Turgor-Regulated Sugar Release from the Source Leaves of Sugarbeet (Beta vulgaris L.)

Under mild water stress conditions, a potential site of regulationfor distribution of sucrose between osmotic adjustment and exportmay be at the mesophyll plasmalemma and/or tonoplast. This possibilitywas examined in attached leaves of sugarbeet (Beta vulgarisL.), labeled with ¹⁴CO₂. Leaf discs were exposed to solutionscontaining 400 or 50 mM mannitol to generate "low" or "high"cellular turgor, respectively and release of labeled soluteswas monitored. Response to changes in cell turgor was rapidand reversible. High turgor increased solute efflux rates todouble those at low turgor conditions. Approximately 30% and55% of the released label was in the sugar (sucrose and hexose)fractions at low and high turgor, respectively. Paramercuribenzenesulfonic acid (PCMBS) had no effect on efflux, but N-ethylmaleimide(NEM) and carbonylcyanide-m-chlorophenyl hydrazone (CCCP) enhancedefflux, especially at high turgor. Presence of unlabeled sucrosegreatly enhanced efflux in a turgor-dependent manner; suggestinga sucrose exchange system. While influx across the plasmalemmais both turgor sensitive and carrier-mediated, turgor-regulatedplasmalemma efflux did not appear to involve a carrier. Boththe tonoplast and plasmalemma appeared to be involved in turgor-inducedsugar efflux. Turgor-regulated efflux of solutes from vacuole-containingcells (mesophyll), may contribute to the establishment of ahomeostatic turgor pressure in these cells. (Received June 9, 1989; Accepted September 5, 1989)     

Sucrose Leakage from Isolated Parenchyma of Sugar Beet Roots

The kinetics of sugar efflux from slices of sugar beet rootswas investigated using washing solutions of different osmoticpressure and calcium concentration. The leakage of sucrose isstrongly reduced in solutions of high osmotic pressure (>0·8MPa) or high calcium concentration (10 mM). Turgor-dependentnecrosis of parenchyma cells (plasmoptysis) is the main causeof sucrose efflux from the tissue in hypotonic media with lowcalcium activity. This was shown by good correlation betweenthe percentage of leaked sucrose and the percentage of tissuewater, which was in the free space after the washing procedure.The kinetics of sugar leakage from beet root parenchyma is nobasis for the estimation of the sugar contents of the free spaceor the cytoplasm in situ.     

Effects of Water and Turgor Potential on Malate Efflux from Leaf Slices of Kalanchoë daigremontiana

Malate efflux from leaf cells of the Crassulacean acid metabolism plant Kalanchoë daigremontiana Hamet et Perrier was studied using leaf slices submerged in experimental solutions. Leaves were harvested at the end of the dark phase and therefore contained high malate levels. Water potentials of solutions were varied between 0 and −5 bar using mannitol (a slowly permeating solute) and ethylene glycol (a rapidly permeating solute), respectively. Mannitol solutions of water potentials down to −5 bar considerably reduced malate efflux. The slowly permeating solute mannitol reduces both water potential and turgor potential of the cells. The water potential of a mannitol solution of −5 bar is just above plasmolyzing concentration. Malate efflux in ethylene glycol at −5 bar was only slightly smaller than at 0 bar, and much higher than in mannitol at −5 bar. Tissues in rapidly permeating ethylene glycol would have turgor potentials similar to tissues in 0.1 mm CaSO₄. The results demonstrate that malate efflux depends on turgor potential rather than on water potential of the cells.     

Effects of osmotic gradients on vacuolar malic Acid storage: a basic principle in oscillatory behavior of crassulacean Acid metabolism

Malate synthesis by CO₂ dark fixation and malate accumulation in the vacuoles of leaf slices of Kalanchoë daigremontiana Hamet et Perrier, a plant performing crassulacean acid metabolism, occurs only in external solutions where the osmotic pressure difference between the cells and the medium is low. Conversely, malate loss from the vacuoles depends on a high osmotic pressure difference between the cells and the medium and is observed in media of low osmotic pressure. This suggests that the diurnal oscillations of malate levels in crassulacean acid metabolism leaf cells are regulated by osmotic gradients. These findings support a model which is introduced to explain how the rhythm of crassulacean acid metabolism may function in the intact plant.     

Derivation of a weighted-average reflection coefficient for mesophyll cell membranes of Kalanchoë daigremontiana

In a study with the crassulacean acid metabolism (CAM) plant Kalanchoë daigremontiana Hamet et Perr. using the pressure probe, Rygol et al. (1987, Planta 172, 487–4493) calculated a value for the reflection coefficient () for malate of 0.6. This value was derived from the relationship between measured changes in cell turgor pressure and malic-acid concentration, and would imply that malate was a relatively ineffective osmoticum. Here we show that the calculation of Rygol et al. (1987) involved the implicit assumption that xylem tension was constant with changing cell turgor pressure and osmotic pressure. This has been shown not to be the case using the pressure-chamber technique. We present an alternative method of deriving a weighted-mean value of a for K. daigremontiana and show that it is not significantly different from 1.0.Part of this work was carried out at the University of Edinburgh, to whom we are grateful for facilities, with funding from the Agricultural and Food Research Council, UK. Murphy is grateful to the board of management of the Glasstone Benefaction for financial support at the University of Oxford. We thank Prof. U. Zimmermann for his comments on an earlier version of this paper.     

Net efflux of Cl− during hypotonic turgor regulation in a brackish water alga Lamprothamnium*

Abstract. Net efflux of Cl^? was measured potentiometrically (Ag/AgCl electrode) during turgor regulation which was induced by hypotonic treatment (hypotonic turgor regulation) in the alga Lamprothamnium succinctum. The efflux of Cl^? reached the peak value (11 μmol m ^?2s^?1) several minutes after the hypotonic treatment was started and then declined. The efflux of Cl^? and inhibition of the cytoplasmic streaming [reflection of an increase in cytoplasmic concentration of free Ca²⁺([Ca²⁺]_c)] were blocked under a low external concentration of Ca²⁺ ([Ca²⁺]_e) (0·01 mol m^?3) and resumed after raising [Ca²⁺]_e to the normal value (3·9 mol m^?3). The decrease in cell-osmotic pressure upon hypotonic treatment was inhibited by lowering either turgor pressure or [Ca^2h]_e. The inhibition was reflected in decreases of both the efflux of Cl^? and the membrane conductance. Recovery of the cytoplasmic streaming from the inhibition was also accelerated by the same treatments. It is concluded that an increase in turgor pressure is continuously sensed by the cells and that continuous presence of external Ca²⁺ is necessary for the hypotonic turgor regulation.     

Turgor and Longitudinal Tissue 12Helianthus annuus

The quantitative relationship between turgor and the pressureexerted by the inner tissues (cortex, vascular tissue, and pith)on the peripheral cell walls (longitudinal tissue pressure)was investigated in hypocotyls of sunflower seedlings (Helianthusannuus L.) In etiolated hypocotyls cell turgor pressures, asmeasured with the pressure probe, were in the range 0·38to 0·55 MPa with an average of 0·48 MPa. In irradiatedhypocotyls turgor pressures varied from 0·40 to 0·57MPa with a, mean at 0·49 MPa. The pressure exerted bythe inner tissues on the outer walls was estimated by incubatingpeeled sections in a series of osmotic test solutions (polyethyleneglycol 8000). The length change was measured with a transducer.In both etiolated and irradiated hypocotyls an external osmoticpressure of 0·5 MPa was required to inhibit elongationof the inner tissues, i.e. the average cell turgor and the longitudinaltissue pressure are very similar quantities. The results indicatethat the turgor of the inner tissues is displaced to and borneby the thick, growth-limiting peripheral cell walls of the hypocotyl. Key words: Helianthus annuus, hypocotyl growth, tissue pressure, turgor pressure, wall stress     

Injection of a Ca2+-Chelating Agent into the Cytoplasm Retards the Progress of Turgor Regulation upon Hypotonic Treatment in the Alga, Lamprothamnium

The turgor regulation induced by hypotonic treatment (hypotonicturgor regulation) in the brackish-water alga Lamprothamniumsuccinctum is accompanied by a transient increase in the electricalconductance of the membrane, membrane depolarization and a transientincrease in the cytoplasmic concentration of free Ca²⁺ ([Ca²⁺([Ca²⁺]_c) (Okazaki and Tazawa 1990). In the present study, weloaded a Ca²⁺-chelating agent, EGTA, into the cytoplasm by mechanicalinjection in order to suppress the increase in [Ca²⁺]_c thatoccurs during the hypotonic turgor regulation. The rate of thecytoplasmic streaming was taken as an indirect indicator of[Ca²⁺]_c, since cytoplasmic streaming has been shown to be inhibitedby high [Ca²⁺]_c in Lamprothamnium cells. The lag time for theinhibition of the cytoplasmic streaming upon hypotonic treatmentwas significantly prolonged in EGTA-loaded cells as comparedto that in intact cells. This result indicates that the loadedcytoplasmic EGTA functioned as a buffer of Ca²⁺ to retard theincrease in [Ca²⁺]_c. It took a longer time for the membraneconductance to reach the peak value in EGTA-loaded cells thanin intact cells. Membrane depolarization was affected to aninsignificant extent by the cytoplasmic EGTA. The regulationof turgor pressure itself was partially inhibited. These resultsstrongly support the idea that the net efflux of ions that occursduring the recovery from hy-potonically induced changes in turgorpressure is controlled by [Ca²⁺]_c. (Received August 22, 1990; Accepted December 6, 1990)     

The effect of cell turgor on sugar uptake in strawberry fruit cortex tissue

A reduction in cell turgor has been shown to stimulate sugar uptake in several plant sink tissues and it may regulate the import of assimilate into the sink apoplast, as well as maintain cell turgor. To determine whether cell turgor influences sugar uptake by strawberry (Fragaria x ananassa Duch. cv. Brighton) fruit cortex tissue, disks were cut from greenhouse-grown primary fruit at the green-white stage of development and placed in buffered incubation solutions containing either mannitol or ethylene glycol as an osmoticum. Cell turgor of fruit disks was calculated from the difference between the water potential of bathing solution and tissue solute potential after incubation at various osmolarities. Cell turgor increased when tissue disks were placed into mannitol incubation solutions more dilute than the water potential of fresh tissue (about 415 mOsmol kg^?1). The rate of uptake of [¹⁴C]-sucrose or [¹⁴C]-glucose decreased as osmolarity of the incubation solution increased, i.e. as cell turgor declined. Cell turgor and the rate of [¹⁴C]-sucrose uptake were unaffected when rapidly permeating ethylene glycol was used as an osmoticum. A decrease in cell turgor reduced both the V_max of the saturable (carrier mediated) kinetic component of sucrose uptake, and the slope of the linear (diffusional) component. The sulfhydryl binding reagent p-chloromercuibenzenesulfonic acid, an inhibitor of the plasma membrane sucrose carrier, strongly inhibited only the saturable component of sucrose uptake. Increased uptake of the nonmetabolizable sugar, O-methyl-glucose, at high turgor was similar to that of glucose, indicating that carrier activity was influenced by cell turgor, not cell metabolism. Turgor did not influence efflux of [¹⁴C]-sucrose from disks and had no effect on cell viability. Strawberry fruit cells do not possess a sugar uptake system that is stimulated by a reduction in turgor.     

Experimental evidence for negative turgor pressure in small leaf cells of Robinia pseudoacacia L versus large cells of Metasequoia glyptostroboides Hu et W.C.Cheng. 1. Evidence from pressure‐volume curve analysis of dead tissue.

This paper provides a mini‐review of evidence for negative turgor pressure in leaf cells starting with experimental evidence in the late 1950s and ending with biomechanical models published in 2014. In the present study, biomechanical models were used to predict how negative turgor pressure might be manifested in dead tissue, and experiments were conducted to test the predictions. The main findings were as follows: (i) Tissues killed by heating to 60 or 80 °C or by freezing in liquid nitrogen all became equally leaky to cell sap solutes and all seemed to pass freely through the cell walls. (ii) Once cell sap solutes could freely pass the cell walls, the shape of pressure‐volume curves was dramatically altered between living and dead cells. (iii) Pressure‐volume curves of dead tissue seem to measure negative turgor defined as negative when inside minus outside pressure is negative. (iv) Robinia pseudoacacia leaves with small palisade cells had more negative turgor than Metasequoia glyptostroboides with large cells. (v) The absolute difference in negative turgor between R. pseudoacacia and M. glyptostroboides approached as much as 1.0 MPa in some cases. The differences in the manifestation of negative turgor in living versus dead tissue are discussed.     

Water relations and growth of tomato fruit pericarp tissue

The water relations of young tomato fruit pericarp tissue were examined and related to tissue expansion. The relationship between bulk turgor pressure and tissue expansion (as change in fresh mass or length of tissue) was determined in slices of pericarp cut from young, growing fruit by incubation in different osmotic concentrations of polyethylene glycol 6000 or mannitol. The bulk turgor of this tissue was low (about 0.2 MPa), even in fruit from plants that were otherwise fully turgid, whether measured psychrometrically or by length change in osmotic solutions. The rate of tissue growth at maximum turgor was less than that at moderate turgor unless calcium was added to the incubation medium. However, added calcium also decreased the rate of growth at lower turgor pressures. Yield turgor was < 0.1 MPa, but it was increased by the addition of calcium ions. Electrolyte leakage from tissue was greatest at maximum turgor pressure but was decreased by the addition of calcium ions or osmoticum. Tissue growth was unaffected by a range of plant growth regulators (IAA, abscisic acid, benzyladenine and GA₃) but was inhibited, particularly at high turgor, by low concentrations of malic or citric acid. The low turgor pressure of pericarp tissue could be due to the presence of apoplastic solutes within the pericarp, and evidence for this is discussed. Thus, fruit tissue may be able to maintain optimal expansion rates only at moderate turgor and low calcium concentration.     

Turgor-dependent unloading of photosynthates from coats of developing seed of Phaseolus vulgaris and Vicia faba. Turgor homeostasis and set points

Key physiological characteristics of turgor-dependent efflux of photosynthates were examined using excised coats and cotyledons of developing Phaseolus vulgaris (cv. Redland Poineer) and Vicia faba (cv. Coles Prolific) seed during the linear phase of seed fill. Exposure to solutions of high osmotic potential inhibited net uptake of [¹⁴C]sucrose by cotyledons at developmental stages less than 60% of their final dry weight. The effect could not be fully reversed by transferring cotyledons to solutions set at lower osmotic potentials. The inhibition became apparent at osmotic potentials that were higher than those that caused stimulation of efflux from seed coats. Net [¹⁴C]sucrose uptake by cotyledons at more advanced stages of development was unaffected by external osmotic potential. Specified tissue layers were removed from seed coats by pretreatment with pectinase. Efflux studies with the pectinase-modified coats of Phaseolus and Vicia seed demonstrated that the cellular site of turgordependent efflux was the ground parenchyma and thin-wall parenchyma transfer cells, respectively. Coats subjected to long-term (hours) incubations, under hypo-osmotic conditions, exhibited the capacity for turgor regulation. This was mediated by turgor-dependent efflux of solutes. The solutes exchanged were of nutritional significance to the developing embryo. The relationship between efflux and coat turgor was characterised by a turgor-independent phase at low turgors. Once turgor exceeded a minimal value (set point), efflux increased in proportion to the magnitude of the turgor deviation (error signal) from the set point. For coats of sink-limited seed of Vicia and Phaseolus, efflux exhibited apparent saturation at turgors above 0.25 and 0.5 MPa respectively. The putative turgor set point and slope of the turgor-dependent component of efflux varied with seed development, the prevailing source/sink ratio and genetic differences in seed growth rate. The nature of these kinetic variations was compatible with the competitive ability of the seed. A turgor homeostat model is proposed that incorporates the observed functional attributes of turgor-dependent efflux. Operationally, the model provides a mechanistic basis for the integration of assimilate demand by the cotyledons with assimilate import into and unloading from the seed coat.     

Increase in cytoplasmic calcium content in internodal cells of Lamprothamnium upon hypotonic treatment

Abstract Internodal cells of Lamprothamnium succinctum, a brackish water Characeae, regulate turgor pressure in response to changes in external osmotic pressure (turgor regulation). When internodal cells were transferred to a hypotonic medium containing 3.9 mol m^?3 Ca²⁺, the cell osmotic pressure decreased and the original turgor pressure was recovered. During turgor regulation Ca content of the cytoplasm increased significantly. Lowering the external Ca²⁺ concentration from 3.9 to 0.01 mol m^?3 inhibited this increase in cytoplasmic calcium content. In a hypotonic medium containing 0.01 mol m^?3 Ca²⁺, turgor regulation was inhibited as previously reported (Okazaki & Tazawa, 1986a). Thus transient increase in cytoplasmic Ca, probably in the ionized form, induced by hypotonic treatment may play an important role in turgor regulation.     

Osmotic regulation of assimilate unloading from seed coats of Vicia faba. Role of turgor and identification of turgor-dependent fluxes

Osmotic regulation of assimilate efflux from excised coats of developing Vicia faba (cv. Coles Prolific) seed was examined by exposing these to bathing solutions (adjusted to –0. 02 to –0. 75 MPa with sorbitol) introduced into the cavity vacated by the embryo. ¹⁴C photosynthate efflux was found to be independent of solution osmotic potentials below –0. 63 MPa. At higher osmotic potentials, efflux was stimulated and exhibited a biphasic response to osmotic potential with apparent saturation being reached at –0. 37 MPa. Efflux could be repeatedly stimulated and slowed by exposing seed coats to solutions of high and low osmotic potentials, respectively. Manipulation of components of tissue water potential, with slowly- and rapidly-permeating osmotica, demonstrated that turgor functioned as the signal regulating ¹⁴C photosynthate efflux. Com-partmental analysis of ¹⁴C photosynthate preloaded seed coats was consistent with exchange from 4 kinetically-distinct compartments. The kinetics of turgor-dependent efflux exhibited characteristics consistent with the transport mechanism residing in the plasma membranes of the unloading cells. These characteristics included the rapidity (<2 min) of the efflux response to turgor increases, similar rate constants for efflux from the putative turgor-sensitive and cytoplasmic compartments and the apparent small pool size from which turgor-dependent efflux could repeatedly occur. In contrast, influx of [¹⁴C] sucrose across the plasma and tonoplast membranes was found to be insensitive to turgor. The plasma membrane [¹⁴C] sucrose influx was unaffected by p-chloromercuribenzenesulfonic acid and erythrosin B and exhibited a linear dependence on the external sucrose concentration. This behaviour suggested that influx across the plasma membrane occurs by passive diffusion. Preloading excised seed coats with a range of solutes demonstrated that turgor-dependent efflux exhibited partial solute selectivity. Based on these findings, it is proposed that turgor controls assimilate exchange from the seed coat by regulating an efflux mechanism located in the plasma membranes of the unloading cells.     

A Comparison of Methods for Measuring Turgor Pressures and Osmotic Pressures of Cells of Red Beet Storage Tissue

Two methods for measuring the turgor pressures of cells in discsof storage tissue of red beet (Beta vulgaris L.) were compared,and a centrifugation method for extracting sap from frozen andthawed tissue was evaluated. Turgor pressures were measureddirectly using a pressure probe, or indirectly using a vapourpressure osmometer. With the latter, discs were placed directlyin the osmometer chamber and turgor was calculated as the differencein osmotic pressure before and after freezing and thawing. Turgorin freshly cut discs, measured with the pressure probe, wasbetween 0-012 MPa and 0.118 MPa with a mean ±s.d. of0.092±;0.032 MPa (n = 24). That measured with the osmometervaried between 0.08 MPa and 0.12 MPa with a mean ±s.d.of 0.09±0.10 MPa (n = 54). After vacuum infiltrationof discs with distilled water, the turgor measured with thepressure probe increased to 1.05–1.12 MPa. Turgor measuredwith the osmometer also increased after vacuum infiltrationbut was, on average, 12% lower than that measured with the pressureprobe. Overall, the results suggest that for routine measurements,the osmometer can provide reasonable estimates of the turgorof cells in beet discs. This is because a number of factorsthat, potentially, could interfere with this method have onlya small effect in this tissue. None of the measured turgorsis indicative of that occurring in intact storage roots becauseboth excision and vacuum infiltration of discs alter the concentrationsof solutes in the extracellular space. The osmotic pressureof sap extracted by centrifugation from frozen and thawed discswas not significantly different from that measured by placingfrozen and thawed discs directly in the osmometer. Solute concentrationsin the sap were not significantly different from those measuredby chemical extraction of discs. Key words: Beta vulgaris, Osmotic pressure, Turgor pressure     

The regulation of turgor pressure during sucrose mobilisation and salt accumulation by excised storage-root tissue of red beet

The changes in turgor pressure that accompany the mobilisation of sucrose and accumulation of salts by excised disks of storage-root tissue of red beet (Beta vulgaris L.) have been investigated. Disks were washed in solutions containing mannitol until all of their sucrose had disappeared and then were transferred to solutions containing 5 mol·m^-3 KCl+5 mol·m^-3 NaCl in addition to the mannitol. Changes in solute contents, osmotic pressure and turgor pressure (measured with a pressure probe) were followed. As sucrose disappeared from the tissue, reducing sugars were accumulated. For disks in 200 mol·m^-3 mannitol, the final reducing-sugar concentration equalled the initial sucrose concentration so there was no change in osmotic pressure or turgor pressure. At lower mannitol concentrations, there was a decrease in tissue osmotic pressure which was caused by a turgor-driven leakage of solutes. At concentrations of mannitol greater than 200 mol·m^-3, osmotic pressure and turgor pressure increased because reducing-sugar accumulation exceeded the initial sucrose concentration. When salts were provided they were absorbed by the tissue and reducing-sugar concentrations fell. This indicated that salts were replacing sugars in the vacuole and releasing them for metabolism. The changes in salf and sugar concentrations were not equal because there was an increase in osmotic pressure and turgor pressure. The amount of salt absorbed was not affected by the external mannitol concentration, indicating that turgor pressure did not affect this process. The implications of the results for the control of turgor pressure during the mobilisation of vacuolar sucrose are discussed.To whom correspondence should be addressed.     

Cell elongation, turgor and osmotic pressure in developing sunflower hypocotyls

The relationship between cell elongation, change in turgor andcell osmotic pressure was investigated in the sub-apical regionof hypocotyls of developing sunflower seedlings (Helianthusannuus L.) that were grown in continuous white light. Cell turgorwas measured with the pressure probe. The same hypocotyl sectionswere used for determination of osmotic pressure of the tissuesap. Acceleration of cell elongation during the early phaseof growth was accompanied by a 25% decrease in both turgor andosmotic pressure. During the linear phase of growth both pressuresremained largely constant. The difference between turgor andosmotic pressure (water potential) was –0.10 to –0.13MPa. Excision of one cotyledon had no effect on growth, turgorand osmotic pressure. However, after removal of both cotyledonscell elongation ceased and a substantial decrease in both pressureswas measured. In addition, we determined the longitudinal tissuepressure in seedlings from which one or both cotyledons hadbeen removed. Tissue pressure and turgor were very similar quantitiesunder all experimental conditions. Our results demonstrate thatturgor and cell osmotic pressure show a parallel change duringdevelopment of the stem. Cessation of cell elongation afterremoval of the cotyledons is attributable to a decrease in turgor(tissue) pressure, which provides the driving force for growthin the hypocotyl of the intact plant. Key words: Cell elongation, Helianthus annuus, osmotic pressure, tissue pressure, turgor     

Effects of turgor potential on 1-aminocyclopropane-1-carboxylic acid uptake into the vacuolar compartment and ethylene production in tomato pericarp slices

While solute transport and ethylene production by plant tissue are sensitive to the osmotic concentration of the solution bathing the tissue, the influence of tissue water relations and specifically tissue turgor potential on the kinetics of 1-aminocyclopropane-1-carboxylic acid (ACC) uptake into the vacuolar compartment and ethylene production have not been examined. 1-Aminocyclopropane-1-carboxylic acid transport and ethylene production were examined in tomato (Lycopersicon esculentum Mill. cv. Liberty) pericarp slices incubated in solutions having a range of mannitol, polyethylene glycol 3350 and ethylene glycol concentrations known to affect tissue water relations. Tissue osmotic and turgor potentials were derived from osmolality measurements of cell saps recovered by freeze-thawing and corrected for the contribution of the free-space solution. When relatively nonpermeable (mannitol or polyethylene glycol 3350) osmotica were used, both ACC uptake and ethylene production were greatest at a solution osmolality of 230 milliosmolal where tissue turgor potential ranged between 120 and 140 kPa. At higher and lower turgor potentials, the high-affinity saturating component of ACC uptake and ethylene production were inhibited, and ACC efflux from the vacuolar compartment was increased. The inhibition of ACC uptake was evident as a decrease in V_max with no effect on K_m. Turgor potential changes caused by adjusting solution osmolality with mannitol or polyethylene glycol 3350 were accompanied by changes in the osmotic potential and water potential of the tissue. The effects of turgor potential vs the osmotic and water potentials of tomato pericarp slices were differentiated by comparing responses to nonpermeable osmotica and mixtures of nonpermeable and permeable osmotica. Ethylene glycol-mannitol mixtures had effects on the osmotic potential and water potential of the tissue similar to those of nonpermeable osmotica but had less effect on tissue turgor, ACC transport and ethylene production. Incubating tissue in solutions without nonpermeable osmotica osmotically shocked the tissue. Increasing solution osmolality with ethylene glycol in the absence of nonpermeable osmotica increased tissue turgor and ethylene production. The present study indicates that tissue turgor is an important factor affecting the kinetics of ACC uptake into the vacuolar compartment and ethylene production in tomato pericarp slices.     

Changes in cell turgor pressure related to uptake of solutes by Microcystis sp. strain 8401

Uptake of several naturally occurring organic solutes by the unicellular cyanobacterium Microcystis sp. caused changes in cell turgor pressure (p(t)), which was determined by measuring the mean critical pressure (p(c)) of gas vesicles in the cells. Cells had an initial p(t) of 0.34 MPa, which decreased to 0.08 MPa in 0.15 M sucrose. In solutions of polyols, p(t) gradually recovered as the solutes penetrated the cytoplasmic membranes. From measurements of the exponential rate of turgor increase, cell volume and surface area, the permeability coefficient of the cytoplasmic membrane to each solute was calculated. Permeabilities to amino acids, ammonium ions and sodium acetate indicated little passive movement of these substances across the cell surface from solutions at high concentrations. We looked for evidence of ion trapping of acetic acid: at low pH there was a rapid rise in turgor pressure indicating a rapid uptake of this weak acid. After 20 min the turgor was lost, apparently due to loss of integrity of the cell membranes. For cells in natural habitats, studies of the permeability of cells to solutes is relevant to the problem of retaining substances that are accumulated by active uptake from solutions of low concentrations in natural waters.     

Effects of Sucrose on Water Relations of Cut, Senescing, Carnation Flowers

Carnation flower stems were stood in water or sucrose solutionand changes in water content, water and osmotic potential, turgorpressure and solutes (sugars, nitrogen, phosphorus, potassium)of petals were measured throughout the flower life. In bothtreatments the petals had a higher specific water content atincipient wilting than when the flowers were first cut. In water,turgor pressure decreased rapidly after the seventh day becauseof a decrease in tissue solute content. In sucrose solution,loss, of solutes was delayed probably because the sugar provideda respiratory substrate to maintain cell membrane integrity.In these cells, sugars and water accumulated causing decreasesin water potential and osmotic potential. Solutes and waterwere lost at about day 15 and turgor pressure decreased. Therewas some evidence that from about day 11 cells were so gorgedwith sugars that they burst when they were placed in water duringthe adjustment of water content prior to water potential measurements. Most of the initial petal osmotic energy content could be accountedfor by sugar, potassium, and anions associated with potassium,but in water, as the petals aged and sugar content decreased,so the potassium ions contributed a larger proportion of theosmotic energy; with stems in sucrose, the endogenous sugarcontent (reducing sugars plus sucrose) contributed an increasingproportion of the total osmotic energy. Dianthus caryophyllus, carnation, flowers, water relations, senescence