Serodetection of viruses associated to barley yellow dwarf (BYD) on cereals in Algeria

La recherche des virus associés à la jaunisse nanisante de l'orge et de leurs vecteurs a été effectuée dans différentes zones céréalieres en Algérie (Guelma, Constantine, Alger, Sidi-bélabès, Adrar) en 1997 et 1998. Le Rhopalosiphum padi est présent dans toutes les zones de culture, alors que R. maidis, Sitobion avenae, S. fragariae et Schizaphis graminum ne montrent qu'une distribution locale. Dans la plupart des parcelles, on observe un nanisme et jaunissement de l'orge (Hordeum vulgare), un rougissement et un nanisme de l'avoine (Avena sativa) et du blé (Triticum aestivum). Des tests sérologiques ont été effectués sur ces cultures en DAS-ELISA (RMV et SGV) ou en TAS-ELISA révélés par un anticorps monoclonal du CYDV-RPV et par différents anticorps monoclonaux du BYDV-PAV (CpA et CpB) et du BYDV-MAV. Le BYDV-PAV est mis en évidence dans toutes les zones étudiées. Peu de plantes se sont révélées porteuses des autres virus (RMV, SGV, BYDV-MAV, CYDV-RPV). Les fréquences relatives des sérotypes BYDV-PAV CpA et CpB sont variables suivant les cultures et les années. Les symptômes induits par les isolats des sérotypes BYDV-PAV CpA et BYDV-PAV CpB d'Algérie sur l'orge sont légers à graves. Le comportement de 21 isolats de BYDV-MAV a été analysé vis-à-vis d'anticorps monoclonaux distinguant deux sérotypes de ce virus. Uniquement un sérotype, le plus répandu en Europe, a été mis en évidence.Surveys on viruses associated with Barley Yellow Dwarf (BYD) and their vectors were carried out in Algerian cereal areas (Guelma, Constantine, Algiers, Sidi-belabes, Adrar) in 1997 and 1998. Rhopalosiphum padi was present in all zones of culture, whereas R. maidis, Sitobion avenae, S. fragariae and Schizaphis graminum had only local distributions. In most areas BYD-like symptoms, i.e. dwarfing and yellowing of barley (Hordeum vulgare), dwarfing and reddening of oat (Avena sativa) and wheat (Triticum aestivum), were observed. Serological tests were done on these crops using DAS-ELISA (RMV and SGV) or TAS-ELISA using monoclonal antibodies specifie to CYDV-RPV or using different variant specifie BYDV-PAV (CpA and CpB) and BYDV-MAV monoclonal antibodies. BYDV-PAV was prevalent and few plant samples carrying RMV, SGV, BYDV-MAV or CYDV-RPV were detected. The relative frequencies of BYDV-PAV CpA and CpB serotypes were variable depending on the area and the crop season. The range of symptoms induced on barley by both Algerian BYDV-PAV CpB and BYDV-PAV CpA serotypes was mild to severe. Twenty-one BYDV-MAV isolates were compared using monoclonal antibodies, which distinguish two serotypes of this virus. Only one serotype was detected. This same serotype is also the most prevalent in Europe

Collisional perturbation of radio-frequency E1 transitions in an atomic beam of dysprosium

We have studied collisional perturbations of radio-frequency (rf) electric-dipole (E1) transitions between the nearly degenerate opposite-parity levels in atomic dysprosium (Dy) in the presence of 10 to 80 $\mu$Torr of H$_\text{2}$, N$_\text{2}$, He, Ar, Ne, Kr, and Xe. Collisional broadening and shift of the resonance, as well as the attenuation of the signal amplitude are observed to be proportional to the foreign-gas density with the exception of H$_2$ and Ne, for which no shifts were observed. Corresponding rates and cross sections are presented. In addition, rates and cross sections for O$_2$ are extracted from measurements using air as foreign gas. The primary motivation for this study is the need for accurate determination of the shift rates, which are needed in a laboratory search for the temporal variation of the fine-structure constant [A. T. Nguyen, D. Budker, S. K. Lamoreaux, and J. R. Torgerson, Phys. Rev. A \textbf{69}, 22105 (2004)].Comment: 11 pages, 8 figure

Phonon anomalies at the valence transition of SmS : An inelasticX-ray scattering study under pressure

The phonon dispersion curve of SmS under pressure was studied by inelastic x-ray scattering around the pressure-induced valence transition. A significant softening of the longitudinal acoustic modes propagating along the [111] direction was observed spanning a wide $q$ region from ($\frac{2\pi}{3a},\frac{2\pi}{3a},\frac{2\pi}{3a}$) up to the zone boundary as SmS becomes metallic. The largest softening occurs at the zone boundary and stays stable up to the highest measured pressure of 80 kbar while a gradual hardening of the low $q$ modes simultaneously appears. This phonon spectrum indicates favorable conditions for the emergence of pressure-induced superconductivity in SmS.Comment: 4 pages, 3 figure

Large Anomalous Hall effect in a silicon-based magnetic semiconductor

Magnetic semiconductors are attracting high interest because of their potential use for spintronics, a new technology which merges electronics and manipulation of conduction electron spins. (GaMn)As and (GaMn)N have recently emerged as the most popular materials for this new technology. While Curie temperatures are rising towards room temperature, these materials can only be fabricated in thin film form, are heavily defective, and are not obviously compatible with Si. We show here that it is productive to consider transition metal monosilicides as potential alternatives. In particular, we report the discovery that the bulk metallic magnets derived from doping the narrow gap insulator FeSi with Co share the very high anomalous Hall conductance of (GaMn)As, while displaying Curie temperatures as high as 53 K. Our work opens up a new arena for spintronics, involving a bulk material based only on transition metals and Si, and which we have proven to display a variety of large magnetic field effects on easily measured electrical properties.Comment: 19 pages with 5 figure

Ubiquitin sets the timer: impacts on aging and longevity

Protein homeostasis is essential for cellular function, organismal growth and viability. Damaged and aggregated proteins are turned over by two major proteolytic routes of the cellular quality-control pathways: the ubiquitin-proteasome system and autophagy. For both these pathways, ubiquitination provides the recognition signal for substrate selection. This Commentary discusses how ubiquitin-dependent proteolytic pathways are coordinated with stress- and aging-induced signals

Reassessment of the Lineage Fusion Hypothesis for the Origin of Double Membrane Bacteria

In 2009, James Lake introduced a new hypothesis in which reticulate phylogeny reconstruction is used to elucidate the origin of Gram-negative bacteria (Nature 460: 967–971). The presented data supported the Gram-negative bacteria originating from an ancient endosymbiosis between the Actinobacteria and Clostridia. His conclusion was based on a presence-absence analysis of protein families that divided all prokaryotes into five groups: Actinobacteria, Double Membrane bacteria (DM), Clostridia, Archaea and Bacilli. Of these five groups, the DM are by far the largest and most diverse group compared to the other groupings. While the fusion hypothesis for the origin of double membrane bacteria is enticing, we show that the signal supporting an ancient symbiosis is lost when the DM group is broken down into smaller subgroups. We conclude that the signal detected in James Lake's analysis in part results from a systematic artifact due to group size and diversity combined with low levels of horizontal gene transfer.Exobiology Program (U.S.) (Grant NNX08AQ10G)Assembling the Tree of Life (Program) (Grant DEB 0830024