Measurement Of Turgor Pressure Research Articles

Xyloglucan deficiency leads to a reduction in turgor pressure and changes in cell wall properties, affecting early seedling establishment

Xyloglucan is believed to play a significant role in cell wall mechanics of dicot plants. Surprisingly, Arabidopsis plants defective in xyloglucan biosynthesis exhibit nearly normal growth and development. We investigated a mutant line, cslc-Δ5, lacking activity in all five Arabidopsis cellulose synthase like-C (CSLC) genes responsible for xyloglucan backbone biosynthesis. We observed that this xyloglucan-deficient line exhibited reduced cellulose crystallinity and increased pectin levels, suggesting the existence of feedback mechanisms that regulate wall composition to compensate for the absence of xyloglucan. These alterations in cell wall composition in the xyloglucan-absent plants were further linked to a decrease in cell wall elastic modulus and rupture stress, as observed through atomic force microscopy (AFM) and extensometer-based techniques. This raised questions about how plants with such modified cell wall properties can maintain normal growth. Our investigation revealed two key factors contributing to this phenomenon. First, measurements of turgor pressure, a primary driver of plant growth, revealed that cslc-Δ5 plants have reduced turgor, preventing the compromised walls from bursting while still allowing growth to occur. Second, we discovered the conservation of elastic asymmetry (ratio of axial to transverse wall elasticity) in the mutant, suggesting an additional mechanism contributing to the maintenance of normal growth. This novel feedback mechanism between cell wall composition and mechanical properties, coupled with turgor pressure regulation, plays a central role in the control of plant growth and is critical for seedling establishment in a mechanically challenging environment by affecting shoot emergence and root penetration.

Quantifying turgor pressure in budding and fission yeasts based upon osmotic properties

Walled cells, such as plants, fungi, and bacteria cells, possess a high internal hydrostatic pressure, termed turgor pressure, that drives volume growth and contributes to cell shape determination. Rigorous measurement of turgor pressure, however, remains challenging, and reliable quantitative measurements, even in budding yeast are still lacking. Here, we present a simple and robust experimental approach to access turgor pressure in yeasts based upon the determination of isotonic concentration using protoplasts as osmometers. We propose three methods to identify the isotonic condition – three-dimensional cell volume, cytoplasmic fluorophore intensity, and mobility of a cytGEMs nano-rheology probe – that all yield consistent values. Our results provide turgor pressure estimates of 1.0 ± 0.1 MPa for Schizosaccharomyces pombe, 0.49 ± 0.01 MPa for Schizosaccharomyces japonicus, 0.5 ± 0.1 MPa for Saccharomyces cerevisiae W303a and 0.31 ± 0.03 MPa for Saccharomyces cerevisiae BY4741. Large differences in turgor pressure and nano-rheology measurements between the Saccharomyces cerevisiae strains demonstrate how fundamental biophysical parameters can vary even among wild-type strains of the same species. These side-by-side measurements of turgor pressure in multiple yeast species provide critical values for quantitative studies on cellular mechanics and comparative evolution.

Equipment and protocol for measurement of extracellular electrical signals, gas exchange and turgor pressure in plants

We present a detailed protocol for measuring extracellular electrical signals in plants using the electrode insertion technique. Using this approach, it is possible to measure long-distance electrical signaling induced by several stimuli, including wounding, current application, irrigation, burning, and others. Additionally, we describe how to associate gas exchange measurements using an infra-red gas analyzer (IRGA, Model Li-6400, Li-Cor) and turgor pressure measurements using a patch clamp pressure probe (ZIM-probe, YARA ZIM-plant Technology) to measure extracellular electrical signals.• The method requires a complete electrical circuit that includes a measuring device (amplifier and voltmeter) and electrodes that provide a contact between the biological material and the equipment.• The infra-red gas analyzer (IRGA), needs to be grounded because it is an important source of noise for electrophysiological measurements.• The ZIM-probe did not cause any interference in electrical signal measure.• Our approach is useful for plant physiologists wishing to implement the technique of measuring electrical signals in plants, in association with other parameters of plant physiology. In addition, our text was written for agricultural and biological scientists who are not electronics specialists.

A Microrobotic System for Simultaneous Measurement of Turgor Pressure and Cell-Wall Elasticity of Individual Growing Plant Cells

Plant growth and morphogenesis is directed by cell division and the expansion of individual cells. How the tightly controlled process of cell expansion is regulated is poorly understood. We introduce a microrobotic platform able to separately measure the turgor pressure and cell wall elasticity of individual growing, turgid cells by combining microindentation with cell compression experiments. The system independently controls two indenters with geometries at different scales. Indentation measurements are performed automatically by deforming the cells with indenters with a spatial resolution in the nanometer range while recording force and displacement. The dual-indentation technique offers a noninvasive, high-throughput method to characterize the cytomechanics of single turgid cells by separately measuring elasticity and turgor pressure. In this way, the expansion regulation of growing cells can be investigated, as demonstrated here using Lilium longiflorum pollen tubes as an example.

How water availability influences morphological and biomechanical properties in the one-leaf plant Monophyllaea horsfieldii.

In its natural habitat, the one-leaf plant Monophyllaea horsfieldii (Gesneriaceae) shows striking postural changes and dramatic loss of stability in response to intermittently occurring droughts. As the morphological, anatomical and biomechanical bases of these alterations are as yet unclear, we examined the influence of varying water contents on M. horsfieldii by conducting dehydration–rehydration experiments together with various imaging techniques as well as quantitative bending and turgor pressure measurements. As long as only moderate water stress was applied, gradual reductions in hypocotyl diameters and structural bending moduli during dehydration were almost always rapidly recovered in acropetal direction upon rehydration. On an anatomical scale, M. horsfieldii hypocotyls revealed substantial water stress-induced alterations in parenchymatous tissues, whereas the cell form and structure of epidermal and vascular tissues hardly changed. In summary, the functional morphology and biomechanics of M. horsfieldii hypocotyls directly correlated with water status alterations and associated physiological parameters (i.e. turgor pressure). Moreover, M. horsfieldii showed only little passive structural–functional adaptations to dehydration in comparison with poikilohydrous Ramonda myconi.

Effect of modified carbon allocation on turgor, osmolality, sugar and potassium content, and membrane potential in the epidermis of transgenic potato (Solanum tuberosum L.) plants

The effects of modification in sugar concentrations on turgor pressure and membrane potential in epidermal leaf cells of transgenic potato (Solanum tuberosum cv. Desiree) plants were studied. Measurements of turgor pressure were performed by insertion of a micro pressure probe. Osmolality and sugar concentrations were determined by micro analysis of single cell extracts. Membrane potentials and cell diameters were calculated from repeated, computer-controlled scans with voltage-sensitive microelectrodes. Epidermal cells of sucrose transporter antisense plants showed a more than 100% elevation in osmolality and turgor pressure compared to the wild-type. As a consequence, cell diameters were enhanced in this transgenic line. However, membrane potentials were only slightly reduced in sucrose transporter antisense plants. In addition to sucrose transporter antisense lines, transgenic plants that were reduced in their capacity to accumulate starch due to antisense inhibition of the chloroplastic fructose-1,6-bisphosphatase (FBPase) were investigated. These ahtisense plants maintained membrane potential and turgor pressure comparable to the wild-type.

Effect of modified carbon allocation on turgor, osmolality, sugar and potassium content, and membrane potential in the epidermis of transgenic potato (Solanum tuberosum L.) plants

The effects of modification in sugar concentrations on turgor pressure and membrane potential in epidermal leaf cells of transgenic potato (Solanum tuberosum cv. Desirée) plants were studied. Measurements of turgor pressure were performed by insertion of a micro pressure probe. Osmolality and sugar concentrations were determined by micro analysis of single cell extracts. Membrane potentials and cell diameters were calculated from repeated, computer-controlled scans with voltage-sensitive microelectrodes. Epidermal cells of sucrose transporter antisense plants showed a more than 100% elevation in osmolality and turgor pressure compared to the wild-type. As a consequence, cell diameters were enhanced in this transgenic line. However, membrane potentials were only slightly reduced in sucrose transporter antisense plants. In addition to sucrose transporter antisense lines, transgenic plants that were reduced in their capacity to accumulate starch due to antisense inhibition of the chloroplastic fructose-1,6-bisphosphatase (FBPase) were investigated. These antisense plants maintained membrane potential and turgor pressure comparable to the wild-type.

Incomplete turgor adjustment in Cladophora rupestrisunder fluctuating salinity regimes

Turgor pressure fluctuates strongly in Cladophora rupestris subjected to low salinities and shows only a small tendency to readjust to the normal value in full seawater (incomplete turgor adjustment). This was revealed by direct turgor pressure measurements and by chemical analyses of osmotic solutes after exposure of upper and lower shore Cladophora to the different salinity regimes occurring in the intertidal zone or representing steady state osmotic acclimation. The main internal osmotic solutes were K + , Cl − , amino acids, NO 3 − and glycine betaine. Na + , SO 4 2− and PO 4 3− were of less importance. The sum of the charges on the cations was similar to that for the anions. K + , Cl − and, to a lesser extent, amino acids were responsible for limited turgor pressure adjustment which did occur. The concentrations of the major osmotic solutes were influenced not only by salinity but also by light: those of amino acids and NO 3 − were increased while those of K + and Cl − were decreased under illumination. Cladophora populations from the upper and lower shore differed in their ability to restore internal K + and Cl − levels on transfer to full seawater after long term exposure to low salinity. This may indicate ecotypic variation.

Turgor Pressure in Mechanically Impeded Lupin Roots

Seedlings of lupin (Lupinus angustifolius cv. 75A-258) were grown in cores of sandy loam which was compacted to bulk densities of 1.6 and 1.8 Mg m-3 . There was a substantial decrease in root elongation rate at the higher bulk density. After 4-7 d, roots were rinsed free of soil and clamped loosely in a Perspex block for measurement of turgor pressure (P) using a pressure probe. Measurements were made at 3-4 positions on each root, each estimation taking 2 min. Turgor pressures in the terminal 15 mm of the axes ranged between 0.213 and 0.530 at 1.6 Mg m-3 and 0.210 and 0.570 MPa at 1.8 Mg m-3; mean P values were 0.365 and 0.351 MPa in roots growing at 1.6 and 1.8 Mg m-3, respectively. These measurements were made on roots removed from the soil; P could have been greater in roots still growing in compact soil. Anatomical studies showed that the distal boundary of the zone of cell expansion was 2-4 mm nearer the apex in roots growing at 1.8 than at 1.6 Mg m-3. Using this information, we showed that the mean P of expanding tissue was the same in roots of the two treatments. The apparent rise in P near the apex of roots at 1.8 Mg m-3 was not statistically significant. Primary roots growing against high mechanical impedance had a 34% lower rate of elongation and a 22% greater diameter, resulting in nearly identical rates of volume expansion (35.1 and 34.9 mm3 d-1 at 1.6 and 1.8 Mg m-3 respectively). Furthermore, the rate of O2 uptake was the same in 10 mm root apices from both treatments so that there was no evidence that the carbohydrate requirement for respiration was enhanced by high soil strength. Moreover, while mechanical impedance decreased root elongation, it did not significantly affect our estimate of P. We believe that P in lupin roots changes in response to mechanical impedance only when volume expansion or utilization of solutes are affected.

Radial and axial turgor pressure measurements in individual root cells of Mesembryanthemum crystallinum grown under various saline conditions

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.

Automatic Turgor Pressure Recording in Plant Cells

An automatically-regulated pressure probe is described, which facilitates the direct and continuous measurement of turgor pressure and water relation parameters in plant cells. An optoelectronic sensor drives a feed back system so that the position of the oil/cell sap interface in the measur­ing capillary remains constant. The sensor is easily applied to most measurement set-ups by mounting it on a focusing screen connected to the microscope used for observation. The position of the oil/cell sap boundary is sensed by its movement along the image of the capillary on the screen and can be set to any appropriate position. The optical coupling of the regulation signal is advantageous because it leaves the experimenter free to measure the electrical or other parameters of the cell. Experiments on cells of Eremosphaera viridis have shown that the device allows much faster and more exact measurements of water rela­tion parameters, and over longer periods, than the earlier method.

Nephelometric determination of turgor pressure in growing gram-negative bacteria.

Gas vesicles were used as probes to measure turgor pressure in Ancylobacter aquaticus. The externally applied pressure required to collapse the vesicles in turgid cells was compared with that in cells whose turgor had been partially or totally removed by adding an impermeable solute to the external medium. Since gram-negative bacteria do not have rigid cell walls, plasmolysis is not expected to occur in the same way as it does in the cells of higher plants. Bacterial cells shrink considerably before plasmolysis occurs in hyperosmotic media. The increase in pressure required to collapse 50% of the vesicles as external osmotic pressure increases is less than predicted from the degree of osmotically inducible shrinkage seen with this organism or with another gram-negative bacterium. This feature complicates the calculation of the turgor pressure as the difference between the collapse pressure of vesicles with and without sucrose present in the medium. We propose a new model of the relationship between turgor pressure and the cell wall stress in gram-negative bacteria based on the behavior of an ideal elastic container when the pressure differential across its surface is decreased. We developed a new curve-fitting technique for evaluating bacterial turgor pressure measurements.

Photocontrol of extension growth: a biophysical approach

The analysis of plant growth as a physical process is briefly reviewed. Growth requires the coordinated uptake of water and the irreversible expansion of the cell wall. Any agent that affects the growth rate must act on one or more of the parameters governing water absorption (e.g. the hydraulic conductivity or the difference in osmotic pressure of the cell contents and the water source) or cell wall expansion (e.g. wall extensibility or the yield threshold). When the hydraulic conductivity of the pathway for water transport is small enough to impede the rate of cell enlargement, a substantial gradient in water potential within the growing tissue will develop to sustain the absorption of water. In such a case, the analysis shows that turgor pressure is a key indicator for determining whether an agent acts predominantly on the osmotic properties of the tissue or on the cell wall properties. Furthermore, the dynamic response to a slight perturbation from steady-state conditions is shown to be a function of parameters for both the water relations and cell wall expansion of the tissue. Blue irradiation of etiolated seedlings causes a large inhibition of stem elongation with lag times as short as 30 s and half-times as short as 20 to 25 s. The biophysical mechanism of blue-light suppression of growth was studied in cucumber and sunflower seedlings by means of direct and indirect measurements of turgor pressure. The results indicate that (a) blue light suppresses growth by influencing the cell wall properties of the growing tissue, and (b) the hydraulic conductivity of the growing tissue is large enough for it not to limit the rate of cell enlargement.

Evaluation of a Non-Destructive Method for Measuring Turgor Pressure inHelianthus

The portable instrument described by Heathcote, Etherington, and Woodward (1979) for the non-destructive measurement of turgor pressure was evaluated in Helianthus annuus and Helianthus paradoxus. A good correlation was obtained between turgor pressure measured with the instrument and turgor pressure estimated by the pressure-volume technique for individual leaves allowed to dry after excision; however, variation in both the intercept and slope of the relationship occurred between leaves. Consequently, there was no correlation between the output of the instrument for individual leaves and the turgor pressure of the same leaves estimated by conventional methods. Moreover, for a given leaf, the instrument had only a limited ability to detect temporal variation in turgor pressure when compared with turgor pressure calculated from measured values of leaf water potential and leaf osmotic potential. The instrument's output was influenced by its proximity to major veins and by leaf thickness. We conclude that variability in leaf thickness and the presence of large veins limits its usefulness for measurement of turgor pressure in Helianthus.

Direct turgor pressure measurements in individual leaf cells of Tradescantia virginiana

The water relations of leaves of Tradescantia virginiana were studied using the miniaturized pressure probe (Hüsken, E. Steudle, Zimmermann, 1978 Plant Physiol. 61, 158-163). Under well-watered conditions cell turgor pressures, P o, ranged from 2 to 8 bar in epidermal cells. In subsidiary cells P o was about 1.5 to 4.5 bar and in mesophyll cells about 2 to 3.5 bar. From the turgor pressure, relaxation induced in individual cells by changing the turgor pressure directly by means of the pressure probe, the half-time of water exchange was measured to be between 3 and 100 s for the epidermal, subsidiary, and mesophyll cells. The volumetric elastic modulus, ε, of individual cells was determined by changing the cell volume by a defined amount and simultaneously measuring the corresponding change in cell turgor pressure. The values for the elastic modulus for epidermal, subsidiary, and mesophyll cells are in the range of 40 to 240 bar, 30 to 200 bar, and 6 to 14 bar, respectively. Using these values, the hydraulic conductivity, L p, for the epidermal, subsidiary, and mesophyll cells is calculated from the turgor pressure relaxation process (on the basis of the thermodynamics of irreversible processes) to be between 1 and 55·10(-7) cm s(-1) bar(-1). The data for the volumetric elastic modulus of epidermal and subsidiary cells indicate that the corresponding elastic modulus for the guard cells should be considerably lower due to the large volume changes of these cells during opening or closing. Recalculation of experimental data obtained by K. Raschke (1979, Encycl. Plant Physiol. N.S., vol. 7, pp 383-441) on epidermal strips of Vicia faba indicates that the elastic modulus of guard cells of V. faba is in the order of 40-80 bar for closed stomata. However, with increasing stomatal opening, i.e., increasing guard cell volume, ε decreases. Therefore, in our opinion Raschke's results would indicate a relationship between guard cell volume and ε which would be inverse to that for plant cells known in the literature. ε assumes values between 20-40 bar when the guard cell colume is soubled.

The Contribution of Photosynthate to Turgor Pressure Rise in the Planktonic Blue-green AlgaAnabaena flos-aquae

The turgor pressure of the cells of the planktonic blue-green alga Anabaena flos-aquae increases following transfer of the alga from low light intensity to high light intensity. Up to half of this rise in turgor pressure may be due to the accumulation of soluble photosynthate. This estimate is based on direct measurement of cell water, extraction and fractionation of re labelled soluble products of photosynthesis, and simultaneous measurement of turgor pressure

Water relations of the epidermal bladder cells of the halophytic species Mesembryanthemum crystallinum: Direct measurements of hydrostatic pressure and hydraulic conductivity

Water exchange between the bladder cells of stems of the halophytic species Mesembryanthemum crystallinum and the subepidermal cortical cell layers was determined by direct cell turgor pressure measurements using a pressure probe. Treating the system bladder cell/subepidermal cortex as two homogeneous elastic compartments the hydraulic conductivity, L p, of the barrier separating both compartments was found to be L p=2·10(-6) cm ·s(-1)·bar(-1). As discussed, this value essentially reflects the hydraulic conductivity of the bladder cell membrane, which is unusually high compared with the values expected for higher plant cells. The L p-values did not show a dependence on cell turgor pressure over a large pressure range (0.1 to 6 bar) nor on the salinity of the bladder sap (osmolarity range: 500 to 1700 mOsmol). Furthermore, the stationary pressure-values obtained in the pressure-flow experiments point to unusually high permeabilities of the bladder membrane to electrolytes (KCl and NaCl). The unique transport properties of the bladder cell membrane for salt and water suggest a special physiological function of the bladders in the water economy of the plant. It is assumed that the bladders form a reservoir for salts and water in the plant which upon osmotic stress acts as a buffering system to protect the photosynthetic tissue from osmotic injury.

Measurement of Turgor Pressure and Its Gradient in the Phloem of Oak

A direct method is described for measuring the pressure in secondary phloem sieve tubes of oak trees. One end of a 26-gauge stainless steel tube was shaped such that when it penetrated the outer bark and transected a few sieve elements, it was stopped by the xylem so that small openings in the end allowed phloem sap to enter the tube. The other end of the stainless tube (phloem needle) was joined to a long glass capillary sealed at its other end to form a manometer for measuring phloem sap pressure. A method for measuring the average osmotic and turgor pressures in cells of leaves is also described. Phloem turgor pressures varied greatly in a series of phloem punctures around the trunk at 1.5 and at 6.3 meters. The variation in turgor pressure was always greater than the variation in osmotic pressure. In a series of turgor pressures arranged in descending order, the values in a sequence for the upper level was usually a little (0-3 atm) larger than the values for the lower level. These results may suggest that translocation of assimilate is favored by a small turgor pressure gradient, but they do more to emphasize the complications in measuring gradients in an elastic low resistance distribution system composed of contiguous longitudinal conduits. The results also imply that the sieve tubes are inflated with assimilate fluid under high pressure which can readily move longitudinally and with less pressure drop than would be necessary if the sieve tubes were rigid.

THE EFFECT OF LEAF WATER BALANCE ON THE SUSCEPTIBILITY OF FRENCH BEAN TO TOBACCO NECROSIS VIRUS

French beans were germinated under constant temperature, relative humidity, and day period, and were transferred to Hoagland's culture solution. Variations of the preinoculation treatment were begun at an age of 10 days for a period of 24 h. Treatments were selected which would induce turgor changes in the primary leaves.It was observed that susceptibility to tobacco necrosis virus infection was increased by preinoculation conditions of continuous darkness, high relative humidity, and low suction tension of the culture solution. Susceptibility was lowered by preinoculation conditions of continuous light, low relative humidity, and high suction tension of the culture solution.Diffusion pressure deficit, osmotic pressure, and turgor pressure measurements were made with the primary leaves at time of inoculation. Considerable agreement was noted between turgor changes and susceptibility.Preinoculation treatments such as darkening will alter susceptibility through changes in turgor pressure. It is suggested that there may be a direct effect of leaf turgor on the number of infectible sites.