1,379 research outputs found
A role for jasmonates in the release of dormancy by cold stratification in wheat
Hydration at low temperatures, commonly referred to as cold stratification, is widely used for releasing dormancy and triggering germination in a wide range of species including wheat. However, the molecular mechanism that underlies its effect on germination has largely remained unknown. Our previous studies showed that methyl-jasmonate, a derivative of jasmonic acid (JA), promotes dormancy release in wheat. In this study, we found that cold-stimulated germination of dormant grains correlated with a transient increase in JA content and expression of JA biosynthesis genes in the dormant embryos after transfer to 20 (o)C. The induction of JA production was dependent on the extent of cold imbibition and precedes germination. Blocking JA biosynthesis with acetylsalicylic acid (ASA) inhibited the cold-stimulated germination in a dose-dependent manner. In addition, we have explored the relationship between JA and abscisic acid (ABA), a well-known dormancy promoter, in cold regulation of dormancy. We found an inverse relationship between JA and ABA content in dormant wheat embryos following stratification. ABA content decreased rapidly in response to stratification, and the decrease was reversed by addition of ASA. Our results indicate that the action of JA on cold-stratified grains is mediated by suppression of two key ABA biosynthesis genes, TaNCED1 and TaNCED2.This project was funded by a CSIRO Office of the Chief Executive PDF
scheme
Critical Behavior of Random Bond Potts Models
The effect of quenched impurities on systems which undergo first-order phase
transitions is studied within the framework of the q-state Potts model. For
large q a mapping to the random field Ising model is introduced which provides
a simple physical explanation of the absence of any latent heat in 2D, and
suggests that in higher dimensions such systems should exhibit a tricritical
point with a correlation length exponent related to the exponents of the random
field model by \nu = \nu_RF / (2 - \alpha_RF - \beta_RF). In 2D we analyze the
model using finite-size scaling and conformal invariance, and find a continuous
transition with a magnetic exponent \beta / \nu which varies continuously with
q, and a weakly varying correlation length exponent \nu \approx 1. We find
strong evidence for the multiscaling of the correlation functions as expected
for such random systems.Comment: 13 pages, RevTeX. 4 figures included. Submitted to Phys.Rev.Let
Evidence for an FU Orionis-like Outburst from a Classical T Tauri Star
We present pre- and post-outburst observations of the new FU Orionis-like
young stellar object PTF 10qpf (also known as LkHa 188-G4 and HBC 722). Prior
to this outburst, LkHa 188-G4 was classified as a classical T Tauri star on the
basis of its optical emission-line spectrum superposed on a K8-type
photosphere, and its photometric variability. The mid-infrared spectral index
of LkHa 188-G4 indicates a Class II-type object. LkHa 188-G4 exhibited a steady
rise by ~1 mag over ~11 months starting in Aug. 2009, before a subsequent more
abrupt rise of > 3 mag on a time scale of ~2 months. Observations taken during
the eruption exhibit the defining characteristics of FU Orionis variables: (i)
an increase in brightness by > 4 mag, (ii) a bright optical/near-infrared
reflection nebula appeared, (iii) optical spectra are consistent with a G
supergiant and dominated by absorption lines, the only exception being Halpha
which is characterized by a P Cygni profile, (iv) near-infrared spectra
resemble those of late K--M giants/supergiants with enhanced absorption seen in
the molecular bands of CO and H_2O, and (v) outflow signatures in H and He are
seen in the form of blueshifted absorption profiles. LkHa 188-G4 is the first
member of the FU Orionis-like class with a well-sampled optical to mid-infrared
spectral energy distribution in the pre-outburst phase. The association of the
PTF 10qpf outburst with the previously identified classical T Tauri star LkHa
188-G4 (HBC 722) provides strong evidence that FU Orionis-like eruptions
represent periods of enhanced disk accretion and outflow, likely triggered by
instabilities in the disk. The early identification of PTF 10qpf as an FU
Orionis-like variable will enable detailed photometric and spectroscopic
observations during its post-outburst evolution for comparison with other known
outbursting objects.Comment: 14 pages, 11 figures, ApJ accepte
Recommended from our members
Development and Validation of Prediction Scores for Early Mortality at Transition to Dialysis.
ObjectiveTo develop and validate a risk prediction model that would help individualize treatment and improve the shared decision-making process between clinicians and patients.Patients and methodsWe developed a risk prediction tool for mortality during the first year of dialysis based on pre-end-stage renal disease characteristics in a cohort of 35,878 US veterans with incident end-stage renal disease who transitioned to dialysis treatment between October 1, 2007, and March 31, 2014 and then externally validated this tool among 4284 patients in the Kaiser Permanente Southern California (KPSC) health care system who transitioned to dialysis treatment between January 1, 2007, and September 30, 2015.ResultsTo ensure model goodness of fit, 2 separate models were selected for patients whose last estimated glomerular filtration rate (eGFR) before dialysis initiation was less than 15 mL/min per 1.73 m2 or 15 mL/min per 1.73 m2 or higher. Model discrimination in the internal validation cohort of veterans resulted in C statistics of 0.71 (95% CI, 0.70-0.72) and 0.66 (95% CI, 0.65-0.67) among patients with eGFR lower than 15 mL/min per 1.73 m2 and 15 mL/min per 1.73 m2 or higher, respectively. In the KPSC external validation cohort, the developed risk score exhibited C statistics of 0.77 (95% CI, 0.74-0.79) in men and 0.74 (95% CI, 0.71-0.76) in women with eGFR lower than 15 mL/min per 1.73 m2 and 0.71 (95% CI, 0.67-0.74) in men and 0.67 (95% CI, 0.62-0.72) in women with eGFR of 15 mL/min per 1.73 m2 or higher.ConclusionA new risk prediction tool for mortality during the first year after transition to dialysis (available at www.DialysisScore.com) was developed in the large national Veterans Affairs cohort and validated with good performance in the racially, ethnically, and gender diverse KPSC cohort. This risk prediction tool will help identify high-risk populations and guide management strategies at the transition to dialysis
Reasoning deficits among illicit drug users are associated with aspects of cannabis use
Background. Deficits in deductive reasoning have been observed among ecstasy/polydrug users. The present study seeks to investigate dose-related effects of specific drugs and whether these vary with the cognitive demands of the task. Methods. One hundred and five participants (mean age 21.33, S.D. 3.14; 77 females, 28 males) attempted to generate solutions for eight one-model syllogisms and one syllogism for which there was no valid conclusion (NVC). All of the one model syllogisms generated at least one valid conclusion and six generated two valid conclusions. In these six cases one of the conclusions was classified as common and the other as non-common. Results. The number of valid common inferences was negatively associated with aspects of short term cannabis use and with measures of IQ. The outcomes observed were more than simple post intoxication effects since cannabis use in the 10 days immediately before testing was unrelated to reasoning performance. Following adjustment for multiple comparisons, the number of non-common valid inferences was not significantly associated with any of the drug use measures. Conclusions. Recent cannabis use appears to impair the processes associated with generating valid common inferences while not affecting the production of non-common inferences. It is possible, therefore, that the two types of inference may recruit different executive resources which may differ in their susceptibility to cannabis-related effects
PTF10nvg: An Outbursting Class I Protostar in the Pelican/North American Nebula
During a synoptic survey of the North American Nebula region, the Palomar
Transient Factory (PTF) detected an optical outburst (dubbed PTF10nvg)
associated with the previously unstudied flat or rising spectrum infrared
source IRAS 20496+4354. The PTF R-band light curve reveals that PTF10nvg
brightened by more than 5 mag during the current outburst, rising to a peak
magnitude of R~13.5 in 2010 Sep. Follow-up observations indicate PTF10nvg has
undergone a similar ~5 mag brightening in the K band, and possesses a rich
emission-line spectrum, including numerous lines commonly assumed to trace mass
accretion and outflows. Many of these lines are blueshifted by ~175 km/s from
the North American Nebula's rest velocity, suggesting that PTF10nvg is driving
an outflow. Optical spectra of PTF10nvg show several TiO/VO bandheads fully in
emission, indicating the presence of an unusual amount of dense (> 10^10
cm^-3), warm (1500-4000 K) circumstellar material. Near-infrared spectra of
PTF10nvg appear quite similar to a spectrum of McNeil's Nebula/V1647 Ori, a
young star which has undergone several brightenings in recent decades, and
06297+1021W, a Class I protostar with a similarly rich near--infrared emission
line spectrum. While further monitoring is required to fully understand this
event, we conclude that the brightening of PTF10nvg is indicative of enhanced
accretion and outflow in this Class-I-type protostellar object, similar to the
behavior of V1647 Ori in 2004-2005.Comment: Accepted to the Astronomical Journal; 21 pages, 11 figures, 6 tables
in emulateapj format; v2 fixes typo in abstract; v3 updates status to
accepted, adjusts affiliations, adds acknowledgmen
PTF10fqs: A Luminous Red Nova in the Spiral Galaxy Messier 99
The Palomar Transient Factory (PTF) is systematically charting the optical
transient and variable sky. A primary science driver of PTF is building a
complete inventory of transients in the local Universe (distance less than 200
Mpc). Here, we report the discovery of PTF10fqs, a transient in the luminosity
"gap" between novae and supernovae. Located on a spiral arm of Messier 99, PTF
10fqs has a peak luminosity of Mr = -12.3, red color (g-r = 1.0) and is slowly
evolving (decayed by 1 mag in 68 days). It has a spectrum dominated by
intermediate-width H (930 km/s) and narrow calcium emission lines. The
explosion signature (the light curve and spectra) is overall similar to thatof
M85OT2006-1, SN2008S, and NGC300OT. The origin of these events is shrouded in
mystery and controversy (and in some cases, in dust). PTF10fqs shows some
evidence of a broad feature (around 8600A) that may suggest very large
velocities (10,000 km/s) in this explosion. Ongoing surveys can be expected to
find a few such events per year. Sensitive spectroscopy, infrared monitoring
and statistics (e.g. disk versus bulge) will eventually make it possible for
astronomers to unravel the nature of these mysterious explosions.Comment: 12 pages, 12 figures, Replaced with published versio
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