The Experts below are selected from a list of 249 Experts worldwide ranked by ideXlab platform
U. Zimmermann - One of the best experts on this subject based on the ideXlab platform.
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xylem and cell turgor Pressure Probe measurements in intact roots of glycophytes transpiration induces a change in the radial and cellular reflection coefficients
Plant Cell and Environment, 1997Co-Authors: H Schneider, U. ZimmermannAbstract:Xylem Probe measurements in the roots of intact plants of wheat and barley revealed that the xylem Pressure decreased rapidly when the roots were subjected to osmotic stress (NaCI or sucrose). The magnitude of the xylem Pressure response and, in turn, that of the radial reflection coefficients (σ r ) depended on the transpiration rate. Under very low transpiration conditions (darkness and high relative humidity), σ r assumed values of the order of about 0.2-0.4. The σ r values of excised roots were also found to be rather low, in agreement with data obtained using the root Pressure Probe of Steudle. For transpiring plants (light intensities at least 10 μmol m -2 s -1 ; relative humidity 20-40%) the response was nearly 1:1, corresponding to radial reflection coefficients of σ r = 1. Further increase of the light intensity to about 400 μmol m -2 s -1 resulted in a slight but significant decrease of the σ r values to about 0.8. Similar measurements on maize roots confirmed our previous results (Zhu et al. 1995, Plant, Cell and Environment 18, 906-912) that, in intact transpiring plants at low light intensities of about 10 μmol m -2 s -l and at relative humidities of 20-40% as well as in excised roots, the xylem Pressure response was much less than expected from the external osmotic Pressure (σ r values 0.3-0.5). In contrast to wheat and barley, very high light intensities (about 700 μmol m -2 s -1 ) were needed to shift the radial reflection coefficients of maize roots to values of about 0.9. Osmotically induced xylem Pressure changes were apparently linked to changes in turgor Pressure in the root cortical parenchyma cells, as shown by simultaneous measurements of xylem and cell turgor Pressure. In analogy to the σ r values of the respective glycophytes, the σ C values of the root cortical cells of wheat and barley were close to unity, whereas σ C for maize was significantly smaller (about 0.7) under laboratory conditions. When the light intensity was increased up to about 700 μmol m -2 s -1 , the cellular reflection coefficient of maize roots increased to about 0.95. In contrast to the σ r values, the σ C values of the three species investigated remained almost unchanged when the leaves were exposed to darkness and humidified air or when the roots were cut. The transpiration-dependent (species-specific) pattern of the cellular and radial reflection coefficients of the root compartment of the three glycophytes apparently resulted from (flow-dependent) concentration-polarization and sweep-away effects in the roots of intact plants. The data could be explained straightforwardly in terms of theoretical considerations outlined previously by Dainty (1985, Acta Horticulturae 171, 21-31). The farreaching consequences of this finding for root Pressure Probe measurements on excised roots, for the occurrence of Pressure gradients under transpiring conditions, and for the non-linear flow-force relationships in roots found by other investigators are discussed.
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radial turgor and osmotic Pressure profiles in intact and excised roots of aster tripolium Pressure Probe measurements and nuclear magnetic resonance imaging analysis
Plant Physiology, 1992Co-Authors: U. Zimmermann, Angelika Balling, Joachim Rygol, Gerd Klock, Alexander Metzler, Axel HaaseAbstract:High-resolution nuclear magnetic resonance images (using very short spin-echo times of 3.8 milliseconds) of cross-sections of excised roots of the halophyte Aster tripolium showed radial cell strands separated by air-filled spaces. Radial insertion of the Pressure Probe (along the cell strands) into roots of intact plants revealed a marked increase of the turgor Pressure from the outermost to the sixth cortical layer (from about 0.1-0.6 megapascals). Corresponding measurements of intracellular osmotic Pressure in individual cortical cells (by means of a nanoliter osmometer) showed an osmotic Pressure gradient of equal magnitude to the turgor Pressure. Neither gradient changed significantly when the plants were grown in, or exposed for 1 hour to, media of high salinity. Differences were recorded in the ability of salts and nonelectrolytes to penetrate the apoplast in the root. The reflection coefficients of the cortical cells were approximately 1 for all the solutes tested. Excision of the root from the stem resulted in a collapse of the turgor and osmotic Pressure gradients. After about 15 to 30 minutes, the turgor Pressure throughout the cortex attained an intermediate (quasistationary) level of about 0.3 megapascals. This value agreed well with the osmotic value deduced from plasmolysis experiments on excised root segments. These and other data provided conclusions about the driving forces for water and solute transport in the roots and about the function of the air-filled radial spaces in water transport. They also showed that excised roots may be artifactual systems.
J. M. Wilczak - One of the best experts on this subject based on the ideXlab platform.
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On the response of a turbulent-Pressure Probe and the measurement of Pressure transport
Boundary-Layer Meteorology, 1994Co-Authors: J. C. Wyngaard, A. Siegel, J. M. WilczakAbstract:Wind-tunnel calibrations of turbulent-Pressure sensors usually reveal deviations from ideal response. These deviations are typically reported in dimensional form (e.g., in microbars) or as a fraction of the dynamic Pressure. Neither presentation gives a direct indication of the reliability of Pressure statistics measured in a turbulent flow. We derive a general response equation for a turbulent-Pressure Probe. The coefficients in the equation are obtainable from standard wind-tunnel calibration results. The form of the response equation makes it straightforward to relate the errors in measured Pressure statistics to the statistics of the turbulence. We demonstrate this by evaluating the reliability of measurements of some important Pressure covariances, including the Pressure-transport term in the turbulent kinetic energy (TKE) budget in the unstable surface layer. The preliminary finding is that the Nishiyama-Bedard sensor is capable of measuring Pressure transport of TKE there to within 10–20%.
Peter J. Franks - One of the best experts on this subject based on the ideXlab platform.
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Use of the Pressure Probe in studies of stomatal function
Journal of experimental botany, 2003Co-Authors: Peter J. FranksAbstract:Over the past few decades the Pressure Probe has been used extensively in studies of the hydromechanical and osmotic properties of plant cells. However, although Pressure Probe techniques have been employed successfully in the study of stomatal function, there is no detailed account of this special application of the Pressure Probe technique. This paper describes the construction and use of the Pressure Probe in studies relating to stomatal function, and reviews the current state of knowledge of stomatal function in relation to guard cell and leaf hydromechanical properties.
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Guard Cell Volume and Pressure Measured Concurrently by Confocal Microscopy and the Cell Pressure Probe
Plant physiology, 2001Co-Authors: Peter J. Franks, Thomas N Buckley, Joseph C. Shope, Keith A. MottAbstract:Guard cell turgor Pressures in epidermal peels of broad bean (Vicia faba) were measured and controlled with a Pressure Probe. At the same time, images of the guard cell were acquired using confocal microscopy. To obtain a clear image of guard cell volume, a fluorescent dye that labels the plasma membrane was added to the solution bathing the epidermal peel. At each Pressure, 17 to 20 optical sections (each 2 μm thick) were acquired. Out-of-focus light in these images was removed using blind deconvolution, and volume was estimated using direct linear integration. As Pressure was increased from as low as 0.3 MPa to as high as 5.0 MPa, guard cell volume increased in a saturating fashion. The elastic modulus was calculated from these data and was found to range from approximately 2 to 40 MPa. The data allow inference of guard cell osmotic content from stomatal aperture and facilitate accurate mechanistic modeling of epidermal water relations and stomatal functioning.
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A study of stomatal mechanics using the cell Pressure Probe
Plant Cell and Environment, 1998Co-Authors: Peter J. Franks, I.r. Cowan, Graham D FarquharAbstract:The relationship between stomatal aperture (a) and guard cell Pressure (Pg) was measured directly in four different species (Vicia faba, Tradescantia virginiana, Ginkgo biloba and Nephrolepis exaltata) using a special cell Pressure Probe technique. The effect of epidermal turgor (Pep) on this relationship was also measured in T. virginiana. The relationship was sigmoidal for V. faba and T. virginiana, but entirely convex for G. biloba and N. exaltata. Epidermal turgor was found to have a pronounced closing effect on stomata of T. virginiana. Maximum aperture with full epidermal turgor (0·92 MPa) was about half that with zero epidermal turgor. Also, with full epidermal turgor stomata of T. virginiana did not begin to open until Pg was more than 1·25 MPa. These characteristics were used to develop an expression for a as a function of Pg and Pep. Results for the different species are compared and discussed in terms of possible advantages and limitations of water economy.
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Guard cell Pressure/aperture characteristics measured with the Pressure Probe
Plant Cell and Environment, 1995Co-Authors: Peter J. Franks, I.r. Cowan, Stephen D Tyerman, A. L. Cleary, Jon Lloyd, Graham D FarquharAbstract:Pressure within guard cells in strips of intact epidermis of Tradescantia virginiana was controlled with a Pressure Probe apparatus after the guard cells had been filled with silicone oil. Pressure was increased and decreased incrementally between 0.0 and 4.1 MPa to cause inflation and deflation of the guard cells. At steady-state guard cell Pressures, the width of the stomatal pore was recorded and plotted against Pressure. The Pressure required for near-maximum aperture was 4.1 MPa. Aperture as a function of Pressure was sigmoidal.
J. A. C. Smith - One of the best experts on this subject based on the ideXlab platform.
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a critical comparison of the Pressure Probe and Pressure chamber techniques for estimating leaf ceil turgor Pressure in kalanchoe daigremontiana
Plant Cell and Environment, 1994Co-Authors: R. Murphy, J. A. C. SmithAbstract:The aim of the present study was to test the accuracy of the Pressure-chamber technique as a method for estimating leaf-cell turgor Pressures. To this end, Pressure-Probe measurements of cell turgor Pressure (Pcell) were made on mesophyll cells of intact, attached leaves of Kalanchoe daigremontiana. Immediately following these measurements, leaves were excised and placed in a Pressure chamber for the determination of balance Pressure (Pbal). Cell-sap osmotic Pressure (?cell) and xylem-sap osmotic Pressure (?xyl) were also measured, and an average cell turgor Pressure calculated as Pcell=?cell–?xyl–Pbal. The apparent value of Pbal was positively correlated with the rate of increase of chamber Pressure, and there was also a time-dependent increase associated with water loss. On expressing sap from the xylem, ?xyl fell to a plateau value that was positively correlated with ?cell. Correcting for these effects yielded estimates of Pbal and ?xyl at the time of leaf excision. On average, the values of Pcell obtained with the two techniques agreed to within ±002 MPa (errors are approximate 95% confidence limits). If ?xyl were ignored, however, the calculated turgor Pressures would exceed the measured values by an average of 0.074 ± 0.012MPa, or 48% at the mean measured Pressure of 0.155 MPa. We conclude that the Pressure-chamber technique allows a good estimate to be made of turgor Pressure in mesophyll cells of K. daigremontiana, provided that ?xyl is included in the determination. The 1:1 relationship between the measured and calculated turgor Pressures also implies that the weighted-average reflection coefficient for the mesophyll cell membranes is close to unity.
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Modification of the Pressure-Probe technique permits controlled intracellular microinjection of fluorescent Probes
Journal of Cell Science, 1991Co-Authors: Karl J. Oparka, R. Murphy, P. M. Derrick, D. A. M. Prior, J. A. C. SmithAbstract:The Pressure Probe has been widely used to study the water relations of plant cells. Here we describe a simple modification of the Pressure-Probe technique that permits the controlled microinjection of fluorescent Probes into plant cells while simultaneously measuring cell turgor Pressure. Using the Pressure Probe, less than 1 nl of the membrane-impermeant fluorescent dye Lucifer Yellow CH was introduced into micropipettes and subsequently injected into leaf trichome cells of Nicotiana clevelandii. Disruption of cell contents could be minimized by raising the hydrostatic Pressure in the Probe prior to impalement to a value approaching the anticipated cell turgor Pressure. Injections to the cytosol resulted in intercellular symplastic transport of the dye in both acropetal and basipetal directions. In contrast, no symplastic transport was observed following an injection of dye into the vacuole. As measured with the Pressure Probe, cell turgor Pressures were in the range 0.18 to 0.36 MPa; the half-time for water exchange across the cell boundary was approximately 10 s. The potential of this technique for the study of turgor-Pressure-dependent intercellular transport and the hydraulic conductivities of the tonoplast, plasmalemma and plasmodesmata is discussed.
Stevens J - One of the best experts on this subject based on the ideXlab platform.
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The Sheffield Nasal Pressure Probe: the development of a new device to measure intranasal pain thresholds.
Rhinology, 1994Co-Authors: J W Fairley, M P Yardley, L H Durham, Stevens JAbstract:We present the development of a mechanical Pressure Probe which was constructed from items readily available to most university departments. The device is simple to operate and gives repeatable determinations. Its main use has been to measure the Pressure thresholds for pain in the nasal mucosa.
