Optogenetic manipulation of stomatal kinetics improves carbon assimilation, water use, and growth

ROOT PHOTOTROPISM 2 (RPT2) is a KAT1 potassium channel regulator required for its accumulation

In plants, inward rectifying potassium channels regulate potassium entry into guard cells and are a key factor controlling stomatal opening. KAT1 is a major inward rectifying potassium channel present in Arabidopsis thaliana guard cell membranes. The identification of regulators of channels like KAT1 is a promising approach for the development of strategies to improve plant drought tolerance. Using a high-throughput Split-ubiquitin screening in yeast, we identified RPT2 (ROOT PHOTOTROPISM 2) as a KAT1 interactor. Here, we present the results of the characterization of this interaction in yeast and plants. Importantly, we also observe increased KAT1-mediated currents in oocytes co-expressing RPT2, suggesting a functional link between the two proteins. Moreover, using stably transformed KAT1-YFP lines, we show that RPT2 is necessary for KAT1 protein accumulation in A. thaliana. Our data suggest an unexpected role for RPT2 in KAT1 post-translational regulation that may represent a novel connection between light signaling and potassium channel activity.

Viewing Stomata in Action: Autonomous in Planta Imaging of Individual Stomatal Movement

Stomata regulate plant gas exchange under changing environments, but observations of single stomata dynamics in planta are sparse. We developed a compact microscope system that can measure the kinetics of tens of stomata in planta simultaneously, with sub-minute time resolution. Darkfield imaging with green light was used to create 3D stacks from which 2D surface projections were constructed to resolve stomatal apertures. Stomatal dynamics of Chrysanthemum morifolium (Chrysanthemum) and Zea mays (Maize) under changing light intensity were categorized, and a kinetic model was fitted to the data for quantitative comparison. Maize stomata transitioned frequently between open and closed states under constant growth light and these 'opening and closing' stomata, when closed, responded faster to a change to saturating light than steady-state closed stomata under the constant growth light. The faster opening response benefits CO2 uptake under saturating light. The slow closure of Chrysanthemum stomata reduced water use efficiency (WUE). Over 50% showed delayed or partial closure, leading to unnecessarily large apertures after reduced light. Stomata with larger apertures had more lag and similar closure speeds compared to those with smaller apertures and lag, further reducing WUE. In contrast, maize stomata with larger apertures closed faster, with no lag.

Impact of climate-driven changes in temperature on stomatal anatomy and physiology

Climate-driven changes in temperature are likely to have major implications for plant performance including impacts on stomatal conductance (gs), gaseous exchange, photosynthesis, leaf temperature and plant water use. Stomatal conductance is not only vital for carbon assimilation but also plays a key role in maintaining optimum leaf temperatures for cellular processes. Higher gs facilitates both CO2 uptake and enhanced evaporative leaf cooling, however, most likely at the cost of greater water loss and lower water-use efficiency. Lower gs helps to maintain overall plant water status but at the expense of C uptake with reduced evaporative cooling which, at elevated temperatures, could be lethal. It is therefore important for gs to balance these competing demands; however, with rapid changes in temperature due to climate change, stomatal engineering may be required to ensure that this balance is achieved and different strategies for different crops in different environments may be needed. Here, we review current knowledge of stomatal anatomical and behavioural responses to temperature-driven changes, focusing on both rising temperatures and extreme heat events and potential genetic targets for manipulation of relevant stomatal characteristics.This article is part of the theme issue 'Crops under stress: can we mitigate the impacts of climate change on agriculture and launch the 'Resilience Revolution'?'.

Metabolic engineering of stomatal precursor cells enhances photosynthetic water-use efficiency and vegetative growth under water-deficit conditions in Arabidopsis thaliana

Stomata are epidermal pores that control the exchange of gaseous CO2 and H2O between plants and their environment. Modulating stomatal density can alter this exchange and thus presents a viable target for engineering improved crop productivity and climate resilience. Here, we show that stomatal density in Arabidopsis thaliana can be decreased by the expression of a water-forming NAD(P)H oxidase targeted to stomatal precursor cells. We demonstrate that this reduction in stomatal density occurs irrespective of whether the expressed enzyme is localized to the cytosol, chloroplast stroma or chloroplast intermembrane space of these cells. We also reveal that this decrease in stomatal density occurs in the absence of any measurable impact on the efficiency and thermal sensitivity of photosynthesis, or on stomatal dynamics. Consequently, overexpression plants exhibit a higher intrinsic water-use efficiency due to an increase in CO2 fixed per unit water transpired. Finally, we demonstrate that this enhanced water-use efficiency translates to an improvement in vegetative growth and biomass accumulation under water-deficit conditions. Together, these results thus provide a novel approach for enhancing plant productivity through metabolic engineering of stomatal density.

Optimizing carbon and nitrogen metabolism in plants: From fundamental principles to practical applications

Carbon (C) and nitrogen (N) are fundamental elements essential for plant growth and development, serving as the structural and functional backbone of organic compounds and driving essential biological processes such as photosynthesis, carbohydrate metabolism, and N assimilation. The metabolism and transport of C involve the movement of sugars between shoots and roots through xylem and phloem transport systems, regulated by a sugar-signaling hub. Nitrogen uptake, transport, and metabolism are equally critical, with plants assimilating nitrate and ammonium through specialized transporters and enzymes in response to varying N levels to optimize growth and development. The coordination of C and N metabolism is key to plant productivity and the maintaining of agroecosystem stability. However, inefficient utilization of N fertilizers results in substantial environmental and economic challenges, emphasizing the urgent need to improve N use efficiency (NUE) in crops. Integrating efficient photosynthesis with N uptake offers opportunities for sustainable agricultural practices. This review discusses recent advances in understanding C and N transport, metabolism, and signaling in plants, with a particular emphasis on NUE-related genes in rice, and explores breeding strategies to enhance crop efficiency and agricultural sustainability.

Engineering plant photoreceptors towards enhancing plant productivity

Light is a critical environmental factor that governs the growth and development of plants. Plants have specialised photoreceptor proteins, which allow them to sense both quality and quantity of light and drive a wide range of responses critical for optimising growth, resource use and adaptation to changes in environment. Understanding the role of these photoreceptors in plant biology has opened up potential avenues for engineering crops with enhanced productivity by engineering photoreceptor activity and/or action. The ability to manipulate plant genomes through genetic engineering and synthetic biology approaches offers the potential to unlock new agricultural innovations by fine-tuning photoreceptors or photoreceptor pathways that control plant traits of agronomic significance. Additionally, optogenetic tools which allow for precise, light-triggered control of plant responses are emerging as powerful technologies for real-time manipulation of plant cellular responses. As these technologies continue to develop, the integration of photoreceptor engineering and optogenetics into crop breeding programs could potentially revolutionise how plant researchers tackle challenges of plant productivity. Here we provide an overview on the roles of key photoreceptors in regulating agronomically important traits, the current state of plant photoreceptor engineering, the emerging use of optogenetics and synthetic biology, and the practical considerations of applying these approaches to crop improvement. This review seeks to highlight both opportunities and challenges in harnessing photoreceptor engineering approaches for enhancing plant productivity. In this review, we provide an overview on the roles of key photoreceptors in regulating agronomically important traits, the current state of plant photoreceptor engineering, the emerging use of optogenetics and synthetic biology, and the practical considerations of applying these approaches to crop improvement.

Induction of Chirality in MXene Nanosheets and Derived Quantum Dots: Chiral Mixed-Low-Dimensional Ti3C2Tx Biomaterials as Potential Agricultural Biostimulants for Enhancing Plant Tolerance to Different Abiotic Stresses

This work presents two advancements in the engineering design and bio-applications of emerging MXene nanosheets and derived quantum dots. First, a facile, versatile, and universal strategy is showcased for inducing the right- or left-handed chirality into the surface of titanium carbide-based MXene (Ti3C2Tx) to form stable mixed-low-dimensional chiral MXene biomaterials with enhanced aqueous colloidal dispersibility and debonding tolerance, mimicking the natural asymmetric bio-structure of most biomolecules and living organisms. In particular, Ti3C2Tx MXene nanosheets are functionalized with carboxyl-based terminals and bound feasibly with the D/L-cysteine amino acid ligands. The physicochemical characterizations of these 2D-0D/1D chiral MXene heterostructures suggest the inclusion of Ti3C2Tx nanosheets and different levels of self-derived MXene quantum dots and surface titanium-oxide nanoparticles, providing enhanced material stability and oxidative degradation resistance for tested months. Further, the interaction and molecular binding at cysteine-Ti3C2Tx/Ti-oxide interfaces, associated ion transport and ionic conductivity analysis, and charge re/distribution mechanisms are evaluated using density functional theory (DFT) calculations and electrochemical impedance spectroscopy (EIS) measurements. The second uniqueness of this study relies on the multifunctional application of optimal chiral MXenes as potential nano-biostimulants for enhancing plant tolerance to different abiotic conditions, including severe drought, salinity, or light stress. This surface tailoring enables high biocompatibility with the seed/seedling/plant of Arabidopsis thaliana alongside promoting multi-bioactivities for enhanced seed-to-seedling transition, seedling germination/maturation, plant-induced stomatal closure, and ROS production eliciting responses. Given that the induced chirality is a pivotal factor in many agro-stimulants and amino acid-containing fertilizers for enhanced interaction with plant cells/enzymes, boosting stress tolerance, nutrient uptake, and growth, these findings open up new avenues toward multiple applications of chiral MXene biomaterials as next-generation carbon-based nano-biostimulants in agriculture.

Propionic Acid Signalling Modulates Stomatal Opening and Drives Energy Metabolism to Enhance Drought Resistance in Wheat (Triticum aestivum L.)

Drought stress caused by global climate change severely imperils crop productivity and increases environmental deterioration. Wheat (Triticum aestivum L.) is an important worldwide food crop. Drought resistance in wheat encompasses functional gene transcription, metabolism, hormone signalling, and protein modifications. However, the underlying mechanisms by which these regulatory responses are coordinated remain unknown. Herein, we report a drought-resistance network in which wheat triggers a dynamic metabolic flux conversion from propionic acid (PA) to the tricarboxylic acid (TCA) cycle through beta-oxidation of fatty acids and stimulates crosstalk of various hormonal signals. It is also possible that P300/CREB regulates histone acetylation to confer drought resistance in wheat. Exogenous PA drives the TCA cycle and glycolysis and promotes stomatal closure through hormones crosstalk. From Aegilops tauschii Cosson (the diploid progenitor of common wheat) to wheat, this novel PA function serves as a survival strategy against environmental changes, and was validated in wheat field experiments. Our results highlight a new survival strategy that triggers the comprehensive and systemic effects of functional genes, metabolomics, hormone signalling, and protein modification on drought resistance to provide novel insights into improving the agroecological environment.

Genome-Wide Identification of the Dof Gene Family and Functional Analysis of PeSCAP1 in Regulating Guard Cell Maturation in Populus euphratica

DNA-binding with one finger (Dof) transcription factors plays critical roles in regulating plant growth and development, as well as modulating responses to biotic and abiotic stresses. While the biological characteristics of the Dof family have been explored across various species, their functions in Populus euphratica remain largely uncharacterized. In this study, we identified 43 PeDof family genes through a genome-wide approach, revealing a total of 10 conserved motifs across all family members. Predictions of cis-acting elements indicated that Dof genes are involved in light signaling, hormone signaling, and stress responses. Phylogenetic analysis classified the 43 Dof genes of P. euphratica into six distinct groups, with genes within the same group exhibiting relatively conserved structures. Expression pattern analyses demonstrated significant regulation of PeDof genes by drought stress, with their expression also being influenced by environmental conditions during seed germination. Furthermore, we identified the Dof gene PeSCAP1, which plays a conserved role in regulating guard cell maturation, underscoring the importance of stomatal morphology and function in leaf water retention. This study enhances our understanding of the role of Dofs in abiotic stress responses and provides valuable insights into their function in Populus euphratica.

Genetic diversity of leaf photosynthesis under fluctuating light conditions among temperate japonica rice varieties

Under field conditions, solar radiation on a crop canopy fluctuates according to clouds, wind, and self-shading. The slower response of photosynthesis compared with the rate of irradiation changes leads to loss of photosynthetic carbon gain. Although some genetic differences in the rate of photosynthetic induction have been reported, the diversity among rice varieties is largely unknown. Here we evaluated genetic variation in the response of photosynthesis to a step increase in light intensity among 166 temperate japonica varieties including landraces and modern varieties. Large genetic variation in photosynthetic induction and less evidence of improvement across modern breeding programmes were acknowledged. In the correlation analysis between physiological traits for all varieties, the efficiency of non-stomatal processes was the major factor affecting the rate of induction. The landrace Aikokumochi, which has intermediate photosynthetic capacity, showed rapid photosynthetic induction-eight times that of the slowest variety. This was attributed to smaller non-stomatal limitation in the initial phase of induction and smaller stomatal limitation in the later phase than in reference varieties. Aikokumochi also had a greater photosynthetic CO2 gain without reduced water use efficiency under repeated fluctuating light. These findings demonstrate the importance of genetic resources to improve photosynthesis while maintaining water use efficiency under fluctuating light conditions.

Dynamics of homeostats: the basis of electrical, chemical, hydraulic, pH and calcium signaling in plants

Homeostats are important to control homeostatic conditions. Here, we have analyzed the theoretical basis of their dynamic properties by bringing the K homeostat out of steady state (i) by an electrical stimulus, (ii) by an external imbalance in the K+ or H+ gradient or (iii) by a readjustment of transporter activities. The reactions to such changes can be divided into (i) a short-term response (tens of milliseconds), where the membrane voltage changed along with the concentrations of ions that are not very abundant in the cytosol (H+ and Ca2+), and (ii) a long-term response (minutes and longer) caused by the slow changes in K+ concentrations. The mechanistic insights into its dynamics are not limited to the K homeostat but can be generalized, providing a new perspective on electrical, chemical, hydraulic, pH and Ca2+ signaling in plants. The results presented here also provide a theoretical background for optogenetic experiments in plants.

GORK K+ channel structure and gating vital to informing stomatal engineering

The Arabidopsis GORK channel is a major pathway for guard cell K+ efflux that facilitates stomatal closure. GORK is an outwardly-rectifying member of the cyclic-nucleotide binding-homology domain (CNBHD) family of K+ channels with close homologues in all other angiosperms known to date. Its bioengineering has demonstrated the potential for enhanced carbon assimilation and water use efficiency. Here we identify critical domains through structural and functional analysis, highlighting conformations that reflect long-lived closed and pre-open states of GORK. These conformations are marked by interactions at the cytosolic face of the membrane between so-called voltage-sensor, C-linker and CNBHD domains, the latter relocating across 10 Å below the voltage sensor. The interactions center around two coupling sites that functional analysis establish are critical for channel gating. The channel is also subject to putative, ligand-like interactions within the CNBHD, which leads to its gating independence of cyclic nucleotides such as cAMP or cGMP. These findings implicate a multi-step mechanism of semi-independent conformational transitions that underlie channel activity and offer promising new sites for optimizing GORK to engineer stomata.

Difference in single-leaf and whole-plant photosynthetic response to light under steady and non-steady states in Arabidopsis thaliana

Although photosynthetic response to light has been extensively studied at the single-leaf level, little is known about the response at the whole-plant level. The present study aims to reveal the differences in the photosynthetic response to light under steady and non-steady states between the single leaf and whole plant in Arabidopsis thaliana and to investigate the mechanisms underlying these differences with respect to leaf aging. First, we developed an open system for gas exchange measurement of the whole plant of Arabidopsis. It enabled the photosynthetic response to dynamic environmental changes to be directly compared between the single leaf and whole plant. The photosynthetic response to the fluctuating light did not differ significantly between the single leaf and whole plant. This result is partly confirmed by the fact that the leaves at different ages showed no difference in the photosynthetic induction after a step change in light. On the other hand, light response analysis for steady-state photosynthesis showed a higher apparent quantum yield in the whole plant than in the single leaf. This difference might be attributed to the difference in the efficiency of light absorption and/or utilization of absorbed light among the leaves at different ages.

A C4 plant K+ channel accelerates stomata to enhance C3 photosynthesis and water use efficiency

Accelerating stomatal kinetics through synthetic optogenetics and mutations that enhance guard cell K+ flux has proven a viable strategy to improve water use efficiency and biomass production. Stomata of the model C4 species Gynandropsis gynandra, a relative of the C3 plant Arabidopsis thaliana, are similarly fast to open and close. We identified and cloned the guard cell rectifying outward K+ channel (GROK) of Gynandropsis and showed that GROK is preferentially expressed in stomatal guard cells. GROK is homologous to the Arabidopsis guard cell K+ channel GORK and, expressed in oocytes, yields a K+ current consistent with that of Gynandropsis guard cells. Complementing the Arabidopsis gork mutant with GROK promoted K+ channel gating and K+ flux, increasing stomatal kinetics and yielding gains in water use efficiency and biomass with varying light, especially under water limitation. Our findings demonstrate the potential for engineering a C4 K+ channel into guard cells of a C3 species, and they speak to the puzzle of how C4 species have evolved mechanisms that enhance water use efficiency and growth under stress.

Light-activated channelrhodopsins: a revolutionary toolkit for the remote control of plant signalling

Channelrhodopsins (CHRs), originating within algae and protists, are membrane-spanning ion channel proteins that are directly activated and/or deactivated by specific wavelengths of light. Since 2005, CHRs have been deployed as genetically encoded optogenetic tools to rapidly advance understanding of neuronal networks. CHRs provide the opportunity to finely tune ion transport across membranes and regulate membrane potential. These are fundamental biochemical signals, which in plants can be translated into physiological and developmental responses such as changes in photosynthesis, growth, turgor, vascular hydraulics, phosphorylation or reactive oxygen species (ROS) status, gene expression, or even cell death. Exploration of CHR family diversity and structure-function engineering has led to the expansion of the CHR optogenetic toolbox, offering unparalleled opportunities to precisely control and understand electrical and secondary messenger signalling in higher plants. In this Tansley Insight, we provide an overview of the recent progress in the application of CHR optogenetics in higher plants and discuss their possible uses in the remote control of plant biology, illuminating a new future domain for plant research enabled through synthetic biology.

Leveraging light-gated channelrhodopsins for strengthening plant physiological responses

Strengthening plant physiological traits is crucial for sustainable plant improvement. The underlying molecular mechanisms of rhodopsin-based plant improvement remain largely unknown. However, a recent study by Ding et al. offers some insights by exploring how light-gated channelrhodopsins regulate cytosolic Ca2+ conductance, reactive oxygen species (ROS) signals, and plant defense responses in tobacco.

Potassium extrusion by plant cells: evolution from an emergency valve to a driver of long-distance transport

The ability to accumulate nutrients is a hallmark for living creatures and plants evolved highly effective nutrient transport systems, especially for the uptake of potassium (K+). However, plants also developed mechanisms that enable the rapid extrusion of K+ in combination with anions. The combined release of K+ and anions is probably an ancient extrusion system, as it is found in the Characeae that are closely related to land plants. We postulate that the ion extrusion mechanisms have developed as an emergency valve, which enabled plant cells to rapidly reduce their turgor, and prevent them from bursting. Later in evolution, seed plants adapted this system for various responses, such as the closure of stomata, long-distance stress waves, dropping of leaves by pulvini, and loading of xylem vessels. We discuss the molecular nature of the transport proteins that are involved in ion extrusion-based functions of plants and describe the functions that they obtained during evolution.

Engineering quantitative stomatal trait variation and local adaptation potential by cis-regulatory editing

Cis-regulatory element editing can generate quantitative trait variation that mitigates extreme phenotypes and harmful pleiotropy associated with coding sequence mutations. Here, we applied a multiplexed CRISPR/Cas9 approach, informed by bioinformatic datasets, to generate genotypic variation in the promoter of OsSTOMAGEN, a positive regulator of rice stomatal density. Engineered genotypic variation corresponded to broad and continuous variation in stomatal density, ranging from 70% to 120% of wild-type stomatal density. This panel of stomatal variants was leveraged in physiological assays to establish discrete relationships between stomatal morphological variation and stomatal conductance, carbon assimilation and intrinsic water use efficiency in steady-state and fluctuating light conditions. Additionally, promoter alleles were subjected to vegetative drought regimes to assay the effects of the edited alleles on developmental response to drought. Notably, the capacity for drought-responsive stomatal density reprogramming in stomagen and two cis-regulatory edited alleles was reduced. Collectively our data demonstrate that cis-regulatory element editing can generate near-isogenic trait variation that can be leveraged for establishing relationships between anatomy and physiology, providing a basis for optimizing traits across diverse environments.

Fast stomatal kinetics in sorghum enable tight coordination with photosynthetic responses to dynamic light intensity and safeguard high water use efficiency

In this study, we assessed 43 accessions of sorghum from 16 countries across three continents. Our objective was to identify stomatal and photosynthetic traits that could be exploited in breeding programmes to increase photosynthesis without increasing water use under dynamic light environments. Under field conditions, sorghum crops often have limited water availability and are exposed to rapidly fluctuating light intensities, which influences both photosynthesis and stomatal behaviour. Our results highlight a tight coupling between photosynthetic rate (A) and stomatal conductance (gs) even under dynamic light conditions that results in steady intrinsic water use efficiency (Wi). This was mainly due to rapid stomatal responses, with the majority of sorghum accessions responding within ≤5 min. The maintenance of the ratio of the concentration of CO2 inside the leaf (Ci) and the surrounding atmospheric concentration (Ca) over a large range of accessions suggests high stomatal sensitivity to changes in Ci, that could underlie the rapid gs responses and extremely close relationship between A and gs under both dynamic and steady-state conditions. Therefore, sorghum represents a prime candidate for uncovering the elusive mechanisms that coordinate A and gs, and such information could be used to design crops with high A without incurring significant water losses and eroding Wi.

Natural genetic variation in dynamic photosynthesis is correlated with stomatal anatomical traits in diverse tomato species across geographical habitats

Plants grown under field conditions experience fluctuating light. Understanding the natural genetic variations for a similarly dynamic photosynthetic response among untapped germplasm resources, as well as the underlying mechanisms, may offer breeding strategies to improve production using molecular approaches. Here, we measured gas exchange under fluctuating light, along with stomatal density and size, in eight wild tomato species and two tomato cultivars. The photosynthetic induction response showed significant diversity, with some wild species having faster induction rates than the two cultivars. Species with faster photosynthetic induction rates had higher daily integrated photosynthesis, but lower average water use efficiency because of high stomatal conductance under natural fluctuating light. The variation in photosynthetic induction was closely associated with the speed of stomatal responses, highlighting its critical role in maximizing photosynthesis under fluctuating light conditions. Moreover, stomatal size was negatively correlated with stomatal density within a species, and plants with smaller stomata at a higher density had a quicker photosynthetic response than those with larger stomata at lower density. Our findings show that the response of stomatal conductance plays a pivotal role in photosynthetic induction, with smaller stomata at higher density proving advantageous for photosynthesis under fluctuating light in tomato species. The interspecific variation in the rate of stomatal responses could offer an untapped resource for optimizing dynamic photosynthetic responses under field conditions.

Dual function of overexpressing plasma membrane H+-ATPase in balancing carbon-water use

Stomata respond slowly to changes in light when compared with photosynthesis, undermining plant water-use efficiency (WUE). We know much about stomatal mechanics, yet efforts to accelerate stomatal responsiveness have been limited despite the breadth of potential targets for manipulation. Here, we use mechanistic modeling to establish a hierarchy of putative targets affecting stomatal kinetics. Counterintuitively, modeling predicted that overexpressing plasma membrane H+-ATPases could speed stomata and enhance WUE under fluctuating light, even though overexpressed H+-ATPases is known to promote stomatal opening and reduce WUE in the steady state. Experiments validated the prediction, implicating an unexpected role of the H+-ATPases in improving WUE under fluctuating light. It suggests that H+-ATPases have a dual function, acting as a facilitator of carbon assimilation and water use, depending on the light conditions. These findings highlight the importance of integrating in silico modeling with experiments in future efforts toward enhancing stomatal function.

Initial stomatal conductance increases photosynthetic induction of trees leaves more from sunlit than from shaded environments: a meta-analysis

It has long been held that tree species/leaves from shaded environments show faster rate of photosynthetic induction than species/leaves from sunlit environments, but the evidence so far is conflicting and the underlying mechanisms are still under debate. To address the debate, we compiled a dataset for 87 tree species and compared the initial increasing slope during the first 2-min induction (SA) and stomatal and biochemical characteristics between sun and shade species from the same study, and those between sun and shade leaves within the same species. In 77% of between-species comparisons, the species with high steady-state photosynthetic rate in the high light (Af) exhibited a larger SA than the species with low Af. In 67% within-species comparisons, the sun leaves exhibited a larger SA than the shade leaves. However, in only a few instances did the sun species/leaves more rapidly achieve 50% of full induction, with an even smaller SA, than the shade species/leaves. At both the species and leaf level, SA increased with increasing initial stomatal conductance before induction (gsi). Despite exhibiting reduced intrinsic water-use efficiency in low light, a large SA proportionally enhances photosynthetic carbon gain during the first 2-min induction in the sun species and leaves. Thus, in terms of the increase in absolute rate of photosynthesis, tree species/leaves from sunlit environments display faster photosynthetic induction responses than those from shaded environments. Our results call for re-consideration of contrasting photosynthetic strategies in photosynthetic adaption/acclimation to dynamic light environments across species.

Hydroponic lettuce in-situ water circulation evaluation via nondestructive mass measurement in controlled environment

This study proposed a hydroponic system with the capacity to acquire high-resolution in situ mass data for non-destructive evaluation of water circulation in lettuce. The system customizes the watering profile, enables high-frequency in situ weight measurement, and monitors multidimensional environment changes. Key air, water, and light parameters were collected to evaluate the plant response, susceptibility, and adaptability to environmental conditions. Multiple physiological indices were defined to characterize the properties of two lettuce varieties in response to different environmental factors.

Perspectives on improving photosynthesis to increase crop yield

Improving photosynthesis, the fundamental process by which plants convert light energy into chemical energy, is a key area of research with great potential for enhancing sustainable agricultural productivity and addressing global food security challenges. This perspective delves into the latest advancements and approaches aimed at optimizing photosynthetic efficiency. Our discussion encompasses the entire process, beginning with light harvesting and its regulation and progressing through the bottleneck of electron transfer. We then delve into the carbon reactions of photosynthesis, focusing on strategies targeting the enzymes of the Calvin-Benson-Bassham (CBB) cycle. Additionally, we explore methods to increase carbon dioxide (CO2) concentration near the Rubisco, the enzyme responsible for the first step of CBB cycle, drawing inspiration from various photosynthetic organisms, and conclude this section by examining ways to enhance CO2 delivery into leaves. Moving beyond individual processes, we discuss two approaches to identifying key targets for photosynthesis improvement: systems modeling and the study of natural variation. Finally, we revisit some of the strategies mentioned above to provide a holistic view of the improvements, analyzing their impact on nitrogen use efficiency and on canopy photosynthesis.

Integrating bioprinting and optogenetic technologies for precision plant tissue engineering

Recent advancements in plant bioprinting and optogenetic tools have unlocked new avenues to revolutionize plant tissue engineering. Bioprinting of plant cells has the potential to craft intricate 3D structures incorporating multiple cell types, replicating the complex microenvironments found in plants. Concurrently, optogenetic tools enable the control of biological events with spatial, temporal, and quantitative precision. Originally developed for human and microbial systems, these two cutting-edge methodologies are now being adapted for plant research. Although still in the early stages of development, we here review the latest progress in plant bioprinting and optogenetics and discuss compelling opportunities for plant biotechnology and research arising from the combination of the two technologies.

A module involving HIGH LEAF TEMPERATURE1 controls instantaneous water use efficiency

Drought stress inhibits plant growth and agricultural production. Improving plant instantaneous water use efficiency (iWUE), which is strictly regulated by stomata, is an effective way to cope with drought stress. However, the mechanisms of iWUE regulation are poorly understood. Through genetic screening for suppressors of mpk12-4, an Arabidopsis (Arabidopsis thaliana) mutant with a major iWUE quantitative trait locus gene MITOGEN-ACTIVATED PROTEIN KINASE12 deleted, we identified HIGH LEAF TEMPERATURE1 (HT1). Genetic interaction and physiological analyses showed that MPK12 controls iWUE through multiple modules in a high CO2-induced stomatal closing pathway that regulate SLOW ANION CHANNEL-ASSOCIATED1 (SLAC1) activity. HT1 acts downstream of MPK12, whereas OPEN STOMATA1 (OST1) and GUARD CELL HYDROGEN PEROXIDE-RESISTANT1 (GHR1) function downstream of HT1 by activating SLAC1 in iWUE. Photosynthetic-CO2 response curves and biomass analyses under different water-supply conditions showed that HT1 dysfunction improved iWUE and also increased plant growth capacity, and products of HT1 putative orthologs from Brassica (Brassica napus) and rice (Oryza sativa) exhibited functions similar to that of Arabidopsis HT1 in iWUE and the CO2-signaling pathway. Our study revealed the mechanism of MPK12-mediated iWUE regulation in Arabidopsis and provided insight into the internal relationship between iWUE and CO2 signaling in guard cells and a potential target for improving crop iWUE and drought tolerance.

Surrounded by luxury: The necessities of subsidiary cells

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

Overexpression of tonoplast Ca2+-ATPase in guard cells synergistically enhances stomatal opening and drought tolerance

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.

Effect of Green Light Replacing Some Red and Blue Light on Cucumis melo under Drought Stress

Light quality not only directly affects the photosynthesis of green plants but also plays an important role in regulating the development and movement of leaf stomata, which is one of the key links for plants to be able to carry out normal growth and photosynthesis. By sensing changes in the light environment, plants actively regulate the expansion pressure of defense cells to change stomatal morphology and regulate the rate of CO2 and water vapor exchange inside and outside the leaf. In this study, Cucumis melo was used as a test material to investigate the mitigation effect of different red, blue, and green light treatments on short-term drought and to analyze its drought-resistant mechanism through transcriptome and metabolome analysis, so as to provide theoretical references for the regulation of stomata in the light environment to improve the water use efficiency. The results of the experiment showed that after 9 days of drought treatment, increasing the percentage of green light in the light quality significantly increased the plant height and fresh weight of the treatment compared to the control (no green light added). The addition of green light resulted in a decrease in leaf stomatal conductance and a decrease in reactive oxygen species (ROS) content, malondialdehyde MDA content, and electrolyte osmolality in the leaves of melon seedlings. It indicated that the addition of green light promoted drought tolerance in melon seedlings. Transcriptome and metabolome measurements of the control group (CK) and the addition of green light treatment (T3) showed that the addition of green light treatment not only effectively regulated the synthesis of abscisic acid (ABA) but also significantly regulated the hormonal pathway in the hormones such as jasmonic acid (JA) and salicylic acid (SA). This study provides a new idea to improve plant drought resistance through light quality regulation.

Architecture and functions of stomatal cell walls in eudicots and grasses

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.

C4 monocots and C4 dicots exhibit rapid photosynthetic induction response in contrast to C3 plants

Considering the prevalence of ever-changing conditions in the natural world, investigation of photosynthetic responses in C4 plants under fluctuating light is needed. Here, we studied the effect of dynamic illumination on photosynthesis in totally 10 C3, C3-C4 intermediate, C4-like and C4 dicots and monocots at CO2 concentrations of 400 and 800 μmol mol-1. C4 and C4-like plants had faster photosynthetic induction and light-induced stomatal dynamics than C3 plants at 400 μmol mol-1, but not at 800 μmol mol-1 CO2, at which the CO2 supply rarely limits photosynthesis. C4 and C4-like plants had a higher water use efficiency than C3 plants at both CO2 concentrations. There were positive correlations between photosynthetic induction and light-induced stomatal response, together with CO2 compensation point, which was a parameter of the CO2-concentrating mechanism of C4 photosynthesis. These results clearly show that C4 photosynthesis in both monocots and dicots adapts to fluctuating light conditions more efficiently than C3 photosynthesis. The rapid photosynthetic induction response in C4 plants can be attributed to the rapid stomatal dynamics, the CO2-concentrating mechanism or both.

A review on strategies for crop improvement against drought stress through molecular insights

The demand for food goods is rising along with the world population growth, which is directly related to the yield of agricultural crops around the world. However, a number of environmental factors, including floods, salinity, moisture, and drought, have a detrimental effect on agricultural production around the world. Among all of these stresses, drought stress (DS) poses a constant threat to agricultural crops and is a significant impediment to global agricultural productivity. Its potency and severity are expected to increase in the future years. A variety of techniques have been used to generate drought-resistant plants in order to get around this restriction. Different crop plants exhibit specific traits that contribute to drought resistance (DR), such as early flowering, drought escape (DE), and leaf traits. We are highlighting numerous methods that can be used to overcome the effects of DS in this review. Agronomic methods, transgenic methods, the use of sufficient fertilizers, and molecular methods such as clustered regularly interspaced short palindromic repeats (CRISPRs)-associated nuclease 9 (Cas9), virus-induced gene silencing (VIGS), quantitative trait loci (QTL) mapping, microRNA (miRNA) technology, and OMICS-based approaches make up the majority of these techniques. CRISPR technology has rapidly become an increasingly popular choice among researchers exploring natural tolerance to abiotic stresses although, only a few plants have been produced so far using this technique. In order to address the difficulties imposed by DS, new plants utilizing the CRISPR technology must be developed.

Effects of Red and Blue Light on the Growth, Photosynthesis, and Subsequent Growth under Fluctuating Light of Cucumber Seedlings

The effects of red and blue light on growth and steady-state photosynthesis have been widely studied, but there are few studies focusing on dynamic photosynthesis and the effects of LED pre-treatment on cucumber seedlings' growth, so in this study, cucumber (Cucumis sativus L. cv. Jinyou 365) was chosen as the test material. White light (W), monochromatic red light (R), monochromatic blue light (B), and mixed red and blue lights with different red-to-blue ratios (9:1, 7:3, 5:5, 3:7, and 1:9) were set to explore the effects of red and blue light on cucumber seedlings' growth, steady-state photosynthesis, dynamic photosynthesis, and subsequent growth under fluctuating light. The results showed that compared with R and B, mixed red and blue light was more suitable for cucumber seedlings' growth, and the increased blue light ratios would decrease the biomass of cucumber seedlings under mixed red and blue light; cucumber seedlings under 90% red and 10% blue mixed light (9R1B) grew better than other treatments. For steady-state photosynthesis, blue light decreased the actual net photosynthetic rate but increased the maximum photosynthetic capacity by promoting stomatal development and opening; 9R1B exhibited higher actual net photosynthetic rate, but the maximum photosynthetic capacity was low. For dynamic photosynthesis, the induction rate of photosynthetic rate and stomatal conductance were also accelerated by blue light. For subsequent growth under fluctuating light, higher maximum photosynthetic capacity and photoinduction rate could not promote the growth of cucumber seedlings under subsequent fluctuating light, while seedlings pre-treated with 9R1B and B grew better under subsequent fluctuating light due to the high plant height and leaf area. Overall, cucumber seedlings treated with 9R1B exhibited the highest biomass and it grew better under subsequent fluctuating light due to the higher actual net photosynthetic rate, plant height, and leaf area.

Estimation of Photosynthetic Induction Is Significantly Affected by Light Environments of Local Leaves and Whole Plants in Oryza Genus

Photosynthetic induction and stomatal kinetics are acknowledged as pivotal factors in regulating both plant growth and water use efficiency under fluctuating light conditions. However, the considerable variability in methodologies and light regimes used to assess the dynamics of photosynthesis (A) and stomatal conductance (gs) during light induction across studies poses challenges for comparison across species. Moreover, the influence of stomatal morphology on both steady-state and non-steady-state gs remains poorly understood. In this study, we show the strong impact of IRGA Chamber Illumination and Whole Plant Illumination on the photosynthetic induction of two rice species. Our findings reveal that these illuminations significantly enhance photosynthetic induction by modulating both stomatal and biochemical processes. Moreover, we observed that a higher density of smaller stomata plays a critical role in enhancing the stomatal opening and photosynthetic induction to fluctuating light conditions, although it exerts minimal influence on steady-state gs and A under constant light conditions. Therefore, future studies aiming to estimate photosynthetic induction and stomatal kinetics should consider the light environments at both the leaf and whole plant levels.

Activating plant immunity: the hidden dance of intracellular Ca2+ stores

Calcium ion (Ca2+) serves as a versatile and conserved second messenger in orchestrating immune responses. In plants, plasma membrane-localized Ca2+-permeable channels can be activated to induce Ca2+ influx from extracellular space to cytosol upon pathogen infection. Notably, different immune elicitors can induce dynamic Ca2+ signatures in the cytosol. During pattern-triggered immunity, there is a rapid and transient increase in cytosolic Ca2+, whereas in effector-triggered immunity, the elevation of cytosolic Ca2+ is strong and sustained. Numerous Ca2+ sensors are localized in the cytosol or different intracellular organelles, which are responsible for detecting and converting Ca2+ signals. In fact, Ca2+ signaling coordinated by cytosol and subcellular compartments plays a crucial role in activating plant immune responses. However, the complete Ca2+ signaling network in plant cells is still largely ambiguous. This review offers a comprehensive insight into the collaborative role of intracellular Ca2+ stores in shaping the Ca2+ signaling network during plant immunity, and several intriguing questions for future research are highlighted.

Guard cell and subsidiary cell sizes are key determinants for stomatal kinetics and drought adaptation in cereal crops

Climate change-induced drought is a major threat to agriculture. C4 crops have a higher water use efficiency (WUE) and better adaptability to drought than C3 crops due to their smaller stomatal morphology and faster response. However, our understanding of stomatal behaviours in both C3 and C4 Poaceae crops is limited by knowledge gaps in physical traits of guard cell (GC) and subsidiary cell (SC). We employed infrared gas exchange analysis and a stomatal assay to explore the relationship between GC/SC sizes and stomatal kinetics across diverse drought conditions in two C3 (wheat and barley) and three C4 (maize, sorghum and foxtail millet) upland Poaceae crops. Through statistical analyses, we proposed a GCSC-τ model to demonstrate how morphological differences affect stomatal kinetics in C4 Poaceae crops. Our findings reveal that morphological variations specifically correlate with stomatal kinetics in C4 Poaceae crops, but not in C3 ones. Subsequent modelling and experimental validation provide further evidence that GC/SC sizes significantly impact stomatal kinetics, which affects stomatal responses to different drought conditions and thereby WUE in C4 Poaceae crops. These findings emphasize the crucial advantage of GC/SC morphological characteristics and stomatal kinetics for the drought adaptability of C4 Poaceae crops, highlighting their potential as future climate-resilient crops.

Synthetic reprogramming of plant developmental and biochemical pathways

Plant synthetic biology (Plant SynBio) is an emerging field with the potential to enhance agriculture, human health, and sustainability. Integrating genetic tools and engineering principles, Plant SynBio aims to manipulate cellular functions and construct novel biochemical pathways to develop plants with new phenotypic traits, enhanced yield, and be able to produce natural products and pharmaceuticals. This review compiles research efforts in reprogramming plant developmental and biochemical pathways. We highlight studies leveraging new gene expression toolkits to alter plant architecture for improved performance in model and crop systems and to produce useful metabolites in plant tissues. Furthermore, we provide insights into the challenges and opportunities associated with the adoption of Plant SynBio in addressing complex issues impacting agriculture and human health.

PIF transcriptional regulators are required for rhythmic stomatal movements

Stomata govern the gaseous exchange between the leaf and the external atmosphere, and their function is essential for photosynthesis and the global carbon and oxygen cycles. Rhythmic stomata movements in daily dark/light cycles prevent water loss at night and allow CO2 uptake during the day. How the actors involved are transcriptionally regulated and how this might contribute to rhythmicity is largely unknown. Here, we show that morning stomata opening depends on the previous night period. The transcription factors PHYTOCHROME-INTERACTING FACTORS (PIFs) accumulate at the end of the night and directly induce the guard cell-specific K+ channel KAT1. Remarkably, PIFs and KAT1 are required for blue light-induced stomata opening. Together, our data establish a molecular framework for daily rhythmic stomatal movements under well-watered conditions, whereby PIFs are required for accumulation of KAT1 at night, which upon activation by blue light in the morning leads to the K+ intake driving stomata opening.

A charged existence: A century of transmembrane ion transport in plants

If the past century marked the birth of membrane transport as a focus for research in plants, the past 50 years has seen the field mature from arcane interest to a central pillar of plant physiology. Ion transport across plant membranes accounts for roughly 30% of the metabolic energy consumed by a plant cell, and it underpins virtually every aspect of plant biology, from mineral nutrition, cell expansion, and development to auxin polarity, fertilization, plant pathogen defense, and senescence. The means to quantify ion flux through individual transporters, even single channel proteins, became widely available as voltage clamp methods expanded from giant algal cells to the fungus Neurospora crassa in the 1970s and the cells of angiosperms in the 1980s. Here, I touch briefly on some key aspects of the development of modern electrophysiology with a focus on the guard cells of stomata, now without dispute the premier plant cell model for ion transport and its regulation. Guard cells have proven to be a crucible for many technical and conceptual developments that have since emerged into the mainstream of plant science. Their study continues to provide fundamental insights and carries much importance for the global challenges that face us today.

Mechanical advantage makes stomatal opening speed a function of evaporative demand

Stomatal opening in the light, observed in nearly all vascular land plants, is essential for providing access to atmospheric CO2 for photosynthesis. The speed of stomatal opening in the light is critical for maximizing carbon gain in environments in which light intensity changes, yet we have little understanding of how other environmental signals, particularly evaporative demand driven by vapor pressure deficit (VPD) influences the kinetics of this response. In angiosperms, and some fern species from the family Marsileaceae, a mechanical interaction between the guard cells and the epidermal cells determines the aperture of the pore. Here, we examine whether this mechanical interaction influences the speed of stomatal opening in the light. To test this, we investigated the speed of stomatal opening in response to light across a range of VPDs in seven plant species spanning the evolutionary diversity of guard cell and epidermal cell mechanical interactions. We found that stomatal opening speed is a function of evaporative demand in angiosperm species and Marsilea, which have guard cell and epidermal cell mechanical interactions. Stomatal opening speeds did not change across a range of VPD in species of gymnosperm and fern, which do not have guard cell mechanical interactions with the epidermis. We find that guard cell and epidermal cell mechanical interactions may play a key role in regulating stomatal responsiveness to light. These results provide valuable insight into the adaptive relevance of mechanical advantage.

Engineering Plant Cell Fates and Functions for Agriculture and Industry

Many plant species are grown to enable access to specific organs or tissues, such as seeds, fruits, or stems. In some cases, a value is associated with a molecule that accumulates in a single type of cell. Domestication and subsequent breeding have often increased the yields of these target products by increasing the size, number, and quality of harvested organs and tissues but also via changes to overall plant growth architecture to suit large-scale cultivation. Many of the mutations that underlie these changes have been identified in key regulators of cellular identity and function. As key determinants of yield, these regulators are key targets for synthetic biology approaches to engineer new forms and functions. However, our understanding of many plant developmental programs and cell-type specific functions is still incomplete. In this Perspective, we discuss how advances in cellular genomics together with synthetic biology tools such as biosensors and DNA-recording devices are advancing our understanding of cell-specific programs and cell fates. We then discuss advances and emerging opportunities for cell-type-specific engineering to optimize plant morphology, responses to the environment, and the production of valuable compounds.

The potassium transporter TaNHX2 interacts with TaGAD1 to promote drought tolerance via modulating stomatal aperture in wheat

Drought is a major global challenge in agriculture that decreases crop production. γ-Aminobutyric acid (GABA) interfaces with drought stress in plants; however, a mechanistic understanding of the interaction between GABA accumulation and drought response remains to be established. Here we showed the potassium/proton exchanger TaNHX2 functions as a positive regulator in drought resistance in wheat by mediating cross-talk between the stomatal aperture and GABA accumulation. TaNHX2 interacted with glutamate decarboxylase TaGAD1, a key enzyme that synthesizes GABA from glutamate. Furthermore, TaNHX2 targeted the C-terminal auto-inhibitory domain of TaGAD1, enhanced its activity, and promoted GABA accumulation under drought stress. Consistent with this, the tanhx2 and tagad1 mutants showed reduced drought tolerance, and transgenic wheat with enhanced TaNHX2 expression had a yield advantage under water deficit without growth penalty. These results shed light on the plant stomatal movement mechanism under drought stress and the TaNHX2-TaGAD1 module may be harnessed for amelioration of negative environmental effects in wheat as well as other crops.

Calvin cycle and guard cell metabolism impact stomatal function

Stomatal conductance (gs) determines CO2 uptake for photosynthesis (A) and water loss through transpiration, which is essential for evaporative cooling and maintenance of optimal leaf temperature as well as nutrient uptake. Stomata adjust their aperture to maintain an appropriate balance between CO2 uptake and water loss and are therefore critical to overall plant water status and productivity. Although there is considerable knowledge regarding guard cell (GC) osmoregulation (which drives differences in GC volume and therefore stomatal opening and closing), as well as the various signal transduction pathways that enable GCs to sense and respond to different environmental stimuli, little is known about the signals that coordinate mesophyll demands for CO2. Furthermore, chloroplasts are a key feature in GCs of many species, however, their role in stomatal function is unclear and a subject of debate. In this review we explore the current evidence regarding the role of these organelles in stomatal behaviour, including GC electron transport and Calvin-Benson-Bassham (CBB) cycle activity as well as their possible involvement correlating gs and A along with other potential mesophyll signals. We also examine the roles of other GC metabolic processes in stomatal function.

Integrative regulatory mechanisms of stomatal movements under changing climate

Global climate change-caused drought stress, high temperatures and other extreme weather profoundly impact plant growth and development, restricting sustainable crop production. To cope with various environmental stimuli, plants can optimize the opening and closing of stomata to balance CO2 uptake for photosynthesis and water loss from leaves. Guard cells perceive and integrate various signals to adjust stomatal pores through turgor pressure regulation. Molecular mechanisms and signaling networks underlying the stomatal movements in response to environmental stresses have been extensively studied and elucidated. This review focuses on the molecular mechanisms of stomatal movements mediated by abscisic acid, light, CO2 , reactive oxygen species, pathogens, temperature, and other phytohormones. We discussed the significance of elucidating the integrative mechanisms that regulate stomatal movements in helping design smart crops with enhanced water use efficiency and resilience in a climate-changing world.

Speedy stomata of a C4 plant correlate with enhanced K+ channel gating

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

Response of WUE of maize at ear stage to the coupling effect of CO2 and temperature

In the face of global warming, the photosynthesis and transpiration of plants will change greatly, which will ultimately affect the water use efficiency (WUE) of plants. In order to study the coupling effects of CO2 and temperature on WUE of maize at ear stage, 'Zhengdan 958' was taken as the research object, and 5 temperatures (20 °C, 25 °C, 30 °C, 35 °C and 40 °C) and 11 CO2 concentration (400, 300, 200, 150, 100, 50, 400, 400, 600, 800 and 1000 μmol mol-1) were set to measure the parameters such as net photosynthetic rate (Pn), transpiration rate (Tr), stomatal conductance (Gs) and intercellular CO2 concentration (Ci) of single leaves. The response of WUE (Pn/Tr) to CO2 and temperature was evaluated by a CO2 response model. The results show that at the same temperature, Pn and WUE increased with CO2 level, while Tr decreased as CO2 level increases; at the same CO2 concentration, Pn and Tr were both positively correlated with temperature, while WUE decreased with the increase of temperature. The maximum value of WUE was obtained when the CO2 concentration was 1000 μmol mol-1 and the temperature was 20.0 °C. The results suggest that global warming will not improve WUE of maize, which will bring more severe challenges to water-saving agriculture and food security.

Dynamic fluctuations in plant leaf interception of airborne microplastics

Plant leaves have been demonstrated to be a crucial sink of airborne microplastics (MPs). However, because of the particular shape of MPs and their relatively weak forces with leaves, the traditional accumulation model used for the adsorption of particulate matter and persistent organic pollutants may not be appropriate for describing the interception of MPs by leaves. Here, we performed a 7-day exploration of the interception of MPs by leaves in downtown Nanning. The abundances and characteristics of leaf-intercepted MPs showed dramatic diurnal fluctuations and interspecies differences (conifers > arbors > shrubs). The fluctuation (Coefficient of Variation (CV) = 0.459; abundances 0.003 ± 0.002 to 0.047 ± 0.005 n·cm-2) was even more drastic than that measured across species (CV = 0.353; 0.06 ± 0.01 to 0.40 ± 0.04 n·cm-2). Further analysis using partial least-squares path modeling demonstrated that stomatal variation and divergence largely dominated diurnal fluctuations and interspecies differences in microplastic interception by leaves, respectively. Our results highlight that the leaf-intercepted MPs is characterized by dynamic fluctuations rather than static equilibrium and reveal the important regulatory roles played by leaf micromorphological structures in intercepting MPs, thus enhancing our understanding of the interactions between terrestrial plants and airborne pollution.

Benzotriazole Ultraviolet Stabilizers (BUVSs) as Potential Protein Kinase Antagonists in Rice

The ubiquitous occurrence of benzotriazole ultraviolet stabilizers (BUVSs) in the environment and organisms has warned of their potential ecological and health risks. Studies showed that some BUVSs exerted immune and chronic toxicities to animals by disturbing signaling transduction, yet limited research has investigated the toxic effects on crop plants and the underlying mechanisms of signaling regulation. Herein, a laboratory-controlled hydroponic experiment was conducted on rice to explore the phytotoxicity of BUVSs by integrating conventional biochemical experiments, transcriptomic analysis, competitive sorption assays, and computational studies. The results showed that BUVSs inhibited the growth of rice by 6.30-20.4% by excessively opening the leaf stomas, resulting in increased transpiration. BUVSs interrupted the transduction of abscisic acid (ABA) signal through competitively binding to Ca2+-dependent protein kinase (CDPK), weakening the CDPK phosphorylation and further inhibiting the downstream signaling. As structural analogues of ATP, BUVSs acted as potential ABA signaling antagonists, leading to physiological dysfunction in mediating stomatal closure under stresses. This is the first comprehensive study elucidating the effects of BUVSs on the function of key proteins and the associated signaling transduction in plants and providing insightful information for the risk evaluation and control of BUVSs.