The circadian clock in the diatom <i>Phaeodactylum tricornutum</i>

International audienceno abstrac

Juxtaposition of Chemical and Mutation-Induced Developmental Defects in Zebrafish Reveal a Copper-Chelating Activity for Kalihinol F

SummaryA major hurdle in using complex systems for drug screening is the difficulty of defining the mechanistic targets of small molecules. The zebrafish provides an excellent model system for juxtaposing developmental phenotypes with mechanism discovery using organism genetics. We carried out a phenotype-based screen of uncharacterized small molecules in zebrafish that produced a variety of chemically induced phenotypes with potential genetic parallels. Specifically, kalihinol F caused an undulated notochord, defects in pigment formation, hematopoiesis, and neural development. These phenotypes were strikingly similar to the zebrafish mutant, calamity, an established model of copper deficiency. Further studies into the mechanism of action of kalihinol F revealed a copper-chelating activity. Our data support this mechanism of action for kalihinol F and the utility of zebrafish as an effective system for identifying therapeutic and target pathways

The origin of the Narrow Line Region of Mrk 3: an overpressured jet cocoon

We have obtained HST FOC long-slit optical spectroscopy of the Narrow Line Region of the Seyfert 2 galaxy Mrk 3. In the region cospatial with the radio-jet the velocity field is highly perturbed and shows two velocity systems separated by as much as 1700 km/s. We interpret this to be the consequence of the rapid expansion of a cocoon of hot gas, shocked and heated by the radio-emitting outflow, which compresses and accelerates the ambient gas. The NLR itself is essentially a cylindrical shell expanding supersonically. From the size and velocity of the expanding region, we derive an upper limit to the radio-source age, ~ 2 E42 erg/s required to inflate the cocoon and estimate that the jet minimum advance speed is 3 E-3 pc per year. The total kinetic energy of the high velocity NLR gas can be estimated as ~6 E54 erg, comparable to the total energy carried by the jet over its lifetime and this quantitatively supports the idea that the NLR gas is accelerated by the jet. If the advance speed of Mrk 3 is representative of the Seyfert population then these sources must also be short lived and probably recurrent. The jet kinetic luminosity of Mrk 3 is between 2 and 3 orders of magnitude smaller than that derived for radio-loud AGNs with similar emission-line luminosity. On the other hand, the fraction of jet power dissipated in radio-emission is similar. We speculate that the main distinction between radio-quiet and radio-loud AGN is ascribed to a difference in jet power rather than to a different efficiency in synchrotron emission production.Comment: 13 pages, 8 figures, Astrophysical Journal in pres

Introducing a new breed of wine yeast: interspecific hybridisation between a commercial Saccharomyces cerevisiae wine yeast and Saccharomyces mikatae

Interspecific hybrids are commonplace in agriculture and horticulture; bread wheat and grapefruit are but two examples. The benefits derived from interspecific hybridisation include the potential of generating advantageous transgressive phenotypes. This paper describes the generation of a new breed of wine yeast by interspecific hybridisation between a commercial Saccharomyces cerevisiae wine yeast strain and Saccharomyces mikatae, a species hitherto not associated with industrial fermentation environs. While commercially available wine yeast strains provide consistent and reliable fermentations, wines produced using single inocula are thought to lack the sensory complexity and rounded palate structure obtained from spontaneous fermentations. In contrast, interspecific yeast hybrids have the potential to deliver increased complexity to wine sensory properties and alternative wine styles through the formation of novel, and wider ranging, yeast volatile fermentation metabolite profiles, whilst maintaining the robustness of the wine yeast parent. Screening of newly generated hybrids from a cross between a S. cerevisiae wine yeast and S. mikatae (closely-related but ecologically distant members of the Saccharomyces sensu stricto clade), has identified progeny with robust fermentation properties and winemaking potential. Chemical analysis showed that, relative to the S. cerevisiae wine yeast parent, hybrids produced wines with different concentrations of volatile metabolites that are known to contribute to wine flavour and aroma, including flavour compounds associated with non-Saccharomyces species. The new S. cerevisiae x S. mikatae hybrids have the potential to produce complex wines akin to products of spontaneous fermentation while giving winemakers the safeguard of an inoculated ferment.Jennifer R. Bellon, Frank Schmid, Dimitra L. Capone, Barbara L. Dunn, Paul J. Chamber

Feeding versus Feedback in NGC 4151 probed with Gemini NIFS. I. Excitation

We have used the Gemini Near-infrared Integral Field Spectrograph (NIFS) to map the emission-line intensity distributions and ratios in the Narrow-Line Region (NLR) of the Seyfert galaxy NGC 4151 in the Z, J, H and K bands at a resolving power ~ 5000, covering the inner 200 pc x 300 pc of the galaxy at a spatial resolution of 8 pc. We present intensity distributions I(r) in 14 emission lines. (1) For the ionized gas, I(r) is extended to ~ 100 pc from the nucleus along pos. angle PA=60/240 deg-- NE--SW), consistent with an origin in the known biconical outflow; while for the recombination lines I(r) ~ r^-1, for the forbidden lines I(r) is flat (r^0). (2) The H_2 emission lines intensity distributions avoid the region of the bicone, extending to r ~ 60 pc, perpendicular to the bicone axis, supporting an origin for the H_2-emitting gas in the galaxy plane. (3) The coronal lines show a steep intensity profile, described by r^-2. Using the line-ratio maps [Fe II]1.644/1.257 and Pa_b/Br_g we obtain a reddening of E(B-V)~0.5 along the NLR and E(B-V)>1 at the nucleus. Our line-ratio map [Fe II] 1.257/[P II] 1.189 is the first such map of an extragalactic source. Together with the [Fe II]/Pa_b map, these line ratios correlate with the radio intensity distribution, mapping the effects of shocks produced by the radio jet, which probably release the Fe locked in grains and produce the enhancement of the [Fe II] emission observed at ~ 1 arcsec from the nucleus. At these regions, we obtain densities N_e ~4000 cm^-3 and temperatures T_e ~ 15000K for the [Fe II]-emitting gas. For the H_2-emitting gas we obtain T ~ 2100K. The distinct intensity distributions, physical properties and locations of the ionized and molecular gas suggest that the H_2-emitting gas traces the AGN feeding, while the ionized gas traces its feedback.Comment: 22 pages. 14 figures, accepted for publication in MNRA

A Variable-Density Absorption Event in NGC 3227 mapped with Suzaku and Swift

The morphology of the circumnuclear gas accreting onto supermassive black holes in Seyfert galaxies remains a topic of much debate. As the innermost regions of Active Galactic Nuclei (AGN) are spatially unresolved, X-ray spectroscopy, and in particular line-of-sight absorption variability, is a key diagnostic to map out the distribution of gas. Observations of variable X-ray absorption in multiple Seyferts and over a wide range of timescales indicate the presence of clumps/clouds of gas within the circumnuclear material. Eclipse events by clumps transiting the line of sight allow us to explore the properties of the clumps over a wide range of radial distances from the optical/UV Broad Line Region (BLR) to beyond the dust sublimation radius. Time-resolved absorption events have been extremely rare so far, but suggest a range of density profiles across Seyferts. We resolve a weeks-long absorption event in the Seyfert NGC 3227. We examine six Suzaku and twelve Swift observations from a 2008 campaign spanning 5 weeks. We use a model accounting for the complex spectral interplay of three differently-ionized absorbers. We perform time-resolved spectroscopy to discern the absorption variability behavior. We also examine the IR-to-X-ray spectral energy distribution (SED) to test for reddening by dust. The 2008 absorption event is due to moderately-ionized ($\log \xi\sim 1.2-1.4$) gas covering 90% of the line of sight. We resolve the density profile to be highly irregular, in contrast to a previous symmetric and centrally-peaked event mapped with RXTE in the same object. The UV data do not show significant reddening, suggesting that the cloud is dust-free. The 2008 campaign has revealed a transit by a filamentary, moderately-ionized cloud of variable density that is likely located in the BLR, and possibly part of a disk wind.Comment: Accepted for publication by A&

A Snapshot of the Continuous Emission of the Active Galactic Nucleus in NGC 3783 from Gamma-Ray to Radio Wavelengths

To better understand the physical processes that produce the continuous emission in active galactic nuclei (AGN), a snapshot of the overall continuous energy distribution of NGC 3783, from gamma ray to radio wavelengths, has been obtained within the framework of the World Astronomy Days. The data collected in this campaign are from GRO, ROSAT, Voyager 2, IUE, HST, CTIO, SAAO, and the VLA. Great care has been taken in disentangling the genuine AGN continusous emission from other contributions; depending on the waveband, the latter might be (1) unrelated contaminating sources in cases where the instrument field of view is large (2) components within which the AGN is embedded, such as the stellar bulge population which accounts for a significant fraction of the optical continuum, and free-bound and FE2 blends wich contribute to the ultraviolet flux. After correction for these other contributins, the continuous emission of the isolated AGN appears to be rather flat (i.e., approximately equal energy per unit logarithmic frequency) from soft gamma ray to infrared wavelengths. At high energies (0.1 MeV to 0.1 keV), the AGN continuum can be fitted by a power law F nu approaches Nu(exp -a) with a spectral index of alpha approximately 1. At longer wavelengths, two excesses above this power law ('bumps') appear: in the ultraviolet, the classical big blue bump, which can be interpreted as thermal emission from the accretion disc surrounding a massive black hole, and in the infrared, a second bump which can be ascribed to thermal emission from dust in the vicinity of the AGN, heated by ultraviolet radiation from the central source. By fitting accretion-disk models to the observed AGN spectral energy distribution, we find values for the accretion disk innermost temperature, accretion rate, and black hole mass, with some differences that depend on whether or not we extrapolate the high energy power law up to infrared wavelengths. A fit to the IR bump above the extended alpha equals 1 power law suggests the presence of a dust component covering the region from a distance rho approximately equals 80 light days (hot grains at a temperature of approximately equals 1500 K) to rho approximately equals 60 light years (cool grains at T approximately equals 200 K). The total mass of dust is around 60 solar masses

The karyotype of Nothoscordum arenarium Herter (Gilliesioideae, Alliaceae): A populational and cytomolecular analysis

The genus Nothoscordum Kunth comprises approximately 20 species native to South America. Karyologically, the genus is remarkable for its large chromosomes and Robertsonian translocations. Variation in chromosome number has been recorded in a few polyploid species and it is unknown among diploids. This study presents the chromosome number and morphology of 53 individuals of seven populations of N. arenarium Herter (2n = 10). In addition, karyotype analyses after C-banding, staining with CMA and DAPI, and in situ hybridization with 5S and 45S rDNA probes were performed in six individuals from one population. All individuals exhibited 2n = 10 (6M + 4A), except for one tetraploid (2n = 20, 12M + 8A) and one triploid (2n = 15, 9M + 6A) plant. C-banding revealed the presence of CMA+ /DAPI - heterochromatin in the short arm and in the proximal region of the long arm of all acrocentric chromosomes. The 45S rDNA sites co-localized with the CMA + regions of the acrocentrics short arms, while the 5S rDNA probe only hybridized with the subterminal region of a pair of metacentric chromosomes. A change in the pattern of CMA bands and rDNA sites was observed in only one individual bearing a reciprocal translocation involving the long arm of a metacentric and the long arm of an acrocentric chromosome. These data suggest that, despite isolated cases of polyploidy and translocation, the karyotype of N. arenarium is very stable and the karyotypic instability described for other species may be associated with their polyploid condition

Steps toward determination of the size and structure of the broad-line region in active galactic nuclei. VI. Variability of NGC 3783 from ground-based data

The Seyfert 1 galaxy NGC 3783 was intensely monitored between 1991 December and 1992 August. We present the results from the ground-based observations in the optical and near-IR, which complement the data-set from the IUE, discussed elsewhere. Spectroscopic and photometric data from many observatories were combined in order to obtain well sampled light curves of the continuum and of H-Beta. During the campaign the source varied significantly. The light curves of the optical continuum and of H-Beta are similar to those obtained with the IUE. The near-IR flux did not vary significantly except for an increase at the end of the campaign. The optical continuum and the flux of H-Beta lag the UV continuum by 1 day or less and by 8 days respectively. These results confirm that the continuum variations are simultaneous or have a very small lag across the entire UV-optical range, and that the lines of NGC 3783 respond to ionizing continuum variations with less delay than those of NGC 5548. As in NGC 5548, the lag of H-Beta is greater than those of the high ionization lines.Comment: 34 pages in LaTeX, 7 postscript figures available on request from [email protected] or 37907::stirpe, BAP#10-1993-035-OA