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Stomata are the key nodes linking photosynthesis and transpiration. By regulating the opening degree of stomata, plants successively achieve the balance between water loss and carbon dioxide acquisition. The dynamic behaviour of stomata is an important cornerstone of plant adaptability. Though there have been miscellaneous experimental results on stomata and their constituent cells, the guard cells and the subsidiary cells, current theory of stomata regulation is far from clear and unified. In this work, we develop an integrated model to describe the stomatal dynamics of seed plants based on existing experimental results. The model includes three parts: (1) a passive mechanical model of the stomatal aperture as a bivariate function of the guard‐cell turgor and the subsidiary‐cell turgor; (2) an active regulation model with a target ion‐content in guard cells as a function of their water potential; and (3) a dynamical model for the movement of potassium ions and water content. Our model has been used to reproduce abundant experimental phenomena semi‐quantitatively. With accurately measured parameters, our model can also be used to predict stomatal responses to changes of environmental conditions. Summary statement: A stomata model is developed based on existing experiments and reproduces important stomatal behaviour. The model takes into account passive mechanical interaction between guard cells and subsidiary cells, active movement of potassium ions, and water transport driven by water potential. [ABSTRACT FROM AUTHOR]

Turgor pressure provides the force needed to stress and deform the cell walls of plants, algae, and fungi during expansive growth. However, turgor pressure plays another subtle but equally important role in expansive growth of walled cells: it connects the two biophysical processes of water uptake and wall deformation to ensure that the volumetric rates of water uptake and enlargement of the cell wall chamber are equal. In this study, the role of turgor pressure as a 'connector' is investigated analytically by employing validated and established biophysical equations. The objective is to determine the effect of 'wall loosening' on the magnitude of turgor pressure. It is known that an increase or decrease in turgor pressure and/or wall loosening rate increases or decreases the expansive growth rate, respectively. Interestingly, it is shown that an increase in the wall loosening rate decreases the turgor pressure slightly, thus reducing the effect of wall loosening on increasing the expansive growth rate. Other analyses reveal that reducing the rate of water uptake results in a larger decrease in turgor pressure with the same increase in wall loosening rate, which further reduces the effect of wall loosening on increasing the expansive growth rate. [ABSTRACT FROM AUTHOR]

Summary: Growth is central to plant morphogenesis. Plant cells are encased in rigid cell walls, and they must overcome physical confinement to grow to specific sizes and shapes. Cell wall tension and turgor pressure are the main mechanical components impacting plant cell growth. Cell wall mechanics has been the focus of most plant biomechanical studies, and turgor pressure was often considered as a constant and largely passive component. Nevertheless, it is increasingly accepted that turgor pressure plays a significant role in plant growth. Numerous theoretical and experimental studies suggest that turgor pressure can be both spatially inhomogeneous and actively modulated during morphogenesis. Here, we revisit the pressure–growth relationship by reviewing recent advances in investigating the interactions between cellular/tissular pressure and growth. [ABSTRACT FROM AUTHOR]

Summary: Despite the importance of understanding plant growth, the mechanisms underlying how plant and fruit growth declines during drought remain poorly understood. Specifically, it remains unresolved whether carbon or water factors are responsible for limiting growth as drought progresses. We examine questions regarding the relative importance of water and carbon to fruit growth depending on the water deficit level and the fruit growth stage by measuring fruit diameter, leaf photosynthesis, and a proxy of cell turgor in olive (Olea europaea). Flow cytometry was also applied to determine the fruit cell division stage. We found that photosynthesis and turgor were related to fruit growth; specifically, the relative importance of photosynthesis was higher during periods of more intense cell division, while turgor had higher relative importance in periods where cell division comes close to ceasing and fruit growth is dependent mainly on cell expansion. This pattern was found regardless of the water deficit level, although turgor and growth ceased at more similar values of leaf water potential than photosynthesis. Cell division occurred even when fruit growth seemed to stop under water deficit conditions, which likely helped fruits to grow disproportionately when trees were hydrated again, compensating for periods with low turgor. As a result, the final fruit size was not severely penalized. We conclude that carbon and water processes are able to explain fruit growth, with importance placed on the combination of cell division and expansion. However, the major limitation to growth is turgor, which adds evidence to the sink limitation hypothesis. Significance Statement: The mechanism by which whole plants/organs reduce their growth during drought is still relatively little studied, the reduction of photosynthesis or turgor being the two major limitations considered. This paper aims at adding some evidence to the current debate on growth limitation thanks to a synchronous estimation of growth, turgor, and photosynthesis in olive trees (Olea europaea) exposed or not to water deficit using sensors and modeling with implications on process‐based models of forest and agriculture productivity. [ABSTRACT FROM AUTHOR]

Mechanical rupture, or lysis, of the cytoplasmic membrane is a common cell death pathway in bacteria occurring in response to β-lactam antibiotics. A better understanding of the cellular design principles governing the susceptibility and response of individual cells to lysis could indicate methods of potentiating β-lactam antibiotics and clarify relevant aspects of cellular physiology. Here, we take a single-cell approach to bacterial cell lysis to examine three cellular features—turgor pressure, mechanosensitive channels, and cell shape changes—that are expected to modulate lysis. We develop a mechanical model of bacterial cell lysis and experimentally analyze the dynamics of lysis in hundreds of single Escherichia coli cells. We find that turgor pressure is the only factor, of these three cellular features, which robustly modulates lysis. We show that mechanosensitive channels do not modulate lysis due to insufficiently fast solute outflow, and that cell shape changes result in more severe cellular lesions but do not influence the dynamics of lysis. These results inform a single-cell view of bacterial cell lysis and underscore approaches of combatting antibiotic tolerance to β-lactams aimed at targeting cellular turgor. [ABSTRACT FROM AUTHOR]

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

The cytoplasm of bacteria is maintained at a higher osmolality than the growth medium, which generates a turgor pressure. The cell membrane (CM) cannot support a large turgor, so there are two possibilities for transferring the pressure to the peptidoglycan cell wall (PGW): (1) the CM could be pressed directly against the PGW, or (2) the CM could be separated from the PGW by a periplasmic space that is isoosmotic with the cytoplasm. There is strong evidence for gram-negative bacteria that a periplasm exists and is isoosmotic with the cytoplasm. No comparable studies have been done for gram-positive bacteria. Here I suggest that a periplasmic space is probably essential in order for the periplasmic proteins to function, including especially the PBPs that remodel the peptidoglycan wall. I then present a semi-quantitative analysis of how teichoic acids could support a periplasm that is isoosmotic with the cytoplasm. The fixed anionic charge density of teichoic acids in the periplasm is ∼0.5 M, which would bring in ∼0.5 M Na+ neutralizing ions. This approximately balances the excess osmolality of the cytoplasm that would produce a turgor pressure of 19 atm. The 0.5 M fixed charge density is similar to that of proteoglycans in articular cartilage, suggesting a comparability ability to support pressure. An isoosmotic periplasm would be especially important for cell division, since it would allow CM constriction and PGW synthesis to avoid turgor pressure. [ABSTRACT FROM AUTHOR]

The process of leaf elongation in grasses is characterized by the creation and transformation of distinct cell zones. The prevailing turgor pressure within these cells is one of the key drivers for the rate at which these cells divide, expand and differentiate, processes that are heavily impacted by drought stress. In this article, a turgor‐driven growth model for grass leaf elongation is presented, which combines mechanistic growth from the basis of turgor pressure with the ontogeny of the leaf. Drought‐induced reductions in leaf turgor pressure result in a simultaneous inhibition of both cell expansion and differentiation, lowering elongation rate but increasing elongation duration due to the slower transitioning of cells from the dividing and elongating zone to mature cells. Leaf elongation is, therefore, governed by the magnitude of, and time spent under, growth‐enabling turgor pressure, a metric which we introduce as turgor‐time. Turgor‐time is able to normalize growth patterns in terms of varying water availability, similar to how thermal time is used to do so under varying temperatures. Moreover, additional inclusion of temperature dependencies within our model pioneers a novel concept enabling the general expression of growth regardless of water availability or temperature. A model for grass leaf elongation is presented, which combines mechanistic growth based on turgor pressure and leaf ontogeny. An inverse relation was found between the rate and duration of the elongation rate, allowing for uniform expression of growth in terms of a new concept called 'turgor‐time'. [ABSTRACT FROM AUTHOR]

Background and Aims Turgor pressure within a plant cell represents the key to the mechanistical descriptiion of plant growth, combining the effects of both water and carbon availability. The high level of spatio-temporal variation and diurnal dynamics in turgor pressure within a single plant make it a challenge to model these on the fine spatial scale required for functional–structural plant models (FSPMs). A conceptual model for turgor-driven growth in FSPMs has been established previously, but its practical use has not yet been explored. Methods A turgor-driven growth model was incorporated in a newly established FSPM for soybean. The FSPM simulates dynamics in photosynthesis, transpiration and turgor pressure in direct relation to plant growth. Comparisons of simulations with field data were used to evaluate the potential and shortcomings of the modelling approach. Key Results Model simulations revealed the need to include an initial seed carbon contribution, a more realistic sink function, an estimation of respiration, and the distinction between osmotic and structural sugars, in order to achieve a realistic model of plant growth. However, differences between simulations and observations remained in individual organ growth patterns and under different environmental conditions. This exposed the need to further investigate the assumptions of developmental and environmental (in)sensitivity of the parameters, which represent physiological and biophysical organ properties in the model, in future research. Conclusions The model in its current form is primarily a diagnostic tool, to better understand and model the behaviour of water relations on the scale of individual plant organs throughout the plant life cycle. Potential future applications include its use as a phenotyping tool to capture differences in plant performance between genotypes and growing environments in terms of specific plant characteristics. Additionally, focused experiments can be used to further improve the model mechanisms to lead to better predictive FSPMs, including scenarios of water deficit. [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]

Bacterial cytokinesis begins with the assembly of FtsZ into a Z ring at the center of the cell. The Z-ring constriction in Gram-negative bacteria may occur in an environment where the periplasm and the cytoplasm are isoosmotic, but in Gram-positive bacteria the constriction may have to overcome a substantial turgor pressure. We address three potential sources of invagination force. (1) FtsZ itself may generate force by curved protofilaments bending the attached membrane. This is sufficient to constrict liposomes in vitro. However, this force is on the order of a few pN, and would not be enough to overcome turgor. (2) Cell wall (CW) synthesis may generate force by pushing the plasma membrane from the outside. However, this would probably require some kind of Brownian ratchet to separate the CW and membrane sufficiently to allow a glycan strand to slip in. The elastic element is not obvious. (3) Excess membrane production has the potential to contribute significantly to the invagination force. If the excess membrane is produced under the CW, it would force the membrane to bleb inward. We propose here that a combination of FtsZ pulling from the inside, and excess membrane pushing membrane inward may generate a substantial constriction force at the division site. This combined force generation mechanism may be sufficient to overcome turgor pressure. This would abolish the need for a Brownian ratchet for CW growth, and would permit CW to operate by reinforcing the constrictions generated by FtsZ and excess membrane. [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 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]

As land plants grow and develop, they encounter complex mechanical challenges, especially from winds and turgor pressure. Mechanosensitive control over growth and morphogenesis is an adaptive trait, reducing the risks of breakage or explosion. This control has been mostly studied through experiments with artificial mechanical loads, often focusing on cellular or molecular mechanotransduction pathway. However, some important aspects of mechanosensing are often neglected. (i) What are the mechanical characteristics of different loads and how are loads distributed within different organs? (ii) What is the relevant mechanical stimulus in the cell? Is it stress, strain, or energy? (iii) How do mechanosensing cells signal to meristematic cells? Without answers to these questions we cannot make progress analyzing the mechanobiological effects of plant size, plant shape, tissue distribution and stiffness, or the magnitude of stimuli. This situation is rapidly changing however, as systems mechanobiology is being developed, using specific biomechanical and/or mechanobiological models. These models are instrumental in comparing loads and responses between experiments and make it possible to quantitatively test biological hypotheses describing the mechanotransduction networks. This review is designed for a general plant science audience and aims to help biologists master the models they need for mechanobiological studies. Analysis and modeling is broken down into four steps looking at how the structure bears the load, how the distributed load is sensed, how the mechanical signal is transduced, and then how the plant responds through growth. Throughout, two examples of adaptive responses are used to illustrate this approach: the thigmorphogenetic syndrome of plant shoots bending and the mechanosensitive control of shoot apical meristem (SAM) morphogenesis. Overall this should provide a generic understanding of systems mechanobiology at work. [ABSTRACT FROM AUTHOR]

Background Turgor pressure is an essential feature of plants; however, whereas its physiological importance is unequivocally recognized, its relevance to development is often reduced to a role in cell elongation. Scope This review surveys the roles of turgor in development, the molecular mechanisms of turgor regulation and the methods used to measure turgor and related quantities, while also covering the basic concepts associated with water potential and water flow in plants. Three key processes in flower development are then considered more specifically: flower opening, anther dehiscence and pollen tube growth. Conclusions Many molecular determinants of turgor and its regulation have been characterized, while a number of methods are now available to quantify water potential, turgor and hydraulic conductivity. Data on flower opening, anther dehiscence and lateral root emergence suggest that turgor needs to be finely tuned during development, both spatially and temporally. It is anticipated that a combination of biological experiments and physical measurements will reinforce the existing data and reveal unexpected roles of turgor in development. [ABSTRACT FROM AUTHOR]

Premise of research. Papaya (Carica papaya L.) is a fast-growing plant that is able to reorient quickly from a tilted position due to a local growth in the basal stem region. This seems to be a necessary adaptation in the struggle for light in the plant's natural habitat, natural forest gaps. Interestingly, the stem anatomy of papaya consists exclusively of parenchymatous wood exhibiting substantial turgor pressure. The only reinforcing tissue is found in the bark, consisting of a lattice-like mesh of lignified fibers filled with parenchyma. This peculiar mechanism of reorientation raised questions concerning the role of turgor pressure during growth and the mechanical interactions between fiber mesh and parenchyma as a consequence of the unusual anatomy. Methodology. A set of mechanical measurements of sections of secondary phloem and xylem were conducted, comparing Young's modulus and turgor pressure of the upper and lower sides of reerecting stems. Additionally, tissues from both sides were microscopically analyzed. Pivotal results. We found that Young's moduli differed significantly between tissues from both sides of reerecting stems due to morphological adaptations. Experimental data showed that turgor pressure remained constant during cell expansion throughout the erecting process. Thus, cell growth and turgor pressure sustaining water inflow are in a state of equilibrium. Microscopic analyses revealed pronounced radially directed cell growth in the upper side of the xylem in comparison to the lower side. Conclusions. The stem bends upward via a coupling effect due to local secondary growth of the xylem affecting the peculiar phloem fiber arrangement. The xylem extends by directed radial growth on the upper side of leaning stems and generates an outward-pointing force. The phloem fiber mesh expands in a tangential direction. As a result, the structure contracts in an axial direction and eventually causes a pulling force on the upper side. [ABSTRACT FROM AUTHOR]

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]

Although most green algae typically occur in aquatic ecosystems, many species also live partly or permanently under aeroterrestrial conditions, where the cells are exposed to the atmosphere and hence regularly experience dehydration.The ability of algal cells to survive in an air-dried state is termed desiccation tolerance.The mechanisms involved in desiccation tolerance of green algae are still poorly understood, and hence the aim of this review is to summarize recent findings on the effects of desiccation and osmotic water loss. Starting from structural changes, physiological, and biochemical consequences of desiccation will be addressed in different green-algal lineages. The available data clearly indicate a range of strategies, which are rather different in streptophycean and non-streptophycean green algae. While members of the Trebouxiophyceae exhibit effective water loss-prevention mechanisms based on the biosynthesis and accumulation of particular organic osmolytes such as polyols, these compounds are so far not reported in representatives of the Streptophyta. In members of the Streptophyta such as Klebsormidium, the most striking observation is the appearance of cross-walls in desiccated samples, which are strongly undulating, suggesting a high degree of mechanical flexibility. This aids in maintaining structural integrity in the dried state and allows the cell to maintain turgor pressure for a prolonged period of time during the dehydration process. Physiological strategies in aeroterrestrial green algae generally include a rapid reduction of photosynthesis during desiccation, but also a rather quick recovery after rewetting, whereas aquatic species are sensitive todrying.The underlying mechanisms suchasthe affected molecular components of the photosynthetic machinery are poorly understood in green algae. Therefore, modern approaches based on transcriptomics, proteomics, and/or metabolomics are urgently needed to better understand the molecular mechanisms involved in desiccation-stress physiology of these organisms. The very limited existing information is described in the present review. [ABSTRACT FROM AUTHOR]

By taking advantage of large cell size of Chara corallina, we analyzed the membrane depolarization induced by decreased turgor pressure (Shimmen in J Plant Res 124:639-644, ). In the present study, the response to increased turgor pressure was analyzed. When internodes were incubated in media containing 200 mM dimethyl sulfoxide, their intracellular osmolality gradually increased and reached a steady level after about 3 h. Upon removal of dimethyl sulfoxide, turgor pressure quickly increased. In response to the increase in turgor pressure, the internodes generated a transient membrane depolarization at its nodal end. The refractory period was very long and it took about 2 h for full recovery after the depolarizing response. Involvement of protein synthesis in recovery from refractoriness was suggested, based on experiments using inhibitors. [ABSTRACT FROM AUTHOR]

A cell-growth-based algorithm is presented based on the biomechanics of plant cells in tissues to help explain the typical differences in cellular architecture found between different pome fruit species, cultivars and tissues. The cell was considered as a closed thin-walled structure, maintained in tension by turgor pressure. The cell walls of adjacent cells were modelled as parallel and linearly elastic elements, which obeyed Hooke's law. A Voronoi tessellation was used to generate the initial topology of the cells. Cell expansion then resulted from turgor pressure acting on the yielding cell wall material. To find the sequence positions of each vertex of the cell walls, and thus, the shape of the cells with time, a system of differential equations for the positions and velocities of each vertex were established and solved using a Runge-Kutta fourth and fifth order (ODE45) method. The model was used to generate realistic 2D fruit tissue structures composed of cells of random shapes and sizes, cell walls and intercellular spaces. Comparison was made with fruit tissue micrographs. The virtual tissues can be used for numerical simulation of heat and mass transfer phenomena or mechanical deformation during controlled atmosphere storage of fresh pome fruit. [ABSTRACT FROM AUTHOR]

Plant cell expansion is controlled by a fine-tuned balance between intracellular turgor pressure, cell wall loosening and cell wall biosynthesis. To understand these processes, it is important to gain in-depth knowledge of cell wall mechanics. Pollen tubes are tip-growing cells that provide an ideal system to study mechanical properties at the single cell level. With the available approaches it was not easy to measure important mechanical parameters of pollen tubes, such as the elasticity of the cell wall. We used a cellular force microscope ( CFM) to measure the apparent stiffness of lily pollen tubes. In combination with a mechanical model based on the finite element method ( FEM), this allowed us to calculate turgor pressure and cell wall elasticity, which we found to be around 0.3 MPa and 20-90 MPa, respectively. Furthermore, and in contrast to previous reports, we showed that the difference in stiffness between the pollen tube tip and the shank can be explained solely by the geometry of the pollen tube. CFM, in combination with an FEM-based model, provides a powerful method to evaluate important mechanical parameters of single, growing cells. Our findings indicate that the cell wall of growing pollen tubes has mechanical properties similar to rubber. This suggests that a fully turgid pollen tube is a relatively stiff, yet flexible cell that can react very quickly to obstacles or attractants by adjusting the direction of growth on its way through the female transmitting tissue. [ABSTRACT FROM AUTHOR]

Turgor pressure in plant cells is involved in many important processes. Stable and normal turgor pressure is required for healthy growth of a plant, and changes in turgor pressure are indicative of changes taking place within the plant tissue. The ability to quantify the turgor pressure of plant cells in vivo would provide opportunities to understand better the process of pressure regulation within plants, especially when plant stress is considered, and to understand the role of turgor pressure in cellular signaling. Current experimental methods do not separate the influence of the turgor pressure from the effects associated with deformation of the cell wall when estimates of turgor pressure are made. In this paper, nanoindentation measurements are combined with finite element simulations to determine the turgor pressure of cells in vivo while explicitly separating the cell-wall properties from the turgor pressure effects. Quasi-static cyclic tests with variable depth form the basis of the measurements, while relaxation tests at low depth are used to determine the viscoelastic material properties of the cell wall. Turgor pressure is quantified using measurements on Arabidopsis thaliana under three pressure states (control, turgid and plasmolyzed) and at various stages of plant development. These measurements are performed on cells in vivo without causing damage to the cells, such that pressure changes may be studied for a variety of conditions to provide new insights into the biological response to plant stress conditions. [ABSTRACT FROM AUTHOR]

The non-invasive leaf patch clamp pressure (LPCP) probe measures the attenuated pressure of a leaf patch, Pp, in response to an externally applied magnetic force. Pp is inversely coupled with leaf turgor pressure, Pc, i.e. at high Pc values the Pp values are small and at low Pc values the Pp values are high. This relationship between Pc and Pp could also be verified for 2-m tall olive trees under laboratory conditions using the cell turgor pressure probe. When the laboratory plants were subjected to severe water stress (Pc dropped below ca. 50 kPa), Pp curves show reverse diurnal changes, i.e. during the light regime (high transpiration) a minimum Pp value, and during darkness a peak Pp value is recorded. This reversal of the Pp curves was completely reversible. Upon watering, the original diurnal Pp changes were re-established within 2-3 days. Olive trees in the field showed a similar turnover of the shape of the Pp curves upon drought, despite pronounced fluctuations in microclimate. The reversal of the Pp curves is most likely due to accumulation of air in the leaves. This assumption was supported with cross-sections through leaves subjected to prolonged drought. In contrast to well-watered leaves, microscopic inspection of leaves exhibiting inverse diurnal Pp curves revealed large air-filled areas in parenchyma tissue. Significantly larger amounts of air could also be extracted from water-stressed leaves than from well-watered leaves using the cell turgor pressure probe. Furthermore, theoretical analysis of the experimental Pp curves shows that the propagation of pressure through the nearly turgorless leaf must be exclusively dictated by air. Equations are derived that provide valuable information about the water status of olive leaves close to zero Pc. [ABSTRACT FROM AUTHOR]

The main goal of this research was to determine the quality by measuring turgor in flowers stems of chrysanthemums stored in tap water and on distilled water, using the method of relative water content (RWC) and the equipment Wiltmeter®. The flower stems were harvested in a commercial field and placed randomly into unitary containers containing distilled water or tap water. In order to monitor the water status of the stems the follow analyses were done: variation of fresh mass, water absorption rate, water transpiration rate, relative water content and turgor pressure. Data were subjected to analysis of variance by F test, means were compared through the days of vase life, using Tukey test at 5% significance level. For comparison of the RWC and the turgor pressure the Pearson correlation coefficient was calculated. Flower stems kept in tap water maintained turgor significantly better than the ones maintained on distilled water. There is a correlation between turgor pressure and relative water content, which remain higher as the plant tissues are new and well hydrated. The estimate of the turgor pressure was effective and sensitive in evaluating the water status of the tissues of the stems of cut chrysanthemums. [ABSTRACT FROM AUTHOR]

The effects of arsenate and arsenite on growth and transpiration were investigated in cucumber plants grown in nutrient solution containing 2, 10, and 100 μM phosphate, respectively. Root and shoot growth decreased by 48-64% compared to the control in all treatments and there was no significant difference between the effects of arsenic As(V) and As(III) except for the lowest phosphate concentration. At 2 μM phosphate As(III) had significantly higher growth inhibition than As(V). The inhibition of transpiration was between 46-68% in all treatments, and As(V) had stronger effect at 10 μM phosphate compared to 100 μM. Arsenic caused fast wilting 2 hours after the commencement of the treatment. However, the formation of adventitious roots prevented the loss of turgor. The hypothesis that aquaporins might be involved in the action of As(V) has been tested by comparison of the effect of As(V) and Hg, the inhibitor of aquaporins. Both treatments resulted in similar inhibition of growth and transpiration, increase in water saturation deficit and decrease in root exudation. Data imply that (i) phosphate reduces arsenate uptake, (ii) arsenate can be at least partially detoxified in cucumber at higher phosphate concentrations, (iii) arsenate may be reduced to arsenite and (iv) As(V) may interfere with the proper functioning of aquaporins. [ABSTRACT FROM AUTHOR]

A portable wiltmeter instrument to estimate leaf turgor pressure according to an adaptation of the flattening method was developed. In the instrument, a flexible inflating membrane presses the leaf against a flattening plate having small orifices surrounded by a finely engraved network of obtuse indentations through which air flow is delivered. During a measurement, as the compression builds up, the leaf is progressively molded against the flattening plate, and as a consequence, the air flow (x) crossing the plate is reduced toward zero. The smallest leaf compression (p0) that blocks the air passage is an estimate of the leaf turgor. Wiltmeter measurements were compared with pressure probe measurements of cell turgor pressure in detached leaves of lettuce (Lactuca sativa L.), kale (Brassica oleracea L. var. Acephala), and chicory (Chichorium endivia L.), which were allowed to suffer diverse levels of wilting caused by transpiration. Such observed wiltmeter readings were a little lower than the cell turgor pressure measured with a pressure probe; the regression coefficients between these methods were: 1.156 for lettuce, 1.13 for kale, and 1.036 for chicory. This portable quantitative procedure to measure leaf firmness has potentially valuable applications related to postharvest and field plant physiology studies. [ABSTRACT FROM AUTHOR]

An advanced non-invasive, field-suitable and inexpensive leaf patch clamp pressure probe for online-monitoring of the water relations of intact leaves is described. The probe measures the attenuated output patch clamp pressure, Pp, of a clamped leaf in response to an externally applied input pressure, Pclamp. Pclamp is generated magnetically. Pp is sensed by a pressure sensor integrated into the magnetic clamp. The magnitude of Pp depends on the transfer function, Tf, of the leaf cells. Tf consists of a turgor pressure-independent (related to the compression of the cuticle, cell walls and other structural elements) and a turgor pressure-dependent term. Tf is dimensionless and assumes values between 0 and 1. Theory shows that Tf is a power function of cell turgor pressure Pc. Concomitant Pp and Pc measurements on grapevines confirmed the relationship between Tf and Pc. Pp peaked if Pc approached zero and assumed low values if Pc reached maximum values. The novel probe was successfully tested on leaves of irrigated and non-irrigated grapevines under field conditions. Data show that slight changes in the microclimate and/or water supply (by irrigation or rain) are reflected very sensitively in Pp. [ABSTRACT FROM AUTHOR]

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: 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]

Log phase Bacillus subtilis cells lacking the mscL gene encoding the mechanosensitive (MS) channel of large conductance are sensitive to an osmotic downshock ≥0.5 M. However, B. subtilis mscL cells develop osmotic downshock resistance in late log and early stationary phase growth that is partially dependent on three likely MS channel proteins of small conductance (MscS), YfkC, YhdY, and YkuT. Bacillus subtilis MS proteins were fused with green fluorescent protein (GFP) at their C termini; at least the MscL-, YfkC-, and YkuT-GFP fusions were functional and overexpression of YkuT-GFP, or YkuT alone abolished log phase mscL cells’ osmotic downshock sensitivity. Western blot analysis found high levels of MscL-GFP in early exponential phase cells with levels subsequently decreasing greatly. MscS-GFP proteins were present in exponential phase cells, but again disappeared almost completely in stationary phase cells and these proteins were not detected in spores. Western blot analyses further showed that MS-GFP proteins were associated with the plasma membrane, as expected. Fluorescence microscopy confirmed the localization of MscL-GFP and YhdY-GFP to the plasma membrane, with non-uniform distribution of these proteins along this membrane consistent with but by no means proving that these proteins are present in a helical array. [ABSTRACT FROM AUTHOR]

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]

A high-precision pressure probe is described which allows non-invasive online-monitoring of the water relations of intact leaves. Real-time recording of the leaf water status occurred by data transfer to an Internet server. The leaf patch clamp pressure probe measures the attenuated pressure, Pp, of a leaf patch in response to a constant clamp pressure, Pclamp. Pp is sensed by a miniaturized silicone pressure sensor integrated into the device. The magnitude of Pp is dictated by the transfer function of the leaf, Tf, which is a function of leaf patch volume and ultimately of cell turgor pressure, Pc, as shown theoretically. The power function Tf=f(Pc) theoretically derived was experimentally confirmed by concomitant Pp and Pc measurements on intact leaflets of the liana Tetrastigma voinierianum under greenhouse conditions. Simultaneous Pp recordings on leaflets up to 10 m height above ground demonstrated that changes in Tf induced by Pc changes due to changes of microclimate and/or of the irrigation regime were sensitively reflected in corresponding changes of Pp. Analysis of the data show that transpirational water loss during the morning hours was associated with a transient rise in turgor pressure gradients within the leaflets. Subsequent recovery of turgescence during the afternoon was much faster than the preceding transpiration-induced water loss if the plants were well irrigated. Our data show the enormous potential of the leaf patch clamp pressure probe for leaf water studies including unravelling of the hydraulic communication between neighbouring leaves and over long distances within tall plants (trees). [ABSTRACT FROM PUBLISHER]

Recent work showed that polygalacturonate (pectate) chemistry controlled the growth rate of the large-celled alga Chara corallina when turgor pressure (P) was normal (about 0.5 MPa). The mechanism involved calcium withdrawal from the wall by newly supplied pectate acting as a chelator. But P itself can affect growth rate. Therefore, pectate chemistry was investigated at various P. A pressure probe varied P in isolated walls, varying the tension on the calcium pectate cross-links bearing the load of P. When soluble pectate was newly supplied, the wall grew irreversibly but the pectate was inactive below a P of 0.2 MPa, indicating that tension was required in the existing wall before new pectate acted. It was suggested that the tension distorted some of the wall pectate (the dominant pectin), weakening its calcium cross-links and causing the calcium to be preferentially lost to the new pectate, which was not distorted. The preferential loss provided a molecular mechanism for loosening the wall structure, resulting in faster growth. However, the resulting relaxation of the vacated wall pectate would cause calcium to be exchanged with load-bearing calcium pectate nearby, auto-propagating throughout the wall for long periods. There is evidence for this effect in isolated walls. In live cells, there is also evidence that auto-propagation is controlled by binding the newly supplied pectate (now calcium pectate) to the wall and/or by additional Ca2+ entering the wall structure. A tension-dependent cycle of pectate chemistry thus appeared to control growth while new wall was deposited as a consequence. [ABSTRACT FROM PUBLISHER]

• 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]

In order to understand how radiata pines respond to declining supply of soil-water in agroforestry systems, we monitored water potential in xylem (ψ x ), osmotic potential (ψ) and relative water content ( q) for fascicles at pre-dawn and at mid-day for 3-year-old trees that were raised from either seedlings (Seedling) or from tissue culture (TC3 and TC4), and grown either alone (Control) or over lucerne ( Medicago sativa) pasture (Lucerne). Water relations at dawn were mostly similar for all the pines, except late in the season when ψ was lower, bulk turgor pressure ( P), deduced as the difference between ψ x and ψ, was higher, for TC3 than for the other two pines. At mid-day, Seedling often had higher ψ x and ψ, but because of its poor osmotic adjustment ( OA) had lower P, than either TC3 or TC4. The cell walls were more elastic in Seedling with modulus of elasticity ( e) of 6.5 MPa compared with 8.1 MPa for both TC3 and TC4, while loss of turgor was estimated to occur at ψ x of −1.45 MPa for Seedling, −1.38 MPa for TC3 and −1.35 MPa for TC4. All trees irrespective of their origin had higher ψ x , P, CO2 assimilation ( A), and stomatal conductance ( g s ), but lower ψ, in Control than in Lucerne in which the soil profile was consistently drier. The trends in ψ x , ψ, q and A did not reflect the known differences in dry weight of trees, P was in the order TC3 > TC4 > Seedling, consistent with previously reported tree weights. Both TC3 and TC4 had higher P, due to their larger OA, than Seedling, although the latter had higher A. Thus ψ x and A that are routinely measured may not always adequately explain differences in growth amongst pines; it is advisable that ψ be determined to allow deductions of P be made when using water relations to analyse plant growth. [ABSTRACT FROM AUTHOR]

Although the decrease in cell turgor by application of sorbitol to the external medium did not inhibit the alkaline band formation in Chara corallina, recovery of normal turgor severely inhibited it. Alkaline-loading analysis suggested that the inhibition of alkaline band formation was caused by inhibition of HCO3– influx but not that of OH– efflux. In the presence of 10 mM CaCl2, the capacity of alkaline band formation was maintained during osmotic treatment. Cells could not form alkaline bands, when plasmolysis was induced by application of sorbitol at a higher concentration. Addition of 10 mM CaCl2 could ameliorate the inhibition caused by plasmolyis. [ABSTRACT FROM AUTHOR]

Abstract Humidity in a small area of a Vicia faba L. leaf was perturbed with a flow of dry air from an 80 µm (inside diameter) needle, while the remainder of the leaf was maintained at high and constant humidity. The influence of the needle flow on the humidity at the leaf surface was quantified by using a spatially explicit dewpoint hygrometer to observe condensation patterns. When the dry air from a needle was applied to the leaf, stomata within the influence of the needle opened within the first few minutes of the perturbation, and local epidermal turgor pressure declined within the same time frame. When the needle flow was removed from the leaf, these responses were reversed, but with more variable kinetics. Stomata and epidermal cells outside the influence of the needle flow, which were exposed to a constant and high humidity, showed similar, but smaller, responses when the needle flow was applied to the leaf. Since the opening of these stomata should have had only a small effect on transpiration (because of the high humidity), it is likely that the reduction in epidermal turgor was the cause (rather than the result) of the stomatal opening. The magnitude of the turgor response was only loosely related to the distance from the needle flow up to distances of almost 400 µm. The data support the idea that neighbouring stomata can interact through the influence of transpiration on epidermal turgor. [ABSTRACT FROM AUTHOR]

We used pressure–volume analysis and dewpoint hygrometry to determine leaf water relation parameters of mangrove (Avicennia germinans L.) seedlings grown at salinities of 0, 8, 20 and 32 ‰. Seedlings responded to an increase in salinity from 0 to 32 ‰ by an increase in leaf succulence as reflected in an increase in leaf water content per unit area from 300 to 360 g m−2. Additionally, osmotic potential at full turgor decreased from –2.3 to –3.5 MPa and osmotic potential at zero turgor decreased from –2.7 to –4.3 MPa. Cell elasticity decreased as salinity increased from 0 to 32 ‰, as indicated by a progressive increase in volumetric modulus of elasticity from 19 to 27 MPa. Increased leaf succulence enabled leaves to sequester large amounts of solutes without adversely increasing cell osmotic pressure. On the other hand, osmotic adjustment facilitated turgor maintenance as water potential diminished. Salinity-induced decreases in tissue elasticity generated greater water potential differences between leaves and soil under saline conditions than under non-saline conditions. [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 (⩽ 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 water content‐water potential relation in stressed and unstressed cassava (Man‐ihot species) was examined to ascertain (i) the magnitude of osmotic adjustment in response to water stress and (ii) the mechanisms of such adjustments. Water stress resulted in a displacement of the water content‐potential relation such that at any leaf water potential the water content was higher in the stressed plants. The osmotic potentials of turgid leaves (100% relative water content) were ‐0.97 and ‐1.00 MPa in the unstressed cultivars CMC 9 and MCOL 113 respectively. In the stressed plants, the values were‐1.13 MPa (CMC 9) and‐1.14 MPa (MCOL 113). The 0.14 to 0.16 MPa osmotic potential difference between the stressed and unstressed plants suggests that a stress‐induced osmotic adjustment occurred in both cultivars. The biiSk volumetric elastic moduli at turgor pressures above 0.10 MPa were 9.84 MPa (CMC 9) and 13.58 MPa (MCOL 113) in the unstressed plants. Tbe higher values found in the stressed plants, 14.56 MPa in CMC 9 and 16.91 MPa in MCOL 113, suggest a stress‐induced decrease in cell wall elasticity. Hence, the observed shift in the wafer content‐potential relations in the cassava involved both an osmotic adjustment and a decrease in cell wall elasticity. Increasing the number of stress cycles per plant did not cause a further displacement of the water content‐potential curves. [ABSTRACT FROM AUTHOR]