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Forest trees generate substantial quantities of organic carbon, recognized as a renewable and economically viable resource for applications in bioenergy and industry. This study specifically focuses on xylan, a major hemicellulose component in poplar, and on the role of PtrPARVUS2—a member of the glycosyltransferase 8 family genes involved in xylan biosynthesis. PtrPARVUS2 is hypothesized to exhibit tissue-specific activity, and here we assessed its promoter via bioinformatic analysis, revealing motifs associated with responsiveness to hormones including Gibberellic Acid (GA), Methyl Jasmonate (MeJA), Auxin, and Abscisic Acid (ABA), among others. Treatment with hormones, including ABA, 1-naphthaleneacetic acid, a synthetic auxin, MeJA, and GA, demonstrated a swift inhibition of PtrPARVUS2 transcription. Analysis of expression patterns in wildtype trees indicated heightened expression in vascular tissues, particularly the bark. Transgenic lines expressing Enhanced Green Fluorescent Protein and β-glucuronidase under the control of the PtrPARVUS2 promoter confirmed tissue-specific activity, particularly in guard cells, stem epidermis, and developing xylem. These results offer understanding into the potential functions of PtrPARVUS2 in terms of phytohormone response and the formation of guard cell walls. The investigation introduces a valuable promoter for specific biotechnological applications in guard cells and stem epidermal cells. Additional research is required to elucidate the precise regulatory mechanisms of PtrPARVUS2 in the future.Key message: This study uncovers tissue-specific and hormone-responsive activity of the PtrPARVUS2 promoter, providing insights into xylan biosynthesis and offering a valuable tool for targeted poplar guard cells and stem epidermis expression. [ABSTRACT FROM AUTHOR]

Grasses form morphologically derived, four-celled stomata, where two dumbbell-shaped guard cells (GCs) are flanked by two lateral subsidiary cells (SCs). This innovative form enables rapid opening and closing kinetics and efficient plant-atmosphere gas exchange. The mobile bHLH transcription factor MUTE is required for SC formation in grasses. Yet whether and how MUTE also regulates GC development and whether MUTE mobility is required for SC recruitment is unclear. Here, we transgenically impaired BdMUTE mobility from GC to SC precursors in the emerging model grass Brachypodium distachyon. Our data indicate that reduced BdMUTE mobility severely affected the spatiotemporal coordination of GC and SC development. Furthermore, although BdMUTE has a cell-autonomous role in GC division orientation, complete dumbbell morphogenesis of GCs required SC recruitment. Finally, leaf-level gas exchange measurements showed that dosage-dependent complementation of the four-celled grass morphology was mirrored in a gradual physiological complementation of stomatal kinetics. Together, our work revealed a dual role of grass MUTE in regulating GC division orientation and SC recruitment, which in turn is required forGCmorphogenesis and the rapid kinetics of grass stomata. [ABSTRACT FROM AUTHOR]

Drought has a significant, negative impact on crop production; and these effects are poised to increase with climate change. Plants acclimate to drought and water stress through diverse physiological responses, primarily mediated by the hormone abscisic acid (ABA). Because plants lose the majority of their water through stomatal pores on aerial surfaces of plants, stomatal closure is one of the rapid responses mediated by ABA to reduce transpirational water loss. The dynamic changes in the transcriptome of stomatal guard cells in response to ABA have been investigated in the model plant Arabidopsis thaliana. However, guard cell transcriptomes have not been analyzed in agronomically valuable crops such as a major oilseed crop, rapeseed. In this study, we investigated the dynamics of ABA-regulated transcriptomes in stomatal guard cells of Brassica napus and conducted comparison analysis with the transcriptomes of A. thaliana. We discovered changes in gene expression indicating alterations in a host of physiological processes, including stomatal movement, metabolic reprogramming, and light responses. Our results suggest the existence of both immediate and delayed responses to ABA in Brassica guard cells. Furthermore, the transcription factors and regulatory networks mediating these responses are compared to those identified in Arabidopsis. Our results imply the continuing evolution of ABA responses in Brassica since its divergence from a common ancestor, involving both protein-coding and non-coding nucleotide sequences. Together, our results will provide a basis for developing strategies for molecular manipulation of drought tolerance in crop plants. [ABSTRACT FROM AUTHOR]

Abstract Drought has a significant, negative impact on crop production; and these effects are poised to increase with climate change. Plants acclimate to drought and water stress through diverse physiological responses, primarily mediated by the hormone abscisic acid (ABA). Because plants lose the majority of their water through stomatal pores on aerial surfaces of plants, stomatal closure is one of the rapid responses mediated by ABA to reduce transpirational water loss. The dynamic changes in the transcriptome of stomatal guard cells in response to ABA have been investigated in the model plant Arabidopsis thaliana. However, guard cell transcriptomes have not been analyzed in agronomically valuable crops such as a major oilseed crop, rapeseed. In this study, we investigated the dynamics of ABA-regulated transcriptomes in stomatal guard cells of Brassica napus and conducted comparison analysis with the transcriptomes of A. thaliana. We discovered changes in gene expression indicating alterations in a host of physiological processes, including stomatal movement, metabolic reprogramming, and light responses. Our results suggest the existence of both immediate and delayed responses to ABA in Brassica guard cells. Furthermore, the transcription factors and regulatory networks mediating these responses are compared to those identified in Arabidopsis. Our results imply the continuing evolution of ABA responses in Brassica since its divergence from a common ancestor, involving both protein-coding and non-coding nucleotide sequences. Together, our results will provide a basis for developing strategies for molecular manipulation of drought tolerance in crop plants.

The endoplasmic reticulum (ER) is the largest organelle in terms of membrane content, occupying the entire cytoplasmic volume. It is tethered to the cell cortex through ER‐plasma membrane contact sites (EPCS). Previous studies have shown that EPCSs labelled by VAP27 align with cortical microtubules, and that ER tubules elongate along microtubules. Here, we addressed the question whether this relationship is bidirectional, with EPCSs influencing microtubule organisation. Using TIRF microscopy to track EPCSs and microtubule dynamics simultaneously, we demonstrate that while EPCSs remain stable, microtubules are highly dynamic and can adjust their positioning based on nearby EPCS in Arabidopsis cotyledon epidermis. In lobes of epidermal cells enclosed by two indentations, where microtubules bundle together, EPCSs flank the bundles and exhibit a distinctive arrangement, forming symmetric arcs in relation to the lobe axis. In guard cells, transversely oriented ER tubules co‐align with microtubules. Disrupting microtubules with the drug oryzalin leads to transient guard cells‐ER remodelling, followed by its reorganisation into transverse tubules before microtubule recovery. Taken together our observations suggest, that the positioning of EPCSs and cortical microtubules, can affect each other and the organisation of cortical ER. [ABSTRACT FROM AUTHOR]

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

Background Like all plant cells, the guard cells of stomatal complexes are encased in cell walls that are composed of diverse, interacting networks of polysaccharide polymers. The properties of these cell walls underpin the dynamic deformations that occur in guard cells as they expand and contract to drive the opening and closing of the stomatal pore, the regulation of which is crucial for photosynthesis and water transport in plants. Scope Our understanding of how cell wall mechanics are influenced by the nanoscale assembly of cell wall polymers in guard cell walls, how this architecture changes over stomatal development, maturation and ageing and how the cell walls of stomatal guard cells might be tuned to optimize stomatal responses to dynamic environmental stimuli is still in its infancy. Conclusion In this review, we discuss advances in our ability to probe experimentally and to model the structure and dynamics of guard cell walls quantitatively across a range of plant species, highlighting new ideas and exciting opportunities for further research into these actively moving plant cells. [ABSTRACT FROM AUTHOR]

SUMMARY: Stomata are pores at the leaf surface that enable gas exchange and transpiration. The signaling pathways that regulate the differentiation of stomatal guard cells and the mechanisms of stomatal pore formation have been characterized in Arabidopsis thaliana. However, the process by which stomatal complexes develop after pore formation into fully mature complexes is poorly understood. We tracked the morphogenesis of young stomatal complexes over time to establish characteristic geometric milestones along the path of stomatal maturation. Using 3D‐nanoindentation coupled with finite element modeling of young and mature stomata, we found that despite having thicker cell walls than young guard cells, mature guard cells are more energy efficient with respect to stomatal opening, potentially attributable to the increased mechanical anisotropy of their cell walls and smaller changes in turgor pressure between the closed and open states. Comparing geometric changes in young and mature guard cells of wild‐type and cellulose‐deficient plants revealed that although cellulose is required for normal stomatal maturation, mechanical anisotropy appears to be achieved by the collective influence of cellulose and additional wall components. Together, these data elucidate the dynamic geometric and biomechanical mechanisms underlying the development process of stomatal maturation. [ABSTRACT FROM AUTHOR]

This article is a Commentary on Meigas et al. (2024), 243: 513–518. [ABSTRACT FROM AUTHOR]

Summary: Stomatal movement involves ion transport across the plasma membrane (PM) and vacuolar membrane (VM) of guard cells. However, the coupling mechanisms of ion transporters in both membranes and their interplay with Ca2+ and pH changes are largely unclear.Here, we investigated transporter networks in tobacco guard cells and mesophyll cells using multiparametric live‐cell ion imaging and computational simulations.K+ and anion fluxes at both, PM and VM, affected H+ and Ca2+, as changes in extracellular KCl or KNO3 concentrations were accompanied by cytosolic and vacuolar pH shifts and changes in [Ca2+]cyt and the membrane potential. At both membranes, the K+ transporter networks mediated an antiport of K+ and H+. By contrast, net transport of anions was accompanied by parallel H+ transport, with differences in transport capacity for chloride and nitrate. Guard and mesophyll cells exhibited similarities in K+/H+ transport but cell type‐specific differences in [H+]cyt and pH‐dependent [Ca2+]cyt signals. Computational cell biology models explained mechanistically the properties of transporter networks and the coupling of transport across the PM and VM.Our integrated approach indicates fundamental principles of coupled ion transport at membrane sandwiches to control H+/K+ homeostasis and points to transceptor‐like Ca2+/H+‐based ion signaling in plant cells. [ABSTRACT FROM AUTHOR]

Pectin has been extensively studied in animal immunity, and exogenous pectin as a food additive can provide protection against inflammatory bowel disease. However, the utility of pectin to improve immunity in plants is still unstudied. Here, we found exogenous application of pectin triggered stomatal closure in Arabidopsis in a dose‐ and time‐dependent manner. Additionally, pectin activated peroxidase and nicotinamide adenine dinucleotide phosphate (NADPH) oxidase to produce reactive oxygen species (ROS), which subsequently increased cytoplasmic Ca2+ concentration ([Ca2+]cyt) and was followed by nitric oxide (NO) production, leading to stomatal closure in an abscisic acid (ABA) and salicylic acid (SA) signalling‐dependent mechanism. Furthermore, pectin enhanced the disease resistance to Pseudomonas syringae pv. tomato DC3000 (Pst DC3000) with mitogen‐activated protein kinases (MPKs) MPK3/6 activated and upregulated expression of defence‐responsive genes in Arabidopsis. These results suggested that exogenous pectin‐induced stomatal closure was associated with ROS and NO production regulated by ABA and SA signalling, contributing to defence against Pst DC3000 in Arabidopsis. [ABSTRACT FROM AUTHOR]

SUMMARY: Leaf plastids harbor a plethora of biochemical reactions including photosynthesis, one of the most important metabolic pathways on Earth. Scientists are eager to unveil the physiological processes within the organelle but also their interconnection with the rest of the plant cell. An increasingly important feature of this venture is to use experimental data in the design of metabolic models. A remaining obstacle has been the limited in situ volume information of plastids and other cell organelles. To fill this gap for chloroplasts, we established three microscopy protocols delivering in situ volumes based on: (i) chlorophyll fluorescence emerging from the thylakoid membrane, (ii) a CFP marker embedded in the envelope, and (iii) calculations from serial block‐face scanning electron microscopy (SBFSEM). The obtained data were corroborated by comparing wild‐type data with two mutant lines affected in the plastid division machinery known to produce small and large mesophyll chloroplasts, respectively. Furthermore, we also determined the volume of the much smaller guard cell plastids. Interestingly, their volume is not governed by the same components of the division machinery which defines mesophyll plastid size. Based on our three approaches, the average volume of a mature Col‐0 wild‐type mesophyll chloroplasts is 93 μm3. Wild‐type guard cell plastids are approximately 18 μm3. Lastly, our comparative analysis shows that the chlorophyll fluorescence analysis can accurately determine chloroplast volumes, providing an important tool to research groups without access to transgenic marker lines expressing genetically encoded fluorescence proteins or costly SBFSEM equipment. [ABSTRACT FROM AUTHOR]

Linker of nucleoskeleton and cytoskeleton (LINC) complexes consist of outer nuclear membrane KASH proteins, interacting in the nuclear envelope lumen with inner nuclear membrane SUN proteins and connecting the nucleus and cytoskeleton. The paralogous Arabidopsis KASH proteins SINE1 and SINE2 function during stomatal dynamics induced by light–dark transitions and abscisic acid (ABA), which requires F-actin reorganization. SINE2 influences actin depolymerization and SINE1 actin repolymerization. The actin-related protein 2/3 (ARP2/3) complex, an actin nucleator, and the plant actin-bundling and -stabilizing factor SCAB1 are involved in stomatal aperture control. Here, we have tested the genetic interaction of SINE1 and SINE2 with SCAB1 and the ARP2/3 complex. We show that SINE1 and the ARP2/3 complex function in the same pathway during ABA-induced stomatal closure, while SINE2 and the ARP2/3 complex play opposing roles. The actin repolymerization defect observed in sine1-1 is partially rescued in scab1-2 sine1-1 , while SINE2 is epistatic to SCAB1. In addition, SINE1 and ARP2/3 act synergistically in lateral root development. The absence of SINE2 renders trichome development independent of the ARP2/3 complex. Together, these data reveal complex and differential interactions of the two KASH proteins with the actin-remodeling apparatus and add evidence to the proposed differential role of SINE1 and SINE2 in actin dynamics. [ABSTRACT FROM AUTHOR]

SUMMARY: Understanding how nutrient stress impacts plant growth is fundamentally important to the development of approaches to improve crop production under nutrient limitation. Here we applied single‐cell RNA sequencing to shoot apices of Pisum sativum grown under boron (B) deficiency. We identified up to 15 cell clusters based on the clustering of gene expression profiles and verified cell identity with cell‐type‐specific marker gene expression. Different cell types responded differently to B deficiency. Specifically, the expression of photosynthetic genes in mesophyll cells (MCs) was down‐regulated by B deficiency, consistent with impaired photosynthetic rate. Furthermore, the down‐regulation of stomatal development genes in guard cells, including homologs of MUTE and TOO MANY MOUTHS, correlated with a decrease in stomatal density under B deficiency. We also constructed the developmental trajectory of the shoot apical meristem (SAM) cells and a transcription factor interaction network. The developmental progression of SAM to MC was characterized by up‐regulation of genes encoding histones and chromatin assembly and remodeling proteins including homologs of FASCIATA1 (FAS1) and SWITCH DEFECTIVE/SUCROSE NON‐FERMENTABLE (SWI/SNF) complex. However, B deficiency suppressed their expression, which helps to explain impaired SAM development under B deficiency. These results represent a major advance over bulk‐tissue RNA‐seq analysis in which cell‐type‐specific responses are lost and hence important physiological responses to B deficiency are missed. The reported findings reveal strategies by which plants adapt to B deficiency thus offering breeders a set of specific targets for genetic improvement. The reported approach and resources have potential applications well beyond P. sativum species and could be applied to various legumes to improve their adaptability to multiple nutrient or abiotic stresses. Significance Statement: Using single‐cell RNA‐seq, our study uncovers cell‐specific responses in peas that enhance adaptability to nutrient stresses, guiding breeders in crop improvement. These insights can extend to other legumes, amplifying our research's reach. [ABSTRACT FROM AUTHOR]

This article provides an in-depth overview of the guard cell signaling network and its role in regulating stomatal aperture in plants via computational algebra. Stomatal pores in plant leaves allow for gas exchange but also result in water loss through transpiration, making the regulation of stomatal aperture critical for plant water balance, photosynthesis, and stress response. The guard cell signaling network is a complex regulatory network that controls the opening and closing of stomatal pores in plants. It consists of a variety of signaling pathways, including those involving calcium, nitric oxide, and second messengers such as Cyclic guanosine monophosphate (cGMP) and cyclic ADP-ribose (cADPR). The article discusses the interactions between these pathways and the mechanisms by which guard cells respond to environmental cues such as light, CO2 levels, and humidity. Overall, this article provides valuable insights into the regulatory structure of the guard cell signaling network and its potential applications in optimizing plant traits. [ABSTRACT FROM AUTHOR]

In plants, epidermal guard cells integrate and respond to numerous environmental signals to control stomatal pore apertures, thereby regulating gas exchange. Chromatin structure controls transcription factor (TF) access to the genome, but whether large-scale chromatin remodeling occurs in guard cells during stomatal movements, and in response to the hormone abscisic acid (ABA) in general, remains unknown. Here, we isolate guard cell nuclei from Arabidopsis thaliana plants to examine whether the physiological signals, ABA and CO2 (carbon dioxide), regulate guard cell chromatin during stomatal movements. Our cell type-specific analyses uncover patterns of chromatin accessibility specific to guard cells and define cis-regulatory sequences supporting guard cell-specific gene expression. We find that ABA triggers extensive and dynamic chromatin remodeling in guard cells, roots, and mesophyll cells with clear patterns of cell type specificity. DNA motif analyses uncover binding sites for distinct TFs enriched in ABA-induced and ABA-repressed chromatin. We identify the Abscisic Acid Response Element (ABRE) Binding Factor (ABF) bZIP-type TFs that are required for ABA-triggered chromatin opening in guard cells and roots and implicate the inhibition of a clade of bHLH-type TFs in controlling ABA-repressed chromatin. Moreover, we demonstrate that ABA and CO2 induce distinct programs of chromatin remodeling, whereby elevated atmospheric CO2 had only minimal impact on chromatin dynamics. We provide insight into the control of guard cell chromatin dynamics and propose that ABA-induced chromatin remodeling primes the genome for abiotic stress resistance. [ABSTRACT FROM AUTHOR]

Starch in the stomatal guard cells is largely synthesized using carbon precursors originating from sugars imported from the leaf mesophyll. Such heterotrophic nature of guard cell starch synthesis prompted us to investigate the role of cytosolic sucrose synthases (SUS) in this pathway. Out of the six members of the Arabidopsis SUS gene family, SUS3 was the most highly expressed isoform in guard cells. The Arabidopsis sus3 mutant displayed changes in guard cell starch contents comparable to the Wild Type (WT) up until 6 h into the day. After this time point, sus3 guard cells surprisingly started to accumulate starch at very high rates, reaching the end of the day with significantly more starch than WT. Based on the phenotype of the sus3 mutant, we suggest that in guard cells, SUS3 is involved in the regulation of carbon fluxes towards starch synthesis during the second half of the day. SUS3 may be part of a previously predicted guard cell futile cycle of metabolic reactions, in which sucrose is re-synthesized from UDP-glucose to avoid excessive starch synthesis toward the end of the day. This is in contrast to typical storage organs, in which cytosolic SUS is required to produce ADP-glucose for starch synthesis.

Red light induces stomatal opening by affecting photosynthesis, metabolism and triggering signal transductions in guard cells. Phytochrome B (phyB) plays a positive role in mediating red light‐induced stomatal opening. However, phyB‐mediated red light guard cell signalling is poorly understood. Here, we found that phyB‐mediated sequential phosphorylation of mitogen‐activated protein kinase kinase 2 (MAPKK2, MKK2) and MPK2 in guard cells is essential for red light‐induced stomatal opening. Mutations in MKK2 and MPK2 led to reduced stomatal opening in response to white light, and these phenotypes could be observed under red light, not blue light. MKK2 interacted with MPK2 in vitro and in plants. MPK2 was directly phosphorylated by MKK2 in vitro. Red light triggered the phosphorylation of MKK2 in guard cells, and MKK2 phosphorylation was greatly reduced in phyB mutant. Simultaneously, red light‐stimulated MPK2 phosphorylation in guard cells was inhibited in mkk2 mutant. Furthermore, mkk2 and mpk2 mutants exhibit significantly smaller stomatal apertures than that of wild type during the stomatal opening stage in the diurnal stomatal movements. Our results indicate that red light‐promoted phyB‐dependent phosphorylation of MKK2‐MPK2 cascade in guard cells is essential for stomatal opening, which contributes to the fine‐tuning of stomatal opening apertures under light. Summary statement: Red light triggers phytochrome B‐dependent phosphorylation of MKK2‐MPK2 cascade in guard cells of Arabidopsis, and MKK2‐MPK2 positively regulates red light‐induced stomatal opening. This regulatory mechanism contributes to the fine‐tuning of stomatal opening under light. [ABSTRACT FROM AUTHOR]

Galanthus transcaucasicus is a less frequently known species with a high distribution in southern regions of the Caspian Sea in Iran. So far, no precise study has been done on Galanthus transcaucasicus in the literatu re. This study aimed to collect and introduce the morphological and anat omical features of endemic Galanthus transcaucasicus in detail. Herewit h, 50 Galanthus transcaucasicus accessions of five populations (10 rand omly selected plants from each population) were collected from four pr ovinces, including Mazandaran, Guilan, Golestan, and Ardabil, Iran. Twel ve morphological traits and ten anatomical parameters were measured. The largest flowers were observed in Shirgah population (22.66 and 11. 97mm for outer perianth-segments length and width). The tallest stems were recorded in the Shirgah population (243.89 mm). The largest bulb size belonged to the Neka population (19.92 and 14.08 mm of bulb lengt h and diameter, respectively). Anatomical analysis showed that the cells on the lower (abaxial) epidermis were spherical and short. On the upper (adaxial) epidermis, however, they were oblong and strongly elongated. G. transcaucasicus had amphistomatous leaves. The number of stomata on the upper surface was less (0.16 to 0.6 per mm2) than that on the low er surface (3.77 to 9.51 per mm2). Anatomically, there was a significant difference between populations from different regions. The results of thi s study revealed low variability among G. transcaucasicus accessions, re presentative of one species' clone-population structure. Therefore, it see ms that the range of environmental conditions in which the species are d istributed can play a role in the morphological and anatomical features of Iranian Galanthus transcaucasicus. [ABSTRACT FROM AUTHOR]

Stomata are the structures responsible for gas exchange in plants. The established framework for stomatal development is based on the model plant Arabidopsis, but diverse patterns of stomatal development have been observed in other plant lineages and species. The molecular mechanisms behind these diversified patterns are still poorly understood. We recently proposed a model for the molecular mechanisms of the diversification of stomatal development based on the genus Callitriche (Plantaginaceae), according to which a temporal shift in the expression of key stomatal transcription factors SPEECHLESS and MUTE leads to changes in the behavior of meristemoids (stomatal precursor cells). In the present study, we genetically manipulated Arabidopsis to test this model. By altering the timing of MUTE expression, we successfully generated Arabidopsis plants with early differentiation or prolonged divisions of meristemoids, as predicted by the model. The epidermal morphology of the generated lines resembled that of species with prolonged or no meristemoid divisions. Thus, the evolutionary process can be reproduced by varying the SPEECHLESS to MUTE transition. We also observed unexpected phenotypes, which indicated the participation of additional factors in the evolution of the patterns observed in nature. This study provides novel experimental insights into the diversification of meristemoid behaviors. [ABSTRACT FROM AUTHOR]

This article is an interview with Rob Roelfsema, a plant scientist who specializes in studying ion transport systems in plants, particularly in guard cells that regulate stomatal movements. Roelfsema discusses his interest in plant science, his decision to pursue a career in research, and what motivates him in his work. He also mentions his role models and favorite papers from the journal New Phytologist. Roelfsema's research focuses on understanding how plants adapt to environmental conditions through ion transport systems. He is a University Professor at the Department of Molecular Plant Biology and Biophysics at the University of Würzburg in Germany. [Extracted from the article]

Stomata are one of the important structures for plants to alleviate metal stress and improve plant resistance. Therefore, a study on the effects and mechanisms of heavy metal toxicity to stomata is indispensable in clarifying the adaptation mechanism of plants to heavy metals. With the rapid pace of industrialization and urbanization, heavy metal pollution has been an environmental issue of global concern. Stomata, a special physiological structure of plants, play an important role in maintaining plant physiological and ecological functions. Recent studies have shown that heavy metals can affect the structure and function of stomata, leading to changes in plant physiology and ecology. However, although the scientific community has accumulated some data on the effects of heavy metals on plant stomata, the systematic understanding of the effects of heavy metals on plant stomata remains limited. Therefore, in this review, we present the sources and migration pathways of heavy metals in plant stomata, analyze systematically the physiological and ecological responses of stomata on heavy metal exposure, and summarize the current mechanisms of heavy metal toxicity on stomata. Finally, the future research perspectives of the effects of heavy metals on plant stomata are identified. This paper can serve as a reference for the ecological assessment of heavy metals and the protection of plant resources. [ABSTRACT FROM AUTHOR]

Summary: Guard cells control the opening of stomatal pores in the leaf surface, with the use of a network of protein kinases and phosphatases. Loss of function of the CBL‐interacting protein kinase 23 (CIPK23) was previously shown to decrease the stomatal conductance, but the molecular mechanisms underlying this response still need to be clarified.CIPK23 was specifically expressed in Arabidopsis guard cells, using an estrogen‐inducible system. Stomatal movements were linked to changes in ion channel activity, determined with double‐barreled intracellular electrodes in guard cells and with the two‐electrode voltage clamp technique in Xenopus oocytes.Expression of the phosphomimetic variant CIPK23T190D enhanced stomatal opening, while the natural CIPK23 and a kinase‐inactive CIPK23K60N variant did not affect stomatal movements. Overexpression of CIPK23T190D repressed the activity of S‐type anion channels, while their steady‐state activity was unchanged by CIPK23 and CIPK23K60N.We suggest that CIPK23 enhances the stomatal conductance at favorable growth conditions, via the regulation of several ion transport proteins in guard cells. The inhibition of SLAC1‐type anion channels is an important facet of this response. [ABSTRACT FROM AUTHOR]

Lettuce (Lactuca sativa L.) prefers cool environments, and high temperatures affect its yield and quality. Polyamines (PAs) have a mitigating effect on plant abiotic stresses. The effect of exogenous spermidine (Spd) on the osmoregulatory substances and stomata of seedlings of the non-heat-tolerant lettuce variety 'Bei San 3' under high temperature stress was investigated at 35 °C/30 °C (day/night) under spray treatment with Spd. The results showed that exogenous Spd increased the total fresh weight, root-to-shoot ratio, leaf length, leaf width, root volume, and root surface area of lettuce under high temperature stress and reduced levels of malondialdehyde. The endogenous polyamine content was changed, and endogenous spermidine (Spd) and putrescine (Put) were increased. The accumulation of six organic osmoregulatory substances was promoted, resulting in enhanced betaine aldehyde dehydrogenase (BADH), choline monooxygenase (CMO), proline catalase pyrroline-5-carboxylate synthase (P5CS), ornithine aminotransferase (OAT), and pyrroline-5-carboxylate reductase (P5CR) activity. The production and activity of the degrading enzymes proline dehydrogenase (PDH) and proline oxidase (POX) were inhibited, and the activity of glutamic acid decarboxylase (GAD), the key enzyme of γ-aminobutyric (GABA), was suppressed. In addition, exogenous Spd increased the contents of Ca, K, Fe, Mn, Zn, and NO3− ions in lettuce leaves under high temperature stress, promoted K+ efflux and Ca2+ influx, and reduced the relative stomatal aperture. In summary, exogenous Spd mitigates lettuce injury caused by high temperature stress by increasing the content of osmoregulatory substances and altering stomatal morphology. [ABSTRACT FROM AUTHOR]

Plants are a vital component of human life on Earth; they provide us with food and essential nutrients as well as the oxygen we breathe. However, the science education community struggles to find ways to make plant processes less abstract and more understandable for learners. In this article we demonstrate how we make plant processes more understandable for learners by observing the behaviors of a specific plant structure, a stoma, which is a microscopic opening that plays a role in the movement of matter into and out of a plant. Recent research across plant-related science fields centers on plant stomata because they protect plants from various environmental strains, including attacks from pathogens. Translating this research into science classroom instruction has not occurred extensively. A key impediment is that few common methods to make stomata visible or demonstrate their dynamic nature to learners are available. The activities we share here make stomata visible utilizing a specific plant, Tradescantia zebrina, and common laboratory equipment. In the first activity, we share how to demonstrate stomata closing and opening by manipulating a combination of these environmental factors. In the second activity, we describe how to create a visual simulation of stomata response to attacks from microorganisms. [ABSTRACT FROM AUTHOR]

Stomatal movements allow the uptake of CO 2 for photosynthesis and water loss through transpiration, therefore play a crucial role in determining water use efficiency. Both red and blue lights induce stomatal opening, and the stomatal apertures under light are finetuned by both positive and negative regulators in guard cells. However, the molecular mechanisms for precisely adjusting stomatal apertures under light have not been completely understood. Here, we provided evidence supporting that Arabidopsis thaliana mitogen-activated protein kinase 11 (MPK11) plays a negative role in red light-induced stomatal opening. First, MPK11 was found to be highly expressed in guard cells, and MPK11-GFP signals were detected in both nuclear and cytoplasm of guard cells. The transcript levels of MPK11 in guard cells were upregulated by white light, and the stomata of mpk11 opened wider than that of wild type under white light. Consistent with the larger stomatal aperture, mpk11 mutant exhibited higher stomatal conductance and CO 2 assimilation rate under white light. The transcript levels of the genes responsible for osmolytes increases were higher in guard cells of mpk11 than that of wild type, which may contribute to the larger stomatal aperture of mpk11 under white light. Furthermore, MPK11 transcript levels in guard cells were upregulated by red light, and mpk11 mutant showed a larger stomatal aperture under red light. Taken together, these results demonstrate that red light-upregulated MPK11 plays a negative role in stomatal opening, which finetuning the stomatal opening apertures and preventing excessive water loss by transpiration under light. • MPK11 is highly expressed in guard cells. • The expressions of MPK11 in guard cells are upregulated by red light. • MPK11 negatively regulates red light-induced stomatal opening. • MPK11 contributes to the fine-tuning of the stomatal apertures under light. [ABSTRACT FROM AUTHOR]

A special feature found in Amaryllidaceae is that some guard cells of the neighboring stomata form a "connection strand" between their dorsal cell walls. In the present work, this strand was studied in terms of both its composition and its effect on the morphology and function of the stomata in Pancratium maritimum L. leaves. The structure of stomata and their connection strand were studied by light and transmission electron microscopy. FM 4–64 and aniline blue staining and application of tannic acid were performed to detect cell membranes, callose, and pectins, respectively. A plasmolysis experiment was also performed. The composition of the connection strand was analyzed by fluorescence microscopy after immunostaining with several cell-wall-related antibodies, while pectinase treatment was applied to confirm the presence of pectins in the connection strand. To examine the effect of this connection on stomatal function, several morphological characteristics (width, length, size, pore aperture, stomatal distance, and cell size of the intermediate pavement cell) were studied. It is suggested that the connecting strand consists of cell wall material laid through the middle of the intermediate pavement cell adjoining the two stomata. These cell wall strands are mainly comprised of pectins, and crystalline cellulose and extensins were also present. Connected stomata do not open like the single stomata do, indicating that the connection strand could also affect stomatal function. This trait is common to other Amaryllidaceae representatives. [ABSTRACT FROM AUTHOR]

The local endocytosis of membrane proteins is critical for many physiological processes in plants, including the regulation of growth, development, nutrient absorption, and osmotic stress response. Much of our knowledge on the local endocytosis of plasma membrane (PM) protein only focuses on the polar growth of pollen tubes in plants and neuronal axon in animals. However, the role of local endocytosis of PM proteins in guard cells has not yet been researched. Here, we first cloned duckweed SUT2 (sucrose transporter 2) protein and then conducted subcellular and histological localization of the protein. Our results indicated that LpSUT2 (Landoltia punctata 0202 SUT2) is a PM protein highly expressed on guard cells. In vitro experiments on WT (wild type) lines treated with high sucrose concentration showed that the content of ROS (reactive oxygen species) in guard cells increased and stomatal conductance decreased. We observed the same results in the lines after overexpression of the LpSUT2 gene with newfound local endocytosis of LpSUT2. The local endocytosis mainly showed that LpSUT2 was uniformly distributed on the PM of guard cells in the early stage of development, and was only distributed in the endomembrane of guard cells in the mature stage. Therefore, we found the phenomenon of guard cell LpSUT2 local endocytosis through the changes of duckweed stomata and concluded that LpSUT2 local endocytosis might be dependent on ROS accumulation in the development of duckweed guard cells. This paper might provide future references for the genetic improvement and water-use efficiency in other crops. [ABSTRACT FROM AUTHOR]

An understanding of stomatal function is vital for the carbon and water cycle in nature. In the past decades, various stomatal models with different functions have been established to investigate and predict stomatal behavior and its association with plants' responses to the changing climate, but with limited biological information provided. On the other hand, many stomatal models at the molecular level focus on simulating and predicting molecular practices and ignore the dynamic quantitative information. As a result, stomatal models are often divided between the microscopic and macroscopic scales. Quantitative systems analysis offers an effective in silico approach to explore the link between microscopic gene function and macroscopic physiological traits. As a first step, a systems model, OnGuard, is developed for the investigation of guard cell ion homeostasis and its relevance to the dynamic stomatal movements. The system model has already yielded a series of important predictions to guide molecular physiological studies in stomata. It also exhibits great potential in breeding practice, which represents a key step toward "Breeding by design" of improving plant carbon–water use efficiency. Here, the development of stomatal models is reviewed, and the future perspectives on stomatal modeling for agricultural and ecological applications are discussed. [ABSTRACT FROM AUTHOR]

Transient stimulus-specific increases in the cytosolic Ca 2+ concentration ("calcium signatures") of guard cells have been proposed to regulate the opening and closure of stomatal pores on plant leaves. However, the mechanism by which these Ca 2+ signatures are generated and translated into stomatal movement is still largely unresolved. We used a light-gated, Ca 2+ -permeable variant of ChannelRhodopsin 2 (ChR2-XXM2.0) that was stimulated by tailored light pulses to investigate this phenomenon. We found that activation of the ChR2-XXM2.0 channel provoked characteristic increases in the cytosolic concentration of Ca 2+ . We also demonstrated that the endoplasmic reticulum (ER) was involved in the generation of these calcium signatures. Using ChR2-XXM2.0 technology, we showed that transient increases in Ca 2+ activated S-type anion channels and determined the extent and speed of stomatal closure with their number and frequency. Our data reveal that guard cells are capable of counting Ca 2+ transients in order to optimize stomatal aperture in the prevailing environmental conditions., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2024 The Authors. Published by Elsevier Inc. All rights reserved.)

Background and Aims: The Montgomery-Koyama-Smith (MKS) equation predicts that total leaf area per shoot is proportional to the product of the sum of individual leaf widths and maximum individual leaf length, which has been validated for some herbaceous and woody plants. The equation is also predicted to be valid in describing the relationship between the total stomatal area per micrograph (AT) and the product of the sum of individual stomatal widths (denoted as LKS) and maximum individual stomatal length (denoted by WKS) in any particular micrograph., Methods: To test the validity of the MKS equation, 69,931 stomata (from 720 stomatal micrographs from 12 Magnoliaceae species) were examined. The area of each stoma was calculated using empirical measurements of stomatal length and width multiplied by a constant. Six equations describing the relationships among AT, LKS, and WKS were compared. The root-mean-square (RMSE) and the Akaike information criterion (AIC) were used to measure the goodness of fit, and the trade-off between the goodness of fit and the structural complexity of each model, respectively., Key Results: Analyses supported the validity of the MKS equation and the power-law equation AT ∝ (LKS∙WKS)α, where a is a scaling exponent. The estimated values of α at the species level and for the pooled data were all statistically smaller than unity, which did not support the hypothesis that AT ∝ LTS∙WTS. The power-law equation had smaller RMSE and AIC values than the MKS equation for the data from the 12 individual species and the pooled data., Conclusions: These results indicate that AT tends to allometrically scale with LKS∙WKS, and that increases in AT do not keep pace with increases in LTS∙WTS. In addition, using the product of LKS and WKS is better than using only one of the two variables., (© The Author(s) 2024. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved. For commercial re-use, please contact reprints@oup.com for reprints and translation rights for reprints. All other permissions can be obtained through our RightsLink service via the Permissions link on the article page on our site—for further information please contact journals.permissions@oup.com.)

Summary: A trait coordination network is constructed through intercorrelations of functional traits, which reflect trait‐based adaptive strategies. However, little is known about how these networks change across spatial scales, and what drivers and mechanisms mediate this change.This study bridges that gap by integrating functional traits related to plant carbon gain and water economy into the coordination network of Siberian elm (Ulmus pumila), a eurybiont that survives along a 3800 km environmental gradient from humid forest to arid desert.Our results demonstrated that both stomatal density and stomatal size reached a physiological threshold at which adjustments in these traits were not sufficient to cope with the increased environmental stress. Network analysis further revealed that the mechanism for overcoming this threshold, the stomatal opening ratio, gratio, was represented by the highest values for centrality across different spatial scales, and therefore mediated the changes in the trait coordination network along environmental gradients. The mediating roles manifested as creating the highest maximum theoretical stomatal conductance (gsmax) but lowest possible gratio for pathogen defense in humid regions, while maintaining the gratio 'sweet spot' (c. 20% in this region) for highest water use efficiency in semihumid regions, and having the lowest gsmax and highest gratio for gas exchange and leaf cooling in arid regions.These results suggested that the stomatal traits related to control of stomatal movement play fundamental roles in balancing gas exchange, leaf cooling, embolism resistance and pathogen defense. These insights will allow more accurate model parameterization for different regions, and therefore better predictions of species' responses to global change. [ABSTRACT FROM AUTHOR]

Guard‐cell‐type aluminium‐activated malate transporters (ALMTs) are involved in stomatal closure by exporting anions from guard cells. However, their physiological and electrophysiological functions are yet to be explored. Here, we analysed the physiological and electrophysiological properties of the ALMT channels in Arabidopsis and tomato (Solanum lycopersicum). SlALMT11 was specifically expressed in tomato guard cells. External malate‐induced stomatal closure was impaired in ALMT‐suppressed lines of tomato and Arabidopsis, although abscisic acid did not influence the stomatal response in SlALMT11‐knock‐down tomato lines. Electrophysiological analyses in Xenopus oocytes showed that SlALMT11 and AtALMT12/QUAC1 exhibited characteristic bell‐shaped current‐voltage patterns dependent on extracellular malate, fumarate, and citrate. Both ALMTs could transport malate, fumarate, and succinate, but not citrate, suggesting that the guard‐cell‐type ALMTs are dicarboxylic anion channels activated by extracellular organic acids. The truncation of acidic amino acids, Asp or Glu, from the C‐terminal end of SlALMT11 or AtALMT12/QUAC1 led to the disappearance of the bell‐shaped current‐voltage patterns. Our findings establish that malate‐activated stomatal closure is mediated by guard‐cell‐type ALMT channels that require an acidic amino acid in the C‐terminus as a candidate voltage sensor in both tomato and Arabidopsis. Summary statement: Apoplastic malate induces stomatal closure mediated by ALMT‐type anion channels (SlALMT11 and AtALMT12/QUAC1) of which voltage gating requires an acidic amino acid at the C‐terminal end. [ABSTRACT FROM AUTHOR]

Drought stress limits plant development and reproduction. Multiple mechanisms in plants are activated to respond to stress. The MYC2 transcription factor is a core regulator of the jasmonate (JA) pathway and plays a vital role in the crosstalk between abscisic acid (ABA) and JA. In this study, we found that SlMYC2 responded to drought stress and regulated stomatal aperture in tomato (Solanum lycopersicum). Overexpression of SlMYC2 repressed SlCHS1 expression and decreased the flavonol content, increased the reactive oxygen species (ROS) content in guard cells and promoted the accumulation of JA and ABA in leaves. Additionally, silencing the SlCHS1 gene produced a phenotype that was similar to that of the MYC2-overexpressing (MYC2-OE) strain, especially in terms of stomatal dynamics and ROS levels. Finally, we confirmed that SlMYC2 directly repressed the expression of SlCHS1. Our study revealed that SlMYC2 drove stomatal closure by modulating the accumulation of flavonol and the JA and ABA contents, helping us decipher the mechanism of stomatal movement under drought stress. [ABSTRACT FROM AUTHOR]

Sodium ions (Na+) negatively affect most land plant species as a consequence of both general osmotic effects and specific ion toxicity. Na+ travels through the plant body via the transpiration stream, and this results in direct exposure of guard cells to apoplastic Na+. This article summarizes extant literature on short- and long-term stomatal conductance responses to salinity, stomatal movements of isolated guard cells in response to NaCl, and guard cell ion content following NaCl exposure. We discuss the potential role of Na+ as an osmoticum that itself could drive guard cell swelling and stomatal opening, possible contributions of carbohydrates in guard cell osmoregulation following NaCl exposure, and the role of ABA in stomatal responses to salinity. We highlight responses of glycophytes vs halophytes when comparative information is available. Based on our integration of published information, we propose that salt sensitivity arises in part by glycophytic guard cell uptake of Na+ and resultant short-term stomatal opening that promotes plant desiccation and toxic accumulation of Na+ in the leaf. However, many aspects of guard cell Na+ sensing, transport, and response remain unknown, and new studies are required both to test this hypothesis and to address numerous knowledge gaps. [ABSTRACT FROM AUTHOR]

Flowers consist of four whorls of organs (sepals, petals, stamens, and carpels), each expressing unique characteristics. In floral homeotic mutants, organs develop abnormally, and floral organs of one whorl express characteristics of another whorl. Much of our current understanding of the development of floral organs has been based on studies of floral homeotic mutants. In the homeotic mutant crinkle-petal (cp) of Clarkia tembloriensis, previous investigations demonstrated that the cp petal is a hybrid organ combining characteristics of sepals and petals. This investigation extends those studies with a comparative anatomical study of trichomes, guard cells, and marginal epidermal cells in wild-type (WT) sepals, WT petals, and cp petals. The aim was to determine if cp petals exhibit a hybrid epidermal anatomy of WT sepals and WT petals. Floral buds 1 day pre-anthesis and flowers 1 day post-anthesis were collected and prepared for light microscopy or scanning electron microscopy. Trichomes and guard cell pairs were described and counted, and marginal cells were observed and described. This anatomical study of trichomes, guard cells, and marginal cells demonstrated that cp petals of C. tembloriensis combine characteristics of both WT sepals and WT petals. These results provide further support for the hybrid nature of cp petals in Clarkia tembloriensis. [ABSTRACT FROM AUTHOR]

Stomata are one of the important structures for plants to alleviate metal stress and improve plant resistance. Therefore, a study on the effects and mechanisms of heavy metal toxicity to stomata is indispensable in clarifying the adaptation mechanism of plants to heavy metals. With the rapid pace of industrialization and urbanization, heavy metal pollution has been an environmental issue of global concern. Stomata, a special physiological structure of plants, play an important role in maintaining plant physiological and ecological functions. Recent studies have shown that heavy metals can affect the structure and function of stomata, leading to changes in plant physiology and ecology. However, although the scientific community has accumulated some data on the effects of heavy metals on plant stomata, the systematic understanding of the effects of heavy metals on plant stomata remains limited. Therefore, in this review, we present the sources and migration pathways of heavy metals in plant stomata, analyze systematically the physiological and ecological responses of stomata on heavy metal exposure, and summarize the current mechanisms of heavy metal toxicity on stomata. Finally, the future research perspectives of the effects of heavy metals on plant stomata are identified. This paper can serve as a reference for the ecological assessment of heavy metals and the protection of plant resources.

The linker of nucleoskeleton and cytoskeleton (LINC) complex is a protein complex spanning the inner and outer membranes of the nuclear envelope. Outer nuclear membrane KASH proteins interact in the nuclear envelope lumen with inner nuclear membrane SUN proteins. The paralogous Arabidopsis KASH proteins SINE1 and SINE2 function during stomatal dynamics induced by light–dark transitions and ABA. Previous studies have shown F-actin organization, cytoplasmic calcium (Ca2+) oscillations, and vacuolar morphology changes are involved in ABA-induced stomatal closure. Here, we show that SINE1 and SINE2 are both required for actin pattern changes during ABA-induced stomatal closure, but influence different, temporally distinguishable steps. External Ca2+ partially overrides the mutant defects. ABA-induced cytoplasmic Ca2+ oscillations are diminished in sine2-1 but not sine1-1 , and this defect can be rescued by both exogenous Ca2+ and F-actin depolymerization. We show first evidence for nuclear Ca2+ oscillations during ABA-induced stomatal closure, which are disrupted in sine2-1. Vacuolar fragmentation is impaired in both mutants and is partially rescued by F-actin depolymerization. Together, these data indicate distinct roles for SINE1 and SINE2 upstream of this network of players involved in ABA-based stomatal closure, suggesting a role for the nuclear surface in guard cell ABA signaling. [ABSTRACT FROM AUTHOR]

The linker of nucleoskeleton and cytoskeleton (LINC) complex is a protein complex spanning the inner and outer membranes of the nuclear envelope. Outer nuclear membrane KASH proteins interact in the nuclear envelope lumen with inner nuclear membrane SUN proteins. The paralogous Arabidopsis KASH proteins SINE1 and SINE2 function during stomatal dynamics induced by light–dark transitions and ABA. Previous studies have shown F-actin organization, cytoplasmic calcium (Ca2+) oscillations, and vacuolar morphology changes are involved in ABA-induced stomatal closure. Here, we show that SINE1 and SINE2 are both required for actin pattern changes during ABA-induced stomatal closure, but influence different, temporally distinguishable steps. External Ca2+ partially overrides the mutant defects. ABA-induced cytoplasmic Ca2+ oscillations are diminished in sine2-1 but not sine1-1, and this defect can be rescued by both exogenous Ca2+ and F-actin depolymerization. We show first evidence for nuclear Ca2+ oscillations during ABA-induced stomatal closure, which are disrupted in sine2-1. Vacuolar fragmentation is impaired in both mutants and is partially rescued by F-actin depolymerization. Together, these data indicate distinct roles for SINE1 and SINE2 upstream of this network of players involved in ABA-based stomatal closure, suggesting a role for the nuclear surface in guard cell ABA signaling.

The use of nanomaterials has been very recently introduced in plant biotechnologies, for both the monitoring and the enhancement of plants functions. Several functional interfaces between living plants and nanotechnology have been successfully reported for diverse applications, from sensing to photosynthesis and energy production and from modulation of physiological activity to controlled delivery of chemicals. In this work, a photoactive, biohybrid interface based on a prototypical semiconducting polymer, sensitive to green light, and Arabidopsis thaliana plants is reported. Optical excitation of polymer beads is shown to deterministically regulate the Arabidopsis stomatal aperture, the leaf pores which regulate the plant carbon dioxide uptake, oxygen release, and transpiration processes. Moreover, it is observed that excitation of bio‐polymer hybrid interfaces optically modulates the cytosolic calcium ions concentration, which is involved, as a second messenger, in the regulation of stomatal movements. The results support the possibility to employ light‐responsive organic materials to regulate on demand the physiological activity of plant systems, in a drug‐free, touchless, and easily controllable way. When transferred to the field, this strategy may represent an innovative approach to optimize the exchange of gases and water loss of plants, and to improve the plant resilience toward environmental constraints. [ABSTRACT FROM AUTHOR]

Stomatal guard cells are specialized epidermal cells regulating gas exchange. The ability to open or close in response to external and internal cues makes stomata a dynamic and fascinating system. Stomatal closure upon infection ensures restriction of pathogen entry into the plant and forms an essential component of innate immunity. The opening or closure of stomata is dependent on the turgidity or flaccidity of guard cells, respectively, facilitated by several signaling components, including reactive oxygen species, nitric oxide (NO) and Ca2+. Among these, NO is the most extensively studied gasotransmitter. Its pivotal role in stomatal closure by modulating various downstream components as well as regulation of crucial proteins by post-translational modifications makes NO an essential factor. Two more gasotransmitters, carbon monoxide and hydrogen sulfide, also trigger stomatal closure. Other gaseous molecules, like ethylene, methane, sulfur dioxide, ozone, and CO2, can modulate stomatal closure, but they are not considered strictly as gasotransmitters due to specific criteria. We review the signaling events in guard cells triggered by these gasotransmitters leading to stomatal closure. We point out the dual role of NO to promote stomatal closure and stomatal opening. Both NO and H2S help in reinforcing the innate immunity against pathogen attack. Although there is extensive information on the mechanism of NO action on stomata, the enzymatic source of NO or CO is still ambiguous. Similarly, research is warranted to establish the relative importance of and interactions among the three main gasotransmitters. Further studies on gasotransmitters would answer the ambiguity about their functions and confirm if they can act independently.

Stomata play a crucial role in plants by controlling water status and responding to drought stress. However, simultaneously improving stomatal opening and drought tolerance has proven to be a significant challenge. To address this issue, we employed the OnGuard quantitative model, which accurately represents the mechanics and coordination of ion transporters in guard cells. With the guidance of OnGuard, we successfully engineered plants that overexpressed the main tonoplast Ca 2+ -ATPase gene, ACA11, which promotes stomatal opening and enhances plant growth. Surprisingly, these transgenic plants also exhibited improved drought tolerance due to reduced water loss through their stomata. Again, OnGuard assisted us in understanding the mechanism behind the unexpected stomatal behaviors observed in the ACA11 overexpressing plants. Our study revealed that the overexpression of ACA11 facilitated the accumulation of Ca 2+ in the vacuole, thereby influencing Ca 2+ storage and leading to an enhanced Ca 2+ elevation in response to abscisic acid. This regulatory cascade finely tunes stomatal responses, ultimately leading to enhanced drought tolerance. Our findings underscore the importance of tonoplast Ca 2+ -ATPase in manipulating stomatal behavior and improving drought tolerance. Furthermore, these results highlight the diverse functions of tonoplast-localized ACA11 in response to different conditions, emphasizing its potential for future applications in plant enhancement., (© 2024 Institute of Botany, Chinese Academy of Sciences.)

Stomata are pores surrounded by a pair of specialized cells, called guard cells, that play a central role in plant physiology through the regulation of gas exchange between plants and the environment. Guard cells have features like cell-autonomous responses and easily measurable readouts that have turned them into a model system to study signal transduction mechanisms in plants. Here, we provide a detailed protocol to analyze different physiological responses specifically in guard cells. We describe, in detail, the steps and conditions to isolate epidermal peels with tweezers and to analyze i) stomatal aperture in response to different stimuli, ii) cytosolic parameters such as hydrogen peroxide (H 2 O 2 ), glutathione redox potential ( E GSH in vivo dynamics using fluorescent biosensors, and iii) gene expression in guard cell-enriched samples. The importance of this protocol lies in the fact that most living cells on epidermal peels are guard cells, enabling the preparation of guard cell-enriched samples. Key features • Isolation of epidermal peels as a monolayer enriched in guard cells • Measurement of cytosolic guard cell signaling component dynamics in isolated epidermal peels through fluorescent biosensor analysis • Gene expression analysis of guard cell-enriched isolated tissue.-2 in vivo dynamics using fluorescent biosensors, and iii) gene expression in guard cell-enriched samples. The importance of this protocol lies in the fact that most living cells on epidermal peels are guard cells, enabling the preparation of guard cell-enriched samples. Key features • Isolation of epidermal peels as a monolayer enriched in guard cells • Measurement of cytosolic guard cell signaling component dynamics in isolated epidermal peels through fluorescent biosensor analysis • Gene expression analysis of guard cell-enriched isolated tissue., Competing Interests: Competing interestsThe authors declare no competing interests., (©Copyright : © 2024 The Authors; This is an open access article under the CC BY-NC license.)

A special feature found in Amaryllidaceae is that some guard cells of the neighboring stomata form a “connection strand” between their dorsal cell walls. In the present work, this strand was studied in terms of both its composition and its effect on the morphology and function of the stomata in Pancratium maritimum L. leaves. The structure of stomata and their connection strand were studied by light and transmission electron microscopy. FM 4–64 and aniline blue staining and application of tannic acid were performed to detect cell membranes, callose, and pectins, respectively. A plasmolysis experiment was also performed. The composition of the connection strand was analyzed by fluorescence microscopy after immunostaining with several cell-wall-related antibodies, while pectinase treatment was applied to confirm the presence of pectins in the connection strand. To examine the effect of this connection on stomatal function, several morphological characteristics (width, length, size, pore aperture, stomatal distance, and cell size of the intermediate pavement cell) were studied. It is suggested that the connecting strand consists of cell wall material laid through the middle of the intermediate pavement cell adjoining the two stomata. These cell wall strands are mainly comprised of pectins, and crystalline cellulose and extensins were also present. Connected stomata do not open like the single stomata do, indicating that the connection strand could also affect stomatal function. This trait is common to other Amaryllidaceae representatives.