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Fertilization of woody plants plays a central role in agriculture and forestry, but little is known about how plant water relations are thereby affected. Here we investigated the impact of fertilization on tree hydraulics, and xylem and pit anatomy in the high-yield apple cultivars Golden and Red Delicious. In fertilized trees of Golden Delicious, specific hydraulic conductivity of branch xylem, hydraulic conductance of the root system, and maximum stomatal conductance increased considerably. In Red Delicious, differences between fertilized and control trees were less pronounced. In both cultivars, xylem embolism resistance of fertilized trees was significantly lower and stomatal closure occurred at lower water potentials. Furthermore, water potential at turgor loss point and osmotic potential at full saturation were higher and cell wall elasticity was lower in fertilized plants, suggesting reduced drought tolerance of leaves. Anatomical differences were observed regarding conduit diameters, cell wall reinforcement, pit membrane thickness, pit chamber depth, and stomatal pore length, with more pronounced differences in Golden Delicious. The findings reveal altered hydraulic behaviour in both apple cultivars upon fertilization. The increased vulnerability to hydraulic failure might pose a considerable risk for apple productivity under a changing climate, which should be considered for future cultivation and management practices. [ABSTRACT FROM AUTHOR]

Preconditions of phloem transport in conifers are relatively unknown. We studied the variation of needle and inner bark axial osmotic gradients and xylem water potential in Scots pine and Norway spruce by measuring needle and inner bark osmolality in saplings and mature trees over several periods within a growing season. The needle and inner bark osmolality was strongly related to xylem water potential in all studied trees. Sugar concentrations were measured in Scots pine, and they had similar dynamics to inner bark osmolality. The sucrose quantity remained fairly constant over time and position, whereas the other sugars exhibited a larger change with time and position. A small osmotic gradient existed from branch to stem base under pre-dawn conditions, and the osmotic gradient between upper stem and stem base was close to zero. The turgor in branches was significantly driven by xylem water potential, and the turgor loss point in branches was relatively close to daily minimum needle water potentials typically reported for Scots pine. Our results imply that xylem water potential considerably impacts the turgor pressure gradient driving phloem transport and that gravitation has a relatively large role in phloem transport in the stems of mature Scots pine trees. [ABSTRACT FROM AUTHOR]

This study investigated the relationship between osmotic potential at full hydration (π100) and turgor loss point (ΨTLP) in wheat ( Triticum aestivum) to determine the potential of using π100 to predict ΨTLP under well-watered (WW) and drought (WS) conditions. Two methods for determining π100 were tested: pressure-volume (PV) analysis and freezing point osmometry. The study also measured π100 in a range of 38 field-grown wheat cultivars to determine whether there is genetic variation in π100 under field conditions. π100 correlated with ΨTLP using both methods under both water treatments, particularly WS. Genetic variation of π100 in the field, under rainfed conditions, was greater than controlled conditions and ranged from −0.94 to −1.95 MPa. Overall, the evidence supports development of π100 as a novel tool for plant breeders to screen large populations of wheat and identify genotypes with lower ΨTLP, an integrative trait that is related to drought tolerance. [ABSTRACT FROM AUTHOR]

This study investigated a possible relationship between the relative change of leaf thickness and the relative degree of turgor pressure in leaf cells. Leaf thickness and turgor pressure were measured simultaneously during forced plant desiccation in bean plants. Although leaf thickness followed closely the steep decline of the total water potential ( Ψ ) during the desiccation process, no conclusive relationship could be observed between leaf thickness and the osmotic water potential ( Ψ s ). Thus, a potential link between the relative change of leaf thickness and the relative degree of turgor pressure could not be verified under the experimental conditions. Earlier findings, that the relative change of leaf thickness is closely related to the relative change of the total water potential of leaf cells, are corroborated. Additional observations were: (i) a potential relationship between the relative change of leaf thickness during desiccation and the totally achieved leaf thickness, and (ii) the apparent decrease of leaf thickness during desiccation in discrete levels rather than a truly continuous decline. [ABSTRACT FROM AUTHOR]

Changes in plant water relations and ionic homoeostasis can determine plant osmoacclimation and tolerance to hypersaline stress. In this study, we examined the role of ion accumulation in short-term osmotic acclimation capacities of two Mediterranean seagrass species ( Posidonia oceanica and Cymodocea nodosa) with differentiated ranges of salinity tolerance. These were tested by exposing plants to a wide range of hypersaline treatments (from 37 to 59.5, practical salinity scale) simulated in a mesocosm system over 7 days. P. oceanica showed a more reduced capacity to adjust its leaf water potential ( Ψ) than C. nodosa, so that the osmotic gradient towards plant tissues was reduced as external salinity increased in this species. Osmotic potential, Ψ, was also reduced in both species, reflecting the activation of osmoregulation. Some ions (as Cl) increased in both species, but ionic uptake (relative to ion concentration in seawater) generally decreased at increasing salinities, suggesting the activation of ion-exclusion mechanisms. In P. oceanica leaves, the percentage of participation of ions in the Ψ was reduced as salinity increased; this indicated that osmotic acclimation was highly dependent on the accumulation of organic osmolytes (i.e. soluble sugars) in this species, which involves higher metabolic costs. The participation of ions was greater in C. nodosa plants exposed to hypersaline treatments, but the contrasting responses of non-structural carbohydrates, turgor pressure, Ψ and ions in the most severe hypersaline treatment, suggested the activation of alternative osmotic strategies. Under normal saline conditions (i.e. controls), C. nodosa plants exhibited higher values of K/Na and Ca/Na and selectivity of K over Na ( S) than P. oceanica, which are typically related to species more tolerant to salinity stress. With regard to photochemistry, F/ F and α was only reduced in P. oceanica exposed to some hypersaline treatments, although reductions in both rETR and ΦPSII were detected in plants of both species at the most severe hypersaline treatments (59.5). Only C. nodosa exhibited the activation of photoprotective mechanisms as NPQ increments. [ABSTRACT FROM AUTHOR]

The drought tolerance of three economically important apple cultivars, Golden Delicious, Braeburn and Red Delicious, was analysed. The work offers insights into the hydraulics of these high-yield trees and indicates a possible hydraulic limitation of carbon gain. The hydraulic safety and efficiency of branch xylem and leaves were quantified, drought tolerance of living tissues was measured and stomatal regulation, turgor-loss point and osmotic potential at full turgor were analysed. Physiological measurements were correlated with anatomical parameters, such as conduit diameter, cell-wall reinforcement, stomatal density and stomatal pore length. Hydraulic safety differed considerably between the three cultivars with Golden Delicious being significantly less vulnerable to drought-induced embolism than Braeburn and Red Delicious. In Golden Delicious, leaves were less resistant than branch xylem, while in the other cultivars leaves were more resistant than branch xylem. Hydraulic efficiency and xylem anatomical measurements indicate differences in pit properties, which may also be responsible for variations in hydraulic safety. In all three cultivars, full stomatal closure occurred at water potentials where turgor had already been lost and severe loss of hydraulic conductivity as well as damage to living cells had been induced. The consequential negative safety margins pose a risk for hydraulic failure but facilitate carbon gain, which is further improved by the observed high stomatal conductance. Maximal stomatal conductance was clearly seen to be related to stomatal density and size. Based on our results, these three high-yield Malus domestica Borkh. cultivars span a wide range of drought tolerances, appear optimized for maximal carbon gain and, thus, all perform best under well-managed growing conditions. [ABSTRACT FROM AUTHOR]

Leaves can be both a hydraulic bottleneck and a safety valve against hydraulic catastrophic dysfunctions, and thus changes in traits related to water movement in leaves and associated costs may be critical for the success of plant growth. A 4-year fertilization experiment with nitrogen (N) and phosphorus (P) addition was done in a semideciduous Atlantic forest in northeastern Argentina. Saplings of five dominant canopy species were grown in similar gaps inside the forests (five control and five N + P addition plots). Leaf lifespan (LL), leaf mass per unit area (LMA), leaf and stem vulnerability to cavitation, leaf hydraulic conductance (Kleaf_area and Kleaf_mass) and leaf turgor loss point (TLP) were measured in the five species and in both treatments. Leaf lifespan tended to decrease with the addition of fertilizers, and LMA was significantly higher in plants with nutrient addition compared with individuals in control plots. The vulnerability to cavitation of leaves (P50leaf) either increased or decreased with the nutrient treatment depending on the species, but the average P50leaf did not change with nutrient addition. The P50leaf decreased linearly with increasing LMA and LL across species and treatments. These trade-offs have an important functional significance because more expensive (higher LMA) and less vulnerable leaves (lower P50leaf) are retained for a longer period of time. Osmotic potentials at TLP and at full turgor became more negative with decreasing P50leaf regardless of nutrient treatment. The Kleaf on a mass basis was negatively correlated with LMA and LL, indicating that there is a carbon cost associated with increased water transport that is compensated by a longer LL. The vulnerability to cavitation of stems and leaves were similar, particularly in fertilized plants. Leaves in the species studied may not function as safety valves at low water potentials to protect the hydraulic pathway from water stress-induced cavitation. The lack of rainfall seasonality in the subtropical forest studied probably does not act as a selective pressure to enhance hydraulic segmentation between leaves and stems. [ABSTRACT FROM AUTHOR]

Abstract: The association between plant water stress and synthesis of red, anthocyanin pigments in leaves has led some plant biologists to propose an osmotic function of leaf reddening. According to this hypothesis, anthocyanins function as a solute in osmotic adjustment (OA), contributing to depression of osmotic potential (Ψ π ) and maintenance of turgor pressure during drought-stressed conditions. Here we calculate the percent contribution of anthocyanin to leaf Ψ π during OA in two angiosperm evergreen species, Galax urceolata and Gaultheria procumbens. Both species exhibit dramatic leaf reddening under high light during winter, concomitant with declines in leaf water potential and accumulation of solutes. Data previously published by the authors on osmotic potential at full turgor (Ψ π,100) of G. urceolata and G. procumbens leaves before and after leaf reddening were used to estimate OA. In vivo molar concentrations of anthocyanin, glucose, fructose, and sucrose measured from the same individuals were converted to pressure equivalents using the Ideal Gas Law, and percent contribution to OA was estimated. Estimated mean OA during winter was −0.7MPa for G. urceolata and −0.8MPa for G. procumbens. In vivo concentrations of anthocyanin (3–10mM) were estimated to account for ∼2% of OA during winter, and comprised <0.7% of Ψ π,100 in both species. Glucose, fructose, and sucrose combined accounted for roughly 50 and 80% of OA for G. urceolata and G. procumbens, respectively, and comprised ∼20% of Ψ π,100. We observed that a co-occurring, acyanic species (Vinca minor) achieved similar OA without synthesizing anthocyanin. We conclude that anthocyanins represent a measurable, albeit meager, component of OA in red-leafed evergreen species during winter. However, due to their low concentrations, metabolic costliness relative to other osmolytes, and striking red color (unnecessary for an osmotic function), it is unlikely that they are synthesized solely for an osmoprotectant role. [Copyright &y& Elsevier]

Abstract: Recent research using Arabidopsis has shown that blue light stimulates the plant through the receptor protein and induces regulations physiologically and morphologically. It is important to know whether the theory can be used in food crop production. In the present study blue light emitted from light-emitting diodes (LED) was used as a stimulus to tomato crop canopy after sunset for 2h to induce xerophytophysiological regulations. Blue (450nm), white and red (660nm) LED lamps, all with a properties of 0.48W, 24V, and 45μmolm2 s−1 at 10cm over the lamp, were compared with non-illumination control. A 2×4 two factor experiment was conducted in a randomized split block design with the two cultivars as the main block. Results showed that the osmotic potential in the symplasm at full turgor was lower and the leaf turgor potential at full turgor was higher in tomato leaves in blue light treatment. The water fraction in the symplasm in the leaf was larger or the apoplastic water fraction was smaller in leaf of blue light irradiated plants. Both osmotic potential and relative water content at the point of incipient plasmolysis were lower in tomato leaves in blue light treatment. More leaf water was lost by stomatal transpiration and less leaf water was lost by cuticular transpiration in leaves of blue light treated tomato plants. Fruit color was improved and redder in blue light treatment. Fruit yield was increased by all light illumination treatments. The damage of fruit caused by Helicoverpa armigera worms was more severely in red light treatment and less severely in blue and white light treatments compared with the control. The leaf blight index was lower in blue and white light illumination treatments than the red light treatment and the control. Both cultivars showed LED illumination responses similar to each other although fruit yield was lower and leaf blight was severer in ‘Baiju’ than in ‘Myoko’. In conclusion, illumination treatment with blue light from LED as a stimulus was effective in fruit yield increase and quality improvement as well as improvement in disease resistance of the tomato crop. [Copyright &y& Elsevier]

Abstract: Adult pomegranate trees (Punica granatum (L.) cv. Mollar de Elche) were submitted to three irrigation treatments. Control (T0) plants were drip irrigated in order to guarantee non-limiting soil water conditions, T1 plants (deficit irrigation) were drip irrigated according to the criteria commonly used by the growers in the area and T2 plants were subjected to water withholding and recovery periods of 34 and 6 days, respectively, during the summer of 2009. The results indicated that pomegranate plants confront water stress by developing stress avoidance and stress tolerance mechanisms. From the time of deficit irrigation (T1) and water withholding (T2) began to be applied, leaf conductance decreased in order to control water loss via transpiration and to avoid leaf turgor loss (stress avoidance mechanism). Close to the end of the stress period, when maximum stress levels had developed, active osmotic adjustment was triggered, contributing to the maintenance of leaf turgor (stress tolerance mechanism). Other drought tolerance characteristics commonly seen in xeromorphic plants were also observed, such as high relative apoplastic water content (42–58%), which would contribute to the retention of water at low leaf water potentials. [Copyright &y& Elsevier]

Solute accumulation in plant leaves during drought through accumulation of organic compounds is known to compensate turgor loss and promote higher stomatal conductance at lower water potentials. Recent studies have involved experiments on saplings and younger stands, while evidence of osmotic adjustment in adult pedunculate oak under natural stand conditions on different sites is scarce. Pressure volume curves technique was used to define differences in osmotic potential - water stress adaptation - of 120 year old pedunculate oak trees in two managed forest complexes and in virgin forest remnant. Tree response between the managed stand after thinning and the stand without any silvicultural measures within same forest complex was also compared during summer months in two consecutive (dry and favourable) years with groundwater table. Significant differences were observed in adaptation between forest complexes and during dry (2003) and favourable (2004) years. Osmotic component of thinned forest was the highest, showing most negative values of stress adjustment. Measured values on all plots responded well to drop in groundwater table, especially in pronounced drought conditions. Such response may be in relation with lower stand density and increased individual space for growth in thinned stand. Adult oaks did not loose their ability to water stress adaptation, in spite of their age and progressively decreasing health conditions. [ABSTRACT FROM AUTHOR]

Abstract: A critical appraisal of the EDTA-enhanced exudation technique was performed and improvements for this technique were proposed. Two buffer solutions were used (HEPES and EDTA) at a concentration of 20mM. HEPES is a buffering agent widely used in cell culture. Exudation from cut-ends of petioles and peduncles of tomato was allowed to occur over a period of 7h. Variations of the buffer solution volume, carbohydrates and potassium concentrations, as well as osmotic pressure, were measured in the exudates. The use of HEPES buffer solution alone is proof of the large uptake of the buffer solution by the plant through the xylem. The effect of this uptake on the classical estimation of the carbohydrate flow and concentration of phloem is presented. An improvement of the technique is proposed in order to correctly estimate: (i) the phloem flow; (ii) its composition (carbohydrates and others solutes); and (iii) the turgor pressure of the phloem. The improved EDTA-enhanced exudation technique was applied to investigate the effect of water stress on the driving variables involved in the carbohydrate allocation within the plant. Phloem composition varied with the date and was affected by water stress as well as turgor pressure, which decreased. Furthermore, differences arose in the turgor pressure at the petiole and peduncle sites. Results showed that the exudation technique could be a useful tool to estimate local phloem composition and turgor pressure and to infer resource allocation within the plant. [ABSTRACT FROM AUTHOR]

Significant controversy still swirls around the regulation of extension by tip-growing cells, particularly during stable, oscillatory growth of pollen tubes. One explanation proposes that turgor pressure is both the controlling and driving force. We refute this hypothesis on theoretical and evidentiary grounds. Direct measurement of intracellular pressure reveals constant turgor even as growth rates change. Measured ion fluxes, notably potassium, are insufficient to account for the requisite osmotic changes. Water movement, and hence pressure gradients, occur throughout the cell, unrestricted to local domains. Increases in hydrostatic pressure alone would force water out of the cell rather than cause increased growth. We have recently demonstrated concomitant changes in the apical cell wall that account fully for observed changes in growth rate. [Copyright &y& Elsevier]

Cell water relationships are important topics to be included in cell biology courses. Differences exist in the control of water relationships in plant cells relative to control in animal cells. One important reason for these differences is that turgor pressure is a consideration in plant cells. Diffusion and osmosis are the underlying factors involved in the control of water in plant cells; however, additional attention must be given to osmotic pressure, osmotic potential, and water potential. This discussion shows how these parameters relate to each other, and how they are explained by thermodynamics and the universal gas laws. Detailed laboratory exercises are described that demonstrate these principles. The laboratory exercises include data collection, graphing of data, statistical analysis of data, and calculations of osmotic potential and diffusion pressure deficit from the data. [ABSTRACT FROM AUTHOR]

Abstract: Postharvest peel pitting at non-chilling temperatures is a physiological disorder that affects fruit of several citrus cultivars worldwide. Although causes of the disorder are not fully understood, evidence indicates that altered water relations in fruit peel is a major factor inducing peel pitting during postharvest storage. In this work, the effect of commercial packingline and manual processing and subsequent storage under low and high RH regimes on water, osmotic and turgor potentials in three layers of ‘Marsh’ grapefruit peel (flavedo and internal and external albedo) was investigated. At the end of the storage period at 45% RH, peel water potential was lower in fruit processed on a commercial packingline compared to those processed manually. Transfer of dehydrated fruit to 95% RH increased water potential of flavedo at the expense of albedo cell layers, which underwent subsequent water loss. Water potential of flavedo in packingline-processed fruit did not recover by transferring to high RH. Osmotic potential in peel tissues did not change as significantly as water potential. As a consequence, turgor pressure decreased in all three peel tissues of fruit stored at 45% RH, this decrease being more pronounced in packingline-processed fruit. In manually wax-coated fruit stored at 45% RH, transfer to 95% RH induced a recovery of turgor potential. In contrast, turgor pressure did not recover in packingline-processed fruit similarly treated, and severe peel pitting developed. The results suggest that the inability to properly carry out water adjustments after prolonged water stress leads to cell collapse and peel damage. Together, the data link alterations in water, osmotic and turgor potential in flavedo and albedo with the induction of postharvest peel pitting in citrus fruit. [Copyright &y& Elsevier]

Abstract: The effect of ethylene (2μLL−1) on total and soft epicuticular wax content and wax morphology has been investigated in mature ‘Navelate’ (Citrus sinensis, L. Osbeck) oranges held under non-stressful environmental conditions (22°C and constant high relative humidity (90–95% RH)). In addition, the objective of the study was to understand whether the ethylene-induced changes in epicuticular wax might participate in the beneficial effect of ethylene reducing non-chilling peel pitting, by modifying peel water, osmotic or turgor potential, or disease incidence caused by Penicillium digitatum (Pers.:Fr.) Sacc. Ethylene increased total and soft epicuticular wax content in ‘Navelate’ fruit and induced structural changes in surface wax that might be related to the formation of new waxes. Changes in epicuticular wax morphology, but not in its content, might be involved in the protective role of ethylene reducing non-chilling peel pitting, although the beneficial effect of the hormone is not related to water stress. Cell water and turgor potentials in freshly harvested fruit and fruit stored in air under non-stressful conditions suggest that water stress is not a limiting factor leading to the development of this physiological disorder. In addition, the results indicated that formation of new waxes in fruit treated with ethylene may partially cover stomata, cracks or areas lacking wax occurring in stored fruit and is likely to improve physical barriers to P. digitatum penetration. [Copyright &y& Elsevier]

Abstract: Rhizomorphs of wood-decay basidiomycetes are root-like structures produced by the coordinated growth of thousands of hyphae. Very little is known about their development nor the way that they penetrate soils and rotting wood. In this study, we applied techniques used in previous studies on hyphae to explore the mechanics of the invasive growth process in Armillaria gallica. Growth rate measurements were made in media with different gel strengths. The osmolyte composition of rhizomorph sap was determined spectroscopically and the forces exerted by growing tips were measured using a force transducer. Cultured rhizomorphs extended at much faster rates than unbundled hyphae (3.5mmd−1 versus 1.5mmd−1) and their growth accelerated in response to increased medium gel strength (to 7.4mmd−1). Measurements of rhizomorph osmolality provided a turgor pressure estimate of 760kPa (7.5atm.), and spectroscopic analysis showed that this pressure was generated by the accumulation of erythritol, mannitol, and KCl. Forces exerted by growing tips ranged from 1 to 6mN, corresponding to pressures of 40–300kPa (0.4–3.0atm.). Pressures exerted by extending rhizomorphs are comparable to those produced by individual vegetative hyphae. This suggests that the mechanical behavior of hyphae is similar whether they grow as unbundled cells or aggregate to form macroscopic rhizomorphs. [Copyright &y& Elsevier]

Abstract: In CAM-plants rising levels of malic acid in the early morning cause elevated turgor pressures in leaf chlorenchyma cells. Under specific conditions this process is lethal for sensitive plants resulting in chlorenchyma cell burst while other species can cope with these high pressures and do not show cell burst under comparable conditions. The non-cellulosic polysaccharide composition of chlorenchyma cell walls was investigated and compared in three cultivars of Aechmea with high sensitivity for chlorenchyma cell burst and three cultivars with low sensitivity. Chlorenchyma layers were cut from the leaf and the non-cellulosic carbohydrate fraction of the cell wall fraction was analyzed by gas–liquid chromatography. Glucuronoarabinoxylans (GAXs) were the major non-cellulosic polysaccharides in Aechmea. The fine structure of these GAXs was strongly related to chlorenchyma wall strength. Chlorenchyma cell walls from cultivars with low sensitivity to cell burst were characterized by an A/X ratio of ca. 0.13 while those from cultivars with high sensitivity showed an A/X ratio of ca. 0.23. Xylose chains from cultivars with high cell burst sensitivity were ca. 40% more substituted with arabinose compared to cultivars with low sensitivity for cell burst. The results indicate a relationship in vivo between glucuronoarabinoxylan fine structure and chlorenchyma cell wall strength in Aechmea. The evidence obtained supports the hypothesis that GAXs with low degrees of substitution cross-link cellulose microfibrils, while GAXs with high degrees of substitution do not. A lower degree of arabinose substitution on the xylose backbone implies stronger cell walls and the possibility of withstanding higher internal turgor pressures without cell bursting. [Copyright &y& Elsevier]

Biophysical characteristics of sapwood and outer parenchyma water storage compartments were studied in stems of eight dominant Brazilian Cerrado tree species to assess the impact of differences in tissue capacitance on whole-plant water relations. The rate of decline in tissue water potential with relative water content ( RWC) was greater in the outer parenchyma than in the sapwood for most of the species, resulting in tissue-and species-specific differences in capacitance. Sapwood capacitance on a tissue volume basis ranged from 40 to 160 kg m−3 MPa−1, whereas outer parenchyma capacitance ranged from 25 to only 60 kg m−3 MPa−1. In addition, osmotic potentials at full turgor and at the turgor loss point were more negative for the outer parenchyma compared with the sapwood, and the maximum bulk elastic modulus was higher for the outer parenchyma than for the sapwood. Sapwood capacitance decreased linearly with increasing sapwood density across species, but there was no significant correlation between outer parenchyma capacitance and tissue density. Midday leaf water potential, the total hydraulic conductance of the soil/leaf pathway and stomatal conductance to water vapour ( gs) all increased with stem volumetric capacitance, or with the relative contribution of stored water to total daily transpiration. However, the difference between the pre-dawn water potential of non-transpiring leaves and the weighted average soil water potential, a measure of the water potential disequilibrium between the plant and soil, increased asymptotically with total stem capacitance across species, implying that overnight recharge of water storage compartments was incomplete in species with greater capacitance. Overall, stem capacitance contributes to homeostasis in the diurnal and seasonal water balance of Cerrado trees. [ABSTRACT FROM AUTHOR]

This work was carried out with the objective of determining the answer to plant growth and water relations of two rice varieties (Oryza sativa L.) when being exposed to different NaCl levels. Plants were developed in a growth chamber under hydroponic conditions. Evaluations were carried out at the beginning of the experiment, at seven and 14 days of having applied treatments and after seven days of recovery. Evaluations consisted of the biomass expressed as fresh and dry matter from roots and the air part, stomatal conductance, transpiration as well as leaf, osmotic, pressure and osmotic potentials at full turgor. The analysis of plant behavior indicated that they modified growth as much as water relations when exposed to saline conditions. It was also appreciated that under these conditions, plants developed the osmotic adjustment mechanism. [ABSTRACT FROM AUTHOR]

Vitis vinifera L. berries are non-climacteric fruits that exhibit a double-sigmoid growth pattern, and at the point known as ‘veraison’, which is just before the beginning of the second period of rapid fruit growth, these berries undergo several abrupt physiological changes. Cell pressure probe was used to examine the in situ turgor (P) of cells in the mesocarp during berry development and in response to plant water deficits. Initial tests comparing attached and detached berries demonstrated that cell P was stable for up to 48 h after detachment from the vine, provided that water loss from the berry was prevented. Cell P at pre-dawn was on the order of 0.25 MPa pre-veraison (PreV) and was reduced by an order of magnitude to 0.02 MPa post veraison (PostV). Cell P declined slightly but significantly with depth from the berry surface PreV, but not PostV. When water was withheld from potted vines, cell P declined about 0.2 Mpa, as pre-dawn vine water potential declined about 0.6 MPa over 12 d, whereas cell P was completely insensitive to a 1.10 MPa decrease in pre-dawn vine water potential after veraison. Rewatering of stressed plants also resulted in a 24 h recovery of cell P before, but not after veraison. The substantial decline in cell P around veraison is consistent with the decline in berry firmness that is known to occur at this time, and the PostV insensitivity of P to changes in vine water status is consistent with current hypotheses that the PostV berry is hydraulically isolated from the vine. The fact that a measurable P of about 0.02 MPa and typical cell hydraulic/osmotic behaviour were exhibited in PostV berries, however, indicates that cell membranes remain intact after veraison, contrary to many current hypotheses that veraison is associated with a general loss of membrane function and cellular compartmentation in the grape berry. We hypothesize that cell P is low in the PostV berry, and possibly other fleshy fruits, because of the presence of regulated quantities of apoplastic solutes. [ABSTRACT FROM AUTHOR]

Water loss from plants is determined by the aperture of stomatal pores in the leaf epidermis, set by the level of vacuolar accumulation of potassium salt, and hence volume and turgor, of a pair of guard cells. Regulation of ion fluxes across the tonoplast, the key to regulation of stomatal aperture, can only be studied by tracer flux measurements. There are two transport systems in the tonoplast. The first is a Ca2+-activated channel, inhibited by phenylarsine oxide (PAO), responsible for the release of vacuolar K+(Rb+) in response to the “drought” hormone, abscisic acid (ABA). This channel is sensitive to pressure, down-regulated at low turgor and up-regulated at high turgor, providing a system for turgor regulation. ABA induces a transient stimulation of vacuolar ion efflux, during which the flux tracks the ion content (volume, turgor), suggesting ABA reduces the set-point of a control system. The second system, which is PAO-insensitive, is responsible for an ion flux from vacuole to cytoplasm associated with inward water flow following a hypo-osmotic transfer. It is suggested that this involves an aquaporin as sensor, and perhaps also as responder; deformation of the aquaporin may render it ion-permeable, or, alternatively, the deformed aquaporin may signal to an associated ion channel, activating it. Treatment with inhibitors of aquaporins, HgCl2 or silver sulfadiazine, produces a large transient increase in ion release from the vacuole, also PAO-insensitive. It is suggested that this involves the same aquaporin, either rendered directly ion-permeable, or signalling to activate an associated ion channel. [ABSTRACT FROM AUTHOR]

• Oxaziclomefone [OAC; IUPAC name 3-(1-(3,5-dichlorophenyl)-1-methylethyl)-3,4-dihydro-6-methyl-5-phenyl-2 H-1,3-oxazin-4-one] is a new herbicide that inhibits cell expansion in grass roots. Its effects on cell cultures and mode of action were unknown. In principle, cell expansion could be inhibited by a decrease in either turgor pressure or wall extensibility. • Cell expansion was estimated as settled cell volume; cell division was estimated by cell counting. Membrane permeability to water was measured by a novel method involving simultaneous assay of the efflux of 3H2O and [14C]mannitol from a ‘bed’ of cultured cells. Osmotic potential was measured by depression of freezing point. • OAC inhibited cell expansion in cultures of maize ( Zea mays), spinach ( Spinacia oleracea) and rose ( Rosa sp.), with an ID50 of 5, 30 and 250 n m, respectively. In maize cultures, OAC did not affect cell division for the first 40 h. It did not affect the osmotic potential of cell sap or culture medium, nor did it impede water transport across cell membranes. It did not affect cells’ ability to acidify the apoplast (medium), which may be necessary for ‘acid growth’. • As OAC did not diminish turgor pressure, its ability to inhibit cell expansion must depend on changes in wall extensibility. It could be a valuable tool for studies on cell expansion. [ABSTRACT FROM AUTHOR]

The hydraulic architecture of sunflower (Helianthus annuus L. cv. Margot) was studied in terms of the partitioning of the hydraulic conductance (Kleaf) of leaves inserted at progressively more apical nodes both in growing plants (GP) and in plants at full anthesis (mature plants, MP). Leaf conductance to water vapour (gL), leaf water potential (ΨL), leaf water potential at zero turgor (Ψtlp), and leaf osmotic potential at full turgor (π0) were also measured. Sunflower plants showed gL and Kleaf values significantly increasing in the acropetal direction, while ΨL of basal leaves was significantly more negative than that of distal leaves; Ψtlp markedly decreased in the acropetal direction in MP so that leaves of MP retained increasingly more turgor the more apical they were. This hydraulic pattern, already present in very young plants (GP), strongly favours apical leaves. These data suggest that the progressive leaf dieback starting from the stem base, as observed when the inflorescence of sunflower reached maturity, might be due to time-dependent loss of hydraulic conductance. In fact, Kleaf loss was correlated with ΨL drop and stomatal closure. Leaf dehydration was aggravated by solute exportation from the basal towards the apical leaves, as revealed by the acropetal decrease of π0. Kleaf was shown to be linearly and positively related to the prevailing ambient irradiance during plant growth, thus suggesting that leaf hydraulics is very sensitive to environmental conditions. It was concluded that the pronounced apical dominance of some sunflower cultivars is determined, among other factors, by plant hydraulic architecture. [ABSTRACT FROM PUBLISHER]

The gravitational component of water potential contributes a standing 0.01 MPa m−1 to the xylem tension gradient in plants. In tall trees, this contribution can significantly reduce the water potential near the tree tops. The turgor of cells in buds and leaves is expected to decrease in direct proportion with leaf water potential along a height gradient unless osmotic adjustment occurs. The pressure–volume technique was used to characterize height-dependent variation in leaf tissue water relations and shoot growth characteristics in young and old Douglas-fir trees to determine the extent to which growth limitation with increasing height may be linked to the influence of the gravitational water potential gradient on leaf turgor. Values of leaf water potential ( Ψl), bulk osmotic potential at full and zero turgor, and other key tissue water relations characteristics were estimated on foliage obtained at 13.5 m near the tops of young (approximately 25-year-old) trees and at 34.7, 44.2 and 55.6 m in the crowns of old-growth (approximately 450-year-old) trees during portions of three consecutive growing seasons. The sampling periods coincided with bud swelling, expansion and maturation of new foliage. Vertical gradients of Ψl and pressure–volume analyses indicated that turgor decreased with increasing height, particularly during the late spring when vegetative buds began to swell. Vertical trends in branch elongation, leaf dimensions and leaf mass per area were consistent with increasing turgor limitation on shoot growth with increasing height. During the late spring (May), no osmotic adjustment to compensate for the gravitational gradient of Ψl was observed. By July, osmotic adjustment had occurred, but it was not sufficient to fully compensate for the vertical gradient of Ψl. In tall trees, the gravitational component of Ψl is superimposed on phenologically driven changes in leaf water relations characteristics, imposing potential constraints on turgor that may be indistinguishable from those associated with soil water deficits. [ABSTRACT FROM AUTHOR]

Spatial distribution of cell turgor pressure, cell osmotic pressure and relative elemental growth rate were measured in growing tall fescue leaves (Festuca arundinacea). Cell turgor pressure (measured with a pressure probe) was c. 0.55 MPa in expanding cells but increased steeply (-0.3 MPa) in cells where elongation had stopped. However, cell osmotic pressure (measured with a picolitre osmometer) was almost constant at 0.85 MI'a throughout the leaf. The water potential difference between the growth zone and the mature zone (0,3 MPa) was interpreted as a growth-induced water potential gradient. This and further implications for the mechanism of growth control are discussed. [ABSTRACT FROM AUTHOR]

Pressure–volume curves were determined for black spruce (Picea mariana (Mill.) BSP) trees from four full-sib families. During the first two years, trees were measured from a plantation on a dry site. In the third year, trees were sampled from the dry site and a wet site. Diurnal measurements of shoot water potential allowed in situ shoot turgor to be estimated in addition to standard water relations traits. Over all years, Female 59 progeny displayed lower osmotic potentials at saturation (Ψsat) than Female 63 progeny. Genetic differences in Ψsat were similar on both the dry and wet sites. Modulus of elasticity (μ) was greater for Female 59 progeny than for Female 63 progeny, producing a compensatory effect resulting in no genetic or site differences in osmotic potential at turgor loss point (Ψtlp) or relative water content at turgor loss point (RWCtlp). Mean and predawn shoot turgor pressures (Px and Ppd) were higher for Female 59 progeny than for Female 63 progeny and higher at the wet site than the dry site. Genotype × environment trends were observed; compared to Female 63 progeny, Female 59 progeny displayed 9.8 and 5.1% higher Ppd on the dry and wet sites, respectively, and 3.4 and 9.8% greater Ppd values in wet and dry years, respectively. Tree volume growth showed no relationship to Ψtlp or RWCtlp, but was correlated with Ψsat and Px; however, the strongest correlation was with Ppd (r = 0.90). [ABSTRACT FROM PUBLISHER]

The effects of potassium deficiency (KD) and all-macronutrient deficiency (MD) on elongation of tap and lateral roots were studied on maritime pine seedlings (Pinus pinaster Ait.) in hydroponic culture. Tap root elongation was unaffected by either of the two deficiencies. By marked contrast, lateral root elongation was strongly reduced. The analyses of cell turgor pressure and relative elemental growth rate (RECK) profile in the growing zone allowed us to determine the effects of the nutrient stresses on cell-wall properties. For both deficiency treatments, elongation rate, (REGR) profile (measured only for control and KD) and turgor pressure in the fastest growing cells were unaffected in the tap root, suggesting that KD and MD did not modify cell-wall properties in the growing zone. In lateral roots, KD shortened the growing zone and significantly reduced REGR. However, turgor pressure remained unaffected in this region. The absence of turgor pressure change suggests that KD reduced elongation of lateral roots by tightening cell walls. In mature cells of the two types of roots, turgor and osmotic pressures tended to be reduced by the nutrient deficiencies, indicating that these parameters were better maintained in the growing cells. Cell turgor and osmotic pressures of control plants were 0.1MPa lower at 30 mm (mature cells) than at 2-4 mm (expanding cells) from the meristem. Moreover, these parameters were 0.1 MPa lower in expanding cells of lateral roots than in those of tap the root. Turgor and osmotic pressures were not homogeneous throughout the root system and were affected differently by the nutrient deficiencies depending on the location in the root system. [ABSTRACT FROM AUTHOR]

The effect of osmotic stress on the regulation of extension of roots of pine seedlings (Pinus pinaster Ait.) was studied. Extension rate (r) was measured as increase in root length, and as local growth rate (LGR) along the growing region. Turgor pressure (P) was measured over the same profile using the cell pressure probe. Correlation of LGR and P allowed changes in cell wall mechanical properties to be followed. In unstressed plants, differences in LGR along the root apex were owing to variations in the mechanical properties of the cell walls since P remained constant at 0.5 MPa along the first 10 mm of the root tip. Contrary to expectation, a moderate water stress of 0.15 MPa stimulated root growth despite a small reduction in P to 0.4 MPa. The walls of the expanding cells became looser, allowing enhanced growth in spite of reduced turgor. Examination of LGR showed that these changes occurred uniformly over the whole elongation zone. The advantage to the plant of this is discussed. Higher stresses (0.45 and 0.66 MPa) decreased cell turgor to a greater degree (&les; 0.3 MPa) and decreased growth rate. At the highest stress (0.66 MPa), P was maximal in cells that were still elongating, resulting in a longitudinal gradient in turgor. In both treatments LGR remained unchanged at the apex of the growing zone. Wall loosening appeared to have occurred in this region. Pine root extension is therefore modulated by changes in cell wall properties, with cell wall loosening resulting in increased growth at moderate stress. It appears that growth under higher stresses is limited by inability to maintain turgor. [ABSTRACT FROM AUTHOR]

The effect of increasing external osmotic pressure on. potassium fluxes in aged and fresh-cut discs of Daucus carota L. storage tissue was investigated. An increase of the external osmotic pressure by 5 bars of mannitol solution increased the rate of K+ net uptake of aged discs to 180% of their control rate. At 3°C and in 0.1 mM azide, in which a net efflux of potassium was observed, the mannitol treatment caused a reduction in the net efflux, In fresh-cut discs, in which the capability of net influx was rather low and a substantial net release of potassium was noted, the increase in the external osmotic pressure by mannitol caused a 70% inhibition in the net efflux. This effect was also observed at 3°C. Measurements of separate fluxes confirmed the assumption that the mannitol treatment brought about two distinct effects on K+ fluxes: (a) raised the metabolically-dependent influx and (b) lowered the membrane permeability-dependent efflux. When a permeating solute (ethylene glycol) was used instead of mannitol, no effect on K+ flux was detectable. Reasons are given for relating the observed changes in K+ fluxes to the reduction in turgor pressure of the cells. [ABSTRACT FROM AUTHOR]

Plant growth is reduced under saline conditions even when turgor in mature leaves is maintained by osmotic adjustment. The objective of this study was to determine if young leaves from salt-affected plants were also osmotically adjusted. Pepper plants (Capsicum annuum L. cv. California Wonder) were grown in several levels of solution osmotic potential and various components of the plants' water relations were measured to determine if young, rapidly growing leaves could accumulate solutes rapidly enough to maintain turgor for normal cell enlargement. Psychrometric measurements indicated that osmotic adjustment is similar for both young and mature leaves although osmotic potential is slightly lower for young leaves. Total water potential is also lower for young leaves, particularly at dawn for the saline treatments. The result is reduced turgor under saline conditions at dawn for young but not mature leaves. This reduced turgor at dawn, and presumably low night value, is possibly a cause of reduced growth under saline conditions. No differences in leaf turgor occur at midday. Porometer measurements indicated that young leaves at a given salinity level have a higher stomatal conductance than mature leaves, regardless of the time of day. The result of stomatal closure is a linear reduction of transpiration. [ABSTRACT FROM AUTHOR]

Experiments were designed to test the hypothesis that the internal water relations of leaves are altered when cotton plants (Gossypium hirsutum L.‘Acala SJ‐2′) are conditioned by several cycles of water stress. Preliminary experiments suggested that plants so conditioned are less sensitive to water deficits and that the change might be partly explained by an accumulation of solutes or by structural alterations attendant on development under conditions of water stress. Leaves of preconditioned plants maintained turgor to lower values of water potential than did leaves of well‐watered plants. Accompanying this change was a lower osmotic potential at any given leaf water content in preconditioned plants. Tissue analysis of several osmotically active solutes indicated that soluble sugars and malate accumulate to about the same levels (dry‐weight basis) in both conditioned and unconditioned plants exposed to stress. These accumulations could not account for the turgor change. Analysis of the data on relative water content indicated that the leaves of conditioned plants had less water per unit dry weight than did leaves of controls. This change accounts for a substantial fraction of the difference between the osmotic potential of conditioned and control plants. The results of a simple model suggest that structural changes may play a significant role in explaining differences in the responses of conditioned and control plants to water stress. [ABSTRACT FROM AUTHOR]

The rate of leaf elongation in radiata pine (Pinus radiata) and wheat seedlings was closely related to the osmotic potential of the rooting solution. Sudden stress application and removal treatments caused immediate changes in the leaf elongation rate and a new steady-state rate independent of the old was quickly established. The osmotic potential in the active elongation zones of a leaf differed from that of the remainder of the leaf and was considered more appropriate for deriving turgor pressure to be related to leaf elongation. Shifts in elongation rate were associated with corresponding shifts in total leaf water potential in both species and with corresponding shifts in turgor pressure in wheat. There was a linear correlation between the pitch of the helical thickenings in the protoxylem of radiata pine needles and their elongation rate. A record of elongation rate is, therefore, preserved in the needle. Developmental aspects of the deposition of the helix are discussed. [ABSTRACT FROM AUTHOR]

In early studies, negative turgor pressure was obtained by indirect methods and was mainly related to inaccurate measurements of osmotic and/or water potential. The uncertainties in the measurements made any discussion of the underlying reasons and phenomena premature and risky, perhaps even useless. Yet, the idea of relating negative turgor to the strength of small-sized cells with thick walls, 10 resist collapse when subjected to water deficit, seemed attractive. Negative turgor pressures are difficult to detect in higher plants, but they are theoretically possible. Regarding their origin, a hypothesis is discussed here, that the negative turgor detected in leaves might indicate a reversal of the water flow that has occurred in roots, under conditions of severe and prolonged drought. [ABSTRACT FROM AUTHOR]

Seasonal and diurnal variation and rehydration effects of pressure-volume param- eters in Pseudotsuga menziesii (Mirb.) Franco from a plantation in central Pennsylvania, USA, were evaluated during May-September. 1989. Predawn elastic modulus was lowest in overwintering and newly expanded shoots in May and June, respectively, whereas predawn osmotic potentials at full and zero turgor were lowest in May and in early September, following an August drought. Seasonal variation in predawn relative water content at zero turgor was highly correlated with increases and decreases in elastic modulus and osmotic potential. Diurnal osmotic adjustment resulted in nearly constant turgor pressure, despite decreases in bulk shoot water potential. Elastic modulus decreased diurnally on 1 August and increased `on 3 September. Decreases in osmotic potential and/or elastic modulus on 24 June and I August lowered the relative water content at zero turgor. Correcting for plauteaus via linear regression had no significant effect on osmotic potential at full turgor: however, uncorrected elastic modulus and relative water content at zero turgor were often significantly lower than the plateau-corrected values, particularly in artificially rehydrated shoots. Plateau-corrected osmotic potential at full turgor and osmotic potential at zero turgor were significantly higher in most artificially re-hydrated shoots than in those naturally rehydrated as the result of loss of symplastic solutes, `Corrected elastic modulus decreased following 12 and 24 h of rehydration and corrected relative water content at zero turgor increased in as little as 3 h of rehydration. These results indicate that seasonal and diurnal patterns of tissue-water parameters in Pseudotsuga menziesii vary with plant phenology and drought conditions, and that the length of rehydration period is an important consideration for pressure-volume studies. [ABSTRACT FROM AUTHOR]

Rose (Rosa hybrida cv. Madame G. Delbard) was micropropagated in vitro on agar at varying concentrations: 0, 4, 5.5, 6, 7.5, 8, 9 and 15 g l-1. Water status of the culture medium, leaf water potential, plant growth and propagation rate were investigated. Water potential of the medium was a linear function of agar concentration, and gel strength increased linearly from zero as agar concentration increased from 5 to 15 g l-1. Except for liquid medium, where shoot proliferation (total shoot number) was imparied by vitrification, fresh and dry weights and number of total shoots decreased linearly with increasing agar concentration. At low agar concentration, where water potential of the gelled medium was high, only few among numerous shoots that had attained a length of > 0.3 cm were usable. Number of usable (elongated) shoots was significantly higher at a moderate level of agar, namely 7.5 g l-1. This can be explained in terms of the antagonistic actions of cytokinin and water on shoot elongation. At low agar concentration, leaf water potential and absolute water content were high. At high agar concentration, under gel water deficit, leaf water potential and absolute water content were low but an osmotic adjustment maintained turgor pressure. At moderate agar concentration, when the number of usable shoots was high, lower leaf turgor was found. [ABSTRACT FROM AUTHOR]

Seasonal changes in the relationship between stomatal responses and water potential components in detached leaves of sweet cherry (Prunus avium L. cv. Bigarreau Morreau) and plum (Prunus domestica L. cv. Queen Victoria) were examined by the simultaneous measurement of stomatal conductance and water relation parameters derived from pressure-volume curves. The water potential threshold for stomatal closure in sweet cherry leaves throughout the season and in plum leaves until mid-July varied nearly in parallel with changes in the osmotic potential at the turgor loss point. From August onward, closing reactions of plum stomata had no relationship to the turgor loss point. Stomata of sweet cherry leaves opened more widely and showed slower reactions to dehydration early in the season than later. Seasonal changes of stomatal conductance and stomatal responses to dehydration in both species seem thus to be influenced by fruit development and ripening. [ABSTRACT FROM AUTHOR]

The diurnal and seasonal changes in plant water relations of two Japonica rice (Oryza sativa L.) cultivars, Nipponbare and Tachiminori, were studied under flooded conditions at Kyoto University. The dryland cv. Tachiminori maintained higher predawn and midday leaf osmotic potentials relative to the wetland cv. Nipponbare during the vegetative stage, but the ranking was reversed after flowering. The relationship between leaf water potential and leaf osmotic potential showed that prior to panicle emergence Nipponbare was able to adjust osmotically to maintain turgor, whereas after heading there was little turgor maintenance. Tachiminori showed little difference in osmotic adjustment before and after panicle emergence. Fertilizer treatment during panicle development also helped to maintain the degree of osmotic adjustment in both cultivars.

Plants often tolerate water deficits by lowering the osmotic potential of their cell sap. This may be achieved by accumulation of solutes which results in the maintenance of a positive turgor potential. In this study, the effect of water deficit on sugar uptake was investigated in leaf discs of Phaseolus coccinius L. (cv. Scarlet). Evidence is presented that cell turgor affects the kinetics of sugar transport at the membrane level. Uptake kinetics of sucrose, glucose and 3‐O‐methyl glucose by tissues equilibrated in solutions of relatively high (200–400 mOsm) osmotic concentration consisted of a sat‐urable and a linear component. Low external osmotic concentration i.e., high cellular turgor inhibited the saturating component of sucrose uptake, resulting in a linear uptake profile. However, high cell turgor had no effect on glucose or 3‐O‐methyl glucose uptake kinetics. The effect of turgor versus osmotic component of water potential was differentiated by comparing responses to non‐penetrating (manmtol) or polyethylene glycol, (3350) and penetrating (ethylene glycal) osmotica. Changes in sucrose uptake rates and kinetics were due to changes in cellular turgor and not osmotic potential. Furthermore, at low cellular turgor, a net increase in sucrose uptake occurred as a consequence of enhanced influx rates and not as a result of reduced efflux rates. The data are consistent with previous findings that sugar uptake rates are enhanced under low turgor. We present first evidence indicating that the mechanism by which higher rates of sucrose uptake are maintained underwater deficit conditions is by the activation of the saturable transport system. This mechanism supports previous suggestions that changes in cell turgor are sensed and manifested at the membrane level. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The water relations of shoots of young jack pine (Pinus banksiana Lamb.) seedlings were examined 6 and 15 weeks after the initiation of four different dynamic nitrogen (N) treatments using a pressure-volume analysis. The N treatments produced a wide range of needle N concentrations from 12 to 32 mg g-1 dry mass and a 10-fold difference in total dry mass at 15 weeks. Osmotic potential at full turgor did not change over the range of needle N concentrations observed. Osmotic potential at turgor-loss point, however, declined as N concentrations decreased, indicating an increased ability of N-deficient jack pine plants to maintain turgor. The Increase could be attributed largely to an increase in cell wall elasticity, suggesting that elasticity changes may be a common, significant adaptation of plants to environmental stresses. Dry mass per unit saturated water almost doubled as needle N level dropped from 32 to 12 mg g-1 and was inversely correlated to the bulk modulus of elasticity. This suggests that cell wall elasticity is determined more by the nature of its cross-linking matrix than by the total amount of cell wall material present. Developmental change was evident in the response of some water relation variables to N limitation. [ABSTRACT FROM AUTHOR]

The aim of the present study was to test the accuracy of the pressure-chamber technique as a method for estimating leaf-cell turgor pressures. To this end, pressure-probe measurements of cell turgor pressure (pcell) were made of mesophyll cells of intact, attached leaves of Kalanchoë daigrernontiana. Immediately following these measurements, leaves were excised and placed in a pressure chamber for the determination of balance pressure (pbal). Cell-sap osmotic pressure (IIcell ) and xylem-sap osmotic pressure (IIXY1) were also measured, and an average cell turgor pressure calculate as Pcell = IIcell-IIxy1-Pbal. The apparent value of PbaI was positively correlated with the rate of increase of chamber pressure, and there was also a time-dependent increase associated with water loss. On expressing sap from the xylem IIxy1 fell to a plateau value that was positively correlated with IIcell. Correcting for these effects yielded estimates of Pbal and IIxy1 at the time of Leaf excision. On average, the values of Pcell obtained with the two techniques agreed to within ±0.02MPa (errors are approximate 95% confidence limits). if IIxy1 were ignored, however, the calculated turgor pressures would exceed the measured values by an average of 0.074 ± 0.012MPa, or 48% at the mean measured pressure of 0.155 MPa. We conclude that the pressure-chamber technique allows a good estimate to be made of turgor pressure in mesophyll cells of K. daigremontiana, provided that IIxy1 is included in the and calculated turgor pressures also implies that the weighted-average reflection coefficient for the mesophyll cell membranes is close to unity. [ABSTRACT FROM AUTHOR]

Electrical impedance measurements made on white spruce, Picea glauca (Moench) Voss, stems were related to shoot free sugar contents and to osmotic, turgor and water potential. During seasonal dormancy induction, there were commensurate increases in free sugar contents, osmotic potential at full turgor and impedance which resulted in linear relationships among these variables. When measured over the course of laboratory drying, impedance increased curvilinearly with decreasing relative water content. There was a linear increase in impedance with decreasing water potential, with a break point coincident with the turgor loss point, possibly attributed to disruption to current flow through broken plasmodesmatal connections between adjacent cells. This technique offers a non-destructive method to measure tissue free sugar content, and therefore, short- and long-term shifts in parameters historically derived from pressure-volume analysis. [ABSTRACT FROM AUTHOR]

This paper discusses the question as to whether or not the seed coat tissues can 'adapt' to a treatment with a solution containing a low osmoticum concentration, representing an environment which is sub-optimal for assimilate transport into attached surgically modified ovules. Before the start of a pulse-labelling procedure, in experiments on [14C] sucrose transport into fruits of pea (Pisum sativum) with four empty ovules, two empty ovules were filled with a low-osmolality solution (a 200 mol m-3 mannitol medium or a solution without mannitol) and the other two ovules were filed with a 400 mol m-3 mannitol medium-Pretreatment with a low-osmolality medium, during a period of 2-3h, enhanced subsequent transport of [14C] sucrose into empty ovules filled with a low-osmolality medium, in comparison with [14C] sucrose transport into empty ovules filled with a 400 mol m-3 mannitol medium during the pretreatment period. This partial recovery if sink strength of attached empty ovules can be explained as the result of a stimulation of solute efflux from seed coat cells at high cell turgor. [ABSTRACT FROM AUTHOR]

Pressure-volume measurements were made on Artemisia tridentata Nutt. ssp. tridentata samples rehydrated for 0, 1.5, 3, 6 or 24 h. Increasing rehydration time caused a significant increase in osmotic potential at turgor loss, cell elasiticity, and the relative water content at turgor loss, and a significant decrease in pressure potential at saturation. Osmotic potential at saturation was changed significantly by rehydration, but no consistent trend was observed. The symplastic water fraction did not differ significantly among treatments. The increase in the osmotic potential at turgor loss did not correspond with decreasing cell elasticity or synthesis of solutes. Instead, the leaf solute content remained constant suggesting a redistribution of solutes between the symplast and apoplast. Using non-rehydrated samples for pressure-volume analysis introduced errors in estimates of the symplastic water fraction, osmotic potential at full turgor, and the relative water content at turgor loss. These errors are due to uncertainties in the determination of saturated weights. [ABSTRACT FROM AUTHOR]

Diurnal cycling of osmotic potential was studied in leaves of cotton plants (Gossypium hirsutum L.) grown in the field. Osmotic potential was determined by a pressure-volume procedure as the value coinciding with zero turgor. In plants grown under favourable conditions (no water stress or N stress), osmotic potential at zero-turgor measured at midday was initially about 0.3 Mpa lower than before dawn, but this cycling disappeared during the season as the number of fruits per plant increased. In water-stressed or N-deficient plants, osmotic cycling was decreased or even eliminated. Across treatments, cycling of osmotic potential occurred only when plants carried at least 560 cm2 of leaf area per fruit. The results are interpreted to mean that diurnal cycling of osmotic potential reveals a 'sink-limited' condition within the plant. [ABSTRACT FROM AUTHOR]

When internodal cells of Lamprothamnium succinctum were exposed to a hypotonic medium containing more than 1 mol m-3Ca2+, the elevated turgor pressure decreased and reached a steady state with 30-60 min. The hypotonic treatment caused the membrane potential to depolarize, with a time lag of ca. 1 min. The membrane conductance increased transiently with the same time lag and reached a peak value within 2-3 min. When the external Ca2+ concentration was lowered to 0.01 mol m-3, both turgor regulation and change in the membrane conductance were strongly inhibited, although the membrane depolarization was not affected. When the Ca2+ level was returned to the normal level, the cells recovered their ability for turgor regulation and the membrane conductance attained a peak value after ca. 15-30 s. This response time is definitely shorter than that needed for the conductance change in cells exposed to a hypotonic medium having a normal level of Ca2+ from the beginning. We thus conclude that at least two sequential processes are involved in turgor regulation: a Ca-2+-independent process, followed by a Ca2+-dependent process. [ABSTRACT FROM AUTHOR]

Midday water potentials of blades of the dune grasses Ammophila arenaria (L.) Link and Elymus mollis Trin. ex Spreng. growing in situ declined over the summer growing period, indicating a trend of increasing water stress. An analysis of the water relations characteristics of these blades using pressure-volume techniques demonstrated that both species increased bulk osmotic pressure at full hydration (̅πo) and, therefore, bulk turgor as an acclimation response. In A. arenaria, however, the increase of osmotic pressure (+0.35 MPa) was entirely the result of decreasing symplasmic water content. The increase of osmotic pressure (+0.54 MPa) observed in E. mollis blades was due to solute accumulation (72% of Δ ̅π o) and to a lesser degree, decreased symplasmic water content (28% of Δ ̅πo). Osmotic adjustment in E. mollis blades was accompanied by a significant decrease in tissue elasticity (̅ εmax went from 12 to 19 MPa). The elastic properties of A. arenaria blades remained constant over the same period and had a maximum modulus (10 MPa) that was always less than that of E. mollis. As estimated from Höfler plots, these seasonal adjustments of osmotic pressure and differences in tissue elasticity enabled plants in situ to maintain turgor pressure in the range of 0.5-0.6 MPa at the lowest water potentials of mid-August. Laboratory-grown plants exhibited the species-specific differences in osmotic pressure, turgor pressure, and tissue elasticity observed in field plants. Although certain alterations of leaf structure were expected to coincide with the observed changes and species-specific differences in symplasmic water content and tissue elasticity, these could not be detected by measurements of specific leaf weight or the ratio of dry matter to saturated water content. [ABSTRACT FROM AUTHOR]