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This study investigated the feasibility of using hyperspectral imaging (HSI) to characterize the diffusion of acid and water within food structures during gastric digestion. Two different sweet potatoes (steamed and fried) and egg white gel (pH5 and pH9 EWGs) structures were exposed to in vitro gastric digestion before scanning by HSI. Afterward, the moisture or acid present in the digested sample was analyzed for calibration purposes. Calibration models were subsequently built using partial least-squares (PLS). The PLS models indicated that the full-wavelength spectral range (550–1700 nm) had a good ability to predict the spatial distribution of acid (Rcal2 > 0.82) and moisture (Rcal2 > 0.88). The spatiotemporal distributions of moisture and acid were mapped across the digested food, and they were shown to depend on the food composition and structure. The kinetic data revealed that the acid and moisture uptakes are governed by Fickian diffusion or by both diffusion and erosion-controlled mechanisms.

International audience; In the quest for sustainable intensification of crop production, we discuss the option of extending the root depth of crops to increase the volume of soil exploited by their root systems. We discuss the evidence that deeper rooting can be obtained by appropriate choice of crop species, by plant breeding, or crop management and its potential contributions to production and sustainable development goals. Many studies highlight the potentials of deeper rooting, but we evaluate its contributions to sustainable intensification of crop production, the causes of the limited research into deep rooting of crops, and the research priorities to fill the knowledge gaps

The endodermis is a key cell layer in plant roots that contributes to the controlled uptake of water and mineral nutrients into plants. In order to provide such functionality the endodermal cell wall has specific chemical modifications consisting of lignin bands (Casparian strips) that encircle each cell, and deposition of a waxy-like substance (suberin) between the wall and the plasma membrane. These two extracellular deposits provide control of diffusion enabling the endodermis to direct the movement of water and solutes into and out of the vascular system in roots. Loss of integrity of the Casparian strip-based apoplastic barrier is sensed by the leakage of a small peptide from the stele into the cortex. Here, we report that such sensing of barrier integrity leads to the rebalancing of water and mineral nutrient uptake, compensating for breakage of Casparian strips. This rebalancing involves both a reduction in root hydraulic conductivity driven by deactivation of aquaporins, and downstream limitation of ion leakage through deposition of suberin. These responses in the root are also coupled to a reduction in water demand in the shoot mediated by ABA-dependent stomatal closure.

Trees can be associated with dozens of fungi helping them to acquire resources from forest soils. The most widespread mutualistic association in boreal and temperate forests is the ectomycorrhizal symbiosis. This symbiosis involves mushroom-forming fungi of basidiomycota, ascomycota, and some zygomycota clades and the roots of woody plant species, including oaks, poplars or pines. Although the impact of this association on ecosystem production and tree nutrition is investigated for about a century, our understanding on the molecular mechanisms that control water and nutrient fluxes between plant and fungal partners is still limited. Here, we review the recent knowledge on the ectomycorrhizal contribution to tree nutrition. We specifically highlight the molecular mechanisms driving the acquisition, translocation and release of water and nutrients in ectomycorrhizal systems. We particularly focus on the transport of macronutrients, including nitrogen, phosphorus, potassium, sulphur and calcium, micronutrients, and water by the symbiotic partner. We also provide background on the evolution, diversity, and importance of this symbiosis, identify knowledge gaps, and propose future research directions.

International audience; Background and Aims: Understanding interactions between water and nitrate fluxes in response to nitrate availability and transpiration rate is crucial to select more efficient plants for the use of water and nitrate. Methods: Some of these interactions were investigated in intact Brassica napus plants by combining a non-destructive gravimetric device with (NO3-)-N-15 labeling. The set-up allowed high-resolution measurement of the effects of a cross-combination of two concentrations of KNO3 or KCl (0.5 and 5 mM) with two different rates of transpiration controlled by the relative humidity during a day-night cycle. Key Results: Results show that (1) high external nitrate concentrations increased root water uptake significantly whatever the transpiration rate, (2) nitrate translocation depended both on the rate of nitrate uptake and loading into xylem (3) dilution-concentration effect of nitrate in the xylem was mainly modulated by both external nitrate availability and transpiration rate, (4) dynamic changes in N-15 translocation in the xylem modified shoot growth and capacitance, and (5) variations in tissue concentrations of NO3- induced by the experimental conditions were balanced by changes in concentrations of chloride and sulfate ions. These effects were even more amplified under low transpiration condition and 0.5 mM external nitrate concentration. Conclusion: Taken together, these results highlight the fine and rapid adjustment of anion contents, nitrate and water flows to changes in transpiration rate and nitrate availability during a day-night cycle. The use of this non-invasive gravimetric device is therefore a powerful tool to assess candidates genes involved in nitrogen and water use efficiency.

Pearl millet plays an important role for food security in arid regions. Improving its root system toward increased water uptake efficiency could improve pearl millet tolerance to drought and lead to a significant production rise under water-limiting conditions. The objective of this work was to provide an integrated description of root system development at early stages and to assess the consequences of these findings for water uptake. A precise description of pearl millet root system development evidenced large variability among lateral root growth profiles. To further analyze this diversity, the growth rates of many lateral roots were measured daily and a statistical model was designed to classify these roots on the basis of their growth profiles. Three categories of lateral roots were identified in this way: (i) roots with high growth rate that could keep on growing after the end of the experiment, (ii) roots with intermediate growth rates and (iii) roots with low growth rates that quickly stop growing. The different lateral root types were randomly distributed along the primary root and there was no influence of root types on the intervals between successive lateral roots. The proportions of these different types were variable between plants of the same genotype, suggesting that small environmental variations could control these proportions. Water movements between soil and roots is modeled with R-SWMS to assess (i) the benefits of the three-type structuring, (ii) the relative contribution of each type to water uptake and (iii) the impact of specific proportions on global water uptake.

Combined adaptation of roots to flooding and soil nutrients: Role of a MAP3K protein kinase; Adaptation conjointe des racines à l'inondation et aux nutriments du sol Rôle d'une protéine kinase de type MAP3K

Biologie Végétale - Nutrition et Métabolisme

Combined adaptation of roots to flooding and soil nutrients: Role of a MAP3K protein kinase; Adaptation conjointe des racines à l'inondation et aux nutriments du sol Rôle d'une protéine kinase de type MAP3K

Les sélectionneurs de graminées fourragères devront dorénavant prendre en compte dans leurs objectifs de sélection une utilisation de leurs variétés avec un niveau d’intrants plus limité, et notamment une fertilisation azotée réduite. Ils devront également prendre en compte des risques de sécheresses plus fréquentes et plus longues dans un contexte de changement climatique d’origine anthropique attendu à assez court terme. Ils devront pour cela disposer de critères de sélection leur permettant de prendre en compte ces nouveaux objectifs. Dans cette perspective, nous avons évalué l’intérêt de la mesure de deux critères écophysiologiques intégratifs réalisée sur des micro-parcelles denses de variétés de ray-grass anglais. Nous avons cherché à évaluer si la variabilité entre variétés de l’indice de nutrition azoté (INN), a priori lié à la capacité des variétés à prélever l’azote du sol, était corrélée à celle du rendement fourrager. Nos résultats ont montré que cela pouvait être le cas lorsque les facteurs environnementaux sont peu limitants et permettent d’obtenir des peuplements productifs en situation de compétition pour la lumière. Nous avons d’autre part recherché si la variabilité entre variétés pour la discrimination isotopique du 13C (δ13C), physiologiquement corrélée à l’efficience photosynthétique de l’eau, était corrélée à celle du rendement fourrager. Nos résultats n’ont pas mis en évidence une telle corrélation dans nos conditions expérimentales mais ils suggèrent une relation entre les variations du δ13C et l’origine géographique du matériel génétique qui pourrait avoir un intérêt dans la gestion des ressources génétiques., In breeding programmes, forage grass breeders have to consider adaptation of cultivars for use in low input conditions, and more specifically under low nitrogen fertilisation conditions. They will also have to consider more frequent and longer drought events induced by ongoing anthropogenic climate change. They will thus need new breeding criteria enabling them to include these objectives in their breeding programmes. With this aim, we assessed relevance of two integrative ecophysiological criteria measured in dense micro-swards of perennial ryegrass. First, we assessed whether variation among cultivars for nitrogen nutrition index (NNI), which is related to the capacity of cultivars to uptake nitrogen from soil, was correlated to variation in forage yield. Our results showed that it can be the case in productive stands whose growth is not limited by environmental factors and whose individuals experience competition for light. Second, we investigated whether variation between cultivars in isotopic discrimination of 13C (δ13C), which is physiologically correlated to water photosynthetic efficiency, was correlated to variation in forage yield. We did not notice such a correlation in our experimental conditions but our results suggested a relationship between δ13C variations and geographical origin of genetic material which could be useful to consider in genetic resources management.

International audience

The aim of this study was the synthesis of a MIP (molecularly imprinted polymer) specific for a fungicide that is found in the majority of the french wine: iprodione. The challenge for extracting iprodione from wine medium was that the hydoralcoholic solution is a dipolar solvent, whereas the interaction between the MIP and iprodione is based on dipolar interactions. The first extraction study of iprodione was made on a MIP synthesized by bulk polymerization using methacrylamide and ethylene glycol dimethacrylate (EGDMA). The MIP was found to be more efficient than the NIP (non-imprinted polymer) in hydroalcoholic solutions which demonstrates that the molecular imprinting was successful. Then we synthesized 8 MIPs and 8 NIPs following an 23 experimental design in order to study the influence of three synthesis factors (the polymerization method, the nature of the crosslinker and the type of the functional monomer) on the iprodione recognition properties of the polymers. The water and the iprodione adsorption isotherms for MIPs and NIPs were determined. The result showed significant differences between the polymers involving a relationship between the water adsorption and the adsorption of iprodione. The molecular imprinting has been demonstrated by several techniques such as the differential scanning calorimetry and the nuclear magnetic resonance. The best recognition properties of iprodione are obtained with the MIP which was synthesized by precipitation polymerization using methacrylamide as functional momonomer and EGDMA as crosslinker. This MIP was used in solid phase extraction (SPE) for pre-concentration of iprodione in a white wine with a pre-concentration factor of 6. Its selectivity versus two fungicides: procymidone and pyrimethanil has been demonstrated., Les travaux de thèse ont porté sur la synthèse d’un MIP (polymère à empreintes moléculaires) spécifique d’un fongicide se trouvant dans la majorité des vins français : l’iprodione. Pour extraire l’iprodione à partir du vin, un challenge important se présentait : le milieu hydroalcoolique est un solvant dipolaire alors que l’interaction du MIP avec l’iprodione se base sur des interactions dipôle-dipôle. Les premières études d’extraction de l’iprodione ont été faites sur un MIP obtenu par polymérisation en masse à partir du méthacrylamide et de l'éthylène glycol diméthacrylate (EGDMA). Le MIP était plus efficace que le NIP (polymère non imprimé) dans des solutions hydroalcooliques ce qui vérifie que l’impression moléculaire était réussie. Un plan d’expériences 23 a été appliqué pour étudier l’influence de 3 facteurs de synthèse de MIP (la méthode de polymérisation, la nature de l'agent réticulant et le type de monomère fonctionnel) sur les propriétés de reconnaissance des polymères vis-à-vis de l’iprodione. 8 MIP et 8 NIP ont été ainsi synthétisés. Les isothermes d'adsorption de l'eau et de l’iprodione par les MIPs et les NIPs ont été déterminées. Des différences significatives entre les polymères ont été mises en évidences impliquant une relation entre l’adsorption de l’eau et l’adsorption de l’iprodione. La formation des empreintes moléculaires au sein des MIP a été démontrée par plusieurs techniques comme la calorimétrie différentielle à balayage et la résonance magnétique nucléaire. Les meilleures propriétés de reconnaissance de l’iprodione sont obtenues avec le MIP synthétisé par précipitation à partir du méthacrylamide comme monomère fonctionnel et de l’EGDMA comme réticulant. Ce MIP a été utilisé en extraction en phase solide (SPE) pour la pré-concentration de l’iprodione dans un vin blanc avec un facteur de pré-concentration égal à 6 et sa sélectivité par rapport à deux fongicides : le pyriméthanil et le procymidone a été démontrée.

Xylem embolism is a limiting factor for woody species worldwide. Conifers at the alpine timberline are exposed to drought and freeze-thaw stress during winter, which induce potentially lethal embolism. Previous studies indicated that timberline trees survive by xylem refilling. In this study on Picea abies, refilling was monitored during winter and spring seasons and analyzed in the laboratory and in situ experiments, based on hydraulic, anatomical, and histochemical methods. Refilling started in late winter, when the soil was frozen and soil water not available for the trees. Xylem embolism caused up to 86.2% +/- 3.1% loss of conductivity and was correlated with the ratio of closed pits. Refilling of xylem as well as recovery in shoot conductance started in February and corresponded with starch accumulation in secondary phloem and in the mesophyll of needles, where we also observed increasing aquaporin densities in the phloem and endodermis. This indicates that active, cellular processes play a role for refilling even under winter conditions. As demonstrated by our experiments, water for refilling was thereby taken up via the branches, likely by foliar water uptake. Our results suggest that refilling is based on water shifts to embolized tracheids via intact xylem, phloem, and parenchyma, whereby aquaporins reduce resistances along the symplastic pathway and aspirated pits facilitate isolation of refilling tracheids. Refilling must be taken into account as a key process in plant hydraulics and in estimating future effects of climate change on forests and alpine tree ecosystems.

2003 drought was exceptionally severe in many European regions (Germany, France), in duration and intensity. The carbon and water net ecosystem exchange, measured continuously at 12 European sites, were reduced by drought, due to stomatal closure, when relative extractable water in the root zone (REW) dropped below 0.4. The question of the tree species influence on the response to drought came up. The behavior of 36 trees (4 broadleaf species) submitted to artificial drought was studied by using stable isotopes of water. The 18O and 2H labeling in surface soil water and deeper layers in the root zone combined with the sampling of tree xylem and transpiration allowed us to identify the different strategies of the tree species when soil water decrease.