Light regulation of stomatal movement

Up-regulation of non-photochemical quenching improves water use efficiency and reduces whole-plant water consumption under drought in Nicotiana tabacum

Water supply limitations will likely impose increasing restrictions on future crop production, underlining a need for crops that use less water per mass of yield. Water use efficiency (WUE) therefore becomes a key consideration in developing resilient and productive crops. In this study, we hypothesized that it is possible to improve WUE under drought conditions via modulation of chloroplast signals for stomatal opening by up-regulation of non-photochemical quenching (NPQ). Nicotiana tabacum plants with strong overexpression of the PsbS gene encoding PHOTOSYSTEM II SUBUNIT S, a key protein in NPQ, were grown under differing levels of drought. The PsbS-overexpressing lines lost 11% less water per unit CO2 fixed under drought and this did not have a significant effect on plant size. Depending on growth conditions, the PsbS-overexpressing lines consumed from 4-30% less water at the whole-plant level than the corresponding wild type. Leaf water and chlorophyll contents showed a positive relation with the level of NPQ. This study therefore provides proof of concept that up-regulation of NPQ can increase WUE, and as such is an important step towards future engineering of crops with improved performance under drought.

The use of LEDs for the stomatal response, light compensation points, and storage of spinach and kale

The spectral composition of some light-emitting diodes (LEDs) reportedly results in higher crop yield, prevents wilting, and reduces thermal damage to plants. The use of LEDs for postharvest storage and shelf-life extension has been limited, but the potential of this technology will allow for greater applications in horticulture and the food industry. In this experiment, 'Winterbor' kale (Brassica oleracea) and 'Melody' spinach (Spinacia oleracea) plants were measured for the light compensation point and stomatal response under 14 different wavelengths of light ranging from 405 to 661 nm. Data collected from these measurements were used to select two different wavelengths of LEDs and determine the proper irradiance levels for an LED irradiance storage test on spinach and kale. Treatments comprising blue, red, and amber lights were effective at increasing the stomatal opening, while the green light resulted in reduced stomatal opening. For spinach, the light response curve showed that light compensation points at 500 nm and 560 nm were 65.3 and 64.7 μmol m-2 s-1, respectively. For kale, the light compensation points at 500 nm and 560 nm were 50.8 and 44.1 μmol m-2 s-1, respectively. For the storage test experiment at room temperature, kale and spinach were stored under four different treatments: dark treatment (control), standard white fluorescent light, 500 nm, and 560 nm LED wavelengths. For spinach, the moisture content was 70.1% at 560 nm and 53.7% for dark, moisture losses of 41.5% under the 560-nm treatment and 52.0% for the dark treatment. The fresh basis moisture content was 74.6% at 560 nm and 59.3% in the dark. Moisture loss under the 560 nm treatment was 39.6% while the dark treatment had a 54.0% moisture loss. A visual assessment scale was monitored, 560 nm resulted in the top visual quality for kale compared to the other treatments with the lowest visual quality under the dark treatment at day 4. For spinach, the visual quality for 560 nm treatment was statistically the standard white fluorescent light and 500 nm, with poor-quality product occurring by day 4 and the lowest-quality product occurring at day 5. The LED treatments improved the shelf life of spinach and kale, likely as a result of stomatal aperture closure, photosynthetic rate near the light compensation point and stability of the atmospheric moisture content. This study provides valuable information on the extension of the shelf life of leafy greens during storage. Reducing fresh produce waste in grocery stores will increase revenue, thereby benefiting the Canadian economy while providing social and environmental benefits that entail increased food security and reduced food waste.

Hydrogen peroxide is required for light-induced stomatal opening across different plant species

Stomatal movement is vital for plants to exchange gases and adaption to terrestrial habitats, which is regulated by environmental and phytohormonal signals. Here, we demonstrate that hydrogen peroxide (H2O2) is required for light-induced stomatal opening. H2O2 accumulates specifically in guard cells even when plants are under unstressed conditions. Reducing H2O2 content through chemical treatments or genetic manipulations results in impaired stomatal opening in response to light. This phenomenon is observed across different plant species, including lycopodium, fern, and monocotyledonous wheat. Additionally, we show that H2O2 induces the nuclear localization of KIN10 protein, the catalytic subunit of plant energy sensor SnRK1. The nuclear-localized KIN10 interacts with and phosphorylates the bZIP transcription factor bZIP30, leading to the formation of a heterodimer between bZIP30 and BRASSINAZOLE-RESISTANT1 (BZR1), the master regulator of brassinosteroid signaling. This heterodimer complex activates the expression of amylase, which enables guard cell starch degradation and promotes stomatal opening. Overall, these findings suggest that H2O2 plays a critical role in light-induced stomatal opening across different plant species.

Transcriptional and physiological analyses uncover the mineralization and uptake mechanisms of phytic acid in symbiotically grown Vicia faba plants

Legume-rhizobia symbiosis requires high phosphorus (P) in the form of ATP to convert atmospheric nitrogen (N) into ammonia. The fixed ammonia is converted to NH4+ by H+-ATPase via protonation. To the best of our knowledge, most of these research works resort to using only inorganic P (Pi) to the neglect of the organic P (Po) counterpart. As it stands, the potential regulating roles of plasma membrane (PM) H+-ATPases during legume-rhizobia symbiosis in response to phytic acid supply and how it alters and modulates the regulation of PM H+-ATPases remain obscure. To contribute to the above hypothesis, we investigate the mechanisms that coordinately facilitate the growth, uptake, and transcript expression of PM H+-ATPase gene isoforms in response to different P sources when hydroponically grown Vicia faba plants were exposed to three P treatments, viz., low- and high-Pi (2.0 and 200 μM KH2PO4; LPi and HPi), and phytic acid (200 μM; Po) and inoculated with Rhizobium leguminosarum bv. viciae 384 for 30 days. The results consistently reveal that the supply of Po improved not only the growth and biomass, but also enhanced photosynthetic parameters, P uptake and phosphatase activities in symbiotically grown Vicia faba relative to Pi. The supply of Po induced higher transcriptional expression of all PM H+-ATPase gene isoforms, with possible interactions between phosphatases and H+-ATPase genes in Vicia faba plants when exclusively reliant on N derived from nodule symbiosis. Overall, preliminary results suggest that Po could be used as an alternative nutrition in symbiotic crops to improve plant growth.

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.

TCP transcription factor StAST1 represses potato tuberization by regulating tuberigen complex activity

Potato (Solanum tuberosum L.) is cultivated worldwide for its underground tubers, which provide an important part of human nutrition and serve as a model system for belowground storage organ formation. Similar to flowering, stolon-expressed FLOWERING LOCUS T-like (FT-like) protein SELF-PRUNING 6A (StSP6A) plays an instrumental role in tuberization by binding to the bZIP transcription factors StABI5-like 1 (StABL1) and StFD-like 1 (StFDL1), causing transcriptional reprogramming at the stolon subapical apices. However, the molecular mechanism regulating the widely conserved FT-bZIP interactions remains largely unexplored. Here, we identified a TCP transcription factor StAST1 (StABL1 and StSP6A-associated TCP protein 1) binding to both StSP6A and StABL1. StAST1 is specifically expressed in the vascular tissue of leaves and developing stolons. Silencing of StAST1 leads to accelerated tuberization and a shortened life cycle. Molecular dissection reveals that the interaction of StAST1 with StSP6A and StABL1 attenuates the formation of the alternative tuberigen activation complex (aTAC). We also observed StAST1 directly activates the expression of potato GA 20-oxidase gene (StGA20ox1) to regulate GA responses. These results demonstrate StAST1 functions as a tuberization repressor by regulating plant hormone levels; our findings also suggest a mechanism by which the widely conserved FT-FD genetic module is fine-tuned.

OPEN STOMATA 1 phosphorylates CYCLIC NUCLEOTIDE-GATED CHANNELs to trigger Ca2+ signaling for abscisic acid-induced stomatal closure in Arabidopsis

Multiple cyclic nucleotide-gated channels (CNGCs) are abscisic acid (ABA)-activated Ca2+ channels in Arabidopsis (Arabidopsis thaliana) guard cells. In particular, CNGC5, CNGC6, CNGC9, and CNGC12 are essential for ABA-specific cytosolic Ca2+ signaling and stomatal movements. However, the mechanisms underlying ABA-mediated regulation of CNGCs and Ca2+ signaling are still unknown. In this study, we identified the Ca2+-independent protein kinase OPEN STOMATA 1 (OST1) as a CNGC activator in Arabidopsis. OST1-targeted phosphorylation sites were identified in CNGC5, CNGC6, CNGC9, and CNGC12. These CNGCs were strongly inhibited by Ser-to-Ala mutations and fully activated by Ser-to-Asp mutations at the OST1-targeted sites. The overexpression of individual inactive CNGCs (iCNGCs) under the UBIQUITIN10 promoter in wild-type Arabidopsis conferred a strong dominant-negative-like ABA-insensitive stomatal closure phenotype. In contrast, expressing active CNGCs (aCNGCs) under their respective native promoters in the cngc5-1 cngc6-2 cngc9-1 cngc12-1 quadruple mutant fully restored ABA-activated cytosolic Ca2+ oscillations and Ca2+ currents in guard cells, and rescued the ABA-insensitive stomatal movement mutant phenotypes. Thus, we uncovered that ABA elicits cytosolic Ca2+ signaling via an OST1-CNGC module, in which OST1 functions as a convergence point of the Ca2+-dependent and -independent pathways in Arabidopsis guard cells.

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.

Noninvasive Abiotic Stress Phenotyping of Vascular Plant in Each Vegetative Organ View

The last decades have witnessed a rapid development of noninvasive plant phenotyping, capable of detecting plant stress scale levels from the subcellular to the whole population scale. However, even with such a broad range, most phenotyping objects are often just concerned with leaves. This review offers a unique perspective of noninvasive plant stress phenotyping from a multi-organ view. First, plant sensing and responding to abiotic stress from the diverse vegetative organs (leaves, stems, and roots) and the interplays between these vital components are analyzed. Then, the corresponding noninvasive optical phenotyping techniques are also provided, which can prompt the practical implementation of appropriate noninvasive phenotyping techniques for each organ. Furthermore, we explore methods for analyzing compound stress situations, as field conditions frequently encompass multiple abiotic stressors. Thus, our work goes beyond the conventional approach of focusing solely on individual plant organs. The novel insights of the multi-organ, noninvasive phenotyping study provide a reference for testing hypotheses concerning the intricate dynamics of plant stress responses, as well as the potential interactive effects among various stressors.

Enhancing genetic variability in Trigonella species through sodium azide induction: morpho-physiological and chromosomal amelioration

Plant breeding, aimed at enhancing desired traits, depends on genetic diversity. Mutation breeding is a powerful method of rapidly expanding genetic diversity, facilitating crop improvement, and ensuring food security. In a recent study, researchers evaluated the genetic variability of Trigonella species using different doses of sodium azide (SA) (0.2%, 0.4%, 0.6%, 0.8%, and 1.0%) through morphological, physiological, and cytogenetic studies. Morphological variations were observed in cotyledonary leaves, vegetative leaves, and overall plant growth and habit. Several quantitative parameters, such as plant height, fertile branches per plant, pods per plant (or clusters), seeds per pod, and seed yield, increased when treated with 0.2% and 0.4% SA compared to the control. Furthermore, the total chlorophyll content and carotenoids increased in the sample treated with 0.2% SA over the control but decreased with higher concentrations. Scanning electron microscopy revealed that stomatal aperture and seed dimensions increased at lower concentrations of sodium azide treatment. The study found a positive correlation between the different parameters studied in the Trigonella species, as indicated by high r-values. Based on their findings, it was concluded that the genotype of fenugreek can be improved by using 0.2% and 0.4% concentrations of sodium azide. However, the evaluation of observed variants in successive generations is a critical and necessary process to validate their potential as keystones for crop genetic improvements.

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.

Improving strawberry plant resilience to salinity and alkalinity through the use of diverse spectra of supplemental lighting

BACKGROUND

This study explores the impact of various light spectra on the photosynthetic performance of strawberry plants subjected to salinity, alkalinity, and combined salinity/alkalinity stress. We employed supplemental lighting through Light-emitting Diodes (LEDs) with specific wavelengths: monochromatic blue (460 nm), monochromatic red (660 nm), dichromatic blue/red (1:3 ratio), and white/yellow (400-700 nm), all at an intensity of 200 µmol m-2 S-1. Additionally, a control group (ambient light) without LED treatment was included in the study. The tested experimental variants were: optimal growth conditions (control), alkalinity (40 mM NaHCO3), salinity (80 mM NaCl), and a combination of salinity/alkalinity.

RESULTS

The results revealed a notable decrease in photosynthetic efficiency under both salinity and alkalinity stresses, especially when these stresses were combined, in comparison to the no-stress condition. However, the application of supplemental lighting, particularly with the red and blue/red spectra, mitigated the adverse effects of stress. The imposed stress conditions had a detrimental impact on both gas exchange parameters and photosynthetic efficiency of the plants. In contrast, treatments involving blue, red, and blue/red light exhibited a beneficial effect on photosynthetic efficiency compared to other lighting conditions. Further analysis of JIP-test parameters confirmed that these specific light treatments significantly ameliorated the stress impacts.

CONCLUSIONS

In summary, the utilization of blue, red, and blue/red light spectra has the potential to enhance plant resilience in the face of salinity and alkalinity stresses. This discovery presents a promising strategy for cultivating plants in anticipation of future challenging environmental conditions.

A novel semi-dominant mutation in brassinosteroid signaling kinase1 increases stomatal density

Stomata play a pivotal role in balancing CO2 uptake for photosynthesis and water loss via transpiration. Thus, appropriate regulation of stomatal movement and its formation are crucial for plant growth and survival. Red and blue light induce phosphorylation of the C-terminal residue of the plasma membrane (PM) H+-ATPase, threonine, in guard cells, generating the driving force for stomatal opening. While significant progress has been made in understanding the regulatory mechanism of PM H+-ATPase in guard cells, the regulatory components for the phosphorylation of PM H+-ATPase have not been fully elucidated. Recently, we established a new immunohistochemical technique for detecting guard-cell PM H+-ATPase phosphorylation using leaves, which was expected to facilitate investigations with a single leaf. In this study, we applied the technique to genetic screening experiment to explore novel regulators for the phosphorylation of PM H+-ATPase in guard cells, as well as stomatal development. We successfully performed phenotyping using a single leaf. During the experiment, we identified a mutant exhibiting high stomatal density, jozetsu (jzt), named after a Japanese word meaning 'talkative'. We found that a novel semi-dominant mutation in BRASSINOSTEROID SIGNALING KINASE1 (BSK1) is responsible for the phenotype in jzt mutant. The present results demonstrate that the new immunohistochemical technique has a wide range of applications, and the novel mutation would provide genetic tool to expand our understanding of plant development mediated by brassinosteroid signaling.

Light-induced stomatal opening requires phosphorylation of the C-terminal autoinhibitory domain of plasma membrane H+-ATPase

Plasma membrane H+-ATPase provides the driving force for light-induced stomatal opening. However, the mechanisms underlying the regulation of its activity remain unclear. Here, we show that the phosphorylation of two Thr residues in the C-terminal autoinhibitory domain is crucial for H+-ATPase activation and stomatal opening in Arabidopsis thaliana. Using phosphoproteome analysis, we show that blue light induces the phosphorylation of Thr-881 within the C-terminal region I, in addition to penultimate Thr-948 in AUTOINHIBITED H+-ATPASE 1 (AHA1). Based on site-directed mutagenesis experiments, phosphorylation of both Thr residues is essential for H+ pumping and stomatal opening in response to blue light. Thr-948 phosphorylation is a prerequisite for Thr-881 phosphorylation by blue light. Additionally, red light-driven guard cell photosynthesis induces Thr-881 phosphorylation, possibly contributing to red light-dependent stomatal opening. Our findings provide mechanistic insights into H+-ATPase activation that exploits the ion transport across the plasma membrane and light signalling network in guard cells.

Phosphorylation of plasma membrane H+-ATPase Thr881 participates in light-induced stomatal opening

Plasma membrane (PM) H+-ATPase is crucial for light-induced stomatal opening and phosphorylation of a penultimate residue, Thr948 (pen-Thr, numbering according to Arabidopsis AHA1) is required for enzyme activation. In this study, a comprehensive phosphoproteomic analysis using guard cell protoplasts from Vicia faba shows that both red and blue light increase the phosphorylation of Thr881, of PM H+-ATPase. Light-induced stomatal opening and the blue light-induced increase in stomatal conductance are reduced in transgenic Arabidopsis plants expressing mutant AHA1-T881A in aha1-9, whereas the blue light-induced phosphorylation of pen-Thr is unaffected. Auxin and photosynthetically active radiation induce the phosphorylation of both Thr881 and pen-Thr in etiolated seedlings and leaves, respectively. The dephosphorylation of phosphorylated Thr881 and pen-Thr are mediated by type 2 C protein phosphatase clade D isoforms. Taken together, Thr881 phosphorylation, in addition of the pen-Thr phosphorylation, are important for PM H+-ATPase function during physiological responses, such as light-induced stomatal opening in Arabidopsis thaliana.

The crucial role of lateral root angle in enhancing drought resilience in cotton

Introduction

Plant responses to drought stress are influenced by various factors, including the lateral root angle (LRA), stomatal regulation, canopy temperature, transpiration rate and yield. However, there is a lack of research that quantifies their interactions, especially among different cotton varieties.

Methods

This experiment included two water treatments: well-watered (75 ± 5% soil relative water content) and drought stress (50 ± 5% soil relative water content) starting from the three-leaf growth stage.

Results

The results revealed that different LRA varieties show genetic variation under drought stress. Among them, varieties with smaller root angles show greater drought tolerance. Varieties with smaller LRAs had significantly increased stomatal opening by 15% to 43%, transpiration rate by 61.24% and 62.00%, aboveground biomass by 54% to 64%, and increased seed cotton yield by 76% to 79%, and decreased canopy temperature by 9% to 12% under drought stress compared to the larger LRAs. Varieties with smaller LRAs had less yield loss under drought stress, which may be due to enhanced access to deeper soil water, compensating for heightened stomatal opening and elevated transpiration rates. The increase in transpiration rate promotes heat dissipation from leaves, thereby reducing leaf temperature and protecting leaves from damage.

Discussion

Demonstrating the advantages conferred by the development of a smaller LRA under drought stress conditions holds value in enhancing cotton's resilience and promoting its sustainable adaptation to abiotic stressors.

Stomatal responses to VPD utilize guard cell intracellular signaling components

Stomatal pores, vital for CO2 uptake and water loss regulation in plants, are formed by two specialized guard cells. Despite their importance, there is limited understanding of how guard cells sense and respond to changes in vapor pressure difference (VPD). This study leverages a selection of CO2 hyposensitive and abscisic acid (ABA) signaling mutants in Arabidopsis, including heterotrimeric G protein mutants and RLK (receptor-like kinase) mutants, along with a variety of canola cultivars to delve into the intracellular signaling mechanisms prompting stomatal closure in response to high VPD. Stomatal conductance response to step changes in VPD was measured using the LI-6800F gas exchange system. Our findings highlight that stomatal responses to VPD utilize intracellular signaling components. VPD hyposensitivity was particularly evident in mutants of the ht1 (HIGH LEAF TEMPERATURE1) gene, which encodes a protein kinase expressed mainly in guard cells, and in gpa1-3, a null mutant of the sole canonical heterotrimeric Gα subunit, previously implicated in stomatal signaling. Consequently, this research identifies a nexus in the intricate relationships between guard cell signal perception, stomatal conductance, environmental humidity, and CO2 levels.

Exogenous application of pectin triggers stomatal closure and immunity in Arabidopsis

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.

Null mutants of a tomato Rho of plants exhibit enhanced water use efficiency without a penalty to yield

Improving water use efficiency in crops is a significant challenge as it involves balancing water transpiration and CO2 uptake through stomatal pores. This study investigates the role of SlROP9, a tomato Rho of Plants protein, in guard cells and its impact on plant transpiration. The results reveal that SlROP9 null mutants exhibit reduced stomatal conductance while photosynthetic CO2 assimilation remains largely unaffected. Notably, there is a notable decrease in whole-plant transpiration in the rop9 mutants compared to the wild type, especially during noon hours when the water pressure deficit is high. The elevated stomatal closure observed in rop9 mutants is linked to an increase in reactive oxygen species formation. This is very likely dependent on the respiratory burst oxidase homolog (RBOH) NADPH oxidase and is not influenced by abscisic acid (ABA). Consistently, activated ROP9 can interact with RBOHB in both yeast and plants. In diverse tomato accessions, drought stress represses ROP9 expression, and in Arabidopsis stomatal guard cells, ABA suppresses ROP signaling. Therefore, the phenotype of the rop9 mutants may arise from a disruption in ROP9-regulated RBOH activity. Remarkably, large-scale field experiments demonstrate that the rop9 mutants display improved water use efficiency without compromising fruit yield. These findings provide insights into the role of ROPs in guard cells and their potential as targets for enhancing water use efficiency in crops.

Effects of light spectra on morphological characteristics, primary and specialized metabolites of Thymus vulgaris L

Light is a crucial environmental factor that profoundly influences the growth and development of plants. However, the precise mechanisms by which light affects biochemical processes and growth and development factors in Thymus vulgaris remain unknown, necessitating further investigation. Hence, this study aimed to investigate the impact of different light spectra, including red, blue, red-blue, and white lights, on the morphological characteristics, primary, and specialized metabolites of T. vulgaris. Compared to white light, red light significantly increased leaf area (by 64 %), the number of branches (by 132 %), and dry weight (by 6.2 %), although a 40 % reduction in fresh weight was observed under red light conditions. Red-blue light notably enhanced canopy width, fresh weight, and dry weight. Gas chromatography/mass spectrometry (GC/MS) analysis of the plant's essential oil (EO) revealed that p-Cymene and γ-Terpinene were present at the highest levels. Notably, p-Cymene exhibited the highest concentrations under white light and blue light treatments, reaching 60.92 % and 59.53 %, respectively. Moreover, under the same light conditions, phenol and antioxidant levels were significantly elevated. Overall, these findings indicate that red and red-blue light spectra are the most favorable for thyme production.

GIGANTEA Unveiled: Exploring Its Diverse Roles and Mechanisms

GIGANTEA (GI) is a conserved nuclear protein crucial for orchestrating the clock-associated feedback loop in the circadian system by integrating light input, modulating gating mechanisms, and regulating circadian clock resetting. It serves as a core component which transmits blue light signals for circadian rhythm resetting and overseeing floral initiation. Beyond circadian functions, GI influences various aspects of plant development (chlorophyll accumulation, hypocotyl elongation, stomatal opening, and anthocyanin metabolism). GI has also been implicated to play a pivotal role in response to stresses such as freezing, thermomorphogenic stresses, salinity, drought, and osmotic stresses. Positioned at the hub of complex genetic networks, GI interacts with hormonal signaling pathways like abscisic acid (ABA), gibberellin (GA), salicylic acid (SA), and brassinosteroids (BRs) at multiple regulatory levels. This intricate interplay enables GI to balance stress responses, promoting growth and flowering, and optimize plant productivity. This review delves into the multifaceted roles of GI, supported by genetic and molecular evidence, and recent insights into the dynamic interplay between flowering and stress responses, which enhance plants' adaptability to environmental challenges.

Stomatal aperture dynamics coupling mechanically passive and ionically active mechanisms

Stomata are the key nodes linking photosynthesis and transpiration. By regulating the opening degree of stomata, plants successively achieve the balance between water loss and carbon dioxide acquisition. The dynamic behaviour of stomata is an important cornerstone of plant adaptability. Though there have been miscellaneous experimental results on stomata and their constituent cells, the guard cells and the subsidiary cells, current theory of stomata regulation is far from clear and unified. In this work, we develop an integrated model to describe the stomatal dynamics of seed plants based on existing experimental results. The model includes three parts: (1) a passive mechanical model of the stomatal aperture as a bivariate function of the guard-cell turgor and the subsidiary-cell turgor; (2) an active regulation model with a target ion-content in guard cells as a function of their water potential; and (3) a dynamical model for the movement of potassium ions and water content. Our model has been used to reproduce abundant experimental phenomena semi-quantitatively. With accurately measured parameters, our model can also be used to predict stomatal responses to changes of environmental conditions.

Small holes, big impact: Stomata in plant-pathogen-climate epic trifecta

The regulation of stomatal aperture opening and closure represents an evolutionary battle between plants and pathogens, characterized by adaptive strategies that influence both plant resistance and pathogen virulence. The ongoing climate change introduces further complexity, affecting pathogen invasion and host immunity. This review delves into recent advances on our understanding of the mechanisms governing immunity-related stomatal movement and patterning with an emphasis on the regulation of stomatal opening and closure dynamics by pathogen patterns and host phytocytokines. In addition, the review explores how climate changes impact plant-pathogen interactions by modulating stomatal behavior. In light of the pressing challenges associated with food security and the unpredictable nature of climate changes, future research in this field, which includes the investigation of spatiotemporal regulation and engineering of stomatal immunity, emerges as a promising avenue for enhancing crop resilience and contributing to climate control strategies.

Physiological responses of coriander (Coriandrum sativum L.) to exogenous 2,4-epibrassinolide at different concentrations

BACKGROUND

Brassinolide, known as the seventh plant hormone, can improve the photosynthetic capacity of plants, promote plant growth and development, promote the formation of horticultural crop yield, improve the quality of horticultural crops, and also improve the ability of plants to resist biological and abiotic stresses.

RESULTS

The effects of different concentrations of exogenously sprayed 2,4-epibrassinolide (EBR) on growth, physiological and photosynthetic characteristics of 'All-round large leaf coriander' were studied in substrate culture. The results showed that 0.05, 0.1, and 0.5 mg.L- 1 EBR promoted the growth of coriander and increased the aboveground fresh and dry weights, with 0.5 mg.L- 1 EBR having the most significant effect. Spraying 0.1 mg.L- 1 EBR increased the content of soluble sugars and protein of coriander leaves. Spraying 0.1 and 0.5 mg.L- 1 EBR significantly increased the chlorophyll content and photosynthetic parameters of coriander leaves, and 0.5 mg.L- 1 EBR also significantly increased the chlorophyll fluorescence parameters of coriander leaves. Spraying 0.5 mg.L- 1 EBR upregulated the expression of CsRbcS, CsFBPase, and CsAld. Correlation analysis showed that aboveground fresh weight under exogenous EBR treatment was significantly positively correlated with aboveground dry weight, plant height, Pn, Gs, Ci, and CsAld (P < 0.05), and soluble sugar content was significantly positively correlated with the number of leaves, Y(II), qP, and CsRbcS. The results of the principal component analysis (PCA) showed that there was a significant separation between the treatment and the control groups. Spraying 0.5 mg.L- 1 EBR can promote the growth of coriander, improve the quality of coriander leaves, and strengthen coriander leaf photosynthetic capacity. This study provides new insights into the promotion of coriander growth and development following the application of exogenous EBR.

CONCLUSION

Exogenous EBR treatment increased coriander plant height, leaf growth and aboveground dry weight, and enhanced photosynthesis. Exogenous spraying of 0.5 mg.L- 1 EBR had the most significant effect.

Pilot-scale genome-wide association mapping in diverse sorghum germplasms identified novel genetic loci linked to major agronomic, root and stomatal traits

This genome-wide association studies (GWAS) used a subset of 96 diverse sorghum accessions, constructed from a large collection of 219 accessions for mining novel genetic loci linked to major agronomic, root morphological and physiological traits. The subset yielded 43,452 high quality single nucleotide polymorphic (SNP) markers exhibiting high allelic diversity. Population stratification showed distinct separation between caudatum and durra races. Linkage disequilibrium (LD) decay was rapidly declining with increasing physical distance across all chromosomes. The initial 50% LD decay was ~ 5 Kb and background level was within ~ 80 Kb. This study detected 42 significant quantitative trait nucleotide (QTNs) for different traits evaluated using FarmCPU, SUPER and 3VmrMLM which were in proximity with candidate genes related and were co-localized in already reported quantitative trait loci (QTL) and phenotypic variance (R2) of these QTNs ranged from 3 to 20%. Haplotype validation of the candidate genes from this study resulted nine genes showing significant phenotypic difference between different haplotypes. Three novel candidate genes associated with agronomic traits were validated including Sobic.001G499000, a potassium channel tetramerization domain protein for plant height, Sobic.010G186600, a nucleoporin-related gene for dry biomass, and Sobic.002G022600 encoding AP2-like ethylene-responsive transcription factor for plant yield. Several other candidate genes were validated and associated with different root and physiological traits including Sobic.005G104100, peroxidase 13-related gene with root length, Sobic.010G043300, homologous to Traes_5BL_8D494D60C, encoding inhibitor of apoptosis with iWUE, and Sobic.010G125500, encoding zinc finger, C3HC4 type domain with Abaxial stomatal density. In this study, 3VmrMLM was more powerful than FarmCPU and SUPER for detecting QTNs and having more breeding value indicating its reliable output for validation. This study justified that the constructed subset of diverse sorghums can be used as a panel for mapping other key traits to accelerate molecular breeding in sorghum.

Spectral composition of LED light differentially affects biomass, photosynthesis, nutrient profile, and foliar nitrate accumulation of lettuce grown under various replacement methods of nutrient solution

To enhance crop yield and quality, plant cultivation in controlled-growing systems is an alternative to traditional open-field farming. The use of light-emitting diode (LED) as an adjustable light source represents a promising approach to improve plant growth, metabolism, and function. The objective of this study was to assess the impact of different light spectra (red, red/blue (3:1), blue, and white) with an emission peak of around 656, 656, 450, and 449 nm, respectively, under various replacement methods of nutrient solution (complete replacement (CR), EC-based replacement (ECBR), and replacing based on plant needs (RBPN)), on biomass, physiological traits, and macro- and micronutrient contents of two best-known lettuce varieties, Lollo Rossa (LR) and Lollo Bionda (LB), in the nutrient film technique (NFT) hydroponic system. The results indicated that mix of red and blue LED spectra under RBPN method is the most effective treatment to enhance fresh and dry weights of lettuce plants. In addition, red LED spectrum under RBPN, and red and blue light under ECBR nutrient solution significantly increased leaf stomatal conductance, net photosynthesis and transpiration rate, and intercellular CO2 concentration of LR variety. Phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mn) content in LR variety, and iron (Fe), zinc (Zn), copper (Cu), and manganese (Mn) content in both varieties increased upon exposure to blue and red LED light spectrum with RBPN method. Our results suggest that exposure to combination of red and blue light along with feeding plants using RBPN and ECBR methods can increase absorption of macro- and micronutrient elements and improve photosynthetic properties, and eventually increase lettuce yield with lower nitrate accumulation.

Model-based inference of a plant-specific dual role for HOPS in regulating guard cell vacuole fusion

Stomata are the pores on a leaf surface that regulate gas exchange. Each stoma consists of two guard cells whose movements regulate pore opening and thereby control CO2 fixation and water loss. Guard cell movements depend in part on the remodeling of vacuoles, which have been observed to change from a highly fragmented state to a fused morphology during stomata opening. This change in morphology requires a membrane fusion mechanism that responds rapidly to environmental signals, allowing plants to respond to diurnal and stress cues. With guard cell vacuoles being both large and responsive to external signals, stomata represent a unique system in which to delineate mechanisms of membrane fusion. Fusion of vacuole membranes is a highly conserved process in eukaryotes, with key roles played by two multi-subunit complexes: HOPS (homotypic fusion and vacuolar protein sorting) and SNARE (soluble NSF attachment protein receptor). HOPS is a vacuole tethering factor that is thought to chaperone SNAREs from apposing vacuole membranes into a fusion-competent complex capable of rearranging membranes. To resolve a counter-intuitive observation regarding the role of HOPS in regulating plant vacuole morphology, we derived a quantitative model of vacuole fusion dynamics and used it to generate testable predictions about HOPS-SNARE interactions. We derived our model by applying simulation-based inference to integrate prior knowledge about molecular interactions with limited, qualitative observations of emergent vacuole phenotypes. By constraining the model parameters to yield the emergent outcomes observed for stoma opening - as induced by two distinct chemical treatments - we predicted a dual role for HOPS and identified a stalled form of the SNARE complex that differs from phenomena reported in yeast. We predict that HOPS has contradictory actions at different points in the fusion signaling pathway, promoting the formation of SNARE complexes, but limiting their activity.

A comparison of stomatal conductance responses to blue and red light between C3 and C4 photosynthetic species in three phylogenetically-controlled experiments

Introduction

C4 photosynthesis is an adaptation that has independently evolved at least 66 times in angiosperms. C4 plants, unlike their C3 ancestral, have a carbon concentrating mechanism which suppresses photorespiration, often resulting in faster photosynthetic rates, higher yields, and enhanced water use efficiency. Moreover, the presence of C4 photosynthesis greatly alters the relation between CO2 assimilation and stomatal conductance. Previous papers have suggested that the adjustment involves a decrease in stomatal density. Here, we tested if C4 species also have differing stomatal responses to environmental cues, to accommodate the modified CO2 assimilation patterns compared to C3 species.

Methods

To test this hypothesis, stomatal responses to blue and red-light were analysed in three phylogenetically linked pairs of C3 and C4 species from the Cleomaceae (Gynandropsis and Tarenaya), Flaveria, and Alloteropsis, that use either C3 or C4 photosynthesis.

Results

The results showed strongly decreased stomatal sensitivity to blue light in C4 dicots, compared to their C3 counterparts, which exhibited significant blue light responses. In contrast, in C3 and C4 subspecies of the monocot A. semialata, the blue light response was observed regardless of photosynthetic type. Further, the quantitative red-light response varied across species, but the presence or absence of a significant stomatal red-light response was not directly associated with differences in photosynthetic pathway. Interestingly, stomatal density and morphology patterns observed across the three comparisons were also not consistent with patterns commonly asserted for C3 and C4 species.

Discussion

The strongly diminished blue-light sensitivity of stomatal responses in C4 species across two of the comparisons suggests a common C4 feature that may have functional implications. Altogether, the strong prevalence of species-specific effects clearly emphasizes the importance of phylogenetic controls in comparisons between C3 and C4 photosynthetic pathways.

Compensation of adverse growing media effects on plant growth and morphology by supplemental LED lighting

There is an increasing interest in alternatives to peat in growing media due to environmental constraints. However, plants grown in peat substitutes often show impaired growth compared to plants grown in peat-based media. Hence, it would be interesting to know whether these deficiencies can be compensated by supplementing other growth factors, e.g. light. The present study aims to investigate the interactive nature between growing media and supplemental lighting on plant growth and morphology, and to examine whether supplemental light emitting diode (LED) lighting may compensate adverse growing media effects. Basil (Ocimum basilicum L.) and Chinese cabbage (Brassica rapa subsp. pekinensis) were grown in different growing media consisting of peat, green compost, coconut pulp, wood fibre, perlite and sphagnum moss under blue, red and far-red supplemental LED lighting. We found significant interactions between growing media and supplemental photosynthetically active radiation (PAR) on plant growth, morphology and development. At low light intensities, peat-based and substituted growing media performed similarly, whereas with increasing light intensities the peat-based growing media significantly outperformed their alternatives. The substrate choice determines the required amount of supplemental light to compensate for adverse growing media effects and the amount varies depending on plant species and season. Thereby, it was indicated that red light alleviates adverse growing media effects best. We also found that far-red light is not effective when background PAR is low and becomes more effective under high background PAR. The implications and prospects of the results are discussed.

Changes in the light environment: Short-term responses of photosynthesis and metabolism in spinach

Modification in the light environment can induce several changes even within a short time. In this article, light intensity and spectrum-dependent changes in photosynthetic and metabolic processes were investigated in spinach leaves. Short-term exposure of the youngest fully developed leaves provided an elevated CO2 assimilation capacity under red light compared with blue or white light, although the electron transport rate was lower. The stomatal opening was mainly stimulated by blue light. These spectrum-induced changes also depended on light intensity. When white light was used to activate the photosynthesis, the white light showed a similar light response to blue light regarding the electron transport processes and red light in terms of stomatal opening. In contrast, concerning CO2 assimilation characteristics, the white light resembled blue light at low and red light at high light intensities. These results indicate that the photosynthetic processes strongly interact with the light intensity and spectral composition. Furthermore, changes in spectral composition modified the primary metabolic processes as well. Red light induced the sugar accumulation, while more organic acids that belong to the respiration pathway were produced under blue and white lights. These changes occurred even within a short (30 min) time frame. These results also draw attention to the importance of the light environment used during the measurements of the photosynthetic activity of plants and/or sample collections.

Leaf starch metabolism sets the phase of stomatal rhythm

In leaves of C3 and C4 plants, stomata open during the day to favor CO2 entry for photosynthesis and close at night to prevent inefficient transpiration of water vapor. The circadian clock paces rhythmic stomatal movements throughout the diel (24-h) cycle. Leaf transitory starch is also thought to regulate the diel stomatal movements, yet the underlying mechanisms across time (key moments) and space (relevant leaf tissues) remain elusive. Here, we developed PhenoLeaks, a pipeline to analyze the diel dynamics of transpiration, and used it to screen a series of Arabidopsis (Arabidopsis thaliana) mutants impaired in starch metabolism. We detected a sinusoidal, endogenous rhythm of transpiration that overarches days and nights. We determined that a number of severe mutations in starch metabolism affect the endogenous rhythm through a phase shift, resulting in delayed stomatal movements throughout the daytime and diminished stomatal preopening during the night. Nevertheless, analysis of tissue-specific mutations revealed that neither guard-cell nor mesophyll-cell starch metabolisms are strictly required for normal diel patterns of transpiration. We propose that leaf starch influences the timing of transpiration rhythm through an interplay between the circadian clock and sugars across tissues, while the energetic effect of starch-derived sugars is usually nonlimiting for endogenous stomatal movements.

The asymmetric photosynthetic characteristics of the isobilateral sorghum leaves under the illumination of the diffuse light

The difference between photosynthesis on the two leaf sides (dorsoventral asymmetry) of photosynthesis is important for light-use patterns, but the asymmetry is environment dependent. Its role in photosynthetic regulation has been intensively studied, but little is known about the impacts of direct and diffuse light on the asymmetry. Because of the current changing fraction of diffuse light in sky radiation, this study investigated the dorsoventral asymmetry of photosynthetic traits under direct and diffuse light conditions in an important food and energy crop, Sorghum bicolor L. A unique method was used to investigate the specific gas exchange of each leaf surface. Anatomical and morphological traits were different between the two surfaces of sorghum leaves, which might result in photosynthetic asymmetry. The variations in photosynthetic rates and stomatal conductance were significant between the two surfaces in direct and diffuse light, but the degree of dorsoventral asymmetry decreased in diffuse light. The integrated P _N and G _s of the adaxial illumination were significantly higher than that of abaxial illumination both in direct and diffuse light in sorghum leaves, but the ASI of the integrated P _Nwas 2.83 in direct light, while significantly dropped to 1.69 in diffuse light. Significant morphological differences between the two surfaces might cause photosynthetic asymmetry in the sorghum leaves. The variations of specific gas exchange were significant between direct and diffuse light, including in the incident and self-transmitted light. Compared with direct light, diffuse light reduced the stomatal sensitivity, with the degree of decline being greater in the adaxial surface, which caused weak dorsoventral asymmetry in photosynthesis. The specific photosynthetic characteristics in sorghum leaves varied obviously in direct and diffuse light, including in the incident and self-transmitted light, which contributed to the different overall gas exchange. Compared with direct light, the decline of stomatal sensitivity, which showed positive correlation with stomatal density, caused weakened dorsoventral asymmetry in photosynthesis in diffuse light. The findings provide new insights into dorsoventral asymmetry and the impact of diffuse light on photosynthesis in isobilateral leaves.

Integration of light and ABA signaling pathways to combat drought stress in plants

Drought is one of the most critical stresses, which causes an enormous reduction in crop yield. Plants develop various strategies like drought escape, drought avoidance, and drought tolerance to cope with the reduced availability of water during drought. Plants adopt several morphological and biochemical modifications to fine-tune their water-use efficiency to alleviate drought stress. ABA accumulation and signaling plays a crucial role in the response of plants towards drought. Here, we discuss how drought-induced ABA regulates the modifications in stomatal dynamics, root system architecture, and the timing of senescence to counter drought stress. These physiological responses are also regulated by light, indicating the possibility of convergence of light- and drought-induced ABA signaling pathways. In this review, we provide an overview of investigations reporting light-ABA signaling cross talk in Arabidopsis as well as other crop species. We have also tried to describe the potential role of different light components and their respective photoreceptors and downstream factors like HY5, PIFs, BBXs, and COP1 in modulating drought stress responses. Finally, we highlight the possibilities of enhancing the plant drought resilience by fine-tuning light environment or its signaling components in the future.

Changes in endogenous abscisic acid and stomata of the resurrection fern, Pleopeltis polypodioides, in response to de- and rehydration

PREMISE

While angiosperms respond uniformly to abscisic acid (ABA) by stomatal closure, the response of ferns to ABA is ambiguous. We evaluated the effect of endogenous ABA, hydrogen peroxide (H₂ O₂ ), nitric oxide (NO), and Ca²⁺ , low and high light intensities, and blue light (BL) on stomatal opening of Pleopeltis polypodioides.

METHODS

Endogenous ABA was quantified using gas chromatography-mass spectrometry; microscopy results and stomatal responses to light and chemical treatments were analyzed with Image J.

RESULTS

The ABA content increases during initial dehydration, peaks at 15 h and then decreases to one fourth of the ABA content of hydrated fronds. Following rehydration, ABA content increases within 24 h to the level of hydrated tissue. The stomatal aperture opens under BL and remains open even in the presence of ABA. Closure was strongly affected by BL, NO, and Ca²⁺ , regardless of ABA, H₂ O₂ effect was weak.

CONCLUSIONS

The decrease in the ABA content during extended dehydration and insensitivity of the stomata to ABA suggests that the drought tolerance mechanism of Pleopeltis polypodioides is independent of ABA.

StomaAI: an efficient and user-friendly tool for measurement of stomatal pores and density using deep computer vision

Using microscopy to investigate stomatal behaviour is common in plant physiology research. Manual inspection and measurement of stomatal pore features is low throughput, relies upon expert knowledge to record stomatal features accurately, requires significant researcher time and investment, and can represent a significant bottleneck to research pipelines. To alleviate this, we introduce StomaAI (SAI): a reliable, user-friendly and adaptable tool for stomatal pore and density measurements via the application of deep computer vision, which has been initially calibrated and deployed for the model plant Arabidopsis (dicot) and the crop plant barley (monocot grass). SAI is capable of producing measurements consistent with human experts and successfully reproduced conclusions of published datasets. SAI boosts the number of images that can be evaluated in a fraction of the time, so can obtain a more accurate representation of stomatal traits than is routine through manual measurement. An online demonstration of SAI is hosted at https://sai.aiml.team, and the full local application is publicly available for free on GitHub through https://github.com/xdynames/sai-app.

Guard cell activity of PIF4 and HY5 control transpiration

Whole-plant transpiration, controlled by plant hydraulics and stomatal movement, is regulated by endogenous and environmental signals, with the light playing a dominant role. Stomatal pore size continuously adjusts to changes in light intensity and quality to ensure optimal CO₂ intake for photosynthesis on the one hand, together with minimal water loss on the other. The link between light and transpiration is well established, but the genetic knowledge of how guard cells perceive those signals to affect stomatal conductance is still somewhat limited. In the current study, we evaluated the role of two central light-responsive transcription factors; a bZIP-family transcription factor ELONGATED HYPOCOTYL5 (HY5) and the basic helix-loop-helix (BHLH) transcription factor PHYTOCHROME INTERACTING FACTOR4 (PIF4), in the regulation of steady-state transpiration. We show that overexpression of PIF4 exclusively in guard cells (GCPIF4) decreases transpiration, and can restrain the high transpiration of the pif4 mutant. Expression of HY5 specifically in guard cells (GCHY5) had the opposite effect of enhancing transpiration rates of WT- Arabidopsis and tobacco plants and of the hy5 mutant in Arabidopsis. In addition, we show that GCHY5 can reverse the low transpiration caused by guard cell overexpression of the sugar sensor HEXOKINASE1 (HXK1, GCHXK), an established low transpiring genotype. Finally, we suggest that the GCHY5 reversion of low transpiration by GCHXK requires the auto-activation of the endogenous HY5 in other tissues. These findings support the existence of an ongoing diurnal regulation of transpiration by the light-responsive transcription factors HY5 and PIF4 in the stomata, which ultimately determine the whole-plant water use efficiency.

Plant biology: Putting a break on stomatal opening

Blue light triggers stomatal opening through the phototropin-mediated pathway. A new study shows that light-induced stomatal opening is negatively regulated by three closely related plastidial phospholipases and their downstream oxylipin product.

Light-induced stomatal opening in Arabidopsis is negatively regulated by chloroplast-originated OPDA signaling

Stomatal movement is orchestrated by diverse signaling cascades and metabolic activities in guard cells. Light triggers the opening of the pores through the phototropin-mediated pathway, which leads to the activation of plasma membrane H⁺-ATPase and thereby facilitates potassium accumulation through K_in⁺ channels. However, it remains poorly understood how phototropin signaling is fine-tuned to prevent excessive stomatal opening and consequent water loss. Here, we show that the stomatal response to light is negatively regulated by 12-oxo-phytodienoic acid (OPDA), an oxylipin metabolite produced through enzymatic oxygenation of polyunsaturated fatty acids (PUFAs). We identify a set of phospholipase-encoding genes, phospholipase (PLIP)1/2/3, which are transactivated rapidly in guard cells upon illumination in a phototropin-dependent manner. These phospholipases release PUFAs from the chloroplast membrane, which is oxidized by guard-cell lipoxygenases and further metabolized to OPDA. The OPDA-deficient mutants had wider stomatal pores, whereas mutants containing elevated levels of OPDA showed the opposite effect on stomatal aperture. Transmembrane solute fluxes that drive stomatal aperture were enhanced in lox6-1 guard cells, indicating that OPDA signaling ultimately impacts on activities of proton pumps and K_in⁺ channels. Interestingly, the accelerated stomatal kinetics in lox6-1 leads to increased plant growth without cost in water or macronutrient use. Together, our results reveal a new role for chloroplast membrane oxylipin metabolism in stomatal regulation. Moreover, the accelerated stomatal opening kinetics in OPDA-deficient mutants benefits plant growth and water use efficiency.

Discovery of 2,6-Dihalopurines as Stomata Opening Inhibitors: Implication of an LRX-Mediated H+-ATPase Phosphorylation Pathway

Stomata are pores in the leaf epidermis of plants and their opening and closing regulate gas exchange and water transpiration. Stomatal movements play key roles in both plant growth and stress responses. In recent years, small molecules regulating stomatal movements have been used as a powerful tool in mechanistic studies, as well as key players for agricultural applications. Therefore, the development of new molecules regulating stomatal movement and the elucidation of their mechanisms have attracted much attention. We herein describe the discovery of 2,6-dihalopurines, AUs, as a new stomatal opening inhibitor, and their mechanistic study. Based on biological assays, AUs may involve in the pathway related with plasma membrane H⁺-ATPase phosphorylation. In addition, we identified leucine-rich repeat extensin proteins (LRXs), LRX3, LRX4 and LRX5 as well as RALF, as target protein candidates of AUs by affinity based pull down assay and molecular dynamics simulation. The mechanism of stomatal movement related with the LRXs-RALF is an unexplored pathway, and therefore further studies may lead to the discovery of new signaling pathways and regulatory factors in the stomatal movement.

Physiological and yield responses of contrasting upland rice genotypes towards induced drought

Drought alters rice morphophysiology and reduces grain yield. This study hypothesized that the combined analysis of morphophysiological and agronomic traits enables a systemic approach to responses to water deficit, allowing the selection of resistance markers to upland rice. The objectives were to evaluate the effects of water deficit applied at the reproductive stage in plant water status, leaf gas exchanges, leaf non-structural carbohydrate contents, and agronomic traits in upland rice genotypes; and to verify if the analyzed variables may be applied to group the genotypes according to their tolerance level. Water deficit was induced by irrigation suppression in eight genotypes at R2-R3. Physiological and biochemical traits were evaluated at the end of the water deficit period, thenceforth irrigation was restored until grain maturation for the analysis of the agronomic traits. Water deficit reduced: Ψw (63.64%, average); gs (28-90%); transpiration rate (40.63-65.45%); RWC from Serra Dourada to Esmeralda (43.36-61.48%); net CO2 assimilation from Serra Dourada to Primavera (70.04-99.91%); iWUE from Esmeralda to Primavera (83.98-99.85%); iCE in Esmeralda (99.92%); 100-grain weight in CIRAD and Soberana (13.65-20.63%); and grain yield from Primavera to IAC 164 (34.60-78.85%). Water deficit increased Ci from Cambará to Early mutant (79.64-215.23%), and did not affect the tiller number, shoot dry biomass, fructose, and sucrose contents. The alterations in the variables distinguished groups according to the water regime. RWC, Ψw, leaf gas exchanges, and iCE were valuable traits to distinguish the water regime treatments, but not to group the genotypes according to the drought tolerance level.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12298-023-01287-8.

Frequency and spectrum of M2 mutants and genetic variability in cyto-agronomic characteristics of fenugreek induced by caffeine and sodium azide

Trigonella foenum graecum L. (Fenugreek) is a valuable medicinal plant cultivated for decades for its therapeutic characteristics. Still no pronounced improvement concerning wild form was accomplished as it is a self-pollinating crop. Induced mutagenesis is encouraged as a remarkable tool on this plant to circumvent the genetic bottleneck of cultivated germplasms. As a result, novel allelomorphic combinations for short-term agronomic attributes were developed. Fenugreek cultivar Pusa Early Bunching, selected for the present experiment, was mutagenized with five doses (0.2%, 0.4%, 0.6%, 0.8%, and 1.0%) of caffeine and sodium azide (SA) to evaluate its impact on the qualitative and quantitative traits of M₁ and M₂ generation conducted in a Complete Randomized Block Design (CRBD), replicated five times during 2019-2020 and 2020-2021, respectively. The frequency of induced phenotypic variations was assessed in M₂ progenies, resulting in the identification and isolation of a broad spectrum of mutants with altered phenotypes. Mutagenic effectiveness and efficiency were found to be maximum at lower concentrations of the mutagen treatments and highest in SA, followed by caffeine. Various morphological mutants with modified characters were observed at different concentrations in M₂ generation. The spectrum of mutations was wider in SA than in caffeine, as caffeine produced 51 while SA produced 54 individual mutants under seven major categories. The maximum frequency of morphological mutants was associated with leaf, followed by plant size, plant growth habit, pod, seed size, seed shape, and seed color. Morphological and structural variations in the guard cells of stomata and seeds were observed through scanning electron microscopy. The variations created in the economically important traits may enrich the genetic diversity of this plant species. Moreover, these morphological mutants may serve as a source of elite genes in further breeding programs of fenugreek.

Multiple cyclic nucleotide-gated channels function as ABA-activated Ca2+ channels required for ABA-induced stomatal closure in Arabidopsis

Abscisic acid (ABA)-activated inward Ca2+-permeable channels in the plasma membrane (PM) of guard cells are required for the initiation and regulation of ABA-specific cytosolic Ca2+ signaling and stomatal closure in plants. But the identities of the PM Ca2+ channels are still unknown. We hypothesized that the ABA-activated Ca2+ channels consist of multiple CYCLIC NUCLEOTIDE-GATED CHANNEL (CNGC) proteins from the CNGC family, which is known as a Ca2+-permeable channel family in Arabidopsis (Arabidopsis thaliana). In this research, we observed high expression of multiple CNGC genes in Arabidopsis guard cells, namely CNGC5, CNGC6, CNGC9, and CNGC12. The T-DNA insertional loss-of-function quadruple mutant cngc5-1 cngc6-2 cngc9-1 cngc12-1 (hereafter c5/6/9/12) showed a strong ABA-insensitive phenotype of stomatal closure. Further analysis revealed that ABA-activated Ca2+ channel currents were impaired, and ABA-specific cytosolic Ca2+ oscillation patterns were disrupted in c5/6/9/12 guard cells compared with in wild-type guard cells. All ABA-related phenotypes of the c5/6/9/12 mutant were successfully rescued by the expression of a single gene out of the four CNGCs under the respective native promoter. Thus, our findings reveal a type of ABA-activated PM Ca2+ channel comprising multiple CNGCs, which is essential for ABA-specific Ca2+ signaling of guard cells and ABA-induced stomatal closure in Arabidopsis.

Deep Transfer Learning-Based Multi-Object Detection for Plant Stomata Phenotypic Traits Intelligent Recognition

Plant stomata phenotypic traits can provide a basis for enhancing crop tolerance in adversity. Manually counting the number of stomata and measuring the height and width of stomata obviously cannot satisfy the high-throughput data. How to detect and recognize plant stomata quickly and accurately is the prerequisite and key for studying the physiological characteristics of stomata. In this research, we consider stomata recognition as a multi-object detection problem, and propose an end-to-end framework for intelligent detection and recognition of plant stomata based on feature weights transfer learning and YOLOv4 network. It is easy to operate and greatly facilitates the analysis of stomata phenotypic traits in high-throughput plant epidermal cell images. For different cultivars, multi-scales, rich background features, high density, and small stomata object images, the proposed method can precisely locate multiple stomata in microscope images and automatically give phenotypic traits of stomata. Users can also adjust the corresponding parameters to maximize the accuracy and scalability of automatic stomata detection and recognition. Experimental results on actual data provided by the National Maize Improvement Center show that the proposed method is superior to the existing methods in high stomata automatic detection and recognition accuracy, low training cost, strong generalization ability.

Different LED light intensity and quality change perennial ryegrass (Lolium perenne L.) physiological and growth responses and water and energy consumption

Light intensity and spectral composition highly affect plant physiology, growth, and development. According to growing conditions, each species and/or cultivar has an optimum light intensity to drive photosynthesis, and different light spectra trigger photosynthetic responses and regulate plant development differently. For the maintenance of natural sports pitches, namely professional football competitions, turf quality is a key condition. Due to the architecture of most football stadiums, the lawns receive low intensities of natural light, so supplementary artificial lighting above the turf is required. The use of light-emitting diodes (LEDs) can have a higher cost-benefit ratio than traditional high-pressure sodium lamps. The continuous emission spectrum, combined with high spectral selectivity and adjustable optical power, can be used to optimize plant growth and development. Thus, perennial ryegrass (Lolium perenne L.) plants, commonly used for lawns, were primarily grown at three different intensities (200, 300, and 400 μmol m^-2 s^-1) of cool white light. Despite the higher water and energy consumption, 400 μmol m^-2 s^-1 maximizes the plant's efficiency, with higher photosynthetic rates and foliar pigment concentration, and more foliar soluble sugars and aboveground biomass accumulation. Then, it was evaluated the perennial ryegrass (Double and Capri cultivars) response to different spectral compositions [100% cool white (W), 80% Red:20% Blue (R80:B20), 90% Red:10% Blue (R90:B10), and 65% Red:15% Green:20% Blue (R65:G15:B20)] at 400 μmol m^-2 s^-1. Both cultivars exhibited similar responses to light treatments. In general, W contributed to the better photosynthetic performance and R90:B10 to the worst one. Water consumption and aboveground biomass were equal in all light treatments. R80:B20 allows energy savings of 24.3% in relation to the W treatment, showing a good compromise between physiological performance and energy consumption.

Leaf physiology variations are modulated by natural variations that underlie stomatal morphology in Populus

Stomata are essential for photosynthesis and abiotic stress tolerance. Here, we used multiomics approaches to dissect the genetic architecture and adaptive mechanisms that underlie stomatal morphology in Populus tomentosa juvenile natural population (303 accessions). We detected 46 candidate genes and 15 epistatic gene-pairs, associated with 5 stomatal morphologies and 18 leaf development and photosynthesis traits, through genome-wide association studies. Expression quantitative trait locus mapping revealed that stomata-associated gene loci were significantly associated with the expression of leaf-related genes; selective sweep analysis uncovered significant differentiation in the allele frequencies of genes that underlie stomatal variations. An allelic regulatory network operating under drought stress and adequate precipitation conditions, with three key regulators (DUF538, TRA2 and AbFH2) and eight interacting genes, was identified that might regulate leaf physiology via modulation of stomatal shape and density. Validation of candidate gene variations in drought-tolerant and F₁ hybrid populations of P. tomentosa showed that the DUF538, TRA2 and AbFH2 loci cause functional stabilisation of spatiotemporal regulatory, whose favourable alleles can be faithfully transmitted to offspring. This study provides insights concerning leaf physiology and stress tolerance via the regulation of stomatal determination in perennial plants.

Plant Plasma Membrane Proton Pump: One Protein with Multiple Functions

In plants, the plasma membrane proton pump (PM H⁺-ATPase) regulates numerous transport-dependent processes such as growth, development, basic physiology, and adaptation to environmental conditions. This review explores the multifunctionality of this enzyme in plant cells. The abundance of several PM H⁺-ATPase isogenes and their pivotal role in energizing transport in plants have been connected to the phenomena of pleiotropy. The multifunctionality of PM H⁺-ATPase is a focal point of numerous studies unraveling the molecular mechanisms of plant adaptation to adverse environmental conditions. Furthermore, PM H⁺-ATPase is a key element in plant defense mechanisms against pathogen attack; however, it also functions as a target for pathogens that enable plant tissue invasion. Here, we provide an extensive review of the PM H⁺-ATPase as a multitasking protein in plants. We focus on the results of recent studies concerning PM H⁺-ATPase and its role in plant growth, physiology, and pathogenesis.

The red/blue light ratios from light-emitting diodes affect growth and flower quality of Hippeastrum hybridum 'Red Lion'

Light quality strongly impacts the growth and flower quality of ornamental plants. The optimum light quality for the growth and flowering of Hippeastrum remains to be validated. In the present study, we investigated the effect of the red/blue light ratio of LEDs on the growth and flowering quality of H. hybrid 'Red Lion'. Two LEDs with red/blue light ratio of 1:9 (R₁₀B₉₀) and 9:1 (R₉₀B₁₀) were designed. LEDs of white light were the control. In the earlier vegetative and reproductive growth phase, R₉₀B₁₀ increased the biomass of the bulbs, leaves, and flowers. Compared with the control and R₁₀B₉₀ group, R₉₀B₁₀ LEDs delayed flowering by 2.30 d and 3.26 d, respectively. Based on chlorophyll contents, photosynthetic capacity, chlorophyll fluorescence parameters, and carbohydrate contents, the photosynthesis rate was higher in the R₁₀B₉₀ group. Optimal red and blue light intensity promoted the accumulation of carbohydrates and early flowering and prolonged the flowering period of H. hybrid. Microscopic analysis showed that stomatal density was high, and the number of chloroplasts was large in the R₁₀B₉₀ treatment group, which enhanced photosynthesis. Particularly, R₁₀B₉₀ promoted the expression of seven key genes related to chlorophyll synthesis. R₁₀B₉₀ also promoted early overexpression of the HpCOL gene that promotes early flowering. Thus, higher blue light and 10% red light intensities promote early and extended flowering, while higher red light and 10% blue light promote vegetative plant growth but delay flowering.

COP1 mutation causes low leaf temperature under various abiotic stresses in Arabidopsis thaliana

Stomata are microscopic pores on epidermal cells of leaves and stems that regulate water loss and gas exchange between the plant and its environment. Constitutive photomorphogenic 1 (COP1) is an E3 ubiquitin ligase that is involved in plant growth and development and multiple abiotic stress responses by regulating the stability of various target proteins. However, little is known about how COP1 controls stomatal aperture and leaf temperature under various environmental conditions. Here, we show that COP1 participates in leaf temperature and stomatal closure regulation under normal and stress conditions in Arabidopsis. Leaf temperature of cop1 mutants was relatively lower than that of wild type (WT) under drought, salt, and heat stress and after abscisic acid (ABA), CaCl₂, and H₂O₂ treatments. However, leaf temperature was generally higher in both WT and cop1 mutants after abiotic stress and chemical treatment than that of untreated WT and cop1 mutants. Stomatal aperture was wider in cop1 mutants than that in WT under all conditions tested, although the extent of stomatal closure varied between WT and cop1 mutants. Under dark conditions, leaf temperature was also lower in cop1 mutants than that in WT. Expression of the genes encoding ABA receptors, ABA biosynthesis proteins, positive regulators of stomatal closure and heat tolerance, and ABA-responsive proteins was lower in cop1 mutants that that in WT. In addition, expression of respiration-related genes was lower in cop1 mutants that that in WT. Taken together, the data provide evidence that mutations in COP1 lead to wider stomatal aperture and higher leaf temperature under normal and stress conditions, indicating that leaf temperature is highly correlated with stomatal aperture.

Elevated CO2 induces rapid dephosphorylation of plasma membrane H+ -ATPase in guard cells

Light induces stomatal opening, which is driven by plasma membrane (PM) H⁺ -ATPase in guard cells. The activation of guard-cell PM H⁺ -ATPase is mediated by phosphorylation of the penultimate C-terminal residue, threonine. The phosphorylation is induced by photosynthesis as well as blue light photoreceptor phototropin. Here, we investigated the effects of cessation of photosynthesis on the phosphorylation level of guard-cell PM H⁺ -ATPase in Arabidopsis thaliana. Immunodetection of guard-cell PM H⁺ -ATPase, time-resolved leaf gas-exchange analyses and stomatal aperture measurements were carried out. We found that light-dark transition of leaves induced dephosphorylation of the penultimate residue at 1 min post-transition. Gas-exchange analyses confirmed that the dephosphorylation is accompanied by an increase in the intercellular CO₂ concentration, caused by the cessation of photosynthetic CO₂ fixation. We discovered that CO₂ induces guard-cell PM H⁺ -ATPase dephosphorylation as well as stomatal closure. Interestingly, reverse-genetic analyses using guard-cell CO₂ signal transduction mutants suggested that the dephosphorylation is mediated by a mechanism distinct from the established CO₂ signalling pathway. Moreover, type 2C protein phosphatases D6 and D9 were required for the dephosphorylation and promoted stomatal closure upon the light-dark transition. Our results indicate that CO₂ -mediated dephosphorylation of guard-cell PM H⁺ -ATPase underlies stomatal closure.

Tryptophan synthase ß subunit 1 affects stomatal phenotypes in Arabidopsis thaliana

Stomata open in response to several environmental stimuli, such as light and low CO₂. Plasma membrane (PM) H⁺-ATPase in guard cells plays a pivotal role for light-induced stomatal opening. In contrast, stomata close in response to the dark or plant hormone abscisic acid (ABA). However, molecular mechanisms of stomatal movements remain unclear. To elucidate the molecular mechanism of stomatal movements, we performed a genetic screen based on stomatal aperture-dependent weight decrease of detached leaves from EMS-treated Arabidopsis thaliana and isolated a rapid transpiration in detached leaves 2 (rtl2). The rtl2 mutant showed constitutive open-stomata phenotype with lower leaf temperature. ABA had no effect on stomatal aperture in rtl2. The rtl2 mutant also showed increased stomatal density, severe dwarf phenotype with pale green leaves and dark veins. Map-based analysis of the RTL2 locus revealed that the rtl2 mutant possesses a single nucleotide substitution, which induces amino acid substitution Gly162 to Glu in the tryptophan synthase ß subunit 1 (TSB1). The TSB1 encodes an enzyme in tryptophan (Trp) biosynthetic pathway. Amount of TSB1 protein was drastically reduced in rtl2 mutant. A different allele of tsb1 mutant (tsb1-1) also showed constitutive open-stomata phenotype with reduced TSB1 protein as in rtl2. Analyses of test-crossed plants of rtl2 and tsb1-1 showed open-stomata and dwarf phenotypes. These results indicate that a responsible gene for rtl2 is TSB1. We further investigated stomatal phenotype in mutants from Trp biosynthetic pathway, such as wei2-1 wei7-1, trp3-1, and tsb2-1. The trp3-1 mutant showed significant wider stomatal aperture as well as tsb1-1. Trp biosynthetic pathway closely relates to auxin biosynthesis. Then, we investigated auxin responsible genes and found that an expression of AUR3 was up in rtl2. In contrast, auxin had no effect on stomatal aperture in Arabidopsis and the phosphorylation status of PM H⁺-ATPase in guard cell protoplasts from Vicia faba. In addition, auxin antagonist had no effect on stomatal aperture. Interestingly, tsb1-1 grown under hydroponic culture system showed normal stomatal aperture by exogenously application of Trp. These results suggest that open stomata phenotype in tsb1-1 is due to Trp deficiency but not auxin.