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The phytohormone abscisic acid (ABA) plays a major role in closing the stomata of angiosperms. However, recent reports of some angiosperm species having a peaking-type ABA dynamic, in which under extreme drought ABA levels decline to pre-stressed levels, raises the possibility that passive stomatal closure by leaf water status alone can occur in species from this lineage. To test this hypothesis, we conducted instantaneous rehydration experiments in the peaking-type species Umbellularia californica through a long-term drought, in which ABA levels declined to pre-stress levels, yet stomata remain closed. We found that when ABA levels were lowest during extreme drought, stomata reopen rapidly to maximum rates of gas exchange on instantaneous rehydration, suggesting that the stomata of U. californica were passively closed by leaf water status alone. This contrasts with leaves early in drought, in which ABA levels were highest and stomata did not reopen on instantaneous rehydration. The transition from ABA-driven stomatal closure to passively driven stomatal closure as drought progresses in this species occurs at very low water potentials facilitated by highly embolism-resistant xylem. These results have important implications for understanding stomatal control during drought in angiosperms. [ABSTRACT FROM AUTHOR]

Background and Aims Many agricultural areas are expected to face hotter, drier conditions from climate change. Understanding the mechanisms that crops use to mitigate these stresses can guide breeding for more tolerant plant material. We tested relationships between traits, physiological function in hot conditions and historical climate associations to evaluate these mechanisms for winegrapes. We expected a more negative leaf osmotic potential at full hydration (π o), which reduces leaf turgor loss during drought, and either a metabolically cheaper or more osmoprotectant leaf chemical composition, to allow cultivars associated with hot, dry regions to maintain greater gas exchange in hot growing conditions. Methods We measured π o, gas exchange and leaf chemistry for seven commercially important winegrape cultivars that vary widely in historical climate associations. Vines were grown in common-garden field conditions in a hot wine-growing region (Davis, CA, USA) and measured over the hottest period of the growing season (July–September). Key Results The value of π o varied significantly between cultivars, and all cultivars significantly reduced π o (osmotically adjusted) over the study period, although osmotic adjustment did not vary across cultivars. The value of π o was correlated with gas exchange and climate associations, but in the direction opposite to expected. Photosynthesis and π o were higher in the cultivars associated with hotter, less humid regions. Leaf chemical composition varied between cultivars but was not related to climate associations. Conclusions These findings suggest that maintenance of leaf turgor is not a primary limitation on grapevine adaptation to hot or atmospherically dry growing conditions. Thus, selecting for a more negative π o or greater osmotic adjustment is not a promising strategy to develop more climate-resilient grape varieties, contrary to findings for other crops. Future work is needed to identify the mechanisms increasing photosynthesis in the cultivars associated with hot, dry regions. [ABSTRACT FROM AUTHOR]

Trees and other woody plants are immensely ecologically important, making it essential to understand the causes of relationships between tree structure and function. To help these efforts, we highlight persistent traditions in plant biology of appealing to environmental factors "limiting" or "controlling" woody plant features. Examples include the idea that inevitable drops in cell turgor with plant height limit cell expansion and thus leaf size and tree height; that low temperatures prohibit lignification of cells and thus the growth of woody plants at high elevation; and notions from dendrochronology and related fields that climate factors such as rainfall and temperature "control" growth ring features. We show that notions of "control," "limitation," and the like imply that selection would favor a given trait value, but that these would-be favored values are developmentally impossible to produce. Such "limitation" scenarios predict trait frequency distributions that are very narrow and are abruptly curtailed at the upper limit of developmental possibility (the right-hand side of the distribution). Such distributions have, to our knowledge, never been observed, so we see little empirical support for "limitation" hypotheses. We suggest that, as a more productive starting point, plant biologists should examine adaptation hypotheses, in which developmental possibility is wide (congruent with the wide ranges of trait variation that really are observed), but only some of the possible variants are favored. We suggest that (1) the traditional the proximate/ultimate causation distinction, (2) purging scenarios of teleology/anthropomorphism, and (3) stating hypotheses in terms of developmental potential and natural selection are three simple ways of making "limitation" hypotheses clearer with regard to biological process and thus empirically testable. [ABSTRACT FROM AUTHOR]

The regulation of water loss and the spread of xylem embolism have mostly been considered separately. The development of an integrated approach taking into account the temporal dynamics and relative contributions of these mechanisms to plant drought responses is urgently needed. Do conifer species native to mesic and xeric environments display different hydraulic strategies and temporal sequences under drought? A dry-down experiment was performed on seedlings of four conifer species differing in embolism resistance, from drought-sensitive to extremely drought-resistant species. A set of traits related to drought survival was measured, including turgor loss point, stomatal closure, minimum leaf conductance, and xylem embolism resistance. All species reached full stomatal closure before the onset of embolism, with all but the most drought-sensitive species presenting large stomatal safety margins, demonstrating that highly drought-resistant species do not keep their stomata open under drought conditions. Plant dry-down time to death was significantly influenced by the xylem embolism threshold, stomatal safety margin, and minimum leaf conductance, and was best explained by the newly introduced stomatal margin retention index (SMRIΨ50) which reflects the time required to cross the stomatal safety margin. The SMRIΨ50 may become a key tool for the characterization of interspecific drought survival variability in trees. [ABSTRACT FROM AUTHOR]

Succulence describes the amount of water stored in cells or organs, regardless of plant life-form, including woody and herbaceous plants. In dry environments, plants with greater survival often have greater leaf succulence. However, it is unclear how leaf succulence relates to plant drought resistance strategies, including isohydry (closing stomata to maintain leaf water status) and anisohydry (adjusting cell turgor to tolerate low leaf water status), which exist on a continuum that can be quantified by hydroscape area (larger hydroscape area indicates more anisohydric). We evaluated 12 woody species with differing leaf succulence in a glasshouse dry-down experiment to determine relationships among leaf succulence (degree of leaf succulence, leaf succulent quotient and leaf thickness) and plant drought response (hydroscape area, plant water use, turgor loss point and predawn leaf water potential when transpiration ceased). Hydroscape areas ranged from 0.72 (Carpobrotus modestus S.T.Blake; crassulacean acid metabolism (CAM) plants) to 7.01 MPa2 (Rhagodia spinescens R.Br.; C3 plants), suggesting that C. modestus was more isohydric and R. spinescens was more anisohydric. More isohydric species C. modestus , Carpobrotus rossii (Haw.) Schwantes and Disphyma crassifolium (L.) L.Bolus (CAM plants) had greater leaf succulence, lower root allocation, used stored water and ceased transpiration at higher predawn leaf water potential, shortly after reaching their turgor loss point. The remaining nine species that are not CAM plants had larger hydroscape areas and ceased transpiration at lower predawn leaf water potential. Greater leaf succulence was not related to cumulative water loss until transpiration ceased in drying soils. All 12 species had high turgor loss points (−1.32 to −0.59 MPa), but turgor loss point was not related to hydroscape area or leaf succulence. Our data suggest that overall greater leaf succulence was related to isohydry, but this may have been influenced by the fact that these species were also CAM plants. [ABSTRACT FROM AUTHOR]

When attacked by herbivores, plants produce electrical signals which can activate the synthesis of the defense mediator jasmonate. These wound-induced membrane potential changes can occur in response to elicitors that are released from damaged plant cells. We list plant-derived elicitors of membrane depolarization. These compounds include the amino acid l -glutamate (Glu), a potential ligand for GLUTAMATE RECEPTOR-LIKE (GLR) proteins that play roles in herbivore-activated electrical signaling. How are membrane depolarization elicitors dispersed in wounded plants? In analogy with widespread turgor-driven cell and organ movements, we propose osmoelectric siphon mechanisms for elicitor transport. These mechanisms are based on membrane depolarization leading to cell water shedding into the apoplast followed by membrane repolarization and water uptake. We discuss two related mechanisms likely to occur in response to small wounds and large wounds that trigger leaf-to-leaf electrical signal propagation. To reduce jasmonate pathway activation, a feeding insect must cut through tissues cleanly. If their mandibles become worn, the herbivore is converted into a robust plant defense activator. Our models may therefore help to explain why numerous plants produce abrasives which can blunt herbivore mouthparts. Finally, if verified, the models we propose may be generalizable for cell to cell transport of water and pathogen-derived regulators. [ABSTRACT FROM AUTHOR]

Cyclic di-AMP is an emerging second messenger that is synthesized by many archaea and bacteria, including the Gram-positive pathogenic bacterium Listeria monocytogenes. Listeria monocytogenes played a crucial role in elucidating the essential function of c-di-AMP, thereby becoming a model system for studying c-di-AMP metabolism and the influence of the nucleotide on cell physiology. c-di-AMP is synthesized by a diadenylate cyclase and degraded by two phosphodiesterases. To date, eight c-di-AMP receptor proteins have been identified in L. monocytogenes , including one that indirectly controls the uptake of osmotically active peptides and thus the cellular turgor. The functions of two c-di-AMP-receptor proteins still need to be elucidated. Here, we provide an overview of c-di-AMP signalling in L. monocytogenes and highlight the main differences compared to the other established model systems in which c-di-AMP metabolism is investigated. Moreover, we discuss the most important questions that need to be answered to fully understand the role of c-di-AMP in osmoregulation and in the control of central metabolism. [ABSTRACT FROM AUTHOR]

Ongoing changes in climate, and the consequent mortality of natural and cultivated forests across the globe, highlight the urgent need to understand the plant traits associated with greater tolerance to drought. Here, we aimed at assessing key foliar traits, with a focus on the hydraulic component, that could confer a differential ability to tolerate drought in three commercial hybrids of the most important Eucalyptus species utilized in tropical silviculture: E. urophyla , E. grandis and E. camaldulensis. All genotypes exhibited similar water potential when the 90% stomatal closure (Ψ g s90) occurs with Ψ g s90 always preceding the start of embolism events. The drought-tolerant hybrid showed a higher leaf resistance to embolism, but the leaf hydraulic efficiency was similar among all genotypes. Other traits presented by the drought-tolerant hybrid were a higher cell wall reinforcement, lower value of osmotic potential at full turgor and greater bulk modulus of elasticity. We also identified that the leaf capacitance after the turgor loss, the ratio between cell wall thickness (t) and lumen breadth (b) ratio (t / b)3, and the minimal conductance might be good proxies for screening drought-tolerant Eucalyptus genotypes. Our findings suggest that xylem resistance to embolism can be an important component of drought tolerance in Eucalyptus in addition to other traits aimed at delaying the development of high tensions in the xylem. Highlight Drought tolerance in tropical Eucalyptus hybrids encompasses a high leaf resistance to embolism and a suite of traits aimed at delaying the development of high tensions in the xylem. [ABSTRACT FROM AUTHOR]

Background and Aims Living root tissues significantly constrain plant water uptake under drought, but we lack functional traits to feasibly screen diverse plants for variation in the drought responses of these tissues. Water stress causes roots to lose volume and turgor, which are crucial to root structure, hydraulics and growth. Thus, we hypothesized that root pressure–volume (p–v) curve traits, which quantify the effects of water potential on bulk root turgor and volume, would capture differences in rootstock drought tolerance. Methods We used a greenhouse experiment to evaluate relationships between root p–v curve traits and gas exchange, whole-plant hydraulic conductance and biomass under drought for eight grapevine rootstocks that varied widely in drought performance in field trials (101-14, 110R, 420A, 5C, 140-Ru, 1103P, Ramsey and Riparia Gloire), grafted to the same scion variety (Vitis vinifera 'Chardonnay'). Key Results The traits varied significantly across rootstocks, and droughted vines significantly reduced root turgor loss point (π tlp), osmotic potential at full hydration (π o) and capacitance (C), indicating that roots became less susceptible to turgor loss and volumetric shrinkage. Rootstocks that retained a greater root volume (i.e. a lower C) also maintained more gas exchange under drought. The rootstocks that previous field trials have classified as drought tolerant exhibited significantly lower π tlp, π o and C values in well-watered conditions, but significantly higher π o and π tlp values under water stress, than the varieties classified as drought sensitive. Conclusions These findings suggest that acclimation in root p–v curve traits improves gas exchange in persistently dry conditions, potentially through impacts on root hydraulics or root to shoot chemical signalling. However, retaining turgor and volume in previously unstressed roots, as these roots deplete wet soil to moderately negative water potentials, could be more important to drought performance in the deep, highly heterogenous rooting zones which grapevines develop under field conditions. [ABSTRACT FROM AUTHOR]

Increasing evidence suggests that tree growth is sink-limited by environmental and internal controls rather than by carbon availability. However, the mechanisms underlying sink-limitations are not fully understood and thus not represented in large-scale vegetation models. We develop a simple, analytically solved, mechanistic, turgor-driven growth model (TDGM) and a phloem transport model (PTM) to explore the mechanics of phloem transport and evaluate three hypotheses. First, phloem transport must be explicitly considered to accurately predict turgor distributions and thus growth. Second, turgor-limitations can explain growth-scaling with size (metabolic scaling). Third, turgor can explain realistic growth rates and increments. We show that mechanistic, sink-limited growth schemes based on plant turgor limitations are feasible for large-scale model implementations with minimal computational demands. Our PTM predicted nearly uniform sugar concentrations along the phloem transport path regardless of phloem conductance, stem water potential gradients and the strength of sink-demands contrary to our first hypothesis, suggesting that phloem transport is not limited generally by phloem transport capacity per se but rather by carbon demand for growth and respiration. These results enabled TDGM implementation without explicit coupling to the PTM, further simplifying computation. We test the TDGM by comparing predictions of whole-tree growth rate to well-established observations (site indices) and allometric theory. Our simple TDGM predicts realistic tree heights, growth rates and metabolic scaling over decadal to centurial timescales, suggesting that tree growth is generally sink and turgor limited. Like observed trees, our TDGM captures tree-size- and resource-based deviations from the classical ¾ power-law metabolic scaling for which turgor is responsible. [ABSTRACT FROM AUTHOR]

Plant cell deformations are driven by cell pressurization and mechanical constraints imposed by the nanoscale architecture of the cell wall, but how these factors are controlled at the genetic and molecular levels to achieve different types of cell deformation is unclear. Here, we used stomatal guard cells to investigate the influences of wall mechanics and turgor pressure on cell deformation and demonstrate that the expression of the pectin-modifying gene PECTATE LYASE LIKE12 (PLL12) is required for normal stomatal dynamics in Arabidopsis thaliana. Using nanoindentation and finite element modeling to simultaneously measure wall modulus and turgor pressure, we found that both values undergo dynamic changes during induced stomatal opening and closure. PLL12 is required for guard cells to maintain normal wall modulus and turgor pressure during stomatal responses to light and to tune the levels of calcium crosslinked pectin in guard cell walls. Guard cell-specific knockdown of PLL12 caused defects in stomatal responses and reduced leaf growth, which were associated with lower cell proliferation but normal cell expansion. Together, these results force us to revise our view of how wall-modifying genes modulate wall mechanics and cell pressurization to accomplish the dynamic cellular deformations that underlie stomatal function and tissue growth in plants. [ABSTRACT FROM AUTHOR]

Chloride (Cl−), traditionally considered harmful for agriculture, has recently been defined as a beneficial macronutrient with specific roles that result in more efficient use of water (WUE), nitrogen (NUE), and CO2 in well-watered plants. When supplied in a beneficial range of 1–5 mM, Cl− increases leaf cell size, improves leaf osmoregulation, and reduces water consumption without impairing photosynthetic efficiency, resulting in overall higher WUE. Thus, adequate management of Cl− nutrition arises as a potential strategy to increase the ability of plants to withstand water deficit. To study the relationship between Cl− nutrition and drought resistance, tobacco plants treated with 0.5–5 mM Cl− salts were subjected to sustained water deficit (WD; 60% field capacity) and water deprivation/rehydration treatments, in comparison with plants treated with equivalent concentrations of nitrate, sulfate, and phosphate salts. The results showed that Cl− application reduced stress symptoms and improved plant growth during water deficit. Drought resistance promoted by Cl− nutrition resulted from the simultaneous occurrence of water deficit avoidance and tolerance mechanisms, which improved leaf turgor, water balance, photosynthesis performance, and WUE. Thus, it is proposed that beneficial Cl− levels increase the ability of crops to withstand drought, promoting a more sustainable and resilient agriculture. [ABSTRACT FROM AUTHOR]

Over their lifetime, trees are repeatedly exposed to droughts. It is therefore important to understand whether repeated drought exposure makes trees more or less drought tolerant. Here, we investigated the effect of repeated droughts on functional trait expression and tree function in Eucalyptus obliqua. Further, we tested whether previous drought exposure enabled trees to avoid leaf death for longer under a subsequent severe drought. Trees were subjected for 1 year to 2 drought–rewatering cycles (drought treatment) or well-watered conditions, before imposing a severe drought. Trees in the drought treatment reduced their overall leaf area and biomass, whereas leaf-level anatomical, morphological and physiological traits remained mostly unaffected. There were no differences in water potential at the turgor loss point, leaf xylem vulnerability to embolism, leaf size, maximum xylem vessel diameter or cell wall thickness between treatments after the conditioning period. When exposed to a subsequent severe drought, trees previously exposed to drought were more drought tolerant due to a lower water potential at leaf death and tree-level morphological rather than physiological adjustments. Trees previously exposed to drought were smaller and used less water, which delayed leaf death for 39 days compared with 22 days for the well-watered trees. Our study indicates that previous drought exposure can facilitate tree-level morphological adjustment, which potentially enhances survival of E. obliqua trees during subsequent drought events. [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]

This document is a correction notice for an article titled "PECTATE LYASE LIKE12 patterns the guard cell wall to coordinate turgor pressure and wall mechanics for proper stomatal function in Arabidopsis" published in The Plant Cell journal. The correction addresses two typographical errors in the "Materials and methods" section related to the concentrations of fusicoccin and ABA used in the study. The correct concentrations should be listed as 1 μM and 50 μM, respectively, instead of 1 mM and 50 mM. The authors apologize for the error and have made the necessary corrections in this notice. [Extracted from the article]

Peptidoglycan, which is the main component of the bacterial cell wall, is a heterogeneous polymer of glycan strands cross-linked with short peptides and is synthesized in cooperation with the cell division cycle. Although it plays a critical role in bacterial survival, its architecture is not well understood. Herein, we visualized the architecture of the peptidoglycan surface in Bacillus subtilis at the nanometer resolution, using quick-freeze, deep-etch electron microscopy (EM). Filamentous structures were observed on the entire surface of the cell, where filaments about 11 nm wide formed concentric circles on cell poles, filaments about 13 nm wide formed a circumferential mesh-like structure on the cylindrical part and a 'piecrust' structure was observed at the boundary. When growing cells were treated with lysozyme, the entire cell mass migrated to one side and came out from the cell envelope. Fluorescence labeling showed that lysozyme preferentially bound to a cell pole and cell division site, where the peptidoglycan synthesis was not complete. Ruffling of surface structures was observed during EM. When cells were treated with penicillin, the cell mass came out from a cleft around the cell division site. Outward curvature of the protoplast at the cleft seen using EM suggested that turgor pressure was applied as the peptidoglycan was not damaged at other positions. When muropeptides were depleted, surface filaments were lost while the rod shape of the cell was maintained. These changes can be explained on the basis of the working points of the chemical structure of peptidoglycan. [ABSTRACT FROM AUTHOR]

As multicellular organisms, plants acquire characteristic shapes through a complex set of biological processes known as morphogenesis. Biochemical signalling underlies much of development, as it allows cells to acquire specific identities based on their position within tissues and organs. However, as growing physical structures, plants, and their constituent cells, also experience internal and external physical forces that can be perceived and can influence key processes such as growth, polarity, and gene expression. This process, which adds another layer of control to growth and development, has important implications for plant morphogenesis. This review provides an overview of recent research into the role of mechanical signals in plant development and aims to show how mechanical signalling can be used, in concert with biochemical signals, as a cue allowing cells and tissues to coordinate their behaviour and to add robustness to developmental processes. [ABSTRACT FROM AUTHOR]

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

Abscission is a developmental process with important implications for agricultural practices. Ethylene has long been considered as a key regulator of the abscission process. The existence of an ethylene-independent abscission pathway, controlled by the complex of INFLORESCENCE DEFICIENT IN ABSCISSION (IDA) peptide and the HAESA (HAE) and HAESA-like2 (HSL2) kinases, has been proposed, based mainly on observations that organ abscission in ethylene-insensitive mutants was delayed but not inhibited. A recent review on plant organ abscission signaling highlighted the IDA–HAE–HSL2 components as the regulators of organ abscission, while the role of auxin and ethylene in this process was hardly addressed. After a careful analysis of the relevant abscission literature, we propose that the IDA–HAE–HSL2 pathway is essential for the final stages of organ abscission, while ethylene plays a major role in its initiation and progression. We discuss the view that the IDA–HAE–HSL2 pathway is ethylene independent, and present recent evidence showing that ethylene activates the IDA–HAE–HSL2 complex. We conclude that the ability of an organ to abscise is tightly linked to cell turgidity in the abscission zone, and suggest that lack of cell turgidity might contribute to the failure of floral organ abscission in the ida mutants. [ABSTRACT FROM AUTHOR]

The last years, Central European forests have suffered from drought as a direct consequence of climate change. All these forests have a long management history and it lies in the landowner's responsibility to replant damaged forests. Hence, landowners and the government are searching currently for species suitable to replant in areas affected by tree die-offs. It is a matter of fact that good knowledge of drought resistance of species is a critical measure for the current replanting efforts. We determined a widely recognized trait for leaf drought tolerance (leaf water potential at turgor loss point at full hydration, π tlp) in 41 woody species native or introduced in Central Europe. The osmometric rapid assessment method was used to measure the leaf osmotic potential at full hydration (π osm) of sun-exposed leaves and converted to π tlp. Mean π tlp of the native species was −2.33 ± 0.33 MPa. The less negative π tlp was found in the introduced species Aesculus hypocastania and was at −1.70 ± 0.11 MPa. The most negative π tlp, and thus the potentially highest drought tolerance, were found in the introduced species Pseudotsuga menzesii and was at −3.02 ± 0.14 MPa. High or less negative π tlp is associated with lower drought tolerance, whereas low or more negative π tlp stands for higher resistance to drought stress. For example, the two native species Illex aquifolium and Alnus glustinosa are species naturally associated with moist habitats and are characterized by the least negative π tlp of −1.75 ± 0.02 and −1.76 ± 0.03 MPa, respectively. [ABSTRACT FROM AUTHOR]

Background and Aims Turgor-driven plant cell growth depends on cell wall structure and mechanics. Strengthening of cell walls on the basis of an association and interaction with silicon (Si) could lead to improved nutrient uptake and optimized growth and metabolism in rice (Oryza sativa). However, the structural basis and physiological mechanisms of nutrient uptake and metabolism optimization under Si assistance remain obscure. Methods Single-cell level biophysical measurements, including in situ non-invasive micro-testing (NMT) of NH4+ ion fluxes, atomic force microscopy (AFM) of cell walls, and electrolyte leakage and membrane potential, as well as whole-cell proteomics using isobaric tags for relative and absolute quantification (iTRAQ), were performed. Key Results The altered cell wall structure increases the uptake rate of the main nutrient NH4+ in Si-accumulating cells, whereas the rate is only half in Si-deprived counterparts. Conclusions Rigid cell walls enhanced by a wall-bound form of Si as the structural basis stabilize cell membranes. This, in turn, optimizes nutrient uptake of the cells in the same growth phase without any requirement for up-regulation of transmembrane ammonium transporters. Optimization of cellular nutrient acquisition strategies can substantially improve performance in terms of growth, metabolism and stress resistance. [ABSTRACT FROM AUTHOR]

Osmotic adjustment (OA), the accumulation of solutes in higher plant cells in response to water deficits, was first reported more than four decades ago. Since then, variation in OA among genotypes/cultivars in response to drought has been reported in many crop plants, but its role in maintaining growth and yield in water-limited environments has been questioned. The role of OA in the physiological and agronomic adaptation to water stress of crops, the methods of reliably measuring the degree of OA among genotypes or species, the range of OA in many studies, and its impact on grain yield in water-limited environments are reviewed. The genetics of OA has received limited study, and the breeding and selection for high OA has only resulted in the release of one commercial cultivar of wheat as far as is known. The reasons for the limited interest in breeding for the OA trait are discussed. [ABSTRACT FROM AUTHOR]

Background and Aims In many scenarios the availability of assimilated carbon is not the constraining factor of plant growth. Rather, organ growth appears driven by sink activity in which water availability plays a determinant role. Current functional--structural plant models (FSPMs) mainly focus on plant-carbon relations and largely disregard the importance of plant water status in organogenesis. Consequently, incorporating a turgor-driven growth concept, coupling carbon and water dynamics in an FSPM, presents a significant improvement towards capturing plant development in a more mechanistic manner. Methods An existing process-based water flow and storage model served as a basis for implementing water control in FSPMs. Its concepts were adjusted to the scale of individual plant organs and interwoven with the basic principles of modelling carbon dynamics to allow evaluation of turgor pressure across the entire plant. This was then linked to plant organ growth by applying the principles of the widely used Lockhart equation. Key results This model successfully integrates a mechanistic understanding of plant water transport dynamics coupled with simple carbon dynamics within a dynamically developing plant architecture. It allows evaluation of turgor pressure on the scale of plant organs, resulting in clear diel and long-term patterns, directly linked to plant organ growth. Conclusions A conceptual sap flow and turgor-driven growth model was introduced for functional--structural plant modelling. It is applicable to any plant architecture and allows visual exploration of the diel patterns of organ water content and growth. Integrated in existing FSPMs, this new concept fosters an array of possibilities for FSPMs, as it presents a different formulation of growth in terms of local processes, influenced by local and external conditions. [ABSTRACT FROM AUTHOR]

Decreasing water availability due to climate change poses the question of whether and to what extent tree species are able to hydraulically acclimate and how hydraulic traits of stems and leaves are coordinated under drought. In a through-fall exclusion experiment, hydraulic acclimation was analyzed in a mixed forest stand of Fagus sylvatica L. and Picea abies (L.) Karst. In droughtstressed (TE, through-fall exclusion over 2 years) and control (CO) trees, hydraulic vulnerability was studied in branches as well as in leaves (F. sylvatica) and end-twigs (P. abies, entirely formed during the drought period) sampled at the same height in sunexposed portions of the tree crown. In addition, relevant xylem anatomical traits and leaf pressure-volume relations were analyzed. The TE trees reached pre-dawn water potentials down to -1.6 MPa. In both species, water potentials at 50% loss of xylem hydraulic conductivity were ~0.4 MPa more negative in TE than in CO branches. Foliage hydraulic vulnerability (expressed as water potential at 50% loss of leaf/end-twig hydraulic conductance) and water potential at turgor loss point were also, respectively, 0.4 and 0.5 MPa lower in TE trees. Minor differences were observed in conduit mean hydraulic diameter and cell wall reinforcement. Our findings indicate significant and fast hydraulic acclimation under relatively mild drought in both tree species. Acclimation was well coordinated between branches and foliage, which might be essential for survival and productivity of mature trees under future drought periods. [ABSTRACT FROM AUTHOR]

Chloride is a nutrient that accumulates to millimolar levels in plants under most growth conditions, including in almost all soil-grown plants. These relatively high chloride concentrations (relative to the demand for chloride in photosynthesis) are beneficial to plants including non-halophytes, as the addition of chloride to the growth medium above the micromolar level increases biomass. As chloride is not metabolized and its only known essential function is in the oxygen-evolving complex in PSII, we discuss how chloride could be beneficial, especially in comparison with nitrate. We review the different routes taken by chloride in plants, from uptake and translocation to the shoot, and inside the cell in different organelles, including different transport mechanisms and the proteins identified. As the selectivity of many proteins to chloride and nitrate is not well established, the mechanisms within proteins to achieve selectivity of one anion over the other are explored. We further discuss the role of chloride as an osmoticum, why it might be preferentially used instead of other anions, and how chloride content in plants might beneficially influence nitrogen use efficiency and water-holding capacity. [ABSTRACT FROM AUTHOR]

Pressure-volume (PV) curve analysis is the most common and accurate way of estimating all components of the water relationships in leaves (water potential isotherms) as summarized in the Höfler diagram. PV curve analysis yields values of osmotic pressure, turgor pressure, and elastic modulus of cell walls as a function of relative water content. It allows the computation of symplasmic/apoplastic water content partitioning. For about 20 years, cavitation in xylem has been postulated as a possible source of error when estimating the above parameters, but, to the best of the authors' knowledge, no one has ever previously quantified its influence. Results in this paper provide independent estimates of osmotic pressure by PV curve analysis and by thermocouple psychrometer measurement. An anatomical evaluation was also used for the first time to compare apoplastic water fraction estimates from PV analysis with anatomical values. Conclusions include: (i) PV curve values of osmotic pressure are underestimated prior to correcting osmotic pressure for water loss by cavitation in Metasequoia glyptostroboides; (ii) psychrometer estimates of osmotic pressure obtained in tissues killed by freezing or heating agreed with PV values before correction for apoplastic water dilution; (iii) after correction for dilution effects, a solute concentration enhancement (0.27 MPa or 0.11 osmolal) was revealed. The possible sources of solute enhancement were starch hydrolysis and release of ions from the Donnan free space of needle cell walls. [ABSTRACT FROM AUTHOR]

Chloride (Cl-) is a micronutrient that accumulates to macronutrient levels since it is normally available in nature and actively taken up by higher plants. Besides a role as an unspecific cell osmoticum, no clear biological roles have been explicitly associated with Cl- when accumulated to macronutrient concentrations. To address this question, the glycophyte tobacco (Nicotiana tabacum L. var. Habana) has been treated with a basal nutrient solution supplemented with one of three salt combinations containing the same cationic balance: Cl--based (CL), nitrate-based (N), and sulphate+phosphate-based (SP) treatments. Under non-saline conditions (up to 5 mM Cl-) and no water limitation, Cl- specifically stimulated higher leaf cell size and led to a moderate increase of plant fresh and dry biomass mainly due to higher shoot expansion. When applied in the 1-5 mM range, Cl- played specific roles in regulating leaf osmotic potential and turgor, allowing plants to improve leaf water balance parameters. In addition, Cl- also altered water relations at the whole-plant level through reduction of plant transpiration. This was a consequence of a lower stomatal conductance, which resulted in lower water loss and greater photosynthetic and integrated water-use efficiency. In contrast to Cl-, these effects were not observed for essential anionic macronutrients such as nitrate, sulphate, and phosphate. We propose that the abundant uptake and accumulation of Cl- responds to adaptive functions improving water homeostasis in higher plants. [ABSTRACT FROM AUTHOR]

The article discusses role of leaf turgor loss as a predictor of plant drought response strategies, referencing a research on leaf turgor loss point (TLP) published in this issue. It states that a meta-analysis of TLP and its relationship was conducted to a range of hydraulic traits linked to drought tolerance, as well as to leaf economic trait, and mentions that that species with higher TLP tend to have wider hydraulic safety margins. It notes role of TLP as an integrated and adaptive trait.

The aim of the present study was to assess the mechanical and hydraulic limitation of growth in leaf epidermal cells of barley (Hordeum vulgare L.) in response to agents which affect cellular water (mercuric chloride, HgCl2) and potassium (cesium chloride, CsCl; tetraethylammonium, TEA) transport, pump activity of plasma membrane H+-ATPase and wall acidification (fusicoccin, FC). Cell turgor (P) was measured with the cell pressure probe, and cell osmotic pressure (ɸ) was analyzed through picoliter osmometry of single-cell extracts. A wall extensibility coefficient (M) and tissue hydraulic conductance coefficient (L) were derived using the Lockhart equation. There was a significant positive linear relationship between relative elemental growth rate and P, which fit all treatments, with an overall apparent yield threshold of 0.368 MPa. Differences in growth between treatments could be explained through differences in P. A comparison of L and M showed that growth in all except the FC treatment was co-limited through hydraulic and mechanical properties, though to various extents. This was accompanied by significant (0.17-0.24 MPa) differences in water potential (ΔΨ) between xylem and epidermal cells in the leaf elongation zone. In contrast, FC-treated leaves showed ΔΨ close to zero and a 10-fold increase in L. [ABSTRACT FROM AUTHOR]

Leaf photosynthesis relies on CO2 diffusing in while water vapour diffuses out. When stomata close, cuticle waxes on the epidermal tissues increasingly affect this diffusion. Also, changes in turgor can shrink or swell a leaf, varying the cuticle size. In this study, the properties of the cuticle were investigated while turgor varied in intact leaves of hypostomatous grape (Vitis vinifera L.) or amphistomatous sunflower (Helianthus annuus L.). For grape, stomata on the abaxial surface were sealed and high CO2 concentrations outside the leaf were used to maximize diffusion through the adaxial, stoma-free cuticle. For sunflower, stomata were closed in the dark or with abscisic acid to maximize the cuticle contribution to the path. In both species, the internal CO2 concentration was measured directly and continuously while other variables were determined to establish the cuticle properties. The results indicated that stomatal closure diminished the diffusion of both gases in both species, but for CO2 more than for water vapour. Decreasing the turgor diminished the movement of both gases through the cuticle of both species. Because this turgor effect was observed in the adaxial surface of grape, which had no stomata, it could only be attributed to cuticle tightening. Comparing calculated and measured concentrations of CO2 in leaves revealed differences that became large as stomata began to close. These differences in transport, together with turgor effects, suggest calculations of the CO2 concentration inside leaves need to be viewed with caution when stomata begin to close. [ABSTRACT FROM AUTHOR]

One of the main differences between plant and animal cells are the walls surrounding plant cells providing structural support during development and protection like an adaptive armor against biotic and abiotic stress. During recent years it has become widely accepted that plant cells use a dedicated system to monitor and maintain the functional integrity of their walls. Maintenance of integrity is achieved by modifying the cell wall and cellular metabolism in order to permit tightly controlled changes in wall composition and structure. While a substantial amount of evidence supporting the existence of the mechanism has been reported, knowledge regarding its precise mode of action is still limited. The currently available evidence suggests similarities of the plant mechanism with respect to both design principles and molecular components involved to the very well characterized system active in the model organism Saccharomyces cerevisiae. There the system has been implicated in cell morphogenesis as well as response to abiotic stresses such as osmotic challenges. Here the currently available knowledge on the yeast system will be reviewed initially to provide a framework for the subsequent discussion of the plant cell wall integrity maintenance mechanism. The review will then end with a discussion on possible design principles for the cell wall integrity maintenance mechanism and the function of the plant turgor pressure in this context. [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]

Background and Aims Tree models simulate productivity using general gas exchange responses and structural relationships, but they rarely check whether leaf gas exchange and resulting water and assimilate transport and driving pressure gradients remain within acceptable physical boundaries. This study presents an implementation of the cohesion–tension theory of xylem transport and the Münch hypothesis of phloem transport in a realistic 3-D tree structure and assesses the gas exchange and transport dynamics. Methods A mechanistic model of xylem and phloem transport was used, together with a tested leaf assimilation and transpiration model in a realistic tree architecture to simulate leaf gas exchange and water and carbohydrate transport within an 8-year-old Scots pine tree. The model solved the dynamics of the amounts of water and sucrose solute in the xylem, cambium and phloem using a fine-grained mesh with a system of coupled ordinary differential equations. Key Results The simulations predicted the observed patterns of pressure gradients and sugar concentration. Diurnal variation of environmental conditions influenced tree-level gradients in turgor pressure and sugar concentration, which are important drivers of carbon allocation. The results and between-shoot variation were sensitive to structural and functional parameters such as tree-level scaling of conduit size and phloem unloading. Conclusions Linking whole-tree-level water and assimilate transport, gas exchange and sink activity opens a new avenue for plant studies, as features that are difficult to measure can be studied dynamically with the model. Tree-level responses to local and external conditions can be tested, thus making the approach described here a good test-bench for studies of whole-tree physiology. [ABSTRACT FROM AUTHOR]

Close hydraulic connection between the xylem and the phloem challenges phloem transport during drought. Current theories suggest that the cause of phloem transport failure during drought depends on the hydraulic permeability of phloem conduit walls.Drought challenges plant water uptake and the vascular system. In the xylem it causes embolism that impairs water transport from the soil to the leaves and, if uncontrolled, may even lead to plant mortality via hydraulic failure. What happens in the phloem, however, is less clear because measuring phloem transport is still a significant challenge to plant science. In all vascular plants, phloem and xylem tissues are located next to each other, and there is clear evidence that these tissues exchange water. Therefore, drought should also lead to water shortage in the phloem. In this review, theories used in phloem transport models have been applied to drought conditions, with the goal of shedding light on how phloem transport failure might occur. The review revealed that phloem failure could occur either because of viscosity build-up at the source sites or by a failure to maintain phloem water status and cell turgor. Which one of these dominates depends on the hydraulic permeability of phloem conduit walls. Impermeable walls will lead to viscosity build-up affecting flow rates, while permeable walls make the plant more susceptible to phloem turgor failure. Current empirical evidence suggests that phloem failure resulting from phloem turgor collapse is the more likely mechanism at least in relatively isohydric plants. [ABSTRACT FROM AUTHOR]

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

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

All Illicium spp. have explosive fruits, which is a unique character among the basal grade of angiosperms. Illicium fruits consist of several ventrally dehiscing follicles developing from conduplicate carpels, with a prominent, slightly postgenitally fused ventral slit. The closure of the ventral slit is also secured by two mirror-symmetrical massive longitudinal sclerenchymatous bands in the mesocarp along the edges and by turgor pressure. The pericarp differentiates into a fleshy (or coriaceous) peripheral zone (exocarp and mesocarp) with numerous ethereal-oil-containing cells and a sclerenchymatous (single-layered, palisade) inner zone (endocarp). Dehydration of the fleshy zone of the pericarp and partial compression of the epidermal sclereids with U-shaped wall thickenings lining the ventral suture are instrumental in explosive fruitlet dehiscence. Generally, the fruit structure of Illicium differs dramatically from those in other early diverging angiosperms. Gynoecium and fruit structure (and a probable early Cretaceous divergence from the Schisandra- Kadsura clade) provide evidence for treatment of Illicium as separate from Schisandraceae s.s. © 2013 The Linnean Society of London [ABSTRACT FROM AUTHOR]

Background Carbon assimilation and leaf-to-fruit sugar transport are, along with plant water status, the driving mechanisms for fruit growth. An integrated comprehension of the plant water and carbon relationships is therefore essential to better understand water and dry matter accumulation. Variations in stem diameter result from an integrated response to plant water and carbon status and are as such a valuable source of information. Methods A mechanistic water flow and storage model was used to relate variations in stem diameter to phloem sugar loading and sugar concentration dynamics in tomato. The simulation results were compared with an independent model, simulating phloem sucrose loading at the leaf level based on photosynthesis and sugar metabolism kinetics and enabled a mechanistic interpretation of the ‘one common assimilate pool’ concept for tomato. Key Results Combining stem diameter variation measurements and mechanistic modelling allowed us to distinguish instantaneous dynamics in the plant water relations and gradual variations in plant carbon status. Additionally, the model combined with stem diameter measurements enabled prediction of dynamic variables which are difficult to measure in a continuous and non-destructive way, such as xylem water potential and phloem hydrostatic potential. Finally, dynamics in phloem sugar loading and sugar concentration were distilled from stem diameter variations. Conclusions Stem diameter variations, when used in mechanistic models, have great potential to continuously monitor and interpret plant water and carbon relations under natural growing conditions. [ABSTRACT FROM AUTHOR]

Intracellular NHX proteins are Na+,K+/H+ antiporters involved in K+ homeostasis, endosomal pH regulation, and salt tolerance. Proteins NHX1 and NHX2 are the two major tonoplast-localized NHX isoforms. Here, we show that NHX1 and NHX2 have similar expression patterns and identical biochemical activity, and together they account for a significant amount of the Na+,K+/H+ antiport activity in tonoplast vesicles. Reverse genetics showed functional redundancy of NHX1 and NHX2 genes. Growth of the double mutant nhx1 nhx2 was severely impaired, and plants were extremely sensitive to external K+. By contrast, nhx1 nhx2 mutants showed similar sensitivity to salinity stress and even greater rates of Na+ sequestration than the wild type. Double mutants had reduced ability to create the vacuolar K+ pool, which in turn provoked greater K+ retention in the cytosol, impaired osmoregulation, and compromised turgor generation for cell expansion. Genes NHX1 and NHX2 were highly expressed in guard cells, and stomatal function was defective in mutant plants, further compromising their ability to regulate water relations. Together, these results show that tonoplast-localized NHX proteins are essential for active K+ uptake at the tonoplast, for turgor regulation, and for stomatal function. [ABSTRACT FROM AUTHOR]

Background and Aims Girdling, or the removal of a strip of bark around a tree's outer circumference, is often used to study carbon relationships, as it triggers several carbon responses which seem to be interrelated. Methods An existing plant model describing water and carbon transport in a tree was used to evaluate the mechanisms behind the girdling responses. Therefore, the (un)loading functions of the original model were adapted and became a function of the phloem turgor pressure. Key Results The adapted model successfully simulated the measured changes in stem growth induced by girdling. The model indicated that the key driving variables for the girdling responses were changes in turgor pressure due to local changes in sugar concentrations. Information about the local damage to the phloem system was transferred to the other plant parts (crown and roots) by a change in phloem pressure. After girdling, the loading rate was affected and corresponded to the experimentally observed feedback inhibition. In addition, the unloading rate decreased after girdling and even reversed in some instances. The model enabled continuous simulation of changes in starch content, although a slight underestimation was observed compared with measured values. Conclusions For the first time a mechanistic plant model enabled simulation of tree girdling responses, which have thus far only been experimentally observed and fragmentally reported in literature. The close agreement between measured and simulated data confirms the underlying mechanisms introduced in the model. [ABSTRACT FROM PUBLISHER]

This study reports the first observations indicating the spatiotemporal relationships among genetic and physiological aspects of ripening in the berry of Vitis vinifera. At the onset of ripening in the red flesh variety Alicante Bouschet, colour development began in the flesh at the stylar end of the fruit and progressed toward the pedicel end flesh and into the skin. Tissue solute potential and cell turgor also decreased first in the flesh. The decrease in flesh solute potential was due to accumulation of sugars, glucose and fructose, an accumulation that is integral to ripening. Expression of the anthocyanin biosynthesis-related genes VvMybA and VvUFGT was linearly related to the decrease in solute potential. Expression of VvMybA, and to a lesser extent VvUFGT, was correspondingly low in green tissue, higher in the red, stylar end flesh of berries beginning to ripen, and greatest in red berries. In contrast, expression of the abscisic acid biosynthesis-related genes VvNCED1 and VvNCED2 was not correlated with the other spatiotemporal aspects of the onset of ripening. These results, together with earlier work showing that sugar accumulation and acid loss also begin in the stylar flesh in other varieties, indicate that ripening in the grape berry originates in the stylar end flesh. [ABSTRACT FROM PUBLISHER]

Natural rubber is synthesized in specialized articulated cells (laticifers) located in the inner liber of Hevea brasiliensis. Upon bark tapping, the laticifer cytoplasm (latex) is expelled due to liber tissue turgor pressure. In mature virgin (untapped) trees, short-term kinetic studies confirmed that ethylene, the rubber yield stimulant used worldwide, increased latex yield, with a concomitant decrease in latex total solid content, probably through water influx in the laticifers. As the mature laticifers are devoid of plasmodesmata, the rapid water exchanges with surrounding liber cells probably occur via the aquaporin pathway. Two full-length aquaporin cDNAs (HbPIP2;1 and HbTIP1;1, for plasma membrane intrinsic protein and tonoplast intrinsic protein, respectively) were cloned and characterized. The higher efficiency of HbPIP2;1 than HbTIP1;1 in increasing plasmalemma water conductance was verified in Xenopus laevis oocytes. HbPIP2;1 was insensitive to HgCl2. In situ hybridization demonstrated that HbPIP2;1 was expressed in all liber tissues in the young stem, including the laticifers. HbPIP2;1 was upregulated in both liber tissues and laticifers, whereas HbTIP1;1 was down-regulated in liber tissues but up-regulated in laticifers in response to bark Ethrel treatment. Ethylene-induced HbPIP2;1 up-regulation was confirmed by western-blot analysis. The promoter sequences of both genes were cloned and found to harbor, among many others, ethylene-responsive and other chemical-responsive (auxin, copper, and sulfur) elements known to increase latex yield. increase in latex yield in response to ethylene was emphasized to be linked with water circulation between the laticifers and their surrounding tissues as well as with the probable maintenance of liber tissue turgor, which together favor prolongation of latex flow. [ABSTRACT FROM AUTHOR]

Natural rubber is synthesized in specialized articulated cells (laticifers) located in the inner liber of Hevea brasiliensis. Upon bark tapping, the laticifer cytoplasm (latex) is expelled due to liber tissue turgor pressure. In mature virgin (untapped) trees, short-term kinetic studies confirmed that ethylene, the rubber yield stimulant used worldwide, increased latex yield, with a concomitant decrease in latex total solid content, probably through water influx in the laticifers. As the mature laticifers are devoid of plasmodesmata, the rapid water exchanges with surrounding liber cells probably occur via the aquaporin pathway. Two full-length aquaporin cDNAs (HbPIP2;1 and HbTIP1;1, for plasma membrane intrinsic protein and tonoplast intrinsic protein, respectively) were cloned and characterized. The higher efficiency of HbPIP2;1 than HbTIP1;1 in increasing plasmalemma water conductance was verified in Xenopus laevis oocytes. HbPIP2;1 was insensitive to HgCl2. In situ hybridization demonstrated that HbPIP2;1 was expressed in all liber tissues in the young stem, including the laticifers. HbPIP2;1 was upregulated in both liber tissues and laticifers, whereas HbTIP1;1 was down-regulated in liber tissues but up-regulated in laticifers in response to bark Ethrel treatment. Ethylene-induced HbPIP2;1 up-regulation was confirmed by western-blot analysis. The promoter sequences of both genes were cloned and found to harbor, among many others, ethylene-responsive and other chemical-responsive (auxin, copper, and sulfur) elements known to increase latex yield. increase in latex yield in response to ethylene was emphasized to be linked with water circulation between the laticifers and their surrounding tissues as well as with the probable maintenance of liber tissue turgor, which together favor prolongation of latex flow. [ABSTRACT FROM AUTHOR]

Root hydraulic conductivity in plants (LPr) exhibits large variations in response to abiotic stimuli, hi this study, we investigated the impact of dynamic, aquaporin-mediated changes of Lpr on leaf growth, water potential, and water flux throughout the plant. For this, we manipulated Lpr by subjecting roots to four independent treatments, with aquaporin inhibitors applied either to transpiring maize (Zea inays) plants grown in hydroponics or to detopped root systems for estimation of Lpr The treatments were acid load at pH 6.0 and 5.0 and hydrogen peroxide and anoxia applied for ito 2 hand subsequently reversed. First, we established that acid load affected cell hydraulic conductivity in maize root cortex. Lpr was reduced by all treatments by 31% to 63%, with half-times of about 15 min, and partly recovered when treatments were reversed. Cell turgor measured in the elongating zone of leaves decreased synchronously with Lpr, and leaf elongation rate closely followed these changes across all treatments in a dose- dependent manner. Leaf and xylem water potentials also followed changes in Lpr. Stomatal conductance and rates of transpiration and water uptake were not affected by Lpr reduction under low evaporative demand. Increased evaporative demand, when combined with acid load at pH 6.0, induced stomatal closure and amplified all other responses without altering their synchrony. Root pressurization reversed the impact of acid load or anoxia on leaf elongation rate and water potential, further indicating that changes in turgor mediated the response of leaf growth to reductions in LPr. [ABSTRACT FROM AUTHOR]

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]

To ensure comparability among leaf fresh mass measurements it is important to handle the leaves in a standardized manner. In the present work constraints of a commonly used method to achieve full turgor, storage between damp paper towels, were investigated. After overnight rehydration in a saturated atmosphere, the fresh mass of leaves of 14 species was measured, and the leaves were stored between paper towels (two treatments: moist and wet) at 4 °C. Their mass was measured after 24, 48, and 72 h. Leaf fresh mass increased during the first 24 h of storage between moist paper towels by an average of 1.8%, between wet towels by 3.3%. Among the species, the increase of leaf fresh mass between moist towels correlated with the species' desiccation propensity, indicating that it was rehydration from water loss during initial handling. On the other hand, between wet towels the fresh mass increase was associated with the species' leaf tissue structure, and it continued to increase beyond 24 h, indicating that the increase was a result of water penetration into the leaf air spaces. It is concluded that storage between moist paper towels results in reliable values of leaf fresh mass, and that desiccated leaves rehydrate well between moist towels. However, care has to be taken to avoid too wet conditions as they may lead to erroneously high fresh mass values, especially in species with large air spaces. Furthermore, exposure to unsaturated atmospheric conditions during handling has to be minimized. [ABSTRACT FROM PUBLISHER]

Diurnal rates of leaf elongation vary in maize (Zea mays L.) and are characterized by a decline each afternoon. The cause of the afternoon decline was investigated. When the atmospheric environment was held constant in a controlled environment, and water and nutrients were adequately supplied to the soil or the roots in solution, the decline persisted and indicated that the cause was internal. Inside the plants, xylem fluxes of water and solutes were essentially constant during the day. However, the forces moving these components changed. Tensions rose in the xylem, and gradients of growth-induced water potentials decreased in the surrounding growing tissues of the leaf. These potentials, measured with isopiestic thermocouple psychrometry, changed because the roots became less conductive to water as the day progressed. The increased tensions were reversed by applying pressure to the soil/root system, which rehydrated the leaf. Afternoon elongation immediately recovered to rapid morning rates. The rapid morning rates did not respond to soil/root pressurization. It was concluded that increased xylem tension in the afternoon diminished the gradients in growth-induced water potential and thus inhibited elongation. Because increased tensions cause a similar but larger inhibition of elongation if maize dehydrates, these hydraulics are crucial for shaping the growth-induced water potential and thus the rates of leaf elongation in maize over the entire spectrum of water availability. [ABSTRACT FROM PUBLISHER]

The physiological mechanisms responsible for reduced extension growth as trees increase in height remain elusive. We evaluated biophysical constraints on leaf expansion in old-growth Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) trees. Needle elongation rates, plastic and elastic extensibility, bulk leaf water (ΨL) and osmotic (Ψπ) potential, bulk tissue yield threshold and final needle length were characterized along a height gradient in crowns of > 50-m-tall trees during the period between bud break and full expansion (May to June). Although needle length decreased with increasing height, there was no height-related trend in leaf plastic extensibility, which was highest immediately after bud break (2.9%) and declined rapidly to a stable minimum value (0.3%) over a 3-week period during which leaf expansion was completed. There was a significant positive linear relationship between needle elongation rates and plastic extensibility. Yield thresholds were consistently lower at the upper and middle crown sampling heights. The mean yield threshold across all sampling heights was 0.12 ± 0.03 MPa on June 8, rising to 0.34 ± 0.03 MPa on June 15 and 0.45 ± 0.05 MPa on June 24. Bulk leaf Ψπ decreased linearly with increasing height at a rate of 0.004 MPa m-1 during the period of most rapid needle elongation, but the vertical osmotic gradient was not sufficient to fully compensate for the 0.015 MPa m-1 vertical gradient in ΨL, implying that bulk leaf turgor declined at a rate of about 0.011 MPa m-1 increase in height. Although height-dependent reductions in turgor appeared to constrain leaf expansion, it is possible that the impact of reduced turgor was mitigated by delayed phenological development with increasing height, which resulted in an increase with height in the temperature during leaf expansion. [ABSTRACT FROM AUTHOR]

In response to light, water relation parameters (turgor, half-time of water exchange, T1/2, and hydraulic conductivity, Lp; T1/2∝ 1/Lp) of individual cells of parenchyma sitting in the midrib of leaves of intact corn (Zea mays L.) plants were investigated using a cell pressure probe. Parenchyma cells were used as model cells for the leaf mesophyll, because they are close to photosynthetically active cells at the abaxial surface, and there are stomata at both the adaxial and abaxial sides. Turgor ranged from 0.2 to 1.0 MPa under laboratory light condition (40 μmol m−2 s−1 at the tissue level), and individual cells could be measured for up to 6 h avoiding the variability between cells. In accordance with earlier findings, there was a big variability in T1/2s measured ranging from 0.5 s to 100 s, but the action of light on T1/2s could nevertheless be worked out for cells having T1/2s greater than 2 s. Increasing light intensity ranging from 100 μmol m−2 s−1 to 650 μmol m−2 s−1 decreased T1/2 by a factor up to five within 10 min and increased Lp (and aquaporin activity) by the same factor. In the presence of light, turgor decreased due to an increase in transpiration, and this tended to compensate or even overcompensated for the effect of light on T1/2. For example, during prolonged illumination, cell turgor dropped from 0.2 to 1.0 MPa to –0.03 to 0.4 MPa, and this drop caused an increase of T1/2 and a reduction of cell Lp, i.e. there was an effect of turgor on cell Lp besides that of light. To separate the two effects, cell turgor (water potential) was kept constant while changing light intensity by applying gas pressure to the roots using a pressure chamber. At a light intensity of 160 μmol m−2 s−1, there was a reduction of T1/2 by a factor of 2.5 after 10–30 min, when turgor was constant within ±0.05 MPa. Overall, the effects of light on T1/2 (Lp) were overriding those of turgor only when decreases in turgor were less than about 0.2 MPa. Otherwise, turgor became the dominant factor. The results indicate that the hydraulic conductivity increased with increasing light intensity tending to improve the water status of the shoot. However, when transpiration induced by light tends to cause a low turgidity of the tissue, cell Lp was reduced. It is concluded that, when measuring the overall hydraulic conductivity of leaves, both the effects of light and turgor should be considered. Although the mechanism(s) of how light and turgor influence the cell Lp is still missing, it most likely involves the gating of aquaporins by both parameters. [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]