Estimation du débit des fleuves à partir de mesures satellitaires des variables de surface sans mesures in situ

The water issue is currently a major challenge for our societies. Even if water is a renewable resource, its natural cycle supports great stresses, both human activity and climate change. River discharge is a key variable of the water cycle, whose quantification requires heavy field measurements. Therefore the global monitoring of river discharge remains problematic and satellite remote sensing techniques could be a major asset. Earth Observation radar techniques are currently limited to the measurement of surface variables and cannot measure river bottom hydraulic parameters. The current study proposes a method to estimate these parameters from surface variables, in order to estimate the river discharge. This method has been validated on exact simulated data and its robustness to measurement noise has been studied on noisy simulated data and on real data. The second part of this work explores the abilities of radar along-track interferometry to measure river surface velocity. Velocity measurements carried out on the Rhône river during an airborne campaign (ONERA-Cemagref) show a strong consistency with ADCP field measurements. M4S backscattering model, tested in the framework of this study, is poorly adapted to river scenes : it appears to be extremely sensitive to wind intensity which could be explained by a poor modeling of surface roughness. As part of the SWOT mission program (NASA-CNES) a method allowing in situ characterization of river surface roughness has been developed. It was validated under laboratory controlled conditions. It was implemented on the Rhône river to characterize water surface and quantify the influence of wind intensity on the water surface roughness parameters.La question de l’eau constitue à l’heure actuelle un enjeu majeur pour nos sociétés. Bien qu’il s’agisse d’une ressource renouvelable, son cycle naturel est soumis à de fortes pressions issues tant de l’activité humaine que des modifications climatiques. Le débit des fleuves constitue une des variables clefs du cycle de l’eau. Sa quantification implique des mesures in situ lourdes. De ce fait, son suivi à l’échelle globale reste problématique, et les techniques de télédétection peuvent représenter un atout majeur. Les techniques satellitaires optiques et radar ne peuvent actuellement que mesurer les variables de surface et n’accèdent pas aux paramètres de fond des cours d’eau. Ce travail propose une méthode d’estimation de ces paramètres hydrauliques de fond à partir des seules mesures des variables de surface, en vue de l’estimation du débit. Cette méthode a été validée sur des données simulées exactes et une étude de sensibilité au bruit de mesure a été menée sur des données simulées bruitées et sur des données réelles. Le second volet de ce travail porte sur le potentiel de l’interférométrie radar temporelle à mesurer la variable de vitesse de surface des fleuves. Une campagne de mesure aéroportée a été réalisée sur le Rhône (ONERA-Cemagref) et a montré des résultats concordants avec les mesures de vitesses réalisées in situ par ADCP. En revanche, le modèle de rétrodiffusion M4S, testé dans le cadre de cette thèse, est apparu peu adapté aux scènes fluviales : il s’avère extrêmement sensible aux conditions de vent, ce qui peut s’expliquer par une faiblesse dans la modélisation des caractéristiques des surfaces de fleuves. Dans le cadre du programme SWOT (NASA-CNES), nous avons développé une méthode de mesure in situ de la rugosité des surfaces fluviales. Validée lors de mesures en laboratoire, cette méthode a été mise en oeuvre sur le Rhône, et a ainsi permis de caractériser la surface et l’influence de l’intensité du vent sur les paramètres de rugosité

L-Tyrosine beta-naphthylamide is a potent competitive inhibitor of tyramine N-(hydroxycinnamoyl)transferase in vitro

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The biosynthesis of acetovanillone in tobacco cell-suspension cultures

International audienceA soluble enzyme, extracted from tobacco cell-suspension cultures 24 h after treatment with 100 μM methyl jasmonate, has been shown to synthesize acetovanillone (apocynin) from feruloyl-CoA in the presence of NAD. The enzyme displayed Michaelis–Menten kinetics with apparent Km values of 5.6 μM for feruloyl-CoA and 260 μM for NAD and exhibited very high specificity for its substrates. The increase in acetovanillone synthase activity was followed by an increase in the concentration of both acetovanillone and acetosyringone in the culture medium. No intermediate could be detected when analysing the reaction medium by HPLC during the formation of acetovanillone in cell-free extracts. The apparent molecular mass estimated by gel permeation on an FPLC column was ca. 79 kDa. To our knowledge, this is the first report of an enzymic system catalysing the synthesis of an acetophenone. This work demonstrates that the biosynthesis of acetophenones in tobacco proceeds from hydroxycinnamic acids through a CoA-dependent β-oxidation pathway. Interestingly in methyl jasmonate-treated cells, which synthesize very large amounts of hydroxycinnamoylputrescines, inhibition of the synthesis of these conjugates increased the concentration of acetovanillone and acetosyringone in the culture medium, suggesting that the two metabolic pathways can compete for their common precursors, i.e. hydroxycinnamoyl-CoA thioesters

Purification and characterization of hydroxycinnamoyl-coenzyme A : omega-hydroxypalmitic acid O-hydroxycinnamoyltranferase from tobacco (Nicotiana tabacum L.) cell-suspension cultures

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In vitro inhibition of shikimate hydroxycinnamoyltransferase by acibenzolar acid, the first metabolite of the plant defence inducer acibenzolar-S-methyl

International audienceAcibenzolar acid, the first metabolite formed in planta from the defence inducer acibenzolar-S-methyl (ASM), has been shown to be an inhibitor of the enzyme shikimate hydroxycinnamoyltransferase (HST), extracted from grapevine or tobacco cell suspension cultures. Using a purified recombinant Arabidopsis thaliana HST, the inhibition was found to be competitive, acibenzolar acid binding reversibly to the shikimate binding site of the HST:p-coumaroyl-CoA complex, with a Ki value of 250 μM. The other hydroxycinnamoyltransferases tested in the course of this study, using either hydroxypalmitic acid, putrescine, tyramine, or quinic acid as acyl acceptors were not, or only slightly, inhibited by acibenzolar acid. To understand the specificity of the interaction of acibenzolar acid with HST, we analyzed the structure-activity relationship of a series of benzoic or acibenzolar acid analogues, tested either as AtHST substrates or as inhibitors. This analysis confirmed previously published data on the substrate flexibility of HST and demonstrated that both the carboxyl group and the thiadiazole moiety of acibenzolar acid are playing an important role in the interaction with the shikimate binding site. Acibenzolar acid, which cannot form an ester bond with p-coumaric acid, was however a less potent inhibitor than protocatechuic or 3-hydroxybenzoic acids, which are used as acyl acceptors by HST. Our results show that the interaction of acibenzolar acid with HST, which is probably directly linked to the substrate promiscuity of HST, is unlikely to play a direct role in the defence-inducing properties of ASM in plants

Estimation du débit des fleuves à partir de mesure satellitaires de variables hydrauliques de surface

International audienceRiver discharge is a key variable to quantify the water cycle, its fluxes and stocks at different scales, from local scale for the efficient management of water resources to global scale for the monitoring of climate change. However, gathering reliable, long term and consistent information on river discharges worldwide or on large transboundary river basins is an extremely complex task, if ever achievable, as Hydrologic Services in different countries have heterogeneous acquisition strategies and data policies. Therefore, developing Earth Observation (EO) techniques for the measurement or estimation of river discharge is a major challenge. A key question deals with the possibility of deriving river discharge values from EO surface variables (width, level, slope, velocity, the only one accessible through EO) without any in situ measurement. Based on a literature study and original developments, the possibilities of estimating water surface variables using remote-sensing techniques have been explored, mainly radar altimetry as well as across-track and along-track interferometry. Then a method has been developed, based in a first phase on the equations of the uniform regime, in order to estimate river discharge from these surface variables only. The river section is simplified assuming to have a rectangular cross-section represented by its mean bottom level and width. Another hypothesis is made on a constant coefficient linking water surface velocity to the river section mean velocity. Based on a set of surface variables measurement at different dates and hydrological regimes, the methods estimates the values of the mean bottom level and mean Manning coefficient. Therefore, to be applied, the method requires a reasonable number of measurements along the complete hydrological cycle. The method has been developed and tested on a dataset of measurements realized on several stations on the Amazon basin (HyBAM ANA-IRD Project). Surface velocities and surface width are provided through ADCP measurements while water level and longitudinal river slopes are provided by in situ monitoring of levelled gauging stations and relevant technique to derive the longitudinal profile and slope. This method has been tested on different stations of the Amazon basin and gives satisfactory results on some of them but discrepancies on others. It appears that time varying surface slope on Amazon stations is in contradiction with the uniform hypothesis; therefore the method has been adapted to a non uniform flow configuration. The new method give relevant results on simulated data and further development are on-going to increase robustness of this method to noisy data

Purification and properties of putrescine hydroxycinnamoyl transferase from tobacco (Nicotiana tabacum) cell suspensions

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Biochemical basis of resistance of tobacco callus tissue cultures to hydroxyphenylethylamines

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