Environmental regulation of stomatal response in the <Emphasis Type="Italic">Arabidopsis</Emphasis> Cvi-0 ecotype

The Arabidopsis Cape Verde Islands (Cvi-0) ecotype is known to differ from other ecotypes with respect to environmental stress responses. We analyzed the stomatal behavior of Cvi-0 plants, in response to environmental signals. We investigated the responses of stomatal conductance and aperture to high [CO₂] in the Cvi-0 and Col-0 ecotypes. Cvi-0 showed constitutively higher stomatal conductance and more stomatal opening than Col-0. Cvi-0 stomata opened in response to light, but the response was slow. Under low humidity, stomatal opening was increased in Cvi-0 compared to Col-0. We then assessed whether low humidity affects endogenous ABA levels in Cvi-0. In response to low humidity, Cvi-0 had much higher ABA levels than Col-0. However, epidermal peels experiments showed that Cvi-0 stomata were insensitive to ABA. Measurements of organic and inorganic ions in Cvi-0 guard cell protoplasts indicated an over-accumulation of osmoregulatory anions (malate and Cl⁻). This irregular anion homeostasis in the guard cells may explain the constitutive stomatal opening phenotypes of the Cvi-0 ecotype, which lacks high [CO₂]-induced and low humidity-induced stomatal closure.     

In the light of stomatal opening: new insights into 'the Watergate'

Stomata can be regarded as hydraulically driven valves in the leaf surface, which open to allow CO2 uptake and close to prevent excessive loss of water. Movement of these 'Watergates' is regulated by environmental conditions, such as light, CO2 and humidity. Guard cells can sense environmental conditions and function as motor cells within the stomatal complex. Stomatal movement results from the transport of K+ salts across the guard cell membranes. In this review, we discuss the biophysical principles and mechanisms of stomatal movement and relate these to ion transport at the plasma membrane and vacuolar membrane. Studies with isolated guard cells, combined with recordings on single guard cells in intact plants, revealed that light stimulates stomatal opening via blue light-specific and photosynthetic-active radiation-dependent pathways. In addition, guard cells sense changes in air humidity and the water status of distant tissues via the stress hormone abscisic acid (ABA). Guard cells thus provide an excellent system to study cross-talk, as multiple signaling pathways induce both short- and long-term responses in these sensory cells.     

Role of plant stomata in bacterial invasion

Stomata are microscopic pores in the epidermis of the aerial parts of terrestrial plants. These pores are essential for photosynthesis, as they allow CO(2) to diffuse into the plant. The size of the stomatal pore changes in response to environmental conditions, such as light intensity, air humidity and CO(2) concentrations, as part of the plant's adaptation to maximize photosynthetic efficiency and, at the same time, to minimize water loss. Historically, stomata have been considered as passive portal of entry for plant pathogenic bacteria. However, recent studies suggest that stomata can play an active role in restricting bacterial invasion as part of the plant innate immune system. Some plant pathogens have evolved specific virulence factors to overcome stomata-based defence. Interestingly, many bacterial disease outbreaks require high humidity, rain, or frost damage, which could promote stomatal opening and/or bypass stomatal defence by creating wounds as alternative entry sites. Further studies on microbial and environmental regulation of stomata-based defence should fill gaps in our understanding of bacterial pathogenesis, disease epidemiology and phyllosphere microbiology.     

Relative humidity is a key factor in the acclimation of the stomatal response to CO(2)

Previous work has shown that stomata of growth chamber-grown Vicia faba leaves have an enhanced CO2 response when compared with stomata of greenhouse-grown plants. This guard cell response to CO2 acclimatizes to the environmental conditions on the transfer of plants between the two environments. In the present study, air relative humidity is identified as a key environmental factor mediating the changes in stomatal sensitivity to CO2. In the greenhouse environment, elevation of relative humidity to growth chamber levels resulted in an enhanced CO2 response, whereas a reduction in the light level to that comparable to growth chamber conditions had no effect on stomatal CO2 sensitivity. The transfer of plants between humidified and normal greenhouse conditions resulted in an acclimation response with a time-course matching that previously obtained in transfers of plants between greenhouse and growth chamber environments. The high stomatal sensitivity to CO2 of growth chamber-grown plants could be reduced by lowering growth chamber relative humidity and then restored with its characteristic acclimation time-course by an elevation of relative humidity. Leaf temperature was unchanged during this restoration, eliminating it as a primary factor in the acclimation response. Humidity regulation of stomatal CO2 sensitivity could function as a signal for leaves inside dense foliage canopies, promoting stomatal opening under low light, low CO2 conditions.     

植物气孔气态失水与SPAC系统液态供水的相互调节作用研究进展

讨论了植物气孔气态失水与SPAC系统液态供水相互作用研究领域的一些重要现象和行为.当植物水力信号和化学信号共同作用促进气孔对叶水势的调节时,植物对叶水势的调节表现为等水行为.气孔对环境湿度变化响应的反馈机制可用来解释土壤干旱条件下气孔和光合的午休现象,以及气孔导度和水流导度之间的相关关系;而气孔对环境湿度变化响应的前馈机制,则可用来解释气孔导度对大气 叶片间水汽饱和差的滞后反应.植物最大限度地利用木质部传输水分的策略,要求气孔快速响应以避免木质部过度气穴化和短时间内将气穴逆转的相应机制.     

Light-regulated stomatal aperture in Arabidopsis

The stomatal pores of plant leaves, situated in the epidermis and surrounded by a pair of guard cells, allow CO2 uptake for photosynthesis and water loss through transpiration. Blue light is one of the dominant environmental signals that control stomatal movements in leaves of plants in a natural environment. This blue light response is mediated by blue/UV A light-absorbing phototropins (phots) and cryptochromes (crys). Red/far-red light-absorbing phytochromes (phys) also play a role in the control of stomatal aperture. The signaling components that link the perception of light signals to the stomatal opening response are largely unknown. This review discusses a few newly discovered nuclear genes, their function with respect to the phot-, cry-, and phy-mediated signal transduction cascades, and possible involvement of circadian clock.     

Long-distance CO(2) signalling in plants.

Stomatal numbers are tightly controlled by environmental signals including light intensity and atmospheric CO(2) partial pressure. This requires control of epidermal cell development during the early phase of leaf growth and involves changes in both the density of cells on the leaf surface and the proportion of cells that adopt a stomatal fate. This paper reviews the current understanding of how stomata develop and describes recent advances that have given insights into the regulatory mechanisms involved using mutant Arabidopsis plants that implicates a role for long-chain fatty acids in cell-to-cell communication. Evidence is presented which indicates that long-distance signalling from mature to newly developing leaves forms part of the mechanism by which stomatal development responds to environmental cues. Analysis of mutant plants suggests that the plant hormones abscisic acid, ethylene and jasmonates are implicated in the long-distance signalling pathway and that the action may be mediated by reactive oxygen species.     

Arabidopsis HT1 kinase controls stomatal movements in response to CO2

Guard cells, which form stomata in leaf epidermes, sense a multitude of environmental signals and integrate this information to regulate stomatal movements. Compared with the advanced understanding of light and water stress responses in guard cells, the molecular mechanisms that underlie stomatal CO(2) signalling have remained relatively obscure. With a high-throughput leaf thermal imaging CO(2) screen, we report the isolation of two allelic Arabidopsis mutants (high leaf temperature 1; ht1-1 and ht1-2) that are altered in their ability to control stomatal movements in response to CO(2). The strong allele, ht1-2, exhibits a markedly impaired CO(2) response but shows functional responses to blue light, fusicoccin and abscisic acid (ABA), indicating a role for HT1 in stomatal CO(2) signalling. HT1 encodes a protein kinase that is expressed mainly in guard cells. Phosphorylation assays demonstrate that the activity of the HT1 protein carrying the ht1-1 or ht1-2 mutation is greatly impaired or abolished, respectively. Furthermore, dominant-negative HT1(K113W) transgenic plants, which lack HT1 kinase activity, show a disrupted CO(2) response. These findings indicate that the HT1 kinase is important for regulation of stomatal movements and its function is more pronounced in response to CO(2) than it is to ABA or light.     

Stomatal behavior of ozone-sensitive and -insensitive coneflowers (Rudbeckia laciniata var. digitata) in Great Smoky Mountains National Park

* Morphological and physiological attributes were assessed to elucidate the underlying mechanisms of ozone (O(3)) sensitivity in a highly sensitive species, cutleaf coneflower (Rudbeckia laciniata var. digitata). * Foliage at the same height in the canopy on paired O(3)-sensitive and -insensitive cutleaf coneflowers was assessed for level of foliar symptoms, stomatal density, stomatal responsiveness to dynamic changes in light and leaf-to-air vapor pressure deficit (VPD), steady-state responses to light and CO(2), intrinsic transpirational efficiency, and plant water balance. * There were no morphological differences between the sensitivity types that might have contributed to greater O(3) uptake in sensitive individuals. Stomata of sensitive plants were less responsive than those of insensitive plants to experimentally increased and decreased light intensities, and to increased VPD. O(3)-insensitive plants had greater intrinsic transpirational efficiencies, greater maximum assimilation rates under saturating CO(2) and light, and greater carboxylation rates. * Different physiological attributes vary independently within an individual plant, which collectively confer sensitivity or insensitivity to O(3) injury.     

The Arabidopsis small G-protein AtRAN1 is a positive regulator in chitin-induced stomatal closure and disease resistance

Chitin, a fungal microbial-associated molecular pattern, triggers various defence responses in several plant systems. Although it induces stomatal closure, the molecular mechanisms of its interactions with guard cell signalling pathways are unclear. Based on screening of public microarray data obtained from the ATH1 Affymetrix and Arabidopsis eFP browser, we isolated a cDNA encoding a Ras-related nuclear protein 1 AtRAN1. AtRAN1 expression was enriched in guard cells in a manner consistent with involvement in the control of the stomatal movement. AtRAN1 mutation impaired chitin-induced stomatal closure and accumulation of reactive oxygen species and nitric oxide in guard cells. In addition, Atran1 mutant plants exhibited compromised chitin-enhanced plant resistance to both bacterial and fungal pathogens due to changes in defence-related genes. Furthermore, Atran1 mutant plants were hypersensitive to drought stress compared to Col-0 plants, and had lower levels of stress-responsive genes. These data demonstrate a previously uncharacterized signalling role for AtRAN1, mediating chitin-induced signalling.     

Reactive oxygen species signaling and stomatal movement in plant responses to drought stress and pathogen attack

Stomata, the pores formed by a pair of guard cells, are the main gateways for water transpiration and photosynthetic CO_2 exchange, as well as pathogen invasion in land plants. Guard cell movement is regulated by a combination of environmental factors, including water status, light, CO_2 levels and pathogen attack, as well as endogenous signals, such as abscisic acid and apoplastic reactive oxygen species(ROS). Under abiotic and bioticstress conditions, extracellular ROS are mainly produced by plasma membrane-localized NADPH oxidases, whereas intracellular ROS are produced in multiple organelles. These ROS form a sophisticated cellular signaling network, with the accumulation of apoplastic ROS an early hallmark of stomatal movement. Here, we review recent progress in understanding the molecular mechanisms of the ROS signaling network,primarily during drought stress and pathogen attack. We summarize the roles of apoplastic ROS in regulating stomatal movement, ABA and CO_2 signaling, and immunity responses.Finally, we discuss ROS accumulation and communication between organelles and cells. This information provides a conceptual framework for understanding how ROS signaling is integrated with various signaling pathways during plant responses to abiotic and biotic stress stimuli.     

Stomata from growth-chamber-grown Vicia faba have an enhanced sensitivity to CO2

Abaxial stomata from Vicia faba leaves grown in a growth chamber under constant light, temperature and humidity showed an elaborate pattern of aperture changes over the course of a light cycle. These aperture changes were tightly correlated with changes in chamber CO2 concentration (r2=0.83). Changes in chamber [CO2] resulted, in turn, from substantial daily fluctuations in ambient [CO2], typical of the Los Angeles environment, with a constant offset caused by photosynthesis and respiration of the plants within the chamber. The dominant role of the stomatal response to CO2 in the control of aperture was confirmed by manipulation of chamber [CO2]. Fast (15 min) increases and decreases in [CO2] caused rapid decreases and increases in aperture, while constant [CO2] resulted in constant aperture. In contrast, aperture changes in comparable plants grown under greenhouse conditions were tightly correlated with changes in incident solar radiation (r2=0.80), and poorly correlated with changes in [CO2] (r2=0.09). Greenhouse-grown plants transferred to growth chamber conditions showed no apparent response to CO2. These data indicate that growth-chamber-grown V. faba leaves provide an experimental system optimally suited for the study of the stomatal response to CO2, and suggest that acclimation to environmental conditions alters the sensitivity of stomata to CO2.     

北方粳稻光合速率、气孔导度对光强和CO2浓度的响应

 以东北地区主栽的粳稻（Oryza sativa var. japonica）品种为对象,用美国LI-cor公司生产的Li 6400光合作用测定仪控制光强、CO2浓度和温度等环境条件,阐述了光合作用和气孔导度对光和CO2浓度的响应特征及其耦合关系。结果表明,光合速率随光强或CO2浓度的提高而增大,均遵循米氏响应;在不同CO2浓度下,表观量子效率随CO2浓度的提高而增大,但CO2浓度达到800 μmol•mol－1以上时,表观量子效率有所减小;在不同光强下,表观羧化效率也随光的增强而增大,但光强达到1 600 μmol•m-2•s-1以上时,表观羧化效率也有所减小;在光强和CO2浓度协同作用下,光合速率的响应遵循双底物的米氏方程,在光强和CO2浓度均趋于饱和时,北方粳稻（品种：辽粳294）剑叶的潜在最大光合速率为71.737 8 μmol•m-2•s-1,表观量子效率为0.056 0 μmolCO2•μmol-1 photons,表观羧化效率为0.103 1 μmol•m-2•s-1/μmol•mol－1。气孔导度也随光的增强而增大,对光强的响应规律也可以用Michaelis-Menten曲线模拟,而叶面CO2浓度的提高会使气孔导度减小,气孔导度（Gs）对叶面CO2浓度（Cs）的响应可以用Gs=Gmax,c/(1+Cs/Cs0)的双曲线方程模拟。在光强(PFD)和CO2浓度协同作用下,气孔导度可以用式Gs=Gmax(PFD/PFDc)/［(1+PFD/PFDc)(1+Cs/Cs0)］+Gct估算,当CO2浓度趋于0而光强趋于饱和时,北方粳稻的潜在最大气孔导度（Gmax）为0.670 9 mol•m-2•s-1。在光强和CO2浓度协同作用下,Ball-Berry模型及其修正形式依然能很好地表达气孔导度-光合速率的耦合关系,并且用叶面饱和水汽压差（Ds）修正耦合关系中的相对湿度可以提高模拟精度。     

Drought-induced responses of photosynthesis and antioxidant metabolism in higher plants

Environmental stresses trigger a wide variety of plant responses, ranging from altered gene expression and cellular metabolism to changes in growth rates and crop yields. A plethora of plant reactions exist to circumvent the potentially harmful effects caused by a wide range of both abiotic and biotic stresses, including light, drought, salinity, high temperatures, and pathogen infections. Among the environmental stresses, drought stress is one of the most adverse factors of plant growth and productivity. Understanding the biochemical and molecular responses to drought is essential for a holistic perception of plant resistance mechanisms to water-limited conditions. Drought stress progressively decreases CO2 assimilation rates due to reduced stomatal conductance. Drought stress also induces reduction in the contents and activities of photosynthetic carbon reduction cycle enzymes, including the key enzyme, ribulose-1,5-bisphosphate carboxylase/oxygenase. The critical roles of proline and glycine-betaine, as well as the role of abscisic acid (ABA), under drought stress conditions have been actively researched to understand the tolerance of plants to dehydration. In addition, drought stress-induced generation of active oxygen species is well recognized at the cellular level and is tightly controlled at both the production and consumption levels in vivo, through increased antioxidative systems. Knowledge of sensing and signaling pathways, including ABA-mediated changes in response to drought stress, is essential to improve crop management. This review focuses on the ability and strategies of higher plants to respond and adapt to drought stress.     

Integration of light and temperature signaling pathways in plants

As two of the most important environmental factors, light and temperature regulate almost all aspects of plant growth and development. Under natural conditions, light is accompanied by warm temperatures and darkness by cooler temperatures, suggesting that light and temperature are tightly associated signals for plants. Indeed, accumulating evidence shows that plants have evolved a wide range of mechanisms to simultaneously perceive and respond to dynamic changes in light and temperature. Notably, the photoreceptor phytochrome B (phyB) was recently shown to function as a thermosensor, thus reinforcing the notion that light and temperature signaling pathways are tightly associated in plants. In this review, we summarize and discuss the current understanding of the molecular mechanisms integrating light and temperature signaling pathways in plants, with the emphasis on recent progress in temperature sensing, light control of plant freezing tolerance, and thermomorphogenesis. We also discuss the questions that are crucial for a further understanding of the interactions between light and temperature signaling pathways in plants.     

Stomatal action directly feeds back on leaf turgor: new insights into the regulation of the plant water status from non‐invasive pressure probe measurements

Uptake of CO₂ by the leaf is associated with loss of water. Control of stomatal aperture by volume changes of guard cell pairs optimizes the efficiency of water use. Under water stress, the protein kinase OPEN STOMATA 1 (OST1) activates the guard‐cell anion release channel SLOW ANION CHANNEL‐ASSOCIATED 1 (SLAC1), and thereby triggers stomatal closure. Plants with mutated OST1 and SLAC1 are defective in guard‐cell turgor regulation. To study the effect of stomatal movement on leaf turgor using intact leaves of Arabidopsis, we used a new pressure probe to monitor transpiration and turgor pressure simultaneously and non‐invasively. This probe permits routine easy access to parameters related to water status and stomatal conductance under physiological conditions using the model plant Arabidopsis thaliana. Long‐term leaf turgor pressure recordings over several weeks showed a drop in turgor during the day and recovery at night. Thus pressure changes directly correlated with the degree of plant transpiration. Leaf turgor of wild‐type plants responded to CO₂, light, humidity, ozone and abscisic acid (ABA) in a guard cell‐specific manner. Pressure probe measurements of mutants lacking OST1 and SLAC1 function indicated impairment in stomatal responses to light and humidity. In contrast to wild‐type plants, leaves from well‐watered ost1 plants exposed to a dry atmosphere wilted after light‐induced stomatal opening. Experiments with open stomata mutants indicated that the hydraulic conductance of leaf stomata is higher than that of the root–shoot continuum. Thus leaf turgor appears to rely to a large extent on the anion channel activity of autonomously regulated stomatal guard cells.     

Stomatal movements and long-distance signaling in plants

As the nerve-mediated signaling in animals, long-distance signaling in plants is a prerequisite for plants to be able to perceive environmental stimuli and initiate adaptive responses. While intracellular signal transduction has been attracting considerable attentions, studies on long-distance signaling in plants has been relatively overlooked. Stomatal movements are well recognized as a model system for studies on cellular signal transduction. It has been demonstrated that the stomatal movements may be frequently tuned by long-distance signaling under various environmental stimuli. Stomatal movements can not only respond to persistent stress stimuli but also respond to shock stress stimuli. Stomatal responses to drought stress situations may be best characterized in terms of interwoven networks of chemical signaling pathways playing predominant roles in these adaptive processes. In cases of shock stress stimuli, stomatal movements can be more sensitively regulated through the long-distance signaling but with distinctive patterns not observed for drought or other persistent stresses. Here, the fundamental characteristics of stomatal movements and associated long-distance signaling are reviewed and the implications for plant responses to environmental stresses are discussed.Key words: stomatal movement, long-distance signaling, environmental stresses, abscisic aci, pH signaling, hydraulic signaling, cytokinins, acetylcholine, heat-shock, electric signal     

Stomatal sensitivities to changes in leaf water potential, air humidity, CO2 concentration and light intensity, and the effect of abscisic acid on the sensitivities in six temperate deciduous tree species

To characterise the stomata of six temperate deciduous tree species, sets of stomatal sensitivities to all the most important environmental factors were measured. To compare the importance of abscisic acid (ABA) in the different stomatal responses, the effect of exogenous ABA on all the stomatal sensitivities was determined.Almost all the stomatal sensitivities: the sensitivity to a decrease in leaf water potential, air humidity, CO₂ concentration ([CO₂]) and light intensity, and to an increase in [CO₂] and light intensity were the highest in the slow-growing species, and the lowest in the fast-growing species. Drought increased the sensitivity to the environmental changes that induce a decrease in the stomatal conductance, and decreased the sensitivity to the changes that induce an increase in this conductance. The sensitivities of the slow-growers were most strongly affected by drought and ABA. Therefore the success of the slow-growers in their ecological niches can be based on the highly sensitive and strictly regulated responses of their stomata. The fast-growers had the highest sensitivity to an increase in leaf water potential and this sensitivity was sharply reduced by drought and ABA. Thus, the dominance of the trees in riparian areas can be based on the ability of their stomata to quickly reach high conductance in well-watered conditions and to efficiently decrease this rate during drought.Stomatal sensitivities to the hydraulic environmental factors (water potentials in plant and air) had higher values in well-watered trees and a more pronounced response to drought than the sensitivities to the photosynthetic environmental factors ([CO₂] and light intensity). Thus, the hydraulic factors most likely prevail over the photosynthetic factors in determining stomatal conductance in these species.In response to exogenous ABA, the rates of stomatal closure, following a decrease in air humidity and light intensity, and an increase in [CO₂], were accelerated. Stomatal opening following an increase in air humidity and light intensity and a decrease in [CO₂] was replaced by slow closing. The rate of stomatal opening following an increase in leaf water potential was reduced. As the sensitivities to changes in light were modified less by the ABA than the other stomatal sensitivities, the prediction of stomatal responses on the basis of the sensitivity to light alone should be excluded in stomatal models.     

气孔导度对CO2浓度变化的模拟及其生理机制

基于气孔运动的生理生化机制重点进行了气孔导度(gs)对CO2浓度变化的响应机制分析,并推导得到气孔导度(gs)对CO2浓度变化响应模型,并以9种植物进行了模型验证。结果表明:随着CO2浓度的升高,气孔导度会逐渐降低,且下降的幅度会随着CO2浓度的升高而逐渐减弱。气孔导度对CO2浓度(Cs)变化的响应模型可以表达为gs=gmax/(1+Cs/Cs0),其中式中gmax是最大气孔导度和Cs0是实验常数。该模型较好地模拟了气孔导度随CO2浓度变化的规律,模型参数具有明确的生理意义,与Jarvis模型和Ball-Berry模型相比,该模型如何实现多种环境因子的耦合有待进一步突破。另外,模型是在短期改变叶片CO2浓度的条件下得出的,在CO2浓度长期胁迫下的适用性也有待进一步确认。