Natural variation at XND1 impacts root hydraulics and trade-off for stress responses in Arabidopsis

Soil water uptake by roots is a key component of plant performance and adaptation to adverse environments. Here, we use a genome-wide association analysis to identify the XYLEM NAC DOMAIN 1 (XND1) transcription factor as a negative regulator of Arabidopsis root hydraulic conductivity (Lp). The distinct functionalities of a series of natural XND1 variants and a single nucleotide polymorphism that determines XND1 translation efficiency demonstrate the significance of XND1 natural variation at species-wide level. Phenotyping of xnd1 mutants and natural XND1 variants show that XND1 modulates Lp through action on xylem formation and potential indirect effects on aquaporin function and that it diminishes drought stress tolerance. XND1 also mediates the inhibition of xylem formation by the bacterial elicitor flagellin and counteracts plant infection by the root pathogen Ralstonia solanacearum. Thus, genetic variation at XND1, and xylem differentiation contribute to resolving the major trade-off between abiotic and biotic stress resistance in Arabidopsis

Supramolecular chiral host–guest nanoarchitecture induced by the selective assembly of barbituric acid derivative enantiomers

International audienceBarbituric acid derivatives are prochiral molecules, i.e. they are chiral upon adsorption on surfaces. Scanning tunneling microscopy reveals that barbituric acid derivatives self-assemble into a chiral guest-host supramolecular architecture at the solid-liquid interface on graphite. The host nanoarchitecture has a sophisticated wavy shape pattern and paired guest molecules are nested insides the cavities of the host structure. Each unit cell of the host structure is composed of both enantiomers with a ratio of 1:1. Furthermore, the wavy patterns of the nanoarchitecture are formed from alternative appearance of left- and right-handed chiral building blocks, which makes the network heterochiral. The functional guest-host nanoarchitecture is the result of two-dimensional chiral amplification from single enantiomers to organizational heterochiral supramolecular self-assembly

Two-Dimensional Hetero- to Homochiral Phase Transition from Dynamic Adsorption of Barbituric Acid Derivatives

International audienceBarbituric acid derivative (TDPT) is an achiral molecule, and its adsorption on a surface results in two opposite enantiomerically oriented motifs, namely TDPT-Sp and Rp. Two types of building blocks can be formed; block I is enantiomer-pure and is built up of the same motifs (format SpSp or RpRp) whereas block II is enantiomer-mixed and composes both motifs (format SpRp), respectively. The organization of the building blocks determines the formation of different nanoarchitectures which are investigated using scanning tunneling microscopy at a liquid/HOPG interface. Sophisticated, highly symmetric “nanowaves” are first formed from both building blocks I and II and are heterochiral. The “nanowaves” are metastable and evolve stepwisely into more close-packed “nanowires” which are formed from enantiomer-pure building block I and are homochiral. A dynamic hetero- to homochiral transformation and simultaneous multi-scale phase transitions are demonstrated at the single-molecule level. Our work provides novel insights into the control and the origin of chiral assemblies and chiral transitions, revealing the various roles of enantiomeric selection and chiral competition, driving forces, stability and molecular coverage

Amélioration de la robustesse des mesures en spectrométrie proche-infrarouge sur produits biologiques

MONTPELLIER-BU Sciences (341722106) / SudocSudocFranceF

Characterization of damage in a cast aluminum alloy during cyclic loading test at high temperature by x-ray tomography

International audienceThe aim of this work is to clarify the role of microstructure heterogeneity in the initiation and growth of cracks in a lost foam cast A319 for low cycle fatigue (LCF) loading condition. Because 2D analysis fail to establish the scenario of damage events, this study is based on 3D in situ analysis using synchrotron X-ray tomography during LCF test performed at 200°C. If X-ray tomography is now an established technique to study damage development in 3D, its application for relatively high temperature cyclic tests has never been done so far. Initial 3D observations of damage show that the cracks that lead to fracture initiate near large pores and propagate into the hard particles 3D network of the eutectic regions

3D characterization and modeling of low cycle fatigue damage mechanisms at high temperature in a cast aluminum alloy

International audienceSynchrotron X-ray tomography was used to monitor damage evolution in three dimensions during in situ Low Cycle Fatigue (LCF) tests at high temperature (250 • C) for an industrial material. The studied material is an AlSi7Cu3Mg aluminum alloy (close to ASTM A319) produced by Lost Foam Casting (LFC), a process which generates coarse microstructures but is nevertheless used for engine parts by the automotive industry. The volume analysis (3D images) has shown that cracks are extremely sensitive to microstructural features: coarse pores and hard particles of the eutectic regions are critical regarding respectively the main crack initiation and the crack growth. Finite Elements (FE) simulations, performed on meshes directly generated from 3D volumes and containing only pores, have revealed that mechanical fields also play a major role on the crack behavior. Initiation sites corresponded to areas of maximum inelastic strain while the crack path was globally correlated to high stress triaxiality and inelastic strain fields

3D characterization and modeling of low cycle fatigue damage mechanisms at high temperature in a cast aluminum alloy

International audienceSynchrotron X-ray tomography was used to monitor damage evolution in three dimensions during in situ Low Cycle Fatigue (LCF) tests at high temperature (250 °C) for an industrial material. The studied material is an AlSi7Cu3Mg aluminum alloy (close to ASTM A319) produced by Lost Foam Casting (LFC), a process which generates coarse microstructures but is nevertheless used for engine parts by the automotive industry. The volume analysis (3D images) has shown that cracks are extremely sensitive to microstructural features: coarse pores and hard particles of the eutectic regions are critical regarding respectively the main crack initiation and the crack growth. Finite Elements (FE) simulations, performed on meshes directly generated from 3D volumes and containing only pores, have revealed that mechanical fields also play a major role on the crack behavior. Initiation sites corresponded to areas of maximum inelastic strain while the crack path was globally correlated to high stress triaxiality and inelastic strain fields

Fatigue crack growth under large scale yielding condition in a cast automotive aluminum alloy

International audienceLow cycle fatigue crack growth tests have been performed at 250 • C in order to study fatigue crack growth under large scale yielding conditions in a material widely used at high temperature by the automotive industry for cylinder head applications. The studied material was a cast aluminum alloy AlSi7Cu3Mg (close to A319) produced by Lost Foam Casting. Two different microstructures were investigated: one containing large natural pores and another where pores have been removed by Hot Isostatic Pressing (HIP). Fatigue Crack Growth Rates (FCGR) have been measured by in situ surface optical microscopy for different loading conditions all inducing generalized plasticity and compared to assess the influence of pores on the FCGR. In situ observations coupled to post mortem analysis revealed strong crack interactions with both pores and large hard particles on specimen surfaces and in the bulk. FCGR ranging between 10 −6 and 10 −4 m/cycle appear to be mainly sensitive to applied strain amplitudes. Although pores promoted secondary crack initiations and crack coalescences, they seemed to have a limited effect on steady-state FCGR which has been analytically modeled using energy densities

Fatigue crack growth under large scale yielding condition in a cast automotive aluminum alloy

International audienceLow Cycle Fatigue crack growth tests have been performed at 250 °C in order to study fatigue crack growth under large scale yielding conditions in a material widely used at high temperature by the automotive industry for cylinder head applications. The studied material was a cast aluminum alloy AlSi7Cu3Mg (close to A319) produced by Lost Foam Casting. Two different microstructures were investigated: one containing large natural pores and another where pores have been removed by Hot Isostatic Pressing (HIP). Fatigue Crack Growth Rates (FCGR) have been measured by in situ surface optical microscopy for different loading conditions all inducing generalized plasticity and compared to assess the influence of pores on the FCGR. In situ observations coupled to post mortem analysis revealed strong crack interactions with both pores and large hard particles on specimen surfaces and in the bulk. FCGR ranging between and  m/cycle appear to be mainly sensitive to applied strain amplitudes. Although pores promoted secondary crack initiations and crack coalescences, they seemed to have a limited effect on steady-state FCGR which has been analytically modeled using energy densities