781 research outputs found
Active auxin uptake by zucchini membrane vesicles: quantitation using ESR volume and delta pH determinations.
Genes encoding major light-harvesting polypeptides are clustered on the genome of the cyanobacterium Fremyella diplosiphon.
The Altered Gravitropic Response of the lazy-2 Mutant of Tomato Is Phytochrome Regulated
A Coordinated X-ray and Optical Campaign of the Nearby Massive Binary Orionis Aa: II. X-ray Variability
We present time-resolved and phase-resolved variability studies of an
extensive X-ray high-resolution spectral dataset of the Orionis Aa
binary system. The four observations, obtained with Chandra ACIS HETGS, have a
total exposure time of ~479 ks and provide nearly complete binary phase
coverage. Variability of the total X-ray flux in the range 5-25 is
confirmed, with maximum amplitude of about +/-15% within a single ~125 ks
observation. Periods of 4.76d and 2.04d are found in the total X-ray flux, as
well as an apparent overall increase in flux level throughout the 9-day
observational campaign. Using 40 ks contiguous spectra derived from the
original observations, we investigate variability of emission line parameters
and ratios. Several emission lines are shown to be variable, including S XV, Si
XIII, and Ne IX. For the first time, variations of the X-ray emission line
widths as a function of the binary phase are found in a binary system, with the
smallest widths at phase=0.0 when the secondary Orionis Aa2 is at
inferior conjunction. Using 3D hydrodynamic modeling of the interacting winds,
we relate the emission line width variability to the presence of a wind cavity
created by a wind-wind collision, which is effectively void of embedded wind
shocks and is carved out of the X-ray-producing primary wind, thus producing
phase-locked X-ray variability.Comment: 36 pages, 14 Tables, 19 Figures, accepted by ApJ, one of 4 related
papers to be published togethe
Chemotaxonomy as a tool for interpreting the cryptic diversity of Poaceae pollen
The uniform morphology of different species of Poaceae (grass) pollen means that identification to below family level using light microscopy is extremely challenging. Poor taxonomic resolution reduces recoverable information from the grass pollen record, for example, species diversity and environmental preferences cannot be extracted. Recent research suggests Fourier Transform Infra-red Spectroscopy (FTIR) can be used to identify pollen grains based on their chemical composition. Here, we present a study of twelve species from eight subfamilies of Poaceae, selected from across the phylogeny but from a relatively constrained geographical area (tropical West Africa) to assess the feasibility of using this chemical method for identification within the Poaceae family. We assess several spectral processing methods and use K-nearest neighbour (k-nn) analyses, with a leave-one-out cross-validation, to generate identification success rates at different taxonomic levels. We demonstrate we can identify grass pollen grains to subfamily level with an 80% success rate. Our success in identifying Poaceae to subfamily level using FTIR provides an opportunity to generate high taxonomic resolution datasets in research areas such as palaeoecology, forensics, and melissopalynology quickly and at a relatively low cost
A Coordinated X-ray and Optical Campaign on the Nearest Massive Eclipsing Binary, Delta Ori Aa: I. Overview of the X-ray Spectrum
We present an overview of four phase-constrained Chandra HETGS X-ray
observations of Delta Ori A. Delta Ori A is actually a triple system which
includes the nearest massive eclipsing spectroscopic binary, Delta Ori Aa, the
only such object which can be observed with little phase-smearing with the
Chandra gratings. Since the fainter star, Delta Ori Aa2, has a much lower X-ray
luminosity than the brighter primary, Delta Ori A provides a unique system with
which to test the spatial distribution of the X-ray emitting gas around Delta
Ori Aa1 via occultation by the photosphere of and wind cavity around the X-ray
dark secondary. Here we discuss the X-ray spectrum and X-ray line profiles for
the combined observation, having an exposure time of nearly 500 ksec and
covering nearly the entire binary orbit. Companion papers discuss the X-ray
variability seen in the Chandra spectra, present new space-based photometry and
ground-based radial velocities simultaneous with the X-ray data to better
constrain the system parameters, and model the effects of X-rays on the optical
and UV spectrum. We find that the X-ray emission is dominated by embedded wind
shock emission from star Aa1, with little contribution from the tertiary star
Ab or the shocked gas produced by the collision of the wind of Aa1 against the
surface of Aa2. We find a similar temperature distribution to previous X-ray
spectrum analyses. We also show that the line half-widths are about
the terminal velocity of the wind of star Aa1. We find a strong
anti-correlation between line widths and the line excitation energy, which
suggests that longer-wavelength, lower-temperature lines form farther out in
the wind. Our analysis also indicates that the ratio of the intensities of the
strong and weak lines of \ion{Fe}{17} and \ion{Ne}{10} are inconsistent with
model predictions, which may be an effect of resonance scatteringComment: accepted by ApJ; revised according to ApJ proo
Specific photoaffinity labeling of two plasma membrane polypeptides with an azido auxin
Plasma membrane vesicles were isolated from zucchini
Protein Kinases in Zucchini (Characterization of Calcium-Requiring Plasma Membrane Kinases)
In Utero Exposure to Environmental Tobacco Smoke Potentiates Adult Responses to Allergen in BALB/c Mice
BACKGROUND: Fetal stress has been linked to adult atherosclerosis, obesity, and diabetes. Epidemiology studies have associated fetal exposure to maternal smoking and postnatal exposure to environmental tobacco smoke (ETS) with increased asthma risk. OBJECTIVE: We tested the hypothesis, in a mouse model of asthma, that in utero ETS exposure alters airway function and respiratory immune responses in adults. METHODS: Pregnant Balb/c mice were exposed daily to ETS or HEPA-filtered air (AIR). Offspring inhaled aerosolized ovalbumin (OVA) or saline in weeks 7–8. Regardless of whether they inhaled OVA or saline, mice were sensitized by OVA injections in weeks 11 and 13 followed by OVA aerosol challenge in weeks 14–15. At three time points, we assessed OVA-specific serum immunoglobins, bronchoalveolar lavage cells and cytokines, lung and nasal histopathology, and airway hyperresponsiveness (AHR). RESULTS: At 6 weeks, we found no significant differences between in utero ETS and AIR mice. At 10 weeks, following OVA aerosol, ETS mice displayed greater AHR than AIR mice (α = 0.05), unaccompanied by changes in histopathology, cytokine profile, or antibody levels. At 15 weeks, mice that had inhaled saline in weeks 7–8 developed airway inflammation: eosinophilia (α = 0.05), interleukin-5 (α = 0.05), and AHR (α = 0.05) were greater in ETS mice than in AIR mice. Mice that had inhaled OVA in weeks 7–8 demonstrated no airway inflammation after sensitization and challenge. CONCLUSION: In utero ETS exposure exacerbates subsequent adult responses to initial allergen exposure
Variability in modern pollen rain from moist and wet tropical forest plots in Ghana, West Africa
How pollen moves within and between ecosystems affects factors such as the genetic structure of populations, how resilient they are to environmental change, and the amount and nature of pollen preserved in the sedimentary record. We set artificial pollen traps in two 100 m by 100 m vegetation plots, one in a wet evergreen forest, and one in a moist semi-deciduous forest in Ghana, West Africa. Five traps from each plot were counted annually from 2011 to 2014, to examine spatial and temporal variation in the pollen rain of the most abundant taxa shared between pollen and vegetation assemblages. Samples from the wet evergreen plot exhibited high variability within years, with the dominant pollen types changing between samples, and many pollen taxa being over-represented relative to their parent plant abundance in some traps whilst being entirely absent from others. The most abundant plant taxa of the wet evergreen plot (Drypetes and Cynometra) do, however, constitute major components of the pollen rain. There is less variation between samples from the moist semi-deciduous plot spatially, as it is dominated by Celtis, which typically comprises >70% of the pollen assemblages. We conclude that pollen rain in these tropical ecosystems is highly heterogeneous, and suggest that pollen assemblages obtained by trapping are susceptible to small-scale variations in forest structure. Conversely, this may mean that current recommendations of more than three years of trapping in tropical systems may be too high, and that space could substitute for time in modern tropical pollen trapping
- …