Stomatal Regulation Research Articles

Responses of winter wheat and maize to varying soil moisture: From leaf to canopy

Drought is a serious constraint to crop growth and production of important staple crops such as winter wheat and maize. Improved understanding of crops' response to drought can be incorporated into cropping system models to support crop breeding, crop and varietal selection and management decisions to minimize negative impacts. Plants may respond to drought through immediate stomatal regulation as well as possibly altering their morphological characteristics over longer periods. The degree and combination of these short- and long-term responses depends on the intensity and duration of drought as well as crop characteristics. However, field observational evidence for different crop types detailing these at short- and longer term responses and for different organizational levels is still limited. Here we examine the effects of various water supply treatments on short-term changes in leaf water potential (LWP) and gas exchange at the leaf level together with the seasonal changes in canopy photosynthesis, transpiration, and cumulative growth of winter wheat and maize based on field data collected in 2016, 2017, and 2018. Leaf and canopy gas exchange and cumulative growth was varied strongly with the duration and intensity of drought stress as well as growing stages. The longer-term morphological drought responses in winter wheat appeared to have a larger effect on regulating transpiration and assimilation rates than shorter-term responses of stomatal control had. Maize (grown in 2017 and 2018) exhibited different responses, with seasonal variations in minimum LWP and complete stomatal closure at LWP of between -1.6 and -2 MPa. While stomata closed with increasing drought, for maize, the physiological advantages of C4 photosynthesis as well as morphological adjustments in leaf area size and leaf-rolling strongly determined crop growth and canopy gas exchange in the drought plots as compared with the irrigated plot. Observations highlight that improvements for soil-vegetation-atmosphere models in simulating gas exchange and crop growth should emphasize the dynamic reduction of leaf area under water stress, as well as stomatal regulation.

Enhancing the Productivity and Sustainability of Bambara Groundnut (<i>Vigna subterranea</i> (L.) Verdc.) Production Using Inorganic Phosphorus Fertilizer

Phosphorus (P) is a vital element required for nodulation, stomatal regulation and photosynthesis in legume crops. P-deficiency in tropical soils limits the growth and productivity of Bambara groundnuts. The current study focused on determining the potential suitability of underutilized crops for food security using phosphorus fertilizer as soil amendment practice. A field trial was carried out at the Council for Scientific and Industrial Research—Crops Research Institute (CSIR-CRI), over two growing seasons to determine the optimum P rate for Bambara production. This trial was laid out in a split plot in a randomized block design with three replications. Bambara genotypes represented the main plots while four P fertilizer rates (0, 30, 45 and 60 kg P2O5 ha-1) were the sub-plots. The appropriate application rate of 60 kg P2O5 ha-1 showed excellent performance based on growth and yield analysis, and the results indicate a positive significant interaction between landraces and phosphorus fertilizer rates. The biological suitability of 60 kg P2O5 ha-1 increased the number of nodules per plant for Tiga Necuru, Kenya Capstone and Nav Red by 42.8%, 51.3% and 42.1% respectively, over control plots. The same for pod yield is 12%, 28% and 52% significantly higher than when P was applied at 45, 30 and 0 kg P2O5 ha-1 respectively. The results further revealed that on days to flowering and maturity, the plant height, the number of branches and dry matter increased significantly at each level of P fertilizer rate applied. Bambara production at 0 kg P fertilizer rate might not be sufficient to enhance Bambara productivity significantly. The outcome of this study reveals the suitability of phosphorus fertilizer application in enhancing the sustainability of Bambara groundnut productivity and the potential of Bambara in diversifying crop production to ensure food security.

Drought response of 10 bermudagrass genotypes under field and controlled environment conditions

AbstractFresh water scarcity is increasingly affecting urban landscapes, and the best strategy for sustaining the turfgrass industry would be to create, select, and use drought‐resistant genotypes. Bermudagrasses (Cynodon spp.) have different mechanisms to survive drought stress either by growing long roots, stomatal regulation, or accumulating biochemical solutes in the leaf. The drought response of 10 bermudagrasses was evaluated under two environments: (a) unrestricted root zone in the field and (b) restricted 17‐cm root zone in a greenhouse. Each study consisted of four commercially available (‘Latitude 36’, ‘Tifway’, ‘TifTuf’, and ‘Celebration’) and six experimental genotypes (OSU1337, OSU1403, OSU1439, TifB16101, TifB16113, and TifB16120). In the field study, all the genotypes survived the 60‐ and 49‐d dry‐down periods in 2017 and 2018, respectively, without completely browning off. Results showed a range of drought performance among genotypes, with TifTuf and Latitude 36 being the best‐ and worst‐performing industry standards, respectively. TifB16101, TifB16120, and TifB16113 were consistently the top performers with a leaf firing (LF) and turf quality (TQ) above 6, lower canopy temperature (CT), and greater normalized difference vegetation index (NDVI) values in the field. However, when grown in 17‐cm pots, TifTuf, TifB16113, and TifB16120 demonstrated a TQ below 6 within 6 and 9 days of drought (DOD) in 2019 and 2020, respectively. The discrepancy between studies suggests that these genotypes may have the ability to extract water from deeper soil profiles when root zones are unrestricted. Furthermore, these findings reinforce the importance of soil depth in maintaining turfgrasses without supplemental irrigation.

High variation in hydraulic efficiency but not xylem safety between roots and branches in four temperate broad‐leaved tree species

Abstract Xylem hydraulic safety and efficiency are key traits determining tree fitness in a warmer and drier world. While numerous plant hydraulic studies have focused on branches, our understanding of root hydraulic functioning remains limited, although roots control water uptake, influence stomatal regulation and have commonly been considered as the most vulnerable organ along the hydraulic pathway. We investigated 11 traits related to xylem safety and efficiency along the hydraulic pathway in four temperate broad‐leaved tree species. Continuous vessel tapering from coarse roots to stems and branches caused considerable reduction in hydraulic efficiency. Wood density was always lowest in roots, but did not decline linearly along the flow path. In contrast, xylem embolism resistance (P50) did not differ significantly between roots and branches, except for one species. The limited variation in xylem safety between organs did not adequately reflect the corresponding reductions in vessel diameter (by ~70%) and hydraulic efficiency (by ~85%). Although we did not observe any trade‐off between xylem safety and specific conductivity, vessel diameter, vessel lumen fraction and wood density were related to embolism resistance, both across and partly within organs. We conclude that coarse roots are not highly vulnerable to xylem embolism as commonly believed, indicating that hydraulic failure during soil drying might be restricted to fine roots. A free Plain Language Summary can be found within the Supporting Information of this article.

Global patterns and ecological implications of diurnal hysteretic response of ecosystem water consumption to vapor pressure deficit

Increasing vapor pressure deficit (VPD) has led to widespread reductions in vegetation carbon uptake by stomatal hydraulic regulation. The response of vegetation to VPD is therefore paramount in the global water and carbon cycle, and draws worldwide attention. However, the hysteretic response of ecosystem water consumption to VPD, although widely reported across the world, is still lack of systematic and consistent research on its global patterns and ecological implications. Based on a newly developed hourly dataset of land-atmosphere fluxes, this study finds that hysteresis increases with climatic aridity and long hysteresis mainly occurs in water-limited areas; the hysteretic response of water consumption to VPD for woody ecosystems is shorter than that for the herbaceous ecosystems; interestingly, gross primary productivity (GPP) increases with hysteresis at the high hysteresis ends in dry environments (dry-humid, semi-arid and arid zones), which might suggest an existence of drought-adapting mechanisms of vegetation growth that is relevant to hysteresis but overlooked before. This study provides important information for projecting future shifts of ecosystem functions under increasing atmospheric dry stress.

Stomatal regulation prevents plants from critical water potentials during drought: Result of a model linking soil–plant hydraulics to abscisic acid dynamics

AbstractUnderstanding stomatal regulation during drought is essential to correctly predict vegetation‐atmosphere fluxes. Stomatal optimization models posit that stomata maximize the carbon gain relative to a penalty caused by water loss, such as xylem cavitation. However, a mechanism that allows the stomata to behave optimally is unknown. Here, we introduce a model of stomatal regulation that results in similar stomatal behaviour without presupposing an optimality principle. By contrast, the proposed model explains stomatal closure based on a well‐known component of stomatal regulation: abscisic acid (ABA). The ABA level depends on its production rate, which is assumed to increase with declining leaf water potential, and on its degradation rate, which is assumed to increase with assimilation rate. Our model predicts that stomata open until the ratio of leaf water potential to assimilation rate, proportional to ABA level, is at a minimum. As a prerequisite, the model simulates soil–plant hydraulics and leaf photosynthesis under varying environmental conditions. The model predicts that in wet soils and at low vapour pressure deficit (VPD), when there is no water limitation, stomatal closure is controlled by the relationship between photosynthesis and stomatal conductance. In dry soils or at high VPD, when the soil hydraulic conductivity limits the water supply, stomatal closure is triggered by the sharp decline in leaf water potential as transpiration rate increases. Being adaptive to changing soil and atmospheric conditions, the proposed model can explain how plants are enabled to avoid critical water potentials during drought for varying soil properties and atmospheric conditions.

Distinct transpiration characteristics of black locust plantations acclimated to semiarid and subhumid sites in the Loess Plateau, China

Black locust (Robinia pseudoacacia) is widely planted throughout semiarid and subhumid regions of the Loess Plateau of China. Determining the changes in transpiration of this species in different climatic areas is important for revealing the acclimation mechanism of black locust and developing suitable forest management practices, particularly in the context of global climate change. Here, sap flow and canopy conductance of black locust plantation trees in semiarid (Yan’an) and subhumid (Yongshou) sites were quantified using Granier-type thermal dissipation probes and concurrent environmental observations from 2012 to 2017. Several physiological parameters were measured throughout the growing season. The results showed that sap flow was correlated with phenological factors across seasons within a year. However, interannual changes in sap flow were affected mainly by the reference evapotranspiration (ET0) at the Yongshou site, and jointly by precipitation (P), soil water content, and P/ET0 at the Yan’an site. Sap flow response to meteorological factors showed less discrepancy between pre- and post-rainfall periods at the Yan’an site. Moreover, canopy conductance fluctuated less with a wider range of vapor pressure deficit (VPD) and the slope of canopy resistance as a function of VPD was lower, indicating relatively lower sensitivity of stomatal conductance to environmental factors in Yan’an site. Physiological parameters, except for predawn leaf water potential, were significantly different between the two sites. The results suggested that black locust tended to reduce transpiration, modify leaf morphology, and improve water use efficiency to enhance its adaptability to the dryer site. The species changes stomatal regulation characteristics and general growth rate to acclimatize to distinct water habitats.

Nocturnal warming accelerates drought-induced seedling mortality of two evergreen tree species.

Extreme drought is one of the key climatic drivers of tree mortality on a global scale. However, it remains unclear whether the drought-induced tree mortality will increase under nocturnal climate warming. Here we exposed seedlings of two wide-ranging subtropical tree species, Castanopsis sclerophylla and Schima superba, with contrasting stomatal regulation strategies to prolonged drought under ambient and elevated night-time temperature by 2°C. We quantified the seedling survival time since drought treatment by measuring multiple leaf traits such as leaf gas exchange, predawn leaf water potential and water-use efficiency. The results showed that all seedlings in the ambient temperature died within 180days and 167days of drought for C. sclerophylla and S. superba, respectively. Night warming significantly shortened the survival time of C. sclerophylla, by 31days, and S. superba by 28days, under the drought treatment. A survival analysis further showed that seedlings under night warming suffered a 1.6 times greater mortality risk than those under ambient temperature. Further analyses revealed that night warming suppressed net leaf carbon gain in both species by increasing the nocturnal respiratory rate of S. superba across the first 120days of drought and decreasing the photosynthetic rate of both species generally after 46days of drought. These effects on net carbon gain were more pronounced in S. superba than C. sclerophylla. After 60days of drought, night warming decreased the predawn leaf water potential and leaf water-use efficiency of C. sclerophylla but not S. superba. These contrasting responses are partially due to variations in stomatal control between the two species. These findings suggest that stomatal traits can regulate the response of leaf gas exchange and plant water-use to nocturnal warming during drought. This study indicates that nocturnal warming can accelerate tree mortality during drought. Night warming accelerates the mortality of two subtropical seedlings under drought.Night warming differently affects the drought response of leaf gas exchange and plant water-use between the two species due to species-specific stomatal morphological traits.Carbon metabolism changes and hydraulic damage play differential roles in driving night-warming impacts on the drought-induced mortality between the two species.

Interpreting the water use strategies of plantation tree species by canopy stomatal conductance and its sensitivity to vapor pressure deficit in South China

Stomatal regulation controls tree transpiration rate and is central to plant function. However, most previous studies that investigated the stomatal regulation of forest trees mainly focused on arid and semi-arid zones, uncertainty remains about how trees adjust their stomatal response to the changing environment in subtropical moist areas. In this study, we investigated the tree transpiration (El), canopy stomatal conductance (Gs), and Gs sensitivity to vapor pressure deficit (VPD) of four typical plantation tree species (Schima wallichii, Acacia mangium, Eucalyptus urophylla, and Cunninghamia lanceolata) in hilly lands of South China. Datasets including the continuously measured sap flow and meteorological parameters, as well as the physiological traits of the four species, were collected during the year of 2018. Our results showed that the coniferous C. lanceolata had significantly lower El, Gs, and weak sensitivity to VPD than the other three broadleaved species. We attributed the different water use and stomatal behavior to the various species-specific traits. The three broadleaved species generally possessed higher leaf area, specific leaf area (SLA), the ratio of sapwood area (As) to leaf area (Al), and deeper root depth, facilitating their transpiration and gas exchange. During the experimental period, a super typhoon “Mangkhut” hit the research site and caused substantial decline in leaf area, while the whole tree transpiration experienced slighter decrease, indicating the rapid compensatory effect of stomatal regulation. Moreover, the increased Gs sensitivity to VPD (m values) and reference Gs for the introduced A. mangium and E. urophylla in the dry season highlighted their ability to function well even under the much drier condition with no strict stomatal control. Our analyses on the response of Gs to the changing environment for typical species in the subtropical moist forests will provide important insights for forest management and ecosystem stability under future climate changes.

Metabolism-mediated mechanisms underpin the differential stomatal speediness regulation among ferns and angiosperms.

Recent results suggest that metabolism-mediated stomatal closure mechanisms are important to regulate differentially the stomatal speediness between ferns and angiosperms. However, evidence directly linking mesophyll metabolism and the slower stomatal conductance (gs ) in ferns is missing. Here, we investigated the effect of exogenous application of abscisic acid (ABA), sucrose and mannitol on stomatal kinetics and carried out a metabolic fingerprinting analysis of ferns and angiosperms leaves harvested throughout a diel course. Fern stomata did not respond to ABA in the time period analysed. No differences in the relative decrease in gs was observed between ferns and the angiosperm following provision of sucrose or mannitol. However, ferns have slower gs responses to these compounds than angiosperms. Metabolomics analysis highlights that ferns have a higher accumulation of secondary rather than primary metabolites throughout the diel course, with the opposite being observed in angiosperms. Our results indicate that metabolism-mediated stomatal closure mechanisms underpin the differential stomatal speediness regulation among ferns and angiosperms, in which the slower stomatal closure in ferns is associated with the lack of ABA-responsiveness, to a reduced capacity to respond to mesophyll-derived sucrose and to a higher carbon allocation toward secondary metabolism, which likely modulates both photosynthesis-gs and growth-stress tolerance trade-offs.

Stomatal closure during water deficit is controlled by below-ground hydraulics.

Stomatal closure allows plants to promptly respond to water shortage. Although the coordination between stomatal regulation, leaf and xylem hydraulics has been extensively investigated, the impact of below-ground hydraulics on stomatal regulation remains unknown. We used a novel root pressure chamber to measure, during soil drying, the relation between transpiration rate (E) and leaf xylem water pressure (ψleaf-x) in tomato shoots grafted onto two contrasting rootstocks, a long and a short one. In parallel, we also measured the E(ψleaf-x) relation without pressurization. A soil-plant hydraulic model was used to reproduce the measurements. We hypothesize that (1) stomata close when the E(ψleaf-x) relation becomes non-linear and (2) non-linearity occurs at higher soil water contents and lower transpiration rates in short-rooted plants. The E(ψleaf-x) relation was linear in wet conditions and became non-linear as the soil dried. Changing below-ground traits (i.e. root system) significantly affected the E(ψleaf-x) relation during soil drying. Plants with shorter root systems required larger gradients in soil water pressure to sustain the same transpiration rate and exhibited an earlier non-linearity and stomatal closure. We conclude that, during soil drying, stomatal regulation is controlled by below-ground hydraulics in a predictable way. The model suggests that the loss of hydraulic conductivity occurred in soil. These results prove that stomatal regulation is intimately tied to root and soil hydraulic conductances.

Stomatal responses in grapevine become increasingly more tolerant to low water potentials throughout the growing season.

The leaf of a deciduous species completes its life cycle in a few months. During leaf maturation, osmolyte accumulation leads to a significant reduction of the turgor loss point (ΨTLP ), a known marker for stomatal closure. Here we exposed two grapevine cultivars to drought at three different times during the growing season to explore if the seasonal decrease in leaf ΨTLP influences the stomatal response to drought. The results showed a significant seasonal shift in the response of stomatal conductance to stem water potential (gs ~Ψstem ), demonstrating that grapevines become increasingly tolerant to low Ψstem as the season progresses in coordination with the decrease in ΨTLP . We also used the SurEau hydraulic model to demonstrate a direct link between osmotic adjustment and the plasticity of gs ~Ψstem . To understand the possible advantages of gs ~Ψstem plasticity, we incorporated a seasonally dynamic leaf osmotic potential into the model that simulated stomatal conductance under several water availabilities and climatic scenarios. The model demonstrated that a seasonally dynamic stomatal closure threshold results in trade-offs: it reduces the time to turgor loss under sustained long-term drought, but increases overall gas exchange particularly under seasonal shifts in temperature and stochastic water availability. A projected hotter future is expected to lower the increase in gas exchange that plants gain from the seasonal shift in gs ~Ψstem . These findings show that accounting for dynamic stomatal regulation is critical for understanding drought tolerance.

Putrescine regulates stomatal opening of cucumber leaves under salt stress via the H2O2-mediated signaling pathway

The stomatal aperture is imperative for photosynthesis in higher plants. The function of polyamines (PAs) in stomatal regulation under a stressful environment has not been fully determined. In this study, we demonstrated the mechanism by which putrescine (Put) regulates stomatal changes in cucumber leaves under salt stress. The results showed that foliar application of Put alleviated the decrease of stomatal aperture and photosynthesis caused by salt stress and promoted plant growth. Exogenous Put caused a significant increase in endogenous PAs and hydrogen peroxide (H2O2) levels by 105.43% and 27.97%, respectively, while decreased abscisic acid (ABA) content by 67.68% under salt stress. However, application of inhibitors of aminoguanidine hydrochloride (AG), 1, 8-diaminooctane (1, 8-DO), diphenyleneiodonium chloride (DPI) and salicylhydroxamic acid (SHAM) upregulated the 9-cis-cyclocarotenoid dioxygenase (NCED) gene and downregulated the reduced glutathione synthetase (GSHS) gene. These inhibitors also decreased the stomatal aperture, levels of H2O2 and reduced glutathione (GSH), but increased the ABA content under salt stress and Put treatment conditions. The order of influence is AG > 1, 8-DO > DPI > SHAM. However, Put-induced downregulation of ABA content and upregulation of GSH content under salt stress were effectively blocked by N, N′-dimethylthiourea (DMTU, H2O2 scavenger) and 1-chloro-2,4-dinitrobenzene (CDNB, GSH scavenger) treatments. Taken together, these results suggest that Put induced the formation of H2O2 signaling mediates the degradation of PAs by diamine oxidase (DAO), increasing GSH content and inhibiting the accumulation of ABA in leaves, thereby promoting stomatal opening in salt-stressed cucumber leaves.

Higher plasticity of water uptake in spruce than larch in an alpine habitat of North-Central China

Understanding interspecific differences in tree water use will aid in the assessment of both tree-level ecophysiological adaptation to climate change and forecasts of forest dynamics. We investigated the seasonal variation of water sources between two co-occurring trees species with contrasting leaf phenology and rooting traits: the deciduous Larix principis-rupprechtii Mayr. and the evergreen Picea meyeri Rehd. et Wils. At weekly/biweekly intervals from September 2013 to October 2014 in the Luya Mountains in North-Central China, we collected and analyzed a total of approximately 2400 samples of δD and δ18O in tree xylem water, potential water sources for all study trees, and the contribution of water at different soil depths. Concurrently, we monitored leaf phenology by direct observation and wood phenology with the microcore method. Microcoring allowed us to trace intra-annual dynamics of word formation (i.e., onset, end, and maximum growth rate). These results, including a seasonal origin index, indicated that winter snowmelt water is sourced for growth initiation for both larch and spruce, although larch relies on it more than spruce. Larch and spruce mainly absorbed water from the same soil layer of 10–20 cm during the growing season (circa 38.9% and 37.5% of total water uptake, respectively). However, this potential inter-specific water competition did not increase until growth rates reached the maximum for the year; larch used more water from deeper soil layers while spruce used water generally equally from each soil layer. Unlike deeper-rooting larch, the more shallow-rooted spruce showed a greater ability to shift water uptake among various soil layers. This plasticity in water uptake was accompanied by tighter stomatal regulation, suggesting spruce growth is generally more tightly coupled to water availability. Such diverging species-specific water use strategies improve our knowledge on tree-level ecophysiological mechanisms, with implications for understanding ecosystem-level forest dynamics and potential resilience to environmental stress.

Unraveling the Genetic Architecture of Two Complex, Stomata-Related Drought-Responsive Traits by High-Throughput Physiological Phenotyping and GWAS in Cowpea (Vigna. Unguiculata L. Walp).

Drought is one of the most devasting and frequent abiotic stresses in agriculture. While many morphological, biochemical and physiological indicators are being used to quantify plant drought responses, stomatal control, and hence the transpiration and photosynthesis regulation through it, is of particular importance in marking the plant capacity of balancing stress response and yield. Due to the difficulties in simultaneous, large-scale measurement of stomatal traits such as sensitivity and speed of stomatal closure under progressive soil drought, forward genetic mapping of these important behaviors has long been unavailable. The recent emerging phenomic technologies offer solutions to identify the water relations of whole plant and assay the stomatal regulation in a dynamic process at the population level. Here, we report high-throughput physiological phenotyping of water relations of 106 cowpea accessions under progressive drought stress, which, in combination of genome-wide association study (GWAS), enables genetic mapping of the complex, stomata-related drought responsive traits “critical soil water content” (θcri) and “slope of transpiration rate declining” (KTr). The 106 accessions showed large variations in θcri and KTr, indicating that they had broad spectrum of stomatal control in response to soil water deficit, which may confer them different levels of drought tolerance. Univariate GWAS identified six and fourteen significant SNPs associated with θcri and KTr, respectively. The detected SNPs distributed in nine chromosomes and accounted for 8.7–21% of the phenotypic variation, suggesting that both stomatal sensitivity to soil drought and the speed of stomatal closure to completion were controlled by multiple genes with moderate effects. Multivariate GWAS detected ten more significant SNPs in addition to confirming eight of the twenty SNPs as detected by univariate GWAS. Integrated, a final set of 30 significant SNPs associated with stomatal closure were reported. Taken together, our work, by combining phenomics and genetics, enables forward genetic mapping of the genetic architecture of stomatal traits related to drought tolerance, which not only provides a basis for molecular breeding of drought resistant cultivars of cowpea, but offers a new methodology to explore the genetic determinants of water budgeting in crops under stressful conditions in the phenomics era.

Crosstalk between H2 S and NO: an emerging signalling pathway during waterlogging stress in legume crops.

In legumes, waterlogging is a major detrimental factor leading to huge yield losses. Generally, legumes lack tolerance to submergence, and conventional breeding to develop tolerant varieties are limited due to the lack of tolerant germplasm and potential target genes. Moreover, our understanding of the various signalling cascades, their interactions and key pathways induced during waterlogging is limited. Here, we focus on the role of two important plant signalling molecules, viz. hydrogen sulphide (H2 S) and nitric oxide (NO), during waterlogging stress in legumes. Plants and soil microbes produce these signalling molecules both endogenously and exogenously under various stresses, including waterlogging. NO and H2 S are known to regulate key physiological pathways, such as stomatal closure, leaf senescence and regulation of numerous stress signalling pathways, while NO plays a pivotal role in adventitious root formation during waterlogging. The crosstalk between H2 S and NO is synergistic because of the resemblance of their physiological effects and proteomic functions, which mainly operate through cysteine-dependent post-translational modifications via S-nitrosation and persulfidation. Such knowledge has provided novel platforms for researchers to unravel the complexity associated with H2 S-NO signalling and interactions with plant stress hormones. This review provides an overall summary on H2 S and NO, including biosynthesis, biological importance, crosstalk, transporter regulation as well as understanding their role during waterlogging using 'multi-omics' approach. Understanding H2 S and NO signalling will help in deciphering the metabolic interactions and identifying key regulatory genes that could be used for developing waterlogging tolerance in legumes.

A Transcriptome Analysis Revealing the New Insight of Green Light on Tomato Plant Growth and Drought Stress Tolerance.

Light plays a pivotal role in plant growth, development, and stress responses. Green light has been reported to enhance plant drought tolerance via stomatal regulation. However, the mechanisms of green light-induced drought tolerance in plants remain elusive. To uncover those mechanisms, we investigated the molecular responses of tomato plants under monochromatic red, blue, and green light spectrum with drought and well-water conditions using a comparative transcriptomic approach. The results showed that compared with monochromatic red and blue light treated plants, green light alleviated the drought-induced inhibition of plant growth and photosynthetic capacity, and induced lower stomatal aperture and higher ABA accumulation in tomato leaves after 9 days of drought stress. A total of 3,850 differentially expressed genes (DEGs) was identified in tomato leaves through pairwise comparisons. Functional annotations revealed that those DEGs responses to green light under drought stress were enriched in plant hormone signal transduction, phototransduction, and calcium signaling pathway. The DEGs involved in ABA synthesis and ABA signal transduction both participated in the green light-induced drought tolerance of tomato plants. Compared with ABA signal transduction, more DEGs related to ABA synthesis were detected under different light spectral treatments. The bZIP transcription factor- HY5 was found to play a vital role in green light-induced drought responses. Furthermore, other transcription factors, including WRKY46 and WRKY81 might participate in the regulation of stomatal aperture and ABA accumulation under green light. Taken together, the results of this study might expand our understanding of green light-modulated tomato drought tolerance via regulating ABA accumulation and stomatal aperture.

Water Stress in Dwarfing Cherry Rootstocks: Increased Carbon Partitioning to Roots Facilitates Improved Tolerance of Drought

Cherry orchards are transitioning to high-density plantings and dwarfing rootstocks to maximize production, but the response of these rootstocks to drought stress is poorly characterized. We used a 16-container, automated lysimeter system to apply repeated water stress to ungrafted Krymsk® 5 and 6 rootstocks during two growing cycles. Drought stress was imposed by withholding irrigation until the daily transpiration rate of each tree was 25% and 30% of the unstressed rate during the first trial and second trial, respectively. After this point was reached, the root-zone water status was restored to field capacity. Whole-tree transpiration measurements were supplemented with leaf-level gas-exchange measurements. Krymsk® 6 had a higher rate of photosynthesis, more vigorous vegetative growth and less conservative stomatal regulation during incipient drought than Krymsk® 5. At harvest, carbon partitioning to roots was greater in Krymsk® 6 than Krymsk® 5. The conservative rate of water use in Krymsk® 5 could be a function of greater stomatal control or reduced carbon partitioning to roots, which thereby limited transpiration rates. Further studies are needed to confirm that these results are applicable to trees grown using a common grafted scion under field conditions.

Thermal infrared imaging study of water status and growth of arbuscular mycorrhizal soybean (Glycine max) under drought stress

The influence of arbuscular mycorrhizal fungi (AMF) on plant water status and growth under drought stress were investigated using soybean subjected to drought stress (40% of soil water-holding capacity (WHC)) and control conditions (60% WHC) either inoculated with AMF or uninoculated controls. Leaf temperature (Tleaf) and stomatal conductance (gs) were determined at 10:00, 12:00 and 18:00 on the harvest day. The effects of AMF on the water physiological status and growth of soybeans under drought stress were examined using thermal infrared imaging technology (TIIT). AMF inoculation under drought stress increased plant above- and below-ground biomass, nutritional status, and nitrogen, phosphorus and potassium uptake rates, and reduced plant root/shoot ratio. Monitoring Tleaf reflected the effect of AMF on plant water physiological status under drought stress. AMF inoculation resulted in a decline in Tleaf of 0.1–0.4 °C as water uptake proceeded compared with an increase of 0.2–1.4 °C in uninoculated controls. Thus, the effects of AMF on soybean drought resistance changed from positive to negative. AMF reduced plant Tleaf, promoted the accumulation of photosynthetic products, reduced malondialdehyde accumulation, and increased stomatal regulation and Tleaf. These preliminary results provide a basis for further studies on the effects of AMF on the water and growth status of plants under drought stress in arid areas.

Identification of Genes Preferentially Expressed in Stomatal Guard Cells of Arabidopsis thaliana and Involvement of the Aluminum-Activated Malate Transporter 6 Vacuolar Malate Channel in Stomatal Opening.

Stomatal guard cells (GCs) are highly specialized cells that respond to various stimuli, such as blue light (BL) and abscisic acid, for the regulation of stomatal aperture. Many signaling components that are involved in the stomatal movement are preferentially expressed in GCs. In this study, we identified four new such genes in addition to an aluminum-activated malate transporter, ALMT6, and GDSL lipase, Occlusion of Stomatal Pore 1 (OSP1), based on the expression analysis using public resources, reverse transcription PCR, and promoter-driven β-glucuronidase assays. Some null mutants of GC-specific genes evidenced altered stomatal movement. We further investigated the role played by ALMT6, a vacuolar malate channel, in stomatal opening. Epidermal strips from an ALMT6-null mutant exhibited defective stomatal opening induced by BL and fusicoccin, a strong plasma membrane H+-ATPase activator. The deficiency was enhanced when the assay buffer [Cl–] was low, suggesting that malate and/or Cl– facilitate efficient opening. The results indicate that the GC-specific genes are frequently involved in stomatal movement. Further detailed analyses of the hitherto uncharacterized GC-specific genes will provide new insights into stomatal regulation.