We investigate the transient optical response in high-quality Cd sub(0.88) Zn sub(0.12) Te crystals in the regime of slow light propagation on the lower exciton-polariton branch. Femtosecond ...photoexcitation leads to very substantial transmission changes in a ~10-meV broad spectral range within the transparency window of the unexcited semiconductor. These nonlinear optical signatures decay on picosecond time scales governed by carrier thermalization and recombination. The temporal and spectral dependence indicate the dynamical optical response as arising from excitation-induced dephasing and perturbed free induction decay. Model simulations for the optical response taking into account the actual exciton-polariton dispersion and excitation-induced dephasing of a nonlinearly driven two-level system support this interpretation.
The glucosinolate content of various organs of the model plant
Arabidopsis thaliana was analysed at different stages during its life cycle. Seeds had the highest concentration (2.5% by dry weight), ...followed by inflorescences, siliques (fruits), leaves and roots. Seeds also had a very distinct glucosinolate composition, including much higher concentrations of methylthioalkyl glucosinolates, hydroxyalkyl glucosinolates and compounds with benzoate esters than other organs. During seed germination and leaf senescence, there were significant declines in glucosinolate concentration.
The glucosinolate content of various organs of the model plant
Arabidopsis thaliana (L.) Heynh., Columbia (Col-0) ecotype, was analyzed at different stages during its life cycle. Significant differences were noted among organs in both glucosinolate concentration and composition. Dormant and germinating seeds had the highest concentration (2.5–3.3% by dry weight), followed by inflorescences, siliques (fruits), leaves and roots. While aliphatic glucosinolates predominated in most organs, indole glucosinolates made up nearly half of the total composition in roots and late-stage rosette leaves. Seeds had a very distinctive glucosinolate composition. They possessed much higher concentrations of several types of aliphatic glucosinolates than other organs, including methylthioalkyl and, hydroxyalkyl glucosinolates and compounds with benzoate esters than other organs. From a developmental perspective, older leaves had lower glucosinolate concentrations than younger leaves, but this was not due to decreasing concentrations in individual leaves with age (glucosinolate concentration was stable during leaf expansion). Rather, leaves initiated earlier in development simply had much lower rates of glucosinolate accumulation per dry weight gain throughout their lifetimes. During seed germination and leaf senescence, there were significant declines in glucosinolate concentration. The physiological and ecological significance of these findings is briefly discussed.
Identification of the causal genes that control complex trait variation remains challenging, limiting our appreciation of the evolutionary processes that influence polymorphisms in nature. We cloned ...a quantitative trait locus that controls plant defensive chemistry, damage by insect herbivores, survival, and reproduction in the natural environments where this polymorphism evolved. These ecological effects are driven by duplications in the BCMA (branched-chain methionine allocation) loci controlling this variation and by two selectively favored amino acid changes in the glucosinolate-biosynthetic cytochrome P450 proteins that they encode. These changes cause a gain of novel enzyme function, modulated by allelic differences in catalytic rate and gene copy number. Ecological interactions in diverse environments likely contribute to the widespread polymorphism of this biochemical function.
Terpenoids, the largest class of plant secondary metabolites, play essential roles in both plant and human life. In higher plants, the five-carbon building blocks of all terpenoids, isopentenyl ...diphosphate (IPP) and dimethylallyl diphosphate, are derived from two independent pathways localized in different cellular compartments. The methylerythritol phosphate (MEP or nonmevalonate) pathway, localized in the plastids, is thought to provide IPP and dimethylallyl diphosphate for hemiterpene, monoterpene, and diterpene biosynthesis, whereas the cytosol-localized mevalonate pathway provides C5 units for sesquiterpene biosynthesis. Stable isotope-labeled, pathway-specific precursors (1-deoxy-5,5-2H2-D-xylulose and 2,2-2H2-mevalolactone) were supplied to cut snapdragon flowers, which emit both monoterpenes and the sesquiterpene, nerolidol. We show that only one of the two pathways, the plastid-localized MEP pathway, is active in the formation of volatile terpenes. The MEP pathway provides IPP precursors for both plastidial monoterpene and cytosolic sesquiterpene biosynthesis in the epidermis of snapdragon petals. The trafficking of IPP occurs unidirectionally from the plastids to cytosol. The MEP pathway operates in a rhythmic manner controlled by the circadian clock, which determines the rhythmicity of terpenoid emission.
Abstract
The class of plasma instabilities known as edge-localized modes (ELMs) is of special concern in tokamaks operating in high-confinement mode, such as ASDEX Upgrade and ITER. One strategy for ...ELM mitigation is the application of resonant magnetic perturbations (RMPs) via external coils. Kinetic modeling accurately describes the plasma response to these RMPs
ab initio
, particularly the parallel shielding currents at resonant surfaces. Away from resonant surfaces, ideal magnetohydrodynamics (iMHD) is expected to yield sufficiently accurate results, providing a computationally less expensive option that could complement kinetic modeling.
The code MEPHIT has been developed to solve the linearized iMHD equations in a way that is compatible with iterative kinetic modeling approaches. We consider an axisymmetric iMHD equilibrium in realistic tokamak geometry under the influence of a quasi-static non-axisymmetric external perturbation from ELM mitigation coils. The plasma responds to this external magnetic perturbation with a current perturbation, which in turn produces a magnetic field perturbation. The resulting fixed-point equation can be solved in a self-consistent manner by preconditioned iterations in which Ampère’s equation and the magnetic differential equations for pressure and current are solved in alternation until convergence is reached. After expansion in toroidal Fourier harmonics, these equations are solved on a triangular mesh in the poloidal plane using finite elements. These results are then benchmarked against established codes.
Since the completion of genome sequences of model organisms, functional
identification of unknown genes has become a principal challenge in biology.
Post-genomics sciences such as transcriptomics, ...proteomics, and metabolomics
are expected to discover gene functions. This report outlines the elucidation
of gene-to-gene and metabolite-to-gene networks via integration of
metabolomics with transcriptomics and presents a strategy for the
identification of novel gene functions. Metabolomics and transcriptomics data
of Arabidopsis grown under sulfur deficiency were combined and
analyzed by batch-learning self-organizing mapping. A group of
metabolites/genes regulated by the same mechanism clustered together. The
metabolism of glucosinolates was shown to be coordinately regulated. Three
uncharacterized putative sulfotransferase genes clustering together with known
glucosinolate biosynthesis genes were candidates for involvement in
biosynthesis. In vitro enzymatic assays of the recombinant gene
products confirmed their functions as desulfoglucosinolate sulfotransferases.
Several genes involved in sulfur assimilation clustered with
O -acetylserine, which is considered a positive regulator of these
genes. The genes involved in anthocyanin biosynthesis clustered with the gene
encoding a transcriptional factor that up-regulates specifically anthocyanin
biosynthesis genes. These results suggested that regulatory metabolites and
transcriptional factor genes can be identified by this approach, based on the
assumption that they cluster with the downstream genes they regulate. This
strategy is applicable not only to plant but also to other organisms for
functional elucidation of unknown genes.
Abstract
Background/Introduction
Activation of ErbB4 by neuregulin 1 (NRG1) promotes cardiomyocyte hypertrophy and proliferation in both adult and neonatal mice, while treatment of patients with NRG1 ...following myocardial infarction reduces scar size and improves function. In mice, deletion of ErbB4 from cardiomyocytes mid-gestation results in development of dilated cardiomyopathy and reduced survival, pointing to a critical role for ErbB4 in the heart.
Purpose
We sought to evaluate the role of ErbB4 in the adult heart.
Methods and results
We deleted ErbB4 in αMHC-MerCreMer (cCre Tg+/)/ErbB4 homozygote floxed (ErbB4 fl/fl) mice at ∼2 months of age with 10 injections of Tamoxifen (20 mg/kg/day). Contractile function was reduced in vivo (echocardiography, 16%) and ex vivo (isolated-perfused, 33%) 3 months after gene deletion, while survival in mice up to 8 months after tamoxifen treatment was mot modified by cardiomyocyte ErbB4 deletion. We next evaluated the role of ErbB4 in response to physiological and pathological hypertrophic stressors. ErbB4 deletion did not modify cardiac enlargement in response to Angiotensin II (1000ng/kg/min, 14 days) or exercise (twice daily swimming, 20 min/session increasing 10 min/day to 90 min followed by 7 days at 90 min/session). Taken together, this indicated that ErbB4 is not essential for survival and adaptation in the adult heart, pointing instead towards a critical window for ErbB4 in neonatal heart development. To test this hypothesis, ErbB4ff and ErbB4ww neonates were injected at P1 with AAV9-cTNT-eGFP-iCre (2.16x1011viral particles, temporal vein) and culled at P6. We confirmed the presence of iCre mRNA, and suppression of ErbB4 in ErbB4 ff/ff mice, coincident with increased NRG1a, and reduced body and ventricular weights. By day 28, a number of hearts showed evidence of dilated cardiomyopathy.
Conclusion
Thus, ErbB4 is critical to cardiac hypertrophy and growth in neonatal mice, and maintains adult heart function.
Acknowledgement/Funding
National Health and Medical Research Council
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