37 research outputs found
Chromium Stress Mitigation by Polyamine-Brassinosteroid Application Involves Phytohormonal and Physiological Strategies in Raphanus sativus L.
Brassinosteroids (BRs) and polyamines (PAs) are well-established growth regulators playing key roles in stress management among plants. In the present study, we evaluated the effects of epibrassinolide (EBL, an active BR) and spermidine (Spd, an active PA) on the tolerance of radish to oxidative stress induced by Cr (VI) metal. Our investigation aimed to study the impacts of EBL (10−9 M) and/or Spd (1 mM) on the biochemical and physiological responses of radish (Raphanus sativus L.) under Cr-stress. Applications of EBL and/or Spd were found to improve growth of Cr-stressed seedlings in terms of root length, shoot length and fresh weight. Our data also indicated that applications of EBL and Spd have significant impacts, particularly when applied together, on the endogenous titers of PAs, free and bound forms of IAA and ABA in seedlings treated with Cr-stress. Additionally, co-applications of EBL and Spd modulated more remarkably the titers of antioxidants (glutathione, ascorbic acid, proline, glycine betaine and total phenol) and activities of antioxidant enzymes (guaicol peroxidase, catalase, superoxide dismutase and glutathione reductase) in Cr-stressed plants than their individual applications. Attenuation of Cr-stress by EBL and/or Spd (more efficient with EBL and Spd combination) was also supported by enhanced values of stress indices, such as phytochelatins, photosynthetic pigments and total soluble sugars, and reduction in malondialdehyde and H2O2 levels in Cr-treated seedlings. Diminution of ROS production and enhanced ROS scavenging capacities were also noted for EBL and/or Spd under Cr-stress. However, no significant reduction in Cr uptake was observed for co-application of EBL and Spd when compared to their individual treatments in Cr-stressed seedlings. Taken together, our results demonstrate that co-applications of EBL and Spd are more effective than their independent treatments in lowering the Cr-induced oxidative stress in radish, leading to improved growth of radish seedlings under Cr-stress
Production of dust by massive stars at high redshift
The large amounts of dust detected in sub-millimeter galaxies and quasars at
high redshift pose a challenge to galaxy formation models and theories of
cosmic dust formation. At z > 6 only stars of relatively high mass (> 3 Msun)
are sufficiently short-lived to be potential stellar sources of dust. This
review is devoted to identifying and quantifying the most important stellar
channels of rapid dust formation. We ascertain the dust production efficiency
of stars in the mass range 3-40 Msun using both observed and theoretical dust
yields of evolved massive stars and supernovae (SNe) and provide analytical
expressions for the dust production efficiencies in various scenarios. We also
address the strong sensitivity of the total dust productivity to the initial
mass function. From simple considerations, we find that, in the early Universe,
high-mass (> 3 Msun) asymptotic giant branch stars can only be dominant dust
producers if SNe generate <~ 3 x 10^-3 Msun of dust whereas SNe prevail if they
are more efficient. We address the challenges in inferring dust masses and
star-formation rates from observations of high-redshift galaxies. We conclude
that significant SN dust production at high redshift is likely required to
reproduce current dust mass estimates, possibly coupled with rapid dust grain
growth in the interstellar medium.Comment: 72 pages, 9 figures, 5 tables; to be published in The Astronomy and
Astrophysics Revie
Changes induced by Cu2+ and Cr6+ metal stress in polyamines, auxins, abscisic acid titers and antioxidative enzymes activities of radish seedlings
Consensus guidelines for the use and interpretation of angiogenesis assays
The formation of new blood vessels, or angiogenesis, is a complex process that plays important roles in growth and development, tissue and organ regeneration, as well as numerous pathological conditions. Angiogenesis undergoes multiple discrete steps that can be individually evaluated and quantified by a large number of bioassays. These independent assessments hold advantages but also have limitations. This article describes in vivo, ex vivo, and in vitro bioassays that are available for the evaluation of angiogenesis and highlights critical aspects that are relevant for their execution and proper interpretation. As such, this collaborative work is the first edition of consensus guidelines on angiogenesis bioassays to serve for current and future reference
Thermal transformations of Cu–Mg (Zn)–Al(Fe) hydrotalcite-like materials into metal oxide systems and their catalytic activity in selective oxidation of ammonia to dinitrogen
Spitzer number counts of active galactic nuclei in the goods fields
We present mid-infrared observations of AGN in the GOODS fields, performed
with the Spitzer Space Telescope. These are the deepest infrared and X-ray
fields to date and cover a total area of ~0.1 square degrees. AGN are selected
on the basis of their hard (2-8 keV) X-ray emission. The median AGN infrared
luminosity is at least 10 times larger than the median for normal galaxies with
the same redshift distribution, suggesting that the infrared emission is
dominated by the central nucleus. The X-ray to infrared luminosity ratios of
GOODS AGN, most of which are at 0.5<z<1.5, are similar to the values obtained
for AGN in the local Universe. The observed infrared flux distribution has an
integral slope of ~1.5 and there are 1000 sources per square degree brighter
than ~50 uJy at 3-6 microns. The counts approximately match the predictions of
models based on AGN unification, in which the majority of AGN are obscured.
This agreement confirms that the faintest X-ray sources, which are dominated by
the host galaxy light in the optical, are obscured AGN. Using these Spitzer
data, the AGN contribution to the extragalactic infrared background light is
calculated by correlating the X-ray and infrared catalogues. This is likely to
be a lower limit given that the most obscured AGN are missed in X-rays. We
estimate the contribution of AGN missed in X-rays, using a population synthesis
model, to be ~45% of the observed AGN contribution, making the AGN contribution
to the infrared background at most ~2-10% in the 3-24 micron range, depending
on wavelength, lower than most previous estimates. The AGN contribution to the
infrared background remains roughly constant with source flux in the IRAC bands
but decreases with decreasing flux in the MIPS 24 um band, where the galaxy
population becomes more important.Comment: ApJ Accepted, 24 pages, 7 figures, author list modifie
Obscured active galactic nuclei and the X-ray, optical, andfar-infrared number counts of active galactic nuclei in the GOODS fields
The deep X-ray, optical, and far-infrared fields that constitute GOODS are
sensitive to obscured AGN (N_H>10^{22} cm^{-2}) at the quasar epoch (z~2-3), as
well as to unobscured AGN as distant as z~7. Luminous X-ray emission is a sign
of accretion onto a supermassive black hole and thus reveals all but the most
heavily obscured AGN. We combine X-ray luminosity functions with appropriate
spectral energy distributions for AGN to model the X-ray, optical and
far-infrared flux distributions of the X-ray sources in the GOODS fields. A
simple model based on the unified paradigm for AGN, with ~3 times as many
obscured AGN as unobscured, successfully reproduces the z-band flux
distributions measured in the deep HST ACS observations on the GOODS North and
South fields. This model is also consistent with the observed spectroscopic and
photometric redshift distributions once selection effects are considered. The
previously reported discrepancy between observed spectroscopic redshift
distributions and the predictions of population synthesis models for the X-ray
background can be explained by bias against the most heavily obscured AGN
generated both by X-ray observations and the identification of sources via
optical spectroscopy. We predict the AGN number counts for Spitzer MIPS 24 um
and IRAC 3.6-8 um observations in the GOODS fields, which will verify whether
most AGN in the early Universe are obscured in the optical. Such AGN should be
very bright far-infrared sources and include some obscured AGN missed even by
X-ray observations.Comment: Accepted by ApJ; 39 pages, 13 figure