Biomedical subjects

E Steudle

Publications and source records attributed to E Steudle.

32 records · Page 2Linked to original sources

PubMed1989

Negative pressures produced in an artificial osmotic cell by extracellular freezing.

A rigid artificial osmotic cell has been constructed using reverse osmosis membranes that were supported by metal grids from both sides to yield a high elastic modulus of the system. The cell could be subjected to changes of external water potential either by evaporation or by application of hypertonic solutions so that negative internal pressures or tensions (i.e. pressures smaller than atmospheric) could be built up. Negative pressures were also obtained by freeze-induced dehydration when the cell was cooled to -1.5 degrees C and ice was formed on the outer surface. Tensions of up to -0.7 megapascals (-7 bars) could be established in the different types of experiments. Smaller tensions could be kept in the cell for several hours. Cavitations caused the pressure to increase instantaneously to values of about -0.1 megapascals (relative to atmospheric pressure) as theoretically expected. Cavitations could be reversed by pressurizing the system. The cell could be cooled to subzero temperatures while the cell solution was under tension. Intracellular freezing could be easily detected from an instantaneous increase in pressure. When the membrane was not supported by a grid from the inside (analogous to the situation in plant cells), no tensions could be built up in the system. The results support the idea of the incidence of negative pressures during freezing, if the wall is sufficiently rigid to prevent cell collapse and if the membrane does not separate from the cell wall.

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PubMed1987

Pressure probe and isopiestic psychrometer measure similar turgor.

Turgor measured with a miniature pressure probe was compared to that measured with an isopiestic thermocouple psychrometer in mature regions of soybean (Glycine max [L.] Merr.) stems. The probe measured turgor directly in cells of intact stems whereas the psychrometer measured the water potential and osmotic potential of excised stem segments and turgor was calculated by difference. When care was taken to prevent dehydration when working with the pressure probe, and diffusive resistance and dilution errors with the psychrometer, both methods gave similar values of turgor whether the plants were dehydrating or rehydrating. This finding, together with the previously demonstrated similarity in turgor measured with the isopiestic psychrometer and a pressure chamber, indicates that the pressure probe provides accurate measurements of turgor despite the need to penetrate the cell. On the other hand, it suggests that as long as precautions are taken to obtain accurate values for the water potential and osmotic potential, turgor can be determined by isopiestic psychrometry in tissues not accessible to the pressure probe for physical reasons.

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PubMed1987

Water transport in maize roots : measurement of hydraulic conductivity, solute permeability, and of reflection coefficients of excised roots using the root pressure probe.

A root pressure probe has been used to measure the root pressure (P(r)) exerted by excised main roots of young maize plants (Zea Mays L.). Defined gradients of hydrostatic and osmotic pressure could be set up between root xylem and medium to induce radial water flows across the root cylinder in both directions. The hydraulic conductivity of the root (Lp(r)) was evaluated from root pressure relaxations. When permeating solutes were added to the medium, biphasic root pressure relaxations were observed with water and solute phases and root pressure minima (maxima) which allowed the estimation of permeability (P(Sr)) and reflection coefficients (sigma(sr)) of roots. Reflection coefficients were: ethanol, 0.27; mannitol, 0.74; sucrose, 0.54; PEG 1000, 0.82; NaCl, 0.64; KNO(3), 0.67, and permeability coefficients (in 10(-8) meters per second): ethanol, 4.7; sucrose, 1.6; and NaCl, 5.7. Lp(r) was very different for osmotic and hydrostatic gradients. For hydrostatic gradients Lp(r) was 1.10(-7) meters per second per megapascal, whereas in osmotic experiments the hydraulic conductivity was found to be an order of magnitude lower. For hydrostatic gradients, the exosmotic Lp(r) was about 15% larger than the endosmotic, whereas in osmotic experiments the polarity in the water movement was reversed. These results either suggest effects of unstirred layers at the osmotic barrier in the root, an asymmetrical barrier, and/or mechanical effects. Measurements of the hydraulic conductivity of individual root cortex cells revealed an Lp similar to Lp(r) (hydrostatic). It is concluded that, in the presence of external hydrostatic gradients, water moves primarily in the apoplast, whereas in the presence of osmotic gradients this component is much smaller in relation to the cell-to-cell component (symplasmic plus transcellular transport).

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PubMed1985

Water transport in the midrib tissue of maize leaves : direct measurement of the propagation of changes in cell turgor across a plant tissue.

WATER MOVEMENT ACROSS PLANT TISSUES OCCURS ALONG TWO PATHS: from cell-to-cell and in the apoplasm. We examined the contribution of these two paths to the kinetics of water transport across the parenchymatous midrib tissue of the maize (Zea mays L.) leaf. Water relations parameters (hydraulic conductivity, Lp; cell elastic coefficient, epsilon; half-time of water exchange for individual cells, T((1/2))) of individual parenchyma cells determined with the pressure probe varied in different regions of the midrib. In the adaxial region, Lp = (0.3 +/- 0.3).10(-5) centimeters per second per bar, epsilon = 103 +/- 72 bar, and T((1/2)) = 7.9 +/- 4.8 seconds (n = seven cells); whereas, in the abaxial region, Lp = (2.5 +/- 0.9).10(-5) centimeters per second per bar, epsilon = 41 +/- 9 bar, and T((1/2)) = 1.3 +/- 0.5 seconds (n = 7). This zonal variation in Lp, epsilon, and T((1/2)) indicates that tissue inhomogeneities exist for these parameters and could have an effect on the kinetics of water transport across the tissue.The diffusivity of the tissue to water (D(t)) obtained from the sorption kinetics of rehydrating tissue was D(t) = (1.1 +/- 0.4).10(-6) square centimeters per second (n = 6). The diffusivity of the cell-to-cell path (D(c)) calculated from pressure probe data ranged from D(c) = 0.4.10(-6) square centimeters per second in the adaxial region to D(c) = 6.1.10(-6) square centimeters per second in the abaxial region of the tissue. D(t) approximately D(c) suggests substantial cell-to-cell transport of water occurred during rehydration. However, the tissue diffusivity calculated from the kinetics of pressure-propagation across the tissue (D(t)') was D(t)' = (33.1 +/- 8.0).10(-6) square centimeters per second (n = 8) and more than 1 order of magnitude larger than D(t). Also, the hydraulic conductance of the midrib tissue (Lp(m) per square centimeter of surface) estimated from pressure-induced flows across several parenchyma cell layers was Lp(m) = (8.9 +/- 5.6).10(-5) centimeters per second per bar (n = 5) and much larger than Lp.These results indicate that the preferential path for water transport across the midrib tissue depends on the nature of the driving forces present within the tissue. Under osmotic conditions, the cell-to-cell path dominates, whereas under hydrostatic conditions water moves primarily in the apoplasm.

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PubMed1984

Determination of Solute Permeability in Chara Internodes by a Turgor Minimum Method : Effects of External pH.

The analysis of Sha'afi et al. (Sha'afi, Rich, Mickulecky, Solomon 1970 J Gen Physiol 55: 427-450) for determining solute permeability in red blood cells has been modified and applied to turgid plant cells. Following the addition of permeating solute to the external medium, a biphasic response of cell turgor can be measured with the pressure probe in isolated internodes of Chara corallina. After an initial decrease in turgor due to water flow (water phase), turgor increases due to the uptake of the solute (solute phase) until the original turgor is reattained. From the pressure/time course in the neighborhood of the minimum turgor, the permeability of the osmotic solute can be determined. The data obtained by the minimum method for rapidly permeating (ethanol, methanol) and slowly permeating (formamide, dimethylformamide) solutes are similar to those calculated from the half-time of pressure changes during the solute phase and to data obtained by other workers using radioactive tracers. The methods employing the pressure probe were applied to examine the effect of high pH (up to pH 11) on the membrane permeability. There appeared to be no effect of high pH on the permeability coefficients, reflection coefficients, and hydraulic conductivity.

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PubMed1981

Water Relations of Leaf Epidermal Cells of Tradescantia virginiana.

Water-relation parameters (cell turgor pressure [P], volumetric elastic modulus [epsilon] and hydraulic conductivity [Lp]) of individual leaf epidermal cells of Tradescantia virginiana have been determined with the pressure-probe technique. Turgor was 4.5 +/- 2.1 [41] bar (mean +/- sd; in brackets the number of cells) and ranged from 0.9 to 9.6 bar. By vacuum infiltration with nutrient solution, it was raised to 7.5 +/- 1.5 [5] bar (range: 5.3-8.8 bar). There was a large variability in the absolute value of epsilon of individual cells. epsilon ranged from 40 to 360 bar; mean +/- sd: 135 +/- 83 bar; n = 50 cells. epsilon values of individual cells seemed to be rather independent of changes in cell turgor. A critical assessment of the errors incurred in determining epsilon by the technique is included. The half-times of water exchange of individual cells ranged from 1 to 35 seconds, which gave values of 0.2 to 11 x 10(-6) centimeters per second per bar for Lp (mean +/- sd: 3.1 +/- 2.3 x 10(-6) centimeters per second per bar; n = 39 cells). The large range in Lp and epsilon is believed to be due to the difficulties in determining the effective surface area of water exchange of the cells. Lp is not influenced by active salt pumping driven by respiration energy inasmuch as it was not altered by 0.1 millimolar KCN. The temperature dependence of Lp (T((1/2))) was measured for the first time in individual higher-plant cells. Lp increased by a factor of 2 to 4, when the temperature was increased by 10 C. The activation energy of water exchange was found to be between 50 and 186 kilojoules per mole. Within the large range of variation it was found that T((1/2)), Lp, and epsilon did not change under various experimental conditions (intact and excised tissue, water content and turgidity, age, etc.). Similar results were obtained for the epidermal cells of Tradescantia andersoniana. The measurements suggest that the entire epidermis would respond very rapidly (i.e. with a half-time of 1 to 30 s) to a demand for water from the stomata.

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PubMed1980

Water-relation Parameters of Individual Mesophyll Cells of the Crassulacean Acid Metabolism Plant Kalanchoë daigremontiana.

Water-relation parameters of leaf mesophyll cells of the CAM plant Kalanchoë daigremontiana have been determined directly in cells of tissue slices using the pressure-probe technique. Turgor pressures measured in cells of the second to fourth layer from the cut surface showed an average of 1.82 +/- 0.62 bar (mean +/- sd; n = 157 cells). This was lower than expected from measurements of the osmotic pressure of the cell sap. The half-time (T(1/2)) for water-flux equilibration of individual cells was 2.5 to 8.8 seconds. This is the fastest T(1/2) found so far for higher-plant cells. The calculated values of the hydraulic conductivity were in the range of 0.20 to 1.6 x 10(-5) centimeters second(-1) bar(-1), with an average of (0.69 +/- 0.46) x 10(-5) centimeters second(-1) bar(-1) (mean +/- sd; n = 8 cells). The T(1/2) values of water exchange of individual cells are consistent with the overall rates of water-flux equilibration measured for tissue slices.The volumetric elastic moduli (in) of individual cells were in the range 13 to 128 bar for turgor pressures between 0.0 and 3.4 bar; the average in value was 42.4 +/- 27.7 bar (mean +/- sd; n = 21 cells). This in value is similar to that observed for other higher-plant cells.The water-storage capacity of individual cells, calculated as C(c) = V/(in + pi(i)) (where V = cell volume and pi(i) = internal osmotic pressure) was 9.1 x 10(-9) cubic centimeters bar(-1) per cell, and the capacity for the tissue was 2.2 x 10(-2) cubic centimeters bar(-1) gram(-1) fresh weight. The significance of the water-relation parameters determined at the cellular level is discussed in terms of the water relations of whole leaves and the high water-use efficiency characteristic of CAM plants.

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PubMed1978

Pressure probe technique for measuring water relations of cells in higher plants.

A new method is described for continuously measuring cell turgor pressure (P), hydraulic conductivity (L(p)), and volumetric elastic modulus (epsilon) in higher plant cells, using a pressure probe. This technique permits volume changes, DeltaV, and turgor pressure changes, DeltaP, to be determined with an accuracy of 10(-5) to 10(-6) mul and 3 to 5.10(-2) bar, respectively.The main principle of the new method is the same as the pressure probe developed by Zimmermann and Steudle in which pressure is transmitted to a pressure transducer by means of an oil-filled capillary introduced into the cell. In order to use the pressure probe for small tissue cells, the effective compressible volume of the apparatus has to be sufficiently small in comparison to the volume of the cell itself. This is achieved by accurately fixing the oil/cell sap boundary in the very tip of the microcapillary by means of an electronic feedback mechanism, so that the effective volume of the apparatus is reduced to about 2 to 10% of the cell volume. In this way also, errors arising from compressibility of the apparatus and temperature fluctuations can be excluded.Measurements on tissues cells of Capsicum annuum fruits yield epsilon values of 2 to 25 bar. Furthermore, epsilon can be shown to be a function of both cell turgor pressure and cell volume; epsilon increases with increasing turgor pressure and is higher in larger cells.

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PubMed1977

Effect of turgor pressure and cell size on the wall elasticity of plant cells.

Direct measurements of the volumetric elastic modulus, in, of cells of a higher plant were performed on the epidermal bladder cells of Mesembryanthemum crystallinum using a pressure probe technique. Measurements on giant algal cells (Valonia, Nitellopsis) are given for comparison. Giant celled algae and M. crystallinum bladders have elastic moduli, in, which depend strongly on turgor pressure, P, and on cell volume, V. The in values of Mesembryanthemum bladders range between 5 bar at zero pressure and 100 bar at full turgor pressure (3-4 bar). in increased with cell size (volume) at a given turgor pressure, and this volume dependence was pronounced more in the high pressure range. From the in (P) characteristics, complete volume-pressure curves were obtained for Mesembryanthemum bladders and giant algal cells. The results suggest that the in (P) and in (V) characteristics of all plant cells are similar. The significance of the pressure and volume effects for the water relations and growth processes of plant cells is discussed briefly.

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PubMed1976

Turgor Pressure Regulation in Valonia utricularis: Effect of Cell Wall Elasticity and Auxin.

The electrical membrane resistance rho(0) of the marine alga Valonia utricularis shows a marked maximum in dependence on the turgor pressure. The critical pressure, P(c), at which the maximum occurs, as well as its absolute value, rho(0) (max), are strongly volume-dependent. Both P(c) and rho(0) (max), increase with decreasing cell volume. It seems likely, that these relationships reflect the elastic properties of the cell wall, because the volumetric elastic modulus, epsilon, is also volume-dependent, increasing hyperbolically with cell volume. Both P(c) and rho(0) (max) can be affected by external application of indole-3-acetic acid at concentrations of 2.10(-7)m to 2 .10(-5)m. The critical pressure is shifted by 1.2 to 6 bars toward higher pressures and the maximum membrane resistance increased up to 5.6-fold. During the course of the experiments (up to 4 hours), however, IAA had no effect on the volumetric elastic modulus, epsilon.The maximum in membrane resistance is discussed in terms of a pressure-dependent change of potassium fluxes. The volume dependence of P(c) and rho(0) (max) suggests that not only turgor pressure but also epsilon must be considered as a regulating parameter during turgor pressure regulation. On this basis a hypothesis is presented for the transformation of both, a pressure signal and of changes in the elastic properties of the cell wall into alterations of ion fluxes. It is assumed that the combined effects of tension and compression of the membranes as well as the interaction between membrane and cell wall opposingly change the number of transport sites for K(+) providing a turgor-sensing mechanism that regulates ion fluxes. The IAA effects demonstrated are consistent with this view, suggesting that the basic mechanisms for turgor pressure regulation and growth regulation are similar.Any relation connecting growth rate with turgor pressure should be governed by two parameters, i.e. by a yielding pressure, at which cell growth starts, and by the critical pressure, at which it ceases again.

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PubMed1974