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Physiologia Plantarum Jun 2021Drought stress, which causes a decline in quality and quantity of crop yields, has become more accentuated these days due to climatic change. Serious measures need to be... (Review)
Review
Drought stress, which causes a decline in quality and quantity of crop yields, has become more accentuated these days due to climatic change. Serious measures need to be taken to increase the tolerance of crop plants to acute drought conditions likely to occur due to global warming. Drought stress causes many physiological and biochemical changes in plants, rendering the maintenance of osmotic adjustment highly crucial. The degree of plant resistance to drought varies with plant species and cultivars, phenological stages of the plant, and the duration of plant exposure to the stress. Osmoregulation in plants under low water potential relies on synthesis and accumulation of osmoprotectants or osmolytes such as soluble proteins, sugars, and sugar alcohols, quaternary ammonium compounds, and amino acids, like proline. This review highlights the role of osmolytes in water-stressed plants and of enzymes entailed in their metabolism. It will be useful, especially for researchers working on the development of drought-resistant crops by using the metabolic-engineering techniques.
Topics: Droughts; Osmoregulation; Osmosis; Proline; Stress, Physiological; Water
PubMed: 33280137
DOI: 10.1111/ppl.13297 -
Acta Anaesthesiologica Scandinavica Sep 2020The Starling Principle states that fluid movements between blood and tissues are determined by differences in hydrostatic and colloid osmotic (oncotic) pressures between... (Review)
Review
The Starling Principle states that fluid movements between blood and tissues are determined by differences in hydrostatic and colloid osmotic (oncotic) pressures between plasma inside microvessels and fluid outside them. The Revised Starling Principle recognizes that, because microvessels are permeable to macromolecules, a balance of pressures cannot halt fluid exchange. In most tissues, steady oncotic pressure differences between plasma and interstitial fluid depend on low levels of steady filtration from plasma to tissues for which the Revised Principle provides the theory. Plasma volume is normally maintained by fluid losses from filtration being matched by fluid gains from lymph. Steady state fluid uptake into plasma only occurs in tissues such as intestinal mucosa and renal peri-tubular capillaries where a protein-free secretion of adjacent epithelia contributes significantly to interstitial fluid volume and keeps interstitial oncotic pressure low. Steady filtration rates in different tissues are disturbed locally by reflex changes in capillary pressure and perfusion. The rapid overall decline in capillary pressure after acute blood loss initiates rapid fluid uptake from tissue to plasma, that is, autotransfusion. Fluid uptake is transient, being rapid at first then attenuating but low levels may continue for more than an hour. The Revised Principle highlights the role of oncotic pressure of small volumes of interstitial fluid within a sub-compartment surrounding the microvessels rather than the tissue's mean interstitial fluid oncotic pressure. This maximizes oncotic pressure differences when capillary pressure are high and enhances initial absorption rates when pressures are low, accelerating short-term regulation of plasma volume.
Topics: Capillary Permeability; Humans; Microvessels; Osmoregulation; Osmotic Pressure; Plasma Volume
PubMed: 32270491
DOI: 10.1111/aas.13603 -
Current Opinion in Plant Biology Oct 2014Plants have adaptive robustness to osmotic stresses such as drought and high salinity. Numerous genes functioning in stress response and tolerance are induced under... (Review)
Review
Plants have adaptive robustness to osmotic stresses such as drought and high salinity. Numerous genes functioning in stress response and tolerance are induced under osmotic conditions in diverse plants. Various signaling proteins, such as transcription factors, protein kinases and phosphatases, play signal transduction roles during plant adaptation to osmotic stress, with involvement ranging from stress signal perception to stress-responsive gene expression. Recent progress has been made in analyzing the complex cascades of gene expression during osmotic stress response, and especially in identifying specificity and crosstalk in abscisic acid (ABA)-dependent and ABA-independent signaling pathways. In this review, we highlight transcriptional regulation of gene expression governed by two key transcription factors: AREB/ABFs and DREB2A operating respectively in ABA-dependent and ABA-independent signaling pathways.
Topics: Abscisic Acid; Arabidopsis; Arabidopsis Proteins; Gene Expression Regulation, Plant; Osmoregulation; Osmotic Pressure; Plant Growth Regulators; Signal Transduction
PubMed: 25104049
DOI: 10.1016/j.pbi.2014.07.009 -
Annual Review of Physiology Feb 2018Bacteria represent one of the most evolutionarily successful groups of organisms to inhabit Earth. Their world is awash with mechanical cues, probably the most ancient... (Review)
Review
Bacteria represent one of the most evolutionarily successful groups of organisms to inhabit Earth. Their world is awash with mechanical cues, probably the most ancient form of which are osmotic forces. As a result, they have developed highly robust mechanosensors in the form of bacterial mechanosensitive (MS) channels. These channels are essential in osmoregulation, and in this setting, provide one of the simplest paradigms for the study of mechanosensory transduction. We explore the past, present, and future of bacterial MS channels, including the alternate mechanosensory roles that they may play in complex microbial communities. Central to all of these functions is their ability to change conformation in response to mechanical stimuli. We discuss their gating according to the force-from-lipids principle and its applicability to eukaryotic MS channels. This includes the new paradigms emerging for bilayer-mediated channel mechanosensitivity and how this molecular detail may provide advances in both industry and medicine.
Topics: Bacteria; Bacterial Proteins; Cell Membrane; Ion Channels; Mechanoreceptors; Mechanotransduction, Cellular; Osmoregulation
PubMed: 29195054
DOI: 10.1146/annurev-physiol-021317-121351 -
Fish Physiology and Biochemistry Jun 2021In most fish exhibiting external fertilization, spermatozoa become motile after release into water, triggered by differences between intracellular and extracellular... (Review)
Review
In most fish exhibiting external fertilization, spermatozoa become motile after release into water, triggered by differences between intracellular and extracellular conditions such as osmotic pressure, ion composition, and pH. The rapid change in osmolarity initiating spermatozoon motility induces osmotic pressure, resulting in active water movement across the cell membrane. Mechanisms of ion and water transport across the plasma membrane and cell volume regulation are important in maintaining structure and functional integrity of the cell. The capacity of the fish spermatozoon plasma membrane to adapt to dramatic environmental changes is an essential prerequisite for motility and successful fertilization. Adaptation to change in external osmolality may be the basis of spermatozoon function and an indicator of sperm quality. The involvement of specific water channels (aquaporins) in cell volume regulation and motility is highly likely. The goal of this review is to describe basic mechanisms of water transport and their role in fish spermatozoon physiology, focusing on osmoresistance, cell volume regulation, motility, and survival.
Topics: Animals; Aquaporins; Cryopreservation; Fishes; Humans; Lipids; Male; Osmoregulation; Semen Preservation; Spermatozoa
PubMed: 34076793
DOI: 10.1007/s10695-021-00958-1 -
Comparative Biochemistry and... Mar 2021In his early career, August Krogh made fundamental discoveries of the properties of cutaneous respiration in fish, frogs and other vertebrates. Following Krogh's... (Review)
Review
In his early career, August Krogh made fundamental discoveries of the properties of cutaneous respiration in fish, frogs and other vertebrates. Following Krogh's example, the study of amphibious fishes provides an excellent model to understand how the skin morphology and physiological mechanisms evolved to meet the dual challenges of aquatic and terrestrial environments. The skin of air-exposed fishes takes on many of the functions that are typically associated with the gills of fish in water: gas exchange, gas sensing, iono- and osmoregulation, and nitrogen excretion. The skin of amphibious fishes has capillaries close to the surface in the epidermis. Skin ionocytes or mitochondrial-rich cells (MRCs) in the epidermis are thought to be responsible for ion exchange, as well as ammonia excretion in the amphibious mangrove rivulus Kryptolebias marmoratus. Ammonia gas (NH) moves down the partial pressure gradient from skin capillaries to the surface through ammonia transporters (e.g., Rhcg) and NH is volatilized from the mucus film on the skin. Future studies are needed on the skin of amphibious fishes from diverse habitats to understand more broadly the role of the skin as a multifunctional organ.
Topics: Animals; Cyprinodontiformes; Ecosystem; Gills; Models, Biological; Nitrogen; Osmoregulation; Respiratory Physiological Phenomena; Skin Physiological Phenomena; Water
PubMed: 33301892
DOI: 10.1016/j.cbpa.2020.110866 -
Annual Review of Microbiology Sep 2019The cytoplasm of bacterial cells is a highly crowded cellular compartment that possesses considerable osmotic potential. As a result, and owing to the semipermeable... (Review)
Review
The cytoplasm of bacterial cells is a highly crowded cellular compartment that possesses considerable osmotic potential. As a result, and owing to the semipermeable nature of the cytoplasmic membrane and the semielastic properties of the cell wall, osmotically driven water influx will generate turgor, a hydrostatic pressure considered critical for growth and viability. Both increases and decreases in the external osmolarity inevitably trigger water fluxes across the cytoplasmic membrane, thus impinging on the degree of cellular hydration, molecular crowding, magnitude of turgor, and cellular integrity. Here, we assess mechanisms that permit the perception of osmotic stress by bacterial cells and provide an overview of the systems that allow them to genetically and physiologically cope with this ubiquitous environmental cue. We highlight recent developments implicating the secondary messenger c-di-AMP in cellular adjustment to osmotic stress and the role of osmotic forces in the life of bacteria-assembled in biofilms.
Topics: Adaptation, Physiological; Bacteria; Environmental Exposure; Osmoregulation; Osmotic Pressure
PubMed: 31180805
DOI: 10.1146/annurev-micro-020518-115504 -
World Journal of Microbiology &... Mar 2015Eukaryotic microorganisms possess mechanisms to detect osmotic variations in their surroundings, from specialized receptors and membrane transporters, to sophisticated... (Review)
Review
Eukaryotic microorganisms possess mechanisms to detect osmotic variations in their surroundings, from specialized receptors and membrane transporters, to sophisticated systems such as two-component histidine kinases. Osmotic stimuli are transduced through conserved phosphorylation cascades that result in a rapid response to mitigate stress. This response allows for the maintenance of an optimal biochemical environment for cell functioning, as well as a suitable recovery in suboptimal environments that would otherwise endanger cell survival. The molecular basis of these responses has been largely studied in yeasts and bacteria. However, fewer studies have been published concerning the molecular basis of osmoregulation in other eukaryotic microorganisms such as protozoans and microalgae. Here, we review the main osmosensors reported in unicellular eukaryotic microorganisms (yeasts, microalgae and protozoa) and the pathways that maintain homeostasis in cells encountering hyperosmotic challenges.
Topics: Eukaryota; Osmoregulation; Osmotic Pressure; Signal Transduction
PubMed: 25638456
DOI: 10.1007/s11274-015-1811-8 -
Physiology (Bethesda, Md.) Jul 2023Reduction of intestinal lumen osmotic pressure by the formation of Ca(Mg)CO, "ichthyocarbonate," is essential for osmoregulation by the only vertebrate group, ray-finned... (Review)
Review
Reduction of intestinal lumen osmotic pressure by the formation of Ca(Mg)CO, "ichthyocarbonate," is essential for osmoregulation by the only vertebrate group, ray-finned fishes, widely capable of hydrating by ingesting seawater. Ichthyocarbonate formation and excretion are under elaborate physiological control and play an important, yet still poorly defined, role in the oceanic carbon cycle.
Topics: Animals; Seawater; Osmoregulation; Water-Electrolyte Balance; Fishes; Vertebrates
PubMed: 36917964
DOI: 10.1152/physiol.00005.2023 -
Comparative Biochemistry and... Mar 2021August Krogh's studies of the frog identified the respiratory function of the skin in 1904 and the osmoregulatory function of the skin in 1937. It is the thesis of my... (Review)
Review
August Krogh's studies of the frog identified the respiratory function of the skin in 1904 and the osmoregulatory function of the skin in 1937. It is the thesis of my review that the osmoregulatory function of the skin has evolved for meeting quite different demands. In freshwater the body fluid homeostasis is challenged by loss of ions to the environment. This is compensated for by active ion uptake energized by the sodium-pump ATPase and the V-type proton pump ATPase. I conclude that Krogh's astonishing observation of cutaneous chloride uptake from μM concentrations of NaCl is compatible with the free energy changes of ATP hydrolysis catalyzed by the sodium‑potassium pump ATPase and the V-type proton pump ATPase operating in series, and in parallel with experimentally verified vanishingly small leak fluxes. On land the frog is challenged by evaporative water loss through the highly water permeable skin, similar to the water permeable conducting airways of terrestrial vertebrates including man. The epithelia serving respiratory gas exchanges are heterocellular and have molecular, structural and functional properties in common. The cutaneous surface liquid of amphibians evolved for protecting the skin epithelium from desiccation like the airway surface liquid of the lung. Published studies of ion transport mechanisms of acinar cells and the two types of epithelial cells, lead to the hypothesis that subepithelial gland secretion, evaporative water loss, and ion reabsorption by the epithelium regulate composition and volume of the cutaneous surface liquid.
Topics: Animals; Anura; Epithelial Cells; Epithelium; Ion Transport; Osmoregulation; Skin Physiological Phenomena; Sodium-Potassium-Exchanging ATPase; Vacuolar Proton-Translocating ATPases; Water-Electrolyte Balance
PubMed: 33326845
DOI: 10.1016/j.cbpa.2020.110869