Utopia and Its Discontents: The Kibbutz and Its Historical Vicissitudes

Following an explication of "utopianism," this article describes the social and cultural systems of the original utopian communes comprising the Israeli kibbutz movement. It then describes the radical changes that have been made in those systems. After accounting for these changes, it assesses their implications for the utopian and cultural determinist theories of human nature.     

Origin of Microglia: Current Concepts and Past Controversies

Microglia are the resident macrophages of the central nervous system (CNS), which sit in close proximity to neural structures and are intimately involved in brain homeostasis. The microglial population also plays fundamental roles during neuronal expansion and differentiation, as well as in the perinatal establishment of synaptic circuits. Any change in the normal brain environment results in microglial activation, which can be detrimental if not appropriately regulated. Aberrant microglial function has been linked to the development of several neurological and psychiatric diseases. However, microglia also possess potent immunoregulatory and regenerative capacities, making them attractive targets for therapeutic manipulation. Such rationale manipulations will, however, require in-depth knowledge of their origins and the molecular mechanisms underlying their homeostasis. Here, we discuss the latest advances in our understanding of the origin, differentiation, and homeostasis of microglial cells and their myelomonocytic relatives in the CNS.Microglia are the resident macrophages of the central nervous system (CNS), which are uniformly distributed throughout the brain and spinal cord with increased densities in neuronal nuclei, including the Substantia nigra in the midbrain (Lawson et al. 1990; Perry 1998). They belong to the nonneuronal glial cell compartment and their function is crucial to maintenance of the CNS in both health and disease (Ransohoff and Perry 2009; Perry et al. 2010; Ransohoff and Cardona 2010; Prinz and Priller 2014).Two key functional features define microglia: immune defense and maintenance of CNS homeostasis. As part of the innate immune system, microglia constantly sample their environment, scanning and surveying for signals of external danger (Davalos et al. 2005; Nimmerjahn et al. 2005; Lehnardt 2010), such as those from invading pathogens, or internal danger signals generated locally by damaged or dying cells (Bessis et al. 2007; Hanisch and Kettenmann 2007). Detection of such signals initiates a program of microglial responses that aim to resolve the injury, protect the CNS from the effects of the inflammation, and support tissue repair and remodeling (Minghetti and Levi 1998; Goldmann and Prinz 2013).Microglia are also emerging as crucial contributors to brain homeostasis through control of neuronal proliferation and differentiation, as well as influencing formation of synaptic connections (Lawson et al. 1990; Perry 1998; Hughes 2012; Blank and Prinz 2013). Recent imaging studies revealed dynamic interactions between microglia and synaptic connections in the healthy brain, which contributed to the modification and elimination of synaptic structures (Perry et al. 2010; Tremblay et al. 2010; Bialas and Stevens 2013). In the prenatal brain, microglia regulate the wiring of forebrain circuits, controlling the growth of dopaminergic axons in the forebrain and the laminar positioning of subsets of neocortical interneurons (Squarzoni et al. 2014). In the postnatal brain, microglia-mediated synaptic pruning is similarly required for the remodeling of neural circuits (Paolicelli et al. 2011; Schafer et al. 2012). In summary, microglia occupy a central position in defense and maintenance of the CNS and, as a consequence, are a key target for the treatment of neurological and psychiatric disorders.Although microglia have been studied for decades, a long history of experimental misinterpretation meant that their true origins remained debated until recently. Although we knew that microglial progenitors invaded the brain rudiment at very early stages of embryonic development (Alliot et al. 1999; Ransohoff and Perry 2009), it has now been established that microglia arise from yolk sac (YS)-primitive macrophages, which persist in the CNS into adulthood (Davalos et al. 2005; Nimmerjahn et al. 2005; Ginhoux et al. 2010, 2013; Kierdorf and Prinz 2013; Kierdorf et al. 2013a). Moreover, early embryonic brain colonization by microglia is conserved across vertebrate species, implying that it is essential for early brain development (Herbomel et al. 2001; Bessis et al. 2007; Hanisch and Kettenmann 2007; Verney et al. 2010; Schlegelmilch et al. 2011; Swinnen et al. 2013). In this review, we will present the latest findings in the field of microglial ontogeny, which provide new insights into their roles in health and disease.     

Focus on Water: Genetic and Physiological Controls of Growth under Water Deficit

The sensitivity of expansive growth to water deficit has a large genetic variability, which is higher than that of photosynthesis. It is observed in several species, with some genotypes stopping growth in a relatively wet soil, whereas others continue growing until the lower limit of soil-available water. The responses of growth to soil water deficit and evaporative demand share an appreciable part of their genetic control through the colocation of quantitative trait loci as do the responses of the growth of different organs to water deficit. This result may be caused by common mechanisms of action discussed in this paper (particularly, plant hydraulic properties). We propose that expansive growth, putatively linked to hydraulic processes, determines the sink strength under water deficit, whereas photosynthesis determines source strength. These findings have large consequences for plant modeling under water deficit and for the design of breeding programs.Evolution has selected plants that reduce leaf area and seed number under water deficit, allowing production of at least a few viable seeds, in such a way that their alleles are not lost during dry years. Reducing transpiration rate by decreasing leaf area saves soil water during vegetative stages in favor of reproductive stages and keeps plants at a better water status (Boyer, 1985). It is safer than stomatal closure, which is usually accompanied by an increase in leaf temperature (Guilioni et al., 2008). However, this conservative strategy decreases carbon acquisition by plants, with two drawbacks. First, it reduces seed number and yield, crucial traits for agriculture but also for natural environments because this reduces the number of potential offspring. Second, conservative altruistic plants may be outgrown by fast-growing plants in natural environments and excluded from their niche (Gordon and Rice, 2000).As a consequence, opposite strategies can lead to drought tolerance, depending on the drought scenario (Tardieu, 2012). The conservative strategy fits most severe and long drought scenarios. A spender strategy involving maintenance of vegetative and reproductive growth allows higher yields under milder drought scenarios at a risk of reproductive failure under severe stresses. Because most species have evolved in a wide range of climatic conditions (Rebourg et al., 2003; Sharbel et al., 2000; Fatichi et al., 2014), the tradeoffs associated with the control of growth result in a wide genetic variability of responses of growth to water deficit. Indeed, a large genetic variability of growth maintenance has been observed in several species: by Tisné et al. (2010) in Arabidopsis (Arabidopsis thaliana), Welcker et al. (2011) in maize (Zea mays), Parent et al. (2010a) in rice (Oryza sativa), and Pereyra-Irujo et al. (2008) in sunflower (Helianthus annuus).We review here the genetic diversity and the potential mechanisms associated with the control of growth under water deficit and their consequences for the modeling of plant growth and for breeding strategies.     

Focus on Water: Biodesalination: A Case Study for Applications of Photosynthetic Bacteria in Water Treatment

Shortage of freshwater is a serious problem in many regions worldwide, and is expected to become even more urgent over the next decades as a result of increased demand for food production and adverse effects of climate change. Vast water resources in the oceans can only be tapped into if sustainable, energy-efficient technologies for desalination are developed. Energization of desalination by sunlight through photosynthetic organisms offers a potential opportunity to exploit biological processes for this purpose. Cyanobacterial cultures in particular can generate a large biomass in brackish and seawater, thereby forming a low-salt reservoir within the saline water. The latter could be used as an ion exchanger through manipulation of transport proteins in the cell membrane. In this article, we use the example of biodesalination as a vehicle to review the availability of tools and methods for the exploitation of cyanobacteria in water biotechnology. Issues discussed relate to strain selection, environmental factors, genetic manipulation, ion transport, cell-water separation, process design, safety, and public acceptance.Bacteria are commonly employed for the purification of municipal and industrial wastewater but until now, established water treatment technologies have not taken advantage of photosynthetic bacteria (i.e. cyanobacteria). The ability of cyanobacterial cultures to grow at high cell densities with minimal nutritional requirements (e.g. sunlight, carbon dioxide, and minerals) opens up many future avenues for sustainable water treatment applications.Water security is an urgent global issue, especially because many regions of the world are experiencing, or are predicted to experience, water shortage conditions: More than one in six people globally are water stressed, in that they do not have access to safe drinking water (United Nations, 2006). Ninety-seven percent of the Earth’s water is in the oceans; consequently, there are many efforts to develop efficient methods for converting saltwater into freshwater. Various processes using synthetic membranes, such as reverse osmosis, are successfully used for large-scale desalination. However, the high energy consumption of these technologies has limited their application predominantly to countries with both relatively limited freshwater resources and high availability of energy, for example, in the form of oil reserves.The development of an innovative, low-energy biological desalination process, using biological membranes of cyanobacteria, would thus be both attractive and pertinent. The core of the proposed biodesalination process (Fig. 1) is a low-salt biological reservoir within seawater that can serve as an ion exchanger. Its development can be separated into several complementary steps. The first step comprises the selection of a cyanobacterial strain that can be grown to high cell densities in seawater with minimal requirement for energy sources other than those that are naturally available. The environmental conditions during growth can be manipulated to enhance natural extrusion of sodium (Na⁺) by cyanobacteria. In the second step, cyanobacterial ion transport mechanisms must be manipulated to generate cells in which sodium export is replaced with intracellular sodium accumulation. This will involve inhibition of endogenous Na⁺ export and expression of synthetic molecular units that facilitate light-driven sodium flux into the cells. A robust control system built from biological switches will be required to achieve precisely timed expression of the salt-accumulating molecular units. The third step consists of engineering efficient separation of the cyanobacterial cells from the desalinated water, using knowledge of physicochemical properties of the cell surface and their natural ability to produce extracellular polymeric substances (EPSs), which aid cell separation while preserving cell integrity. The fourth step integrates the first three steps into a manageable and scalable engineering process. The fifth and final step assesses potential risks and public acceptance issues linked to the new technology.Open in a separate windowFigure 1.Proposed usage of cyanobacterial cultures for water treatment. A, Hypothetical water treatment station. Situated in basins next to the water source, sun-powered cell cultures remove unwanted elements from the water. The clean water is separated from the cells for human uses. The produced biomass is available for other industries. The proposed biodesalination process is based on the following steps. B, Photoautotrophic cells divide to generate high-density cultures. C, The combined cell volume is low in salt as a result of transport proteins in the cell membrane that export sodium using photosynthetically generated energy. D, Through environmental and genetic manipulation, salt export is inhibited and replaced with transport modules that accumulate salt inside the cells. This process is again fueled by light energy. E, Manipulation of cell surface properties separates the salt-enriched cells from the desalinated water.In this review, we outline the state of knowledge and available technology for each of the steps, as well as summarize the current knowledge gaps and technical limitations in employing a large-scale water treatment process using cyanobacteria. Before discussing these issues, we provide some background information on the usage of cyanobacteria in biotechnology and the impact of sodium on cellular functions of cyanobacteria. The example of biodesalination provides a good vehicle to discuss the suitability of photosynthetic bacteria for water treatment more generally. The issues addressed in this review are relevant for a wide range of biotechnological applications of cyanobacteria, including bioremediation and biodegradation as well as the generation of biofuels, natural medicines, or cosmetics.     

Focus: Bioethics: Practical and Ethical Considerations in Telehealth: Pitfalls and Opportunities

Telehealth has been a long-awaited advancement with the potential to improve efficiency, convenience, and quality in healthcare. However, as telehealth becomes integrated into routine clinical care, it is imperative to consider the practical and ethical implications that could undermine or devalue care delivery. The medical profession must ensure that it is implemented judiciously and with robust quality standards, guided by fair and equitable policies that balance patient autonomy with rigorous standards of care and access. Such a system must recognize the opportunity for more patient input as stakeholders to tailor care to their needs and preferences, while also acknowledging the risk of suboptimal care if convenience is prioritized over quality. More studies of optimal care models are needed to integrate data in terms of both stakeholder input and outcomes.     

Plant Pathogens in Irrigation Water: Challenges and Opportunities

Plant pathogens in irrigation water were recognized early in the last century as a significant crop health issue. This issue has increased greatly in scope and degree of impact since that time and it will continue to be a problem as agriculture increasingly depends on the use of recycled water. Plant pathogens detected from water resources include 17 species of Phytophthora, 26 of Pythium, 27 genera of fungi, 8 species of bacteria, 10 viruses, and 13 species of plant parasitic nematodes. There is substantial evidence demonstrating that contaminated irrigation water is a primary, if not the sole, source of inoculum for Phytophthora diseases of numerous nursery, fruit, and vegetable crops. These findings pose great challenges and opportunities to the plant pathology community. A variety of water treatment methods are available but few have been assessed for agricultural purposes under commercial conditions. Investigations into their technical feasibility and economics are urgently needed. Aquatic ecology of plant pathogens is an emerging field of research that holds great promise for developing ecologically based water decontamination and other strategies of pathogen mitigation. Pathogen detection and monitoring as well as biological and economic thresholds are much-needed IPM tools and should be priorities of future research. Teaming with hydrologists, agricultural engineers, ecologists, geneticists, economists, statisticians, and farmers is essential to effectively attack such a complex issue of growing global importance. Research should proceed in conjunction with nutrient and pesticide management studies in a coordinated and comprehensive approach as they are interrelated components of water resource conservation and protection.     

Focus on Water: Systems Analysis of Guard Cell Membrane Transport for Enhanced Stomatal Dynamics and Water Use Efficiency

Stomatal transpiration is at the center of a crisis in water availability and crop production that is expected to unfold over the next 20 to 30 years. Global water usage has increased 6-fold in the past 100 years, twice as fast as the human population, and is expected to double again before 2030, driven mainly by irrigation and agriculture. Guard cell membrane transport is integral to controlling stomatal aperture and offers important targets for genetic manipulation to improve crop performance. However, its complexity presents a formidable barrier to exploring such possibilities. With few exceptions, mutations that increase water use efficiency commonly have been found to do so with substantial costs to the rate of carbon assimilation, reflecting the trade-off in CO₂ availability with suppressed stomatal transpiration. One approach yet to be explored in detail relies on quantitative systems analysis of the guard cell. Our deep knowledge of transport and homeostasis in these cells gives real substance to the prospect for reverse engineering of stomatal responses, using in silico design in directing genetic manipulation for improved water use and crop yields. Here we address this problem with a focus on stomatal kinetics, taking advantage of the OnGuard software and models of the stomatal guard cell recently developed for exploring stomatal physiology. Our analysis suggests that manipulations of single transporter populations are likely to have unforeseen consequences. Channel gating, especially of the dominant K⁺ channels, appears the most favorable target for experimental manipulation.Stomata are pores that provide the major route for gaseous exchange across the impermeable cuticle of leaves and stems (Hetherington and Woodward, 2003). They open and close in response to exogenous and endogenous signals and thereby control the exchange of gases, most importantly water vapor and CO₂, between the interior of the leaf and the atmosphere. Stomata exert major controls on the water and carbon cycles of the world (Schimel et al., 2001) and can limit photosynthetic rates by 50% or more when demand exceeds water supply (Ni and Pallardy, 1992). Stomatal transpiration is at the center of a crisis in water availability and crop production that is expected to unfold over the next 20 to 30 years; indeed, global water usage has increased 6-fold in the past 100 years, twice as fast as the human population, and is expected to double again before 2030, driven mainly by irrigation and agriculture (United Nations Educational, Scientific and Cultural Organization, 2009).Guard cell transport is integral to controlling stomatal aperture. Guard cells surround the stomatal pore and respond in a well-defined manner to an array of extracellular signals, including light, to regulate its aperture. Guard cells coordinate membrane transport within a complex network of intracellular signals (Willmer and Fricker, 1996; Blatt, 2000a, 2000b; Hetherington and Woodward, 2003; Shimazaki et al., 2007) to regulate fluxes, mainly of K⁺, Cl⁻, and malate, driving cell turgor and stomatal aperture. Our deep knowledge of these processes has made the guard cell the best known of plant cell models for membrane transport, signaling, and homeostasis (Willmer and Fricker, 1996; Blatt, 2000b; Roelfsema and Hedrich, 2010; Hills et al., 2012). This knowledge gives real substance to the prospect for reverse engineering of stomatal responses, using in silico design in directing genetic manipulation for improved crop yields, especially under water-limited conditions.Water use efficiency (WUE; defined as the amount of dry matter produced per unit of water transpired) is directly related to stomatal function. Thus, at the practical level, stomata represent an important target for breeders interested in manipulating crop performance. A large body of data relates stomata, transpiration, and carbon assimilation (Willmer and Fricker, 1996; Farquhar et al., 2001; Hetherington and Woodward, 2003; Lawson et al., 2011). Several examples illustrate how manipulating of stomatal characteristics can affect WUE (Fischer et al., 1998; Rebetzke et al., 2002; Masle et al., 2005; Eisenach et al., 2012). With few exceptions, however, mutations that increase WUE commonly do so at the expense of carbon assimilation, reflecting the trade-off in CO₂ availability with suppressed stomatal transpiration.Stomatal movements generally lag behind short-term changes in available light associated with sunflecks and shadeflecks (Pearcy, 1990; Lawson et al., 2012; Lawson and Blatt, 2014). This hysteresis in response, between stomatal aperture and gas exchange on one hand and photosynthetic capacity on the other, can lead alternately to periods of assimilation limited by stomatal conductance, and of high transpiration without corresponding rates of assimilation (Lawson et al., 2011). It has been argued that such hysteresis in stomatal responsiveness with the demand for CO₂ erodes assimilation and WUE, with substantial consequences for long-term yield (Vico et al., 2011; Eisenach et al., 2012; Lawson et al., 2012; Lawson and Blatt, 2014). If so, then improving WUE with gains in assimilation should be possible if the speed of stomatal responsiveness can be enhanced. However, the complexity of guard cell transport presents a formidable barrier to exploring such possibilities. Here we address this problem, taking advantage of OnGuard models of the stomatal guard cell. We explore in silico the potential for enhancing stomatal kinetics through single transporter (single gene product) manipulations. Our results identify the gating of the dominant K⁺ channels as the most promising target for experimental manipulation.     

Focus on Water: Stomatal Size,Speed, and Responsiveness Impact on Photosynthesis and Water Use Efficiency

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.In order for plants to function efficiently, they must balance gaseous exchange between inside and outside the leaf to maximize CO₂ uptake for photosynthetic carbon assimilation (A) and to minimize water loss through transpiration. Stomata are the “gatekeepers” responsible for all gaseous diffusion, and they adjust to both internal and external environmental stimuli governing CO₂ uptake and water loss. The pathway for CO₂ uptake from the bulk atmosphere to the site of fixation is determined by a series of diffusional resistances, which start with the layer of air immediately surrounding the leaf (the boundary layer). Stomatal pores provide a major resistance to flux from the atmosphere to the substomatal cavity within the leaf. Further resistance is encountered by CO₂ across the aqueous and lipid boundaries into the mesophyll cell and chloroplasts (mesophyll resistance). Water leaving the leaf largely follows the same pathway in reverse, but without the mesophyll resistance component. Guard cells surround the stomatal pore. They increase or decrease in volume in response to external and internal stimuli, and the resulting changes in guard cell shape adjust stomatal aperture and thereby affect the flux of gases between the leaf internal environment and the bulk atmosphere. Stomatal behavior, therefore, controls the volume of CO₂ entering the intercellular air spaces of the leaf for photosynthesis. It also plays a key role in minimizing the amount of water lost. Transpiration, by virtue of the concentration differences, is an order of magnitude greater than CO₂ uptake, which is an inevitable consequence of free diffusion across this pathway. Although the cumulative area of stomatal pores only represents a small fraction of the leaf surface, typically less than 3%, some 98% of all CO₂ taken up and water lost passes through these pores. When fully open, they can mediate a rate of evaporation equivalent to one-half that of a wet surface of the same area (Willmer and Fricker, 1996).Early experiments illustrated that photosynthetic rates were correlated with stomatal conductance (g_s) when other factors were not limiting (Wong et al., 1979). Low g_s limits assimilation rate by restricting CO₂ diffusion into the leaf, which, when integrated over the growing season, will influence the carbohydrate status of the leaf with consequences for crop yield. Stomata of well-watered plants are thought to reduce photosynthetic rates by about 20% in most C3 species and by less in C4 plants in the field (Farquhar and Sharkey, 1982; Jones, 1987). However, even this restriction has been shown to impact substantially on yield. For example, Fischer et al. (1998) demonstrated a close correlation between g_s and yield in eight different wheat (Triticum aestivum) cultivars. Those studies highlighted the effects g_s can have on crop yield, not only through reduced CO₂ diffusion but also through the impact on water loss and evaporative cooling of the leaf. Indeed, enhancing photosynthesis yields by only 2% to 3% is sufficient to substantially increase plant growth and biomass over the course of a growing season (Lefebvre et al., 2005; Zhu et al., 2007).Stomata and their behavior profoundly affect the global fluxes of CO₂ and water, with an estimated 300 × 10¹⁵ g of CO₂ and 35 × 10¹⁸ g of water vapor passing through stomata of leaves every year (Hetherington and Woodward, 2003). Changes in stomatal behavior in response to changing climatic conditions are thought to impact on water levels and fluxes. For example, it is estimated that partial stomatal closure driven by increasing CO₂ concentration over the past two decades has led to increased CO₂ uptake and reduced evapotranspiration in temperate and boreal northern hemisphere forests (Keenan et al., 2013), with implications for continental runoff and freshwater availability associated with the global rise in CO₂ (Gedney et al., 2006). Concurrently, the increase in global water usage over the past 100 years and the expectation that this is set to double before 2030 (UNESCO, 2009) has put pressure on breeders and scientists to find new crop varieties, breeding traits, or potential targets for manipulation that would result in crop plants that are able to sustain yield with less water input. The fact that stomata are major players in plant water use and the entire global water cycle makes the functional and physical attributes of stomata potential targets for manipulation to improve carbon gain and plant productivity as well as global water fluxes.There are several approaches for improving carbon gain and plant water use efficiency (WUE) that focus on stomata. It is possible to increase or decrease the gaseous conductance of the ensemble of stomata per unit of leaf area (g_s) through the manipulation of stomatal densities (Büssis et al., 2006). In addition, there is potential to alter the stomatal response or sensitivity to environmental signals through the manipulation of guard cell characteristics that affect stomatal mechanics (e.g. OPEN STOMATA [ost] mutants; Merlot et al., 2002). Such approaches have produced an array of mutant plants with altered characteristics and varying impacts on CO₂ uptake and transpiration, several of which we discuss in greater detail below. An intuitive measure of the efficacy of such manipulations is the WUE, commonly defined as the amount of carbon fixed in photosynthesis per unit of water transpired. In general, higher WUE values have been observed in plants with lower g_s, but these gains are usually achieved together with a reduction in A and slower plant growth. Plants with higher g_s have greater assimilation rates and grow faster under optimal conditions, but they generally exhibit lower WUE. An approach that has not been fully explored or considered in any depth is to select plants for differences in the kinetics of stomatal response or to manipulate stomatal kinetics in ways that improve the synchrony with mesophyll CO₂ demand (Lawson et al., 2010, 2012). To date, the majority of studies assessing the impact of stomatal behavior on photosynthetic carbon gain have focused on steady-state measurements of g_s in relation to photosynthesis. These studies do not take account of the dynamic situation in the field. As we discuss below, a cursory analysis of stomatal synchrony with mesophyll CO₂ demand suggests that gains of 20% to 30% are theoretically possible.Here, we address the question of the kinetics of the stomatal response to the naturally fluctuating environment, notably to fluctuations in light that are typical of the conditions experienced in the field. We focus on vascular seed plants, to which crop plants belong, and do not address seedless vascular plants, such as ferns. The characteristics of the latter, and hence the issues and challenges they present, are very different. In our minds, of paramount importance is whether there is potential for engineering guard cells of crop plants to manipulate the dynamic behavior of stomata so as to improve WUE without substantial cost in assimilation. Of course, in many circumstances, stomata are not the only factor to limit water flux through the plant (see other articles in this issue), but they are one of the most important “gatekeepers” and therefore, serve as a good starting point for such considerations. Thus, we explore the physical and functional attributes of stomata, their signaling, and the solute transport mechanisms that determine pore aperture as targets for potential manipulation of stomatal responses to changing environmental cues.     

Focus on Water: Polarity of Water Transport across Epidermal Cell Membranes in Tradescantia virginiana

Using the automated cell pressure probe, small and highly reproducible hydrostatic pressure clamp (PC) and pressure relaxation (PR) tests (typically, applied step change in pressure = 0.02 MPa and overall change in volume = 30 pL, respectively) were applied to individual Tradescantia virginiana epidermal cells to determine both exosmotic and endosmotic hydraulic conductivity (L_pOUT and L_pIN, respectively). Within-cell reproducibility of measured hydraulic parameters depended on the method used, with the PR method giving a lower average coefficient of variation (15.2%, 5.8%, and 19.0% for half-time, cell volume [V_o], and hydraulic conductivity [L_p], respectively) than the PC method (25.4%, 22.0%, and 24.2%, respectively). V_o as determined from PC and PR tests was 1.1 to 2.7 nL and in the range of optically estimated V_o values of 1.5 to 4.9 nL. For the same cell, V_o and L_p estimates were significantly lower (about 15% and 30%, respectively) when determined by PC compared with PR. Both methods, however, showed significantly higher L_pOUT than L_pIN (L_pOUT/L_pIN ≅ 1.20). Because these results were obtained using small and reversible hydrostatically driven flows in the same cell, the 20% outward biased polarity of water transport is most likely not due to artifacts associated with unstirred layers or to direct effects of externally applied osmotica on the membrane, as has been suggested in previous studies. The rapid reversibility of applied flow direction, particularly for the PR method, and the lack of a clear increase in L_pOUT/L_pIN over a wide range of L_p values suggest that the observed polarity is an intrinsic biophysical property of the intact membrane/protein complex.The conductivity of membranes to water (hydraulic conductivity [L_p]) is an important property of the cells of all organisms, and whether plant cell membranes exhibit a polarity in this property has been debated for a number of decades (Dainty and Hope, 1959; Steudle, 1993). Most early evidence for polarity was based on transcellular osmotic experiments using giant algal cells in the Characeae, in which the relative areas of cell membrane exposed to conditions of osmotic inflow (endosmosis) or outflow (exosmosis) could be varied and, hence, L_p for both directions determined (Tazawa and Shimmen, 2001). Interpretation of these experiments is complicated by unstirred layer (USL) effects (Dainty, 1963), but even after accounting for these, it was concluded that inflow L_p (L_pIN) was higher than outflow L_p (L_pOUT) in these cells, with L_pOUT/L_pIN of about 0.65 (Dainty, 1963). When using osmotic driving forces in algal cells, L_pOUT/L_pIN values of between 0.5 and 0.91 have been reported in many studies (Steudle and Zimmermann, 1974; Steudle and Tyerman, 1983; Tazawa et al., 1996), and the same direction of polarity was also reported using osmotic driving forces in whole roots of maize (Zea mays; Steudle et al., 1987). When applying hydrostatic driving forces in algal cells using the pressure probe (Steudle, 1993), which is less influenced by USL effects (Steudle et al., 1980), L_pOUT/L_pIN has been closer to 1 (0.83–1; Steudle and Zimmermann, 1974; Steudle and Tyerman, 1983). However, in higher plant cells, an analysis of the data presented by Steudle et al. (1980, 1982) and Tomos et al. (1981) indicates the opposite polarity, with L_pOUT/L_pIN averaging from 1.2 to 1.4. Moore and Cosgrove (1991) used two contrasting hydrostatic methods to measure L_p in sugarcane (Saccharum spp.) stem cells: (1) the most commonly used pressure relaxation (PR) method, in which cell turgor pressure (P_cell) changes during the measurement, and (2) the more technically demanding pressure clamp (PC) method, in which P_cell is maintained constant. Consistent with other studies in higher plant cells, Moore and Cosgrove (1991) reported average L_pOUT/L_pIN from 1.15 (PC) to 1.65 (PR). Using the PR method in epidermal cells of barley (Hordeum vulgare), Fricke (2000) reported only a modest L_pOUT/L_pIN (based on reported half-time [T_1/2]) of 1.08. In view of the contribution of proteins (e.g. aquaporins) to overall membrane L_p, Tyerman et al. (2002) suggested that polarity may result either from asymmetry in the pores themselves or from an active regulation of the conductive state of the pores in response to the experimental conditions that cause inflow or outflow. Either of these mechanisms may explain the wide range of values reported in the literature for L_pOUT/L_pIN. Cosgrove and Steudle (1981) reported that a substantial (6-fold) and rapid (within 20 s) reduction in L_p could occur in the same cell, and in hindsight, this presumably reflected the influence of aquaporins. Cosgrove and Steudle (1981) did not consider the lower L_p as indicative of the L_p in situ, and Wan et al. (2004) reported that a reduction in L_p was associated with perturbations to P_cell on the order of 0.1 MPa. Hence, if measured membrane L_p itself can exhibit substantial changes over relatively short periods of time in the same cell, then further study of systematic differences between L_pOUT and L_pIN will require a robust hydrostatic methodology (PC or PR) that can reversibly and reproducibly apply small perturbations in pressure (P) to individual cells over short periods of time.For the PR method, a T_1/2 of water exchange is measured by fitting an exponential curve to the observed decay in P_cell over time following a step change in volume, and membrane L_p can be calculated if cell surface area (A), cell volume (V_o), and volumetric elastic modulus (ε) are known (Steudle, 1993). In practice, A and V_o are typically calculated from optical measurements of individual cell dimensions or estimates using average values, and ε is calculated based on V_o and an empirical change in pressure (dP) to change in volume (dV) relation for each cell (Steudle, 1993; Tomos and Leigh, 1999). In the PC method, first developed by Wendler and Zimmermann (1982), V_o (and, given reasonable assumptions about cell geometry, A) is estimated without the need for optical measurements, and L_p can be measured without the need to determine dP/dV or ε. However, this method is technically more demanding because it requires precise P control as well as a continuous record of the volume flow of water across the cell membrane (as measured by changes in the position of the cell solution/oil meniscus within the glass capillary over time) and has rarely been used (Wendler and Zimmermann, 1982, 1985; Cosgrove et al., 1987; Moore and Cosgrove, 1991; Zhang and Tyerman, 1991; Murphy and Smith, 1998). Since volume (V) is continuously changing over time, this approach may also be influenced by the hydraulic conductance of the capillary tip (K_h) used to make the measurements as well as surface tension effects due to the progressive changes in capillary diameter with meniscus position, and these influences have not been quantitatively addressed.Automation of the pressure probe operation, particularly automatic tracking of the meniscus location in the glass microcapillary tip, would address many of the above-mentioned issues, and to date, several attempts have been made to monitor the meniscus location using electrical resistance (Hüsken et al., 1978) or hardware-based image analysis (Cosgrove and Durachko, 1986; Murphy and Smith, 1998). Recently, Wong et al. (2009) redesigned the automated cell pressure probe (ACPP), originally proposed by Cosgrove and Durachko (1986), using a software-based meniscus detection system and a precise pressure control system. In the new ACPP system, both the position of the meniscus and oil pressure (P_oil) are recorded frequently (typically at 10 Hz), and P_oil is controlled with a resolution of ±0.002 MPa. We have combined the ACPP with a new technique to reproducibly fabricate microcapillary tips of known hydraulic properties (Wada et al., 2011) in order to correct for K_h and surface tension effects in both PC and PR estimates of the water relations parameters of Tradescantia virginiana epidermal cells and have determined the relation of L_pOUT to L_pIN in these cells.     

Focus on mast cells in the tumor microenvironment: Current knowledge and future directions

Mast cells (MCs) are crucial cells participating in both innate and adaptive immune processes that play important roles in protecting human health and in the pathophysiology of various diseases, such as allergies, cardiovascular diseases, and autoimmune diseases. In the context of tumors, MCs are a non-negligible population of immune cells in the tumor microenvironment (TME). In most tumor types, MCs accumulate in both the tumor tissue and the surrounding tissue. MCs interact with multiple components of the TME, affecting TME remodeling and the tumor cell fate. However, controversy persists regarding whether MCs contribute to tumor progression or trigger an anti-tumor immune response. This review focuses on the context of the TME to explore the specific properties and functions of MCs and discusses the crosstalk that occurs between MCs and other components of the TME, which affect tumor angiogenesis and lymphangiogenesis, invasion and metastasis, and tumor immunity through different mechanisms. We also anticipate the potential role of MCs in cancer immunotherapy, which might expand upon the success achieved with existing cancer therapies.     

Epilepsy Associated Depression: An Update on Current Scenario,Suggested Mechanisms,and Opportunities

Depression is one of the most frequent psychiatric comorbidities associated with epilepsy having a major impact on the patient’s quality of life. Several screening tools are available to identify and follow up psychiatric disorders in epilepsy. Out of various psychiatric disorders, people with epilepsy (PWE) are at greater risk of developing depression. This bidirectional relationship further hinders pharmacotherapy of comorbid depression in PWE as some antiepileptic drugs (AEDs) worsen associated depression and coadministration of existing antidepressants (ADs) to alleviate comorbid depression has been reported to worsen seizures. Selective serotonin reuptake inhibitors (SSRIs) and selective serotonin and norepinephrine reuptake inhibitors (SNRIs) are first choice of ADs and are considered safe in PWE, but there are no high-quality evidences. Similar to observations in people with depression, PWE also showed pharmacoresistant to available SSRI/SNRIs, which further complicates the disease prognosis. Randomized double-blind placebo-controlled clinical trials are necessary to report efficacy and safety of available ADs in PWE. We should also move beyond ADs, and therefore, we reviewed common pathological mechanisms such as neuroinflammation, dysregulated hypothalamus pituitary adrenal (HPA) axis, altered neurogenesis, and altered tryptophan metabolism responsible for coexistent relationship of epilepsy and depression. Based on these common pertinent pathways involved in the genesis of epilepsy and depression, we suggested novel targets and therapeutic approaches for safe management of comorbid depression in epilepsy.

     

Cumulative Human Impacts on Mediterranean and Black Sea Marine Ecosystems: Assessing Current Pressures and Opportunities

Management of marine ecosystems requires spatial information on current impacts. In several marine regions, including the Mediterranean and Black Sea, legal mandates and agreements to implement ecosystem-based management and spatial plans provide new opportunities to balance uses and protection of marine ecosystems. Analyses of the intensity and distribution of cumulative impacts of human activities directly connected to the ecological goals of these policy efforts are critically needed. Quantification and mapping of the cumulative impact of 22 drivers to 17 marine ecosystems reveals that 20% of the entire basin and 60–99% of the territorial waters of EU member states are heavily impacted, with high human impact occurring in all ecoregions and territorial waters. Less than 1% of these regions are relatively unaffected. This high impact results from multiple drivers, rather than one individual use or stressor, with climatic drivers (increasing temperature and UV, and acidification), demersal fishing, ship traffic, and, in coastal areas, pollution from land accounting for a majority of cumulative impacts. These results show that coordinated management of key areas and activities could significantly improve the condition of these marine ecosystems.