Etude par spectroscopie EXAFS au seuil K du cuivre des phases cristalline et colomnaire du stéarate de cuivre

Copper-K edge EXAFS spectroscopy has been used to probe the local environment of copper atoms in the crystalline and columnar mesomorphic phases of copper stearate. In the columns of the mesophase, polar groups are stacked one over the other very regularly ; the soap molecules are dimerized, and form binuclear complexes like in the crystalline state. The copper atoms are closer within a single dimer (2.7 Å) than between two successive dimers (3.2 Å) along the axis of the column in the mesophase.La spectroscopie EXAFS au seuil K du cuivre a été utilisée pour décrire l'environnement local des atomes de cuivre dans les phases cristalline et mésomorphe colomnaire du stéarate de cuivre. Dans les colonnes de la phase mésomorphe, les groupes polaires s'empilent de manière très régulière ; les molécules de savon y interviennent à l'état dimérisé, formant des complexes binucléaires de géométrie « plan-carré » comme à l'état cristallin. Les atomes de cuivre sont beaucoup plus proches entre eux à l'intérieur d'un même dimère (2,7 Å) qu'entre deux dimères successifs (3,2 Å) le long de l'axe des colonnes de la phase mésomorphe

Copper K edge EXAFS spectroscopy of the crystalline and columnar phases of copper (II) carboxylates

EXAFS spectra were obtained at the copper-K edge for a series of binuclear copper (II) complexes of fatty acids with 6,12,18 and 22 carbon atoms, in both their crystalline phase and their columnar mesophase. Curve-fitting analysis, using backscattering phases and amplitudes obtained from the structurally characterized copper (II) acetate and copper (II) propionate, gave comparative information on the coordination spheres of copper in both phases. It appeals that the binuclear structure of the complexes and the five-coordination of copper are maintained in the columnar mesophase, with insignificant changes in bond lengths of the binuclear core

The availability of filament ends modulates actin stochastic dynamics in live plant cells.

International audienceA network of individual filaments that undergoes incessant remodeling through a process known as stochastic dynamics comprises the cortical actin cytoskeleton in plant epidermal cells. From images at high spatial and temporal resolution, it has been inferred that the regulation of filament barbed ends plays a central role in choreographing actin organization and turnover. How this occurs at a molecular level, whether different populations of ends exist in the array, and how individual filament behavior correlates with the overall architecture of the array are unknown. Here we develop an experimental system to modulate the levels of heterodimeric capping protein (CP) and examine the consequences for actin dynamics, architecture, and cell expansion. Significantly, we find that all phenotypes are the opposite for CP-overexpression (OX) cells compared with a previously characterized cp-knockdown line. Specifically, CP OX lines have fewer filament-filament annealing events, as well as reduced filament lengths and lifetimes. Further, cp-knockdown and OX lines demonstrate the existence of a subpopulation of filament ends sensitive to CP concentration. Finally, CP levels correlate with the biological process of axial cell expansion; for example, epidermal cells from hypocotyls with reduced CP are longer than wild-type cells, whereas CP OX lines have shorter cells. On the basis of these and other genetic studies in this model system, we hypothesize that filament length and lifetime positively correlate with the extent of axial cell expansion in dark-grown hypocotyls

Strigolactone analog GR24 triggers changes in PIN2 polarity, vesicle trafficking and actin filament architecture

Strigolactones (SLs) are plant hormones that regulate shoot and root development in a MAX2-dependent manner. The mechanism underlying SLs' effects on roots is unclear. We used root hair elongation to measure root response to SLs. We examined the effects of GR24 (a synthetic, biologically active SL analog) on localization of the auxin efflux transporter PIN2, endosomal trafficking, and F-actin architecture and dynamics in the plasma membrane (PM) of epidermal cells of the primary root elongation zone in wildtype (WT) Arabidopsis and the SL-insensitive mutant max2. We also recorded the response to GR24 of trafficking (tir3), actin (der1) and PIN2 (eir1) mutants. GR24 increased polar localization of PIN2 in the PM of epidermal cells and accumulation of PIN2-containing brefeldin A (BFA) bodies, increased ARA7-labeled endosomal trafficking, reduced F-actin bundling and enhanced actin dynamics, all in a MAX2-dependent manner. Most of the der1 and tir3 mutant lines also displayed reduced sensitivity to GR24 with respect to root hair elongation. We suggest that SLs increase PIN2 polar localization, PIN2 endocytosis, endosomal trafficking, actin debundling and actin dynamics in a MAX2-dependent fashion. This enhancement might underlie the WT root's response to SLs, and suggests noncell autonomous activity of SLs in roots. © 2014 New Phytologist Trust

Arabidopsis response to low-phosphate conditions includes active changes in actin filaments and PIN2 polarization and is dependent on strigolactone signalling

© The Author 2015. Published by Oxford University Press on behalf of the Society for Experimental Biology. Strigolactones (SLs) are plant hormones that regulate the plant response to phosphate (Pi) growth conditions. At least part of SL-signalling execution in roots involves MAX2-dependent effects on PIN2 polar localization in the plasma membrane (PM) and actin bundling and dynamics. We examined PIN2 expression, PIN2 PM localization, endosome trafficking, and actin bundling under low-Pi conditions: a MAX2-dependent reduction in PIN2 trafficking and polarization in the PM, reduced endosome trafficking, and increased actin-filament bundling were detected in root cells. The intracellular protein trafficking that is related to PIN proteins but unassociated with AUX1 PM localization was selectively inhibited. Exogenous supplementation of the synthetic SL GR24 to a SL-deficient mutant (max4) led to depletion of PIN2 from the PM under low-Pi conditions. Accordingly, roots of mutants in MAX2, MAX4, PIN2, TIR3, and ACTIN2 showed a reduced low-Pi response compared with the wild type, which could be restored by auxin (for all mutants) or GR24 (for all mutants except max2-1). Changes in PIN2 polarity, actin bundling, and vesicle trafficking may be involved in the response to low Pi in roots, dependent on SL/MAX2 signalling