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Global warming is exposing plants to increased risks of drought-driven mortality. Recent advances suggest that hydraulic failure is a key process leading to plant death, and the identification of simple and reliable proxies of species-specific risk of irreversible hydraulic damage is urgently required. We assessed the predictive power of leaf water content and shrinkage for monitoring leaf hydraulic failure in two Mediterranean native species, Salvia ceratophylloides (Sc) and S. officinalis (So). The study species showed significant differences in relative water content (RWC) thresholds inducing loss of rehydration capacity, as well as leaf hydraulic conductance (K L) impairment. Sc turned out to be more resistant to drought than So. However, Sc and So showed different leaf saturated water content values, so that different RWC values actually corresponded to similar absolute leaf water content. Our findings suggest that absolute leaf water content and leaf water potential, but not RWC, are reliable parameters for predicting the risk of leaf hydraulic impairment of two Salvia species, and their potential risk of irreversible damage under severe drought. Moreover, the lack of any K L decline until the turgor loss point in Sc , coupled to consistent leaf shrinkage, rejects the hypothesis to use leaf shrinkage as a proxy to predict K L vulnerability, at least in species with high leaf capacitance. Robust linear correlations between K L decline and electrolyte leakage measurements suggested a role of membrane damage in driving leaf hydraulic collapse. • Hydraulic failure is a major correlate of drought-driven plant death. • Simple parameters predicting the risk of irreversible hydraulic failure are needed. • Leaf hydraulic damage occurred at different RWC values in two Salvia species. • Absolute water content and cell membrane integrity predicted hydraulic failure. [ABSTRACT FROM AUTHOR]

• Leaf turgor pressure varied significantly in the azimuthal, vertical, and radial apple canopies under drip irrigation. • Water potential, leaf thickness, and solar radiation affected the variation in canopy leaf turgor. • MaxP p was optimal for soil moisture monitoring based on the XGBoost model. • The LPCP probe should be installed in the middle position of the east canopy's central layer for apple trees. Leaf turgor pressure is a relevant metric for determining plant water content. To diagnose an apple tree water shortage, it is critical to precisely establish the features of leaf turgor pressure change in the canopy. In the current study, we continually monitored the leaf turgor pressure parameter (P p) at different azimuthal, vertical, and radial locations of the apple canopy based on leaf patch clamp pressure (LPCP) probes. The results demonstrated that the P p curves on sunny and rainy days were significantly different. A peak occurred on sunny days, during which the turgor pressure remained constant around midday. Under full irrigation, there was a greater change rate and daily maximum of P p (maxP p) at the east (azimuthal), upper layer (vertical), and distal (radial) positions. While leaf turgor pressure dramatically decreased with incomplete watering, maxP p significantly increased at the central and lower layers of the east canopy, as well as on the proximal and middle of the radial parts. This spatial heterogeneity in canopy leaf turgor pressure was related to the soil water potential, midday leaf water potential, sponge tissue thickness, and canopy solar radiation. Then, the ideal drought stress indicator parameter (maxP p) and canopy turgor monitoring leaf location (the middle position of the eastern canopy central layer's radial branch) were determined by multiparameter assessment. The findings presented above serve as a theoretical foundation for the construction of an intelligent irrigation system based on apple tree water status monitoring. [ABSTRACT FROM AUTHOR]

An intimate interplay of the plasma membrane with curvature-sensing and curvature-inducing proteins would allow for defining specific sites or nanodomains of action at the plasma membrane, for example, for protrusion, invagination, and polarization. In addition, such connections are predestined to ensure spatial and temporal order and sequences. The combined forces of membrane shapers and the cortical actin cytoskeleton might hereby in particular be required to overcome the strong resistance against membrane rearrangements in case of high plasma membrane tension or cellular turgor. Interestingly, also the opposite might be necessary, the inhibition of both membrane shapers and cytoskeletal reinforcement structures to relieve membrane tension to protect cells from membrane damage and rupturing during mechanical stress. In this review article, we discuss recent conceptual advances enlightening the interplay of plasma membrane curvature and the cortical actin cytoskeleton during endocytosis, modulations of membrane tensions, and the shaping of entire cells. [ABSTRACT FROM AUTHOR]

How the plant cell wall expands and forms shapes is a long-standing mystery. Traditional thought is that turgor pressure drives these processes. However, a recent study by Haas and colleagues shows for the first time that the expansion of pectin homogalacturonan nanofilaments drives morphogenesis without turgor pressure in plant epidermal cells. [ABSTRACT FROM AUTHOR]

• Leaf turgor pressure changes to D changes relate to maximum stomatal conductance. • We derived a physiological-based indicator from a leaf turgor pressure-related sensor. • g s,max can be automatically estimated from this indicator previous calibration. • We demonstrated this for three seasons in a commercial olive hedgerow orchard. • Results apply for moderate water stress levels within stomatal functioning ranges. Effective study and management of crops and forests would benefit greatly from useful plant-based indicators of the biological controls on evapotranspiration, and particularly stomatal conductance (g s). Given the strong influence of g s on bulk leaf water potential and turgor pressure (P), in vivo measurement of P may provide useful information about diurnal or seasonal dynamics of g s. Moderate plant water stress affects the diurnal dynamics of P as leaf-to-air vapour pressure deficit (D) varies, and these dynamics correlate to g s. Here, we explored relative changes in P in response to changes in D under mild drought conditions, and how these changes are linked to stomatal behaviour, and specifically to diurnal maximum g s (g s,max), one of the best indicators of plant water stress. We monitored ecophysiological and environmental variables, as well as a relative proxy for P , during three consecutive seasons in a hedgerow olive orchard where trees were supplied with different irrigation treatments to create well-watered and moderately water-stressed conditions. Our results demonstrated that the sensitivity of P to D correlated well with g s,max reached by the trees within a range in which variations in g s are the main diffusional limitation to photosynthesis. We further showed that this correlation held under a wide range of meteorological conditions and soil water availability. This turgor proxy measurement, which is much easier to measure than g s , can facilitate the use of g s,max as an indicator of plant water stress and evapotranspiration in agriculture and plant science research. [ABSTRACT FROM AUTHOR]

Drought tolerance shapes the distribution of plant species, and it is mainly determined by the osmotic potential at full turgor (π 0) and the water potential at turgor loss point (Ψ tlp). We provide a simplified framework for π 0 and Ψ tlp measurements based on osmometer determination of π 0 (π 0_osm). Specifically, we ran regression models to i) improve the predictive power of the estimation of π 0 from π 0_osm and morpho-anatomical traits; ii) obtain the most accurate model to predict Ψ tlp on the basis of the global relationship between π 0 and Ψ tlp. The inclusion of the leaf dry matter content (LDMC), an easy-to-measure trait, in the regression model improved the predictive power of the estimation of π 0 from π 0_osm. When π 0_osm was used as a simple predictor of Ψ tlp , discrepancies arose in comparison with global relationship between π 0 and Ψ tlp. Ψ tlp values calculated as a function of the π 0 derived from π 0_osm and LDMC (π 0_fit) were consistent with the global relationship between π 0 and Ψ tlp. The simplified framework provided here could encourage the inclusion of mechanistically sound drought tolerance traits in ecological studies. • Leaf turgor loss point (Ψ tlp) defines drought tolerance of plant species. • Ψ tlp could be estimated from the osmotic potential at full turgor (π 0). • π 0 could be easily measured with a dewpoint hygrometer. • Accounting for leaf dry matter content improves estimates of Ψ tlp from π 0. [ABSTRACT FROM AUTHOR]

Highlights • Range and duration of HHP treatment affected turgor. • A turgor of 0.1 MPa denotes a threshold for irreversible HHP-dependent effects. • HHP-dependent variations in tuber stiffness are closely related to turgor losses. • Colour changes reflect anthocyanin redistribution due to high membrane permeability. • Irreversibility resulted from combined damage of membranes and membrane proteins. Abstract The impacts of high hydrostatic pressure (HHP) treatments on metabolic functionality and quality of fruit and vegetables are still poorly understood. The effects of pressure intensity (100, 150 and 200 MPa) and holding time (5 and 10 min), and temperatures (20, 30 and 40 °C) during HHP treatment on fresh radish tubers has been studied. Colour, stiffness and turgor of the tubers were evaluated using colorimetry, texture analyses and direct turgor measurements with the cell pressure probe techniques. Comparison of turgor and stiffness losses, and colour changes, of skin and thin-walled parenchymatous inner radish tissue showed the effects of the various HHP treatment parameters on the permeability of biomembranes. HHP treatment resulted in a rapid reduction of cell turgor and, concomitantly of tuber stiffness, but also in a cellular redistribution of anthocyanins as indicated by colour changes. These responses were partially reversible up to 100 MPa applied pressure at 20-40 °C for 5–10 min, yielding a turgor threshold of 0.1 MPa. Beyond these limits, changes were irreversible, most probably due to the denaturation of membrane bound proteins such as ion channels and pumps. Overall, even short-term HHP treatments at room temperature are not suitable for sanitation by inactivating bacteria of perishable produce. [ABSTRACT FROM AUTHOR]

The resistance and ecotoxicity of fungicides seriously restrict our ability to effectively control Magnaporthe oryzae. Discovering fungicidal agents based on novel targets, including Mo TPS1, could efficiently address this situation. Here, we identified a hit VS-10 containing an isopropanolamine fragment as a novel Mo TPS1 inhibitor through virtual screening, and forty-four analogs were synthesized by optimizing the structure of VS-10. Utilizing our newly established ion-pair chromatography (IPC) and leaf inoculation methods, we found that compared to VS-10, its analog j11 exhibited substantially greater inhibitory activity against both Mo TPS1 and the pathogenicity of M. oryzae. Molecular simulations clarified that the electrostatic interactions between the bridging moiety of isopropanolamine and residue Glu396 of contributed significantly to the binding of j11 and Mo TPS1. We preliminarily revealed the unique fungicidal mechanism of j11 , which mainly impeded the infection of M. oryzae by decreasing sporulation, killing a small portion of conidia and interfering with the accumulation of turgor pressure in appressoria. Thus, in this study, a novel fungicide candidate with a unique mechanism targeting Mo TPS1 was screened and discovered. [Display omitted] • An isopropanolamine inhibitor against Mo TPS1, VS-10, was discovered by virtual screening. • The optimized isopropanolamine compound j11 substantially inhibited Mo TPS1 and the pathogenicity of M. oryzae. • The electrostatic interaction of isopropanolamine compound j11 and Glu396 in Mo TPS1 was vital for their binding. • Isopropanolamine compound j11 had unique fungicidal mechanisms differing from those of commercial fungicides. [ABSTRACT FROM AUTHOR]

We evaluated the suitability of scheduling a regulated deficit irrigation strategy in a hedgerow olive orchard with high plant density from leaf turgor related measurements. Measurements were made for two consecutive years at an olive orchard with 1667 ‘Arbequina’ trees per hectare where we had two deficit irrigation treatments, 45RDI CC and 45RDI TP , plus a full irrigation as a control. The two 45RDI treatments consisted on applying the same regulated deficit irrigation strategy, aimed to supply a total of 45% of the irrigation needs. The 45RDI CC treatment however, was scheduled with the crop coefficient approach, while the 45RDI TP treatment was scheduled with an irrigation scheduling approach based on leaf turgor related measurements, first suggested by Padilla-Díaz et al. (2016, Agric. Water Manage. 164:28–37). They worked at the orchard in 2014, and made a preliminary evaluation of the irrigation scheduling approach by comparing 45RDI TP versus 45RDI CC in terms of irrigation dose and frequency, predawn and midday stem water potential ( Ψ stem ), and the fruit yields of each treatment. In this work, we considered the same variables as well as maximum daily values of stomatal conductance and CO 2 net assimilation, the seasonal courses of the number of internodes in current-year shoots, leaf area and oil accumulation in the fruits, and total fruit and oil yields. All those variables were monitored both in 2014 and 2015, and we found no differences between the 45RDI TP and the 45RDI CC treatments, for any of them. The irrigation amounts applied to each treatment differed occasionally, but the total water supplies were similar to both 45RDI treatments. Our results, therefore, confirm the suitability of the irrigation scheduling approach proposed by Padilla-Díaz et al. (2016) to apply regulated deficit irrigation in commercial hedgerow olive orchards. We found additional evidence for the 15% changes on the irrigation amount recommended by the irrigation scheduling approach as being suitable for the orchard conditions. Caution must be taken when applying this approach to other olive orchards, since the relations between the tree water status and the shape of the daily curves recorded with the ZIM probes may depend on the cultivar and orchard conditions. [ABSTRACT FROM AUTHOR]

Bacteria use second-messenger molecules to adapt to their environment. Several second messengers, among them cyclic di-AMP (c-di-AMP), have been discovered and intensively studied. Interestingly, c-di-AMP is essential for growth of Gram-positive bacteria such as Bacillus subtilis, Listeria monocytogenes , and Staphylococcus aureus . Many studies demonstrated that perturbation of c-di-AMP metabolism affects the integrity of the bacterial cell envelope. Therefore, it has been assumed that the nucleotide is essential for proper cell envelope synthesis. In this Opinion paper, we propose that the cell envelope phenotypes caused by perturbations of c-di-AMP metabolism can be interpreted differently: c-di-AMP might indirectly control cell envelope integrity by modulating the turgor, a physical variable that needs to be tightly adjusted. We also discuss open questions related to c-di-AMP metabolism that need to be urgently addressed by future studies. [ABSTRACT FROM AUTHOR]

Skin shrivelling of sweet cherry ( Prunus avium L.), referred to here as ‘orange-peel’ disorder, compromises fruit appearance and thus market value. The objectives were to establish a protocol to describe and quantify orange peel disorder and to identify the mechanism and factors determining its incidence. Fruit was stored for 28 to 33 d at 2 °C and 76% RH and orange peel disorder was quantified as a topographical roughness using an interferometer or by rating the fruit for orange peel using a four-step scoring scheme. Fruit with orange peel disorder had a skin topography similar to that of a citrus fruit − just on a finer scale. Under the conditions of the test, orange peel was first visible after ∼7 d and continued to increase in severity thereafter. Orange peel was most severe on the shoulder and in the equatorial and distal regions of the fruit. There was no relationship between the distribution of orange peel and that of stomata or of microcracking. At a microscopic level, the depressions in the fruit surface were markedly larger than the periclinal areas of individual epidermal cells, but similar in size to the mesh formed by the network of minor veins visible just beneath the skin. Susceptibility to orange peel differed among cultivars. Least susceptible were ‘Dönissens Gelbe’ and, ‘Gil Peck’, intermediate were ‘Sam’, ‘Kordia’, ‘Merchant’, and the sour cherry ‘Ungarische Traubige’, and most susceptible were ‘Adriana’, ‘Regina’, and ‘Hedelfinger’. Incidence of orange peel during storage was negatively related to relative humidity (more at lower humidities) but also developed at 100% RH in the absence of transpiration. Submerging fruit in water for 2 d partly reversed orange peel. There was no significant difference in the permeance of the skins or in turgors of cells of the outer mesocarp between fruit without and with orange peel. There was a significant difference between the osmotic potential of the flesh (more negative) and that of the skin (less negative). During storage, the osmotic potentials of flesh and skin both decreased slightly, but the difference between them remained constant. The results show water loss from the skin is causal in orange peel disorder. The water loss from the skin occurs both by two routes: (1) transpiration to the atmosphere and also (2) by osmotic dehydration to the flesh. [ABSTRACT FROM AUTHOR]

The leaf patch clamp pressure (LPCP) probe is being used to remotely assess leaf turgor pressure. Recently, different shapes of the LPCP daily curves have been suggested as potential water stress indicators for irrigation scheduling. These curves shapes, called states, have been studied and related to different water stress levels for olives. To our knowledge, the only way to differentiate these curves shapes or states is through the visual observation of the dynamics of the LPCP records during the day, which is highly time-consuming and reduces its potential to automatically schedule irrigation. The aims of this study were: (i) to obtain a random forest model to automatically identify the states from daily LPCP curves recorded in olive trees, by using visually identified states to train the model; (ii) to improve the identification of state II through a second random forest model, relating this state to the midday stem water potential, and; (iii) to obtain a random forest model to identify the states based on ranges of stem water potential. We used LPCP daily curves collected in a commercial olive orchard from 2011 to 2015. The states were visually identified for the days on which concomitant measurements of stem water potential and leaf stomatal conductance were made. We had a data set of 307 LPCP daily curves, being 157 curves in state I, 78 in state II and 71 in state III. The two biggest inflection points of the LPCP curves were used to adjust the models through the use of the R package “randomForest”, using the Leave-p-Out Cross-Validation method. With the first model, which was obtained from the whole dataset, its data regarding the inflection points and the visually identified states, we obtained an overall accuracy of 94.37%. With the second model, obtained with the use of the data regarding curves visually identified as state II only, the overall accuracy was of 88.64%. This model was adjusted to be used after the first model, to narrow the stem water potential range of state II curves. Finally, the third model was obtained using the whole dataset and the states established from ranges of stem water potential. This last model did not consider the visual identification, and yielded an overall accuracy of 88.08%. Our results facilitate the use of LPCP probes, since it allows for the automatic identification of the states related to leaf turgor pressure, a key information to schedule irrigation. [ABSTRACT FROM AUTHOR]

To improve the safety of fresh high quality convenience products, high hydrostatic pressure treatments (HHP) may provide a gentle, quality retainion alternative to traditional chemical preservation. However, information about the potential impact of HHP on metabolic functionality of fresh produce is rare; the few published studies indicate HHP has effects on physiological activity. These effects were highly product specific due to pronounced variations in both pressure sensitivity and stress responsivity. Biomembranes generally seem to be major physiological targets of HHP treatments. Cell turgor inevitably requires fully intact cell membranes. Turgor has an important impact on the fresh appearance of fresh produce, especially texture. Up to now, there is no investigation available that has directly evaluated the effects of HHP treatments on turgor of fresh vegetable tissue. In this study, the pressure probe technique was applied to comprehensively analyse the turgor of red cabbage tissue by directly measuring the hydrostatic pressure of individual cells. The effects of HHP on the cell turgor were tested at pressures ranging between 150 MPa and 250 MPa, applied for 5, 10, 15 and 20 min. As pronounced changes in pressure could result in related temperature changes, the effects of temperature (35 °C to 55 °C) on turgor was characterised separately. At 35 °C and 45 °C, leaf turgor transiently declined after HHP treatment of 150 MPa (for up to 10 min) but recovered again within 24 h; at 55 °C, however, it irreversibly dropped to near zero. The same occurred when HHP of 175 MPa or above was applied. In general, HHP treatment and temperature increases as well as the duration of treatments interactively affected cell turgor of red cabbage leaves. Critical process parameters derived for gentle application of HHP were 150 MPa at 45 °C for 10 min treatment time. [ABSTRACT FROM AUTHOR]

The effects of soil amendment with the hydrophilic polymer Stockosorb ® on the physical properties of the soil as well as on physiological parameters (turgor pressure, stomatal conductance, chlorophyll fluorescence) and yield (vegetative growth, fruit characteristics, oil yield and quality) of an established olive crop cultivated under rainfed conditions, were investigated in Tunisia during the 2014 growing season. Stockosorb ® hydrogel was applied by injection in the soil around olive trees (TS) and compared to a control plot (TC) without hydrogel application. The results showed that water content was generally higher in hydrogel amended soils compared to the control soil. The seasonal leaf patch output pressure ( P p ) readings revealed that trees with Stockosorb ® treatment had the highest water status and were moderately stressed in comparison to control trees which were severely stressed due to the poor water status during the vegetative growth and fruiting period. The application of Stockosorb ® in the root zone of olive trees significantly increased midday stomatal conductance ( g s ) and the maximal quantum efficiency (Fv/Fm). Shoot growth, oil yield and rainwater use efficiency were strongly improved by the Stockosorb ® amendment to the soil, however oil quality still within the threshold limits set for an ‘Extra virgin' classified olive oil. [ABSTRACT FROM AUTHOR]

Control of cell volume and osmolarity is central to cellular homeostasis in all eukaryotes. It lies at the heart of the century-old problem of how plants regulate turgor, mineral and water transport. Plants use strongly electrogenic H + -ATPases, and the substantial membrane voltages they foster, to drive solute accumulation and generate turgor pressure for cell expansion. Vesicle traffic adds membrane surface and contributes to wall remodelling as the cell grows. Although a balance between vesicle traffic and ion transport is essential for cell turgor and volume control, the mechanisms coordinating these processes have remained obscure. Recent discoveries have now uncovered interactions between conserved subsets of soluble N -ethylmaleimide-sensitive factor attachment protein receptor (SNARE) proteins that drive the final steps in secretory vesicle traffic and ion channels that mediate in inorganic solute uptake. These findings establish the core of molecular links, previously unanticipated, that coordinate cellular homeostasis and cell expansion. [ABSTRACT FROM AUTHOR]

While many molecular players involved in growth control have been identified in the past decades, it is often unknown how they mechanistically act to induce specific shape changes during development. Plant morphogenesis results from the turgor-induced yielding of the extracellular and load-bearing cell wall. Its mechanochemical equilibrium appears as a fundamental link between molecular growth regulation and the effective shape evolution of the tissue. We focus here on force-driven polymerization of the cell wall as a central process in growth control. We propose that mechanical forces facilitate the insertion of wall components, in particular pectins, a process that can be modulated through genetic regulation. We formalize this idea in a mathematical model, which we subsequently test with published experimental results. [ABSTRACT FROM AUTHOR]

Mechanical–electrochemical theory and nanoindentation response of a bacterial cell. [Display omitted] • Bacterial model consisting of a negatively charged capsule and an elastic envelope subjected to turgor pressure is established. • Thermodynamics-based mechanical–electrochemical theory of bacterial cells is given. • Mechanisms underlying the three-stage nanoindentation response of bacterial cells are revealed. The environmental adaption, growth, motion, and other dynamic behaviors of bacteria are closely associated with the coupled mechanical–electrochemical properties of their subcellular structures, but the underlying regulatory mechanisms remain unclear. The mechanical responses of bacteria are difficult to elucidate by traditional models without considering the mechanical, chemical, and electric coupling effects. In this paper, a mechanical–electrochemical theory is constructed to investigate the deformation behavior of bacterial cells. A bacterium is treated as a bilayer structure consisting of a negatively charged polysaccharide capsule and an elastic envelope subjected to turgor pressure. This model is used to reveal the regulating roles of the electrostatic double-layer force and osmosis under different electrolyte conditions. Good agreement is found between the theoretical predictions and the experimentally observed three-stage nanoindentation responses of Klebsiella pneumoniae (K. pneumoniae) bacterial cells. Furthermore, we investigate the mechanical–electrochemical coupling mechanisms in the compression resistance of the bacterial capsule. The results reveal that the osmosis induced by ionic imbalance and polysaccharide–solvent aggregates plays a significant role in the compression resistance of the capsule. The present model not only deepens our understanding of the mechanical–electrochemical coupling mechanisms of bacterial cells at the subcellular scale, but also holds promise for applications in characterizing their mechanical properties. [ABSTRACT FROM AUTHOR]

During desiccation, plant cells are subjected to very low water potentials. Osmoregulation through increase of soluble materials ( e.g. soluble sugars, compatible inorganic ions) is a response to the decreasing turgor pressure in the cells. In bryophytes, sucrose acts as an osmolyte and also stabilizing membranes and proteins through vitrification. We used psychrometric measurements in the aquatic bryophyte Fontinalis antipyretica Hedw. to construct pressure–volume isotherms and determine the water relations parameters under fast and slow dehydration rates. Sucrose was also quantified. The starting hypothesis was that a slow dehydration rate would increase sucrose concentration, thereby decreasing the osmotic potential at turgor loss point, and would also increase cell wall elasticity, postponing turgor loss and allowing time for induction of molecular and structural acclimation mechanisms. In fact, we found that slowly dehydrated samples presented more elastic cell walls, allowing cells to shrink and maintain turgor, helping to better preserve their metabolic functions and therefore to induce desiccation tolerance (DT). On the other hand, in fast dehydrated samples the osmotic potential at turgor loss point decreased, indicating the activity of osmoregulation processes, possibly connected to the increase observed in sucrose content. Upon rehydration, fast dried samples lost 50% of the sucrose through leakage due to cell membrane rupture, while slow dehydrated leaves maintained their sucrose content constant. DT appears to be achieved through slow dehydration, meaning that a high sucrose content alone does not contribute to DT establishment. Moreover, in natural conditions external water can be maintained at very high values due to the life form of F. antipyretica , which grows in long and compact floating stems in streams, allowing a slow dehydration rate required for induction of other DT mechanisms. [ABSTRACT FROM AUTHOR]

The integration of biochemical and biomechanical elements is at the heart of morphogenesis. While animal cells are relatively soft objects which shape and mechanics is mostly regulated by cytoskeletal networks, walled cells including those of plants, fungi and bacteria are encased in a rigid cell wall which resist high internal turgor pressure. How these particular mechanical properties may influence basic cellular processes, such as growth, shape and division remains poorly understood. Recent work using the model fungal cell fission yeast, Schizosaccharomyces pombe , highlights important contribution of cell mechanics to various morphogenesis processes. We envision this genetically tractable system to serve as a novel standard for the mechanobiology of walled cell. [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]

In recent years, Central European forests and trees have been severely suffered from drought events in the growing season. To examine the tree growth response to drought stress, measurements of annual shoot lengths (ASL) of various tree species with distinct ages and habitats were taken in southeast Germany. The index of relative ASL increase (RAI), which is a standardized ASL increase, was calculated to indicate the growth rate of various tree species between the non-drought (2015–2017) and the drought period (2018–2020). The results showed the ASLs of most early-young trees (< 10 years) significantly showed a decreasing tendency in the drought period, whereas the middle-young (11–15 years) and late-young trees (> 16 years) presented a relatively stable trend. The ring-porous species with anisohydric behavior were likely to have higher RAIs associated with higher drought tolerance than diffuse-porous species with isohydric behavior. However, tree growth rate did not correlate with drought tolerance (resistance) of tree species indicated by leaf turgor loss point (Ψ tlp , MPa). Therefore, this study suggested parameters, such as growth rate, age phases, and microhabitats, should be considered to predict tree species' drought tolerance other than Ψ tlp. Finally, we emphasized tree shoot growth responses to drought were affected by multiple internal and external factors, and strongly depended on species- and site-specific characteristics, such as age phases, xylem structure, hydraulic strategy, microhabitat, grafting effect, and competition. ASL measurement can be recommended to be an easy, fast, and effective method to detect tree growth rate and response to environmental stress. [ABSTRACT FROM AUTHOR]

Abstract: An experiment was conducted over a 3-year period to investigate the aeolian soil water dynamics and ecophysiological characteristics of Haloxylon ammodendron in Ulan Buh Desert, northwest China. Three different communities of H. ammodendron, which consist of two 8- to 10-year plantations and one natural stand, were selected in this study. As a result, the “economic water threshold” of H. ammodendron was expressed at about 2.0% of the absorbed water content. Above this threshold, the aeolian soil water potential decreased by −0.18MPa with a 1.0% decrease in the water content. Below this threshold, the aeolian soil water potential decreased by −2.09MPa with a 1.0% decrease in the water content. The predawn water potential of the shoot can recover to an above zero turgor pressure when the aeolian soil water content exceeded the “economic water threshold”. However, the predawn water potential of the shoot became −3.50MPa, which was lower than that at zero turgor (−3.41MPa) when the aeolian soil water content was about 1.0%. This results indicated that the shoot cannot recover its turgor. Therefore, 1.0% of the aeolian soil water content was defined as the “survival water threshold” of the growth of H. ammodendron. [Copyright &y& Elsevier]

Highlights: [•] A generalized form of a strain energy function is proposed. [•] A mathematical relation between turgor pressure and stretch ratio is developed. [•] The developed relation shows good fit with experimental data. [•] Effects of turgor pressure on cell walls of apple and potato tissues are discussed. [ABSTRACT FROM AUTHOR]

Highlights: [•] Apparent cortex tissue water conductivity of ‘Conference’ pear was calculated from simulation. [•] Simulations with different tissue structures has been done. [•] The model was validated based on the overall shrinkage of the sample. [•] The sensitivity with respect to the membrane permeability and elastic modulus of the cellwall was calculated. [Copyright &y& Elsevier]

Abstract: The growth of hypocotyls and epicotyls has been attributed to the turgor-driven enlargement of cells, a process that is under the control of phytohormones such as auxin. However, the experiments presented here and elsewhere using developing sunflower (Helianthus annuus L.) seedlings raised either in darkness (skotomorphogenesis) or in white light (WL) (photomorphogenesis) indicate that auxin-mediated segment elongation ceases after 1 day, whereas hypocotyl growth continues in the intact system. Based on these results and data from the literature, we propose that hypocotyl growth consists of three inter-related processes: (1) cell division in the apical meristematic regions; (2) turgor-driven cell elongation along the stem; and (3) cell maturation in the basal region of the organ. We document that the closed apical hook (or the corresponding region after opening in WL) is the location where cell division occurs, and suggest that the epidermis and the outer cortex plays an important role in a “pacemaker system” for cell division. Results from the literature support the hypothesis that pectin metabolism in the expansion-limiting epidermal cell wall(s) is involved in wall-loosening and -stiffening. During hypocotyl growth in darkness and WL, turgor pressure is largely maintained, i.e., in H. annuus no hydrostatic pressure-regulated growth occurs. These data do not support the “loss of stability theory” of cell expansion. Finally, we document that turgor maintenance during organ elongation is caused by sucrose catabolism via vacuolar acid invertases, resulting in the generation of hexoses (osmoregulation). Based on these data, we present an integrative model of axial elongation in developing seedlings of dicotyledonous plants and discuss open questions. [Copyright &y& Elsevier]

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: It has been well-established that many epiphytic bromeliads of the atmospheric-type morphology, i.e., with leaf surfaces completely covered by large, overlapping, multicellular trichomes, are capable of absorbing water vapor from the atmosphere when air humidity increases. It is much less clear, however, whether this absorption of water vapor can hydrate the living cells of the leaves and, as a consequence, enhance physiological processes in such cells. The goal of this research was to determine if the absorption of atmospheric water vapor by the atmospheric epiphyte Tillandsia usneoides results in an increase in turgor pressure in leaf epidermal cells that subtend the large trichomes, and, by using chlorophyll fluorescence techniques, to determine if the absorption of atmospheric water vapor by leaves of this epiphyte results in increased photosynthetic activity. Results of measurements on living cells of attached leaves of this epiphytic bromeliad, using a pressure probe and of whole-shoot fluorescence imaging analyses clearly illustrated that the turgor pressure of leaf epidermal cells did not increase, and the photosynthetic activity of leaves did not increase, following exposure of the leaves to high humidity air. These results experimentally demonstrate, for the first time, that the absorption of water vapor following increases in atmospheric humidity in atmospheric epiphytic bromeliads is mostly likely a physical phenomenon resulting from hydration of non-living leaf structures, e.g., trichomes, and has no physiological significance for the plant''s living tissues. [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: Stem sap flow (Q) and leaf turgor pressure (P c) were measured simultaneously on 4-year-old, 2.4m tall ‘Arbequina’ olive trees in a hedgerow orchard. Measurements were performed on well-watered control trees as well as on 60RDI and 30RDI trees (RDI=regulated deficit irrigation). The 60RDI trees received 59.2% of the crop water needs (ETc), and the 30RDI trees received 29.4% of ETc. P c was determined non-invasively using the magnetic leaf patch clamp pressure probe (ZIM probe). The patch pressure P p measured by the probe is inversely correlated with turgor pressure at P c > ca. 50kPa. P c is coupled with xylem pressure; thus P p yields information about the development of tension in xylem. In the case of the control trees a positive correlation between Q and P p was generally found, i.e. Q increased usually with increasing P p and decreased with decreasing P p, as expected. However, Q peaking did not always coincided with P p peaking at noon. Occasionally, Q peaking preceded or followed P p peaking with a time difference of up to 3h in both cases. Under some circumstances, the onset of Q after sunrise was greatly delayed, even though a pronounced increase of P p was observed. A delayed onset of Q after sunrise resulted in hysteresis phenomena, i.e. the linear increase of Q and P p in the morning hours did not coincide with the corresponding decrease of Q and P p in the afternoon. The development of severe water stress (P c < ca. 50kPa) associated with the increase in the intercellular spaces of the spongy tissue in the leaves resulted in inverted diurnal P p curves, i.e. minimum P p values were recorded at noon and maximum P p values during the night on the 30RDI trees. The effects were reversible as shown by re-watering. By contrast, the magnitude of Q decreased continuously from the turgescent state to the state of severe water stress; maximum Q values were still recorded around noon. The data suggests that short-range tension forces are responsible for water lifting in olive trees and that water uptake from water storage reservoirs must play an important role in the supply of the leaves with water. Furthermore, for setting of irrigation thresholds the finding of shape changes of the P p curves upon severe water stress seems to be a useful indicator. Such shape changes are detected and monitored more sensitively than changes in the magnitude of sap flow rates or of turgor pressure. [Copyright &y& Elsevier]

Peptidoglycan is the major structural component of the bacterial cell wall. It provides resistance against turgor and its cleavage by hydrolases such as lysozymes results in bacteriolysis. Most, if not all, animals produce lysozymes as key effectors of their innate immune system. Recently, highly specific bacterial proteinaceous lysozyme inhibitors against the three major animal lysozyme families have been discovered in bacteria, and these may represent a bacterial answer to animal lysozymes. Here, we will review their properties and phylogenetic distribution, present their structure and molecular interaction mechanism with lysozyme, and discuss their possible biological functions and potential applications. [ABSTRACT FROM AUTHOR]

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]

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]

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: Young mahogany (Swietenia macrophylla King) plants were grown under either well-watered (pre-dawn leaf water potential, Ψ pd, ca. −0.40MPa) or drought (Ψ pd, ca. −3.52MPa) conditions to examine some physiological strategies that allow the maintenance of leaf turgor. In well-watered plants, stomatal conductance (g s) was nearly constant (440mmolm−2 s−1) between 7:00 and 13:00h. This was accomplished by significant increases in transpiration (E) and apparent total hydraulic conductance (K T), in which averages were higher at 13:00h. From 13:00 to 17:00h, g s, E, and K T decreased sharply, reaching their lower values at 17:00h. In these plants, significant increases in height (116%), stem diameter (50%) and leaf area (200%) were registered over the experimental period (20 days). Analyses of linear regression between g s or E and leaf-to-air vapor pressure deficit (Δ w) were not significant. In water-stressed plants, g s and E were higher at 7:00h and lower from 9:00 to 17:00h, while K T was higher in early morning (7:00h) and in late afternoon (17:00h) than between 9:00 and 15:00h. Moreover, both g s and E decreased potentially (P <0.001) with the diurnal increases on Δ w. Drought also decreased leaf and leaflet numbers and reduced total leaf area, but had no effect on stem height and diameter. Leaf proline was higher (ca. 400%, between 13:00 and 15:00h) in water-stressed plants, suggesting osmotic adjustment under drought. Twelve hours after resumption of irrigation, Ψ pd was similar (P >0.05) between well-watered and drought-stressed plants, suggesting an ability of plants to recover turgor after stress cessation. Altogether, our data support the hypothesis that young mahogany plants have the ability to satisfactorily tolerate or postpone drought. [Copyright &y& Elsevier]

We outline several principles that we believe define the gating of two bacterial mechanosensitive channels, MscL and MscS. Serving as turgor regulators in bacteria and other walled cells, these molecules are tangible models for studying conformational transitions in membrane proteins driven directly by membrane tension. MscL, a compact pentamer, reversibly opens a gigantic 30-A pore at near-lytic tensions. MscS, a heptameric complex, exhibits transient activation of a smaller pore at moderate tensions, thereby entering a tension-insensitive inactivated state. By comparing the structures and predicted transitions in these channels, we concluded that opening is commonly achieved through tilting and outward motion of the porelining helices, which is kinetically limited by hydration of the pore. The intricate adaptive behavior in MscS appears to depend on specific interhelical associations and the flexibility of the pore-lining helices. We discuss physical factors that may direct the transitions and stabilize main functional states in these channels. [ABSTRACT FROM AUTHOR]

Abstract: The gas vesicles of the cyanobacterium Microcystis sp. collapse under pressures ranging from 0.65–1.10 MPa, determined from turbidity changes in a pressure nephelometer. In turgid cells, collapse occurs at a lower range of pressures; the difference is equal to the cell turgor pressure. The turgor pressure decreases, however, as gas vesicles collapse; this decrease is minimised by calculating the turgor pressure in samples with few of their gas vesicles collapsed. Previously, pressure and turbidity were measured in discrete steps, using analogue meters, or continuously, using chart recorders: turgor pressure was calculated from the mean or median collapse pressures. We describe modifications allowing continuous digital recording; the output was modelled with polynomial or sigmoid functions, the latter providing the best fit over the full collapse-pressure curve; turgor pressure could then be calculated for any point on the collapse-pressure curve. The shape of the collapse-pressure curve was affected by the rate of pressure rise; curves were similar to those from step-wise methods when the pressure was raised at approximately 4 kPa s−1. Under a rapid, almost instantaneous, rise in pressure there was a larger initial decrease in turgor and from the subsequent recovery the hydraulic conductivity of the cell surface could be calculated; the new method gave improved measurements of the cell volumetric elastic modulus. Following collapse of half the gas vesicles, cells recovered their full turgor pressure after 3 h. This suggests turgor homeostasis. These methods are applicable to other bacteria with gas vesicles, including Escherichia coli, if it could be genetically modified to express transgenic gas vesicles. [Copyright &y& Elsevier]

• Hard leaves commonly occur in water- and nutrient-limited habitats. • Some anatomical features conferring mechanical resistance can also assure drought tolerance. • Thick cell walls and high major vein density allow leaves to endure water shortage. Leaves of terrestrial plants vary tremendously in size, shape, and stiffness. Hard leaves with high mass per unit area (LMA) occur more frequently in water- and nutrient-limited habitats, where stress-tolerance is key to survival. Coordination between leaf mechanical properties and drought tolerance can arise because some (but not all) of the anatomical modifications leading to high LMA are mechanistically correlated to physiological traits conferring tolerance to dehydration. Thick cell walls are frequently coupled with low turgor loss point values, and also prevent cell shrinkage and collapse after turgor loss has occurred. This also protects the leaf against shrinking-induced loss of water transport capacity in the extra-vascular pathway. In turn, vascular water transport in the leaf veins is at risk of embolism-induced disruption under drought, but higher length of major veins per unit area can provide alternative pathways for water delivery to the mesophyll, while contributing to increased leaf stiffness. Water shortage in dry and warm habitats implies the risk of reduced photosynthetic rates, apparently favouring species that produce hard and drought-tolerant leaves, to warrant long leaf life span and to maintain gas exchange and positive carbon gain when conditions become harsh. [ABSTRACT FROM AUTHOR]

Abstract: We have studied interactions between leaf abscisic acid (ABA) and the response of gas exchange and solute synthesis in the three major species of the Canarian laurel forest (Laurus azorica (Seub.) Franco, Persea indica (L.) K. Spreng and Myrica faya Aiton). Trees were subjected to drought under controlled conditions by withholding water until leaf relative water content (RWC) reached 50–55%. Drought treatment reduced predawn leaf Ψ together with Ψ s in all the studied species. At moderate drought (RWC ca. 80%) L. azorica showed higher net assimilation rate than the other species. In addition, this species showed significant accumulation of ABA, total soluble sugars (TSS) and proline in leaves, contributing to lowered that might result in maintenance of leaf turgor. By contrast, M. faya showed the lowest Ψ that was not accompanied by changes in , neither ABA concentration nor in leaf solutes. P. indica performed similarly to M. faya but it had the lowest rates of gas exchange indicating that this species was the most sensitive to drought treatment. All results clearly indicate that L. azorica exhibited higher capacity for drought acclimation than the other laurel species. This response seems to be mediated by ABA synthesis because significant relationships between leaf ABA, and solute accumulation were found. These data provide new information about the role of ABA in the physiological responses of laurel tree species to drought. [Copyright &y& Elsevier]

Abstract: Due to an absence of published primary data, this study explores dehydration prevalence and the change in physiological parameters frequently used to assess dehydration (fluid deficit) in older hospitalized people, as no standard measurement method exists. This observational longitudinal cohort study recruited 43 people aged 60 years or over, voluntarily admitted to a tertiary teaching hospital''s Geriatric and Rehabilitation Unit (GARU). Over 40 clinical, hematological and urinary biochemical parameters employed by medical officers during dehydration assessment, identified through literature, interviews and focus group were investigated. Short-term weight changes, intra- and inter-rater repeatability of dehydration assessments were completed to assess validation and precision of the clinician''s clinical dehydration assessment. Systolic blood pressure drop on standing, sternal skin turgor, tongue dryness and body mass index (BMI) were associated with hydration status; demonstrated clinically meaningful differences between groups. BMI negatively confounded the association between dehydration and systolic blood pressure drop on standing. Physical, rather than biochemical, parameters more often identified mild dehydration. The findings challenge common expectations of hematological and physiological measurement changes occurring in older people clinically assessed as dehydrated and emphasize the need to adjust for potential confounders during exploration of the associations of clinical parameters with dehydration status. [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]

Summary: We describe the involvement of abscisic acid (ABA) in the control of differential growth of roots and shoots of nutrient limited durum wheat plants. A ten-fold dilution of the optimal concentration of nutrient solution inhibited shoot growth, while root growth remained unchanged, resulting in a decreased shoot/root ratio. Addition of fluridone (inhibitor of ABA synthesis) prevented growth allocation in favour of the roots. This suggests the involvement of ABA in the redirecting of growth in favour of roots under limited nutrient supply. The ABA content was greater in shoots and growing apical root parts of starved plants than in nutrient sufficient plants. Accumulation of ABA in shoots of nutrient deficient plants was linked to a decrease in leaf turgor. Increased flow of ABA in the phloem apparently contributed to the accumulation of ABA in the apical part of the roots. Thus, partitioning of growth between roots and shoots of wheat plants limited in mineral nutrients appears to be modulated by accumulation of ABA in roots. This ABA may originate in the shoots, where its synthesis is stimulated by the loss of leaf turgor. [Copyright &y& Elsevier]

Cells store lipids in droplets. Studies addressing how mammals control lipid-based energy homeostasis have implicated proteins of the PAT domain family, such as perilipin that surrounds the lipid droplets. Perilipin knock-out mice are lean and resistant to obesity. Factors that mediate lipid storage in fungi are still unknown. Here we describe a gene (Mpl1) in the economically important insect fungal pathogen Metarhizium anisopliae that has structural similarities to mammalian perilipins. Consistent with a role in lipid storage, Mpl1 is predominantly expressed when M. anisophiae is engaged in accumulating lipids and ectopically expressed green fluorescent protein-tagged MPL1 (Metarhizium periipin-like protein) localized to lipid droplets. Mutant M anisophiae lacking MPL1 have thinner hyphae, fewer lipid droplets, particularly in appressoria (specialized infection structures at the end of germ tubes), and a decrease in total lipids. Mpl1 therefore acts in a perilipin-like manner suggesting an evolutionary conserved function in lipid metabolism. However, reflecting general differences between animal and fungal lineages, these proteins have also been selected to cope with different tasks. Thus, turgor generation by ΔMpl1 appressoria is dramatically reduced indicating that lipid droplets are required for solute accumulation. This was linked with the reduced ability to breach insect cuticle so that Mpl1 is a pathogenicity determinant. Blast searches of fungal genomes revealed that perilipin homologs are found only in pezizomycotinal ascomycetes and occur as single copy genes. Expression of Mpl1 in yeast cells, a fungus that lacks a perilipin-like gene, blocked their ability to mobilize lipids during starvation conditions. [ABSTRACT FROM AUTHOR]

Abstract: The effect of turgor on the micromechanical properties of apples (Malus domestica Borkh. cv Jonagored) and its relation to structural parameters of the cells was investigated. Mechanical measurements were carried out using a miniature tensile stage mounted under a microscope. Turgor was manipulated by soaking tissue samples in iso-, hypo- or hypertonic mannitol solutions. Samples were then subjected to tensile and compression tests, during which the deformation of the individual cells was recorded. In both tests, sigmoidal stress–strain curves were found, where stiffness increases with strain. With increasing turgor, strain at maximum stress became significantly (p <0.05) lower while stiffness increased, but no clear effect on failure stress was found. As expected, fresh apples proved to be firmer and stiffer than stored apples, while the influence of turgor was the same. Measurement of initial cell parameters (area, length, width, aspect, roundness) showed that the apples in the experiment were homogeneous, having comparable cell sizes. Manipulation of turgor did not affect initial cell parameters, but the magnitude of cell deformations was clearly influenced. Larger deformations were found in flaccid cells. Changes in length and width were closely related to strain measurements. In conformity with micromechanical parameters, deformations were smaller in stored than in fresh apples. [Copyright &y& Elsevier]

Summary: The premetamorphotic morphology and metamorphotic degeneration of the tail notochord of anuran tadpoles has been investigated. For this purpose the functional anatomy and origin of the notochord turgor was analysed in 10 species macroscopically and using light, transmission and scanning electron microscopic techniques. The notochord consists of the fibrous notochord sheath, which surrounds the notochord cells. Within the sheath these cells form a net-like unit. The inner cells are derived from the marginal notochord cells (chordoblasts). They are protected from mechanical overload by intracellular filaments and desmosomes. Due to their vacuoles, which are filled with a hyaline liquid, they have a constant volume but are deformable. Dissolved substances may pass from the vascularized fin to the notochord cells. The transport from marginal to inner cells occurs via cytopempsis and micropinocytosis. The morphological correlation of this process consists of multiple membrane invaginations and intracellular vesicles. Within the notochord cells a high turgor pressure has been observed. During metamorphosis the membrane vesiculation persists and the notochord cells degenerate. Due to the loss of turgor pressure the tight consistency of the notochord is lost. The collagen filaments and the elastic membrane of the notochord sheath dissolve. Notochord cells with their filaments, high turgor pressure and their central vacuole can function as a combined mechanical and physiological system, which is adaptable to the needs of pressure, compression, tensile and bending forces. [Copyright &y& Elsevier]

Abstract: The exposure to irradiation pretreatment results in increase in cell wall permeabilization, leading to softening of tissue and the loss of turgor pressure, thereby affecting the reconstitution properties. Rehydration kinetics of gamma-irradiated (3.0–9.0kGy) and water (0°Brix) or osmotic pretreated (up to 50°Brix) carrot samples were studied. The diffusion coefficient for water infusion and solute loss during rehydration of irradiated and osmotically pretreated and finally dried samples were estimated considering Fickian diffusion. The results shows that as increase in doses of gamma irradiation resulted in decrease in water and increase in solute diffusion coefficient. The pretreatment with water (0°Brix) resulted in increased water gain and reduced solute loss during rehydration for irradiated samples. The samples pretreated with osmotic solution of 10°Brix (concentration more than the natural cell water concentration) could not absorb more water in comparison with control because of cell permeabilization caused by the osmotic treatment due to osmotic stress. The water diffusion coefficient values decreased and solute diffusion coefficient increased with an increase in dose rates. The equilibrium moisture as well as equilibrium solid content were dependent on the treatment conditions. [Copyright &y& Elsevier]

Pearl millet (Pennisetum glaucum [L.] Leeke) is known to adapt to very dry conditions, however, the control of water loss and dehydration tolerance to drought is still not completely understood. Effects of water stress on root morphologies, osmotic relations, and stomatal conductance contributing to plant growth or turgor maintenance was investigated. Water stress was imposed by withholding water for 3 weeks at the seedling stage in a greenhouse. Irrigated treatments and two stress treatments were conducted in a tube culture experiment. One stress treatment was done by imposing water deficit, particularly in shallow areas of the soil (semi-drought), and the other was done by imposing widespread water deficit in the soil (drought).The genetic diversities in the total root length (TRL) were significantly related to the relative growth ratio of the shoot (RGR) within 4–21 days after withholding water in both stress treatments. On the other hand, osmotic adjustment was also strongly correlated with RGR and leaf turgor potential (LTP) in both stress treatments, but the effects of TRL and OA in terms of contributing to the variance in RGR was comparatively low under drought conditions. These results demonstrated that OA and TRL were dependent on the degree of water deficit, and these traits were the most important factors regarding turgor maintenance and plant growth under drought conditions during the seedling stage. [Copyright &y& Elsevier]

Transmembrane ion transport processes play a key role in the adaptation of cells to hyperosmotic conditions. Previous work has shown that the disruption of a ktrB/ntpJ-like putative Na+/K+ transporter gene in the cyanobacterium Synechocystis sp. PCC 6803 confers increased Na+ sensitivity, and inhibits HCO3- uptake. Here, we report on the mechanistic basis of this effect. Heterologous expression experiments in Escherichia coli show that three Synechocystis genes are required for K+ transport activity. They encode an NAD+-binding peripheral membrane protein (ktrA; s110493), an integral membrane protein, belonging to a superfamily of K+ transporters (ktrB; formerly ntpJ; sir1509), and a novel type of ktr gene product, not previously found in Ktr systems (ktrE; slr1508). In E. coli, Synechocystis KtrABE- mediated K+ uptake occurred with a moderately high affinity (Km of about 60 μM), and depended on both Na+ and a high membrane potential, but not on ATP. KtrABE neither mediated Na+ uptake nor Na+ efflux. In Synechocystis sp. PCC 6803, KtrB-mediated K+ uptake required Na+ and was inhibited by protonophore. A ΔktrB strain was sensitive to long term hyperosmotic stress elicited by either NaC1 or sorbitol. Hyperosmotic shock led initially to loss of net K+ from the cells. The ΔktrB cells shocked with sorbitol failed to reaccumulate K+ up to its original level. These data indicate that in strain PCC 6803 K+ uptake via KtrABE plays a crucial role in the early phase of cell turgor regulation after hyperosmotic shock. [ABSTRACT FROM AUTHOR]