Identifying Natural Products (NPs) as potential UPR inhibitors for crop protection

As far as the future of agriculture is concerned, one major challenge will be to face an expected increase in health risks due to pesticides together with a lower efficiency of crop treatments. Therefore it is today necessary to develop new strategies to enhance the effectiveness and sustainability of current control methods. The so-called “Alternaria Leaf Spot“ is a common disease of crucifers caused by the fungal pathogen Alternaria brassicicola which affects different crops including cabbage, kale, Brussels sprout, cauliflower and broccoli. Indole phytoalexins camalexin and brassinin play in planta a key role in crop protection against this necrotrophic agent. However it has been shown that mutants become phytoalexin-resistant by activating at least three signaling pathways named as Cell Wall Integrity (CWI), High Osmolarity Glycerol (HOG) and Unfolded Protein Response (UPR) [1,2]. The latter is particularly involved in the fungus protection against phytoalexins since UPR deficient avirulent mutants of A. brassicicola appear as hypersensitive to camalexin and brassinin [3]. Since very few UPR inhibitors such as the synthetic STF-083010 [4] are known we decided to develop an original screening assay, detecting the production of a HAC1 fluorescence-induced protein, i.e. a transcriptional activator involved in the UPR pathway, in Saccharomyces cerevisiae cultures (Figure 1). The preliminary screening of an in-house NPs library [c.a. 70 compounds (polyphenols, terpenoids and alkaloids)] clearly revealed aescin (Aesculus hippocastanum)] as a potential UPR inhibitor

Tuning complex shapes in Pt(0) nanoparticles : from cubic dendrites to five-fold stars

A platinum star performance: Quasi-single-crystalline Pt nanoparticles with peculiar morphologies—cubic dendrites, planar tripods, and fivefold stars—were synthesized in high yield. Shape selectivity was achieved by finely tuning the growth kinetics under a dihydrogen atmosphere

FORC signatures and switching-field distributions of dipolar coupled nanowire-based hysterons

International audienceAnalysis of first-order reversal curves (FORCs) is a powerful tool to probe irreversible switching events in nanomagnet assemblies. As in essence switching events are related to the intrinsic properties of the constituents and their interactions, resulting FORC diagrams contain much information that can be crosslinked and complex to deconvoluate. In order to quantify the relevant parameters that drive the FORC diagrams of arrays of perpendicularly magnetized nanomagnets, we present step-by-step simulations of assemblies of hysterons to determine the specific signatures related to different known inputs. While we explored the consequences of dipolar interactions using either mean field or magnetostatic approaches, we completed by taking the hysteron switching-field distribution (SFD) as either normal or log-normal. We demonstrated that the transition between FORC diagrams composed of an isolated interaction field distribution (IFD) and a wishbone shape operates via the SFD deviation, , in the presence of a weakly dispersed interaction field. In the presence of a magnetostatic interaction field, the IFD profile is peaked and a coercive field distribution (CFD) sums to the IFD as increases. A transition between IFD+CFD and wishbone shapes is clearly demonstrated as a function of the interaction field deviation. In addition, we demonstrate that whatever the considered cases, can be quantitatively extracted from the FORC diagrams within an error inferior to 10%. These findings are of interest for dipolar coupled perpendicularly magnetized nanomagnets, as in assemblies of magnetic nanowires and nanopillars, as well as bit patterned media

Effects of layering on the magnetostatic interactions in microstructures of CoxCu1-x/Cu nanowires

Arrays of electrodeposited CoCu/Cu multilayered nanowires have been characterized by ferromagnetic resonance and magnetometry measurements in order to study the effect of the dipolar interactions on the effective anisotropy field as a function of the magnetic and nonmagnetic layer thicknesses. Breaking the continuous cylinder geometry results in a reduction of the effective anisotropy field, which can be modified over a large range of values starting from 7 kOe in the case of nonlayered continuous nanowires down to nearly zero for the thinnest magnetic layers. An analytical model is presented to describe the magnetostatic interactions between magnetic layers and their effect on the total anisotropy field which shows a very good agreement with the experiments. Moreover, the model allows generalizing the description of the effective magnetostatic field as a function of the aspect ratio of both the magnetic and the nonmagnetic layers for multilayered nanowires of any combination of materials. A general anisotropy diagram is presented that describes the geometrical conditions required to obtain an easy axis parallel or perpendicular to the wire axis, thus providing a guide for the engineering and fine-tuning of the magnetic properties of these systems

Magnetism of single-crystalline Co nanorods

We report on the synthesis and preparation of oriented nanomaterials of single crystalline metallic Co nanorods of 6 nm in diameters and two different aspect ratios (7 and 15). They display optimized magnetic properties, with a spontaneous magnetization just below the bulk one, and large coercive fields (up to 6.5 kOe at 300 K) as a result of coherent switching (i.e., Stoner and Wohlfarth mechanism). We measured a strong effective anisotropy very close to the expected value resulting from the sum of shape and magnetocrystalline contributions. (C) 2009 American Institute of Physics. [doi:10.1063/1.3237157

Towards a room temperature organic spin valve: structural, magnetic and transport properties of Fe3O4/PTCTE/Co devices

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Transport polarisé en spin dans des vannes de spin organiques à base de dérivés de thiophènes

National audienc

Magnétorésistance dans des vannes de spin organiques à base d'un dérivé de thiophène donneur d'électrons

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