The Experts below are selected from a list of 321 Experts worldwide ranked by ideXlab platform
François Tardieu - One of the best experts on this subject based on the ideXlab platform.
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Genetic control of stomatal conductance in maize and conditional effects to water deficit and Evaporative Demand as revealed by phenomics
2018Co-Authors: Santiago Alvarez Prado, Llorenç Cabrera Bosquet, Antonin Grau, Aude Coupel-ledru, Emilie Millet, François TardieuAbstract:Plants tend to decrease transpiration under water deficit and/or high Evaporative Demand by closing stomata. Stomatal conductance is central for the trades‐off between hydraulics and photosynthesis. We aimed at deciphering its genetic control and that of its responses to Evaporative Demand and water deficit, a nearly impossible task with gas exchanges measurements. Whole‐plant stomatal conductance was estimated via inversion of the Penman–Monteith equation from data of transpiration and plant architecture collected in a phenotyping platform. We have analyzed jointly 4 experiments with contrasting environmental conditions imposed to a panel of 254 maize hybrids. Estimated whole‐plant stomatal conductance closely correlated with gas‐exchange measurements and biomass accumulation rate. Sixteen robust quantitative trait loci (QTLs) were identified by genome wide association studies and co‐located with QTLs of transpiration and biomass. They accounted for 58% of the additive genetic variance and 40% of the genotype × environment interaction. Light, vapour pressure deficit (VPD), or soil water potential largely accounted for the differences in allelic effects between experiments, thereby providing strong hypotheses for mechanisms of stomatal control and explaining part of the observed genotype × environment interaction. Light positively affected the allelic effects of three QTLs (e.g. R2 = 0.74), whereas VPD and water deficit negatively affected the allelic effects of other four QTLs. The combination of SNP effects, as affected by environmental conditions, accounted for the variability of stomatal conductance across a range of hybrids and environmental conditions (R2 = 0.86). This approach may therefore contribute prediction of stomatal control in diverse environments and to breeding for water efficient maize.
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Phenomics allows identification of genomic regions affecting maize stomatal conductance with conditional effects of water deficit and Evaporative Demand
Plant cell & environment, 2017Co-Authors: Santiago Alvarez Prado, Emilie J. Millet, Claude Welcker, Llorenç Cabrera Bosquet, Antonin Grau, Aude Coupel-ledru, François TardieuAbstract:Stomatal conductance is central for the trades-off between hydraulics and photosynthesis. We aimed at deciphering its genetic control and that of its responses to Evaporative Demand and water deficit, a nearly impossible task with gas exchanges measurements. Whole-plant stomatal conductance was estimated via inversion of the Penman Monteith equation from data of transpiration and plant architecture collected in a phenotyping platform. We have analyzed jointly four experiments with contrasting environmental conditions imposed to a panel of 254 maize hybrids. Estimated whole-plant stomatal conductance closely correlated with gas-exchange measurements and biomass accumulation rate. Sixteen robust quantitative trait loci (QTLs) were identified by genome wide association studies (GWAS), and co-located with QTLs of transpiration and biomass. Light, vapour pressure deficit or soil water potential largely accounted for the differences in allelic effects between experiments, thereby providing strong hypotheses for mechanisms of stomatal control and a way to select relevant candidate genes among the 1-19 genes harboured by QTLs. The combination of allelic effects as affected by environmental conditions accounted for the variability of stomatal conductance across a range of hybrids and environmental conditions. This approach may therefore contribute to genetic analysis and prediction of stomatal control in diverse environments.
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Distinct controls of leaf widening and elongation by light and Evaporative Demand in maize.
Plant cell & environment, 2017Co-Authors: Sébastien Lacube, Christian Fournier, Carine Palaffre, Emilie J. Millet, François Tardieu, Boris ParentAbstract:Leaf expansion depends on both carbon and water availabilities. In cereals, most of experimental effort has focused on leaf elongation, with essentially hydraulic effects. We have tested if Evaporative Demand and light could have distinct effects on leaf elongation and widening, and if short term effects could translate into final leaf dimensions. For that, we have monitored leaf widening and elongation in a field experiment with temporary shading, and in a platform experiment with 15-min temporal resolution and contrasting Evaporative Demands. Leaf widening showed a strong (positive) sensitivity to whole-plant intercepted light and no response to Evaporative Demand. Leaf elongation was (negatively) sensitive to Evaporative Demand, without effect of intercepted light per se. We have successfully tested resulting equations to predict leaf length and width in an external dataset of 15 field and 6 platform experiments. These effects also applied to a panel of 251 maize hybrids. Leaf length and width presented quantitative trait loci (QTLs) whose allelic effects largely differed between both dimensions but were consistent in the field and the platform, with high QTLxEnvironment interaction. It is therefore worthwhile to identify the genetic and environmental controls of leaf width and leaf length for prediction of plant leaf area.
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Genetic variability of plant responses to Evaporative Demand and water deficit, a forward integration from phenotyping to simulation of plant performances in the field
2017Co-Authors: Boris Parent, Sébastien Lacube, Claude Welcker, Santiago Alvarez Prado, Llorenç Cabrera Bosquet, Aude Coupel-ledru, Emilie Millet, Adel Meziane, François TardieuAbstract:Crop improvement for drought is based on the selection of alleles that increase yield in dry or hot conditions. The Genotype by Environment Interactions (GxE) is typically high in these environments, with alleles conferring either positive or negative effects, depending on drought scenarios (Tardieu, 2012). Rather than trying to over-simplify GxE, for instance, in managed drought experiments, we propose an integrative approach using genome wide association studies (GWAS), phenotyping and modelling. It aims at predicting in which drought scenarios a combination of trait/allele could confer advantages (Parent and Tardieu, 2015). Indeed, (i) we phenotype the intra- and inter- specific variability of development and growth responses to temperature, Evaporative Demand and water deficit with phenotyping platforms. (ii) We develop ecophysiological models with parameters which can be directly extracted from measurements in platforms and in the field. (iii) We carry out GWAS at different scales, from -omic to plant scale in platform, and to yield components in network of field experiments to identify QTLs linked to conditional allelic effects depending on environmental conditions, and to values of model parameters. (iv) We use either direct measurements or the allelic compositions at target QTLs to determine the phenotypic profiles (set of parameter values) of real or virtual genotypes. (v) We simulate genotypic performance and the contribution of genomic regions under current and future stress situations over Europe via modelling. Results are compared to the observed genetic variability in networks of field experiments and are used as feedbacks for improving our phenotyping routines and ecophysiological models.
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The growth of vegetative and reproductive structures (leaves and silks) respond similarly to hydraulic cues in maize
New Phytologist, 2016Co-Authors: Olivier Turc, Claude Welcker, Marie Bouteillé, Avan Fuad-hassan, François TardieuAbstract:The elongation of styles and stigma (silks) of maize (Zea mays) flowers is rapid (1–3 mm h−1), occurs over a short period and plays a pivotal role in reproductive success in adverse environments. Silk elongation rate was measured using displacement transducers in 350 plants of eight genotypes during eight experiments with varying Evaporative Demand and soil water status. Measured time courses revealed that silk elongation rate closely followed changes in soil water status and Evaporative Demand, with day–night alternations similar to those in leaves. Day–night alternations were steeper with high than with low plant transpiration rate, manipulated via Evaporative Demand or by covering part of the leaf area. Half times of changes in silk elongation rate upon changes in Evaporative Demand or soil water status were 10–30 min, similar to those in leaves. The sensitivity of silk elongation rate to xylem water potential was genetically linked to that of leaf elongation rate. Lines greatly differed for these sensitivities. These results are consistent with a common hydraulic control of expansive growth in vegetative and reproductive structures upon changes in environmental conditions via a close connection with the xylem water potential. They have important implications for breeding, modelling and phenotyping.
Boris Parent - One of the best experts on this subject based on the ideXlab platform.
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Distinct controls of leaf widening and elongation by light and Evaporative Demand in maize.
Plant cell & environment, 2017Co-Authors: Sébastien Lacube, Christian Fournier, Carine Palaffre, Emilie J. Millet, François Tardieu, Boris ParentAbstract:Leaf expansion depends on both carbon and water availabilities. In cereals, most of experimental effort has focused on leaf elongation, with essentially hydraulic effects. We have tested if Evaporative Demand and light could have distinct effects on leaf elongation and widening, and if short term effects could translate into final leaf dimensions. For that, we have monitored leaf widening and elongation in a field experiment with temporary shading, and in a platform experiment with 15-min temporal resolution and contrasting Evaporative Demands. Leaf widening showed a strong (positive) sensitivity to whole-plant intercepted light and no response to Evaporative Demand. Leaf elongation was (negatively) sensitive to Evaporative Demand, without effect of intercepted light per se. We have successfully tested resulting equations to predict leaf length and width in an external dataset of 15 field and 6 platform experiments. These effects also applied to a panel of 251 maize hybrids. Leaf length and width presented quantitative trait loci (QTLs) whose allelic effects largely differed between both dimensions but were consistent in the field and the platform, with high QTLxEnvironment interaction. It is therefore worthwhile to identify the genetic and environmental controls of leaf width and leaf length for prediction of plant leaf area.
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Genetic variability of plant responses to Evaporative Demand and water deficit, a forward integration from phenotyping to simulation of plant performances in the field
2017Co-Authors: Boris Parent, Sébastien Lacube, Claude Welcker, Santiago Alvarez Prado, Llorenç Cabrera Bosquet, Aude Coupel-ledru, Emilie Millet, Adel Meziane, François TardieuAbstract:Crop improvement for drought is based on the selection of alleles that increase yield in dry or hot conditions. The Genotype by Environment Interactions (GxE) is typically high in these environments, with alleles conferring either positive or negative effects, depending on drought scenarios (Tardieu, 2012). Rather than trying to over-simplify GxE, for instance, in managed drought experiments, we propose an integrative approach using genome wide association studies (GWAS), phenotyping and modelling. It aims at predicting in which drought scenarios a combination of trait/allele could confer advantages (Parent and Tardieu, 2015). Indeed, (i) we phenotype the intra- and inter- specific variability of development and growth responses to temperature, Evaporative Demand and water deficit with phenotyping platforms. (ii) We develop ecophysiological models with parameters which can be directly extracted from measurements in platforms and in the field. (iii) We carry out GWAS at different scales, from -omic to plant scale in platform, and to yield components in network of field experiments to identify QTLs linked to conditional allelic effects depending on environmental conditions, and to values of model parameters. (iv) We use either direct measurements or the allelic compositions at target QTLs to determine the phenotypic profiles (set of parameter values) of real or virtual genotypes. (v) We simulate genotypic performance and the contribution of genomic regions under current and future stress situations over Europe via modelling. Results are compared to the observed genetic variability in networks of field experiments and are used as feedbacks for improving our phenotyping routines and ecophysiological models.
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A hydraulic model is compatible with rapid changes in leaf elongation under fluctuating Evaporative Demand and soil water status.
Plant physiology, 2014Co-Authors: Cecílio Frois Caldeira, Boris Parent, Mickael Bosio, Linda Jeanguenin, François Chaumont, François TardieuAbstract:Plants are constantly facing rapid changes in Evaporative Demand and soil water content, which affect their water status and growth. In apparent contradiction with a hydraulic hypothesis, leaf elongation rate (LER) declined in the morning and recovered upon soil rehydration considerably quicker than transpiration rate and leaf water potential (typical half times, 30 min vs 1-2 h). The morning decline of LER began at very low light and transpiration, and closely followed the stomatal opening of leaves receiving direct light which represent a small fraction of leaf area. A simulation model suggests that these findings are still compatible with a hydraulic hypothesis. The small water flux linked to stomatal aperture would be sufficient to decrease water potentials of the xylem and growing tissues, thereby causing a rapid decline of simulated LER, while the simulated water potential of mature tissues declines more slowly due to a high hydraulic capacitance. The model also captured growth patterns in the evening or upon soil rehydration. Changes in plant hydraulic conductance partly counteracted those of transpiration. Root hydraulic conductivity increased continuously in the morning, consistent with the transcript abundance of ZmPIPs aquaporins. Transgenic lines under-producing ABA, with lower hydraulic conductivity and higher stomatal conductance, had a LER declining more rapidly than that of WT plants. Whole genome transcriptome and phosphoproteome suggested that the hydraulic processes proposed here might be associated with other rapidly occurring mechanisms. Overall, mechanisms and models presented here may be an essential component of drought tolerance in naturally fluctuating Evaporative Demand and soil moisture.
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A hydraulic model is compatible with rapid changes in leaf elongation under fluctuating Evaporative Demand and soil water status
Plant Physiology, 2014Co-Authors: Cecilio Frois Caldeira Junior, Boris Parent, Mickael Bosio, Linda Jeanguenin, François Chaumont, François TardieuAbstract:Plants are constantly facing rapid changes in Evaporative Demand and soil water content, which affect their water status and growth. In apparent contradiction to a hydraulic hypothesis, leaf elongation rate (LER) declined in the morning and recovered upon soil rehydration considerably quicker than transpiration rate and leaf water potential (typical half-times of 30 min versus 1–2 h). The morning decline of LER began at very low light and transpiration and closely followed the stomatal opening of leaves receiving direct light, which represent a small fraction of leaf area. A simulation model in maize (Zea mays) suggests that these findings are still compatible with a hydraulic hypothesis. The small water flux linked to stomatal aperture would be sufficient to decrease water potentials of the xylem and growing tissues, thereby causing a rapid decline of simulated LER, while the simulated water potential of mature tissues declines more slowly due to a high hydraulic capacitance. The model also captured growth patterns in the evening or upon soil rehydration. Changes in plant hydraulic conductance partly counteracted those of transpiration. Root hydraulic conductivity increased continuously in the morning, consistent with the transcript abundance of Zea maize Plasma Membrane Intrinsic Protein aquaporins. Transgenic lines underproducing abscisic acid, with lower hydraulic conductivity and higher stomatal conductance, had a LER declining more rapidly than wild-type plants. Whole-genome transcriptome and phosphoproteome analyses suggested that the hydraulic processes proposed here might be associated with other rapidly occurring mechanisms. Overall, the mechanisms and model presented here may be an essential component of drought tolerance in naturally fluctuating Evaporative Demand and soil moisture.
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Rice leaf growth and water potential are resilient to Evaporative Demand and soil water deficit once the effects of root system are neutralized
Plant cell & environment, 2010Co-Authors: Boris Parent, Benoit Suard, Rachid Serraj, François TardieuAbstract:Rice is known to be sensitive to soil water deficit and Evaporative Demand, with a greatest sensitivity of lowland-adapted genotypes. We have analysed the responses of plant water relations and of leaf elongation rate (LER) to soil water status and Evaporative Demand in seven rice genotypes belonging to different species, subspecies, either upland- or lowland-adapted. In the considered range of soil water potential (0 to -0.6 MPa), stomatal conductance was controlled in such a way that the daytime leaf water potential was similar in well-watered, droughted or flooded conditions (isohydric behaviour). A low sensitivity of LER to Evaporative Demand was observed in the same three conditions, with small differences between genotypes and lower sensitivity than in maize. The sensitivity of LER to soil water deficit was similar to that of maize. A tendency towards lower sensitivities was observed in upland than lowland genotypes but with smaller differences than expected. We conclude that leaf water status and leaf elongation of rice are not particularly sensitive to water deficit. The main origin of drought sensitivity in rice may be its poor root system, whose effect was alleviated in the study presented here by growing plants in pots whose soil was entirely colonized by roots of all genotypes.
Claude Welcker - One of the best experts on this subject based on the ideXlab platform.
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Phenomics allows identification of genomic regions affecting maize stomatal conductance with conditional effects of water deficit and Evaporative Demand
Plant cell & environment, 2017Co-Authors: Santiago Alvarez Prado, Emilie J. Millet, Claude Welcker, Llorenç Cabrera Bosquet, Antonin Grau, Aude Coupel-ledru, François TardieuAbstract:Stomatal conductance is central for the trades-off between hydraulics and photosynthesis. We aimed at deciphering its genetic control and that of its responses to Evaporative Demand and water deficit, a nearly impossible task with gas exchanges measurements. Whole-plant stomatal conductance was estimated via inversion of the Penman Monteith equation from data of transpiration and plant architecture collected in a phenotyping platform. We have analyzed jointly four experiments with contrasting environmental conditions imposed to a panel of 254 maize hybrids. Estimated whole-plant stomatal conductance closely correlated with gas-exchange measurements and biomass accumulation rate. Sixteen robust quantitative trait loci (QTLs) were identified by genome wide association studies (GWAS), and co-located with QTLs of transpiration and biomass. Light, vapour pressure deficit or soil water potential largely accounted for the differences in allelic effects between experiments, thereby providing strong hypotheses for mechanisms of stomatal control and a way to select relevant candidate genes among the 1-19 genes harboured by QTLs. The combination of allelic effects as affected by environmental conditions accounted for the variability of stomatal conductance across a range of hybrids and environmental conditions. This approach may therefore contribute to genetic analysis and prediction of stomatal control in diverse environments.
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Genetic variability of plant responses to Evaporative Demand and water deficit, a forward integration from phenotyping to simulation of plant performances in the field
2017Co-Authors: Boris Parent, Sébastien Lacube, Claude Welcker, Santiago Alvarez Prado, Llorenç Cabrera Bosquet, Aude Coupel-ledru, Emilie Millet, Adel Meziane, François TardieuAbstract:Crop improvement for drought is based on the selection of alleles that increase yield in dry or hot conditions. The Genotype by Environment Interactions (GxE) is typically high in these environments, with alleles conferring either positive or negative effects, depending on drought scenarios (Tardieu, 2012). Rather than trying to over-simplify GxE, for instance, in managed drought experiments, we propose an integrative approach using genome wide association studies (GWAS), phenotyping and modelling. It aims at predicting in which drought scenarios a combination of trait/allele could confer advantages (Parent and Tardieu, 2015). Indeed, (i) we phenotype the intra- and inter- specific variability of development and growth responses to temperature, Evaporative Demand and water deficit with phenotyping platforms. (ii) We develop ecophysiological models with parameters which can be directly extracted from measurements in platforms and in the field. (iii) We carry out GWAS at different scales, from -omic to plant scale in platform, and to yield components in network of field experiments to identify QTLs linked to conditional allelic effects depending on environmental conditions, and to values of model parameters. (iv) We use either direct measurements or the allelic compositions at target QTLs to determine the phenotypic profiles (set of parameter values) of real or virtual genotypes. (v) We simulate genotypic performance and the contribution of genomic regions under current and future stress situations over Europe via modelling. Results are compared to the observed genetic variability in networks of field experiments and are used as feedbacks for improving our phenotyping routines and ecophysiological models.
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The growth of vegetative and reproductive structures (leaves and silks) respond similarly to hydraulic cues in maize
New Phytologist, 2016Co-Authors: Olivier Turc, Claude Welcker, Marie Bouteillé, Avan Fuad-hassan, François TardieuAbstract:The elongation of styles and stigma (silks) of maize (Zea mays) flowers is rapid (1–3 mm h−1), occurs over a short period and plays a pivotal role in reproductive success in adverse environments. Silk elongation rate was measured using displacement transducers in 350 plants of eight genotypes during eight experiments with varying Evaporative Demand and soil water status. Measured time courses revealed that silk elongation rate closely followed changes in soil water status and Evaporative Demand, with day–night alternations similar to those in leaves. Day–night alternations were steeper with high than with low plant transpiration rate, manipulated via Evaporative Demand or by covering part of the leaf area. Half times of changes in silk elongation rate upon changes in Evaporative Demand or soil water status were 10–30 min, similar to those in leaves. The sensitivity of silk elongation rate to xylem water potential was genetically linked to that of leaf elongation rate. Lines greatly differed for these sensitivities. These results are consistent with a common hydraulic control of expansive growth in vegetative and reproductive structures upon changes in environmental conditions via a close connection with the xylem water potential. They have important implications for breeding, modelling and phenotyping.
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A Common Genetic Determinism for Sensitivities to Soil Water Deficit and Evaporative Demand: Meta-Analysis of Quantitative Trait Loci and Introgression Lines of Maize
Plant physiology, 2011Co-Authors: Claude Welcker, Walid Sadok, Grégoire Dignat, Morgan Renault, Silvio Salvi, Alain Charcosset, François TardieuAbstract:Evaporative Demand and soil water deficit equally contribute to water stress and to its effect on plant growth. We have compared the genetic architectures of the sensitivities of maize leaf elongation rate to Evaporative Demand and to soil water deficit. The former was measured via the response to leaf-to-air vapour pressure deficit in well-watered plants, the latter via the response to soil water potential in the absence of Evaporative Demand. Genetic analyses of each sensitivity were performed over 21 independent experiments with (i) three mapping populations, with temperate or tropical materials, (ii) one population resulting from the introgression of a tropical drought tolerant line in a temperate line (iii) two introgression libraries genetically independent from mapping populations. A very large genetic variability was observed for both sensitivities. Some lines maintained leaf elongation at very high Evaporative Demand or water deficit while others stopped elongation in mild conditions. A complex architecture arose from analyses of mapping populations, with 19 major metaQTLs involving strong effects and/or more than one mapping population. 68% of those QTLs affected sensitivities to both Evaporative Demand and soil water deficit. In introgressed lines, 73% of the tested genomic regions affected both sensitivities. This study is the first genetic demonstration that hydraulic processes, which drive the response to Evaporative Demand, also have a large contribution to the genetic variability of plant growth under water deficit in a large range of genetic material.
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A common genetic determinism for sensitivities to soil water deficit and Evaporative Demand: meta-analysis of quantitative trait loci and introgression lines of maize
Plant Physiology, 2011Co-Authors: Claude Welcker, Walid Sadok, Grégoire Dignat, Morgan Renault, Silvio Salvi, Alain Charcosset, François TardieuAbstract:Evaporative Demand and soil water deficit equally contribute to water stress and to its effect on plant growth. We have compared the genetic architectures of the sensitivities of maize (Zea mays) leaf elongation rate with Evaporative Demand and soil water deficit. The former was measured via the response to leaf-to-air vapor pressure deficit in well-watered plants, the latter via the response to soil water potential in the absence of Evaporative Demand. Genetic analyses of each sensitivity were performed over 21 independent experiments with (1) three mapping populations, with temperate or tropical materials, (2) one population resulting from the introgression of a tropical drought-tolerant line in a temperate line, and (3) two introgression libraries genetically independent from mapping populations. A very large genetic variability was observed for both sensitivities. Some lines maintained leaf elongation at very high Evaporative Demand or water deficit, while others stopped elongation in mild conditions. A complex architecture arose from analyses of mapping populations, with 19 major metaquantitative trait loci involving strong effects and/or more than one mapping population. A total of 68% of those quantitative trait loci affected sensitivities to both Evaporative Demand and soil water deficit. In introgressed lines, 73% of the tested genomic regions affected both sensitivities. To our knowledge, this study is the first genetic demonstration that hydraulic processes, which drive the response to Evaporative Demand, also have a large contribution to the genetic variability of plant growth under water deficit in a large range of genetic material.
Thierry Simonneau - One of the best experts on this subject based on the ideXlab platform.
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Leaf growth and turgor in growing cells of maize (Zea mays L.) respond to Evaporative Demand under moderate irrigation but not in water-saturated soil.
Plant cell & environment, 2006Co-Authors: Oumaya Bouchabke, François Tardieu, Thierry SimonneauAbstract:To test whether the inhibition of leaf expansion by high Evaporative Demand is a result of hydraulic processes, we have followed both leaf elongation rate (LER) and cell turgor in leaves of maize plants either normally watered or in water-saturated soil in which hydraulic resistance at the soil-root interface was abolished. Cell turgor was measured in situ with a pressure probe in the elongating zone of the first and sixth leaves, and LERs of the same leaves were measured continuously with transducers or by following displacements of marks along the growing leaves. Both variables displayed spatial variations along the leaf and positively correlated within the elongating zone. Values peaked at mid-distance of this zone, where the response of turgor to Evaporative Demand was further dissected. High Evaporative Demand decreased both LER and turgor for at least 5 h, with dose-effect linear relations. This was observed in five genotypes with appreciable differences in turgor maintenance among genotypes. In contrast, the depressing effects of Evaporative Demand on both turgor and LER disappeared when the soil was saturated, thereby opposing a negligible resistance to water flow at the soil-root interface. These results suggest that the response of LER to Evaporative Demand has a hydraulic origin, enhanced by the resistance to water flux at the soil-root interface. They also suggest that turgor is not completely maintained under high Evaporative Demand, and may therefore contribute to the reductions in LER observed in non-saturated soils.
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Variability among species of stomatal control under fluctuating soil water status and Evaporative Demand: modelling isohydric and anisohydric behaviours
Journal of Experimental Botany, 1998Co-Authors: François Tardieu, Thierry SimonneauAbstract:Stomatal control of species with contrasting stomatal behaviours have been investigated under natural fluctuations of Evaporative Demand and soil water status. Sunflower and barley (anisohydric behaviour) have a daytime leaf water potential (ψ l ) which markedly decreases with Evaporative Demand during the day and is lower in droughted than in watered plants. In contrast, maize and poplar (isohydric behaviour) maintain a nearly constant ψ l during the day at a value which does not depend on soil water status until plants are close to death. Plants were also subjected to a range of soil water potentials under contrasting air vapour pressure deficits (VPD, from 0.5 to 3 kPa) in the field, in the greenhouse or in a growth chamber. Finally, plants or detached leaves were fed with varying concentrations of artificial ABA. Stomatal conductance of well-watered plants had no response to VPD when plants were grown in natural soils, suggesting that the opposite result observed in many laboratory experiments might be linked to the low unsaturated hydraulic conductivity of usual potting substrates. The response of stomatal conductance of all studied species to the concentration of ABA in pressurized xylem sap ([ABA] xyl ) was the same whether ABA had an endogenous origin (droughted plants) or was artificially fed. However stomatal response of maize and poplar to [ABA] xyl markedly changed with varying Evaporative Demand or ψ l , whereas this was not the case in sunflower or barley. This suggests that isohydric behaviour is linked to an interaction between hydraulic and chemical information, while anisohydric behaviour is linked to an absence of interaction. In all cases, [ABA] xyl was related to soil water status with common relationships for different experimental conditions, but with markedly different responses among species. Diurnal variations of [ABA] xyl with Evaporative Demand were small in all studied species. Results are synthesized in a model which accounts for observed behaviours of g s , ψ l and [ABA] xyl in fluctuating conditions and for several species. The validity of this model, in particular the physiological meaning of [ABA] xyl , is discussed.
M. Walid Sadok - One of the best experts on this subject based on the ideXlab platform.
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Variability in temperature-independent transpiration responses to Evaporative Demand correlate with nighttime water use and its circadian control across diverse wheat populations.
Planta, 2019Co-Authors: Bishal Gole Tamang, Rémy Schoppach, Daniel Monnens, Brian J. Steffenson, James A. Anderson, M. Walid SadokAbstract:Nocturnal transpiration, through its circadian control, plays a role in modulating daytime transpiration response to increasing Evaporative Demand, to potentially enable drought tolerance in wheat. Limiting plant transpiration rate (TR) in response to increasing vapor pressure deficit (VPD) has been suggested to enable drought tolerance through water conservation. However, there is very little information on the extent of diversity of TR response curves to “true” VPD (i.e., independent from temperature). Furthermore, new evidence indicate that water-saving could operate by modulating nocturnal TR (TRN), and that this response might be coupled to daytime gas exchange. Based on 3 years of experimental data on a diverse group of 77 genotypes from 25 countries and 5 continents, a first goal of this study was to characterize the functional diversity in daytime TR responses to VPD and TRN in wheat. A second objective was to test the hypothesis that these traits could be coupled through the circadian clock. Using a new gravimetric phenotyping platform that allowed for independent temperature and VPD control, we identified three and fourfold variation in daytime and nighttime responses, respectively. In addition, TRN was found to be positively correlated with slopes of daytime TR responses to VPD, and we identified pre-dawn variation in TRN that likely mediated this relationship. Furthermore, pre-dawn increase in TRN positively correlated with the year of release among drought-tolerant Australian cultivars and with the VPD threshold at which they initiated water-saving. Overall, the study indicates a substantial diversity in TR responses to VPD that could be leveraged to enhance fitness under water-limited environments, and that TRN and its circadian control may play an important role in the expression of water-saving.
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Higher forage yields under temperate drought explained by lower transpiration rates under increasing Evaporative Demand
European Journal of Agronomy, 2016Co-Authors: Pierre Hainaut, Thibaut Remacle, Christian Decamps, Richard Lambert, M. Walid SadokAbstract:Abstract In temperate regions, perennial forage-based cropping systems are expected to face an increasing frequency of summer droughts over the next decades prompting the need for more resilient cultivars. However, most efforts mainly focus on Mediterranean-type environments where the plant survival is often engaged. Under temperate environments, vapor pressure deficit (VPD) is a key component of drought, because its variation alters the crop transpiration rate (TR) and therefore its ability to fix carbon even in well-watered conditions. Despite this knowledge, there is no available data about the diversity of whole-plant TR responses to VPD and soil moisture among key forage crops such as alfalfa, red clover, cock’s foot and perennial ryegrass. Further, field-based evidence is lacking regarding the links between TR responses to VPD and yield under drought. Here, we combined experimental approaches characterizing gas exchange responses to VPD and soil moisture at scales that ranged from the growth chamber to the field, where yields were characterized both quantitatively and qualitatively over the course of 2 years on 8 genotypes from the 4 above species. A significant variability in TR responses to increasing VPD and soil water deficit was found among locally-adapted cultivars. More importantly, TR responses to VPD – but not to decreasing soil moisture – were found to be consistently correlated to relative yield performances under drought, in a way indicating that conservative water use under high Evaporative Demand promoted higher yield outputs. In contrast, yields under drought were unrelated to canopy temperature and leaf gas exchange measured in the field. Further, no link was found between TR responses to VPD and qualitative yield traits such as digestibility indicating that the hypothesized water saving strategy does not improve yield at the expense of forage quality. This study opens the way for future forage breeding and management strategies taking advantage of the diversity of TR responses to drought to implement climate-change resilient forage-based systems.
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Conservative water use under high Evaporative Demand associated with smaller root metaxylem and limited trans-membrane water transport in wheat
Functional plant biology : FPB, 2014Co-Authors: Rémy Schoppach, Linda Jeanguenin, Diego Wauthelet, M. Walid SadokAbstract:Efficient breeding of drought-tolerant wheat (Triticum spp.) genotypes requires identifying mechanisms underlying exceptional performances. Evidence indicates that the drought-tolerant breeding line RAC875 is water-use conservative, limiting its transpiration rate (TR) sensitivity to increasing vapour pressure deficit (VPD), thereby saving soil water moisture for later use. However, the physiological basis of the response remains unknown. The involvement of leaf and root developmental, anatomical and hydraulic features in regulating high-VPD, whole-plant TR was investigated on RAC875 and a drought-sensitive cultivar (Kukri) in 12 independent hydroponic and pot experiments. Leaf areas and stomatal densities were found to be identical between lines and de-rooted plants didn’t exhibit differential TR responses to VPD or TR sensitivity to four aquaporin (AQP) inhibitors that included mercury chloride (HgCl2). However, intact plants exhibited a differential sensitivity to HgCl2 that was partially reversed by β-mercaptoethanol. Further, root hydraulic conductivity of RAC875 was found to be lower than Kukri’s and root cross-sections of RAC875 had significantly smaller stele and central metaxylem diameters. These findings indicate that the water-conservation of RAC875 results from a root-based hydraulic restriction that requires potentially heritable functional and anatomical features. The study revealed links between anatomical and AQP-based processes in regulating TR under increasing Evaporative Demand.