Lattice dynamics of BaFe2Se3.

This paper presents a study of the lattice dynamics in BaFe2Se3. We combined first-principle calculations, infrared measurements and a thorough symmetry analysis. Our study confirms thatPnmacannot be the space group of BaFe2Se3, even at room temperature. The phonons assignment requiresPmto be the BaFe2Se3space group, not only in the magnetic phase, but also in the paramagnetic phase at room temperature. This is due to a strong coupling between a short-range spin-order along the ladders, and the lattice degrees of freedom associated with the Fe-Fe bond length. This coupling induces a change in the bond-length pattern from an alternated trapezoidal one (as inPnma) to an alternated small/large rectangular one. Out of the two patterns, only the latter is fully compatible with the observed block-type magnetic structure. Finally, we propose a complete symmetry analysis of the BaFe2Se3phase diagram in the 0-600 K range.

Analysis of the magnetic properties of Ce3Pt23Si11: orthorhombic crystal field and mean-field approximation.

We present here a quantitative analysis of the ground state and magnetic properties of Ce3Pt23Si11, based on a crystalline electric field description within the mean-field approximation. In this face-centered cubic compound, the point group symmetry at the Ce site is orthorhombic. One main difficulty in this low symmetry case is that the CEF potential for Ce3+ ions is determined by five independent parameters, while only two magnetic excitations are observed by inelastic neutron scattering. Moreover the anisotropy of the magnetic susceptibility of the Ce ion, that permits an independent determination of the second-order CEF parameters is hidden by the cubic symmetry of the compound. A specific procedure is developed for this purpose that combines genetic algorithms and more conventional optimization methods. A set of CEF parameters is found that best reproduces the different experimental observations in both the paramagnetic and ferromagnetic phases of Ce3Pt23Si11. The analysis accounts for two seemingly contradictory properties: a strong local anisotropy that aligns the moment along a fourfold axis and a rather weak anisotropy of the bulk magnetization with an easy threefold magnetization axis. Ce3Pt23Si11 is shown to be a model system where single site anisotropies compete within a crystal structure of overall high symmetry.

3d-4f coupling and multiferroicity in frustrated Cairo Pentagonal oxide DyMn2O5.

In solid state science, multifunctional materials and especially multiferroics have attracted a great deal of attention, as they open the possibility for next generation spintronic and data storage devices. Interestingly, while many of them host coexisting 3d and 4f elements, the role of the coupling between these two magnetic entities has remained elusive. By means of single crystal neutron diffraction and inelastic neutron scattering experiments we shed light on this issue in the particular case of the multiferroic oxide DyMn2O5. This compound undergoes a first order magnetic transition from a high temperature incommensurate phase to a low temperature commensurate one. Our investigation reveals that although these two phases have very different magnetic structures, the spin excitations are quite similar indicating a fragile low temperature ground state with respect to the high temperature one. Such a rare scenario is argued to be a manifestation of the competition between the exchange interaction and 4f magnetic anisotropy present in the system. It is concluded that the magnetic structure, hence the ferroelectricity, can be finely tuned depending on the anisotropy of the rare earth.

Evidence for room temperature electric polarization in RMn(2)O(5) multiferroics.

It is established that the multiferroics RMn(2)O(5) crystallize in the centrosymmetric Pbam space group and that the magnetically induced electric polarization appearing at low temperature is accompanied by a symmetry breaking. However, both our present x-ray study-performed on compounds with R=Pr,Nd,Gd,Tb, and Dy-and first-principles calculations unambiguously rule out this picture. Based on structural refinements, geometry optimization, and physical arguments, we demonstrate in this Letter that the actual space group is likely to be Pm. This turns out to be of crucial importance for RMn(2)O(5) multiferroics since Pm is not centrosymmetric. Ferroelectricity is thus already present at room temperature, and its enhancement at low temperature is a spin-enhanced process. This result is also supported by direct observation of optical second harmonic generation. This fundamental result calls into question the actual theoretical approaches that describe the magnetoelectric coupling in this multiferroic family.

An ab initio study of magneto-electric coupling of YMnO3.

This paper proposes the direct calculation of the microscopic contributions to the magneto-electric coupling, using ab initio methods. The electrostrictive and the Dzyaloshinskii-Moriya contributions were evaluated individually. For this purpose a specific method was designed, combining density functional theory calculations and embedded fragment, explicitly correlated, quantum chemical calculations. This method allowed us to calculate the evolution of the magnetic couplings as a function of an applied electric field. We found that in YMnO3 the Dzyaloshinskii-Moriya contribution to the magneto-electric effect is three orders of magnitude weaker than the electrostrictive contribution. Strictive effects are thus dominant in the magnetic exchange evolution under an applied electric field, and by extension in the magneto-electric effect. These effects however, remain quite small, and the modifications of the magnetic excitations under an applied electric field will be difficult to observe experimentally. Another important conclusion is that it can be shown that the linear magneto-electric tensor is null due to the inter-layer symmetry operations.

[Dementia: Where are the Lewy bodies?]. / Démences : où sont les corps de Lewy ?

Dementia with Lewy bodies (DLB) is the second cause of degenerative dementia in autopsy studies. In clinical pratice however, the prevalence of DLB is much lower with important intercenter variations. Among the reasons for this low sensitivity of DLB diagnosis are (1) the imprecision and subjectivity of the diagnostic criteria; (2) the underestimation of non-motor symptoms (REM-sleep behavior disorder, dysautonomia, anosmia); mostly (3) the nearly constant association of Lewy bodies with Alzheimer's disease pathology, which dominates the clinical phenotype. With the avenue of targeted therapies against the protein agregates, new clinical scales able to apprehend the coexistence of Lewy pathology in Alzheimer's disease are expected.

Molecular and functional regulation of two NO3- uptake systems by N- and C-status of Arabidopsis plants.

Root NO3- uptake and expression of two root NO3- transporter genes (Nrt2;1 and Nrt1) were investigated in response to changes in the N- or C-status of hydroponically grown Arabidopsis thaliana plants. Expression of Nrt2;1 is up-regulated by NO3 - starvation in wild-type plants and by N-limitation in a nitrate reductase (NR) deficient mutant transferred to NO3- as sole N source. These observations show that expression of Nrt2;1 is under feedback repression by N-metabolites resulting from NO3- reduction. Expression of Nrt1 is not subject to such a repression. However, Nrt1 is over-expressed in the NR mutant even under N-sufficient conditions (growth on NH4NO3 medium), suggesting that expression of this gene is affected by the presence of active NR, but not by N-status of the plant. Root 15NO3- influx is markedly increased in the NR mutant as compared to the wild-type. Nevertheless, both genotypes have similar net 15NO3- uptake rates due to a much larger 14NO3- efflux in the mutant than in the wild-type. Expressions of Nrt2;1 and Nrt1 are diurnally regulated in photosynthetically active A. thaliana plants. Both increase during the light period and decrease in the first hours of the dark period. Sucrose supply prevents the inhibition of Nrt2;1 and Nrt1 expressions in the dark. In all conditions investigated, Nrt2;1 expression is strongly correlated with root 15NO3- influx at 0.2 mM external concentration. In contrast, changes in the Nrt1 mRNA level are not always associated with similar changes in the activities of high- or low-affinity NO3- transport systems.

Isolation of a cDNA from Arabidopsis thaliana that complements the sec14 mutant of yeast.

The SEC14 gene of Saccharomyces cerevisiae codes for a phosphatidylinositol-transfer protein (Sec14p(sc)) which is capable of transferring both phosphatidylinositol and phosphatidylcholine between membranes in vitro. Genetic and biochemical studies conducted in S. cerevisiae have shown that this protein acts as an inhibitor of phosphatidylcholine biosynthesis via the so-called Kennedy pathway only. This inhibition is controlled by the binding of phospholipids to the Sec14p(sc) protein. Here we describe the isolation of a cDNA from Arabidopsis thaliana by functional complementation of a sec14(ts) mutant of S. cerevisiae. This cDNA, designated AtSEC14, is capable of restoring the growth of the sec14(ts) mutant at the restrictive temperature of 37 degrees C. Extracellular invertase measurements indicated that the cDNA can partly restore protein secretion. In addition, the phosphatidylinositol-transfer activity measured in protein extracts is greatly enhanced in the complemented mutant strain when compared with the sec14(ts) mutant. The best sequence similarity at the amino acid level is found with the Sec14p protein of S. cerevisiae (36.5% similarity), and most of the amino acids that are thought to be involved in the binding of phospholipids in the yeast protein are conserved in the AtSEC14 gene product. Southern analysis suggests the presence of a single gene in the Arabidopsis genome, although the existence of distantly related sequences cannot be excluded. This gene is expressed in roots, leaves, flowers and siliques of Arabidopsis.

Tissue-specific expression of Arabidopsis AKT1 gene is consistent with a role in K+ nutrition.

AKT1, a putative inwardly directed K+ channel of Arabidopsis, restores long-term potassium uptake in a yeast mutant defective in K+ absorption. In this paper, the expression pattern of the gene encoding AKT1 is described. Northern blots indicate that AKT1 transcripts are preferentially accumulated in Arabidopsis roots. Owing to the difficulties in producing large quantities of Arabidopsis roots under hydroponic conditions, experiments were undertaken with Brassica napus, a related species. Potassium starvation experiments on B. napus plants show that changes in the K+ status of the organs do not modify AKT1 mRNA accumulation. Western blot analysis of B. napus proteins confirms the presence of AKT1 at the root plasma membrane. Tissue-specific expression directed by the Arabidopsis AKT1 gene promoter was investigated by analysis of beta-glucuronidase (GUS) activity in transgenic Arabidopsis containing an AKT1-GUS gene fusion. As determined by fluorimetric and histochemical tests, the AKT1 promoter directs preferential expression in the peripheral cell layers of root mature regions. The discrete activity found in leaves relates to leaf primordia and to small groups of cells, hydathodes, found on toothed margins of the Arabidopsis leaf lamina. These data are discussed with regard to a possible role of AKT1 in K+ nutrition of plants.

Organization and expression of the gene coding for the potassium transport system AKT1 of Arabidopsis thaliana.

We have isolated and sequenced the genomic clone coding for the potassium transport system AKT1 of Arabidopsis thaliana. Southern blot analysis indicated that the gene is present in one copy in the Arabidopsis genome. The coding sequence is interrupted by ten introns. Sequence comparisons of AKT1 polypeptide with the voltage-gated inward rectifying Arabidopsis K+ channel KAT1, and with voltage- or cyclic nucleotide-gated channels from insects and mammals, revealed a highly conserved domain found specifically in both plant polypeptides, and corresponding to about the last 50 amino acids of their C-terminal region. Northern blot analysis of AKT1 expression in Arabidopsis seedlings indicated that AKT1 is preferentially expressed in roots. No transcript was detected in extracts from heterotrophic suspension culture cells. Depleting K+ in the Arabidopsis seedling culture medium for 4 days led to a strong decrease in K+ tissue content (ca. 50%), but did not affect AKT1 transcript level.

Mutations that enhance the cap2 null mutant phenotype in Saccharomyces cerevisiae affect the actin cytoskeleton, morphogenesis and pattern of growth.

Mutations conferring synthetic lethality in combination with null mutations in CAP2, the gene encoding the beta subunit of capping protein of Saccharomyces cerevisiae, were obtained in a colony color assay. Monogenic inheritance was found for four mutations, which were attributed to three genetic loci. One mutation, sac6-69, is in the gene encoding fimbrin, another actin-binding protein, which was expected because null mutations in SAC6 and CAP2 are known to be synthetic-lethal. The other two loci were designated slc for synthetic lethality with cap2. These loci include the mutations slc1-66, slc1-87 and slc2-107. The slc mutations are semi-dominant, as shown by incomplete complementation in slc/SLC cap2/cap2 heterozygotes. The slc mutations and sac6-69 interact with each other, as shown by enhanced phenotypes in diheterozygotes. Moreover, the haploid slc2-107 sac6-69 double mutant is inviable. In a CAP2 background, the slc mutations lead to temperature and osmotic sensitivity. They alter the distribution of the actin cytoskeleton, including deficits in the presence of actin cables and the polarization of cortical actin patches. The slc mutations also lead to a pseudomycelial growth pattern. Together these results suggest that slc1 and slc2 encode components of the actin cytoskeleton in yeast and that the actin cytoskeleton can regulate the patterns of growth.

Nuclease sensitivity and functional analysis of a maize histone H3 gene promoter.

A 1 kb region of a maize H3 histone gene promoter has been analysed at a structural and functional level. Micrococcal nuclease digestion of isolated nuclei showed that the promoter region is organized into nucleosomes but a zone extending over approximately one nucleosome (20 to 230 bp upstream of the TATA box) displays remarkable accessibility to digestion. Three DNase I-hypersensitive sites were found within this zone at the vicinity of consensus sequences, some of which are already known to act as cis elements. This promoter region is able to direct faithful expression of the GUS reporter gene in meristematic tissues of transgenic tobacco plants.

A plant histone gene promoter can direct both replication-dependent and -independent gene expression in transgenic plants.

Chimeric genes containing the beta-glucuronidase (GUS) gene under the control of different Arabidopsis histone H3 and H4 promoters were found to be highly expressed in transient expression experiments using tobacco protoplasts. The activity of one of these promoters, H4A748, was further analyzed. The kinetics of H4A748-GUS activity are very similar to these of a CaMV 35S-GUS constitutive gene during protoplast culture. No increase in H4A748-GUS activity was found after 24 h of protoplast culture when DNA synthesis starts, nor was the GUS activity affected when an inhibitor of DNA synthesis was included in the culture medium. This failure to detect any replication-dependent activity is most likely to be due to the fact that transient transcription of the introduced construct is restricted to the first 24 h following transfection. Stable integration of the H4A748-GUS gene into tobacco plants showed that the histone promoter could confer increased expression in meristematic tissues but it is also expressed to significant levels in non-proliferating tissues. Protoplasts prepared from these transgenic tobacco plants were cultivated under different conditions that affect DNA synthesis. Analysis of H4A748-GUS activity revealed (i) the existence of a basal replication-independent activity and (ii) a replication-dependent activity induced in parallel with DNA synthesis. These results show that the histone H4 promoter is able to direct both replication-dependent and -independent gene expression.

An internal standard improves the reliability of transient expression studies in plant protoplasts.

Transient expression of foreign genes introduced on a plasmid into isolated plant protoplasts is widely used to study the control of gene expression. Unfortunately, many experimental variables implicated in this technique are difficult or impossible to control, resulting in a disturbing degree of variability between otherwise identical experiments. We have studied the co-expression of two constitutively expressed genes located on the same plasmid. This has allowed us to identify the lot of plasmid DNA as an important source of variation, along with the protoplast lot. Plasmid DNA concentration was found to be of minor importance. Since the variation of expression level of the two genes was identical for the two genes in all experiments, we propose the use of an internal standard in all comparative transient expression studies, which allows the reduction of the variation between experiments by one order of magnitude.

[Must acute carotid thrombosis be surgically treated? 1962-1973: long-term results]. / Fallait-il opérer les thromboses carotidiennes aiguës? 1962-1973: résultats à long terme.

A study of long-term results (mean follow-up: 10.6 years) in 22 patients operated on for acute carotid thrombosis between 1962 and 1973 is reported. In most instances, surgery was performed at the acute phase of a massive cerebrovascular occlusion, usually more than 8 hours after onset (10 cases). Five of these patients (22%) died in the postoperative period. Eight (35%) recovered without residual disease. In six, the condition improved, while it remained unchanged or worsened in three (14%). There were ten delayed deaths, including two from a recurrent cerebrovascular episode and four from cardiac disease. The actuarial survival curve does not differ from that of patients treated conservatively, with rates being 60% at five years, 36% at ten years and 28% at thirteen years. The quality of certain postoperative results suggests that surgical indications at the acute stage of carotid occlusion be reviewed. The study of thirty series from the literature (1 046 cases) shows a 17% mortality rate, while 50% of patients recover or improve. This mortality is significantly lower in recent statistics, under 10%: this improvement may be ascribable to more rigid surgical indications (delay under 6 hours, operation in variable neurologic deficiencies, early diagnosis by the Doppler procedure, better postoperative management). The authors conclude that surgical management of acute carotid thrombosis should no longer be systematically dismissed.