Un exemple de résistance induite chez les végétaux (stimulation des mécanismes de défense par l'éliciteur Stifenia® et phénomène de priming)

MONTPELLIER-BU Sciences (341722106) / SudocSudocFranceF

Contaminants ochratoxinogènes du raisin (biodiversité et facteurs de toxinogénèse)

La filière viti-vinicole, notamment en région Languedoc-Roussillon, est touchée par la problématique Ochratoxine A (OTA). L'ochratoxine A est une toxine fongique néphrotoxique, neurotoxique, cancérogène et tératogène. Le vin est considéré comme le second contributeur à l'ingestion de cette toxine dans l'alimentation derrière les céréales. De ce fait, la réglementation européenne a fixé la limite maximale de teneur en OTA des vins et jus de raisins à 2 g/Kg. La production de toxine est due à des contaminations du raisin par des souches fongiques d'Aspergillus section Nigri. Pour aider à lutter contre ce problème, la biodiversité fongique des raisins et la toxinogenèse des contaminants identifiés ainsi que la teneur en toxine des jus de raisins ont été caractérisées et suivies pour 4 années de récolte sur différentes zones géographiques, différents cépages et en fonction du traitement de la vigne. Un traitement naturel agissant comme stimulateur des défenses a été comparé à un traitement chimique pour assurer la protection sanitaire du raisin et du vin contre les contaminants fongiques ochratoxinogènes. Les principaux résultats ont permis de montrer une diversité importante des souches fongiques selon le cépage, le traitement, la région géographique et l'année de récolte. Grâce au traitement biologique une réduction maximale de 50 à 80 % du taux d'OTA est obtenue sur 60% des échantillons des jus de raisin et des vins. Afin de comprendre et expliquer les mécanismes mis en jeu dans l'action des traitements alternatifs, des analyses de composition des raisins et des composés volatils des feuilles ont été réalisées. La production des feuilles et des fruits peut, en effet, être modifiée par stimulation des défenses naturelles et peut engendrer la production de facteurs de sélection ou d'inhibition de la croissance fongique ou de la toxinogenèse. Les résultats préliminaires obtenus laissent voir qu'il y a, en effet, une action au niveau des raisins traités biologiquement qui ont des peaux plus épaisses et des teneurs en acides différentes des raisins traités chimiquement, ce qui pourrait gêner la pénétration des moisissures dans les baies et leur toxinogenèse. De plus, des différences de composition et teneur en composés volatils des feuilles issues des 2 types de traitement sont observées, avec notamment des teneurs en aldéhydes plus élevées après stimulation des défenses de la plante. Certains de ces composés pourraient avoir une action antifongique se traduisant par une diminution de la croissance et de la toxinogenèse des contaminants ochratoxinogènesThe wine-producing sector, notably in region Languedoc-Roussillon, is touched by the Ochratoxine A problem. Ochratoxine A is a fungal toxin with nephrotoxic, neurotoxic, carcinogenic and teratogenic effects. The wine is considered as the second cause in the ingestion of this toxin in the food behind cereal. Therefore, the European rule fixed the maximal limit of OTA content of wines and juice to 2 g/Kg. The production of toxin is due to contamination of the grape by fungal strains of Aspergillus section Nigri. To help to fight against this problem, the fungal biodiversity of grapes and the toxigenesis of contaminants identified as well as the content in toxin of grape juices were characterized and followed for 4 years of harvest, on various geographical zones, various grape varieties and according to the treatment of the vine. A natural active treatment as stimulating of the defences was compared with a chemical treatment to assure the sanitary protection of the grape and the wine against the fungal ochratoxigenic contaminants. The main results allowed to show an important diversity of fungal strains according to grape variety, the treatment, the geographical region and the year of harvest. The use of the biological treatment leads to a maximal reduction from 50 to 80 % of the rate of OTA on 60 % of the samples of grape juices and wines. To understand and explain mechanisms involved in the action of the alternate treatments, the analyses of composition of grapes and volatile compounds of leaves were realized. The production of leaves and fruits can, indeed, be modified by stimulation of the natural defences and can lead to the production of factors of selection or inhibition of the fungal growth or the toxigenesis. The obtained preliminary results let see that there is, indeed, an action at the level of grapes treated biologically which have more thick skins and contents in acids different from grapes treated chemically, what could hamper the penetration of moulds in berries and interfere with their toxigenesis. Furthermore, differences of composition and content in volatile compounds of leaves stemming from 2 types of treatment are observed, with notably contents in aldehydes more raised after stimulation of the defences of the plant. Some of these compounds could have an antifungal action being translated by a decrease of the growth and the toxigenesis of ochratoxigenic contaminantsMONTPELLIER-BU Sciences (341722106) / SudocSudocFranceF

Insights on the robustness, sensitivity and expressivity of simple many-body potentials: application to a-Zr

International audienceComputational material science, including irradiation physics, has been relying on classical in teratomic potentials for decades: they efficiently allow to simulate complex phenomena at lengthand time scales that outrun the capacity of the most accurate ab initio approaches. Two differentclasses of interatomic potentials are currently used. The so-called machine learning potentials[1],on one hand, have a high number of parameters and thus a high flexibility to reproduce a numberof physical quantities, but a high computational cost. On the other hand, many-body interatomicpotentials, like Embedded Atom Method (EAM) and tight binding Second Moment Approximation(SMA) potentials, have a more limited accuracy due to a reduced number of parameters. However,they are based on physically-inspired functional forms which ensures a reasonable transferability.Their low computational cost thus allow studies that require multiple evaluations of system en ergy and forces[2]. The identification of the potential parameters for a given system is of crucialimportance, but challenging.In this work, we apply efficient tools of model screening and sensitivity analysis to get insightson the capabilities of two SMA potentials [3, 4], in the context of irradiated α-zirconium. We focuson properties that are relevant for irradiation, i.e. elastic constants, point defect properties andstacking faults energies. The local screening of the potential parameters appears to be an efficientmethod to check the robstness of the potential, i.e. to identify the possible artefacts related to theroughness of the potential. After correcting for these artefacts, the most influencial parameterson the computed properties are identified. In particular, one parameter affects most of the self interstitial properties, while having a limited effect on bulk and vacancy properties. This suggestsa sensitivity indices-oriented technique to refit existing potentials. Following this approach, werefine a potential for irradiation defects in α-Zr, thanks to a multi-objective optimisation package

Insights on the robustness, sensitivity and expressivity of simple many-body potentials: application to a-Zr

International audienceComputational material science, including irradiation physics, has been relying on classical in teratomic potentials for decades: they efficiently allow to simulate complex phenomena at lengthand time scales that outrun the capacity of the most accurate ab initio approaches. Two differentclasses of interatomic potentials are currently used. The so-called machine learning potentials[1],on one hand, have a high number of parameters and thus a high flexibility to reproduce a numberof physical quantities, but a high computational cost. On the other hand, many-body interatomicpotentials, like Embedded Atom Method (EAM) and tight binding Second Moment Approximation(SMA) potentials, have a more limited accuracy due to a reduced number of parameters. However,they are based on physically-inspired functional forms which ensures a reasonable transferability.Their low computational cost thus allow studies that require multiple evaluations of system en ergy and forces[2]. The identification of the potential parameters for a given system is of crucialimportance, but challenging.In this work, we apply efficient tools of model screening and sensitivity analysis to get insightson the capabilities of two SMA potentials [3, 4], in the context of irradiated α-zirconium. We focuson properties that are relevant for irradiation, i.e. elastic constants, point defect properties andstacking faults energies. The local screening of the potential parameters appears to be an efficientmethod to check the robstness of the potential, i.e. to identify the possible artefacts related to theroughness of the potential. After correcting for these artefacts, the most influencial parameterson the computed properties are identified. In particular, one parameter affects most of the self interstitial properties, while having a limited effect on bulk and vacancy properties. This suggestsa sensitivity indices-oriented technique to refit existing potentials. Following this approach, werefine a potential for irradiation defects in α-Zr, thanks to a multi-objective optimisation package

Handling uncertainties in the development of tight-binding potentials : application to zirconium hydride

International audienceIn the field of material science for energy applications, zirconium hydrides are studied both fortheir useful application for hydrogen storage and for their negative effect on mechanical propertiesof the nuclear fuel cladding material (zirconium) in water cooled reactors. At the atomic scale,the tight-binding (TB) approximation has proven to be a satisfying method to develop potentialsthat are both accurate and computationally tractable to model zirconium hydrides. Such poten tials are defined by a fixed number of parameters that need to be accurately identified for themodel to be reliable. The reliability is indeed closely related to the uncertainties associated withparameters [1]. Even if the use of parametric potentials, TB or semi-empirical ones, is widely es tablished in the literature [2], very few studies discuss the quantification of such uncertainties [3–5].This work aims at quantifying the uncertainty associated with the calibration of TB poten tials. A previously developed TB potential [6]is used, focusing on its ability to reproduce elasticconstants and lattice parameters of δ (cubic) and (tetragonal) zirconium hydrides. UncertaintyQuantification (UQ) methods, based on polynomial chaos expansion and Bayesian inference, areused to estimate the parameters uncertainties, through their a posteriori probability distributionsand starting from a limited number of experimental and DFT data. The accuracy of the TBpotential - with respect to the available data - is thus improved. In addition, having characterizedthe uncertainty on the model parameters, we can estimate the uncertainty propagation on anycomputed property

Salicylic Acid and Ethylene Pathways Are Differentially Activated in Melon Cotyledons by Active or Heat-Denatured Cellulase from Trichoderma longibrachiatum

Infiltration of cellulase (EC 3.2.1.4) from Trichoderma longibrachiatum into melon (Cucumis melo) cotyledons induced several key defense mechanisms and hypersensitive reaction-like symptoms. An oxidative burst was observed 3 hours after treatment and was followed by activation of ethylene and salicylic acid (SA) signaling pathways leading to marked induction of peroxidase and chitinase activities. The treatment of cotyledons by heat-denatured cellulase also led to some induction of peroxidase and chitinase activities, but the oxidative burst and SA production were not observed. Co-infiltration of aminoethoxyvinil-glycine (an ethylene inhibitor) with the active cellulase did not affect the high increase of peroxidase and chitinase activities. In contrast, co-infiltration of aminoethoxyvinil-glycine with the denatured enzyme blocked peroxidase and chitinase activities. Our data suggest that the SA pathway (induced by the cellulase activity) and ethylene pathway (induced by heat-denatured and active protein) together coordinate the activation of defense mechanisms. We found a partial interaction between both signaling pathways since SA caused an inhibition of the ethylene production and a decrease in peroxidase activity when co-infiltrated with denatured cellulase. Treatments with active or denatured cellulase caused a reduction in powdery mildew (Sphaerotheca fuliginea) disease

Handling uncertainties in the development of tight-binding potentials : application to zirconium hydride

International audienceIn the field of material science for energy applications, zirconium hydrides are studied both fortheir useful application for hydrogen storage and for their negative effect on mechanical propertiesof the nuclear fuel cladding material (zirconium) in water cooled reactors. At the atomic scale,the tight-binding (TB) approximation has proven to be a satisfying method to develop potentialsthat are both accurate and computationally tractable to model zirconium hydrides. Such poten tials are defined by a fixed number of parameters that need to be accurately identified for themodel to be reliable. The reliability is indeed closely related to the uncertainties associated withparameters [1]. Even if the use of parametric potentials, TB or semi-empirical ones, is widely es tablished in the literature [2], very few studies discuss the quantification of such uncertainties [3–5].This work aims at quantifying the uncertainty associated with the calibration of TB poten tials. A previously developed TB potential [6]is used, focusing on its ability to reproduce elasticconstants and lattice parameters of δ (cubic) and (tetragonal) zirconium hydrides. UncertaintyQuantification (UQ) methods, based on polynomial chaos expansion and Bayesian inference, areused to estimate the parameters uncertainties, through their a posteriori probability distributionsand starting from a limited number of experimental and DFT data. The accuracy of the TBpotential - with respect to the available data - is thus improved. In addition, having characterizedthe uncertainty on the model parameters, we can estimate the uncertainty propagation on anycomputed property

Salicylic Acid Mediated by the Oxidative Burst Is a Key Molecule in Local and Systemic Responses of Cotton Challenged by an Avirulent Race of Xanthomonas campestris pv malvacearum

We analyzed the production of reactive oxygen species, the accumulation of salicylic acid (SA), and peroxidase activity during the incompatible interaction between cotyledons of the cotton (Gossypium hirsutum) cv Reba B50/Xanthomonas campestris pv malvacearum (Xcm) race 18. SA was detected in petioles of cotyledons 6 h after infection and 24 h post inoculation in cotyledons and untreated leaves. The first peak of SA occurred 3 h after generation of superoxide (O(2)(·−)), and was inhibited by infiltration of catalase. Peroxidase activity and accumulation of SA increased in petioles of cotyledons and leaves following H(2)O(2) infiltration of cotyledons from 0.85 to 1 mm. Infiltration of 2 mm SA increased peroxidase activity in treated cotyledons and in the first leaves, but most of the infiltrated SA was rapidly conjugated within the cotyledons. When increasing concentrations of SA were infiltrated 2.5 h post inoculation at the beginning of the oxidative burst, the activity of the apoplastic cationic O(2)(·−)-generating peroxidase decreased in a dose-dependent manner. We have shown that during the cotton hypersensitive response to Xcm, H(2)O(2) is required for local and systemic accumulation of SA, which may locally control the generation of O(2)(·−). Detaching cotyledons at intervals after inoculation demonstrated that the signal leading to systemic accumulation of SA was emitted around 3 h post inoculation, and was associated with the oxidative burst. SA produced 6 h post infection at HR sites was not the primary mobile signal diffusing systemically from infected cotyledons