The Experts below are selected from a list of 231 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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effects of environmental parameters and irrigation on the Turgor Pressure of banana plants measured using the non invasive online monitoring leaf patch clamp Pressure probe
Plant Biology, 2010Co-Authors: U Zimmermann, Lars H. Wegner, Or Shapira, Simon Ruger, M Westhoff, Randolph Reuss, P Gessner, Gertraud Zimmermann, Yair Israeli, Aihua ZhouAbstract:Turgor Pressure provides a sensitive indicator for irrigation scheduling. Leaf Turgor Pressure of Musa acuminate was measured by using the so-called leaf patch clamp Pressure probe, i.e. by application of an external, magnetically generated and constantly retained clamp Pressure to a leaf patch and determination of the attenuated output Pressure Pp that is highly correlated with the Turgor Pressure. Real-time recording of Pp values was made using wireless telemetric transmitters, which send the data to a receiver base station where data are logged and transferred to a GPRS modem linked to an Internet server. Probes functioned over several months under field and laboratory conditions without damage to the leaf patch. Measurements showed that the magnetic-based probe could monitor very sensitively changes in Turgor Pressure induced by changes in microclimate (temperature, relative humidity, irradiation and wind) and irrigation. Irrigation effects could clearly be distinguished from environmental effects. Interestingly, oscillations in stomatal aperture, which occurred frequently below Turgor Pressures of 100 kPa towards noon at high transpiration or at high wind speed, were reflected in the Pp values. The period of Pressure oscillations was comparable with the period of oscillations in transpiration and photosynthesis. Multiple probe readings on individual leaves and/or on several leaves over the entire height of the plants further emphasised the great impact of this non-invasive Turgor Pressure sensor system for elucidating the dynamics of short- and long-distance water transport in higher plants.
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Radial and axial Turgor Pressure measurements in individual root cells of Mesembryanthemum crystallinum grown under various saline conditions
Plant Cell and Environment, 2006Co-Authors: J. Rygol, U ZimmermannAbstract:Abstract. Radial and axial Turgor Pressure profiles were measured with the Pressure probe in untreated and salt-treated intact roots of Mesembryanthemum crystallinum. The microcapillary of the Pressure probe was inserted step-wise into the root tissue 5, 25 and 50 mm away from the root cap. For evaluation of the data, only those recordings on a given root were used in which four discontinuous increases in Turgor Pressure occurred. These four Turgor Pressure increases could be related to the rhizodermal cells and to the cells in the three cortical layers. The measurements showed that a radial Turgor Pressure gradient of the same magnitude (directed from the third cortical layer to the external medium) existed along the root axis. The magnitude of this Turgor Pressure gradient decreased with increasing salinity (up to 400 mol m-3 NaCl) in the growth medium. Addition of 10 mol m-3 CaCl2 to the 400 mol m-3 NaCl medium partly reduced the salt-induced decrease in Turgor Pressure, but only in cells 25–50 mm away from the root tip. Combined with this effect, a small axial Turgor Pressure gradient was generated, therefore, in the cortex layers which was directed to the root tip. Measurements of the volumetric elastic modulus, ɛ, of the wall of the individual cells showed that the presence of salt considerably reduced the magnitude of this parameter and that addition of Ca2+ to the strongly saline medium partially diminished this decrease. This effect was strongest in cells 50 mm away from the root tip. The magnitude of ɛ of rhizodermal and cortical cells increased along the root axis both in untreated and in salt-treated roots. The ɛ value was significantly smaller for rhizodermal cells compared to the cortical cells, with the exception of cells 50 mm from the tip. In this tissue, rhizodermal and cortical cells exhibited nearly the same values. The decrease of the ɛ-values with salt and the increase along the root axis under the various growth conditions could be correlated with corresponding changes in cell volume. Diurnal changes in Turgor Pressure could not be detected in the individual root cells, with the notable exception of the rhizodermal and cortical cells located in the region 50 mm away from the root tip of the control plants. In these cells, an increase in Turgor Pressure was observed during the morning hours. Determination of the average osmotic Pressure in tissue sections along the roots of control and salt-treated plants revealed that at 400 mol m-3 NaCl the osmotic Pressure gradient between the tissue and the medium is exo-directed, provided that the water is not (partly) immobilized.
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Turgor Pressure changes trigger characteristic changes in the electrical conductance of the tonoplast and the plasmalemma of the marine alga Valonia utricularis
Plant Cell and Environment, 2003Co-Authors: M. Heidecker, L. H. Wegner, K. A. Binder, U ZimmermannAbstract:The giant marine alga Valonia utricularis is capable of regulating its Turgor Pressure in response to changes in the osmotic Pressure of the sea water. The Turgor Pressure response comprises two phases, a fast, exponential phase arising exclusively from water shifting between the vacuole and the external medium (time constant about 10 min) and a second very slow, almost exponential phase adjusting (but not always) the Turgor Pressure near to the original value by release or uptake of KCl (time constant about 5 h). The changes in the vacuolar membrane potential as well as in the individual conductances of the tonoplast and plasmalemma accompanying Turgor Pressure regulation were measured by using the vacuolar perfusion assembly (with integrated microelectrodes, Pressure transducers and Pressure-regulating valves) as described by Wang et al . (J. Membrane Biology 157, 311-321, 1997). Measurements on Pressure-clamped cells gave strong evidence that the Turgor Pressure, but not effects related to water flow (i.e. electro-osmosis or streaming potential) or changes in the internal osmotic Pressure and in the osmotic gradients, triggers the cascade of osmotic and electrical events recorded after disturbance of the osmotic equilibrium. The findings definitely exclude the existence of osmosensors as postulated for other plant cells and bacteria. There was also evidence that Turgor Pressure signals were primarily sensed by ion transporters in the vacuolar membrane because conductance changes were first recorded in the many-folded tonoplast and then significantly delayed in the plasmalemma independent of the direction of the osmotic challenge. Consistently, Turgor Pressure up-regulation (but not down-regulation) could be inhibited reversibly by external addition of the K+ transport inhibitor Ba2+ and/or by the Cl- transport inhibitor 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS). Extensive studies under iso-, hyper- and hypo-osmotic conditions revealed that K+ and Cl- contribute predominantly to the plasmalemma conductance. Addition of 0.3 mm NaCN showed further that part of the K+ and Cl- transporters depended on ATP. These transporters are apparently up-regulated upon hyper-osmotic, but not hypo-osmotic challenge. These findings explain the strong increase of the K+ influx upon lowering Turgor Pressure and the less pronounced Pressure-dependence of the Cl- influx of V. utricularis reported in the literature. The data derived from the blockage experiments under hypo-osmotic conditions were also equally consistent with the experimental findings that the K+ efflux is solely passive and progressively increases with increasing Turgor Pressure due to an increase of the volumetric elastic modulus of the cell wall. However, despite unravelling some of the sequences and other components involved in Turgor Pressure regulation of V. utricularis the co-ordination between the ion transporters in the tonoplast and plasmalemma remains unresolved because of the failure to block the tonoplast transporters by addition of Ba2+ and DIDS from the vacuolar side. [References: 65]
Ulrich Zimmermann - One of the best experts on this subject based on the ideXlab platform.
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Elucidation of the Mechanisms Underlying Hypo-osmotically Induced Turgor Pressure Regulation in the Marine Alga Valonia utricularis
The Journal of Membrane Biology, 2007Co-Authors: Karl-andree Binder, Frank Heisler, Markus Westhoff, Lars H. Wegner, Ulrich ZimmermannAbstract:Exposure of the giant marine alga Valonia utricularis to acute hypo-osmotic shocks induces a transient increase in Turgor Pressure and subsequent back-regulation. Separate recording of the electrical properties of tonoplast and plasmalemma together with Turgor Pressure was performed by using a vacuolar perfusion assembly. Hypo-osmotic Turgor Pressure regulation was inhibited by external addition of 300 μ M of the membrane-permeable ion channel blocker 5-nitro-2-(3-phenylpropylamino)benzoic acid (NPPB). In the presence of 100 μ M NPPB, regulation could only be inhibited by simultaneous external addition of 200 μ M 4,4′-diisothiocyanatostilbene-2,2′-disulfonic acid (DIDS), a membrane-impermeable inhibitor of Cl^− transport. At concentrations of about 100 μ M , NPPB seems to selectively inhibit Cl^− transporters in the tonoplast and K^+ transporters in the plasmalemma, whereas 300 μ M NPPB inhibits K^+ and Cl^− transporters in both membranes. Evidence was achieved by measuring the tonoplast and plasmalemma conductances ( G _t and G _p) in low-Cl^− and K^+-free artificial seawater. Inhibition of Turgor Pressure regulation by 300 μ M NPPB was accompanied by about 85% reduction of G _t and G _p. Vacuolar addition of sulfate, an inhibitor of tonoplast Cl^− transporters, together with external addition of DIDS and Ba^2+ (an inhibitor of K^+ transporters) also strongly reduced G _p and G _t but did not affect hypo-osmotic Turgor Pressure regulation. These and many other findings suggest that KCl efflux partly occurs via electrically silent transport systems. Candidates are vacuolar entities that are disconnected from the huge and many-folded central vacuole or that become disconnected upon disproportionate swelling of originally interconnected vacuolar entities upon acute hypo-osmotic challenge.
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Turgor Pressure changes trigger characteristic changes in the electrical conductance of the tonoplast and the plasmalemma of the marine alga valonia utricularis
Plant Cell and Environment, 2003Co-Authors: M. Heidecker, K. A. Binder, Lars H. Wegner, Ulrich ZimmermannAbstract:The giant marine alga Valonia utricularis is capable of regulating its Turgor Pressure in response to changes in the osmotic Pressure of the sea water. The Turgor Pressure response comprises two phases, a fast, exponential phase arising exclusively from water shifting between the vacuole and the external medium (time constant about 10 min) and a second very slow, almost exponential phase adjusting (but not always) the Turgor Pressure near to the original value by release or uptake of KCl (time constant about 5 h). The changes in the vacuolar membrane potential as well as in the individual conductances of the tonoplast and plasmalemma accompanying Turgor Pressure regulation were measured by using the vacuolar perfusion assembly (with integrated microelectrodes, Pressure transducers and Pressure-regulating valves) as described by Wang et al. (J. Membrane Biology 157, 311–321, 1997). Measurements on Pressure-clamped cells gave strong evidence that the Turgor Pressure, but not effects related to water flow (i.e. electro-osmosis or streaming potential) or changes in the internal osmotic Pressure and in the osmotic gradients, triggers the cascade of osmotic and electrical events recorded after disturbance of the osmotic equilibrium. The findings definitely exclude the existence of osmosensors as postulated for other plant cells and bacteria. There was also evidence that Turgor Pressure signals were primarily sensed by ion transporters in the vacuolar membrane because conductance changes were first recorded in the many-folded tonoplast and then significantly delayed in the plasmalemma independent of the direction of the osmotic challenge. Consistently, Turgor Pressure up-regulation (but not down-regulation) could be inhibited reversibly by external addition of the K+ transport inhibitor Ba2+ and/or by the Cl– transport inhibitor 4,4′-diisothiocyanatostilbene-2,2′-disulfonic acid (DIDS). Extensive studies under iso-, hyper- and hypo-osmotic conditions revealed that K+ and Cl– contribute predominantly to the plasmalemma conductance. Addition of 0.3 mm NaCN showed further that part of the K+ and Cl– transporters depended on ATP. These transporters are apparently up-regulated upon hyper-osmotic, but not hypo-osmotic challenge. These findings explain the strong increase of the K+ influx upon lowering Turgor Pressure and the less pronounced Pressure-dependence of the Cl– influx of V. utricularis reported in the literature. The data derived from the blockage experiments under hypo-osmotic conditions were also equally consistent with the experimental findings that the K+ efflux is solely passive and progressively increases with increasing Turgor Pressure due to an increase of the volumetric elastic modulus of the cell wall. However, despite unravelling some of the sequences and other components involved in Turgor Pressure regulation of V. utricularis the co-ordination between the ion transporters in the tonoplast and plasmalemma remains unresolved because of the failure to block the tonoplast transporters by addition of Ba2+ and DIDS from the vacuolar side.
Roberto L Salomon - One of the best experts on this subject based on the ideXlab platform.
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daytime depression in temperature normalised stem co2 efflux in young poplar trees is dominated by low Turgor Pressure rather than by internal transport of respired co2
New Phytologist, 2018Co-Authors: Roberto L Salomon, Veerle De Schepper, Maria Valbuenacarabana, Kathy SteppeAbstract:Summary Daytime decreases in temperature-normalised stem CO2 efflux (EA_D) are commonly ascribed to internal transport of respired CO2 (FT) or to an attenuated respiratory activity due to lowered Turgor Pressure. The two are difficult to separate as they are simultaneously driven by sap flow dynamics. To achieve combined gradients in Turgor Pressure and FT, sap flow rates in poplar trees were manipulated through severe defoliation, severe drought, moderate defoliation and moderate drought. Turgor Pressure was mechanistically modelled using measurements of sap flow, stem diameter variation, and soil and stem water potential. A mass balance approach considering internal and external CO2 fluxes was applied to estimate FT. Under well-watered control conditions, both Turgor Pressure and sap flow, as a proxy of FT, were reliable predictors of EA_D. After tree manipulation, only Turgor Pressure was a robust predictor of EA_D. Moreover, FT accounted for < 15% of EA_D. Our results suggest that daytime reductions in Turgor Pressure and associated constrained growth are the main cause of EA_D in young poplar trees. Turgor Pressure is determined by both carbohydrate supply and water availability, and should be considered to improve our widely used but inaccurate temperature-based predictions of woody tissue respiration in global models.
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Daytime depression in temperature‐normalised stem CO2 efflux in young poplar trees is dominated by low Turgor Pressure rather than by internal transport of respired CO2
New Phytologist, 2017Co-Authors: Roberto L Salomon, Veerle De Schepper, María Valbuena-carabaña, Kathy SteppeAbstract:Summary Daytime decreases in temperature-normalised stem CO2 efflux (EA_D) are commonly ascribed to internal transport of respired CO2 (FT) or to an attenuated respiratory activity due to lowered Turgor Pressure. The two are difficult to separate as they are simultaneously driven by sap flow dynamics. To achieve combined gradients in Turgor Pressure and FT, sap flow rates in poplar trees were manipulated through severe defoliation, severe drought, moderate defoliation and moderate drought. Turgor Pressure was mechanistically modelled using measurements of sap flow, stem diameter variation, and soil and stem water potential. A mass balance approach considering internal and external CO2 fluxes was applied to estimate FT. Under well-watered control conditions, both Turgor Pressure and sap flow, as a proxy of FT, were reliable predictors of EA_D. After tree manipulation, only Turgor Pressure was a robust predictor of EA_D. Moreover, FT accounted for
Kathy Steppe - One of the best experts on this subject based on the ideXlab platform.
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daytime depression in temperature normalised stem co2 efflux in young poplar trees is dominated by low Turgor Pressure rather than by internal transport of respired co2
New Phytologist, 2018Co-Authors: Roberto L Salomon, Veerle De Schepper, Maria Valbuenacarabana, Kathy SteppeAbstract:Summary Daytime decreases in temperature-normalised stem CO2 efflux (EA_D) are commonly ascribed to internal transport of respired CO2 (FT) or to an attenuated respiratory activity due to lowered Turgor Pressure. The two are difficult to separate as they are simultaneously driven by sap flow dynamics. To achieve combined gradients in Turgor Pressure and FT, sap flow rates in poplar trees were manipulated through severe defoliation, severe drought, moderate defoliation and moderate drought. Turgor Pressure was mechanistically modelled using measurements of sap flow, stem diameter variation, and soil and stem water potential. A mass balance approach considering internal and external CO2 fluxes was applied to estimate FT. Under well-watered control conditions, both Turgor Pressure and sap flow, as a proxy of FT, were reliable predictors of EA_D. After tree manipulation, only Turgor Pressure was a robust predictor of EA_D. Moreover, FT accounted for < 15% of EA_D. Our results suggest that daytime reductions in Turgor Pressure and associated constrained growth are the main cause of EA_D in young poplar trees. Turgor Pressure is determined by both carbohydrate supply and water availability, and should be considered to improve our widely used but inaccurate temperature-based predictions of woody tissue respiration in global models.
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Daytime depression in temperature‐normalised stem CO2 efflux in young poplar trees is dominated by low Turgor Pressure rather than by internal transport of respired CO2
New Phytologist, 2017Co-Authors: Roberto L Salomon, Veerle De Schepper, María Valbuena-carabaña, Kathy SteppeAbstract:Summary Daytime decreases in temperature-normalised stem CO2 efflux (EA_D) are commonly ascribed to internal transport of respired CO2 (FT) or to an attenuated respiratory activity due to lowered Turgor Pressure. The two are difficult to separate as they are simultaneously driven by sap flow dynamics. To achieve combined gradients in Turgor Pressure and FT, sap flow rates in poplar trees were manipulated through severe defoliation, severe drought, moderate defoliation and moderate drought. Turgor Pressure was mechanistically modelled using measurements of sap flow, stem diameter variation, and soil and stem water potential. A mass balance approach considering internal and external CO2 fluxes was applied to estimate FT. Under well-watered control conditions, both Turgor Pressure and sap flow, as a proxy of FT, were reliable predictors of EA_D. After tree manipulation, only Turgor Pressure was a robust predictor of EA_D. Moreover, FT accounted for
Lars H. Wegner - One of the best experts on this subject based on the ideXlab platform.
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effects of environmental parameters and irrigation on the Turgor Pressure of banana plants measured using the non invasive online monitoring leaf patch clamp Pressure probe
Plant Biology, 2010Co-Authors: U Zimmermann, Lars H. Wegner, Or Shapira, Simon Ruger, M Westhoff, Randolph Reuss, P Gessner, Gertraud Zimmermann, Yair Israeli, Aihua ZhouAbstract:Turgor Pressure provides a sensitive indicator for irrigation scheduling. Leaf Turgor Pressure of Musa acuminate was measured by using the so-called leaf patch clamp Pressure probe, i.e. by application of an external, magnetically generated and constantly retained clamp Pressure to a leaf patch and determination of the attenuated output Pressure Pp that is highly correlated with the Turgor Pressure. Real-time recording of Pp values was made using wireless telemetric transmitters, which send the data to a receiver base station where data are logged and transferred to a GPRS modem linked to an Internet server. Probes functioned over several months under field and laboratory conditions without damage to the leaf patch. Measurements showed that the magnetic-based probe could monitor very sensitively changes in Turgor Pressure induced by changes in microclimate (temperature, relative humidity, irradiation and wind) and irrigation. Irrigation effects could clearly be distinguished from environmental effects. Interestingly, oscillations in stomatal aperture, which occurred frequently below Turgor Pressures of 100 kPa towards noon at high transpiration or at high wind speed, were reflected in the Pp values. The period of Pressure oscillations was comparable with the period of oscillations in transpiration and photosynthesis. Multiple probe readings on individual leaves and/or on several leaves over the entire height of the plants further emphasised the great impact of this non-invasive Turgor Pressure sensor system for elucidating the dynamics of short- and long-distance water transport in higher plants.
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a non invasive probe for online monitoring of Turgor Pressure changes under field conditions
Plant Biology, 2009Co-Authors: M Westhoff, Lars H. Wegner, Yishai Netzer, Dirk Zimmermann, Randolph Reuss, Gertraud Zimmermann, Albert Gessner, P Gesner, Ernst Bamberg, Amnon SchwartzAbstract:An advanced non-invasive, field-suitable and inexpensive leaf patch clamp Pressure probe for online-monitoring of the water relations of intact leaves is described. The probe measures the attenuated output patch clamp Pressure, Pp, of a clamped leaf in response to an externally applied input Pressure, Pclamp .P clamp is generated magnetically. Pp is sensed by a Pressure sensor integrated into the magnetic clamp. The magnitude of Pp depends on the transfer function, Tf, of the leaf cells. Tf consists of a Turgor Pressureindependent (related to the compression of the cuticle, cell walls and other structural elements) and a Turgor Pressure-dependent term. Tf is dimensionless and assumes values between 0 and 1. Theory shows that Tf is a power function of cell Turgor Pressure Pc. Concomitant Pp and Pc measurements on grapevines confirmed the relationship between Tf and Pc .P p peaked if Pc approached zero and assumed low values if Pc reached maximum values. The novel probe was successfully tested on leaves of irrigated and nonirrigated grapevines under field conditions. Data show that slight changes in the microclimate and ⁄or water supply (by irrigation or rain) are reflected very sensitively in Pp.
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Elucidation of the Mechanisms Underlying Hypo-osmotically Induced Turgor Pressure Regulation in the Marine Alga Valonia utricularis
The Journal of Membrane Biology, 2007Co-Authors: Karl-andree Binder, Frank Heisler, Markus Westhoff, Lars H. Wegner, Ulrich ZimmermannAbstract:Exposure of the giant marine alga Valonia utricularis to acute hypo-osmotic shocks induces a transient increase in Turgor Pressure and subsequent back-regulation. Separate recording of the electrical properties of tonoplast and plasmalemma together with Turgor Pressure was performed by using a vacuolar perfusion assembly. Hypo-osmotic Turgor Pressure regulation was inhibited by external addition of 300 μ M of the membrane-permeable ion channel blocker 5-nitro-2-(3-phenylpropylamino)benzoic acid (NPPB). In the presence of 100 μ M NPPB, regulation could only be inhibited by simultaneous external addition of 200 μ M 4,4′-diisothiocyanatostilbene-2,2′-disulfonic acid (DIDS), a membrane-impermeable inhibitor of Cl^− transport. At concentrations of about 100 μ M , NPPB seems to selectively inhibit Cl^− transporters in the tonoplast and K^+ transporters in the plasmalemma, whereas 300 μ M NPPB inhibits K^+ and Cl^− transporters in both membranes. Evidence was achieved by measuring the tonoplast and plasmalemma conductances ( G _t and G _p) in low-Cl^− and K^+-free artificial seawater. Inhibition of Turgor Pressure regulation by 300 μ M NPPB was accompanied by about 85% reduction of G _t and G _p. Vacuolar addition of sulfate, an inhibitor of tonoplast Cl^− transporters, together with external addition of DIDS and Ba^2+ (an inhibitor of K^+ transporters) also strongly reduced G _p and G _t but did not affect hypo-osmotic Turgor Pressure regulation. These and many other findings suggest that KCl efflux partly occurs via electrically silent transport systems. Candidates are vacuolar entities that are disconnected from the huge and many-folded central vacuole or that become disconnected upon disproportionate swelling of originally interconnected vacuolar entities upon acute hypo-osmotic challenge.
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Turgor Pressure changes trigger characteristic changes in the electrical conductance of the tonoplast and the plasmalemma of the marine alga valonia utricularis
Plant Cell and Environment, 2003Co-Authors: M. Heidecker, K. A. Binder, Lars H. Wegner, Ulrich ZimmermannAbstract:The giant marine alga Valonia utricularis is capable of regulating its Turgor Pressure in response to changes in the osmotic Pressure of the sea water. The Turgor Pressure response comprises two phases, a fast, exponential phase arising exclusively from water shifting between the vacuole and the external medium (time constant about 10 min) and a second very slow, almost exponential phase adjusting (but not always) the Turgor Pressure near to the original value by release or uptake of KCl (time constant about 5 h). The changes in the vacuolar membrane potential as well as in the individual conductances of the tonoplast and plasmalemma accompanying Turgor Pressure regulation were measured by using the vacuolar perfusion assembly (with integrated microelectrodes, Pressure transducers and Pressure-regulating valves) as described by Wang et al. (J. Membrane Biology 157, 311–321, 1997). Measurements on Pressure-clamped cells gave strong evidence that the Turgor Pressure, but not effects related to water flow (i.e. electro-osmosis or streaming potential) or changes in the internal osmotic Pressure and in the osmotic gradients, triggers the cascade of osmotic and electrical events recorded after disturbance of the osmotic equilibrium. The findings definitely exclude the existence of osmosensors as postulated for other plant cells and bacteria. There was also evidence that Turgor Pressure signals were primarily sensed by ion transporters in the vacuolar membrane because conductance changes were first recorded in the many-folded tonoplast and then significantly delayed in the plasmalemma independent of the direction of the osmotic challenge. Consistently, Turgor Pressure up-regulation (but not down-regulation) could be inhibited reversibly by external addition of the K+ transport inhibitor Ba2+ and/or by the Cl– transport inhibitor 4,4′-diisothiocyanatostilbene-2,2′-disulfonic acid (DIDS). Extensive studies under iso-, hyper- and hypo-osmotic conditions revealed that K+ and Cl– contribute predominantly to the plasmalemma conductance. Addition of 0.3 mm NaCN showed further that part of the K+ and Cl– transporters depended on ATP. These transporters are apparently up-regulated upon hyper-osmotic, but not hypo-osmotic challenge. These findings explain the strong increase of the K+ influx upon lowering Turgor Pressure and the less pronounced Pressure-dependence of the Cl– influx of V. utricularis reported in the literature. The data derived from the blockage experiments under hypo-osmotic conditions were also equally consistent with the experimental findings that the K+ efflux is solely passive and progressively increases with increasing Turgor Pressure due to an increase of the volumetric elastic modulus of the cell wall. However, despite unravelling some of the sequences and other components involved in Turgor Pressure regulation of V. utricularis the co-ordination between the ion transporters in the tonoplast and plasmalemma remains unresolved because of the failure to block the tonoplast transporters by addition of Ba2+ and DIDS from the vacuolar side.
