolism and methyltransferase activity. In conclusion, the present study suggested that mud crab exploited a combination of extracellular anisosmotic regulation and intracellular isosmotic regulation for osmoregulation under the low salinity stress. Hangzhou Bay population showed a greater osmoregulatory capacity, which is probably due to the enhanced ion transport, energy supply, and osmolytes regulation. Meanwhile, epigenetic modification might also contribute to an inherent osmoregulation ability for Hangzhou Bay population to response to salinity fluctuation rapidly.

A crucial role in osmoregulation against hyperosmotic stress: Carbohydrate and inositol metabolism in Nile tilapia (Oreochromis niloticus)

The purpose of this study was to explore the relationship between inositol metabolism and carbohydrate metabolism in Nile tilapia (Oreochromis niloticus) under acute hyperosmotic stress. 50 mg/mL glucose solution and PBS was injected to the fish of experimental group and the control group, respectively. The fish were then transferred to 16 psu brackish water for hyperosmotic stress immediately, and sampled at 0, 1, 3, 6, 12, 24, and 48 h post stress. The hyperosmotic stress significantly increased the osmotic pressure, glucose content of serum, the process of glycolysis and gluconeogenesis in the liver of fish in both groups over time. The expression of genes involved in myo-inositol (MI) synthesis and transport was all induced by hypertonicity in gill, kidney and liver of fish in both groups. The injection of glucose solution significantly decreased MI synthesis in gill, kidney and liver, and relieved the apoptosis of liver under acute hyperosmotic stress. However, glucose injection significantly increased Na+K+-ATPase activity in the gill, as well as serum osmotic pressure, and the decomposition of carbohydrate, indicating that additional glucose promoted osmoregulation ability of fish. The results of this research suggested that during the hyperosmotic stress, the injection of exogenous glucose could not only provide energy that required for osmoregulation, but also participate in the osmoregulation by acting as an osmolyte itself.

The Benefit of Optimal Dietary Lipid Level for Black Seabream Acanthopagrus schlegelii Juveniles under Low-Salinity Environment.

The present study was aimed at evaluating the regulatory effects of dietary lipid levels on growth performance, osmoregulation, fatty acid composition, lipid metabolism, and physiological response in Acanthopagrus schlegelii under low salinity (5 psu). An 8-week feeding trial was conducted in juvenile A. schlegelii with an initial weight of 2.27 ± 0.05 g, and six isonitrogenous experimental diets were formulated with graded levels of lipid: 68.7 g/kg (D1), 111.7 g/kg (D2), 143.5 g/kg (D3), 188.9 g/kg (D4), 239.3 g/kg (D5), and 269.4 g/kg (D6), respectively. Results indicated that fish fed with diet containing 188.9 g/kg lipid significantly improved growth performance. Dietary D4 improved ion reabsorption and osmoregulation by increasing the concentrations of Na+, K+, and cortisol in serum and activities of Na+/K+-ATPase as well as expression levels of osmoregulation related to gene expression levels in the gill and intestine. The expression levels of long chain polyunsaturated fatty acid biosynthesis-related genes were dramatically upregulated when dietary lipid levels increased from 68.7 g/kg to 189.9 g/kg with levels of docosahexaenoic (DHA), eicosapentaenoic (EPA), and DHA/EPA ratio being highest in the D4 group. When fish fed dietary lipid levels from 68.7 g/kg to 188.9 g/kg, lipid homeostasis could be maintained by upregulating sirt1 and pparα expression levels, whereas lipid accumulation was observed in dietary lipid levels of 239.3 g/kg and over. Fish fed with high dietary lipid levels resulted in physiological stress related to oxidative stress and endoplasmic reticulum stress. In conclusion, based on weight gain, the optimal dietary lipid requirement of juvenile A. schlegelii reared at low-salinity water is 196.0 g/kg. These findings indicate that the optimal dietary lipid level can improve growth performance, n-3 LC-PUFA accumulation, and osmoregulatory ability and maintain lipid homeostasis and normal physiological functions of juvenile A. schlegelii.

Dietary phosphatidylcholine improved the survival, growth performance, antioxidant, and osmoregulation ability of early juvenile mud crab Scylla paramamosain

A 60-day culture experiment was designed to investigate the effect of dietary phosphatidylcholine/soybean lecithin (PC/SL) levels on survival, growth, body composition, antioxidant, and osmoregulation ability of early juvenile mud crab Scylla paramamosain. Six isonitrogenous and isolipidic experimental diets were formulated with five graded PC levels (0.1% (PC0.1), 0.5% (PC0.5), 1.0% (PC1.0), 2.0% (PC2.0), and 4.0% (PC4.0)) and one SL level (2.0%, SL2.0) to fed early juvenile S. paramamosain (8.70 ± 0.19 mg/crab). The results showed a significantly low survival in the PC0.1 group. Mud crabs obtained the highest growth performance in the PC2.0 and SL2.0 groups, but there was no significant difference with crabs in the PC0.5, PC1.0, and PC4.0 groups. The expression of the target of rapamycin (tor) gene was positively correlated with growth performance. The crab's whole-body crude lipid, triglyceride (TG), and total cholesterol (T-CHO) content rose significantly with increasing dietary PC levels. At the same time, the crab whole-body long-chain polyunsaturated fatty acids (lc-PUFA) proportion increased significantly, accompanied by a decrease in the proportion of C18:2n6. The expression of fatty acid synthesis-related genes decreased significantly with the increase in dietary PC levels. Dietary PC levels ≥1% significantly increased the antioxidant capacity of the mud crabs. Crabs obtained the highest total antioxidant capacity (T-AOC) and superoxide dismutase (SOD) activities in the PC1.0 group; the catalase (CAT) activity was positively correlated with dietary PC levels; significantly lower malondialdehyde (MDA) content was found when dietary PC ≥ 1%. Na+/K+-ATPase (NKA) activity increased with increasing dietary PC levels, and the expression of Na+/K+/2Cl−-cotransporter (nkcc) and nka genes were also significantly elevated. The results of the salinity challenge showed that the crabs obtained the highest survival in the PC4.0 group. In summary, the second-order polynomial regression analysis of weight gain and specific growth rate showed that early juvenile S. paramamosain obtained the highest growth at a dietary PC level of 2.60–2.62%.

Biodesalination performance of Phormidium keutzingianum concentrated using two methods (immobilization and centrifugation)

The biodesalination performance of the cyanophycean Phormidium keutzingianum concentrated using two methods (centrifugation and immobilization) was evaluated for the first time at NaCl concentrations of 10, 30, 50, and 70 g/L. In addition, the osmoregulation ability of P. keutzingianum was assessed at high salinities (50, 70, 85, and 100 g/L) over a relatively short time period. The pH, electrical conductivity, and chloride, nitrate, and phycocyanin concentrations were measured during all experiments. The immobilization method of concentration resulted in a chloride removal rate of up to 44 % during the osmoregulation experiment at a salinity of 100 g/L. For the centrifugation method, the chloride removal rate was 26 % on the 20th day of observation for 10 g/L. Thus, the immobilization method resulted in faster chloride ion removal than the centrifugation method. The findings demonstrate that biodesalination efficiency can be enhanced by the use of different P. keutzingianum preparation methods.