Increase In Stomatal Conductance Research Articles

A seed-borne endophyte mediates plant drought responses and intergenerational effects on seed characteristics

Global warming is expected to increase drought severity in diverse environments, impacting plant performance. Plants acclimate to drought by mechanisms like stomatal closure and osmotic adjustment. Maternally inherited symbiotic microorganisms with capacity to regulate these mechanisms have the potential to influence intergenerational plant drought responses. We studied how a seedborne endophyte affects maternal drought effects on seed germination water requirements and specialized metabolites. Isotopic analysis of seed cellulose indicated that drought led to improved water use efficiency (WUE; higher δ13C) in endophyte-free mother plants, seemingly without affecting stomatal conductance (non-significant δ18O change). Alternatively, endophyte-symbiotic plants did not exhibit a change in WUE but apparently an increase in stomatal conductance (significant δ18O decrease). Regardless of the symbiosis, drought reduced seed production but not seed size. Endophyte symbiosis improved the seed concentration of mannitol and sorbitol, but this increment was higher under drought. Maternal plant responses to drought did not increase seed germination under reduced water potential but induced dormancy in seeds from endophyte-free but not endophyte-symbiotic plants. Our findings suggest that although differential accumulation of metabolites in seeds results from how endophyte-symbiotic plants perceive and respond to drought, this response may not form part of a mechanism that would enhance seed performance of progeny under drought.

Influence of N-Acetylglucosamine and Melatonin Interaction in Modeling the Photosynthetic Component and Metabolomics of Cucumber under Salinity Stress.

The application of N-acetylglucosamine (GlcNAc) and melatonin (Mel) in agriculture could be a promising avenue for improving crop resilience and productivity, especially under challenging environmental conditions. In the current study, we treated the cucumber plant with GlcNAc and Mel solely and combinedly under salt stress (150 mM) then studied photosynthetic attributes using the transient OJIP fluorescence method. The results showed that the combination of GlcNAc × Mel significantly improved the plant morphological attributes, such as root and shoot biomass, and also improved chlorophyll and photosynthetic components. The mineral elements such as K, Mg, Ca, and P were significantly elevated, whereas a lower influx of Na was observed in GlcNAc × Mel treated cucumber shoots. A significant reduction in abscisic acid was observed, which was validated by the reduction in proline content and the increase in stomatal conductance (Gs), transpiration rate (E), and substomatal CO2 concentration (Ci). Furthermore, the activities of antioxidants such as polyphenol and flavonoid were considerably improved, resulting in a decrease in SOD and CAT with GlcNAc × Mel treatment. In addition, GlcNAc × Mel treatment dropped levels of the toxic radical Malondialdehyde (MDA) and elevated amino acids in cucumber shoots. These findings suggest that the combination of GlcNAc × Mel could be an effective elicitor for modeling plant metabolism to confer stress tolerance in crops.

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

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

Zn-quantum dot biochar regulates antioxidants and nutrient uptake to improve rapeseed growth and yield in drought stress

Drought stress is one of the major abiotic factors that cause a significant decline in the crop's productivity. It can disturb photosynthesis by inducing oxidative stress by producing reactive oxygen species. Recently, the use of quantum has gained the attention of scientists due to its potential positive impacts on plants under stress conditions. That's why a current study was conducted to explore the impact of Zn-quantum dot biochar (QDB) on rapeseed growth under drought stress. There were four levels of QDB, i.e., control (no QDB), 0.2 %, 0.4 %, and 0.8 %, applied on a w/w basis in soil under normal irrigation and drought stress. Results showed that 0.8 %QDB performed significantly better in improving seedling's emergence, plant height, number of branches/plants, number of pods/plants, pod length, seed weight/plant, 1000 seeds weight, and total biomass of rapeseed under normal irrigation and drought stress. At 0.2 %, 0.4 %, and 0.8 % QDB levels, the photosynthetic rate was 9.19 %, 11.78 %, and 13.46 % higher than the control under drought stress. Compared to the control, the transpiration rate increased by 61.40 % with 0.2 % QDB, 123.46 % with 0.4 % QDB, and 199.71 % with 0.8 % QDB. The percentage increase in stomatal conductance ranged from 44 % for 0.2 % QDB to 129 % for 0.8 % QDB under drought stress. In conclusion, 0.8 %QDB can potentially reduce drought stress and improve the leaf water contents and nutrient uptake in rapeseed.

Enhancing cabbage resilience against heavy metal stress through silicon amendments and melatonin: A depth investigation

This study investigated the phytotoxic toxic effects of heavy metals and evaluated the ameliorative effects of exogenously applied silicon (Si) in cabbage. Three experiments were conducted to assess the morphological, physiological, and biochemical changes associated with heavy metal toxicity and the potential mitigation by Si. The threshold level of cabbage plants was determined in the first experiment using nickel (Ni), cadmium (Cd), and arsenic (As) as selected heavy metals. Significant reductions in growth attributes, such as plant biomass, leaf area, and root weight, were observed at all heavy metal concentrations. Physiological parameters, including photosynthetic rate, transpiration rate and stomatal conductance were also significantly reduced due to heavy metal toxicity. In the second experiment, foliar application of Si at different concentrations mitigated the negative impacts of heavy metals on plant growth and physiological attributes. Maximum mitigation was observed at Si concentrations of 2 mM and 3 mM. The third experiment confirmed the efficacy of Si at 2 mM in reducing heavy metal toxicity and improving physiological attributes. Si application significantly decreased the uptake of Cd, Ni, and As in cabbage plants. Chlorophyll contents and antioxidant enzyme activities indicated the positive impact of Si on growth and development under heavy metal stress. Heavy metals exhibited toxic effects on cabbage plants, but exogenous application of Si, particularly at 2 mM, effectively mitigated these effects and enhanced plant growth. Si application at 3mM exhibited the maximum reduction in Cd toxicity, leading to a 79% increase in fresh biomass. When Ni and Cd-stressed plants were treated with silicon at 2mM, there was maximum reduction in toxicity, resulting in a 75% and 71% increase in the photosynthetic rate. Maximum mitigation of Cd toxicity was achieved by applying silicon at 2mM, resulting in a 94% increase in stomatal conductance. Furthermore, under a-biotic stress cabbage increased the concentration of melatonin that help the plant to cope from stress. These findings demonstrate the potential of Si application as a strategy to alleviate heavy metal toxicity and improve the growth of cabbage plants

Leaf relative water content at 50% stomatal conductance measured by noninvasive NMR is linked to climate of origin in nine species of eucalypt.

Stomata are the gatekeepers of plant water use and must quickly respond to changes in plant water status to ensure plant survival under fluctuating environmental conditions. The mechanism for their closure is highly sensitive to disturbances in leaf water status, which makes isolating their response to declining water content difficult to characterise and to compare responses among species. Using a small-scale non-destructive nuclear magnetic resonance spectrometer as a leaf water content sensor, we measure the stomatal response to rapid induction of water deficit in the leaves of nine species of eucalypt from contrasting climates. We found a strong linear correlation between relative water content at 50% stomatal conductance (RWCgs50 ) and mean annual temperature at the climate of origin of each species. We also show evidence for stomata to maintain control over water loss well below turgor loss point in species adapted to warmer climates and secondary increases in stomatal conductance despite declining water content. We propose that RWCgs50 is a promising trait to guide future investigations comparing stomatal responses to water deficit. It may provide a useful phenotyping trait to delineate tolerance and adaption to hot temperatures and high leaf-to-air vapour pressure deficits.

Quantifying the physiological, yield, and quality plasticity of Southern USA soybeans under heat stress

Climate change is causing an increase in air temperature during the reproductive and grain-filling stages, which is detrimental to soybean production and quality. Assessing the variability induced by heat stress in morpho-physiological, yield, and quality traits is an effective strategy for identifying heat-tolerant cultivars. In this study, ten soybean cultivars were exposed to temperatures 4.6 °C above the optimum (32 °C) from the R1 to R6 stages to investigate the heat stress-induced variability in morpho-physiological, yield, and quality traits. On average, stomatal conductance decreased by 11% under heat stress compared to the control. However, the cultivar R01–416F had the maximum increase in stomatal conductance (34%), and the least increase in canopy temperature ( + 2 °C) under the heat stress as compared to the control. Heat-stressed plants recorded a 3% reduction in chlorophyll content, with the cultivar DM45X61 experiencing the greatest decline of 22%. Across cultivars, specific leaf area decreased by 17% under heat stress, with G4620RX recording the highest reduction (28%). The results revealed a significant reduction in pod number (3.8%), pod weight (4%), seed number (4.2%), seed weight (5%), and hundred-seed weight (1.1%) per °C increase in temperature over the control. However, among the ten cultivars, R15–2422 and LS5009XS displayed relatively less reduction in seed number under heat stress. In comparison to the control, the cultivar R01–416F had the highest reduction in seed protein (4.4%) under heat stress, while it recorded a 16.6% increase in oil. Based on the phenotypic plasticity index, the cultivars R15–2422, and LS5009XS demonstrated the potential of maintaining higher yields under hot conditions. These findings highlight the significant impact of heat stress on soybean plasticity. The knowledge generated in this study helps in selecting and developing cultivars that can withstand heat stress, thus maintaining productivity and quality in warmer climates.

Altered cell wall hydroxycinnamate composition impacts leaf- and canopy-level CO2 uptake and water use in rice.

Cell wall properties play a major role in determining photosynthetic carbon uptake and water use through their impact on mesophyll conductance (CO2 diffusion from substomatal cavities into photosynthetic mesophyll cells) and leaf hydraulic conductance (water movement from xylem, through leaf tissue, to stomata). Consequently, modification of cell wall (CW) properties might help improve photosynthesis and crop water use efficiency (WUE). We tested this using 2 independent transgenic rice (Oryza sativa) lines overexpressing the rice OsAT10 gene (encoding a "BAHD" CoA acyltransferase), which alters CW hydroxycinnamic acid content (more para-coumaric acid and less ferulic acid). Plants were grown under high and low water levels, and traits related to leaf anatomy, CW composition, gas exchange, hydraulics, plant biomass, and canopy-level water use were measured. Alteration of hydroxycinnamic acid content led to statistically significant decreases in mesophyll CW thickness (-14%) and increased mesophyll conductance (+120%) and photosynthesis (+22%). However, concomitant increases in stomatal conductance negated the increased photosynthesis, resulting in no change in intrinsic WUE (ratio of photosynthesis to stomatal conductance). Leaf hydraulic conductance was also unchanged; however, transgenic plants showed small but statistically significant increases in aboveground biomass (AGB) (+12.5%) and canopy-level WUE (+8.8%; ratio of AGB to water used) and performed better under low water levels than wild-type plants. Our results demonstrate that changes in CW composition, specifically hydroxycinnamic acid content, can increase mesophyll conductance and photosynthesis in C3 cereal crops such as rice. However, attempts to improve photosynthetic WUE will need to enhance mesophyll conductance and photosynthesis while maintaining or decreasing stomatal conductance.

Warming reduces both photosynthetic nutrient use efficiency and water use efficiency in Mediterranean shrubsWarming reduces nutrient use efficiency

The ratio between net photosynthetic rates and the foliar contents of essential plant macronutrients (N, P, K) is termed photosynthetic nutrient use efficiency (PNutUE). A universal trade-off exists whereby plants cannot maximize their PNutUE and their intrinsic water use efficiency (WUEi, carbon gain per unit water spent) simultaneously, because any increase in intercellular CO2 concentration (ci) through a greater stomatal opening would increase PNutE but also enhances transpiration and therefore decreases WUEi. Rising temperatures associated with climate change can result in large decreases in WUEi in semiarid shrubs through photosynthetic machinery impairment and enhanced stomatal conductance and transpiration, but we know remarkably little about the influence of warming and drought on PNutUE and its interplay with WUEi in dryland vegetation. Using a 6-year (2011–2017) manipulative field experiment, we examined the effects of warming (2.5ºC, W), rainfall reduction (30%, RR), and their combination (W+RR) on the photosynthetic use efficiency of three essential nutrients (PNUE, PPUE and PKUE) and on WUEi in three shrub species growing at two semiarid shrublands for the years 2015–2017. Across species, warming (W and W+RR) reduced PNUE by 42.9%, PPUE by 43.8% and PKUE by 41.5% on average relative to shrubs growing under ambient temperatures, whereas RR did not significantly affect their PNutUE. These drastic reductions in PNutUE with warming were mainly driven by non-stomatal and largely non-nutritional decreases in net photosynthetic rates, which were almost halved in warmed shrubs. The photosynthetic use efficiencies of N, P and K were inversely related to foliar δ13C, a proxy for time integrated WUEi, in both ambient (control and RR) and warmed (W and W+RR) shrubs, but with significantly smaller slopes and intercepts for warmed shrubs. Thus, plants achieve a smaller gain in PNutUE for any given increase in stomatal conductance (and reduction in WUEi) under warmer climatic conditions. The strong negative impact of warming on PNutE, along with the warming-induced shift in the trade-off between PNutUE and WUEi, could be indicative of an increasing inability of native plants to cope with warmer conditions, with dire implications for dryland vegetation productivity and survival under climate change.

Physiological Comparison of Wheat and Maize Seedlings Responses to Water Stresses

The aim of the study was to investigate specific responses of spring wheat (C3 photosynthesis) and maize (C4 photosynthesis) to drought and flooding stress. Analyses of water content, gas exchange intensity, photosynthetic apparatus activity, chlorophyll content, plant height and biological membrane integrity were performed on the 10th day of drought and flooding in both species at the third leaf stage. A specific response of wheat under both drought and flooding conditions involved an increase in ETo/RC ratio, describing electron transport flux converted into a single reaction center in PSII. Correlations between electrolyte leakage and the probability of electron transport beyond the plastoquinone QA, and the amount of energy used for the electron transport were also found. A specific response of maize during flooding was the increase of stomatal conductance. Additionally, a significant correlation between PN/Ci and relative water content was exhibited. Furthermore, the parameters differentiating the studied species only under stressful conditions were rendered. The application of such parameters can be widely used, e.g., for studying the reaction of a potential cultivars to drought and flooding. Providing such information to potential farmers can help better select cultivars for their environmental conditions.

Morphophysiological responses of table beet irrigated with saline water under application of humic substances

The use of saline water is an alternative for irrigating agricultural crops, especially in the Brazilian Northeastern semi-arid region, where water quality is limited in most cases. Thus, the objective was to evaluate the morphophysiological responses of table beet cv. “Wonder” irrigated with saline waters under the application of humic substances. The experiment was conducted under a randomized block design, with six replications in a 6 x 4 x 5 factorial scheme, referring to six electrical conductivities of irrigation water (ECw): 0.5; 1.5; 2.5; 3.5; 4.5 and 5.5 dS m-¹, four humic substances rates (HS) (0; 10; 20 and 30 ml per plant), and five stages of assessment (23, 38, 53, 68 and 83 days after emergency). The characteristics evaluated were: plant height, number of leaves, leaf area, chlorophyll content (a, b and total), stomatal conductance, transpiration, net photosynthesis and CO2 internal concentration, and in the soil, the soil pH and the electrical conductivity of saturated paste extract. The increase of salinity reduced growth, chlorophyll a content, and the stomatal conductance of beet plants. The application rate of 30 ml per plant of humic substances promotes an increase in stomatal conductance. The application of humic substances raises the pH in sandy acidic soils. It is recommended to irrigate table beet plants with water of 0.5 dS m-1 associated with the application of 30 mL per plant of humic substances

Yield, Physiological Performance, and Phytochemistry of Basil (Ocimum basilicum L.) under Temperature Stress and Elevated CO2 Concentrations.

Early season sowing is one of the methods for avoiding yield loss for basil due to high temperatures. However, basil could be exposed to sub-optimal temperatures by planting it earlier in the season. Thus, an experiment was conducted that examines how temperature changes and carbon dioxide (CO2) levels affect basil growth, development, and phytonutrient concentrations in a controlled environment. The experiment simulated temperature stress, low (20/12 °C), and high (38/30 °C), under ambient (420 ppm) and elevated (720 ppm) CO2 concentrations. Low-temperature stress prompted the rapid closure of stomata resulting in a 21% decline in net photosynthesis. Chlorophylls and carotenoids decreased when elevated CO2 interacted with low-temperature stress. Basil exhibited an increase in stomatal conductance, intercellular CO2 concentration, apparent quantum yield, maximum photosystem II efficiency, and maximum net photosynthesis rate when subjected to high-temperature stress. Under elevated CO2, increasing the growth temperature from 30/22 °C to 38/30 °C markedly increased the antioxidants content of basil. Taken together, the evidence from this research recommends that varying the growth temperature of basil plants can significantly affect the growth and development rates compared to increasing the CO2 concentrations, which mitigates the adverse effects of temperature stress.

Stomatal Behaviors and Physiological Responses Affected by Iron Deficiency in Peach Plants Grafted onto Garnem and GF 677

Iron (Fe) is a pivotal nutrient taking roles in respiration, photosynthesis and many plant metabolisms. Chlorosis caused by Fe deficiency generally occurs in high pH environments and many fruit trees including peach are known sensitive to iron starvation. Fe starvation declines leaf chlorophyll and carotenoid contents, supresses plant growth and declines photosynthetic capacity. Iron deficiency induces responses in plants and different stomatal behaviors and physiological alterations occur to sustain the increased iron uptake capacity of Fe-deficient plants. In this study, the effects of iron deficiency on stomatal morphology and leaf physiological responses in peach variety Rich May grafted onto Garnem and GF 677 rootstocks were investigated. Plants were exposed to Fe deficient conditions for 3 months. End of the experiment, many leaf and stomatal properties were evaluated. The highest decrease in plant growth (relative growth rates of shoot diameter and length) induced by Fe deficiency was found in Rich May grafted onto Garnem. SPAD and relative anthocyanin decreased by 52 and 70% in Fe deficient Rich May/Garnem grafting combination. Decreases in SPAD and relative anthocyanin values were lower with GF 677. In GF 677, LRWC decreased by 1.8% and membrane permeability increased by 10%. Fe controlled stomatal behaviors in peach plants. Stomatal factors were found more sensitive to Fe deficiency in sensitive rootstock, Garnem. The increment in stomatal and pore areas leaded increase in stomatal conductance. The damage by Fe depletion was found higher in Garnem due to higher loss in SPAD, anthocyanin and increasing membrane permeability. Thus, GF 677 can be used in peach orchards under Fe deficiency conditions.

Site-level soil moisture controls water-use efficiency improvement and climate response in sugar maple: a dual dendroisotopic study

Given the large contribution of forests to terrestrial carbon storage, there is a need to resolve the environmental and physiological drivers of tree-level response to rising atmospheric CO2. This study examines how site-level soil moisture influences growth and intrinsic water-use efficiency in sugar maple (Acer saccharum Marsh.). We construct tree-ring, δ18O, and Δ13C chronologies for trees across a soil moisture gradient in Ontario, Canada, and employ a structural equation modelling approach to ascertain their climatic, ontogenetic, and environmental drivers. Our results support previous evidence for the presence of strong developmental effects in tree-ring isotopic chronologies — in the range of −4.7‰ for Δ13C and +0.8‰ for δ18O — across the tree life span. Additionally, we show that the physiological response of sugar maple to increasing atmospheric CO2 depends on site-level soil moisture variability, with trees only in relatively wet plots exhibiting temporal increases in intrinsic water-use efficiency. These results suggest that trees in wet and mesic plots have experienced temporal increases in stomatal conductance and photosynthetic capacity, whereas trees in dry plots have experienced decreases in photosynthetic capacity. This study is the first to examine sugar maple physiology using a dendroisotopic approach and broadens our understanding of carbon–water interactions in temperate forests.

Cell damage, gas exchange, and growth of Annona squamosa L. under saline water irrigation and potassium fertilization

The semi-arid region of Northeastern Brazil has water limitations in terms of both quantity and quality, with salt stress as a limiting factor for increasing yield in most crops. In this context, the present study aimed to evaluate cell damage, gas exchange, and growth of custard apple under salt stress and potassium fertilization. The research was carried out at the Experimental Farm of CCTA/UFCG, in São Domingos-PB, Brazil. A randomized block design was arranged in a 2 × 5 factorial scheme, with two levels of electrical conductivity of irrigation water (ECw; 1.3 and 4.0 dS m-1) and five potassium doses (10, 15, 20, 25, and 30 g of K2O per plant per year). Water salinity of 4.0 dS m-1 negatively affected the stem diameter and number of leaves in custard apple at 179 and 210 days after transplanting (DAT). The highest relative growth in stem diameter in the period of 179-245 DAT was obtained in plants irrigated with 4.0 dS m-1 water and fertilized with 20 g of K2O per plant. Potassium doses of up to 30 g of K2O resulted in a higher percentage of cell damage and relative water content in custard apple leaf tissue. Water saturation deficit decreased with the increase in K2O doses in plants irrigated with water of 1.3 dS m-1. Irrigation with 1.3 dS m-1 water and estimated K2O doses ranging from 16 to 22 g per plant resulted in an increase in stomatal conductance, transpiration, CO2 assimilation rate, and instantaneous carboxylation efficiency in custard apple plants at 210 DAT.

Rice cultivars responses to different salinity levels at coastal agricultural land of Yogyakarta

At present, the coastal sandy soil in special region of Yogyakarta has developed to be a potential agricultural field. Salinity has become one main obstacle in this specific field. The research aimed to examine the growth and yield responses of three rice cultivars in several salinity levels in this coastal sandy soil. The research was carried out in Srigading and Baros Villages, Bantul District of Yogyakarta Special Region, Indonesia. A split plot design was applied, with salinity levels (0.1; 1.0 and 2.5) dS.m−1 as main plot and rice varieties (IR 64, Situbagendit and Dendang) as sub plot. The treatments were replicated three times. The results showed that there was hardly significant difference in most of the growth and yield variables in IR 64 and Situbagendit. However, at 2.5 dS.m−1 Dendang (the salt resistant rice) performed the highest chlorophyll content. With salinity up to 2.5 dS.m−1, there was an increase in stomatal conductance, shoot dry biomass and grain yield. Overall, adding salinity up to 2.5 dS. m−1 in coastal sandy soil promoted better growth and yield of rice. However, with higher salinity levels, grain yields decreased. The decrease in grain yield was larger in salt resistant variety, than in salt sensitive varieties.

Alien introgression and morpho-agronomic characterization of diploid progenies of Solanum lycopersicoides monosomic alien addition lines (MAALs) toward pre-breeding applications in tomato (S. lycopersicum)

Key messageAlien introgressions that were captured in the genome of diploid plants segregating from progenies of monosomic alien addition lines of S. lycopersicoides confer novel phenotypes with commercial and agronomic value in tomato breeding.Solanum lycopersicoides is a wild relative of tomato with a natural adaptation to a wide array of biotic and abiotic challenges. In this study, we identified and characterized diploid plants segregating from the progenies of monosomic alien addition lines (MAALs) of S. lycopersicoides to establish their potential as donors in breeding for target trait improvement in tomato. Molecular genotyping identified 28 of 38 MAAL progenies having the complete chromosome complement of the cultivated tomato parent and limited chromosome introgressions from the wild S. lycopersicoides parent. Analysis of SSR and indel marker profiles identified 34 unique alien introgressions in the 28 MAAL-derived introgression lines (MDILs) in the genetic background of tomato. Conserved patterns of alien introgressions were detected among sibs of MDILs 2, 3, 4 and 8. Across MDILs, a degree of preferential transmission of specific chromosome segments was also observed. Morphologically, the MDILs closely resembled the cultivated tomato more than S. lycopersicoides. The appearance of novel phenotypes in the MDILs that are lacking in the cultivated parent or the source MAALs indicates the capture of novel genetic variation by the diploid introgression lines that can add commercial and agronomic value to tomato. In particular, screening of representative MDILs for drought tolerance at the vegetative stage identified MDIL 2 and MDIL 11III as drought tolerant based on visual scoring. A regulated increase in stomatal conductance of MDIL 2 under drought stress indicates better water use efficiency that allowed it to survive for 7 days under 0% moisture level.

Duration of Weed Presence Influences the Recovery of Photosynthetic Efficiency and Yield in Common Bean (Phaseolus vulgaris L.)

Photosynthetic responses of common bean (Phaseolus vulgaris L.) to increasing durations of weed-free and weedy environments were investigated using a critical period for weed control study under field conditions. The presence of weeds induced the shade avoidance response and was accompanied by a reduced red to far-red ratio (R/Fr) of reflected light supporting previous assertions it is an important signal regulating crop-weed interactions. Despite increases in stomatal conductance and leaf intercellular [CO2] with increasing duration of weed presence, CO2 assimilation and photosynthetic efficiency continually declined. This coincided with reduced Calvin cycle capacity suggesting induction of biochemical rather than stomatal limitations on photosynthesis. Weed removal prior to reproductive stages resulted in maintenance of high photosynthetic capacity. When weed presence extended to reproductive stages and beyond the critical period for weed control, however, CO2 assimilation and photosynthetic efficiency never recovered. Yield was highly correlated with photosynthetic efficiency and in a similar manner, declined with increasing durations of weed presence through reduced seeds per plant. We conclude that the lasting consequence of weed competition is impairment of photosynthesis, which may provide an important mechanism to explain yield loss.

Ascophyllum nodosum extract improves leaf thermoregulation by reducing stomatal sensitivity to VPD in Vitis vinifera L.

Climate change scenarios and the need of sustainable tools to reduce global warming impact on agriculture have led to the formulation of a large number of natural products or biostimulants that should increase plant resilience to abiotic stress. Ascophyllum nodosum (AN) extract is one of the most studied biostimulants to increase tolerance to drought stress, but the physiological mechanism underlying its action is still poorly understood. The aim of the present work was to determine AN extract impact on grapevine gas exchange under well-watered and water stress conditions and to examine its mode of action under stress (light and temperature). AN caused a slight increase in stomatal conductance that resulted in an increase of water plant conductivity to atmosphere. Increased transpiration induced by AN improved leaf thermoregulation, facilitating vine recovery after a stress period. AN increased transpiration through a reduction of stomatal sensitivity to VPD. AN action on stomata regulation indicated that this biostimulant could be a new potential tool to limit leaf damage during events of extreme temperature, even when they are not combined with water stress conditions.

Natural Diversity in Stomatal Features of Cultivated and Wild Oryza Species

BackgroundStomata in rice control a number of physiological processes by regulating gas and water exchange between the atmosphere and plant tissues. The impact of the structural diversity of these micropores on its conductance level is an important area to explore before introducing stomatal traits into any breeding program in order to increase photosynthesis and crop yield. Therefore, an intensive measurement of structural components of stomatal complex (SC) of twenty three Oryza species spanning the primary, secondary and tertiary gene pools of rice has been conducted.ResultsExtensive diversity was found in stomatal number and size in different Oryza species and Oryza complexes. Interestingly, the dynamics of stomatal traits in Oryza family varies differently within different Oryza genetic complexes. Example, the Sativa complex exhibits the greatest diversity in stomatal number, while the Officinalis complex is more diverse for its stomatal size. Combining the structural information with the Oryza phylogeny revealed that speciation has tended towards increasing stomatal density rather than stomatal size in rice family. Thus, the most recent species (i.e. the domesticated rice) eventually has developed smaller yet numerous stomata. Along with this, speciation has also resulted in a steady increase in stomatal conductance (anatomical, gmax) in different Oryza species. These two results unambiguously prove that increasing stomatal number (which results in stomatal size reduction) has increased the stomatal conductance in rice. Correlations of structural traits with the anatomical conductance, leaf carbon isotope discrimination (∆13C) and major leaf morphological and anatomical traits provide strong supports to untangle the ever mysterious dependencies of these traits in rice. The result displayed an expected negative correlation in the number and size of stomata; and positive correlations among the stomatal length, width and area with guard cell length, width on both abaxial and adaxial leaf surfaces. In addition, gmax is found to be positively correlated with stomatal number and guard cell length. The ∆13C values of rice species showed a positive correlation with stomatal number, which suggest an increased water loss with increased stomatal number. Interestingly, in contrast, the ∆13C consistently shows a negative relationship with stomatal and guard cell size, which suggests that the water loss is less when the stomata are larger. Therefore, we hypothesize that increasing stomatal size, instead of numbers, is a better approach for breeding programs in order to minimize the water loss through stomata in rice.ConclusionCurrent paper generates useful data on stomatal profile of wild rice that is hitherto unknown for the rice science community. It has been proved here that the speciation has resulted in an increased stomatal number accompanied by size reduction during Oryza’s evolutionary course; this has resulted in an increased gmax but reduced water use efficiency. Although may not be the sole driver of water use efficiency in rice, our data suggests that stomata are a potential target for modifying the currently low water use efficiency in domesticated rice. It is proposed that Oryza barthii can be used in traditional breeding programs in enhancing the stomatal size of elite rice cultivars.