Changes In Turgor Pressure Research Articles

Day-night changes in leaf water relations associated with the rhythm of crassulacean acid metabolism in Kalanchoë daigremontiana

A study was made of the day-night changes under controlled environmental conditions in the bulk-leaf water relations of Kalanchoë daigremontiana, a plant showing Crassulacean acid metabolism. In addition to nocturnal stomatal opening and net CO2 uptake, the leaves of well-watered plants showed high rates of gas exchange during the whole of the second part of the light period. Measurements with the pressure chamber showed that xylem tension increased during the night and then decreased towards a minimum at about midday; a significant increase in xylem tension was also seen in the late afternoon. Cell-sap osmotic pressure paralleled leaf malate content and was maximum at dawn and minimum at dusk. The relationship between these two variables indicated that the nocturnally synthesized malate was apparently behaving as an ideal osmoticum. To estimate bulk-leaf turgor pressure, values for water potential were derived by correcting the pressurechamber readings for the osmotic pressure of the xylem sap. This itself was found to depend on the malate content of the leaves. Bulk-leaf turgor pressure changed rhythmically during the day-night cycle; turgor was low during the late afternoon and for most of the night, but increased quickly to a maximum of 0.20 MPa around midday. In water-stressed plants, where net CO2 uptake was restricted to the dark period, there was also an increase in bulk-leaf turgor pressure at the start of the light period, but of reduced magnitude. Such changes in turgor pressure are likely to be of considerable ecological importance for the water economy of crassulacean-acid-metabolism plants growing in their natural habitats.

Genetic Relationship between Turgor Maintenance and Growth in Cotton Germplasm1

Seventeen photoperiodic sensitive cotton (Gossypium hirsutum L.) stocks were grown for 2 years (1980 and 1981) at Big Spring, Tex. to evaluate the relationship between turgor maintenance and shoot dry matter accumulation (growth). During each year, leaf‐cutter thermocouple psychrometers were used to measure predawn and midday leaf water and osmotic potentials and to estimate turgor pressure at 50 and 80 days after planting (DAP). Shoot dry weights were measured also at 50 and 80 DAP. The 1st year was hot and dry while the 2nd year had about average temperatures and rainfall. Linear regressions between predawn and midday water and turgor potentials were used to estimate turgor maintenance as i) the change in turgor pressure per unit change of water potential (slope) and, ii) the osmotic potential where zero turgor pressure occurred (X intercept). Significant differences did not occur among the stocks for changes in turgor pressure per unit change in water potential (slope), but they did occur among stocks for osmotic potential at zero turgor (πo) all four sampling dates. Analysis over‐all of the sampling dates, identified a consistently low (T178) and high (T292) stock for πo. Linear correlation and regression coefficients between shoot dry weights and πo were negative and statistically significant during the sampling period (80 DAP, 1980) when the plants were water‐stressed. The linear correlation and regression coefficients were negative, but not statistically significant during the other sampling periods (50 DAP, 1980, and 50 and 80 DAP, 1981). Linear correlation coefficients between the change in shoot dry weights between 50 and 80 DAP in 1980 and the change in πo were negative (r = ‐0.82) and statistically significant. These relationships suggesthat if selection pressure is directed towards enhancing osmotic adjustment under water stress, a reduced growth potential may result.

Effects of external NaCI, and of changes in turgor pressure and volume, on K+ concentrations in Chlorella emersonii

Summary. Soluble potassium concentrations were determined for the slightly vacuolated, unicellular, walled alga Chlorella emersonii. Sap of cells grown in 1 mol m−3 NaCI contained 140 mol m−3 K+ and sap of cells grown in 125, 200, and 335 mol m−3 NaCI contained 160‐180 mol m−3 K +.The possible regulation of K + concentrations by a system of lurgor and volume maintenance was investigated by supplying 3‐0‐methylglucose. This solute accumulates to 85‐230 mol m−3 in C. emersonii, but is not metabolized. Accumulation of 3‐0‐methylglucose increased the volume of cells grown at both low and high NaCI by about 10%. Furthermore, accumulation of 3‐0‐methylglucose also increased turgor pressures of cells grown in 1 and 125 mol m−3 NaCI by 0.3 and 0.2 MPa, respectively. (Similar measurements were not attempted for cells grown in 200 and 335 mol m−3 NaCI, because of the insensitivity of available methods to measure turgor pressure of cells exposed to high external osmotic pressures.)At all NaCI concentrations, the K + concentrations of cells which had accumulated 3‐0‐methylglucose were only 10‐20 mol m−3 lower than K+ in cells which had not been supplied with 3‐0‐methylglucose. In contrast, accumulation of 3‐0‐methylglucose greatly decreased concentrations of the endogenous osmotic solutes, proline and sucrose, which accumulated in cells grown in 125 mol m−3 and higher NaCI concentrations.It is concluded that K+ concentrations in Chlorella emersonii are not controlled by a system of turgor and volume maintenance.

Variation in Leaflet Orientation among Soybean Cultivars1

The degree of leaflet orientation was measured for five soybean (Glycine max L., Merr.) cultivars on an hourly basis from 0620 (0700 EST) until 1820 (1900 EST) hours Local Solar Time during the 10 node stage of development (V10) and from 0520 (0700 EDT) until 1820 (2000 EDT) hours during the beginning pod stage (R3). Measurements were taken on 4 separate days during each growth stage. Our primary objective was to determine if differences exist among soybean cultivars in degree of leaflet orientation.There was significant variation among cultivars in the degree of orientation of the center and the side leaflets of trifoliolates at different times of the day.during both growth stages. The orientation of the center leaflets of a trifoliolate differed from that of the side leaflets. The vertical inclination of the center leaflets tended to change over time while the horizontal inclination remained relatively constant. On the other hand, the horizontal inclination of the side leaflets tended to change over time while their vertical orientation remained relatively constant. However, due to their location relative to each other, the different directions of movement of the center vs. side leaflets seem necessary in order for all three leaflets to attain similar exposures to incoming radiation.Maximum variation in leaf movement was noted from 0820 until 1620 hours during both V10 and R3 stages of development. Higher angles of inclination were obtained and maintained during R3 than V10.The K concentration in pulvini was significantly higher (p < 0.01) during the tense state (higher angles of leaflet orientation) than during the relaxed state. It appears that the K concentration in the pulvinus might have some role in regulating the bending and straightening movements of the pulvini, perhaps by inducing changes in turgor pressure.

Turgor pressure and water transport properties of suspension-cultured cells of Chenopodium rubrum L.

The turgor pressure and water relation parameters were determined in single photoautotrophically grown suspension cells and in individual cells of intact leaves of Chenopodium rubrum using the miniaturized pressure probe. The stationary turgor pressure in suspension-cultured cells was in the range of betwen 3 and 5 bar. From the turgor pressure relaxation process, induced either hydrostatically (by means of the pressure probe) or osmotically, the halftime of water exchange was estimated to be 20±10 s. No polarity was observed for both ex- and endosmotic water flow. The volumetric elastic modulus, ε, determined from measurements of turgor pressure changes, and the corresponding changes in the fractional cell volume was determined to be in the range of between 20 and 50 bar. ε increases with increasing turgor pressure as observed for other higher plant and algal cells. The hydraulic conductivity, Lp, is calculated to be about 0,5-2·10(-6) cm s(-1) bar(-1). Similar results were obtained for individual leaf cells of Ch. rubrum. Suspension cells immobilized in a cross-linked matrix of alginate (6 to 8% w/w) revealed the same values for the half-time of water exchange and for the hydraulic conductivity, Lp, provided that the turgor pressure relaxation process was generated hydrostatically by means of the pressure probe. Thus, it can be concluded that the unstirred layer from the immobilized matrix has no effect on the calculation of Lp from the turgor pressure relaxation process, using the water transport equation derived for a single cell surrounded by a large external volume. By analogy, this also holds true for Lp-values derived from turgor pressure changes generated by the pressure probe in a single cell within the leaf tissue. The fair similarity between the Lp-values measured in mesophyll cells in situ and mesophyll-like suspension cells suggests that the water transport relations of a cell within a leaf are not fundamentally different from those measured in a single cell.

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.

Turgor pressure and cell volume relaxation inHalicystis parvula

The elastic modulus, e, for the cell wall ofHalicystis parvula (defined by $$\varepsilon = V\frac{{dP}}{{dV}}$$ ) was determined by two different ways: On the other hand, e assumes values of about 1 to 2 bar at a low pressure (about 0.05 to 0.15 bar) and increases to about 16 bar at 0.9 bar turgor pressure. Evidence is presented that the short-term elastic coefficient, e, determined from differential changes in cell turgor pressure,dP, and cell volume,dV, reflects the true elastic properties of the cell wall, whereas the long-term elastic coefficient,ɛ s, also includes other mechanical properties of the cell wall, which could not be identified up to now. The hydraulic conductivity,L p, of the cell membrane ofH. parvula was determined by directly measuring both the turgor pressure relaxation process (pressure probe) and the volume changes (microscope) in response to osmotic stress.L p was calculated from the slope of volume-time curves without knowledge of the elastic modulus. It has a value of about 0.8 to 2×10−6 cm sec−1 bar−1. The calculation ofL p from the turgor pressure relaxation process leads to identical results when using the short-term elastic coefficient. Under these conditionsL p assumes values of about 1.5 to 2.5×10−6 cm sec−1 bar−1.L p increases as the plasmolytic point is approached. The result demonstrates that the short-term elastic coefficient determined by the pressure probe technique controls the instantaneous water transport between the cell interior and the external medium. The high extensibility of the cell wall (resulting from the low elastic coefficient) is the reason whyH. parvula exhibits a change in cell volume rather than a change in cell turgor. The results are discussed in relation to pressure measurements in individual cells of higher plant tissues.

Growth and cell wall changes in rice coleoptiles growing under different conditions I. Changes in turgor pressure and cell wall polysaccharides during intact growth

Growth and cell wall changes in rice coleoptiles growing under different conditions I. Changes in turgor pressure and cell wall polysaccharides during intact growth

Dynamics of indirect germination in Phytophthora cactorum sporangia

Indirect germination of the sporangia of the facultative parasite Phytophthora cactorum (Leb. & Cohn) Schroet. (Oomycetes) is described in detail. The significance of the germination vesicle, the cover of the papilla and the opening mechanism of the sporangium are discussed in particular. The entire process of germination is characterized in a mathematical-physical way. The opening of the sporangium and the release of the zoospores are understood as being passive responses to a change of osmotic gradient and turgor pressure inside the sporangium. This release of the zoospores and the nature of the enlargement of the germination vesicle are shown to correspond qualitatively to a curve of pressure decrease and to a model of the stretching of plastic substances, respectively. The maximum size reached by the germination vesicle is approximately the size of the sporangium, and has a surface area 25 times that of the original papilla. The sporangium is only emptied completely if the first eight zoospores pass the pore with more than a certain critical velocity.

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.

Potassium Chloride in the Motor Tissue of Stylidium

Electron probe micro-analysis of the motor tissue in the column of S. graminifolium shows a relatively high concentration of potassium and chloride (about 600 mM) in the anterior cells of the tissue compared with other regions, prior to and immediately after the rapid movement of the column. The distribution of KCl is more widespread during the slower resetting movement of the column. It is suggested that the fast movement (a cross-fertilization mechanism) and the subsequent slow resetting movement are brought about by changes in turgor pressure in the anterior cells, with the principal osmoticum being KCl. The fast movement could be produced by a sudden loss of KCl and water from the anterior cells to the extra-cellular space, after which the KCl would diffuse into other regions of the column, while at the same time being reaccumulated into the anterior cells during the slower time of resetting of the column. When the column is fully reset, most of the KCl would again be in the anterior cells.

Generation of action potentials in Chara corallina by turgor pressure changes

A depolarisation of the membrane potential difference (about-170 mV) of Chara corallina is observed in response to changes in cell turgor pressure using the pressure probe technique. The depolarisation occurs in phase with the pressure pulse (0.2 s duration) and is independent of the direction of the applied pressure gradient. This latter finding is in contradiction to results predicted on the basis of electro-kinetic phenomena. Pressure induced electrical leakages were ruled out by measuring the depolarisation in response to pressure in individual segments of the internode which were electrically isolated from one another. The changes in potential were recorded by external electrodes and an internal electrode which was positioned close to the micropipette of the pressure probe inserted through one of the electrically isolated nodes. The depolarisation in response to increasing positive or negative pressure gradients in the intact node region and in the intact middle segments was comparable to that monitored in the node region containing the pressure probe. Action potentials were initiated when the pressure gradients exceeded at least 2 bar. The action potentials were elicited at random in one of the two compartments adjacent to the node regions, but were never found to be initiated in the node regions themselves. The pressure-induced action potentials are explained in terms of an electro-mechanical compression (or expansion) of a local membrane area and discussed in their relevance to the propagation of pressure signals in response to water and salt stress in higher plants.

Osmotic regulation in the marine alga, Codium decorticatum. I. Regulation of turgor pressure by control of ionic composition.

Codium decorticatum regulates its internal ionic composition and osmotic pressure in response to changes in external salinity. Over a salinity range of 23 to 37% (675 to 1120 mosmol/kg) Codium maintains a constant turgor pressure of 95 mosmol/kg (2.3 atm), observed as a constant difference between internal and external osmotic pressures. The changes in internal osmotic pressure are due to changes in intracellular inorganic ions. At 30 0/00 salinity the major intracellular ions are present in the following concentrations (mmol/kg cell H20): K+, 295; Na+, 255; Cl-, 450. At different salinities intracellular ion concentrations remain in constant proportion to the external ion concentrations, and thus the equilibrium potentials are approximately constant. The potential difference between the vacuole and seawater (-76 mV), whici is predominantly a K+ diffusion potential, is also constant with changing salinity. Comparison of the equilibrium potentials with the vacuole potential suggests that Cl- is actively absorbed and Na+ actively extruded, whereas K+ may be passively distributed between the vacuole and seawater. Turgor pressure does not change with environmental hydrostatic pressure, and increasing the external osmotic pressure with raffinose elicits a response similar to that obtained by increasing the salinity. These two results suggest that the stimulus for turgor regulation is a change in turgor pressure rather than a change in internal hydrostatic pressure or ion concentrations.

Stomatal movements and ion fluxes within epidermis of Commelina communis L.

STOMATAL movements are brought about by differential changes in turgor pressure between guard cells and other epidermal cells1,2. The mechanism by which the turgor changes occur has been investigated for well over a century and a number of hypotheses have been proposed but none has been found to be completely satisfactory. Research in recent years has provided increasing evidence that active ion transport plays a major role in the stomatal mechanism3–6. It has been shown that, as stomata open, certain ions move into the guard cells and that this ion influx may be a dominant factor in raising the guard cell osmotic concentration. As a result, water enters the guard cells and brings about the opening movement. During closure of stomata the process seems to reverse whereby ions are lost by the guard cells. Cl− and K+ seem to be the major ions involved in the stomatal mechanism4,6–10.

Control of RNA level and of RNA ratios in the latex ofHevea brasiliensis Müll. Arg. effect of latex tapping and of growth regulators

The association between latex RNA and latex production was examined using MAK column chromatography techniques. In young untapped trees the introduction of tapping or the treatment of bark with growth regulators resulted in an increase of RNA level and of rRNA/tRNA ratio in the latex. In regularly tapped trees an increase in rRNA but not in tRNA was brought about by increasing the tapping frequency. Treatment with growth regulators had the same effect but essentially only through the related enhancement of latex export from latex vessels. During latex flow, the highest RNA level was registered in latex fractions originating from the most heavily drained areas of bark. Using32P labeling, evidence was obtained that the export of latex results in an enhancement of rRNA migration into the inner latex containing space of the vessels. This is considered as the reason of the generally observed association of high RNA level and of high rRNA/tRNA ratio with high latex yield. It is proposed that in controlling the RNA level and RNA proportions in the latex an important role is played by changes in turgor pressure associated with the loss of latex which may influence the export of RNA from the nucleus through related induction of pressure disequilibrium between the nucleoplasm and the latex cytoplasm.

Plant responses to water deficits, water-use efficiency, and drought resistance

This paper reviews some of the more recent findings on metabolic and physiological aspects of plant—water relations within the context of the topic of this symposium. Examined first are some of the physiological bases for differences among species in water-use efficiency and drought resistance, with special attention given to CO 2 assimilation and transpiration. This is followed by a summary of important known plant responses to water deficits, mainly at the cellular level, and with some emphasis placed on growth as affected by changes in turgor pressure. Possible physicochemical mechanisms underlying these responses are also briefly discussed. The final section speculates on what several of these responses to water deficits may mean in terms of yield for some simple cases. Aspects considered include leaf area development, dry matter accumulation, and the growth of roots relative to that of leaves.

Analysis of transcellular water movement inNitella

The mechanism of transcellular osmosis was analyzed on the assumption that the driving force, which is equal to the osmotic pressure of the mannitol solution given to the exosmosis side, is divided into two parts; one causing the inward water flow on the water side, the other causing the outward water flow on the solution side, when each force drives an equal amount of water. Based on this analysis a new procedure was developed to measure the endosmotic and exosmotic water permeabilities of the membranes independently. It involved measurement of volume of water transported transcellularly, change in turgor pressure, and water permeability of the cell wall alone. Experiments following the new procedure revealed that in aNitella internode positioned across a partition wall with equal length both the endosmotic and exosmotic water permeabilities remained constant during transcellular osmosis induced with 0.4M mannitol, at least for the first minute. It was found that the permeability coefficient for endosmosis (3.9 × 10−5 cm sec−1 atm−1) was very much higher than that for exosmosis (1.4× 10−5 cm sec−1 atm−1). Treatment of the endosmotic cell part with 5% ethanol conspicuously decreased the water permeability of the cell on this side down to 1/2.4 the value obtained without ethanol but never affected the permeability on the other side (exosmosis side).

The water relations of hemlock (Tsuga canadensis). II. The kinetics of water exchange between the symplast and apoplast

We present a theoretical analysis of the events that occur while a plant enclosed in a pressure bomb evolves from one equilibrium balancing pressure to another. The initial rate of efflux from any one cell in response to a pressure increment of ΔP equals (ALp)i ΔP, where (ALp)i is the surface area times hydraulic conductivity of the cell's semipermeable membrane(s). If the volume changes and pressure increment are small, the cell will approach equilibrium exponentially. The half time of the exponential process is governed by (ALp)iki, where ki is the cell constant (= the combined rate of change of osmotic and turgor pressure with the volume expressed from the cell). Experimental studies of the kinetics of water exchange between the symplast and apoplast of hemock (Tsuga canadensis) shoots in a pressure bomb reveal that the cells collectively behave as though they fall into three distinct populations which approach equilibrium with different half times.

Turgor Differences and Water Stress in Maize and Sorghum Leaves During Drought and Recovery

The pressure potentials (turgor pressure) in leaves of maize (Zea mays L.) and grain sorghum (Sorghum vulgare Pers.) plants subjected to water stress in a controlled environment were estimated from measurements of water and osmotic potentials. Changes in turgor pressure were larger in sorghum than in maize during the development of water stress and after re watering. It is suggested that this indicates a lower cell wall elasticity in sorghum than in maize. This fact may affect some of the physiological activities of sorghum.

Cell turgor and selective ion transport of Chaetomorpha linum

The littoral alga Chaetomorpha linum is especially able to maintain a constant turgor pressure in the cell by regulating the internal osmotic pressure, if the salt content of the sea water changes. Experiments in artificial isotonic sea water with a constant sodium concentration, but variable potassium concentrations (from 1 to 50 mMol/1) prove, that the decrease or increase of the potassium concentration in the medium (CK a) is an essential cause for this regulation of the turgor pressure besides the change of the osmotic pressure of the medium, which was thought to be the predominant cause till now. In the examined concentration range the ratio CK a to CK 1 (potassium concentration in the cell) depends linear on CK a in the steady state. At low values of CK a (< 10 mMol/1) the decrease in CK 1 is compensated by a reversible sodium uptake only in part, and this leads to partly high changes in the cell turgor pressure, although the osmotic pressure of the medium remains constant. The results are discussed on the basis of carrier models.