Spatiotemporal coordination of cell division and growth during organ morphogenesis

A developing plant organ exhibits complex spatiotemporal patterns of growth, cell division, cell size, cell shape, and organ shape. Explaining these patterns presents a challenge because of their dynamics and cross-correlations, which can make it difficult to disentangle causes from effects. To address these problems, we used live imaging to determine the spatiotemporal patterns of leaf growth and division in different genetic and tissue contexts. In the simplifying background of the speechless (spch) mutant, which lacks stomatal lineages, the epidermal cell layer exhibits defined patterns of division, cell size, cell shape, and growth along the proximodistal and mediolateral axes. The patterns and correlations are distinctive from those observed in the connected subepidermal layer and also different from the epidermal layer of wild type. Through computational modelling we show that the results can be accounted for by a dual control model in which spatiotemporal control operates on both growth and cell division, with cross-connections between them. The interactions between resulting growth and division patterns lead to a dynamic distributions of cell sizes and shapes within a deforming leaf. By modulating parameters of the model, we illustrate how phenotypes with correlated changes in cell size, cell number, and organ size may be generated. The model thus provides an integrated view of growth and division that can act as a framework for further experimental study

Ontogeny of hydraulic and metabolic controls of leaf growth in Arabidopsis thaliana

La performance d'une plante repose en partie sur sa capacité à capturer l'énergie lumineuse via la croissance foliaire. La littérature souligne deux limitations majeures de la croissance, de nature métabolique ou hydraulique. Nous testons ici l'hypothèse originale que l'importance relative de ces deux limitations est structurée par l'ontogenèse de la feuille chez Arabidopsis thaliana. Nous montrons que la disponibilité en carbone restreint la croissance des jeunes feuilles, tandis qu'une compétition hydraulique entre croissance et transpiration s'accroît au cours de l'ontogenèse. La mise en place de cette limitation hydraulique s'explique par une dégradation de la capacité du xylème et probablement des aquaporines à approvisionner la feuille en eau, malgré une diminution ontogénétique de la transpiration. Cette dernière est la conséquence de l'acquisition progressive de la sensibilité des stomates aux signaux de fermeture, notamment l'obscurité et l'acide abscissique (ABA), hormone induite par la sécheresse. Enfin, nous mettons en évidence une nouvelle composante de la sensibilité stomatique à l'ABA, conservée chez des mutants décrits comme insensibles à cette hormone : l'ABA induit une diminution de la conductance hydraulique foliaire qui abaisse le potentiel hydrique foliaire et in fine la conductance stomatique. Ce mécanisme chez les feuilles développées contribuerait sous stress hydrique à rediriger le flux d'eau vers les feuilles en croissance. Plus généralement, le contrôle des stomates par des mécanismes hydrauliques induits par l'ABA pourrait être une composante majeure de l'ajustement entre offre et demande en eau chez les plantes soumises à un stress hydrique.In plants, leaf growth is the central process allowing energy capture and space colonization. The literature suggests that leaf growth is predominantly determined by metabolic and hydraulic limitations. Here, we test the original hypothesis that the relative importance of metabolics and hydraulics on the control of leaf growth is organized according to leaf ontogeny in Arabidopsis thaliana. We show that leaf carbon balance limits growth of the young leaves which therefore grow at a slower rate in the nighttime, while a hydraulic limitation gradually establishes in the daytime, when growth and transpiration competes for water. This gradual hydraulic limitation is underlain by a deterioration of leaf venation and probably aquaporins capacity to supply water to the leaf, despite an ontogenetic decrease in transpiration. This decline in transpiration occurs because stomata acquire throughout leaf ontogeny their sensitivity to the major closure signals, including darkness and abscisic acid (ABA), a hormone induced by drought. Finally, we discover a novel component of stomatal sensitivity to ABA, conserved in mutants described as insensitive to ABA in isolated epidermis: ABA induces a decrease in leaf hydraulic conductance which lowers leaf water potential and stomatal conductance according to a hydraulic cascade. Decreasing leaf hydraulic conductance through ABA action in fully expanded leaves would contribute to redirect water flow to the young leaves under water stress. More generally, controlling stomata by ABA-induced hydraulic mechanisms could be a crucial component of the coordination between water supply and water demand in plants under water challenging conditions

Ontogenèse des déterminismes hydrauliques et métaboliques de la croissance foliaire chez Arabidopsis thaliana

La performance d'une plante repose en partie sur sa capacité à capturer l'énergie lumineuse via la croissance foliaire. La littérature souligne deux limitations majeures de la croissance, de nature métabolique ou hydraulique. Nous testons ici l'hypothèse originale que l'importance relative de ces deux limitations est structurée par l'ontogenèse de la feuille chez Arabidopsis thaliana. Nous montrons que la disponibilité en carbone restreint la croissance des jeunes feuilles, tandis qu'une compétition hydraulique entre croissance et transpiration s'accroît au cours de l'ontogenèse. La mise en place de cette limitation hydraulique s'explique par une dégradation de la capacité du xylème et probablement des aquaporines à approvisionner la feuille en eau, malgré une diminution ontogénétique de la transpiration. Cette dernière est la conséquence de l'acquisition progressive de la sensibilité des stomates aux signaux de fermeture, notamment l'obscurité et l'acide abscissique (ABA), hormone induite par la sécheresse. Enfin, nous mettons en évidence une nouvelle composante de la sensibilité stomatique à l'ABA, conservée chez des mutants décrits comme insensibles à cette hormone : l'ABA induit une diminution de la conductance hydraulique foliaire qui abaisse le potentiel hydrique foliaire et in fine la conductance stomatique. Ce mécanisme chez les feuilles développées contribuerait sous stress hydrique à rediriger le flux d'eau vers les feuilles en croissance. Plus généralement, le contrôle des stomates par des mécanismes hydrauliques induits par l'ABA pourrait être une composante majeure de l'ajustement entre offre et demande en eau chez les plantes soumises à un stress hydrique.In plants, leaf growth is the central process allowing energy capture and space colonization. The literature suggests that leaf growth is predominantly determined by metabolic and hydraulic limitations. Here, we test the original hypothesis that the relative importance of metabolics and hydraulics on the control of leaf growth is organized according to leaf ontogeny in Arabidopsis thaliana. We show that leaf carbon balance limits growth of the young leaves which therefore grow at a slower rate in the nighttime, while a hydraulic limitation gradually establishes in the daytime, when growth and transpiration competes for water. This gradual hydraulic limitation is underlain by a deterioration of leaf venation and probably aquaporins capacity to supply water to the leaf, despite an ontogenetic decrease in transpiration. This decline in transpiration occurs because stomata acquire throughout leaf ontogeny their sensitivity to the major closure signals, including darkness and abscisic acid (ABA), a hormone induced by drought. Finally, we discover a novel component of stomatal sensitivity to ABA, conserved in mutants described as insensitive to ABA in isolated epidermis: ABA induces a decrease in leaf hydraulic conductance which lowers leaf water potential and stomatal conductance according to a hydraulic cascade. Decreasing leaf hydraulic conductance through ABA action in fully expanded leaves would contribute to redirect water flow to the young leaves under water stress. More generally, controlling stomata by ABA-induced hydraulic mechanisms could be a crucial component of the coordination between water supply and water demand in plants under water challenging conditions.MONTPELLIER-BU Sciences (341722106) / SudocSudocFranceF

Stomatal response to humidity: blurring the boundary between active and passive movement

No abstract available

Control of Leaf Expansion: A Developmental Switch from Metabolics to Hydraulics1[W][OA]

Leaf expansion is the central process by which plants colonize space, allowing energy capture and carbon acquisition. Water and carbon emerge as main limiting factors of leaf expansion, but the literature remains controversial about their respective contributions. Here, we tested the hypothesis that the importance of hydraulics and metabolics is organized according to both dark/light fluctuations and leaf ontogeny. For this purpose, we established the developmental pattern of individual leaf expansion during days and nights in the model plant Arabidopsis (Arabidopsis thaliana). Under control conditions, decreases in leaf expansion were observed at night immediately after emergence, when starch reserves were lowest. These nocturnal decreases were strongly exaggerated in a set of starch mutants, consistent with an early carbon limitation. However, low-light treatment of wild-type plants had no influence on these early decreases, implying that expansion can be uncoupled from changes in carbon availability. From 4 d after leaf emergence onward, decreases of leaf expansion were observed in the daytime. Using mutants impaired in stomatal control of transpiration as well as plants grown under soil water deficit or high air humidity, we gathered evidence that these diurnal decreases were the signature of a hydraulic limitation that gradually set up as the leaf developed. Changes in leaf turgor were consistent with this pattern. It is concluded that during the course of leaf ontogeny, the predominant control of leaf expansion switches from metabolics to hydraulics. We suggest that the leaf is better armed to buffer variations in the former than in the latter

A role for carbon metabolism in plant growth response to soil water deficit? An integrated perspective

International audiencePlant growth relies on C metabolism because carbohydrates fuel main metabolic pathways for the build-up of structures, for ATP production, and exert some transcriptional control on the metabolic and developmental machinery. When plants are exposed to drought, both growth and C management are affected leading to the simple idea that growth changes could be triggered by C metabolism and partitioning changes. We tested this idea in the model plant Arabidopsis - At the whole plant level, leaf expansion is reduced while photosynthesis is maintained leading to C compounds accumulation, in particular organic acids, which contribute to osmotic adjustment while C export to roots is promoted. These changes occur in the absence of major reprogramming of C metabolism (as seen by the analysis of 30 enzymes) and contribute to the improvement of C status (as seen by the expression of sugar responsive genes). - At the single leaf level, the expansion of young visible leaves show strong night growth depressions in a series of mutants impaired in starch management in phase with the fluctuations of their C status. Drought improves the C status of these mutants at night and releases the relationship between C availability and growth. - At the root level, elongation that was earlier found to be tightly related to the hexose content in the root tip vanishes under drought suggesting that C flux and utilization become uncoupled. Together, these data suggest that drought affects C metabolism and partitioning mainly as a consequence of growth change

A role for carbon metabolism in plant growth response to soil water deficit? An integrated perspective

International audiencePlant growth relies on C metabolism because carbohydrates fuel main metabolic pathways for the build-up of structures, for ATP production, and exert some transcriptional control on the metabolic and developmental machinery. When plants are exposed to drought, both growth and C management are affected leading to the simple idea that growth changes could be triggered by C metabolism and partitioning changes. We tested this idea in the model plant Arabidopsis - At the whole plant level, leaf expansion is reduced while photosynthesis is maintained leading to C compounds accumulation, in particular organic acids, which contribute to osmotic adjustment while C export to roots is promoted. These changes occur in the absence of major reprogramming of C metabolism (as seen by the analysis of 30 enzymes) and contribute to the improvement of C status (as seen by the expression of sugar responsive genes). - At the single leaf level, the expansion of young visible leaves show strong night growth depressions in a series of mutants impaired in starch management in phase with the fluctuations of their C status. Drought improves the C status of these mutants at night and releases the relationship between C availability and growth. - At the root level, elongation that was earlier found to be tightly related to the hexose content in the root tip vanishes under drought suggesting that C flux and utilization become uncoupled. Together, these data suggest that drought affects C metabolism and partitioning mainly as a consequence of growth change

Analyse des risques psychosociaux et de la qualité de vie au travail. Diagnostic et préconisations (UMR LEPSE)

il s'agit d'un type de produit dont les métadonnées ne correspondent pas aux métadonnées attendues dans les autres types de produit : ACTIVITY_REPORTAnalyse des risques psychosociaux et de la qualité de vie au travail. Diagnostic et préconisations (UMR LEPSE

Breeding grapevine for an efficient use of water by lowering night-time transpiration

Drought is the major constraint causing considerable yieldreduction in chickpea. Roots play a critical role in enhancingdrought tolerance. The main objective of the study was to introgressdrought tolerant root traits into Kenyan chickpea varietiesthrough marker assisted breeding (MABC). Eight simplesequence repeat (SSR) markers, linked to quantitative trait loci(QTL) for root and yield traits, were used to screen the parentsat ICRISAT, India. In addition, 1144 single nucleotide polymorphicmarkers (SNPs) were also used in genotyping theseparents at Legume Genomics Center, United Kingdom. Crosseswere made between two selected varieties, ICCV 92944 (ChaniaDesi II) and ICCV 00108 (LDT 068) and ‘QTL-hotspot’ donorparent ICC 4958 that has extensive rooting system. Polymorphic phic SSR and SNP markers were used to select progenies withroot QTL at F1, BC1F1 and BC2F1 that were later advanced toBC2F3. The BC2F3 populations were evaluated for root traitsat Egerton University in randomized complete block designwith two replications in pot experiment. The BC2F3 familieswere significantly different for root dry weight (RDW), shootdry weight (SDW), total plant dry weight (PDW) and root toshoot dry weight (R/S) ratio (R/S) for Chania Desi II x ICC 4958and R/S for LDT 068 x ICC 4958. These lineshad significantlyimproved root traits compared the recurrent parents. MABCis aneffective and efficient method of introgressing complexdrought tolerant traits which leads to improvement in yield especiallyunder drought conditions