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The evolution of stomata marks one of the key advances that enabled plants to colonise dry land while allowing gas exchange for photosynthesis. In large measure, stomata retain a common design across species that incorporates paired guard cells with little variation in structure. By contrast, the cells of the stomatal complex immediately surrounding the guard cells vary widely in shape, size and count. Their origins in development are similarly diverse. Thus, the surrounding cells are likely a luxury that the necessity of stomatal control cannot do without (with apologies to Oscar Wilde). Surrounding cells are thought to support stomatal movements as solute reservoirs and to shape stomatal kinetics through backpressure on the guard cells. Their variety may also reflect a substantial diversity in function. Certainly modelling, kinetic analysis and the few electrophysiological studies to date give hints of much more complex contributions in stomatal physiology. Even so, our knowledge of the cells surrounding the guard cells in the stomatal complex is far from complete. Summary statement: Stomata largely retain a common design across all species of land plants. By contrast, the cells immediately surrounding the guard cells vary widely in nature and origin. Such variety likely reflects a functional diversity in supporting stomatal movements and shaping stomatal kinetics. Yet, our knowledge of the cells surrounding the guard cells in the stomatal complex remains fragmentary at best. [ABSTRACT FROM AUTHOR]

If the past century marked the birth of membrane transport as a focus for research in plants, the past 50 years has seen the field mature from arcane interest to a central pillar of plant physiology. Ion transport across plant membranes accounts for roughly 30% of the metabolic energy consumed by a plant cell, and it underpins virtually every aspect of plant biology, from mineral nutrition, cell expansion, and development to auxin polarity, fertilization, plant pathogen defense, and senescence. The means to quantify ion flux through individual transporters, even single channel proteins, became widely available as voltage clamp methods expanded from giant algal cells to the fungus Neurospora crassa in the 1970s and the cells of angiosperms in the 1980s. Here, I touch briefly on some key aspects of the development of modern electrophysiology with a focus on the guard cells of stomata, now without dispute the premier plant cell model for ion transport and its regulation. Guard cells have proven to be a crucible for many technical and conceptual developments that have since emerged into the mainstream of plant science. Their study continues to provide fundamental insights and carries much importance for the global challenges that face us today. Membrane transport accounts for one third of energy consumption in plant cells; its study is about growth, development, and survival, not just for the plant but also for the planet. [ABSTRACT FROM AUTHOR]

This article discusses the importance of stomata, which are pores on the surfaces of plants that allow for the exchange of CO2 and water vapor. Stomata play a crucial role in photosynthesis and are connected to global carbon and water cycles. The article explores various aspects of stomatal function, including their development, evolution, and the molecular mechanics behind their opening and closing. It also examines the implications of stomatal research for climate change, water availability, and crop production. The article concludes by highlighting the interdisciplinary nature of stomatal research and its significance in understanding plant physiology in the global environment. [Extracted from the article]

Stomatal pores facilitate gaseous exchange between the inner air spaces of the leaf and the atmosphere. The pores open to enable CO 2 entry for photosynthesis and close to reduce transpirational water loss. How stomata respond to the environment has long attracted interest in modeling as a tool to understand the consequences for the plant and for the ecosystem. Models that focus on stomatal conductance for gas exchange make intuitive sense, but such models need also to connect with the mechanics of the guard cells that regulate pore aperture if we are to understand the 'decisions made' by stomata, their impacts on the plant and on the global environment. Stomata are pores in the epidermis of plant leaves that facilitate gaseous exchange of water and atmospheric CO 2 , thereby connecting the water and carbon cycles of the world and exerting a major influence on both. Ecosystem models generally deal with stomata phenomenologically with respect to water availability, atmospheric humidity, CO 2 , and light but without connection to the physiology of the guard cells that regulate stomatal aperture. Guard cell physiology emerges as an important component missing from ecosystem models that will be essential to advance an understanding of the decisions 'made by' stomata in regulating the pore aperture. Guard cell models that capture the mechanics of guard cell transport and metabolism connect environmental inputs with stomatal behavior to accurately predict whole-plant gas exchange and photosynthetic carbon assimilation. [ABSTRACT FROM AUTHOR]

Plants acclimate to various types of mechanical stresses through thigmomorphogenesis and alterations in their mechanical properties. Although resemblance between wind- and touchinduced responses provides the foundation for studies where wind influence was mimicked by mechanical perturbations, factorial experiments revealed that it is not always straightforward to extrapolate results induced by one type of perturbation to the other. To investigate whether wind-induced changes in morphological and biomechanical traits can be reproduced, we subjected Arabidopsis thaliana to two vectorial brushing treatments. Both treatments significantly affected the length, mechanical properties and anatomical tissue composition of the primary inflorescence stem. While some of themorphological changeswere found to be in line with those induced by wind, changes in the mechanical properties exhibited opposite trends irrespective of the brushing direction. Overall, a careful design of the brushing treatment gives the possibility to obtain a closer match to wind-induced changes, including a positive tropic response. [ABSTRACT FROM AUTHOR]

Claims that plants have conscious experiences have increased in recent years and have received wide coverage, from the popular media to scientific journals. Such claims are misleading and have the potential to misdirect funding and governmental policy decisions. After defining basic, primary consciousness, we provide new arguments against 12 core claims made by the proponents of plant consciousness. Three important new conclusions of our study are (1) plants have not been shown to perform the proactive, anticipatory behaviors associated with consciousness, but only to sense and follow stimulus trails reactively; (2) electrophysiological signaling in plants serves immediate physiological functions rather than integrative-information processing as in nervous systems of animals, giving no indication of plant consciousness; (3) the controversial claim of classical Pavlovian learning in plants, even if correct, is irrelevant because this type of learning does not require consciousness. Finally, we present our own hypothesis, based on two logical assumptions, concerning which organisms possess consciousness. Our first assumption is that affective (emotional) consciousness is marked by an advanced capacity for operant learning about rewards and punishments. Our second assumption is that image-based conscious experience is marked by demonstrably mapped representations of the external environment within the body. Certain animals fit both of these criteria, but plants fit neither. We conclude that claims for plant consciousness are highly speculative and lack sound scientific support. [ABSTRACT FROM AUTHOR]

This article discusses various aspects of plant cell exocytosis and defense mechanisms. It highlights the importance of studying exocytosis in plant cells, which is often overlooked compared to endocytosis. The article explores the regulation and spatial control of exocytosis, the role of formins and ROP guanine exchange factors in membrane dynamics, the organization of the secretory pathway for cell wall remodeling, the involvement of RHO/RAC/ROP GTPases in cell wall defense, and the secretion of small proteins in plants. The authors also mention emerging areas of research, such as the formation of exocytotic vesicles and liquid-liquid phase separation. Overall, this article provides valuable insights into the complex processes involved in plant cell exocytosis and defense. [Extracted from the article]

Stomatal guard cells are widely recognized as the premier plant cell model for membrane transport, signaling, and homeostasis. This recognition is rooted in half a century of research into ion transport across the plasma and vacuolar membranes of guard cells that drive stomatal movements and the signaling mechanisms that regulate them. Stomatal guard cells surround pores in the epidermis of plant leaves, controlling the aperture of the pore to balance CO2 entry into the leaf for photosynthesis with water loss via transpiration. The position of guard cells in the epidermis is ideally suited for cellular and subcellular research, and their sensitivity to endogenous signals and environmental stimuli makes them a primary target for physiological studies. Stomata underpin the challenges of water availability and crop production that are expected to unfold over the next 20 to 30 years. A quantitative understanding of how ion transport is integrated and controlled is key to meeting these challenges and to engineering guard cells for improved water use efficiency and agricultural yields. [ABSTRACT FROM AUTHOR]

Abstract: It is widely recognized that the nature and characteristics of transport across eukaryotic membranes are so complex as to defy intuitive understanding. In these circumstances, quantitative mathematical modeling is an essential tool, both to integrate detailed knowledge of individual transporters and to extract the properties emergent from their interactions. As the first, fully integrated and quantitative modeling environment for the study of ion transport dynamics in a plant cell, OnGuard offers a unique tool for exploring homeostatic properties emerging from the interactions of ion transport, both at the plasma membrane and tonoplast in the guard cell. OnGuard has already yielded detail sufficient to guide phenotypic and mutational studies, and it represents a key step toward ‘reverse engineering’ of stomatal guard cell physiology, based on rational design and testing in simulation, to improve water use efficiency and carbon assimilation. Its construction from the HoTSig libraries enables translation of the software to other cell types, including growing root hairs and pollen. The problems inherent to transport are nonetheless challenging, and are compounded for those unfamiliar with conceptual ‘mindset’ of the modeler. Here we set out guidelines for the use of OnGuard and outline a standardized approach that will enable users to advance quickly to its application both in the classroom and laboratory. We also highlight the uncanny and emergent property of OnGuard models to reproduce the ‘communication’ evident between the plasma membrane and tonoplast of the guard cell. [Copyright &y& Elsevier]

The control of gaseous exchange between the leaf and bulk atmosphere by stomata governs CO2 uptake for photosynthesis and transpiration, determining plant productivity and water use efficiency. The balance between these two processes depends on stomatal responses to environmental and internal cues and the synchrony of stomatal behavior relative to mesophyll demands for CO2. Here we examine the rapidity of stomatal responses with attention to their relationship to photosynthetic CO2 uptake and the consequences for water use. We discuss the influence of anatomical characteristics on the velocity of changes in stomatal conductance and explore the potential for manipulating the physical as well as physiological characteristics of stomatal guard cells in order to accelerate stomatal movements in synchrony with mesophyll CO2 demand and to improve water use efficiency without substantial cost to photosynthetic carbon fixation. We conclude that manipulating guard cell transport and metabolism is just as, if not more likely to yield useful benefits as manipulations of their physical and anatomical characteristics. Achieving these benefits should be greatly facilitated by quantitative systems analysis that connects directly the molecular properties of the guard cells to their function in the field. [ABSTRACT FROM AUTHOR]

The article examines whether calcineurin B-like proteins (CBL) interact independently of the serine threonine kinase CIPK23 with the K+ channel AKT1. It was noted that despite the absence of AKT1, KC1 grew with the Nub-2xHA-CIPK23 prey. On the other hand, the presence of AKT1 enhances the interaction between CIPK23 and KC1.

Eukaryotic cells expand using vesicle traffic to increase membrane surface area. Expansion in walled eukaryotes is driven by turgor pressure which depends fundamentally on the uptake and accumulation of inorganic ions. Thus, ion uptake and vesicle traffic must be controlled coordinately for growth. How this coordination is achieved is still poorly understood, yet is so elemental to life that resolving the underlying mechanisms will have profound implications for our understanding of cell proliferation, development, and pathogenesis, and will find applications in addressing the mineral and water use by plants in the face of global environmental change. Recent discoveries of interactions between trafficking and ion transport proteins now open the door to an entirely new approach to understanding this coordination. Some of the advances to date in identifying key protein partners in the model plant Arabidopsis and in yeast at membranes vital for cell volume and turgor control are outlined here. Additionally, new evidence is provided of a wider participation among Arabidopsis Kv-like K+ channels in selective interaction with the vesicle-trafficking protein SYP121. These advances suggest some common paradigms that will help guide further exploration of the underlying connection between ion transport and membrane traffic and should transform our understanding of cellular homeostasis in eukaryotes. [ABSTRACT FROM PUBLISHER]

Gating of K+ and other ion channels is ‘hard-wired’ within the channel protein. So it remains a puzzle how closely related channels in plants can show an unusually diverse range of biophysical properties. Gating of these channels lies at the heart of K+ mineral nutrition, signalling, abiotic and biotic stress responses in plants. Thus, our knowledge of the molecular mechanics underpinning K+ channel gating will be important for rational engineering of related traits in agricultural crops. Several key studies have added significantly to our understanding of channel gating in plants and have challenged current thinking about analogous processes found in animal K+ channels. Such studies highlight how much of K+ channel gating remains to be explored in plants. [Copyright &y& Elsevier]

Contents In addition to light, water and CO2, plants require a number of mineral nutrients, in particular the macronutrients nitrogen, sulphur, phosphorus, magnesium, calcium and potassium. After uptake from the soil by the root system they are either immediately assimilated into organic compounds or distributed within the plant for usage in different tissues. A good understanding of how the transport of macronutrients into and between plant cells is adjusted to different environmental conditions is essential to achieve an increase of nutrient usage efficiency and nutritional value in crops. Here, we review the current state of knowledge regarding the regulation of macronutrient transport, taking both a physiological and a mechanistic approach. We first describe how nutrient transport is linked to environmental and internal cues such as nutrient, carbon and water availability via hormonal, metabolic and physical signals. We then present information on the molecular mechanisms for regulation of transport proteins, including voltage gating, auto-inhibition, interaction with other proteins, oligomerization and trafficking. Combining of evidence for different nutrients, signals and regulatory levels creates an opportunity for making new connections within a large body of data, and thus contributes to an integrative understanding of nutrient transport. [ABSTRACT FROM AUTHOR]

The author comments on the decision of Brandon Stell, Richard Smith and George Smith to reveal themselves as creators of PubPeer, a website that sought to facilitate community-wide, postpublication critique of scientific articles. He discusses the controversy surrounding the site's policies, his support for a place for independent, postpublication discussion that is linked to individual articles, and the reason behind Stell and colleagues' action. A brief background on the website is cited.

SNARE (soluble N-ethylmaleimide-sensitive factor protein attachment protein receptor) proteins drive membrane fusion and contribute to membrane and protein targeting and delivery in all eukaryotic cells. SNAREs are essential to the mechanics of cell growth and development, and they facilitate a number of homeostatic and evoked responses in plants, from hormone signalling to pathogen defence. Additionally, there is now unambiguous evidence that SNAREs play roles in anchoring other membrane proteins and in facilitating ion channel gating through direct, physical interaction with channel proteins. What is the physiological significance of these additional features of plant SNAREs? We explore possible interpretations and suggest functions as scaffolds for effective signal transmission between proteins and, by analogy with a mechanical device invented by James Watt, as molecular governors to coordinate solute transport with cell expansion and growth. [Copyright &y& Elsevier]

The article discusses the significance of soluble N-ethylmaleimide-sensitive fusion protein attachment protein receptor (SNARE) on plant signaling and development. It is noted that SNARE proteins facilitate vesicle traffic by overcoming the immense dehydration forces associated with bringing two lipid bilayers together in an aqueous environment and by matching vesicles with their destinations. In addition, it is stated that the formation of a SNARE complex is sufficient to drive fusion.

Root hairs and pollen tubes extend by rapid elongation that occurs exclusively at the tip. Fundamental for such local, tip-focused growth (so-called ‘tip growth’) is the polarization of the cytoplasm that directs secretory events to the tip, and the presence of internal gradients and transmembrane flux of ions, notably Ca2+, H+, K+, and Cl−. Electrophysiological and imaging studies using fluorescent markers have sought to link ion gradients with growth and membrane trafficking. Current models recognize membrane trafficking as fundamental to tip growth, notably its role in supplying lipid and protein to the new plasma membrane and cell wall that extend the apex of the cell, and a complementary role for endocytosis in retrieving excess membrane and in recycling various protein fractions. The current state of knowledge is reviewed here in order to highlight the major gaps in the present understanding of trafficking as it contributes to polar growth in these cells and recent results, that suggest a role for membrane trafficking in the active regulation of ion channel turnover and activity during polar tip growth, are discussed. [ABSTRACT FROM PUBLISHER]

Recent work has indicated that nitric oxide (NO) and its synthesis are important elements of signal cascades in plant pathogen defense and are a prerequisite for drought and abscisic acid responses in Arabidopsis (Arabidopsis thaliana) and Vicia faba guard cells. Nonetheless, its mechanism(s) of action has not been well defined. NO regulates inward-rectifying K+ channels of Vicia guard cells through its action on Ca2+ release from intercellular Ca2+ stores, but alternative pathways are indicated for its action on the outward-rectifying K+ channels (IK,out), which are Ca2+ insensitive. We report here that NO affects IK,out when NO is elevated above approximately 10 to 20 nM. NO action on IK,out was consistent with oxidative stress and was suppressed by several reducing agents, the most effective being British anti-Lewisite (2,3-dimercapto-1-propanol). The effect of NO on the K+ channel was mimicked by phenylarsine oxide, an oxidizing agent that cross-links vicinal thiols. Neither intracellular pH buffering nor the phosphotyrosine kinase antagonist genistein affected NO action on IK,out, indicating that changes in cytosolic pH and tyrosine phosphorylation are unlikely to contribute to NO or phenylarsine oxide action in this instance. Instead, our results strongly suggest that NO directly modifies the K+ channel or a closely associated regulatory protein, probably by nitrosylation of cysteine sulfhydryl groups. [ABSTRACT FROM AUTHOR]

Summary Vesicular trafficking and membrane fusion are integral to cell growth and development with SNARE proteins, RabGTPases and their associates implicated in membrane fusion and secretion throughout the plant endomembrane system. Although the overall pattern of function is similar to that of animals and yeast, many aspects of endomembrane organization and vesicle trafficking appear unique to plants, for example, the control of cell and vacuolar expansion, asymmetric growth and cell division. However, the dominant membrane trafficking pathways have yet to be defined. Comparative genomics provide important information about vesicle trafficking elements but assigning biological roles based on sequence similarities is extremely difficult. Cellular and genetic approaches are reviewed here that have allowed visualization of vesicle trafficking in plants, including capacitance and dye methods, imaging and marker techniques, protein interactions and reverse genetics. Stomatal guard cells are discussed as cell models for identifying vesicle trafficking pathways and evidence points to a role for vesicle trafficking in stomatal function. For plants generally, kinetic analyses and biochemical studies suggest that several different pools of vesicles, and possibly different mechanisms for delivery, are available for vesicle traffic between endomembrane compartments and the plasma membrane. Characterizing these pathways, their functions and controls provides a major challenge for the future. [ABSTRACT FROM AUTHOR]

Stomatal guard cells are unique as a plant cell model and, because of the depth of present knowledge on ion transport and its regulation, offer a first look at signal integration in higher plants. A large body of data indicates that Ca[sup 2+] and H[sup +] act independently, integrating with protein kinases and phosphatases, to control the gating of the K[sup +] and Cl[sup -] channels that mediate solute flux for stomatal movements. Oscillations in the cytosolic-free concentration of Ca[sup 2+] contribute to a signaling cassette, integrated within these events through an unusual coupling with membrane voltage for solute homeostasis. Similar cassettes are anticipated to include control pathways linked to cytosolic pH. Additional developments during the last two years point to events in membrane traffic that play equally important roles in stomatal control. Research in these areas is now adding entirely new dimensions to our understanding of guard cell signaling. [ABSTRACT FROM AUTHOR]

Stomata play a crucial role in plants by controlling water status and responding to drought stress. However, simultaneously improving stomatal opening and drought tolerance has proven to be a significant challenge. To address this issue, we employed the OnGuard quantitative model, which accurately represents the mechanics and coordination of ion transporters in guard cells. With the guidance of OnGuard, we successfully engineered plants that overexpressed the main tonoplast Ca2+‐ATPase gene, ACA11, which promotes stomatal opening and enhances plant growth. Surprisingly, these transgenic plants also exhibited improved drought tolerance due to reduced water loss through their stomata. Again, OnGuard assisted us in understanding the mechanism behind the unexpected stomatal behaviors observed in the ACA11 overexpressing plants. Our study revealed that the overexpression of ACA11 facilitated the accumulation of Ca2+ in the vacuole, thereby influencing Ca2+ storage and leading to an enhanced Ca2+ elevation in response to abscisic acid. This regulatory cascade finely tunes stomatal responses, ultimately leading to enhanced drought tolerance. Our findings underscore the importance of tonoplast Ca2+‐ATPase in manipulating stomatal behavior and improving drought tolerance. Furthermore, these results highlight the diverse functions of tonoplast‐localized ACA11 in response to different conditions, emphasizing its potential for future applications in plant enhancement. [ABSTRACT FROM AUTHOR]

Eukaryotic cells share a set of secretory pathways for the flux of membrane and protein material. In 1993, ideas about the functioning of three major proteins of the neurosecretory complex were consolidated in the SNARE hypothesis, which proposed that the interaction of these proteins provides both the specificity for vesicle targeting and the molecular machinery for fusion between vesicle and target membranes. Subsequently the organization, molecular mechanics and control of vesicle trafficking have become topics of intense research, and the organization, molecular mechanics and control of visicle trafficking have become topics of intense research, and the hypothesis has evolved to accummodate new discoveries from the analysis of secretion in yeast and mammals. It is likely to be challenged again as more information comes to light about secretory processes in plants. New tools for measuring and manipulating vesicle traffic and secretion are now being used, drawing on in vivo fluorescence and capacitance recording as well as genetic engineering. These new technologies have already begun to yield details wholly unexpected from past studies. Here we focus on recent findings relating to the mechanisms of vesicle trafficking and the background to these developments, highlighting both current understanding of the molecular events of secretion and the gaps therein, as well as discussing emerging themes from work with plants. [ABSTRACT FROM AUTHOR]

Summary: The Cf-9 gene encodes an extracytosolic leucine-rich repeat (LRR) protein that is membrane anchored near its C-terminus. The protein confers resistance in tomato to races of the fungus Cladosporium fulvum expressing the corresponding avirulence gene Avr9. In Nicotiana tabacum the Cf-9 transgene confers sensitivity to the Avr9 elicitor, and leads on elicitation to a subset of defence responses qualitatively similar to those normally seen in the tomato host. One of the earliest responses, both in the native and transgenic hosts, results in K[sup +] salt loss from the infected tissues. However, the mechanism(s) underlying this solute flux and its control is poorly understood. We have explored the actions of Avr9 on Cf-9 transgenic Nicotiana using guard cells as a model. Much detail of guard cell ion channels and their regulation is already known. Measurements were carried out on intact guard cells in epidermal peels, and the currents carried by inward- (I[sub K,in]) and outward-rectifying (I[sub K,out]) K[sup +] channels were characterized under voltage clamp. Exposures to Avr9-containing extracts resulted in a 2.5- to 3-fold stimulation of I[sub K,out] and almost complete suppression of I[sub K,in] within 3–5 min. The K[sup +] channel responses were irreversible. They were specific for the Avr9 elicitor, were not observed in guard cells of Nicotiana lacking the Cf-9 transgene and, from kinetic analyses, could be ascribed to changes in channel gating. Both K[sup +] channel responses were found to be saturable functions of Avr9 concentration and were completely blocked in the presence of 0.5 μM staurosporine and 100 μM H7, both broad-range protein kinase antagonists. These results demonstrate the ability of the Cf-9 transgene to couple Avr9 elicitation specifically to a concerted action on two discrete K[sup +] channels and they indicate a role for protein phosphorylation in Avr9/Cf-9 signal transduction leading to transport control. [ABSTRACT FROM AUTHOR]

The complexity of cellular signals related to cytosolic free Ca2+ concentration is well-illustrated in stomatal guard cells. Guard cells are unique as a higher plant cell model, because of the depth of knowledge to hand about ion channels at the plasma membrane and their regulation. A large body of data indicates actions of Ca2+ in controlling the gating of K+ and Cl- channels, and there is now growing evidence for transients and oscillations in cytosolic free Ca2+ concentration based on a mechanism with some similarities to Ca2+-induced Ca2+ release in animals. While these new discoveries offer a possible explanation for the specificity and diversity of Ca2+-dependent signalling, they raise a question about the immediate role(s) for Ca2+ as a primary signal intermediate in some instances. [ABSTRACT FROM PUBLISHER]

Presents a study which discusses the membrane voltage and the calcium (Ca2+) waves and potentiates with abscisic acid in stomatal guard cells. Description of the calcium ions; Information on the activities in the stomatal guard cells; What the results indicated.

Multiple signalling pathways and their messengers - entailing changes in cytosolic-free Ca2+ ([Ca2+]1), pH (pH1) and protein phosphorylation - underpin K+ and anion channel control during stomatal movements. This redundancy is wholly consistent with the ability of the guard cells to integrate the wide range of environmental and hormonal stimuli that affect stomatal aperture. Signal redundancy effects a spectrum of graded responses by linking pathways to gate signal transmission, and so boosts or mutes the final 'integrated signal' that reaches each ion channel. All evidence supports a role for the ABII protein phosphatase and protein kinase elements in gating K- channel sensitivity to pH and ABA. Changes in [Ca2+]1, in turn, are demonstrably sensitive to pH1. Because each of these signal elements modulate and, in turn, are influenced by the activity of different sets of ion channels, the additional couplings engender a remarkably complex network, layering positive and negative controls with the ion channels that facilitate ion fluxes for stomatal movement. [ABSTRACT FROM AUTHOR]

Stomata are pores that form between pairs of guard cells and are commonly found in the leaf epidermis. The pores allow gaseous exchange between the inner air spaces of the leaf and the atmosphere, opening for CO2 entry to support photosynthesis and closing to reduce transpirational water loss. Guard cell membrane transport and its coordination play a central part in regulating the pore aperture. We know how guard cells respond to light, CO2 and drought with sufficient detail to model with quantitative accuracy their mechanics. By contrast, there is surprisingly little detail about the impact of salt stress on guard cells. Here we review the topic and introduce Na+ transport within the proven OnGuard3 modeling platform to question the mechanics of stomatal responses to salinity. The analysis indicates a critical role for ABA-mediated Ca2+ signaling as an early and overriding process leading to stomatal closure, a beneficial behavior for plants in the face of salt stress. [ABSTRACT FROM AUTHOR]

An introduction is presented in which the editor discusses various reports within the issue on topics including the rapidity of stomatal responses, acceleration of stomatal movements by acceleration of guard cell transport in silico, and the origin of hormone abscisic acid (ABA).

SUMMARY: In plants so‐called plasma membrane intrinsic proteins (PIPs) are major water channels governing plant water status. Membrane trafficking contributes to functional regulation of major PIPs and is crucial for abiotic stress resilience. Arabidopsis PIP2;1 is rapidly internalised from the plasma membrane in response to high salinity to regulate osmotic water transport, but knowledge of the underlying mechanisms is fragmentary. Here we show that PIP2;1 occurs in complex with SYNTAXIN OF PLANTS 132 (SYP132) together with the plasma membrane H+‐ATPase AHA1 as evidenced through in vivo and in vitro analysis. SYP132 is a multifaceted vesicle trafficking protein, known to interact with AHA1 and promote endocytosis to impact growth and pathogen defence. Tracking native proteins in immunoblot analysis, we found that salinity stress enhances SYP132 interactions with PIP2;1 and PIP2;2 isoforms to promote redistribution of the water channels away from the plasma membrane. Concurrently, AHA1 binding within the SYP132‐complex was significantly reduced under salinity stress and increased the density of AHA1 proteins at the plasma membrane in leaf tissue. Manipulating SYP132 function in Arabidopsis thaliana enhanced resilience to salinity stress and analysis in heterologous systems suggested that the SNARE influences PIP2;1 osmotic water permeability. We propose therefore that SYP132 coordinates AHA1 and PIP2;1 abundance at the plasma membrane and influences leaf hydraulics to regulate plant responses to abiotic stress signals. Significance Statement: We uncover a new role for the plasma membrane trafficking SNARE SYP132 in the regulation of PIP2;1 density and function in response to salinity and osmotic stress. Remarkably these pathways appear to intersect with coordinate regulation of AHA1 that is governed by the SYP132 during pathogenesis, thus suggesting that the SNARE is at the centre of an antiparallel association of PIP2 and the H+‐ATPase affected by salinity. [ABSTRACT FROM AUTHOR]

Membrane voltage arises from the transport of ions through ion-translocating ATPases, ion-coupled transport of solutes, and ion channels, and is an integral part of the bioenergetic "currency" of the membrane. The dynamics of membrane voltage--so-called action, systemic, and variation potentials--have also led to a recognition of their contributions to signal transduction, both within cells and across tissues. Here, we review the origins of our understanding of membrane voltage and its place as a central element in regulating transport and signal transmission. We stress the importance of understanding voltage as a common intermediate that acts both as a driving force for transport--an electrical "substrate"--and as a product of charge flux across the membrane, thereby interconnecting all charge-carrying transport across the membrane. The voltage interconnection is vital to signaling via second messengers that rely on ion flux, including cytosolic free Ca2+, H+, and the synthesis of reactive oxygen species generated by integral membrane, respiratory burst oxidases. These characteristics inform on the ways in which long-distance voltage signals and voltage oscillations give rise to unique gene expression patterns and influence physiological, developmental, and adaptive responses such as systemic acquired resistance to pathogens and to insect herbivory. [ABSTRACT FROM AUTHOR]

Stomata are microscopic pores at the surface of plant leaves that facilitate gaseous diffusion to support photosynthesis. The guard cells around each stoma regulate the pore aperture. Plants that carry out C4 photosynthesis are usually more resilient than C3 plants to stress, and their stomata operate over a lower dynamic range of CO2 within the leaf. What makes guard cells of C4 plants more responsive than those of C3 plants? We used gas exchange and electrophysiology, comparing stomatal kinetics of the C4 plant Gynandropsis gynandra and the phylogenetically related C3 plant Arabidopsis thaliana. We found, with varying CO2 and light, that Gynandropsis showed faster changes in stomata conductance and greater water use efficiency when compared with Arabidopsis. Electrophysiological analysis of the dominant K+ channels showed that the outward‐rectifying channels, responsible for K+ loss during stomatal closing, were characterised by a greater maximum conductance and substantial negative shift in the voltage dependence of gating, indicating a reduced inhibition by extracellular K+ and enhanced capacity for K+ flux. These differences correlated with the accelerated stomata kinetics of Gynandropsis, suggesting that subtle changes in the biophysical properties of a key transporter may prove a target for future efforts to engineer C4 stomatal kinetics. Summary Statement: Compared with Arabidopsis, the outward‐rectifying K+ channels in guard cells of the C4 plant Gynandropsis gynandra incorporate gating that is displaced to favour enhanced K+ efflux and promote K+ influx. These characteristics are likely to underpin the faster stomatal that are observed in the C4 plant. [ABSTRACT FROM AUTHOR]

We have analyzed the claims made in two highly popular books, which promulgate the idea that trees possess a number of human characteristics for which there is no sound scientific evidence. A critical evaluation of the mother tree hypothesis also reveals that much of the data given in support of this concept is flawed and perhaps even non-existent. This concept is also incompatible with many well-known observations on the growth of forest trees. Moreover, there is no evidence from peer-reviewed published studies to support the claim that mature trees in forests communicate preferentially with offspring through a common mycelial network. It also remains unclear whether carbon compounds transmitted in the mycorrhizae actually enter the root tissue of the receiver tree. In any event, numerous studies indicate that the amounts of carbon transferred are physiologically insignificant. There are growing doubts about the true role of the common mycorrhizal networks (CMN or wood wide web) connecting the roots of trees in forests. We question the claims of a substantial carbon transfer from 'mother trees' to their offspring and nearby seedlings through the CMN. Recent reviews show that evidence for the 'mother tree concept' is inconclusive or absent. The origin of this concept seems to stem from a desire to humanize plant life but can lead to misunderstandings and false interpretations and may eventually harm rather than help the commendable cause of preserving forests. Two recent books serve as examples: The Hidden Life of Trees and Finding the Mother Tree. A recent article highlights the growing doubts about the true role of the common mycorrhizal networks [CMN or wood wide web (WWW)] connecting the roots of trees in forests. It questions the claim of a substantial carbon transfer from 'mother trees' to their offspring and nearby seedlings through the CMN. Recent reviews show that evidence for the 'mother tree concept' is inconclusive or absent. The origin of this concept seems to stem from a desire to humanize plant life but can lead to misunderstandings and false interpretations and may eventually harm rather than help the commendable cause of preserving forests. Two recent books serve as examples: The Hidden Life of Trees and Finding the Mother Tree. [ABSTRACT FROM AUTHOR]

Plant membrane transport, like transport across all eukaryotic membranes, is highly nonlinear and leads to interactions with characteristics so complex that they defy intuitive understanding. The physiological behaviour of stomatal guard cells is a case in point in which, for example, mutations expected to influence stomatal closing have profound effects on stomatal opening and manipulating transport across the vacuolar membrane affects the plasma membrane. Quantitative mathematical modelling is an essential tool in these circumstances, both to integrate the knowledge of each transport process and to understand the consequences of their manipulation in vivo. Here, we outline the OnGuard modelling environment and its use as a guide to predicting the emergent properties arising from the interactions between non-linear transport processes. We summarise some of the recent insights arising from OnGuard, demonstrate its utility in interpreting stomatal behaviour, and suggest ways in which the OnGuard environment may facilitate 'reverse-engineering' of stomata to improve water use efficiency and carbon assimilation. [ABSTRACT FROM AUTHOR]

Gas exchange across the stomatal pores of leaves is a focal point in studies of plant‐environmental relations. Stomata regulate atmospheric exchange with the inner air spaces of the leaf. They open to allow CO2 entry for photosynthesis and close to minimize water loss. Models that focus on the phenomenology of stomatal conductance generally omit the mechanics of the guard cells that regulate the pore aperture. The OnGuard platform fills this gap and offers a truly mechanistic approach with which to analyse stomatal gas exchange, whole‐plant carbon assimilation and water‐use efficiency. Previously, OnGuard required specialist knowledge of membrane transport, signalling and metabolism. Here we introduce OnGuard3e, a software package accessible to ecophysiologists and membrane biologists alike. We provide a brief guide to its use and illustrate how the package can be applied to explore and analyse stomatal conductance, assimilation and water use efficiencies, addressing a range of experimental questions with truly predictive outputs. Summary statement: OnGuard3e offers a truly mechanistic approach with which to analyse stomatal gas exchange, whole‐plant carbon assimilation and water‐use efficiency. The software package seamlessly connects whole‐plant gas exchange and photosynthesis with the microscopic mechanics of stomata and is accessible to ecophysiologists and membrane biologists alike. We provide a brief guide to its use and illustrate how the package can be applied to explore and analyse stomatal conductance, assimilation and water use efficiencies, addressing a range of experimental questions with truly predictive outputs. [ABSTRACT FROM AUTHOR]

The guard cells that surround each stoma regulate stomatal aperture and, hence, gaseous conductance, through osmotically driven water fluxes that commonly accompany ion transport and the metabolism of organic solutes. Manipulating stomatal density at the leaf surface yields significant improvements in plant water use efficiency and drought resilience by reducing steady-state gaseous conductance, but also reduces net carbon fixation and can affect vegetative growth. Engineering strategies that focus on the kinetics of stomatal opening and closing offer a means to circumvent the trade-off in the steady-state exchange of atmospheric CO 2 for water in the plant. Both synthetic optogenetics and manipulations of the activity of ion channels native to guard cells demonstrate the gains in both water use efficiency and carbon fixation that are possible by engineering stomatal kinetics. Stomatal pores facilitate gaseous exchange between the inner air spaces of the leaf and the atmosphere. As gatekeepers that balance CO 2 entry for photosynthesis against transpirational water loss, they are a focal point for efforts to improve crop performance, especially in the efficiency of water use, within the changing global environment. Until recently, engineering strategies had focused on stomatal conductance in the steady state. These strategies are limited by the physical constraints of CO 2 and water exchange such that gains in water-use efficiency (WUE) commonly come at a cost in carbon assimilation. Attention to stomatal speed and responsiveness circumvents these constraints and offers alternatives to enhancing WUE that also promise increases in carbon assimilation in the field. [ABSTRACT FROM AUTHOR]

Models of guard cell dynamics, built on the OnGuard platform, have provided quantitative insights into stomatal function, demonstrating substantial predictive power. However, the kinetics of stomatal opening predicted by OnGuard models were threefold to fivefold slower than observed in vivo. No manipulations of parameters within physiological ranges yielded model kinetics substantially closer to these data, thus highlighting a missing component in model construction. One well‐documented process influencing stomata is the constraining effect of the surrounding epidermal cells on guard cell volume and stomatal aperture. Here, we introduce a mechanism to describe this effect in OnGuard2 constructed around solute release and a decline in turgor of the surrounding cells and its subsequent recovery during stomatal opening. The results show that this constraint–relaxation–recovery mechanism in OnGuard2 yields dynamics that are consistent with experimental observations in wild‐type Arabidopsis, and it predicts the altered opening kinetics of ost2 H+‐ATPase and slac1 Cl− channel mutants. Thus, incorporating solute flux of the surrounding cells implicitly through their constraint on guard cell expansion provides a satisfactory representation of stomatal kinetics, and it predicts a substantial and dynamic role for solute flux across the apoplastic space between the guard cells and surrounding cells in accelerating stomatal kinetics. Models of stomatal function build on the OnGuard platform and our deep knowledge of guard cell transport and metabolism have provided quantitative insights into stomatal function. However, the kinetics of stomatal opening predicted by OnGuard models have consistently failed to match the accelerated opening observed in vivo, thus highlighting a missing component in model construction. Incorporating explicitly a solute flux‐based mechanism of constraint relaxation and recovery between cells surrounding the stoma and the stomatal guard cells accommodates the accelerated stomatal opening kinetics observed in vivo and accurately predicts the slowed kinetics of stomatal opening in guard cell transport mutants. [ABSTRACT FROM AUTHOR]

The photoreceptor UVR8 has a pivotal role in mediating plant responses to UV-B wavelengths. Dimeric UVR8 dissociates into monomers following UV-B photoreception, and there is evidence that this process is accompanied by conformational changes that may facilitate interaction of UVR8 with other proteins to initiate signaling. Hence monitoring UVR8 dimer/monomer status and conformation is key to understanding UVR8 action. Here we have used Fluorescence Resonance Energy Transfer (FRET) to study these processes in both wild-type and mutant UVR8 proteins in vivo. UVR8 was fused to GFP and mCherry at the C- and N-termini, respectively and both the FRET efficiency and loss of GFP fluorescence after photobleaching were measured. In addition, measurements were made for UVR8 fused to either GFP or mCherry to eliminate intra-molecular FRET signals. The results indicate that dissociation of UVR8 dimer to monomer principally accounts for the loss of FRET signal for wild-type UVR8 and there is little evidence of a contribution from conformational change in vivo. Examination of plants expressing UVR8W285F and UVR8D96N,D107N are consistent with these mutant proteins being constitutively dimeric and monomeric, respectively. The methods employed here will be valuable for monitoring UVR8 dimer/monomer status in vivo in relation to signaling, and will facilitate characterization of dimer/monomer status and conformation of further UVR8 mutants. [ABSTRACT FROM AUTHOR]

Summary Stomata open at the leaf epidermis, driven by solute accumulation in the surrounding guard cells. Transmembrane ion transport has long been recognised to contribute to this process. A new study makes it clear that guard cells also metabolise starch to accelerate opening. [ABSTRACT FROM AUTHOR]

Presents an expanded abstract from the research paper "A Simple Technique Employing Fiber Optics to Measure Chloroplast Movements in Single Cells". Use of optical methods to study chloroplast movements both in algae and in higher plant leaves; Development of a recording microphotometer; Vaucheria chloroplast aggregation.