Comparaison moléculaire des graines orthodoxes de Medicago truncatula et récalcitrantes de Castanospermum australe : une nouvelle approche pour comprendre l’acquisition de la tolérance à la dessiccation

Desiccation tolerance (DT) is defined as the ability to survive in the dry state and resume metabolic activity upon imbibition. Unlike orthodox seeds, that acquire DT during their maturation, recalcitrant seeds do not survive desiccation. A comparative analysis of orthodox and recalcitrant seeds development constitutes an interesting model to highlight mechanisms that are involved in DT. Using proteomic and transcriptomic analyses, the development of the recalcitrant Castanospermum australe seeds was characterized and compared to development of orthodox Medicago truncatula seeds, species from the same sub-family of Fabaceae. Our results show that most LEA (Late Embryogenesis Abundant) proteins are absent or faintly accumulated in mature seeds of C. australe compared to M. truncatula. The LEA protein profile is similar to seeds of the Mtabi3 mutant that is deficient in the expression of the major regulator of orthodox seed maturation ABI3 (ABscissic acid Insensitive 3). Transcriptome analysis reveals a strong repression of CaABI3 and its putative targets at the end of C. australe seed development while the transcript levels of these target genes remain high until the end of maturation of M. truncatula seeds. Two genes coding for ABI3 were cloned in C. australe: CaABI3 and CaABI3-like. Ectopic expression in M. truncatula roots demonstrated that only CaABI3-like is able to activate the same targets as MtABI3. Moreover, CaABI3 does not complement the abi3-5 mutant of Arabidopsis thaliana. This analysis strengthens the implication of ABI3 in the desiccation sensitivity of recalcitrant seeds. In addition, mature C. australe seeds display certain characteristics of a seed that is preparing for germination and express many stress response genes

LEA polypeptide profiling of recalcitrant and orthodox legume seeds reveals ABI3-regulated LEA protein abundance linked to desiccation tolerance

In contrast to orthodox seeds that acquire desiccation tolerance during maturation, recalcitrant seeds are unable to survive drying. These desiccation-sensitive seeds constitute an interesting model for comparative analysis with phylogenetically close species that are desiccation tolerant. Considering the importance of LEA (late embryogenesis abundant) proteins as protective molecules both in drought and in desiccation tolerance, the heat-stable proteome was characterized in cotyledons of the legume Castanospermum australe and it was compared with that of the orthodox model legume Medicago truncatula. RNA sequencing identified transcripts of 16 homologues out of 17 LEA genes for which polypeptides are detected in M. truncatula seeds. It is shown that for 12 LEA genes, polypeptides were either absent or strongly reduced in C. australe cotyledons compared with M. truncatula seeds. Instead, osmotically responsive, non-seed-specific dehydrins accumulated to high levels in the recalcitrant cotyledons compared with orthodox seeds. Next, M. truncatula mutants of the ABSCISIC ACID INSENSITIVE3 (ABI3) gene were characterized. Mature Mtabi3 seeds were found to be desiccation sensitive when dried below a critical water content of 0.4g H2O g DW–1. Characterization of the LEA proteome of the Mtabi3 seeds revealed a subset of LEA proteins with severely reduced abundance that were also found to be reduced or absent in C. australe cotyledons. Transcripts of these genes were indeed shown to be ABI3 responsive. The results highlight those LEA proteins that are critical to desiccation tolerance and suggest that comparable regulatory pathways responsible for their accumulation are missing in both desiccation-sensitive genotypes, revealing new insights into the mechanistic basis of the recalcitrant trait in seeds

Comparing transcriptome of orthodox and recalcitrant Legume seeds: a new model to unravel desiccation tolerance acquisition

Comparing transcriptome of orthodox and recalcitrant Legume seeds: a new model to unravel desiccation tolerance acquisitionComparing transcriptome of orthodox and recalcitrant Legume seeds: a new model to unravel desiccation tolerance acquisitio

Progress in Modeling Clad Ballooning During the NSRR RIA Tests Using ALCYONE Fuel Performance Code

International audienceALCYONE simulations of integral RIA transients performed on UO2 fuel rods prior to or within the ALPS program in the Japanese NSRR facility with stagnant liquid water coolant conditions are presented in this paper. The 11 selected tests which cover a wide range of fuel enthalpy increases (200 J/g – 800 J/g) aimed at assessing/challenging ALCYONE capabilities on four quantities of interest: clad outer surface peak temperature (293 K – 1200 K), film boiling duration (0 s – 2 s), clad residual hoop strain (0% – 25%) and transient fission gas release (2% – 25%). Despite a global consistency between measurements and ALCYONE predictions, paths are investigated to explain and reduce discrepancies. In particular, the reevaluation of fuel enthalpies by JAEA has led to revisit ALCYONE clad-to-water coolant heat exchange models which were derived from previous values of fuel enthalpies and suggested a recalibration of some of their parameters. Then, modeling the delayed gas axial flow in the free volumes of the rod is shown essential to achieve better residual hoop strain predictions in case of clad ballooning if proper timing of fission gas release, rod internal pressure increase and clad temperature elevation can be simulated. Key experimental and/or modelling research areas are shown to be at stake for future work

Characterization of a recalcitrant legume seed towards a better understanding of desiccation tolerance mechanisms

Castanospermum australe is a tree species from the Fabaceae family, native to Australia but now found in as an ornamental in countries such as South Africa and USA. Its seeds are recalcitrant and, it is phylogenetically the closest recalcitrant species to Medicago truncatula, one of the genomic and genetic models of the Fabaceae. The latter species produces seeds that are orthodox and its seed development is well characterized at the molecular level by our group. Our objective is to identify genes and molecules involved in desiccation tolerance on the basis of their differential expression/accumulation between seeds of these two species. This comparative analysis first requires the physiological and molecular characterization of C. australe recalcitrant seeds

State of the art of the conceptual designs for ASTRID control and shutdown rods

International audienceA critical look at the conceptual designs of control and shutdown rods and absorber elements, along with the lessons learnt from the operation of French fast reactors (Phénix and Super-Phénix especially) and the associated irradiation tests, has yielded improved and even innovative absorber assembly design concepts which are presented in this paper. To comply with the GEN IV objectives set for the 600 MWe Advanced Sodium Technological Reactor for Industrial Demonstration (ASTRID), these design concepts have been researched with a view to improved economy/sustainability and enhanced safety. The two main measures undertaken to achieve economy, among many others, have been to reduce the absorber subassembly dimensions and boron carbide enrichment, as well as to extend the residence time. To achieve enhanced safety, measures could include improved components and/or structural materials and guidance surface coatings/hard-facings in active shutdown systems. As part of these measures, a new kind of absorber assembly has also been designed – called SEPIA 1 – pertaining to safety devices for the passive insertion of negative reactivity in the core. Preliminary thermal-hydraulic and structural mechanical analyses have been carried out with the CADET and LICOS project codes to show their feasibility. Further detailed analyses need to be carried out to achieve optimum dimensions that comply with the RAMSES II design rules. The paper discusses the basis of the conceptual designs, giving due consideration to emerging design concepts, analysis backups and further R&D required for design qualification

SIMULATION OF RIA TRANSIENTS ON MOX FUEL RODS WITH ALCYONE FUEL PERFORMANCE CODE

International audienceAs regards Reactivity-Initiated Accidents (RIAs), the ALCYONE multidimensional fuel performance code co-developed by CEA, EDF and Framatome within the PLEIADES software environment is intended to predictively simulate the response of a fuel rod by taking account of mechanisms in a way that models the physics as closely as possible, encompassing all possible stages of the transient (PCMI and post-DNB phases) as well as various fuel/cladding material types and irradiation conditions of interest. Validated for PWR-UO2 fuels, it is now being adapted to simulate the behaviour of Zircaloy-4-based claddings shrouding MOX fuel pellets. ALCYONE V1.4 RIA-related features and modelling are first presented. The constitutive model for the oxide fuel includes cracking in tension, thermal creep and grain-boundary cracking. The modelling of grain-boundary cracking-induced fission gas release (the dominant release mechanism in RIAs) and swelling are discussed in this paper. Simulations of RIA transients performed on MOX fuel rods from the French CABRI REP-Na programme in flowing sodium coolant conditions are then compared to relevant experimental results. This paper shows to what extent ALCYONE-starting from base irradiation conditions it itself computes-is currently ready to simulate and analyse further tests on MOX fuel to be performed under prototypical PWR conditions within the CABRI International Programme. The homogeneous modelling gives satisfactory results. An alternative and heterogeneous approach may be a complementary path towards a more local description of the MOX fuel behaviour under RIA conditions: if both heterogeneous and homogeneous approaches will give the same information and results at the macroscopic level, the heterogeneous one will enable to understand, via numerical simulations, what happens at lower (meso-and microscopic) scales

The role of selection and historical factors in driving population differentiation along an elevational gradient in an island bird

International audienc