6,109 research outputs found
Induced resistance to periwinkle grazing in the brown seaweed Fucus vesiculosus (Phaeophyceae): molecular insights and seaweed-mediated effects on herbivore interactions
Herbivory is a key factor for controlling seaweed biomass and community structure. To cope with
grazers, constitutive and inducible defenses have evolved in macroalgae. Inducible chemical defenses
show grazer-specificity and, at the same time, have the potential to mediate interactions among different
herbivores. Furthermore, temporal variations in defense patterns, which may adjust antiherbivory
responses to grazing pressure, were reported in two brown seaweeds. However, underlying cellular
processes are only rudimentarily characterized. To investigate the response of Fucus vesiculosus (L.) to
periwinkle (Littorina obtusata) grazing, feeding assays were conducted at several times during a 33 d
induction experiment. Underlying cellular processes were analyzed through gene expression profiling.
Furthermore, direct processes driving the antiherbivory response to periwinkle grazing and
indirect effects on another herbivore, the isopod Idotea baltica, were elucidated. F. vesiculosus showed
multiple defense pulses in response to periwinkle grazing, suggesting a high level of temporal
variability in antiherbivory traits. Defense induction was accompanied by extensive transcriptome
changes. Approximately 400 genes were significantly up-/down-regulated relative to controls, including
genes relevant for translation and the cytoskeleton. Genes involved in photosynthesis were mostly downregulated, while genes related to the respiratory chain were up-regulated, indicating alterations in
resource allocation. The comparison of genes regulated in response to isopod (previous study) and
periwinkle grazing suggests specific induction of several genes by each herbivore. However, grazing by
both herbivores induced similar metabolic processes in F. vesiculosus. These common defense-related
processes reflected in strong indirect effects as isopods were also repelled after previous grazing by
L. obtusata
Alternative mechanisms of structuring biomembranes: Self-assembly vs. self-organization
We study two mechanisms for the formation of protein patterns near membranes
of living cells by mathematical modelling. Self-assembly of protein domains by
electrostatic lipid-protein interactions is contrasted with self-organization
due to a nonequilibrium biochemical reaction cycle of proteins near the
membrane. While both processes lead eventually to quite similar patterns, their
evolution occurs on very different length and time scales. Self-assembly
produces periodic protein patterns on a spatial scale below 0.1 micron in a few
seconds followed by extremely slow coarsening, whereas self-organization
results in a pattern wavelength comparable to the typical cell size of 100
micron within a few minutes suggesting different biological functions for the
two processes.Comment: 4 pages, 5 figure
Short-Pathlength, High-Pressure Flow Cell for Static and Time-Resolved Infrared Spectroscopy Suitable for Supercritical Fluid Solutions Including Hydrothermal Systems
An optical flow cell for high pressures and temperatures is described. The use of a novel window design allows for a precise, fixed optical pathlength that can be varied by use of spacers that range from a few micrometers to several millimeters. The cell pathlength is not affected by changes in pressure or temperature. The novel window design may be applicable to other high-pressure spectroscopic cells. The flow-cell design has a minimal sample dead volume, which is important for kinetic studies. The design eliminates the need for brazing or for a soft-sealing material for the optical windows, thereby minimizing the number of materials in contact with the sample. Using only diamond and platinum or platinum alloys as the corrosion resistant materials, the design is optimized for the study of aqueous solutions at high temperatures. Infrared spectra of an aqueous sodium tungstate solution up to 400â°C and 380 bar pressure are presented. Time-resolved infrared data are also presented for the ultraviolet photolysis reaction of ÎČ-naphthoyl azide in supercritical carbon dioxide
Molecular support for temporal dynamics of induced anti-herbivory defenses in the brown seaweed Fucus Vesiculosus
Grazing by the isopod Idotea baltica induces chemical defenses in the brown seaweed Fucus vesiculosus. A combination of a 33 day induction experiment, feeding choice assays and functional genomic analyses was used to investigate temporal defense patterns and to
correlate changes in palatability to changes in gene expression. Despite permanent grazing, seaweed palatability varied over time. Controls were significantly more consumed than grazed pieces only after 18 and 27 days of grazing. Relative to controls, 562/402 genes were up-/down-regulated in seaweed pieces that were grazed for 18 days, i.e. when defense
induction was detected. Reprogramming of the
regulative expression orchestra (translation,
transcription), up-regulation of genes involved in lipid and carbohydrate metabolism, intracellular trafficking, defense and stress response, as well as downregulation of photosynthesis was found in grazed seaweed. These findings indicate short-term temporal
variation in defenses and that modified gene
expression patterns arise at the same time when grazed seaweed pieces show reduced palatability. Several genes with putative defensive functions and cellular processes potentially involved in defence, such as
reallocation of resources from primary to secondary metabolism, were reveale
Bioinformatics prediction of overlapping frameshifted translation products in mammalian transcripts
<p>Abstract</p> <p>Background</p> <p>Exceptionally, a single nucleotide sequence can be translated <it>in vivo </it>in two different frames to yield distinct proteins. In the case of the G-protein alpha subunit XL-alpha-s transcript, a frameshifted open reading frame (ORF) in exon 1 is translated to yield a structurally distinct protein called Alex, which plays a role in platelet aggregation and neurological processes. We carried out a novel bioinformatics screen for other possible dual-frame translated sequences, based on comparative genomics.</p> <p>Results</p> <p>Our method searched human, mouse and rat transcripts in frames +1 and -1 for ORFs which are unusually well conserved at the amino acid level. We name these conserved frameshifted overlapping ORFs 'matreshkas' to reflect their nested character. Select findings of our analysis revealed that the G-protein coupled receptor GPR27 is entirely contained within a frame -1 matreshka, thrombopoietin contains a matreshka which spans ~70% of its length, platelet glycoprotein IIIa (ITGB3) contains a matreshka with the predicted characteristics of a secreted peptide hormone, while the potassium channel KCNK12 contains a matreshka spanning >400 amino acids.</p> <p>Conclusion</p> <p>Although the <it>in vivo </it>existence of translated matreshkas has not been experimentally verified, this genome-wide analysis provides strong evidence that substantial overlapping coding sequences exist in a number of human and rodent transcripts.</p
The ACS Virgo Cluster Survey. XIV. Analysis of Color-Magnitude Relations in Globular Cluster Systems
We examine the correlation between globular cluster (GC) color and magnitude
using HST/ACS imaging for a sample of 79 early-type galaxies (-21.7<M_B<-15.2
mag) with accurate SBF distances from the ACS Virgo Cluster Survey. Using the
KMM mixture modeling algorithm, we find a highly significant correlation,
d(g-z)/dz = -0.037 +- 0.004, between color and magnitude for the subpopulation
of blue GCs in the co-added GC color-magnitude diagram of the three brightest
Virgo galaxies (M49, M87 and M60): brighter GCs are redder than their fainter
counterparts. For the single GC systems of M87 and M60, we find similar
correlations; M49 does not appear to show a significant trend. There is no
correlation between (g-z) and M_z for GCs of the red subpopulation. The
correlation d(g-z)/dg for the blue subpopulation is much weaker than d(g-z)/dz.
Using Monte Carlo simulations, we attribute this to the fact that the blue
subpopulation in M_g extends to higher luminosities than the red subpopulation,
which biases the KMM fits. The correlation between color and M_z thus is a real
effect. This conclusion is supported by biweight fits to the same color
distributions. We identify two environmental dependencies of the
color-magnitude relation: (1) the slope decreases in significance with
decreasing galaxy luminosity; and (2) the slope is stronger for GCs at smaller
galactocentric distances. We examine several mechanisms that might give rise to
the observed color-magnitude relation: (1) presence of contaminators; (2)
accretion of GCs from low-mass galaxies; (3) stochastic effects; (4) capture of
field stars by individual GCs; and (5) GC self-enrichment. We conclude that
self-enrichment and field-star capture, or a combination of these processes,
offer the most promising means of explaining our observations.Comment: 15 pages, 12 figures, accepted for publication in the Astrophysical
Journal. Uses emulateapj.cl
Spectroscopy of Globular Clusters in M81
We present moderate-resolution spectroscopy of globular clusters (GCs) around
the Sa/Sb spiral galaxy M81 (NGC 3031). Sixteen candidate clusters were
observed with the Low Resolution Imaging Spectrograph on the Keck I telescope.
All are confirmed as bona fide GCs, although one of the clusters appears to
have been undergoing a transient event during our observations. In general, the
M81 globular cluster system (GCS) is found to be very similar to the Milky Way
(MW) and M31 systems, both chemically and kinematically. A kinematic analysis
of the velocities of 44 M81 GCS, (the 16 presented here and 28 from previous
work) strongly suggests that the red, metal-rich clusters are rotating in the
same sense as the gas in the disk of M81. The blue, metal-poor clusters have
halo-like kinematics, showing no evidence for rotation. The kinematics of
clusters whose projected galactocentric radii lie between 4 and 8 kpc suggest
that they are rotating much more than those which lie outside these bounds. We
suggest that these rotating, intermediate-distance clusters are analogous to
the kinematic sub-population in the metal-rich, disk GCs observed in the MW and
we present evidence for the existence of a similar sub-population in the
metal-rich clusters of M31. With one exception, all of the M81 clusters in our
sample have ages that are consistent with MW and M31 GCs. One cluster may be as
young as a few Gyrs. The correlations between absorption-line indices
established for MW and M31 GCs also hold in the M81 cluster system, at least at
the upper end of the metallicity distribution (which our sample probes). On the
whole, the mean metallicity of the M81 GCS is similar to the metallicity of the
MW and M31 GCSs. The projected mass of M81 is similar to the masses of the MW
and M31. Its mass profile indicates the presence of a dark matter halo.Comment: 35 pages, including 11 figures and 9 tables. Accepted for publication
in the Astronomical Journa
Decoherence in Josephson Qubits from Dielectric Loss
Dielectric loss from two-level states is shown to be a dominant decoherence
source in superconducting quantum bits. Depending on the qubit design,
dielectric loss from insulating materials or the tunnel junction can lead to
short coherence times. We show that a variety of microwave and qubit
measurements are well modeled by loss from resonant absorption of two-level
defects. Our results demonstrate that this loss can be significantly reduced by
using better dielectrics and fabricating junctions of small area . With a redesigned phase qubit employing low-loss
dielectrics, the energy relaxation rate has been improved by a factor of 20,
opening up the possibility of multi-qubit gates and algorithms.Comment: shortened version submitted to PR
- âŠ