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A Mg2+‐dependent, K+‐stimulated ATPase activity was detected in microsomal preparations from guard cell protoplasts of Commelina communis L. The ATPase activity was oligomycin‐insensitive, highly specific for ATP and strongly inhibited by pentavanadate and CaSO4. It is possible that this ATPase is associated with the plasmalemma and its activity linked with K+ uptake by guard cells. [ABSTRACT FROM AUTHOR]

Isolated epidermal protoplasts of Commelina communis L. increase in volume in the presence of KCl. Since this swelling is an osmotic phenomenon it reflects K+ influx. ATP slightly decreased the volume of the protoplasts, pointing towards the possibility that K+ uptake is passive. On the other hand abscisic acid (ABA) and sodium orthovanadate increased the swelling, and their effect was reversed by ATP. This may support the suggestion that ABA inhibits the active and ATPase‐mediated relase of K+ from epidermal cells. Mg2+‐dependent, K+‐stimulated ATPase activity was found in the microsomal fraction from epidermal cells. This activity was vandadate sensitive. ABA increased the basal activity in the presence of Mg2+ but inhibited the K+ stimulation. [ABSTRACT FROM AUTHOR]

Turgor, and osmotic and water potentials of subsidiary cells, epidermal cells and mesophyll cells were measured with a pressure probe and a nanoliter osmometer in intact transpiring leaves of Tradescantia virginiana L. Xylem water potential was manipulated by changing air humidity, light, and water supply. In a transpiring leaf the water potential of mesophyll cells was lower, but turgor was higher, than in cells surrounding the stomatal cavity owing to the presence of a cuticle layer which covers the internal surface of subsidiary and guard cells. Cuticular transpiration from the outer leaf surface was negligibly small. When stomata closed in dry air, transpiration decreased despite an increasing vapor-pressure difference between leaf and air, and the water potential of subsidiary cells dropped to the level of the water potential in mesophyll cells. We suggest that the observed decrease of transpiration at increasing vapor-pressure difference can be attributed to a shortage of water supply to the guard cells from subsidiary cells, causing turgor to decrease in the former more than in the latter. The leafs internal cuticle appears to play a special role in channelling the internal water flow during a water shortage. [ABSTRACT FROM AUTHOR]

Isolated epidermis of Commelina communis L. and Tulipa gesneriana L. assimilated CO into malic acid and its metabolites but not into sugars or their phosphates; epidermis could not reduce CO by photosynthesis and therefore must be heterotrophic (Raschke and Dittrich, 1977). If, however, isolated epidermis of Commelina communis was placed on prelabelled mesophyll (obtained by an exposure to CO for 10 min), radioactive sugars appeared in the epidermis, most likely by transfer from the mesophyll. Of the radioactivity in the epidermis, 60% was in sucrose, glucose, fructose, 3-phosphoglyceric acid and sugar phosphates. During a 10-min exposure to CO, epidermis in situ incorporated 16 times more radioactivity than isolated epidermal strips. Isolated epidermis of Commelina communis and Tulipa gesneriana took up C-labelled glucose-1-phosphate (without dephosphorylation), glucose, sucrose and maltose. These substances were transformed into other sugars and, simultaneously, into malic acid. Carbons-1 through-3 of malic acid in guard cells can thus be derived from sugars. Radioactivity appeared also in the hydrolysate of the ethanol-insoluble residue and in compounds of the tricarboxylic-acid cycle, including their transamination products. The hydrolysate contained glucose as the only radioactive compound. Radioactivity in the hydrolysate was therefore considered an indication of starch. Starch formation in the epidermis began within 5 min of exposure to glucose-1-phosphate. Autoradiograms of epidermal sections were blackened above the guard cells. Formation of starch from radioactive sugars therefore occurred predominantly in these cells. Epidermis of tulip consistently incorporated more C into malic and aspartic acids than that of Commelina communis (e.g. after a 4-h exposure to [C]glucose in the dark, epidermis, with open stomata, of tulip contained 31% of its radioactivity in malate and aspartate, that of Commelina communis only 2%). The results of our experiments allow a merger of the old observations on the involvement of starch metabolism in stomatal movement with the more recent recognition of ion transfer and acid metabolism as causes of stomatal opening and closing. [ABSTRACT FROM AUTHOR]

Epidermal strips with closed stomata were exposed to malic acid labelled with C either uniformly or in 4-C only. During incubation with [U-C]malate, radioactivity appeared in products of the tricarboxylic-acid cycle and in transamination products within 10 min, in sugars after 2 h. Hardly any radioactivity was found in sugars if [4-C]malate had been offered. This difference in the degree of labelling of sugars indicates that gluconeogenesis can occur in epidermal tissue, involving the decarboxylation of malate. Epidermis incubated with labelled malate was hydrolyzed after extraction with aqueous ethanol. The hydrolysate contained glucose as the only radioactive product, indicating that starch had been formed from malate. Microautoradiograms were black above stomatal complexes, showing that the latter were sites of starch formation. In order to follow the fate of malate during stomatal closure, malate was labelled in guard cells by exposing epidermes with open stomata to CO and then initiating stomatal closure. Of the radioactive fixation products of CO only malate was released into the water on which the epidermal samples floated; the epidermal strips retained some of the malate and all of its metabolites. In the case of rapid stomatal closure initiated by abscisic acid and completed within 5 min, 63% of the radioactivity was in the malate released, 22% in the malate retained, the remainder in aspartate, glutamate, and citrate. We conclude that during stomatal closing guard cells can dispose of malate by release, gluconeogenesis, and consumption in the tricarboxylic-acid cycle. [ABSTRACT FROM AUTHOR]

• AtRabE1c is highly induced by drought stress and expressed abundantly in guard cells. • AtRabE1c loss-of-function mutants show decreased ABA sensitivity of stomatal movements and reduced drought tolerance. • PYL ABA receptors interact with AtRabE1c. • Loss of function of RabE1c showed reduced accumulation of PYL4 protein. • The over-expression of AtRabE1c improves drought tolerance not only in Arabidopsis but in Chinese cabbage. Drought represents a leading constraint over crop productivity worldwide. The plant response to this stress is centered on the behavior of the cell membrane, where the transduction of abscisic acid (ABA) signaling occurs. Here, the Ras-related small GTP-binding protein RabE1c has been shown able to bind to an ABA receptor in the Arabidopsis thaliana plasma membrane, thereby positively regulating ABA signaling. RabE1c is highly induced by drought stress and expressed abundantly in guard cells. In the loss-of-function rabe1c mutant, both stomatal closure and the whole plant drought stress response showed a reduced sensitivity to ABA treatment, demonstrating that RabE1c is involved in the control over transpirative water loss through the stomata. Impairment of RabE1c's function suppressed the accumulation of the ABA receptor PYL4. The over-expression of RabE1c in A. thaliana enhanced the plants' ability to tolerate drought, and a similar phenotypic effect was achieved by constitutively expressing the gene in Chinese cabbage (Brassica rapa ssp. pekinensis). The leading conclusion was that RabE1c promotes the degradation of PYL4, suggesting a possible genetic strategy to engineer crop plants to better withstand drought stress. [ABSTRACT FROM AUTHOR]

Drought is the most serious abiotic stress, which significantly reduces crop productivity. The phytohormone ABA plays a pivotal role in regulating stomatal closing upon drought stress. Here, we characterized the physiological function of AtBBD1, which has bifunctional nuclease activity, on drought stress. We found that AtBBD1 localized to the nucleus and cytoplasm, and was expressed strongly in trichomes and stomatal guard cells of leaves, based on promoter:GUS constructs. Expression analyses revealed that AtBBD1 and AtBBD2 are induced early and strongly by ABA and drought, and that AtBBD1 is also strongly responsive to JA. We then compared phenotypes of two AtBBD1-overexpression lines (AtBBD1-OX), single knockout atbbd1, and double knockout atbbd1/atbbd2 plants under drought conditions. We did not observe any phenotypic difference among them under normal growth conditions, while OX lines had greatly enhanced drought tolerance, lower transpirational water loss, and higher proline content than the WT and KOs. Moreover, by measuring seed germination rate and the stomatal aperture after ABA treatment, we found that AtBBD1-OX and atbbd1 plants showed significantly higher and lower ABA-sensitivity, respectively, than the WT. RNA sequencing analysis of AtBBD1-OX and atbbd1 plants under PEG-induced drought stress showed that overexpression of AtBBD1 enhances the expression of key regulatory genes in the ABA-mediated drought signaling cascade, particularly by inducing genes related to ABA biosynthesis, downstream transcription factors, and other regulatory proteins, conferring AtBBD1-OXs with drought tolerance. Taken together, we suggest that AtBBD1 functions as a novel positive regulator of drought responses by enhancing the expression of ABA- and drought stress-responsive genes as well as by increasing proline content. [ABSTRACT FROM AUTHOR]

Plant guard cell is essential for photosynthesis and transpiration. The aperture of stomata is sensitive to various environment factors. Carbon dioxide (CO2) is an important regulator of stomatal movement, and its signaling includes the perception, transduction and gene expression. The intersections with many other signal transduction pathways make the regulation of CO2 more complex. High levels of CO2 trigger stomata closure, and reactive oxygen species (ROS) as the key component has been demonstrated function in this regulation. Additional research is required to understand the underlying molecular mechanisms, especially for the detailed signal factors related with ROS in this response. This review focuses on Arabidopsis stomatal closure induced by high-level CO2, and summarizes current knowledge of the role of ROS involved in this process. [ABSTRACT FROM AUTHOR]

• UVR8-COP1-HY5 signaling pathway mediates UV-B-induced ethylene production by activating the ACS expression • Ethylene synthesis and signaling are involved in UVR8 pathway mediation of UV-B-triggered H 2 O 2 and NO production and subsequent stomata closing • COP1 and HY5 also act without UVR8 to transduce the H 2 O 2 signal in guard cells • COP1 and HY5 function downstream of EIN2 and EIN3 to mediate H 2 O 2 -induced NO synthesis in UV-B stomata signaling Although the UV RESISTANCE LOCUS 8 (UVR8)-CONSTITUTIVELY PHOTOMORPHOGENIC1 (COP1)-ELONGATED HYPOCOTYL5 (HY5) signaling pathway, ethylene, hydrogen peroxide (H 2 O 2), and nitric oxide (NO) all participate in ultraviolet-B (UV-B)-triggered stomatal closing, their interrelationship is not clear. Here, we found that UV-B-induced the expression of ethylene biosynthetic genes, production of ethylene, H 2 O 2 , and NO, and stomata closing were impaired in uvr8 , cop1 , and hy5 mutants. UV-B-induced NO production and stomata closing were also defective in mutants for ETHYLENE RESPONSE 1 (ETR1), ETHYLENE INSENSITIVE 2 (EIN2), and EIN3 , but UV-B-triggered H 2 O 2 generation was only inhibited in etr1. In either the absence or presence of UV-B, ethylene triggered H 2 O 2 production but not NO generation and stomatal closure in cop1 and hy5 , and stomata closing in cop1 and hy5 was induced by NO but not H 2 O 2. Moreover, NO production and stomatal closure were constitutively caused by over-expression of COP1 or HY5 in ein2 and ein3 , but not by over-expression of EIN2 or EIN3 in cop1 and hy5. Our data indicate that the UVR8-COP1-HY5 signaling module mediates UV-B-induced ethylene production, ethylene is then perceived by ETR1 to induce H 2 O 2 synthesis. H 2 O 2 induces NO generation and subsequent stomata closing via an EIN2, EIN3, COP1, and HY5-dependent pathway(s). [ABSTRACT FROM AUTHOR]

Nitric oxide (NO) and hydrogen peroxide (H 2 O 2 ) are gradually becoming established as critical regulators in plants under physiological and stressful conditions. Strong spatiotemporal correlations in their production and distribution have been identified in various plant biological processes. In this context, NO and H 2 O 2 act synergistically or antagonistically as signals or stress promoters depending on their respective concentrations, engaging in processes such as the hypersensitive response, stomatal movement, and abiotic stress responses. Moreover, proteins identified as potential targets of NO-based modifications include a number of enzymes related to H 2 O 2 metabolism, reinforcing their cross-talk. In this review, several processes of well-characterized functional interplay between H 2 O 2 and NO are discussed with respect to the most recent reported evidence on hypersensitive response-induced programmed cell death, stomatal movement, and plant responses to adverse conditions and, where known, the molecular mechanisms and factors underpinning their cross-talk.

Hydrogen sulfide (H2S) is a signaling molecule that regulates critical processes and allows plants to adapt to adverse conditions. The molecular mechanism underlying H2S action relies on its chemical reactivity, and the most-well characterized mechanism is persulfidation, which involves the modification of protein thiol groups, resulting in the formation of persulfide groups. This modification causes a change of protein function, altering catalytic activity or intracellular location and inducing important physiological effects. H2S cannot react directly with thiols but instead can react with oxidized cysteine residues; therefore, H2O2 signaling through sulfenylation is required for persulfidation. A comparative study performed in this review reveals 82% identity between sulfenylome and persulfidome. With regard to abscisic acid (ABA) signaling, widespread evidence shows an interconnection between H2S and ABA in the plant response to environmental stress. Proteomic analyses have revealed persulfidation of several proteins involved in the ABA signaling network and have shown that persulfidation is triggered in response to ABA. In guard cells, a complex interaction of H2S and ABA signaling has also been described, and the persulfidation of specific signaling components seems to be the underlying mechanism., (© The Author(s) 2021. Published by Oxford University Press on behalf of the Society for Experimental Biology.)

• VaCIPK02 , a CBL -interacting protein kinase gene from Chinese wild-growing V. amurensis accession 'Zuoshan-1', was isolated and analyzed. • VaCIPK02 could physically interact with four Ca2+ sensor proteins CBLs and one PYL9 in regulating multiple signaling pathways. • Overexpression of VaCIPK02 enhanced tolerance to drought but decreased its tolerance to salt stress. • VaCIPK02 positively regulates drought-tolerance through regulation of ABA accumulation, ABA-induced stomatal movement and ROS production. Calcineurin B-like proteins (CBL) and CBL-interacting protein kinases (CIPK) play critical roles in mediating plant responses to various biotic and abiotic stresses. However, the underlying molecular mechanisms by which these complex functions and the potential cross talk between the diverse downstream signaling networks are regulated still remain elusive. Here we characterized a VaCIPK02 from Vitis amurensis , and show it functions in salt and drought stresses. We have identified that, at least, the domain at C terminus of VaCIPK02 involved in transcriptional activation. VaCIPK02 could strongly interact with four Ca2+ sensor proteins, VaCBL1, 4, 5 and 8, respectively. A Y2H-based screen to isolate genes encoding VaCIPK02 -interacting proteins identified 12 additional partners, including an ABA receptor PYL9, which interacts with VaCIPK02 in vivo. Constitutive expression of VaCIPK02 in Arabidopsis showed extremely sensitive to salt stress, but displayed increased tolerance to drought stress accompanied by ABA-hypersensitive stomata closure, improved water-conserving capacity, and increased cellular ABA levels. Moreover, overexpression of VaCIPK02 caused reduced cellular levels of ABA-induced reactive oxygen species (ROS) by regulating the expression levels of many ABA-responsive genes to scavenge and modulate ROS levels. Our results provide evidence for the involvement of VaCIPK02 along with its diverse interacting proteins in regulating salt and drought stress signal pathway. [ABSTRACT FROM AUTHOR]

By screening an expressed sequence tag (EST) library of Salvia miltiorrhiza , we detected an acidic protein, SmGRP1, with no significant similarities to the other sequences in public databases. SmGRP1 encodes a peptide of 151 amino acids, 33.77 % of which are glutamic acid residues, and the peptide was positive according to "stains-all" staining. Expression analysis revealed that SmGRP1 was expressed in all examined tissues of S. miltiorrhiza but was most highly expressed in the leaves and stems. Without a signal peptide, SmGRP1 localized to the cytoplasm in protoplasts in subcellular localization experiments. SmGRP1 expression was prominently enhanced by ABA and darkness treatments; the protein could also be induced by high temperature, NaCl, and dehydration treatments, while low temperature suppressed its expression. Furthermore, although there were no obvious phenotypic differences in SmGRP1 overexpression and SmGRP1 knockdown mutants compared with control plants under normal culture conditions, the stomata of the knockdown lines remained open when treated with ABA, darkness, NO, and H 2 O 2. In addition, the water loss rate of the knockdown mutants was faster than that of the control lines and overexpression mutants when exposed to air. These observations indicate that SmGRP1 is a novel acidic protein with potential calcium-binding capability and is involved in stomatal movement and stress resistance. [ABSTRACT FROM AUTHOR]

Hydrogen sulphide (H 2 S) is an endogenously produced gasotransmitter that has rapidly emerged as an active signalling component of several plant processes, stomatal movement regulation among them. The guard cells (GCs), pairs of cells that neighbour the stomatal pores, transduce endogenous and environmental signals, through signalling network, to control stomatal pore size. In this complex network, which has become a model system for plant signalling, few highly connected components form a core that links most of the pathways. The evidence summarized in this insight, on the interplay between H 2 S and different key components of the GC networks, points towards H 2 S as a regulator of the GC core signalling pathway., (© 2020 The Authors. New Phytologist © 2020 New Phytologist Foundation.)

Plant stomata play a crucial role in leaf function, controlling water transpiration in response to environmental stresses and modulating the gas exchange necessary for photosynthesis. The phytohormone abscisic acid (ABA) promotes stomatal closure and inhibits light-induced stomatal opening. The Arabidopsis thaliana E3 ubiquitin ligase COP1 functions in ABA-mediated stomatal closure. However, the underlying molecular mechanisms are still not fully understood. Yeast two-hybrid assays were used to identify ABA signaling components that interact with COP1, and biochemical, molecular and genetic studies were carried out to elucidate the regulatory role of COP1 in ABA signaling. The cop1 mutants are hyposensitive to ABA-triggered stomatal closure under light and dark conditions. COP1 interacts with and ubiquitinates the Arabidopsis clade A type 2C phosphatases (PP2Cs) ABI/HAB group and AHG3, thus triggering their degradation. Abscisic acid enhances the COP1-mediated degradation of these PP2Cs. Mutations in ABI1 and AHG3 partly rescue the cop1 stomatal phenotype and the phosphorylation level of OST1, a crucial SnRK2-type kinase in ABA signaling. Our data indicate that COP1 is part of a novel signaling pathway promoting ABA-mediated stomatal closure by regulating the stability of a subset of the Clade A PP2Cs. These findings provide novel insights into the interplay between ABA and the light signaling component in the modulation of stomatal movement., (© 2020 The Authors. New Phytologist © 2020 New Phytologist Foundation.)

Water availability is a main limiting factor for plant growth, development, and distribution throughout the world. Stomatal movement mediated by abscisic acid (ABA) is particularly important for drought adaptation, but the molecular mechanisms in trees are largely unclear. Here, we isolated an ABA-responsive element binding factor, PeABF3, in Populus euphratica. PeABF3 was preferentially expressed in the xylem and young leaves, and was induced by dehydration and ABA treatments. PeABF3 showed transactivation activity and was located in the nucleus. To study its functional mechanism in poplar responsive to drought stress, transgenic triploid white poplars (Populus tomentosa 'YiXianCiZhu B385') overexpressing PeABF3 were generated. PeABF3 overexpression significantly enhanced stomatal sensitivity to exogenous ABA. When subjected to drought stress, PeABF3 overexpression maintained higher photosynthetic activity and promoted cell membrane integrity, resulting in increased water-use efficiency and enhanced drought tolerance compared with wild-type controls. Moreover, a yeast one-hybrid assay and an electrophoretic mobility shift assay revealed that PeABF3 activated the expression of Actin-Depolymerizing Factor-5 (PeADF5) by directly binding to its promoter, promoting actin cytoskeleton remodeling and stomatal closure in poplar under drought stress. Taken together, our results indicate that PeABF3 enhances drought tolerance via promoting ABA-induced stomatal closure by directly regulating PeADF5 expression., (© The Author(s) 2020. Published by Oxford University Press on behalf of the Society for Experimental Biology. All rights reserved. For permissions, please email: journals.permissions@oup.com.)

Stomata are valves on the leaf surface controlling carbon dioxide (CO 2 ) influx for photosynthesis and water loss by transpiration. Thus, plants have to evolve elaborate mechanisms controlling stomatal aperture to allow efficient photosynthesis while avoid excessive water loss. Light is not only the energy source for photosynthesis but also an important signal regulating stomatal movement during dark-to-light transition. Our knowledge concerning blue and red light signaling and light-induced metabolite changes that contribute to stomatal opening are accumulating. This review summarizes recent advances on the signaling components that lie between the perception of blue/red light and activation of the PM H + -ATPases, and on the negative regulation of stomatal opening by red light-activated phyB signaling and ultraviolet (UV-B and UV-A) irradiation. Besides, light-regulated guard cell (GC)-specific metabolic levels, mesophyll-derived sucrose, and CO 2 concentration within GCs also play dual roles in stomatal opening. Thus, light-induced stomatal opening is tightly accompanied by brake mechanisms, allowing plants to coordinate carbon gain and water loss. Knowledge on the mechanisms regulating the trade-off between stomatal opening and closure may have potential applications toward generating superior crops with improved water use efficiency (CO 2 gain vs. water loss)., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2020 Yang, Li, Kong, Guo and Wei.)

Auxins (Aux) are primary growth regulators that regulate almost every aspect of growth and development in plants. It plays a vital role in various plant processes besides controlling the key aspects of cell division, cell expansion, and cell differentiation. Considering the significance of Aux, and its potential applications, a study was conducted to observe the impact of indole acetic acid (IAA), a most active and abundant form of Aux on Brassica juncea plants growing under natural environmental conditions. Different concentrations (0, 10 -10 , 10 -8 , 10 -6  M) of IAA were applied once in a day at 25-day stage of growth for 5 days, consecutively. Various parameters (growth, photosynthetic, biochemical, oxidative biomarkers and nutrient composition) were assessed at different days after sowing (DAS). Scanning electron microscopy (SEM) of leaf stomata, reactive oxygen species (ROS) localization in leaf and roots, and confocal microscopy were also conducted. The results revealed that all the IAA concentrations were effective in growth promotion and ROS reduction, however, the 10 -8  M of IAA exhibited the maximum improvement in all the above mentioned parameters as compared to the control., Competing Interests: Conflict of interestAuthors declare that there is no conflict of interest., (© Prof. H.S. Srivastava Foundation for Science and Society 2020.)

Reactive oxygen species (ROS) are plant metabolic and signaling molecules involved in responses to various external stresses, but the existence of ROS receptors and how plants respond to ROS remain largely unknown. Here we report that the plasma membrane-localized phospholipase D δ (PLDδ) protein is crucial for sensing heat shock-induced ROS to initiate reorganization of guard cell microtubules in Arabidopsis cotyledons. Heat shock of wild-type Arabidopsis cotyledons stimulated ROS production which disrupted microtubule organization and induced stomatal closure, whereas this process was markedly impaired in pldδ mutants. Moreover, wild-type PLDδ, but not the Arg622-mutated PLDδ, complemented the pldδ phenotypes in heat shock-treated plants. ROS activated PLDδ by oxidizing cysteine residues, an action that was required for its functions in ROS-induced depolymerization of guard cell microtubules, stomatal closure, and plant thermotolerance. Additionally, lipid profiling reveals involvement of microtubule organization in the feedback regulation of glycerolipid metabolism upon heat stress. Together, our findings highlight a potential mechanosensory role for PLDδ in regulating the dynamic organization of microtubules and stomatal movement, as part of the ROS-sensing pathway, during the response to external stresses., (© The Author(s) 2020. Published by Oxford University Press on behalf of the Society for Experimental Biology. All rights reserved. For permissions, please email: journals.permissions@oup.com.)

Trehalose plays important roles in plant growth and stress responses and is synthesized from trehalose-6-phosphate by trehalose-6-phosphate phosphatase (TPP). Here, we show that trehalose and abscisic acid (ABA) have synergistic effects on root growth and stomatal closure. The Arabidopsis thaliana genome contains ten genes encoding TPPs and the expression level of one, TPPE, and trehalose contents increased in response to ABA. In the presence of ABA, the ABA-responsive transcription factor ABA RESPONSE ELEMENT BINDING FACTOR2 (ABF2) directly binds to the TPPE promoter to activate its expression. Genetic analysis revealed that TPPE acts downstream of ABF2, which is supported by the findings that TPPE expression and trehalose content are reduced in the abf2 mutant and that a mutation in TPPE abolished the ABA-sensitive root elongation phenotype of 35S:ABF2 plants. Reactive oxygen species (ROS) accumulation in response to ABA failed to occur in tppe mutant plants, suggesting that TPPE is involved in ABA-controlled root elongation and stomatal movement by inducing ROS accumulation. This study uncovers a new branch of the ABA signaling pathway and provides a molecular basis for the role of trehalose in plant responses to abiotic stress., (© 2020 The Authors. Journal of Integrative Plant Biology Published by John Wiley & Sons Australia, Ltd on behalf of Institute of Botany, Chinese Academy of Sciences.)

Main Conclusion: Dynamic protein and phosphoprotein profiles uncovered the overall regulation of stomata movement against pathogen invasion and phosphorylation states of proteins involved in ABA, SA, calcium and ROS signaling, which may modulate the stomatal immune response. Stomatal openings represent a major route of pathogen entry into the plant, and plants have evolved mechanisms to regulate stomatal aperture as innate immune response against bacterial invasion. However, the mechanisms underlying stomatal immunity are not fully understood. Taking advantage of high-throughput liquid chromatography mass spectrometry (LC-MS), we performed label-free proteomic and phosphoproteomic analyses of enriched guard cells in response to a bacterial pathogen Pseudomonas syringae pv. tomato (Pst) DC3000. In total, 495 proteins and 1229 phosphoproteins were identified as differentially regulated. These proteins are involved in a variety of signaling pathways, including abscisic acid and salicylic acid hormone signaling, calcium and reactive oxygen species signaling. We also showed that dynamic changes of phosphoprotein WRKY transcription factors may play a crucial role in regulating stomata movement in plant immunity. The identified proteins/phosphoproteins and the pathways form interactive molecular networks to regulate stomatal immunity. This study has provided new insights into the multifaceted mechanisms of stomatal immunity. The differential proteins and phosphoproteins are potential targets for engineering or breeding of crops for enhanced pathogen defense.

The ubiquitin-proteasome system (UPS) is one of the main ways of eukaryotic protein degradation and post-translational modification. It has proven as an essential process for plants to respond to abiotic stresses. Plant U-box (PUB) protein acts as a ubiquitin ligase, which recognizes and ubiquitinates the target proteins. Many PUBs have been involved in water stress in Arabidopsis and rice, but similar comprehensive studies in potato remained limited. In this study, the overexpressed and interfered transgenic potato plants of StPUB27 were obtained and their performances were evaluated under osmotic stress. The result showed that overexpression of StPUB27 accelerated the dehydration of detached leaves companied with greater stomatal conductance, while the down-regulated StPUB27 expression by RNA interference (RNAi) showed a smaller stomatal conductance and a lower rate of water loss in detached leaves, thus showing higher tolerance to osmotic stress. In addition, no significant changes in the proline content were observed between StPUB27 overexpressed and RNAi potato plants. The result demonstrated that potato E3 ubiquitin ligase PUB27 may negatively regulate drought tolerance by mediating stomatal conductance., (Copyright © 2020 Elsevier Masson SAS. All rights reserved.)

The composition and crystallization process are essential for high-quality perovskite films. Cesium (Cs) and methylammonium chlorine (MACl) were found to affect the crystallization kinetics of perovskite, and the performance and stability of corresponding devices were greatly improved. We adopted an ion exchange method to remove MACl vapor and add Cs to form a multiple-cation-based perovskite film. With the increase of annealing time, Cl - from cesium chloride (CsCl) and MA from methylammonium bromide (MABr) formed gradually MACl vapor, and the porosity of surface morphology improved accordingly. The highly crystallized and compact Cs y MA x  -  y FA 1 -  x PbI 3 -  x Br x perovskite film with different compositions was eventually obtained. The effects of the amount of MABr on the property of perovskite films and on the performance of the corresponding perovskite solar cells (PerSCs) were systematically studied. The PerSCs derived from 12 mg of MABr exhibit the best photovoltaic performance with a power conversion efficiency of 21.57% under 1 sun illumination.

A stable leaf temperature provides plants with a suitable microenvironment for photosynthesis. With global warming, extreme temperatures have become more frequent and severe; therefore, it is increasingly important to understand the fine regulation of leaf temperature under heat stress. In this study, five poplar species (Populus tomentosa, Populus simonii, Populus euphratica, Populus deltoides and Populus trichocarpa) that live in different native environments were used to analyze leaf temperature regulation. Leaf temperatures were more stable in Populus simonii and Populus euphratica (adapted to water-deficient regions) under elevated ambient temperature. Although transpiration contributes strongly to leaf cooling in poplar, the thicker epidermis and mesophyll and lower absorbance of Populus simonii and Populus euphratica leaves also help reduce leaf temperature, since their leaves absorb less radiation. Co-expression network and association analysis of a natural population of P. simonii indicated that PsiMYB60.2, PsiMYB61.2 and PsiMYB61.1 play dominant roles in coordinating leaf temperature, stomatal conductance and transpiration rate in response to heat stress. Individuals with CT-GT-GT genotypes of these three candidate genes have significantly higher water-use efficiency, and balance leaf temperature cooling with photosynthetic efficiency. Therefore, our findings have clarified the genetic basis of leaf cooling among poplar species and laid the foundation for molecular breeding of thermostable, water-conserving poplar varieties., (© The Author(s) 2020. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: journals.permission@oup.com.)

The stomata of maize (Zea mays) contain a pair of guard cells and a pair of subsidiary cells. To determine whether H 2 O 2 , Ca 2+ , and K + in subsidiary cells were involved in stomatal movement, we treated four-week-old maize (Zhengdan 958) leaves with H 2 O 2 , diphenylene iodonium (DPI), CaCl 2 , and LaCl 3 . Changes in content and distribution of H 2 O 2 , Ca 2+ , and K + during stomatal movement were observed. When exogenous H 2 O 2 was applied, Ca 2+ increased and K + decreased in guard cells, while both ions increased in subsidiary cells, leading to stomatal closure. After DPI treatment, Ca 2+ decreased and K + increased in guard cells, but both Ca 2+ and K + decreased in subsidiary cells, resulting in open stomata. Exogenous CaCl 2 increased H 2 O 2 and reduced K + in guard cells, while significantly increasing them in subsidiary cells and causing stomatal closure. After LaCl 3 treatment, H 2 O 2 decreased and K + increased in guard cells, whereas both decreased in subsidiary cells and stomata became open. Results indicate that H 2 O 2 and Ca 2+ correlate positively with each other and with K + in subsidiary cells during stomatal movement. Both H 2 O 2 and Ca 2+ in subsidiary cells promote an inflow of K + , indirectly regulating stomatal closure., Competing Interests: Declaration of competing interest We declare that there are no competing interests., (Copyright © 2020 Elsevier Masson SAS. All rights reserved.)

Elevated CO 2 (eCO 2 ) often reduces leaf stomatal aperture and density thus impacts plant physiology and productivity. We have previously demonstrated that the Arabidopsis BIG protein distinguishes between the processes of eCO 2 -induced stomatal closure and eCO 2 -inhibited stomatal opening. However, the mechanistic basis of this action is not fully understood. Here we show that eCO 2 -elicited reactive oxygen species (ROS) production in big mutants was compromised in stomatal closure induction but not in stomatal opening inhibition. Pharmacological and genetic studies show that ROS generated by both NADPH oxidases and cell wall peroxidases contribute to eCO 2 -induced stomatal closure, whereas inhibition of light-induced stomatal opening by eCO 2 may rely on the ROS derived from NADPH oxidases but not from cell wall peroxidases. As with JA and ABA, SA is required for eCO 2 -induced ROS generation and stomatal closure. In contrast, none of these three signals has a significant role in eCO 2 -inhibited stomatal opening, unveiling the distinct roles of plant hormonal signaling pathways in the induction of stomatal closure and the inhibition of stomatal opening by eCO 2 . In conclusion, this study adds SA to a list of plant hormones that together with ROS from distinct sources distinguish two branches of eCO 2 -mediated stomatal movements., (Copyright © 2020 He, Zhang, Kim, Sun, Liu, Liu, Hetherington and Liang.)

Plants exposed to the combination of drought and pathogen infections are in a unique state, different from that of plants exposed to each stress alone. Plants undergo major hormonal changes during drought and/or pathogen infection, highlighting the importance of hormones as crucial mediators of plant stress responses. Evidence from individual stress studies has shown that drought and pathogen infection have both different and overlapping impacts on hormone metabolism and hormone-associated signal transduction pathways. Thus, under the combination of drought and pathogen infection, a reprograming of hormone levels and related signaling networks is inevitable. This process delivers data from plants exposed to individual stressors inadequate for predicting how hormone levels and related signaling networks will change in plants exposed to a combination of stressors. Furthermore, the yield of crop plants, determined by their capacity for stress acclimatization and resistance to pathogen infection, will be underpinned by interactions among the hormone pathways. Although many studies have been conducted to understand the molecular mechanisms associated with plant responses to combinations of stressors, the interactions that occur among hormones are far from being well-understood. We provide here an overview and evaluation of various reports on crosstalk or overlapping hormonal responses from individual stress studies and how the combination of drought and pathogen infection modulates hormone levels and their associated signaling pathways in plant responses to these combined stresses. We also give a brief overview of the importance of overlapping plant responses for the production of crop plants resistant to individual and combined stressors under natural environmental conditions.

Background: The increase in atmospheric CO 2 is causing a number of changes in plant growth such as increases in leaf area and number, branching, plant size and biomass, and growth rate. Despite the importance of stomatal responses to CO 2 , little is known about the genetic and molecular mechanisms that mediate stomatal development and movement in response to CO 2 levels. Deciphering the mechanisms that sense changes in CO 2 and/or HCO 3 - concentration is critical for unraveling the role of CO 2 in stomatal development movement. In Arabidopsis , CO 2 -induced stomatal closure is strongly Ca 2+ -dependent. To further dissect this signaling pathway and identify new components in the CO 2 response pathway, we recorded [Ca 2+ ] cyt changes in mutagenized Arabidopsis leaves and screened for mutants with abnormal guard cell behavior in response to CO 2 /HCO 3 - ., Results: We observed that 1 mM HCO 3 - induces [Ca 2+ ] cys transient changes in guard cells and stomatal closure both in light and darkness. The changes in [Ca 2+ ] cys induced by HCO 3 - could be detected by an aequorin-based calcium imaging system. Using this system, we identified a number of Arabidopsis mutants defective in both [Ca 2+ ] cyt changes and the stomatal response to CO 2 /HCO 3 - ., Conclusions: We provide a sensitive method for isolating stomatal CO 2 /HCO 3 - response genes that function early in stomatal closure and that have a role in regulating [Ca 2+ ] cyt . This method will be helpful in elucidating the Ca 2+ -dependent regulation of guard cell behavior in response to CO 2 /HCO 3 - ., Competing Interests: Competing interestsThe authors declare that they have no competing interests., (© The Author(s) 2020.)

The opening and closure of stomata depend on the turgor pressure adjustment by the influx or efflux of ions and water in guard cells. In this process, aquaporins may play important roles by facilitating the transport of water and other small molecules. In this perspective, we consider the potential roles of aquaporins in the membrane diffusion of different molecules (H 2 O, CO 2 , and H 2 O 2 ), processes dependent on abscisic acid and CO 2 signaling in guard cells. While the limited data already available emphasizes the roles of aquaporins in stomatal movement, we propose additional approaches to elucidate the specific roles of single or several aquaporin isoforms in the stomata and evaluate the perspectives aquaporins might offer to improve stomatal dynamics., (Copyright © 2020 Ding and Chaumont.)

Drought is a major threat to wheat growth and crop productivity. However, there has been only limited success in developing drought-hardy cultivars. This lack of progress is due, at least in part, to a lack of understanding of the molecular mechanisms of drought tolerance in wheat. Here, we evaluated the potential role of three cytosolic glyceraldehyde-3-phosphate dehydrogenases (TaGAPC2/5/6) under drought stress in wheat and Arabidopsis. We found that TaGAPC2/5/6 all positively responded to drought stress via reactive oxygen species (ROS) scavenging and stomatal movement. The results of yeast co-transformation and electrophoretic mobility shift assay showed that TaWRKY33 acted as a direct regulator of TaGAPC2/5/6 genes. The dual luciferase reporter assay indicated that TaWRKY33 positively activated the expression of TaGAPC2/5/6. The results of bimolecular fluorescence complementation and yeast two-hybrid system demonstrated that TaGAPC2/5/6 interacted with phospholipase Dδ (PLDδ). We then demonstrated that TaGAPC2/5/6 positively promoted the activity of TaPLDδ in vitro and in vivo. Furthermore, lower PLDδ activity in RNAi wheat could lead to less PA accumulation, causing higher stomatal aperture sizes under drought stress. In summary, our results establish a new positive regulatory mechanism of TaGAPCs which helps wheat fine-tune their drought responses., (© 2019 John Wiley & Sons Ltd.)

Salmonella enterica is one of the most common pathogens associated with produce outbreaks worldwide; nonetheless, the mechanisms uncovering their interaction with plants are elusive. Previous reports demonstrate that S. enterica ser. Typhimurium (STm), similar to the phytopathogen Pseudomonas syringae pv. tomato (Pst) DC3000, triggers a transient stomatal closure suggesting its ability to overcome this plant defense and colonize the leaf apoplast. In order to discover new molecular players that function in the stomatal reopening by STm and Pst DC3000, we performed an Arabidopsis mutant screening using thermal imaging. Further stomatal bioassay confirmed that the mutant plants exo70h4-3 , sce1-3 , bbe8 , stp1 , and lsu2 have smaller stomatal aperture widths than the wild type Col-0 in response to STm 14028s. The mutants bbe8 , stp1 and lsu2 have impaired stomatal movement in response to Pst DC3000. These findings indicate that EXO70H4 and SCE1 are involved in bacterial-specific responses, while BBE8, STP1, and LSU2 may be required for stomatal response to a broad range of bacteria. The identification of new molecular components of the guard cell movement induced by bacteria will enable a better understanding of the initial stages of plant colonization and facilitate targeted prevention of leaf contamination with harmful pathogens. [ABSTRACT FROM AUTHOR]