Stomatal Regulation Research Articles

High sensitivity of hop plants (Humulus lupulus L.) to limited soil water availability: the role of stomata regulation and xylem vulnerability to embolism

Drought poses a serious threat to the productivity of hop, an important perennial crop. However, the precise physiological mechanisms that make it highly susceptible to drought are not yet fully understood. In this study, we investigated stomatal regulation and xylem vulnerability to embolism, which are important traits closely associated with plant drought resistance. In a glasshouse cultivation experiment, we monitored changes in leaf water potential, stem elongation rates, and leaf gas exchange, including net photosynthetic rates, stomatal conductance, and intrinsic water use efficiency, on relatively young hop plants (traditional Saaz - Osvald’s clone 31) exposed to declining soil water availability. The transpiration rate and stem elongation of plants decreased significantly with a small decline in substrate water potential (ΨSUB), indicating a highly sensitive stomata response during early phases of soil dehydration. The stem elongation was completely halted, and the transpiration rate dropped to less than 50% of its maximum at ΨSUB levels below − 0.8 MPa. In well-watered hop plants, xylem in stems operates near the initial point of embolization and is highly vulnerable to embolism, with a water potential corresponding to a 50% loss of xylem conductivity at -1.6 MPa. The sensitive stomatal response to declining ΨSUB likely helps to mitigate the risk of hydraulic failure, albeit at the cost of impaired growth. Scheduled irrigation, particularly during the sensitive stem elongation stage, may be a promising approach to mitigate the detrimental effects of reduced soil water availability on hop growth and yield while also conserving water resources.

Coordinated hydraulic traits influence the two phases of time to hydraulic failure in five temperate tree species differing in stomatal stringency.

Worldwide, forests are increasingly exposed to extreme droughts causing tree mortality. Because of the complex nature of the mechanisms involved, various traits have been linked to tree drought responses with contrasting results. This may be due to species-specific strategies in regulating water potential, a process that unfolds in two distinct phases: a first phase until stomatal closure, and a second phase until reaching lethal xylem hydraulic thresholds. We conducted dry-down experiments with five broadleaved temperate tree species differing in their degree of isohydry to estimate the time to stomatal closure (tsc) and subsequent time to critical hydraulic failure (tcrit). We measured various traits linked to tree drought responses, such as the water potentials at turgor loss point (Ptlp), stomatal closure (Pgs90), and 12%, 50% and 88% loss of xylem hydraulic conductance (P12, P50, P88), hydraulic capacitance (C), minimum leaf conductance (gmin), hydroscape area (HSA) and hydraulic safety margins (HSM). We found that Pgs90 followed previously recorded patterns of isohydry and was associated with HSA. Species ranked from more to less isohydric in the sequence Acer pseudoplatanus<Betula pendula<Tilia cordata<Sorbus aucuparia<Fagus sylvatica. Their degree of isohydry was associated with leaf safety (Ptlp and gmin), drought avoidance (C) and tsc, but decoupled from xylem safety (HSM and P88) and tcrit. Regardless of their stomatal stringency, species with wider HSM and lower P88 reached critical hydraulic failure later. We conclude that the duration of the first phase is determined by stomatal regulation, while the duration of the second phase is associated with xylem safety. Isohydry is thus linked to water use rather than to drought survival strategies, confirming the proposed use of HSA as a complement to HSM for describing plant drought responses before and after stomatal closure.

Incorporating photosynthetic acclimation improves stomatal optimisation models.

Stomatal opening in plant leaves is regulated through a balance of carbon and water exchange under different environmental conditions. Accurate estimation of stomatal regulation is crucial for understanding how plants respond to changing environmental conditions, particularly under climate change. A new generation of optimality-based modelling schemes determines instantaneous stomatal responses from a balance of trade-offs between carbon gains and hydraulic costs, but most such schemes do not account for biochemical acclimation in response to drought. Here, we compare the performance of six instantaneous stomatal optimisation models with and without accounting for photosynthetic acclimation. Using experimental data from 37 plant species, we found that accounting for photosynthetic acclimation improves the prediction of carbon assimilation in a majority of the tested models. Photosynthetic acclimation contributed significantly to the reduction of photosynthesis under drought conditions in all tested models. Drought effects on photosynthesis could not accurately be explained by the hydraulic impairment functions embedded in the stomatal models alone, indicating that photosynthetic acclimation must be considered to improve estimates of carbon assimilation during drought.

Enhanced photosynthesis, transpiration regulation, water use-efficiency and growth in buckwheat outperforms wheat response to high [CO2], high temperature and drought

The rising atmospheric [CO2] levels will increase global temperature and drought events, threatening wheat (Triticum aestivum) production. In recent years, buckwheat (Fagopyrum esculentum) has emerged as an alternative crop to wheat under extreme drought. However, it is essential to understand the ability of these species to withstand future climatic conditions where drought and high temperature will occur simultaneously in a high [CO2] environment. Since the mitigating effect of high [CO2] is strongly influenced by the severity of the stress, we compared the response of wheat and buckwheat, differently sensitive to drought, to future climatic scenarios. In wheat, high temperature and high [CO2] passively decreased water potential, as shown by the higher dehydration. Likewise, future drought extremely increased water requirements, causing extreme reductions in the photosynthetic rate and in the quantum yield of PSII, as well as changes in the antioxidant metabolism. Conversely, buckwheat maintained optimal hydration levels, promoted higher photosynthetic rates and increased water-use efficiency under the combination of high [CO2] and high temperature, with and without drought. The improved response of buckwheat was attributed to an enhanced stomatal regulation and water-use efficiency, and resulted in an outperforming growth under future climatic conditions compared to the growth in wheat. Our research highlights the promising potential of buckwheat as an alternative crop to wheat under future climatic scenarios.

SHOOT GRAVITROPISM 5 mediates the stomatal response to darkness in Arabidopsis.

Stomatal regulation, a multifaceted mechanism enabling plants to adapt to diverse environmental conditions and optimize photosynthesis for survival and growth, is considered crucial in drought stress tolerance research. To further enhance our understanding of stomatal regulation, we investigated the novel transcription factors involved in this process. Our findings reveal that SHOOT GRAVITROPISM 5 (SGR5) is involved in the stomatal response to darkness in Arabidopsis. Water loss measurements showed that SGR5-overexpressing plants retained more water, whereas SGR5-knockout lines exhibited increased water loss compared with the control. Unexpectedly, our analyses indicated that SGR5 was not associated with the abscisic acid signaling pathway, in contrast to its homologous transcription factor, INDETERMINATE DOMAIN 14. Instead, SGR5-knockout lines exhibited weakened stomatal closure responses upon transition to darkness. Collectively, our results highlight the regulatory role of SGR5 in mediating stomatal movement in response to darkness.

A review of the interaction between potassium nutrition and plant disease control

AbstractPotassium (K) is an essential macronutrient involved in many physiological and biochemical functions that affect a plant's susceptibility to disease. These processes include stomatal regulation, enzyme activation, and solute transport, each of which is often discussed through the lens of either plant nutrition or plant disease control. However, the interaction between these stresses and the resulting physiological and agronomic impact is an important consideration when managing a cropping system as a whole and is scarcely addressed in the literature. Therefore, a review of the literature was focused on the interaction of K nutrition and the resulting impact on plant disease control. Nutrient management, especially K, can manipulate these essential plant processes to provide the host plant with either an advantage or disadvantage in disease susceptibility, depending on the pathogen and the situation. Numerous studies have been conducted investigating the individual pathogen and host relationships, concluding that the majority of bacterial and fungal diseases decreased with increasing K nutrition, while viral diseases and nematode infections had inconsistent responses to K nutrition. These differences in the response of disease to K nutrition complicate generalizations across species and environments. Similarly, the impact of K on plant growth is affected by the concentration of each nutrient and its ratio with other nutrients. Therefore, a review of the major physiological processes that depend on plant K nutrition is discussed below with the resulting impact on plant disease control.

Xylem safety in relation to the stringency of plant water potential regulation of European beech, Norway spruce, and Douglas-fir trees during severe drought

Key messageNorway spruce operates with larger hydraulic safety margins (HSM) than beech and Douglas-fir despite the known drought sensitivity of spruce, questioning a pivotal role of HSM in drought tolerance.The exceptional 2018/2019 drought exposed Central Europe’s forests to severe stress, highlighting the need to better understand stomatal regulation strategies and their relationship to xylem safety under extreme drought. We studied diurnal, seasonal, and inter-annual variation in stomatal conductance (gs) and leaf water potential (ΨLeaf) in co-occurring European beech (F. sylvatica), Norway spruce (P. abies), and Douglas-fir (P. menziesii) trees in the two summers and related them to hydraulic traits characterizing drought resistance. In 2018, F. sylvatica exhibited a continuous ΨLeaf decline from June to September, as is characteristic for an anisohydric strategy, while P. abies closed stomata early and reached the least negative ΨLeaf-values at the end of summer. P. menziesii showed low ΨLeaf-values close to P12 (the xylem pressure at onset of embolism) already in July. Both conifers closed stomata when approaching P12 and maintained low gs-levels throughout summer, indicative for isohydric regulation. In 2019, all three species showed a linear decline in ΨLeaf, but F. sylvatica crossed P12 in contrast to the conifers. The three species exhibited similar water potentials at turgor loss point (− 2.44 to − 2.51 MPa) and branch P50 (xylem pressure at 50% loss of hydraulic conductance; − 3.3 to − 3.8 MPa). Yet, F. sylvatica and P. menziesii operated with smaller hydraulic safety margins (HSM means: 0.79 and 0.77 MPa) than P. abies (1.28 MPa). F. sylvatica reduced leaf size and specific leaf area in 2019 and increased Huber value. Our species comparison during extreme drought contradicts the general assumption that conifers operate with larger HSMs than angiosperm trees. Contrary to expectation, P. abies appeared as hydraulically less vulnerable than Douglas-fir.

Thinning vs. Pruning: Impacts on Sap Flow Density and Water Use Efficiency in Young Populus tomentosa Plantations in Northern China

Water is a vital resource for tree growth, and changes in plantation and canopy structure can affect stand transpiration (Ec), consequently influencing water use efficiency (WUE). Populus tomentosa is a fast-growing and productive timber species in China. In recent years, thinning combined with pruning has become a widely used silvicultural practice for timber management. However, its effect on water utilization has been less well studied. To address this gap, we designed experiments with two thinning intensities and three pruning treatments. Thermal dissipation probes were employed to monitor tree sap flow density (Js), and estimated Ec and canopy conductance (gc). We established a relationship between the canopy transpiration per unit leaf area (EL) and gc and climatic factors. Finally, we compared basal area increment (BAI) and WUE among treatments under different rainfall conditions. The results indicated that: (1) The pattern of transpiration changes was consistent at both the individual tree and stand level. (2) The combined effect of T1 (thinning intensity of 833 trees per hectare) and pruning reduced Ec, decreasing the sensitivity of tree transpiration to the climate, with no discernible impact on EL and gc. Conversely, T2 (thinning intensity of 416 trees per hectare) and pruning increased EL and gc but had no effect on Ec, enhancing the sensitivity of tree transpiration to the climate. The sensitivity of gc to VPD suggested a flexible stomatal regulation of transpiration under different combined thinning and pruning treatments. (3) Under T1, only P2 (4 m pruning from ground) promoted WUE, while pruning effects significantly reduced WUE under T2. Overall, the WUE of T2P0 (thinning intensity of 416 trees per hectare combined with no pruning) was significantly higher than that of the other treatments, and that of T1P0 (thinning intensity of 833 trees per hectare combined with no pruning) was significantly lower than that of the other treatments. Additionally, significant differences in Ec and BAI were observed among treatments under different rainfall conditions, with the promotion effect of Ec on BAI being more pronounced in the dry season.

Save or spend? Diverging water‐use strategies of grasses and encroaching clonal shrubs

Abstract Shrub encroachment is one of the primary threats to mesic grasslands around the world. This dramatic shift in plant cover has the potential to alter ecosystem‐scale water budgets and responses to novel rainfall regimes. Understanding divergent water‐use strategies among encroaching shrubs and the grasses they replace is critical for predicting shifts in ecosystem‐scale water dynamics as a result of shrub encroachment, particularly if drought events become more frequent and/or severe in the future. In this study, we assessed how water‐use traits of a rapidly encroaching clonal shrub (Cornus drummondii) and a dominant C4 grass (Andropogon gerardii) impact responses to changes in water availability in tallgrass prairie. We assessed intra‐annual change in depth of water uptake, turgor loss point and stomatal regulation in each species. Sampling took place at Konza Prairie Biological Station (northeastern KS, USA) during the 2021 and 2022 growing seasons. Cornus drummondii shifted from shallow to deep soil water sources across the 2021 and 2022 growing seasons. This plasticity in depth of water uptake facilitated a ‘wasteful’ water‐use strategy in C. drummondii, where stomatal conductance and transpiration rates continued to increase even when no further gain in photosynthetic rate occurred. A. gerardii photosynthetic rates and stomatal conductance were more variable through time and were more responsive to changes in leaf water potential than C. drummondii. However, intra‐annual adjustment of turgor loss point was more pronounced in C. drummondii (ΔπTLP = −0.48 MPa ± 0.15 SD) than in A. gerardii (ΔπTLP = −0.29 MPa ± 0.19 SD). Synthesis. These results suggest that C. drummondii is highly resilient to changes in water availability in surface soils and will likely remain unaffected by future droughts unless they are severe enough to reduce the availability of deep soil water. Given that clonal shrubs are key invaders of grasslands world‐wide, increased leaf‐level water loss is expected to accelerate ecosystem‐level drying as clonal shrub encroachment proceeds in mesic grasslands.

Stomatal response to VPD is not triggered by changes in soil-leaf hydraulic conductance in Arabidopsis or Callitris.

Stomatal closure under high VPDL (leaf to air vapour pressure deficit) is a primary means by which plants prevent large excursions in transpiration rate and leaf water potential (Ψleaf) that could lead to tissue damage. Yet, the drivers of this response remain controversial. Changes in Ψleaf appear to drive stomatal VPDL response, but many argue that dynamic changes in soil-to-leaf hydraulic conductance (Ks-l) make an important contribution to this response pathway, even in well-hydrated soils. Here, we examined whether the regulation of whole plant stomatal conductance (gc) in response to typical changes in daytime VPDL is influenced by dynamic changes in Ks-l. We use well-watered plants of two species with contrasting ecological and physiological features: the herbaceous Arabidopsis thaliana (ecotype Columbia-0) and the dry forest conifer Callitris rhomboidea. The dynamics of Ks-l and gc were continuously monitored by combining concurrent in situ measurements of Ψleaf using an open optical dendrometer and whole plant transpiration using a balance. Large changes in VPDL were imposed to induce stomatal closure and observe the impact on Ks-l. In both species, gc was observed to decline substantially as VPDL increased, while Ks-l remained stable. Our finding suggests that stomatal regulation of transpiration is not contingent on a decrease in Ks-l. Static Ks-l provides a much simpler explanation for transpiration control in hydrated plants and enables simplified modelling and new methods for monitoring plant water use in the field.

Variable Responses of Plant Water Use to Soil Water Availability in Robinia Pseudoacacia under Prolonged Drought

Abstract Large-scale afforestation on the Loess Plateau has been subjected to more frequent and severe drought due to climate change. However, there is a lack of definite evidence elucidating the adjustments in water supply-demand relationships under prolonged drought. In this study, we investigated the responses of plant characteristics related to plant water supply and demand in 2-year-old Robinia pseudoacacia seedlings to soil water availability (SWA). We systemically analyzed the acclimation of plant water use to prolonged drought. A logistic function was used to fit relationships between normalized net photosynthetic rate (Pn), transpiration rate (Tr), stomatal conductance (Gs), soil-root hydraulic conductance (Ksr), root-leaf hydraulic conductance (Krl), and whole plant hydraulic conductance (Kplant) with SWA. The results revealed significant difference in responses of these parameters to SWA (p &amp;lt; .001). The sensitivities of Pn, Tr, and Gs to drought increased from 60-day to 120-day drought, contributing to reduce water consumption. Meanwhile, the relative stable sensitivities of hydraulic conductance (Ksr, Ksr, and Kplant) promoted a consistent water supply at different ecological levels. Additionally, coordination between Gs with hydraulic conductance helped maintain normal physiological activities under drought. These findings enhance our understanding of adjustments in plant water use in response to prolonged drought in Robinia pseudoacacia. Study Implications: Our findings have implications for better understanding the acclimation of Robinia pseudoacacia to prolonged drought. First, our results suggest decreased water demand (water consumption) by Robinia pseudoacacia under prolonged drought because the sensitivities of net photosynthetic rate (Pn), transpiration rate (Tr), and stomatal conductance (Gs) to drought increased from 60-day to 120-day drought treatments. Second, our study indicates a relative stable water supply (soil-root, root-leaf, and whole plant hydraulic conductance; Ksr, Krl, and Kplant) of Robinia pseudoacacia at different ecological levels under prolonged drought. Finally, our research has implications for the coordination of stomatal and hydraulic regulation.

Ethylene-mediated stomatal responses to dehydration and rehydration in seed plants.

Ethylene, a plant hormone that significantly influences both plant growth and response to stress, plays a well-established role in stress signaling. However, its impact on stomatal opening and closure during dehydration and rehydration remains relatively unexplored and is still debated. Exogenous ethylene has been proven to induce stomatal closure through a series of signaling pathways, including the accumulation of reactive oxygen species (ROS), subsequent synthesis of nitric oxide (NO) and hydrogen sulfide (H2S), and SLOW ANION CHANNEL-ASSOCIATED 1 (SLAC1) activation. Thus, it has been suggested that ethylene might function to induce stomatal closure synergistically with abscisic acid (ABA). Furthermore, it has also been shown that increased ethylene can inhibit ABA- and jasmonic acid (JA)-induced stomatal closure, thus hindering drought-induced closure during dehydration. Simultaneously, other stresses, such as chilling, ozone pollution and K+ deficiency, inhibit drought and ABA-induced stomatal closure through an ethylene synthesis dependent way. However, ethylene has been shown to take on an opposing role during rehydration, preventing stomatal opening in the absence of ABA through its own signaling pathway. These findings offer novel insights into the function of ethylene in stomatal regulation during dehydration and rehydration, gaining a better understanding of the mechanisms underlying ethylene-induced stomatal movement in seed plants.

Biochar Mitigates the Harmful Effects of Drought in Soybean Through Changes in Leaf Development, Stomatal Regulation, and Gas Exchange

Biochar Mitigates the Harmful Effects of Drought in Soybean Through Changes in Leaf Development, Stomatal Regulation, and Gas Exchange

Combined application of acetylcholine (ACh) and gamma-aminobutyric acid (GABA) mitigates the effects of water deficit in soybean

Bioregulatory substances, such as acetylcholine (ACh) and γ-aminobutyric acid (GABA), have shown promise in mitigating water deficit effects on plants. Their action on plant physiology, particularly in stomatal regulation and osmoprotection, contributes to enhanced agricultural productivity. Regarding soybean plants, changes in the metabolic profile that could justify the improvement in physiological performance and growth are still unknown. This study investigated the impact of combined ACh:GABA application during soybean V4 and R2 stages using physiological assessments and NMR-based metabolomics. Two equimolar doses (2 and 8 mM) of ACh:GABA were applied to soybean plants subjected to two water regimes: 100 % of field capacity (continuously irrigated) and water deficit (water suspension). Results demonstrated enhanced gas exchange, biomass, and chlorophyll content, alongside favorable enzymatic activity. NMR analysis revealed metabolites countering oxidative stress, supporting osmoprotection, and contributing to soybean development and energy supply. The 8 mM ACh:GABA application notably improved plant performance, showcasing potential for water deficit mitigation in soybeans.

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

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. 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. 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. 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.

Pushing the limits of C3 intrinsic water use efficiency in Mediterranean semiarid steppes: Responses of a drought‐avoider perennial grass to climate aridification

Abstract Intrinsic water use efficiency (WUEi) reflects the trade‐off between photosynthetic carbon gain and water loss through stomatal conductance and is key for understanding dryland plant responses to climate change. Stipa tenacissima is a perennial tussock C3 grass with an opportunistic, drought‐avoiding water use strategy that dominates arid and semiarid steppes across the western Mediterranean region. However, its ecophysiological responses to aridification and woody shrub encroachment, a major land‐use change in drylands worldwide, are not well‐understood. We investigated the variations in leaf stable isotopes (δ18O, δ13C, δ15N), nutrient concentrations (N, P, K), and culm water content and isotopic composition (δ18O, δ2H) of paired pure‐grass and shrub‐encroached S. tenacissima steppes along a 350 km aridity gradient in Spain (10 sites, 160 individuals). Culm water isotopes revealed that S. tenacissima is a shallow‐rooted grass that depends heavily on recent rainwater for water uptake, which may render it vulnerable to increasingly irregular rainfall combined with faster topsoil drying under climate warming and aridification. With increasing aridity, S. tenacissima enhanced leaf‐level WUEi through more stringent stomatal regulation of plant water flux and carbon assimilation (higher δ13C and δ18O), reaching exceptionally high δ13C values (−23‰ to −21‰) at the most arid steppes. Foliar N concentration was remarkably low across sites regardless of woody shrub encroachment, evidencing severe water and N co‐limitation of photosynthesis and productivity. Shrub encroachment decreased leaf P and K but did not affect S. tenacissima water status. Perennial grass cover decreased markedly with both declining winter rainfall and shrub encroachment suggesting population‐level rather than individual‐level responses of S. tenacissima to these changes. The fundamental physiological constraints of photosynthetic C3 metabolism combined with low foliar N content may hamper the ability of S. tenacissima and other drought‐avoider species with shallow roots to achieve further adaptive improvements in WUEi under increasing climatic stress. A drought‐avoiding water use strategy based on early stomatal closure and photosynthesis suppression during prolonged rainless periods may thus compromise the capacity of semiarid S. tenacissima steppes to maintain perennial grass cover, sustain productivity and cope with ongoing climate aridification at the drier parts of their current distribution. Read the free Plain Language Summary for this article on the Journal blog.

MsABCG1, ATP-Binding Cassette G transporter from Medicago Sativa, improves drought tolerance in transgenic Nicotiana Tabacum.

Drought has a devastating impact, presenting a formidable challenge to agricultural productivity and global food security. Among the numerous ABC transporter proteins found in plants, the ABCG transporters play a crucial role in plant responses to abiotic stress. In Medicago sativa, the function of ABCG transporters remains elusive. Here, we report that MsABCG1, a WBC-type transporter highly conserved in legumes, is critical for the response to drought in alfalfa. MsABCG1 is localized on the plasma membrane, with the highest expression observed in roots under normal conditions, and its expression is induced by drought, NaCl and ABA signalling. In transgenic tobacco, overexpression of MsABCG1 enhanced drought tolerance, evidenced by increased osmotic regulatory substances and reduced lipid peroxidation. Additionally, drought stress resulted in reduced ABA accumulation in tobacco overexpressing MsABCG1, demonstrating that overexpression of MsABCG1 enhanced drought tolerance was not via an ABA-dependent pathway. Furthermore, transgenic tobacco exhibited increased stomatal density and reduced stomatal aperture under drought stress, indicating that MsABCG1 has the potential to participate in stomatal regulation during drought stress. In summary, these findings suggest that MsABCG1 significantly enhances drought tolerance in plants and provides a foundation for developing efficient drought-resistance strategies in crops.

Temporal dynamics of stomatal regulation and carbon- and water-related traits for a native tree species in low subtropical China.

Stomata are pivotal in modulating water and carbon processes within plants. However, our understanding of the temporal dynamics of water- and carbon-related traits, as influenced by stomatal behavior, remains limited. Here, we explore how stomatal regulation behavior and water- and carbon-related traits vary with changing environments by examining the seasonal variations in these traits of the native tree species Schima superba in low subtropical China. In February, April, and July of 2022, a series of water- and carbon-related traits were measured in the leaves and stems. The results showed that S. superba exhibited isohydric behavior in February when the soil dried out and vapor pressure deficit (VPD) was lower but anisohydric behavior in April and July when the soil was wetter and VPD was higher. In February, NSC and their components increased, and a relatively large contribution of soluble sugars to the change in NSC was observed. In the branches and phloem, NSC and their components displayed a relatively high monthly variability, suggesting their role in maintaining carbon balance within the trees. Conversely, the NSC in the leaves demonstrated minimal monthly variability. The specific leaf area, as well as the concentration of nitrogen (N) and phosphorus (P) per unit mass in leaves and the cumulative stem water release, exhibited a decrease with a reduction in soil water potential. Interestingly, the hydraulic conductivity remained consistent throughout this process. Furthermore, the relatively low monthly growth rate observed in February could suggest a carbon sink limitation. In conclusion, the increased NSC and decreased water status of S. superba under relatively stressed soil conditions indicated a trade-off between water and carbon storage. Our findings enhance our comprehension of the dynamics and regulation of water and carbon status in forests, thereby advancing the development of plant carbon and water process models under climate change scenarios.

Morphological, Physiological, and Molecular Stomatal Responses in Local Watermelon Landraces as Drought Tolerance Mechanisms

Drought-tolerant plants have become a convenient model to study the mechanisms underlying drought tolerance in order to improve susceptible domesticated relatives. Various studies have shown that local landraces possess superior qualities that help them survive in harsh environmental conditions. One of the key mechanisms that helps with tolerance in crops is timely stomatal regulation. In this study, the physiological, morphological, and molecular stomatal responses in three drought-tolerant landraces (Clm-01–03) and hybrid (Clm-04) watermelons were evaluated under drought stress. The watermelon plants were grown under a water deficit (complete withholding of water) and non-stress conditions. The highest SPAD values were recorded for the Clm-03 and Clm-02 (50 ± 3) watermelon genotypes, and the lowest for Clm-04 (27 ± 0.37), showing this genotype’s tolerance and ability to maintain its systems during drought stress. Fluorescence parameters also gave important clues to the tolerant genotypes of Clm-02 and Clm-03 under drought stress, while the domesticated genotype showed a slow response to fluorescence parameters, which could lead to damage to the photosynthesis apparatus. During the drought period, the wild watermelon was found to have a limited stomatal opening as the drought progressed, and on day 9, it had the smallest opening of 23.1 ± 1.2 µm compared to any other genotype; most importantly, upon re-watering, it showed more rapid recovery than any other genotype. This was also expressed by mRNA quantification of stomatal aperture TFs, with an eight-fold increase in Cla004380 TFs recorded for wild watermelon. All of these mechanisms have been attributed to the tolerance mechanisms of the drought-tolerant watermelon genotype. This study provides important insight into the stomatal responses of probable tolerant watermelon accessions and suggests that improving the stomatal aperture of susceptible domesticated species would also improve their tolerance.

The Zymoseptoria tritici Avirulence Factor AvrStb6 Accumulates in Hyphae Close to Stomata and Triggers a Wheat Defense Response Hindering Fungal Penetration.

Zymoseptoria tritici, the causal agent of Septoria tritici blotch, is one of Europe's most damaging wheat pathogens, causing significant economic losses. Genetic resistance is a common strategy to control the disease, Stb6 being a resistance gene used for more than 100 years in Europe. This study investigates the molecular mechanisms underlying Stb6-mediated resistance. Utilizing confocal microscopy imaging, we determined that Z.tritici epiphytic hyphae mainly accumulate the corresponding avirulence factor AvrStb6 in close proximity to stomata. Consequently, the progression of AvrStb6-expressing avirulent strains is hampered during penetration. The fungal growth inhibition co-occurs with a transcriptional reprogramming in wheat characterized by an induction of immune responses, genes involved in stomatal regulation, and cell wall-related genes. Overall, we shed light on the gene-for-gene resistance mechanisms in the wheat-Z. tritici pathosystem at the cytological and transcriptomic level, and our results highlight that stomatal penetration is a critical process for pathogenicity and resistance. [Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.