4,582 research outputs found
The heterotrimeric G-protein complex modulates light sensitivity in arabidopsis thaliana seed germination
Release of dormancy and induction of seed germination are complex traits finely regulated by hormonal signals and environmental cues such as temperature and light. The Red (R):Far-Red (FR) phytochrome photoreceptors mediate light regulation of seed germination. We investigated the possible involvement of heterotrimeric G-protein complex in the phytochrome signaling pathways of Arabidopsis thaliana seed germination. Germination rates of null mutants of the alpha (Gα) and beta (Gβ) subunits of the G-protein (Atgpa1-4 and agb1-2, respectively) and the double mutant (agb1-2/gpa1-4) are lower than the wildtype (WT) under continuous or pulsed light. The Gα and Gβ subunits play a role in seed germination under hourly pulses of R lower than 0.1 μmol m -2 s -1 whereas the Gβ subunit plays a role in higher R fluences. The germination of double mutants of G-protein subunits with phyA-211 and phyB-9 suggests that AtGPA1 seems to act as a positive regulator of phyA and probably phyB signaling pathways, while the role of AGB1 is ambiguous. The imbibition of seeds at 4°C and 35°C alters the R and FR light responsiveness of WT and G-protein mutants to a similar magnitude. Thus, Gα and Gβ subunits of the heterotrimeric G-protein complex modulate light induction of seed germination by phytochromes and are dispensable for the control of dormancy by low and high temperatures prior to irradiation. We discuss the possible indirect role of the G-protein complex on the phytochrome-regulated germination through hormonal signaling pathways.Fil: Botto, Javier Francisco. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; ArgentinaFil: Ibarra, Silvia Elizabeth. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; ArgentinaFil: Jones, Alan M.. University of North Carolina; Estados Unido
Hyperons analogous to the \Lambda(1405)
The low mass of the hyperon with , which is
higher than the ground state mass by 290 MeV, is difficult to
understand in quark models. We analyze the hyperon spectrum in the bound state
approach of the Skyrme model that successfully describes both the
and the . This model predicts that several
hyperon resonances of the same spin but with opposite parity form parity
doublets that have a mass difference of around 300 MeV, which is indeed
realized in the observed hyperon spectrum. Furthermore, the existence of the
and the of is predicted by this model.
Comments on the baryons and heavy quark baryons are made as well.Comment: 4 pages, talk presented at the Fifth Asia-Pacific Conference on
Few-Body Problems in Physics 2011 (APFB2011), Aug. 22-26, 2011, Seoul, Kore
2-C-methylated nucleotides terminate virus RNA synthesis by preventing active site closure of the viral RNA-dependent RNA polymerase
The 2-C-methyl ribonucleosides are nucleoside analogs representing an important class of antiviral agents, especially against positive-strand RNA viruses. Their value is highlighted by the highly successful anti-hepatitis C drug sofosbuvir. When appropriately phosphorylated, these nucleotides are successfully incorporated into RNA by the virally encoded RNA-dependent RNA polymerase (RdRp). This activity prevents further RNA extension, but the mechanism is poorly characterized. Previously, we had identified NMR signatures characteristic of formation of RdRp-RNA binary and RdRp-RNA-NTP ternary complexes for the poliovirus RdRp, including an open-to-closed conformational change necessary to prepare the active site for catalysis of phosphoryl transfer. Here we used these observations as a framework for interpreting the effects of 2-C-methyl adenosine analogs on RNA chain extension in solution-state NMR spectroscopy experiments, enabling us to gain additional mechanistic insights into 2-C-methyl ribonucleoside-mediated RNA chain termination. Contrary to what has been proposed previously, poliovirus RdRp that was bound to RNA with an incorporated 2-C-methyl nucleotide could still bind to the next incoming NTP. Our results also indicated that incorporation of the 2-C-methyl nucleotide does not disrupt RdRp-RNA interactions and does not prevent translocation. Instead, incorporation of the 2-C-methyl nucleotide blocked closure of the RdRp active site upon binding of the next correct incoming NTP, which prevented further nucleotide addition. We propose that other nucleotide analogs that act as nonobligate chain terminators may operate through a similar mechanism
A Long Term Results of External Beam Radiation Therapy in Hemophilic Arthropathy of the Ankle in Children
Bleeding into joint space is critical to develop hemophilic arthropathy. To reduce the frequency of bleeding in the ankle joint of children with hemophilic arthropathy, low dose external beam irradiation was performed for 37 patients. Among them, 35 patients followed-up for longer than 1 yr (median 87 months) were enrolled for analysis. The average number of bleedings per month was 3.6 during one year prior to radiation therapy. After radiation therapy, it was decreased to 2.1 during the first year, after then it was maintained in the range of 1.0 to 1.5 until the tenth year. The bleeding frequency was reduced to 42% at the first year and it was maintained in the range of 58% to 73% from the second to the tenth year. Especially the patients who had 3 or more bleedings per month, and who had MRI score more than 3 showed significant decreases. During the follow-up period, growth disturbances and secondary malignancies were not found. External beam radiotherapy can be considered for the hemophilic patients with surgical or isotope therapies are not amenable
(Anti)symmetric matter and superpotentials from IIB orientifolds
We study the IIB engineering of N=1 gauge theories with unitary gauge group
and matter in the adjoint and (anti)symmetric representations. We show that
such theories can be obtained as Z2 orientifolds of Calabi-Yau A2 fibrations,
and discuss the explicit T-duality transformation to an orientifolded
Hanany-Witten construction. The low energy dynamics is described by a geometric
transition of the orientifolded background. Unlike previously studied cases, we
show that the orientifold 5-`plane' survives the transition, thus bringing a
nontrivial contribution to the effective superpotential. We extract this
contribution by using matrix model results and compare with geometric data. A
Higgs branch of our models recovers the engineering of SO/Sp theories with
adjoint matter through an O5-`plane' T-dual to an O6-plane. We show that the
superpotential agrees with that produced by engineering through an O5-`plane'
dual to an O4-plane, even though the orientifold of this second construction is
replaced by fluxes after the transition.Comment: 40 page
On the Temperature Dependence of the Shear Viscosity and Holography
We examine the structure of the shear viscosity to entropy density ratio
eta/s in holographic theories of gravity coupled to a scalar field, in the
presence of higher derivative corrections. Thanks to a non-trivial scalar field
profile, eta/s in this setup generically runs as a function of temperature. In
particular, its temperature behavior is dictated by the shape of the scalar
potential and of the scalar couplings to the higher derivative terms. We
consider a number of dilatonic setups, but focus mostly on phenomenological
models that are QCD-like. We determine the geometric conditions needed to
identify local and global minima for eta/s as a function of temperature, which
translate to restrictions on the signs and ranges of the higher derivative
couplings. Finally, such restrictions lead to an holographic argument for the
existence of a global minimum for eta/s in these models, at or above the
deconfinement transition.Comment: references adde
Proximity effects at ferromagnet-superconductor interfaces
We study proximity effects at ferromagnet superconductor interfaces by
self-consistent numerical solution of the Bogoliubov-de Gennes equations for
the continuum, without any approximations. Our procedures allow us to study
systems with long superconducting coherence lengths. We obtain results for the
pair potential, the pair amplitude, and the local density of states. We use
these results to extract the relevant proximity lengths. We find that the
superconducting correlations in the ferromagnet exhibit a damped oscillatory
behavior that is reflected in both the pair amplitude and the local density of
states. The characteristic length scale of these oscillations is approximately
inversely proportional to the exchange field, and is independent of the
superconducting coherence length in the range studied. We find the
superconducting coherence length to be nearly independent of the ferromagnetic
polarization.Comment: 13 Pages total. Compressed .eps figs might display poorly, but will
print fin
Orbital Magnetism in the Ballistic Regime: Geometrical Effects
We present a general semiclassical theory of the orbital magnetic response of
noninteracting electrons confined in two-dimensional potentials. We calculate
the magnetic susceptibility of singly-connected and the persistent currents of
multiply-connected geometries. We concentrate on the geometric effects by
studying confinement by perfect (disorder free) potentials stressing the
importance of the underlying classical dynamics. We demonstrate that in a
constrained geometry the standard Landau diamagnetic response is always
present, but is dominated by finite-size corrections of a quasi-random sign
which may be orders of magnitude larger. These corrections are very sensitive
to the nature of the classical dynamics. Systems which are integrable at zero
magnetic field exhibit larger magnetic response than those which are chaotic.
This difference arises from the large oscillations of the density of states in
integrable systems due to the existence of families of periodic orbits. The
connection between quantum and classical behavior naturally arises from the use
of semiclassical expansions. This key tool becomes particularly simple and
insightful at finite temperature, where only short classical trajectories need
to be kept in the expansion. In addition to the general theory for integrable
systems, we analyze in detail a few typical examples of experimental relevance:
circles, rings and square billiards. In the latter, extensive numerical
calculations are used as a check for the success of the semiclassical analysis.
We study the weak-field regime where classical trajectories remain essentially
unaffected, the intermediate field regime where we identify new oscillations
characteristic for ballistic mesoscopic structures, and the high-field regime
where the typical de Haas-van Alphen oscillations exhibit finite-size
corrections. We address the comparison with experimental data obtained in
high-mobility semiconductor microstructures discussing the differences between
individual and ensemble measurements, and the applicability of the present
model.Comment: 88 pages, 15 Postscript figures, 3 further figures upon request, to
appear in Physics Reports 199
- …