Identification and disruption of a plant shaker-like outward channel involved in K+ release into the xylem sap

SKOR, a K+ channel identified in Arabidopsis, displays the typical hydrophobic core of the Shaker channel superfamily, a cyclic nucleotide-binding domain, and an ankyrin domain. Expression in Xenopus oocytes identified SKOR as the first member of the Shaker family in plants to be endowed with outwardly rectifying properties. SKOR expression is localized in root stelar tissues. A knockout mutant shows both lower shoot K+ content and lower xylem sap K+ concentration, indicating that SKOR is involved in K+ release into the xylem sap toward the shoots. SKOR expression is strongly inhibited by the stress phytohormone abscisic acid, supporting the hypothesis that control of K+ translocation toward the shoots is part of the plant response to water stress.     

Fourier-transform infrared spectra of fatty acid salts—Kinetics of high-oleic sunflower oil saponification

Sodium, lithium, and calcium soaps obtained by saponification of high-oleic sunflower oil were studied by Fourier-transform infrared spectroscopy. Spectra of crude mixtures containing soap, glycerin, residual alkali, and triacylglycerols were compared to those of pure soaps obtained from fatty acids. The infrared spectra of crude soaps showed the same characteristic bands as pure ones. The absorption bands of asymmetric (ω₂) and symmetric (ω₁) stretching vibrations of the carboxylate group indicated that the metal-oxygen bonds of these soaps had an ionic character whose strength differed from one cationic counterion to another. Once the characteristic absorption bands of the soaps were assigned, a kinetics study of saponification was performed. Saponification by sodium, anhydrous lithium, and calcium hydroxides was an autocatalytic reaction, characterized by an S-shaped kinetics curve, whereas saponification by aqueous lithium hydroxide was stoichiometric. The structure of the metal-oxygen bond played a role in the kinetic mechanisms.     

Intraoperative radiotherapy in 1997

Codon usage bias of 1,117 Drosophila melanogaster genes, as well as fewer D. pseudoobscura and D. virilis genes, was examined from the perspective of relative abundance of isoaccepting tRNAs and their changes during development. We found that each amino acid contributes about equally and highly significantly to overall codon usage bias, with the exception of Asp which had very low contribution to overall bias. Asp was also the only amino acid that did not show a clear preference for one of its synonymous codons. Synonymous codon usage in Drosophila was consistent with "optimal" codons deduced from the isoaccepting tRNA availability. Interestingly, amino acids whose major isoaccepting tRNAs change during development did not show as strong bias as those with developmentally unchanged tRNA pools. Asp is the only amino acid for which the major isoaccepting tRNAs change between larval and adult stages. We conclude that synonymous codon usage in Drosophila is well explained by tRNA availability and is probably influenced by developmental changes in relative abundance.     

Influence of multiple scattering on three-dimensional imaging with optical diffraction tomography

Optical diffraction tomography is an imaging technique that permits retrieval of the map of permittivity of an object from its scattered far field. Most reconstruction procedures assume that single scattering is dominant so that the scattered far field is linearly linked to the permittivity. In this work, we present a nonlinear inversion method and apply it to complex three-dimensional samples. We show that multiple scattering permits one to obtain a power of resolution beyond the classical limit imposed by the use of propagative incident and diffracted waves. Moreover, we stress that our imaging method is robust with respect to correlated and uncorrelated noise.     

Effective-medium theory for finite-size aggregates

We propose an effective-medium theory for random aggregates of small spherical particles that accounts for the finite size of the embedding volume. The technique is based on the identification of the first two orders of the Born series within a finite volume for the coherent field and the effective field. Although the convergence of the Born series requires a finite volume, the effective constants that are derived through this identification are shown to admit of a large-scale limit. With this approach we recover successively, and in a simple manner, some classical homogenization formulas: the Maxwell Garnett mixing rule, the effective-field approximation, and a finite-size correction to the quasi-crystalline approximation (QCA). The last formula is shown to coincide with the usual low-frequency QCA in the limit of large volumes, while bringing substantial improvements when the dimension of the embedding medium is of the order of the probing wavelength. An application to composite spheres is discussed.     

Superresolution in total internal reflection tomography

We simulate a total internal reflection tomography experiment in which an unknown object is illuminated by evanescent waves and the scattered field is detected along several directions. We propose a full-vectorial three-dimensional nonlinear inversion scheme to retrieve the map of the permittivity of the object from the scattered far-field data. We study the role of the solid angle of illumination, the incident polarization, and the position of the prism interface on the resolution of the images. We compare our algorithm with a linear inversion scheme based on the renormalized Born approximation and stress the importance of multiple scattering in this particular configuration. We analyze the sensitivity to noise and point out that using incident propagative waves together with evanescent waves improves the robustness of the reconstruction.     

Full wave optical profilometry

We show that tomographic diffractive microscopy can be used for profilometry applications with high transverse resolution. We present an iterative reconstruction procedure, based on a rigorous wave scattering model, that permits us to retrieve the profile of rough metallic interfaces from the complex scattered field. The transversal resolution is subwavelength, and can even fall below the classical resolution limit if the profile is rough enough for multiple interactions to occur. Large profiles, with tens of wavelength size, can be investigated.     

Inward and outward rectifying potassium currents in Saccharomyces cerevisiae mediated by endogenous and heterelogously expressed ion channels

Disruption of genes encoding endogenous transport proteins in Saccharomyces cerevisiae has facilitated the recent cloning, by functional expression, of cDNAs encoding K+ channels and amino acid transporters from the plant Arabidopsis thaliana [1-4]. In the present study, we demonstrate in whole-cell patch clamp experiments that the inability of trk1deltatrk2delta mutants of S. cerevisiae to grow on submillimolar K+ correlates with the lack of K+ inward currents, which are present in wild-type cells, and that transformation of the trk1deltatrk2delta double-deletion mutant with KAT1 from Arabidopsis thaliana restores this phenotype by encoding a plasma membrane protein that allows large K+ inward currents. Similar K+ inward currents are induced by transformation of a trk1 mutant with AKT1 from A. thaliana.