REMPLISSAGE EN AZOTE DES TISSUS REPRODUCTEURS DE BRASSICA NAPUS L. (ESTIMATION DES FLUX PAR MARQUAGE ISOTOPIQUE, CARACTERISATION DES PROTEINES IMPLIQUEES DANS LA MISE EN RESERVE ET DES FACTEURS INDUISANT LEUR ACCUMULATION)

CAEN-BU Sciences et STAPS (141182103) / SudocSudocFranceF

Methods for preparing polymer-decorated single exchange-biased magnetic nanoparticles for application in flexible polymer-based films

Background: Magnetic nanoparticles (NPs) must not only be well-defined in composition, shape and size to exhibit the desired properties (e.g., exchange-bias for thermal stability of the magnetization) but also judiciously functionalized to ensure their stability in air and their compatibility with a polymer matrix, in order to avoid aggregation which may seriously affect their physical properties. Dipolar interactions between NPs too close to each other favour a collective magnetic glass state with lower magnetization and coercivity because of inhomogeneous and frustrated macrospin cluster freezing. Consequently, tailoring chemically (through surface functionalization) and magnetically stable NPs for technological applications is of primary importance.Results: In this work, well-characterized exchange-biased perfectly epitaxial CoxFe3−xO4@CoO core@shell NPs, which were isotropic in shape and of about 10 nm in diameter, were decorated by two different polymers, poly(methyl methacrylate) (PMMA) or polystyrene (PS), using radical-controlled polymerization under various processing conditions. We compared the influence of the synthesis parameters on the structural and microstructural properties of the resulting hybrid systems, with special emphasis on significantly reducing their mutual magnetic attraction. For this, we followed two routes: the first one consists of the direct grafting of bromopropionyl ester groups at the surface of the NPs, which were previously recovered and redispersed in a suitable solvent. The second route deals with an “all in solution” process, based on the decoration of NPs by oleic acid followed by ligand exchange with the desired bromopropionyl ester groups. We then built various assemblies of NPs directly on a substrate or suspended in PMMA.Conclusion: The alternative two-step strategy leads to better dispersed polymer-decorated magnetic particles, and the resulting nanohybrids can be considered as valuable building blocks for flexible, magnetic polymer-based devices

Dynamics of Nitrogen Uptake and Mobilization in Field-grown Winter Oilseed Rape (Brassica napus) From Stem Extension to Harvest. II. An 15 N-labelling-based Simulation Model of N Partitioning Between Vegetative and Reproductive Tissues

International audienceBackground and Aims Oilseed rape (Brassica napus) has often been used as a catch crop to deal with the issue of N leaching, but for this to be effective, prediction of the crop's N uptake capability and N partitioning is required. The aim of this work was to build a compartmental model of N dynamics in oilseed rape, based on the kinetic description of N uptake, partitioning and mobilization in each organ. Model In this study, logistic and exponential equations were fitted to the N relations of each compartment, especially the leaf at each node. Data previously obtained from an 15 N-labelling field experiment was used to quantify the partitioning of total N content, the allocation of N taken up and subsequent changes in the sink/source status for endogenous N in each tissue throughout the growth cycle. Key Results and Conclusions This modelling approach provides a unique tool for the quantitative estimation of cycling of endogenous N in relation to changes in N uptake at the whole-plant level. Furthermore, as oilseed rape is known to release large amounts of N to the soil during spring through leaf loss, this model was used to identify potential methods for improving the N harvest index of the crop. Simulations showed that N content or yield could be improved by 15 % by optimizing N transfer from vegetative to reproductive tissues and by reducing the residual %N (DW) in abscised leaves

Modeling Nitrogen Uptake in Oilseed Rape cv Capitol during a Growth Cycle Using Influx Kinetics of Root Nitrate Transport Systems and Field Experimental Data

International audienceThe use of kinetic equations of NO 3 transport systems in oilseed rape (Brassica napus), determined by 15 NO 3 labeling under controlled conditions, combined with experimental field data from the INRA-Châlons rape database were used to model NO 3 uptake during the plant growth cycle. The quantitative effects of different factors such as day/night cycle, ontogenetic stages, root temperature, photosynthetically active radiation, and soil nitrate availability on different components of the constitutive high-affinity transport systems, constitutive low-affinity transport systems, inducible low-affinity transport systems, and inducible high-affinity transport systems of nitrate were then determined to improve the model's predictions. Simulated uptake correlated well with measured values of nitrogen (N) uptake under field conditions for all N fertilization rates tested. Model outputs showed that the high-affinity transport system accounted for about 89% of total NO 3 uptake (18% and 71% for constitutive high-affinity transport systems and inducible high-affinity transport systems, respectively) when no fertilizer was applied. The low-affinity transport system accounted for a minor proportion of total N uptake, and its activity was restricted to the early phase of the growth cycle. However, N fertilization in spring increased the duration of its contribution to total N uptake. Overall, data show that this mechanistic and environmentally regulated approach is a powerful means to simulate total N uptake in the field with the advantage of taking both physiologically regulated processes at the overall plant level and specific nitrate transport system characteristics into account

Effects of altered source–sink relationships on N allocation and vegetative storage protein accumulation in Brassica napus L.

Growth, N allocation and involvement of vegetative storage protein (VSP) in the temporary N accumulation were evaluated infield conditions of oilseed rape grown with altered source-sink relationships (by leaf halving or removal of stem, flowers or pods). As compared to control plants, removal of half the leaves early in the vegetative period-induced delayed flowering, a lower accumulation of the taproot 23 kDa VSP and finally a decreased pod production. Stem removal, when flower buds were still covered by leaves, increased taproot biomass and its N concentration but prevented taproot VSP accumulation. Continuous removal of flowers or pods increased the shoot growth and N uptake duration (for deflowered plants). When foliar senescence finally occurred in plants continuously subjected to flower or pod removal, the N was allocated in a large proportion to buffering organs (taproot and stem) and it led to an increased and late VSP accumulation without subsequent mobilization. In control plants, N stored as VSP was remobilized during late pod filling concomitant with stem and taproot sink to source transition. A summarized scheme of N source-sink relationships during the growth cycle is presented where the 23 kDa VSP may act as an N storage buffer in response to an asynchronism between mobilization of foliar N and N requirements for seed formation. (C) 2004 Elsevier Ireland Ltd. All rights reserved

Magnetic filaments for anisotropic composite polymers

International audienceThe use of contactless magnetic forces meets numerous needs in microelectromechanical systems (MEMS) or microfluidic devices. In this view, heterogeneous materials integrating magnetic nanostructures within a non-magnetic matrix such as polymer can produce local variations of magnetic field, at the sub-micrometer scale. Here we report on the synthesis of magnetic composites using electrospun nanofilaments and a polydimethylsiloxane (PDMS) matrix. Varying the precursor nature and heat treatment conditions, we obtained single phase filaments of Fe, FeNi, and MFe2O4 (M = Co, Fe, Ni). Thanks to a fine investigation of their structure and morphology, it was possible to measure from magnetically-soft (µ0HC ≤ 5 mT) to relatively hard (µ0HC up to 93 mT, MR/MS up to 0.5) behaviors. The common one-dimensional shape of these filaments leads to an anisotropic magnetic response. This can be exploited to achieve self-organization of the filaments in arrays within the non-magnetic matrix. We show the first step towards the development of magnetically anisotropic membranes of PDMS with 0.23 wt% Fe filaments. These composite materials are promising for implementing magnetic functions in microsystems while circumventing complex micro-fabrication steps

Anisotropic ferromagnetic polymer: A first step for their implementation in microfluidic systems

International audienceHere we report on the influence of anisotropic microstructure on the performances of magnetically soft micro-patterns intended to integrate microfluidic systems. These micro-patterns are made of a composite obtained by mixing carbonyl iron particles with polydimethylsiloxane, which offers practical integration advantages. We investigated a wide range of magnetic particle loadings, from 10wt% to 83wt%, reaching magnetization as high as 630 kA/m. A homogeneous field was applied during the polymer's cross-linking phase so that to obtain a 1D arrangement of the particles in the solidified polymer, along the field direction. Here we present the results obtained for square-based micro-pillars prepared under a magnetic field applied along one of its diagonal. We assessed the magnetic anisotropy owing to the particles' spatial arrangement by comparing the magnetization processes along the two diagonals of the micro-pillar's base. The magnetic susceptibilities along the two directions differ from a factor greater than three. The results can be described in terms of high aspect ratio and porous magnetic agglomerates. C 2016 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License. [http://dx