Stomatal Closure Research Articles

Low internal air space in plants with crassulacean acid metabolism may be an anatomical spandrel.

Crassulacean acid metabolism (CAM) is a photosynthetic adaptation found in at least 38 plant families. Typically, the anatomy of CAM plants is characterized by large photosynthetic cells and a low percentage of leaf volume consisting of internal air space (% IAS). It has been suggested that reduced mesophyll conductance (gm) arising from low % IAS benefits CAM plants by preventing the movement of CO2 out of cells and ultimately minimizing leakage of CO2 from leaves into the atmosphere during day-time decarboxylation. Here, we propose that low % IAS does not provide any adaptive benefit to CAM plants, because stomatal closure during phase III of CAM will result in internal concentrations of CO2 becoming saturated, meaning low gm will not have any meaningful impact on the flux of gases within leaves. We suggest that low % IAS is more likely an indirect consequence of maximizing the cellular volume within a leaf, to provide space for the overnight storage of malic acid during the CAM cycle.

Defining Mechanisms of C3 to CAM Photosynthesis Transition toward Enhancing Crop Stress Resilience.

Global climate change and population growth are persistently posing threats to natural resources (e.g., freshwater) and agricultural production. Crassulacean acid metabolism (CAM) evolved from C3 photosynthesis as an adaptive form of photosynthesis in hot and arid regions. It features the nocturnal opening of stomata for CO2 assimilation, diurnal closure of stomata for water conservation, and high water-use efficiency. To cope with global climate challenges, the CAM mechanism has attracted renewed attention. Facultative CAM is a specialized form of CAM that normally employs C3 or C4 photosynthesis but can shift to CAM under stress conditions. It not only serves as a model for studying the molecular mechanisms underlying the CAM evolution, but also provides a plausible solution for creating stress-resilient crops with facultative CAM traits. This review mainly discusses the recent research effort in defining the C3 to CAM transition of facultative CAM plants, and highlights challenges and future directions in this important research area with great application potential.

Expression analysis of candidate genes as indicators for commencing drought stress in starch potatoes

AbstractDrought stress is a major problem for potato production and will be of grave importance due to climate change and the resulting temperature peaks along with drought periods in the vegetative growth phase of potato. Plants, as sessile organisms, adapt to their environment morphologically as well as biochemically. To cope better with abiotic stresses like drought, plants developed strategies like reactive oxygen species (ROS) detoxification and fast reacting stomatal closure, as well as signalling cascades leading to a quick response to stress. This study aimed at analysing eight genes of interest, derived from a former proteomic study, and determining their suitability for detection of commencing drought stress in early growth stages of potato. For this aim, six starch potato genotypes, which differed in stress response in previous studies, were examined for plant growth and physiological parameters in two experiments in an open greenhouse after seven and 14 days of stress. Besides lower shoot biomass after drought stress, which was already visible after seven days and became stronger after 14 days, weaker root growth was also detected after 14 days. The observed differences between the experiments can presumably be explained by temperature peaks and high radiation prior to and during the first experiment, which took place earlier in the year. The expression of the eight genes was studied in young leaves of four genotypes after 7 days of water withdrawal. Gene expression patterns were dependent on the studied genes. Three genes, cell wall/vacuolar inhibitor of fructosidase (INH1), peroxidase 51‐like (POD) and subtilase family protein (SBT1.7) showed consistent changes in gene expression after seven days of stress between all genotypes. The INH1 gene was found to be upregulated in all genotypes in two independent experiments after drought stress. This correlates with the results at the protein level, where INH1 was also found to be higher abundant in two genotypes of potato (Wellpott et al., DGG‐Proceedings 10, 2021). Therefore, this gene might be an appropriate candidate for the detection of commencing drought stress in potato.

Comparative study of stress generated by osmolytes on the growth, photosynthesis and metabolic responses in Nigellasativa

Several abiotic stresses generate osmotic stress which alters physio-biochemical and metabolic responses in plant. In the present experiment, the impact of different osmolytes on the germination, morphological, and physio-biochemical responses of Nigella sativa L. (black cumin) was investigated. Nigella seeds were subjected to treatments with sodium chloride (NaCl), polyethylene glycol (PEG-6000), mannitol, or sorbitol, resulting in a reduction of the osmotic potential in soil. The osmolyte treatments reduced germination traits (germination percentage, germination index, and vigour index) and seedling growth in treated plants. The decline in seedling establishment and growth is attributed to higher accumulation of various reactive oxygen species like hydrogen peroxide (H2O2) and superoxides (O2−) and lipid peroxidation in treated plants. Furthermore, osmolyte stress induced stomatal closure caused decline in water-related parameters (transpiration, stomatal conductance, internal CO2 concentration) which consequently restrained plant growth and development. In addition, Osmolyte treatments reduced the chlorophyll levels, and photosynthetic activity, while increasing proline and carbohydrate content. Protein, nitrate reductase, and carbonic anhydrase activities were depleted, and root cell death was elevated. To counteract this oxidative damage and mitigate stress, the plant enhances its antioxidant enzymatic defense. Notably, in the present study, the activity of catalase (CAT), superoxide dismutase (SOD), and peroxidase (POX) is upregulated to efficiently scavenge ROS and alleviate the impact of the stress. The current study demonstrated that different osmolytes elicit diverse effects on the morpho-physiological, biochemical, and metabolic responses of Nigella. Among the tested osmolytes, NaCl had the most pronounced and deleterious impact on the plant, followed by mannitol and sorbitol. On the other hand, PEG had the least toxic outcomes on the physiological processes and overall health of plant.

Enhancing rice resilience to drought by applying biochar–compost mixture in low-fertile sandy soil

BackgroundClimate change alters modern drought episode patterns by making them longer, more frequent and more severe, in particular in arid and semi-arid agroecosystems. Amending soil properties and enhancing its fertility is a needed sustainable strategy for mitigating drought’s damaging effects on crop production and food security. Here, we planned to investigate the potential benefits of biochar–compost mixture (B×C) as a biochar-based fertilizer (BCF) in enhancing the drought tolerance of rice plants cultivated in low-fertile sandy soil.ResultsUnder drought stress, rice plants cultivated in unamended soil (no B×C) exhibited severely wilted, rolled and discolored shoots. Furthermore, the shoot dry biomass reduction ratio was 73.3% compared to 44.2 and 27.6% for plants treated with 5 and 15% B×C, respectively. Root anatomical and architectural traits were significantly less impaired in B×C plants and reflected better performance under drought compared to no B×C plants. During the induced drought episode, soil moisture content was enhanced by 2.5-fold through adding B×C, compared to unamended soil, thereby reducing the negative impact of drought stress. Moreover, the less drought-stressed rice plants (B×C-treated) rapidly recovered after rewatering and displayed the unwinding of previously rolled leaves and reproduced panicles. On the other hand, no B×C plants failed to recover and eventually perished completely. The expression profiles of several drought responsive genes suggest that leaves of more stressed rice plants (no B×C) significantly accumulated more cytosolic free calcium (OsCML3) and apoplastic H2O2 (OsOXO4) which eventually may trigger fast and prolonged stomatal closure (OsSRO1c). In addition, more drought-stressed plants (no B×C) may over-produce the reactive oxygen species (ROS) superoxide anion molecules (OsRbohB), the negative situation that has been further complicated by a possible reduction in the activity of the antioxidative enzyme SOD (OsSOD), and thus more lipid peroxidation (3.5-fold increase MDA) in drought-stressed (no B×C) plant shoots compared to B×C plants.ConclusionIt is suggested that soil amendment B×C (biochar–compost mixture) could promote drought stress tolerance in rice plants by retaining more soil moisture content, thereby mitigating the negative effects of drought stress, such as the over-production of ROS in leaves, and thus eventually facilitating recovery after rewatering.

Molecular mechanism underlying regulation of Arabidopsis CLCa transporter by nucleotides and phospholipids

Chloride channels (CLCs) transport anion across membrane to regulate ion homeostasis and acidification of intracellular organelles, and are divided into anion channels and anion/proton antiporters. Arabidopsis thaliana CLCa (AtCLCa) transporter localizes to the tonoplast which imports NO3− and to a less extent Cl− from cytoplasm. The activity of AtCLCa and many other CLCs is regulated by nucleotides and phospholipids, however, the molecular mechanism remains unclear. Here we determine the cryo-EM structures of AtCLCa bound with NO3− and Cl−, respectively. Both structures are captured in ATP and PI(4,5)P2 bound conformation. Structural and electrophysiological analyses reveal a previously unidentified N-terminal β-hairpin that is stabilized by ATP binding to block the anion transport pathway, thereby inhibiting the AtCLCa activity. While AMP loses the inhibition capacity due to lack of the β/γ- phosphates required for β-hairpin stabilization. This well explains how AtCLCa senses the ATP/AMP status to regulate the physiological nitrogen-carbon balance. Our data further show that PI(4,5)P2 or PI(3,5)P2 binds to the AtCLCa dimer interface and occupies the proton-exit pathway, which may help to understand the inhibition of AtCLCa by phospholipids to facilitate guard cell vacuole acidification and stomatal closure. In a word, our work suggests the regulatory mechanism of AtCLCa by nucleotides and phospholipids under certain physiological scenarios and provides new insights for future study of CLCs.

Role of ABA in the adaptive response of Arabidopsis plants to long-term boron toxicity treatment

Boron (B) toxicity causes impairments in several plant metabolic and physiological processes. Under conditions of excessive B availability, this micronutrient is passively transported through the transpiration stream and accumulates in leaves, causing the development of necrotic regions in leaf tips. Some plants have developed adaptive mechanisms to minimize the toxic effects of excessive B accumulation in their tissues. Thus, for instance, in Arabidopsis it has been described an ABA-dependent decrease in the transpiration rate that would restrict B accumulation in aerial plant tissues in response to short-term B toxicity, this effect being mediated by AtNCED3 (which encodes a key enzyme for ABA biosynthesis). The present work aimed to study the possible involvement of ABA in the adjustment of plant water balance and B homeostasis during the adaptive response of Arabidopsis to prolonged B toxicity. For this purpose, Arabidopsis wild-type and the ABA-deficient nced3-2 mutant plants were subjected to B toxicity for 7 days. We show that ABA-dependent stomatal closure is determinant for the adjustment of plant water relations under conditions of prolonged B toxicity. Results suggest that, in addition to the AtNCED3 gene, the AtNCED5 gene could also be involved in this ABA-dependent stomatal closure. Finally, our results also indicate the possible role of endogenous root ABA content in the mechanism of active efflux of B via BOR4 (efflux-type B transporter) from the root to the external environment under excess B conditions.

Drought conditioning of rhizosphere microbiome influences maize water use traits

Background and AimsBeneficial plant–microbe interactions can improve plant performance under drought; however, we know less about how drought-induced shifts in microbial communities affect plant traits.MethodsWe cultivated Zea mays in fritted clay with soil microbiomes originating from contrasting environments (agriculture or forest) under two irrigation treatments (well-watered or water limited). Using this design, we investigated whether water conditioning was carried forward through the microbiome to affect a subsequent plant cohort that was subjected to either a well-watered or water limited treatment.ResultsRegardless of the microbiome-origin, plants inoculated with a microbiome from a water limited legacy had traits that allowed them to avoid stress but conserve water. They produced longer roots to explore soil, generated greater soil dissolved organic carbon, potentially stimulating the microbiome, and slower soil water content loss during drought. A well-watered legacy resulted in plants that delayed permanent stomatal closure and higher photosynthetic nitrogen use efficiency. In plants with a forest-originated microbiome, a well-watered legacy and water treatment also resulted in higher rates of photosynthesis and stomatal conductance.ConclusionThese results demonstrate that soil microbiomes can be developed to influence plant drought performance, impacting crop resilience, using short-term microbial conditioning.

Leaf rolling precedes stomatal closure in rice (Oryza sativa) under drought conditions.

Leaf rolling is a physiological response to drought that may help to reduce water loss, but its significance as a contribution to drought tolerance is uncertain. We scored the leaf rolling of four rice genotypes along an experimental drought gradient using an improved cryo-microscopy method. Leaf water potential (Ψleaf), gas exchange, chlorophyll fluorescence, leaf hydraulic conductance, rehydration capacity, and the bulk turgor loss point were also analysed. During the drought process, stomatal conductance declined sharply to reduce water loss, and leaves rolled up before the stomata completely closed. The leaf water loss rate of rolled leaves was significantly reduced compared with artificially flattened leaves. The Ψleaf threshold of initial leaf rolling ranged from -1.95 to -1.04 MPa across genotypes. When a leaf rolled so that the leaf edges were touching, photosynthetic rate and stomatal conductance declined more than 80%. Across genotypes, leaf hydraulic conductance declined first, followed by gas exchange and chlorophyll fluorescence parameters. However, the Ψleaf threshold for a given functional trait decline differed significantly among genotypes, with the exception of leaf hydraulic conductance. Our results suggested that leaf rolling was mechanistically linked to drought avoidance and tolerance traits and might serve as a useful phenotypic trait for rice breeding in future drought scenarios.

Antagonistic or Compensatory: Crosstalk between ABA and Ethylene in Regulating Stomatal Behavior under High CO2 and Progressive Soil Drying.

Increasing atmospheric CO2 concentrations accompanied by intensified drought stress have a significant impact on plant growth and physiology. The aim of this study was to explore the role of abscisic acid (ABA) in mediating the response of stomata to elevated CO2 (e[CO2]) and soil water deficits. Tomato plants with different endogenous ABA concentrations (Ailsa Craig (AC), its ABA-deficient mutant (flacca) and ABA-overproduction transgenic tomato (SP5)) were grown in ambient (a[CO2], 400 μmol mol -1) and elevated (800 μmol mol -1) CO2 environments and were subjected to progressive soil drying at six-leaf stage. Results showed that, compared to plants grown under a[CO2], e[CO2]-plants had significantly lower stomatal conductance in AC and SP5 but not in flacca. Under drought, e[CO2]-plants had better water status and higher water use efficiency at both leaf and whole plant levels. e[CO2] had no effects on the ABA concentration of plants under well-watered conditions but promoted the accumulation of ABA in leaves of plants subjected to drought stress, which coincided with the upregulated expression of ABA biosynthetic genes and downregulated expression of ABA metabolic genes. Although in flacca, the increase of ABA induced by drought was much less than in AC and SP5, it accumulated large amounts of ethylene, suggesting that in plants with ABA deficiency, ethylene may play a compensatory role in inducing stomatal closure during soil drying. Collectively, these findings improve our understanding of plant performances to a future drier and CO2-enriched environment.

RING finger ubiquitin E3 ligase CsCHYR1 targets CsATAF1 for degradation to modulate the drought stress response of cucumber through the ABA-dependent pathway

CsCHYR1 (CHY ZINC-FINGER AND RING PROTEIN1) encodes a RING (Really Interesting New Gene) finger E3 ubiquitin ligase involved in ubiquitin-mediated protein degradation and plays an important role for cucumber to resist drought stress. Here, we obtain one of the candidate proteins CsCHYR1 that probably interacts with CsATAF1 by yeast-two hybrid screening. Subsequently, it is verified that CsCHYR1 interacts with CsATAF1 and has self-ubiquitination activity. When the cysteine residue at 180 in the RING domain of CsCHYR1 is replaced by serine or alanine, ubiquitin could not be transported from E2 to the substrate. CsCHYR1 ubiquitinates CsATAF1 and affects the stability of CsATAF1 when plants are subjected to drought stress. The expression level of CsCHYR1 is increased by 4-fold after ABA treatment at 9 h. The Atchyr1 mutants perform an ABA-hyposensitive phenotype and have a lower survival rate than Col-0 and CsCHYR1 Atchyr1 lines. In addition, CsCHYR1 interacts with CsSnRK2.6. Therefore, our study reveals a CsSnRK2.6-CsCHYR1-CsATAF1 complex to promote the drought stress response by decreasing CsATAF1 protein accumulation and inducing stomatal closure. Those findings provide new ideas for cucumber germplasm innovation from the perspective of biochemistry and molecular biology.

Ethylene inhibits ABA-induced stomatal closure via regulating NtMYB184-mediated flavonol biosynthesis in tobacco.

Stomatal movement can be regulated by ABA signaling through synthesis of reactive oxygen species (ROS) in guard cells. By contrast, ethylene triggers the biosynthesis of antioxidant flavonols to suppress ROS accumulation and prevent ABA-induced stomatal closure; however, the underlying mechanism remains largely unknown. In this study, we isolated and characterized the tobacco (Nicotiana tabacum) R2R3-MYB transcription factor NtMYB184, which belongs to the flavonol-specific SG7 subgroup. RNAi suppression and CRISPR/Cas9 mutation (myb184) of NtMYB184 in tobacco caused down-regulation of flavonol biosynthetic genes and decreased the concentration of flavonols in the leaves. Yeast one-hybrid assays, transactivation assays, EMSAs, and ChIP-qPCR demonstrated that NtMYB184 specifically binds to the promoters of flavonol biosynthetic genes via MYBPLANT motifs. NtMYB184 regulated flavonol biosynthesis in guard cells to modulate ROS homeostasis and stomatal aperture. ABA-induced ROS production was accompanied by the suppression of NtMYB184 and flavonol biosynthesis, which may accelerate ABA-induced stomatal closure. Furthermore, ethylene stimulated NtMYB184 expression and flavonol biosynthesis to suppress ROS accumulation and curb ABA-induced stomatal closure. In myb184, however, neither the flavonol and ROS concentrations nor the stomatal aperture varied between the ABA and ABA+ethylene treatments, indicating that NtMYB184 was indispensable for the antagonism between ethylene and ABA via regulating flavonol and ROS concentrations in the guard cells.

Plants lacking OST1 show conditional stomatal closure and wildtype-like growth sensitivity at high VPD.

Climate change-associated rise in VPD (atmospheric vapor pressure deficit) results in increased plant transpiration and reduced stomatal conductance, photosynthesis, biomass, and yield. High VPD-induced stomatal closure of Arabidopsis is an active process regulated via the kinase SnRK2.6 (OPEN STOMATA 1, OST1). Here, we performed gas exchange, leaf water potential and rosette growth measurements to study, whether (1) high VPD-induced stomatal closure is detected in plants carrying loss-of-function mutations in OST1 (ost1-3) when they are grown at reduced soil water content or measured at increased air temperature; (2) ost1-3 plants expressing OST1 construct with no ABA-activation domain, but intact ABA-independent activation, show stronger stomatal VPD response compared with ost1-3 plants; and (3) rosette area and biomass of ost1-3 are more affected by growth at high VPD compared with Col-0. The stomata of well-watered ost1-3 plants were insensitive to high VPD regardless of air temperature, but in deficit-irrigated ost1-3, leaf water potential decreased the most and stomata closed at high VPD. Differences between VPD-induced stomatal closures of ost1-3 plants and ost1-3 plants expressing OST1 with no ABA-activation domain point at gradual VPD-induced ABA-independent activation of OST1. High VPD conditions led to similar reductions in rosette area and specific leaf area of well-watered Col-0 and ost1-3 plants. Rosette dry mass was unaffected by high VPD. Our results show that OST1 loss-of-function plants display conditional stomatal closure and no extra sensitivity of rosette area growth compared with Col-0 wildtype under high VPD conditions.

Photosynthesis, leaf hydraulic conductance and embolism dynamics in the resurrection plant Barbacenia purpurea.

The main parameters determining photosynthesis are stomatal and mesophyll conductance and electron transport rate, and for hydraulic dynamics they are leaf hydraulic conductance and the spread of embolism. These parameters have scarcely been studied in desiccation-tolerant (resurrection) plants exposed to drought. Here, we characterized photosynthesis and hydraulics during desiccation and rehydration in a poikilochlorophyllous resurrection plant, Barbacenia purpurea (Velloziaceae). Gas exchange, chlorophyll fluorescence, and leaf water status were monitored along the whole dehydration-rehydration cycle. Simultaneously, embolism formation and hydraulic functioning recovery were measured at leaf level using micro-computed tomography imaging. Photosynthesis and leaf hydraulic conductance ceased at relatively high water potential (-1.28 and -1.54 MPa, respectively), whereas the onset of leaf embolism occurred after stomatal closure and photosynthesis cessation (<-1.61 MPa). This sequence of physiological processes during water stress may be associated with the need to delay dehydration, to prepare the molecular changes required in the desiccated state. Complete rehydration occurred rapidly in the mesophyll, whereas partial xylem refilling, and subsequent recovery of photosynthesis, occurred at later stages after rewatering. These results highlight the importance of stomata as safety valves to protect the vascular system from embolism, even in a plant able to fully recover after complete embolism.

Evaluation of the effect of different culture systems on photomixotrophic capacity during in vitro multiplication of pitahaya (Hylocereus undatus)

Pitahaya (Hylocereus undatus) micropropagation is an alternative for obtaining invigorated plants with high phytosanitary quality. The objective of this research was to evaluate different culture systems on photomixotrophic capacity during in vitro multiplication and their effect on survival in the acclimatization stage of H. undatus. Different temporary immersion systems (TIS) were used: temporary immersion bioreactors (TIB), Ebb-and-Flow bioreactor, Recipient for Automated Temporary Immersion (RITA), and semi-solid (SS) culture medium. At 60 d of culture, the percentage of explant response, developmental variables, chlorophyll and carotene content, stomatal index (SI), percentage of closed stomata (CS), PEP (Phosphoenolpyruvate) and Rubisco (Ribulose-1,5-bisphosphate carboxylase oxygenase) content and the percentage of survival in the greenhouse acclimatization stage were evaluated. The culture systems with the highest percentage of response were the SS culture medium (96%), Ebb-and-Flow (93%) and RITA (90%). The Ebb-and-Flow and RITA bioreactors showed the highest number of shoots, with 9.5 and 9.0, respectively, the greatest length, with 2.62 and 2.71 cm, the highest chlorophyll, with 0.30 and 0.28 mg g–1 FW, and carotenoid content, with 2.25 and 2.20 mg g–1 FW. The SS medium culture system showed the highest SI with (57%), while the TIB had the highest CS, with (85%). The Ebb-and-Flow and RITA culture systems showed the highest PEP content, with 15 and 18 nmol g–1 FW, respectively; whereas, for Rubisco content, no differences were found in the different culture systems. The Ebb-and-Flow and RITA culture systems presented the highest survival rate, with 99.6% during acclimatization. The use of Ebb-and-Flow and RITA bioreactors are a biotechnological alternative for in vitro propagation of H. undatus and guarantee high survival rates during acclimatization without going through a rooting stage.

AeWRKY32 from okra regulates anthocyanin accumulation and cold tolerance in Arabidopsis

Okra (Abelmoschus esculentus L.) is a tropical crop species, and its growth and development are severely affected by cold stress. Recent studies have identified a potential association between WRKY transcription factors and the cold response mechanism of crops. In this study, the AeWRKY32 transcription factor that encodes 482 amino acids was amplified from A. esculentus, and its expression level was found to be the highest in the okra flower. AeWRKY32 localized to the nucleus and displayed transcriptional activation capability. Under normal conditions, overexpression of AeWRKY32 induced anthocyanin accumulation, with higher expression levels of AtCHS1, AtCHI4, AtF3H1, and AtDFR2 in transgenic Arabidopsis. Under cold stress, anthocyanin levels were further elevated in transgenic Arabidopsis plants. At the same time, AeWRKY32 overexpression promoted ABA biosynthesis, inhibited H2O2 and O2− generation, induced stomatal closure, reduced electrolyte leakage, and thus improved the cold resistance of transgenic Arabidopsis. Furthermore, under cold stress, the expression profiles of AtCOR413, AtCOR15B, AtCBF1, and AtCBF2 were upregulated in transgenic Arabidopsis. Overall, our study provides evidence that AeWRKY32 serves as a crucial regulator in both anthocyanin accumulation and cold tolerance of transgenic Arabidopsis. Our findings could provide insights into the molecular mechanism linking AeWRKYs to plant cold tolerance.

Cell type-specific proteomics uncovers a RAF15-SnRK2.6/OST1 kinase cascade in guard cells.

Multicellular organisms such as plants contain various cell types with specialized functions. Analyzing the characteristics of each cell type reveals specific cell functions and enhances our understanding of organization and function at the organismal level. Guard cells (GC) are specialized epidermal cells that regulate the movement of the stomata and gaseous exchange, and provide a model genetic system for analyzing cell fate, signaling and function. Several proteomics analyses of GC are available, but these are limited in depth. Here we used enzymatic isolation and flow cytometry to enrich for GC and mesophyll cell protoplasts and perform in-depth proteomics in these two major cell types in Arabidopsis leaves. We identified ~3,000 proteins not previously found in the GC proteome and more than 600 proteins that may be specific to GC. The depth of our proteomics enabled us to uncover a guard cell-specific kinase cascade whereby Raf15 and Snf1-related kinase2.6 (SnRK2.6)/OST1(open stomata 1) mediate abscisic acid (ABA)-induced stomatal closure. RAF15 directly phosphorylated SnRK2.6/OST1 at the conserved Ser175 residue in its activation loop and was sufficient to reactivate the inactive form of SnRK2.6/OST1. ABA-triggered SnRK2.6/OST1 activation and stomatal closure was impaired in raf15 mutants. We also showed enrichment of enzymes and flavone metabolism in GC, and consistent, dramatic accumulation of flavone metabolites. Our study answers the long-standing question of how ABA activates SnRK2.6/OST1 in guard cells and represents a resource potentially providing further insights into the molecular basis of GC and mesophyll cell development, metabolism, structure, and function. This article is protected by copyright. All rights reserved.

CmoNAC1 in pumpkin rootstocks improves salt tolerance of grafted cucumbers by binding to the promoters of CmoRBOHD1, CmoNCED6, CmoAKT1;2 and CmoHKT1;1 to regulate H2O2, ABA signaling and K+/Na+ homeostasis.

The NAC transcription factor is a type of plant-specific transcription factor that can regulate plant salt tolerance, but the underlying mechanism is unclear in grafted vegetables. H2O2 and ABA in pumpkin rootstocks can be transported to cucumber scion leaves, promoting stomatal closure to improve salt tolerance of grafted cucumbers. Despite these observations, the regulatory mechanism is unknown. Here, our research revealed that CmoNAC1 is a key transcription factor that regulates H2O2 and ABA signaling in pumpkin roots under salt stress. The function of CmoNAC1 was analyzed using root transformation and RNA-seq, and we found that pumpkin CmoNAC1 promoted the production of H2O2 and ABA via CmoRBOHD1 and CmoNCED6, respectively, and regulated K+/Na+ homeostasis via CmoAKT1;2, CmoHKT1;1, and CmoSOS1 to improve salt tolerance of grafted cucumbers. Root knockout of CmoNAC1 resulted in a significant decrease in H2O2 (52.9% and 32.1%) and ABA (21.8% and 42.7%) content and K+/Na+ ratio (81.5% and 56.3%) in leaf and roots of grafted cucumber, respectively, while overexpression showed the opposite effect. The root transformation experiment showed that CmoNCED6 could improve salt tolerance of grafted cucumbers by regulating ABA production and K+/Na+ homeostasis under salt stress. Finally, we found that CmoNAC1 bound to the promoters of CmoRBOHD1, CmoNCED6, CmoAKT1;2, and CmoHKT1;1 using yeast one-hybrid, luciferase, and electrophoretic mobility shift assays. In conclusion, pumpkin CmoNAC1 not only binds to the promoters of CmoRBOHD1 and CmoNCED6 to regulate the production of H2O2 and ABA signals in roots, but also binds to the promoters of CmoAKT1;2 and CmoHKT1;1 to increase the K+/Na+ ratio, thus improving salt tolerance of grafted cucumbers.

TaTIP41 and TaTAP46 positively regulate drought tolerance in wheat by inhibiting PP2A activity.

Drought is a major environmental stress limiting global wheat (Triticum aestivum) production. Exploring drought tolerance genes is important for improving drought adaptation in this crop. Here, we cloned and characterized TaTIP41, a novel drought tolerance gene in wheat. TaTIP41 is a putative conserved component of target of rapamycin (TOR) signaling, and the TaTIP41 homoeologs were expressed in response to drought stress and abscisic acid (ABA). The overexpression of TaTIP41 enhanced drought tolerance and the ABA response, including ABA-induced stomatal closure, while its downregulation using RNA interference (RNAi) had the opposite effect. Furthermore, TaTIP41 physically interacted with TaTAP46, another conserved component of TOR signaling. Like TaTIP41, TaTAP46 positively regulated drought tolerance. Furthermore, TaTIP41 and TaTAP46 interacted with type-2A protein phosphatase (PP2A) catalytic subunits, such as TaPP2A-2, and inhibited their enzymatic activities. Silencing TaPP2A-2 improved drought tolerance in wheat. Together, our findings provide new insights into the roles of TaTIP41 and TaTAP46 in the drought tolerance and ABA response in wheat, and their potential application in improving wheat environmental adaptability. This article is protected by copyright. All rights reserved.

Zinc oxide nanoparticles mitigated the arsenic induced oxidative stress through modulation of physio-biochemical aspects and nutritional ions homeostasis in rice (Oryza sativa L.)

Zinc oxide nanoparticles (nZn) have emerged as vital agents in combating arsenic (As) stress in plants. However, their role in mitigation of As induced oxidative stress is less studied. Therefore, this study aimed to assess the comparative role of nZn and ZnO in alleviating As toxicity in rice genotype “9311”. The results of this study revealed that nZn demonstrated superior efficacy compared to ZnO in mitigating As toxicity. This superiority can be attributed to the unique size and structure of nZn, which enhances its ability to alleviate As toxicity. Exposure to As at a concentration of 25 μM L-1 led to significant reductions in shoot length, root length, shoot dry weight, and root dry weight by 39%, 51%, 30%, and 46%, respectively, while the accumulation of essential nutrients such as magnesium (Mg), potassium (K), iron (Fe), manganese (Mn), and zinc (Zn) decreased by 25%–47% compared to the control plants. Additionally, As exposure resulted in stomatal closure and structural damage to vital cellular components such as grana thylakoids (GT), starch granules (SG), and the nucleolus. However, the application of nZn at a concentration of 30 mg L−1 exhibited significant alleviation of As toxicity, resulting in a reduction of As accumulation by 54% in shoots and 62% in roots of rice seedlings. Furthermore, nZn demonstrated the ability to scavenge reactive oxygen species (ROS) like hydrogen peroxide (H2O2) and superoxide anion (O2.-), while significantly promoted the gas exchange parameters, chlorophyll content (SPAD value), fluorescence efficiency (Fv/m) and antioxidant enzyme activities under As-induced stress. These findings highlight the potential of nZn in mitigating the adverse impacts of As contamination in rice plants. However, further research is necessary to fully comprehend the underlying mechanisms responsible for the protective effects of nZn and to determine the optimal conditions for their application in real-world agricultural settings.