175 research outputs found
Impact of ubiquitous inhibitors on the GUS gene reporter system: evidence from the model plants Arabidopsis, tobacco and rice and correction methods for quantitative assays of transgenic and endogenous GUS
<p>Abstract</p> <p>Background</p> <p>The β-glucuronidase (GUS) gene reporter system is one of the most effective and employed techniques in the study of gene regulation in plant molecular biology. Improving protocols for GUS assays have rendered the original method described by Jefferson amenable to various requirements and conditions, but the serious limitation caused by inhibitors of the enzyme activity in plant tissues has thus far been underestimated.</p> <p>Results</p> <p>We report that inhibitors of GUS activity are ubiquitous in organ tissues of Arabidopsis, tobacco and rice, and significantly bias quantitative assessment of GUS activity in plant transformation experiments. Combined with previous literature reports on non-model species, our findings suggest that inhibitors may be common components of plant cells, with variable affinity towards the <it>E. coli </it>enzyme. The reduced inhibitory capacity towards the plant endogenous GUS discredits the hypothesis of a regulatory role of these compounds in plant cells, and their effect on the bacterial enzyme is better interpreted as a side effect due to their interaction with GUS during the assay. This is likely to have a bearing also on histochemical analyses, leading to inaccurate evaluations of GUS expression.</p> <p>Conclusions</p> <p>In order to achieve reliable results, inhibitor activity should be routinely tested during quantitative GUS assays. Two separate methods to correct the measured activity of the transgenic and endogenous GUS are presented.</p
Stylar peroxidases and heteromorphic incompatibility reactions in Primula acaulis Hill («thrum» morph)
SUMMARYIn non-, self- and cross-pollinated styles of Primula acaulis «thrum» morph, the distribution of apoplastic peroxidase activity has been investigated, by means of the cytochemical treatment with diaminobenzidine. Apoplastic peroxidase activity was detected throughout the transmitting tract (at the «neck» region level) in non- and self-pollinated styles. The enzyme has been related to the predisposition of incompatible pollen tube rejection, no appreciable differences in enzyme distribution having been found between non- and self-pollinated styles since, in this morph, incompatible pollen tubes hardly ever reach the stylar neck. Compatible intermorph pollination caused the disappearance of apoplastic peroxidase activity in the central portion of the transmitting tract, where pollen tubes elongated, utilizing the reserves of the stylar cells, which appeared highly degenerate. Stylar apoplastic peroxidases seem then to play a role in heteromorphic incompatibility responses
Stochastic processes, galactic star formation, and chemical evolution. Effects of accretion, stripping, and collisions in multiphase multi-zone models
This paper reports simulations allowing for stochastic accretion and mass
loss within closed and open systems modeled using a previously developed
multi-population, multi-zone (halo, thick disk, thin disk) treatment. The star
formation rate is computed as a function of time directly from the model
equations and all chemical evolution is followed without instantaneous
recycling. Several types of simulations are presented here: (1) a closed system
with bursty mass loss from the halo to the thick disk, and from the thick to
the thin disk, in separate events to the thin disk; (2) open systems with
random environmental (extragalactic) accretion, e.g. by infall of high velocity
clouds directly to the thin disk; (3) schematic open system single and multiple
collision events and intracluster stripping. For the open models, the mass of
the Galaxy has been explicitly tracked with time. We present the evolution of
the star formation rate, metallicity histories, and concentrate on the light
elements. We find a wide range of possible outcomes, including an explanation
for variations in the Galactic D/H ratio, and highlight the problems for
uniquely reconstructing star forming histories from contemporary abundance
measurements.Comment: 12 pages, 12 Postscript figures, uses A&A style macros. Accepted for
publication by Astronomy & Astrophysic
Spectrophotometric Observations of Blue Compact Dwarf Galaxies: Mrk 370
We present results from a detailed spectrophotometric analysis of the blue
compact dwarf galaxy (BCD) Mrk 370, based on deep UBVRI broad-band and Halpha
narrow-band observations, and long-slit and two-dimensional spectroscopy of its
brightest knots. The spectroscopic data are used to derive the internal
extinction, and to compute metallicities, electronic density and temperature in
the knots. By subtracting the contribution of the underlying older stellar
population, modeled by an exponential function, removing the contribution from
emission lines, and correcting for extinction, we can measure the true colors
of the young star-forming knots. We show that the colors obtained this way
differ significantly from those derived without the above corrections, and lead
to different estimates of the ages and star-forming history of the knots. Using
predictions of evolutionary synthesis models, we estimate the ages of both the
starburst regions and the underlying stellar component. We found that we can
reproduce the colors of all the knots with an instantaneous burst of star
formation and the Salpeter initial mass function with an upper mass limit of
100 solar masses. The resulting ages range between 3 and 6 Myrs. The colors of
the low surface brightness component are consistent with ages larger than 5
Gyr. The kinematic results suggest ordered motion around the major axis of the
galaxy.Comment: 26 pages with 14 figures; accepted for publication in Ap
Reduction of chemical networks. I. The case of molecular clouds
We present a new method to analyse and reduce chemical networks and apply
this technique to the chemistry in molecular clouds. Using the technique, we
investigated the possibility of reducing the number of chemical reactions and
species in the UMIST 95 database simultaneously. In addition, we did the same
reduction but with the ``objective technique'' in order to compare both
methods. We found that it is possible to compute the abundance of carbon
monoxide and fractional ionisation accurately with significantly reduced
chemical networks in the case of pure gas-phase chemistry. For gas-grain
chemistry involving surface reactions reduction is not worthwhile. Compared to
the ``objective technique'' our reduction method is more effective but more
time-consuming as well.Comment: 15 pages, 7 postscript figures, accepted for publication in A&
Peculiar Features of the Velocity Field of OB Associations and the Spiral Structure of the Galaxy
Some of the peculiar features of the periodic velocity-field structure for OB
associations can be explained by using the model of Roberts and Hausman (1984),
in which the behavior of a system of dense clouds is considered in a perturbed
potential. The absence of statistically significant variations in the azimuthal
velocity across the Carina arm, probably, results from its sharp increase
behind the shock front, which is easily blurred by distance errors. The
existence of a shock wave in the spiral arms and, at the same time, the
virtually free motion of OB associations in epicycles can be reconciled in the
model of particle clouds with a mean free path of 0.2-2 kpc. The velocity field
of OB associations exhibits two appreciable nonrandom deviations from an ideal
spiral pattern: a 0.5-kpc displacement of the Cygnus- and Carina-arm fragments
from one another and a weakening of the Perseus arm in quadrant III. However,
the identified fragments of the Carina, Cygnus, and Perseus arms do not belong
to any of the known types of spurs.Comment: 14 pages, 3 postscript figures, to be published in Astronomy Letter
Tracing spiral density waves in M81
We use SPITZER IRAC 3.6 and 4.5micron near infrared data from the Spitzer
Infrared Nearby Galaxies Survey (SINGS), optical B, V and I and 2MASS Ks band
data to produce mass surface density maps of M81. The IRAC 3.6 and 4.5micron
data, whilst dominated by emission from old stellar populations, is corrected
for small-scale contamination by young stars and PAH emission. The I band data
are used to produce a mass surface density map by a B-V colour-correction,
following the method of Bell and de Jong. We fit a bulge and exponential disc
to each mass map, and subtract these components to reveal the non-axisymmetric
mass surface density. From the residual mass maps we are able to extract the
amplitude and phase of the density wave, using azimuthal profiles. The response
of the gas is observed via dust emission in the 8micron IRAC band, allowing a
comparison between the phase of the stellar density wave and gas shock. The
relationship between this angular offset and radius suggests that the spiral
structure is reasonably long lived and allows the position of corotation to be
determined.Comment: 15 pages, 17 figures, accepted for publication in MNRA
PREVALENCE OH HYPOSPADIAS IN ITALY ACCORDING TO SEVERITY, GESTATIONAL AGE AND BIRTWEIGHT: AN EPIDEMIOLOGICAL STUDY
Integral Field Spectroscopy of Blue Compact Dwarf Galaxies
We present results on integral-field optical spectroscopy of five luminous
Blue Compact Dwarf galaxies. The data were obtained using the fiber system
INTEGRAL attached at the William Herschel telescope. The galaxies Mrk 370, Mrk
35, Mrk 297, Mrk 314 and III Zw 102 were observed. The central 33"x29" regions
of the galaxies were mapped with a spatial resolution of 2"/spaxel, except for
Mrk 314, in which we observed the central 16"x12" region with a resolution of
0.9"/spaxel$. We use high-resolution optical images to isolate the star-forming
knots in the objects; line ratios, electron densities and oxygen abundances in
each of these regions are computed. We build continuum and emission-line
intensity maps as well as maps of the most relevant line ratios: [OIII]5007\Hb,
[NII]6584\Ha, and Ha\Hb, which allow us to obtain spatial information on the
ionization structure and mechanisms. We also derive the gas velocity field from
the Ha and [OIII]5007 emission lines.
We find that all the five galaxies are in the high end of the metallicity
range of Blue Compact Dwarf galaxies, with oxygen abundances varying from
Z\sun~0.3 to Z\sun~1.5. The objects show HII-like ionization in the whole field
of view, except the outer regions of IIIZw102 whose large [NII]6584/Ha values
suggest the presence of shocks. The five galaxies display inhomogeneous
extinction patterns, and three of them have high Ha/Hb ratios, indicative of a
large dust content; all galaxies display complex, irregular velocity fields in
their inner regions.Comment: 26 pages, 14 figures, 5 tables. Accepted for publication in the Ap
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