Properties of Hemoglobin Solutions in Red Cells

The present studies are concerned with a detailed examination of the apparent anomalous osmotic behavior of human red cells. Red cell water has been shown to behave simultaneously as solvent water for nonelectrolytes and nonsolvent water, in part, for electrolytes. The nonsolvent properties are based upon assumptions inherent in the conventional van't Hoff equation. However, calculations according to the van't Hoff equation give osmotic volumes considerably in excess of total cell water when the pH is lowered beyond the isoelectric point for hemoglobin; hence the van't Hoff equation is inapplicable for the measurement of the solvent properties of the red cell. Furthermore, in vitro measurements of osmotic and other properties of 3.7 millimolal solutions of hemoglobin have failed to reveal the presence of any salt exclusion. A new hypothesis has been developed from thermodynamic principles alone, which predicts that, at constant pH, the net charge on the hemoglobin molecule decreases with increased hemoglobin concentration. The existence of such cooperative interaction may be inferred from the effect of pH on the changes in hemoglobin net charge as the spacing between the molecules decreases. The resultant movement of counterions across the cell membrane causes the apparent anomalous osmotic behavior. Quantitative agreement has been found between the anion shift predicted by the equation and that observed in response to osmotic gradients. The proposed mechanism appears to be operative in a variety of tissues and could provide an electrical transducer for osmotic signals.     

Two applications of the thermogram of the alcohol/water binary system with compositions of cryobiological interests

Quantitative analyses of the bound water content in the alcohol aqueous solution and its osmotic behavior should be cryobiologically significant. This paper has presented two applications of the thermogram of the alcohol/water system recorded by differential scanning calorimeter (DSC). Both applications are: (1) generating the quantitative relationship between the bound water content and the solution composition; (2) calculating the osmotic virial coefficients for alcohols. Five alcohols including methanol, ethanol, ethylene glycol, propylene glycol and glycerol are investigated. In the present study, partial binary phase diagrams of these five alcohol solutions are determined in the first place. The bound water contents in these solutions are quantitatively evaluated by three criteria afterwards. In the end, the osmotic virial coefficients for these alcohols are calculated according to the osmotic virial equation. It is turned out that the bound water fraction out of the total water content increases with a rising molality. The ability of the solute to restrict water molecules can be weakened when the solution becomes more concentrated. The results also indicate that propylene glycol should be the strongest “water-blocker” while methanol the weakest one. These findings can deepen our understanding of the cryoprotective properties of the alcohols from the perspectives of their roles in binding free water and promoting the osmotic efflux of cell water.     

Permeation of water through the KcsA K+ channel

Previous studies have reported that the KcsA potassium channel has an osmotic permeability coefficient of 4.8 x 10(-12) cm3/s, giving it a significantly higher osmotic permeability coefficient than that of some membrane channels specialized in water transport. This high osmotic permeability is proposed to occur when the channel is depleted of potassium ions, the presence of which slow down the water permeation process. The atomic structure of the potassium-depleted KcsA channel and the mechanisms of water permeation have not been well characterized so far. Here, all-atom molecular dynamics simulations, in conjunction with an umbrella sampling strategy and a nonequilibrium approach to simulate pressure gradients are employed to illustrate the permeation of water in the absence of ions through the KcsA K+ channel. Equilibrium molecular dynamics simulations (95 ns combined total length) identified a possible structure of the potassium-depleted KcsA channel, and umbrella sampling calculations (160 ns combined total length) revealed that this structure is not permeable by water molecules moving along the channel axis. The simulation of a pressure gradient across the channel (30 ns combined total length) identified an alternative permeation pathway with a computed osmotic permeability of approximately (2.7 +/- 0.9) x 10(-13) cm3/s. Water fluxes along this pathway did not proceed through collective water motions or transitions to vapor state. All of the major results of this study were robust against variations in a wide set of simulation parameters (force field, water model, membrane model, and channel conformation).     

High CO2 levels reduce ethylene production in kiwifruit

We examined the roles of turgor potential and osmotic adjustment in plant growth by comparing the growth of spring wheat ( Triticum aestivum cv. Siete cerrors) and sudangrass ( Sorghum vulgare var. Piper) seedlings in response to soil water and temperature stresses. The rates of leaf area expansion, leaf water potential and osmotic potential were measured at combinations of 5 soil water potentials ranging from −0.03 to −0.25 MPa and 6 soil temperatures ranging from 14 to 36°C. Spring wheat exhibited little osmotic adjustment while sudangrass exhibited a high degree of osmotic adjustment. However, the rate of leaf area growth for sudangrass was more sensitive to water stress than that of spring wheat. These results were used to evaluate the relationship between growth and turgor potential. The modified Arrhenius equation based on thermodynamic considerations of the growth process was evaluated. This equation obtains growth rate as a function of activation energy, enthalpy difference between active and inactive states of enzymes, base growth rate and optimum temperature. Analyses indicate that the modified Arrhenius equation is consistent with the Lockhart equation with a metabolically controlled cell wall extensibility.     

Apparent activation volumes of hydrophobic ions and carriers in planar lipid bilayers

Summary The role of large amounts of membrane-bound water in regulating various functions of the membrane is not clear at present. We have investigated the effect of perturbing the interfacial water structure on the osmotic shrinkage properties, such as water permeability and extent of shrinkage of egg lecithin liposomes. Water structure was perturbed by a series of reagents which have been earlier reported to affect phase transition of dipalmitoyl phosphatidylcholine liposomes by perturbing interfacial water structure. Anomalous variations of osmotic shrinkage properties with concentration of structure maker and breaker reagents have been interpreted to arise from concentration-dependent structural transitions of the ordered water at the membrane-aqueous interface. Various modes of interaction of these reagents on interfacial structured water have been suggested. Influence of molecular size and functional groups on the molecule in actions of some structure makers and breakers were also observed.     

Differences in the way potassium chloride and sucrose solutions effect osmotic potential of significance to stomata aperture modulation

Guard cell solution osmotic potential changes resulting in the opening and closing of stomata apertures follow an initial influx of potassium ions, their substitution with sucrose molecules and the subsequent reduction of the latter. To provide an insight into the osmotic mechanism of the changes, the new equation for calculating osmotic pressure, which equates the difference between the energy of pure water across a semi-permeable membrane interface with that of solution water, was used to compare the osmotic properties of KCl and sucrose. For sucrose solutions, the effect of the sucrose molecules in increasing the spacing of the solution water was mainly responsible for osmotic potential; this contrasted with K⁺ + Cl^? ions where their spacing effect was only a little higher to that of water held to those ions. At solute concentrations giving an osmotic potential level of ?3.0 MPa near that of turgid guard cells, the spacing effect on the potential of the unattached solution water molecules caused by sucrose, but in its theoretical absence, was estimated as ?2.203 MPa compared with ?1.431 MPa for KCl. In contrast, the potential attributed to water molecules firmly held to the K⁺ + Cl^? ions was ?1.212 MPa versus zero for sucrose. The potential to keep the sucrose molecules in solution was ?0.797 MPa compared with ?0.357 MPa for KCl. The findings illustrate that the way KCl effects osmotic pressure is very different to that of sucrose. It is concluded that stomata aperture modulation is closely linked to the osmotic properties of its guard cell solution solutes.     

Osmotic adjustment inSorghum bicolor (L. Moench) grown under moisture stress in soil and osmotically modified solution cultures

Sorghum (Sorghum bicolor L. Moench) plants were grown in solution culture and stressed at three rates of decreasing leaf water potential (−0.123, −0.068 and −0.029 MPa day⁻¹) achieved by the incremental addition of an osmoticum, polyethylene glycol (PEG) 6000 to the solutions. Plants were also grown in soil and given different amounts of water which resulted in rates of decreasing leaf water potentials of −0.130 and −0.073 MPa day⁻¹. The rate of stress and the culture system influenced the accumulation of solutes in the cell, but not cell volume. A rapid stress (−0.123 and −0.130 MPa day⁻¹) to approximately −1.6 MPa leaf water potential resulted in 0.75 and 0.16 MPa of osmotic adjustment in the PEG and soil culture respectively. At moderate stress (−0.068 and −0.073 MPa day⁻¹) respective values were 1.68 and 0.58 MPa. There were some visual symptoms in the solution grown plants characteristic of uptake of high molecular weight PEG. However the relative growth rates of these plants were equal to or greater than those of the soil grown plants. In view of the differences in plant water status of soil and PEG solution cultured plants it was concluded that the use of the latter system would not be entirely suitable for some studies of drought resistance in sorghum, as related to crop performance in the field.     

Osmotic Biosensors. How to Use a Characean Internode for Measuring the Alcohol Content of Beer

Isolated internodes of Chara corallina and Nitella flexilis have been used to determine the concentration of one passively permeating solute in the presence of non-permeating solutes. The technique was based on the fact that the shape of the peaks of the biphasic responses of cell turgor (as measured in a conventional way using the cell pressure probe) depended on the concentration and composition of the solution and on the permeability and reflection coefficients of the solutes. Peak sizes were proportional to the concentration of the permeating solute applied to the cell. Thus, using the selective properties of the cell membrane as the sensing element and changes of turgor pressure as the physical signal, plant cells have been used as a new type of biosensor based on osmotic principles. Upon applying osmotic solutions, the responses of cell turgor (P) exactly followed the P(t) curves predicted from the theory based on the linear force/flow relations of irreversible thermodynamics. The complete agreement between theory and experiment was demonstrated by comparing measured curves with those obtained by either numerically solving the differential equations for volume (water) and solute flow or by using an explicit solution of the equations. The explicit solution neglected the solvent drag which was shown to be negligible to a very good approximation. Different kinds of local beers (regular and de-alcoholized) were used as test solutions to apply the system for measuring concentrations of ethanol. The results showed a very good agreement between alcohol concentrations measured by the sensor technique and those obtained from conventional techniques (enzymatic determination using alcohol dehydrogenase or from measurement of the density and refraction index of beer). However, with beer as the test solution, the characean internodes did show irreversible changes of the transport properties of the membranes leading to a shift in the responses when cells were treated for longer than 1 h with diluted beer. The accuracy and sensitivity of the osmotic biosensor technique as well as its possible applications are discussed.     

Accumulation of an apoplastic solute in the guard-cell wall is sufficient to exert a significant effect on transpiration in Vicia faba leaflets

Accumulation of recently photosynthesized sucrose in the guard‐cell wall is the empirical foundation for a hypothesis that links the rates of photosynthesis, translocation, and transpiration (Plant Physiology 114, 109–118). Critical assumptions of this hypothesis were tested by use of Vicia faba, an apoplastic phloem loader. Following measurements of the leaflet‐apoplastic‐water volume (by P–V isotherm analysis) and the guard‐cell wall volume (by 3‐D analysis), intact leaflets were fed dilute solutions of mannitol, an impermeant non‐toxic osmolyte. Even at bulk‐leaflet mannitol concentrations that would have only a negligible osmotic effect on stomata, transpiration at constant temperature, water‐vapour pressure, air movement and irradiance was diminished up to 25%, compared with controls. This effect on transpiration, a manifestation of smaller stomatal aperture size, was explained by accumulation of mannitol, up to 350 mol m ^{? 3}, in the estimated aqueous volume of the guard‐cell wall. The conclusion is that mannitol, a xenobiotic with structural similarity to sucrose, can move throughout the apoplast of a transpiring leaflet and accumulate in an osmotically significant concentration in the guard‐cell wall. These data therefore provide support for a new role for sucrose as a signal metabolite that integrates essential functions of the whole leaf. In addition, the results raise questions about the physiological or experimental accumulation of other guard‐cell‐targeted apoplastic solutes such as plant growth regulators, particularly abscisic acid, and ions.     

Contrasting physiological responses of six eucalyptus species to water deficit

BACKGROUND AND AIMS: The genus Eucalyptus occupies a broad ecological range, forming the dominant canopy in many Australian ecosystems. Many Eucalyptus species are renowned for tolerance to aridity, yet inter-specific variation in physiological traits, particularly water relations parameters, contributing to this tolerance is weakly characterized only in a limited taxonomic range. The study tests the hypothesis that differences in the distribution of Eucalyptus species is related to cellular water relations. METHODS: Six eucalypt species originating from (1) contrasting environments for aridity and (2) diverse taxonomic groups were grown in pots and subjected to the effects of water deficit over a 10-week period. Water potential, relative water content and osmotic parameters were analysed by using pressure-volume curves and related to gas exchange, photosynthesis and biomass. KEY RESULTS: The six eucalypt species differed in response to water deficit. Most significantly, species from high rainfall environments (E. obliqua, E. rubida) and the phreatophyte (E. camaldulensis) had lower osmotic potential under water deficit via accumulation of cellular osmotica (osmotic adjustment). In contrast, species from low rainfall environments (E. cladocalyx, E. polyanthemos and E. tricarpa) had lower osmotic potential through a combination of both constitutive solutes and osmotic adjustment, combined with reductions in leaf water content. CONCLUSIONS: It is demonstrated that osmotic adjustment is a common response to water deficit in six eucalypt species. In addition, significant inter-specific variation in osmotic potential correlates with species distribution in environments where water is scarce. This provides a physiological explanation for aridity tolerance and emphasizes the need to identify osmolytes that accumulate under stress in the genus Eucalyptus.     

一种体内恒速持续给药的方法—微量渗透泵

利用微量渗透泵给药是一种崭新的动物实验性持续给药方法。泵体由３个同心层（由内向外）—贮药池、渗透性套筒及控制渗透泵药物释放速度的半透膜组成。泵在被水激活后,因水可按渗透梯度渗入渗透性套筒部分,压迫泵体以恒定速度持续释放药物几天至若干星期,其渗透速度与被释放药物的理化性质无关,因而适用于多种药物     

Contribution of osmotic adjustment to the dehydration tolerance of water-stressed pigeon pea (Cajanus cajan (L.) millsp.) leaves

Abstract Water-stressed pigeonpea leaves have high levels of osmotic adjustment at low leaf water potentials. The possible contribution of this adjustment of dehydration tolerance of leaves was examined in plants grown in a controlled environment. Osmotic adjustment was varied by withholding water from plants growing in differing amounts of soil, which resulted in different rates of decline of leaf water potential. The level of osmotic adjustment was inversely related to leaf water potential in all treatments. In addition, at any particular water potential, plants that had experienced a rapid development of stress exhibited less osmotic adjustment than plants that experienced a slower development of stress. Leaves with different levels of osmotic adjustment died at water potentials between –3.4 and –6.3 MPa, but all leaves died at a similar relative water content (32%). Consequently, leaves died when relative water content reached a lethal value, rather than when a lethal leaf water potential was reached. Osmotic adjustment delayed the time and lowered the leaf water potential when the lethal relative water content occurred, because it helped maintain higher relative water contents at low leaf water potentials. The consequences of osmotic adjustment for leaf survival in water-stressed pigeonpea are discussed.     

Calorimetric and molecular simulation study on unfrozen water characteristics in aqueous sugar solutions: implications for biopreservation

Intensive studies have been conducted to determine the protective mechanisms of sugars that have proven beneficial to the biopreservation application. However, little has been known about the unfrozen water content that aqueous sugar solutions can possess when frozen at cryogenic temperatures. This study conducted calorimetric measurements to determine the unfrozen water content in frozen aqueous solutions of glucose, fructose, sucrose and trehalose of multiple concentrations. The hydrogen-bonding network in these solutions was characterised by molecular simulations. The experimental results showed that more water could be prevented from ice crystallisation in a more concentrated solution. Disaccharides, especially trehalose, are more effective than other protectants (e.g., glucose, glycerol and dimethyl sulfoxide) for detaining water in the unfrozen state. Moreover, it was found that, at molecular levels, there were more hydrogen bonds between sugar and water molecules in a more concentrated solution. From both macro- and microscopic perspectives, trehalose was demonstrated to be a much more effective cryoprotectant than others. This comparative study proved that the unfrozen water should be mainly attributed to hydrogen bonds between sugar and water in the mixture. Our findings will provide valuable information for determining the physical state of cryopreserved biomatrix and guiding the preparation of protective formulations.     

Comparison of osmotic and allelopathic effects of grass leaf extracts on grass seed germination and radicle elongation

The influence of osmotic effects of aqueous plant extracts on the results of allelopathy bioassays was investigated for four pasture grass species. It was found that allelopathic effects were substantially overestimated when osmotic effects were not taken into account. It is concluded that bioassays using aqueous plant extracts are more realistic when osmotically adjusted control values (with the same osmotic potential as the plant extract being tested) are used.     

Simplified calculation of cell water content during freezing and thawing in nonideal solutions of cryoprotective agents and its possible application to the study of “solution effects” injury

A simplified equation has been derived which reduces the time and complexity of calculating subzero cell water content during freezing and thawing as compared to calculation by means of the Mazur equation. The simplified equation also allows inclusion of the effects of nonideality of glycerol and dimethyl sulfoxide aqueous electrolyte solutions. Furthermore, a very simple, iterative method of solving the simplified equation has been shown to give results which are equivalent to those obtained using the far more difficult and involved Runge-Kutta technique. It is hoped that these simplifications will make calculation of cell water content accessible to more cryobiologists. In addition, possible applications of such calculations to mechanistic issues in the area of “solution effects” injury are discussed.     

Investigating and modeling the combined effects of pH and osmotic pressure on seed germination for use in phytoactivity and allelopathic research

Phytoactivity and allelopathic studies are heavily dependent on germination bioassays of water solutions of allelochemical(s), which necessarily imply that pH and osmotic pressure vary among treatments and between treatments and controls and are therefore a confounding factor in the assessment of seed germination responses to allelochemical(s). When the contribution of pH and osmotic pressure to seed germination responses is considered in experimental designs their effects are almost without exceptions examined separately being assumed, without any evidences, that pH and osmotic pressure act independently on seed germination responses. The objectives of this work were to examine experimentally such assumption using wheat, lettuce, and subterranean clover cultivars to evaluate and model the combined effects on germination of pH and osmotic pressure in the range between 3.0–6.0 and 0–100 mOsmol kg^?1, respectively. Empirical equations are fitted, discussed, and the need to consider the simultaneous effects of pH and osmotic pressure firmly established. Finally, the use of the equations fitted and its impact on conclusions is exemplified in a dose-response bioassay of water extracts of Cistus ladanifer on seed germination using subterranean clover as target species where hormesis was found before allelochemical effects were corrected for pH and osmotic pressure values of control and extracts.     

Changes in ionic selectivity with changes in density of water in gels and cells

Gels equilibrated with aqueous solutions of impermeant solutes reached a steady state in which, in the absence of a pressure difference, the activity of water in the pores of the gel was higher than that of water in the external solution. The chemical potential of water in the gel/polymer solution slurry was higher than that in the supernatant polymer solution removed from the gel. Water in the pores of the gel decreased in density to 0.96 as increasing osmotic stress was applied. It is argued that at constant temperature and pressure water can equilibrate between two compartments of unequal osmolality only by adjusting its molar volume. Experiments showed that when gel water had a higher activity than external water it was K⁺ selective; when it had a lower activity it was Na⁺ selective. It is proposed that a continuous spectrum of water structures can exist in these two compartment systems from dense, reactive, weakly-bonded water which selects highly hydrated ions, to expanded, stretched, unreactive, viscous water which is strongly hydrogen bonded and selects K⁺ and univalent anions. These findings are related to the state and properties of cytoplasmic water which is probably held under osmotic stress by the activity of the sodium pump.     

Osmotic regulation of assimilate unloading from seed coats of Vicia faba. Role of turgor and identification of turgor-dependent fluxes

Osmotic regulation of assimilate efflux from excised coats of developing Vicia faba (cv. Coles Prolific) seed was examined by exposing these to bathing solutions (adjusted to –0. 02 to –0. 75 MPa with sorbitol) introduced into the cavity vacated by the embryo. ¹⁴C photosynthate efflux was found to be independent of solution osmotic potentials below –0. 63 MPa. At higher osmotic potentials, efflux was stimulated and exhibited a biphasic response to osmotic potential with apparent saturation being reached at –0. 37 MPa. Efflux could be repeatedly stimulated and slowed by exposing seed coats to solutions of high and low osmotic potentials, respectively. Manipulation of components of tissue water potential, with slowly- and rapidly-permeating osmotica, demonstrated that turgor functioned as the signal regulating ¹⁴C photosynthate efflux. Com-partmental analysis of ¹⁴C photosynthate preloaded seed coats was consistent with exchange from 4 kinetically-distinct compartments. The kinetics of turgor-dependent efflux exhibited characteristics consistent with the transport mechanism residing in the plasma membranes of the unloading cells. These characteristics included the rapidity (<2 min) of the efflux response to turgor increases, similar rate constants for efflux from the putative turgor-sensitive and cytoplasmic compartments and the apparent small pool size from which turgor-dependent efflux could repeatedly occur. In contrast, influx of [¹⁴C] sucrose across the plasma and tonoplast membranes was found to be insensitive to turgor. The plasma membrane [¹⁴C] sucrose influx was unaffected by p-chloromercuribenzenesulfonic acid and erythrosin B and exhibited a linear dependence on the external sucrose concentration. This behaviour suggested that influx across the plasma membrane occurs by passive diffusion. Preloading excised seed coats with a range of solutes demonstrated that turgor-dependent efflux exhibited partial solute selectivity. Based on these findings, it is proposed that turgor controls assimilate exchange from the seed coat by regulating an efflux mechanism located in the plasma membranes of the unloading cells.