430 research outputs found
The distribution of ATP within tomato (Lycopersicon esculentum Mill.) embryos correlates with germination whee as total ATP concentration does not
The distribution of ATP in tomato seeds was visualized by monitoring the luminescence of frozen sections on top of a gel containing all the components of the luciferase reaction, but excluding ATP. ATP was imaged in germinating tomato seeds at intervals of 3, 6, 17, 24 and 48 h and in seeds with primary or secondary dormancy. ATP was present mainly in the embryo and concentrated in the radicle tip towards the completion of germination. In contrast to germinating seeds, ATP was distributed more evenly in dormant seeds. For germination, the ratio of ATP concentration in the radicle tip versus cotyledons was decisive, rather than the absolute concentration
Clinical Medicine and Clinical Trials
The author discusses the role of clinical trials in clinical medicine
Germination and dormancy of single tomato seeds : a study using non-invasive molecular and biophysical techniques
Formation , germination and dormancy of seeds are important steps in the life cycle of higher plants. The seed is the generative dispersal unit, which enables plants to spread and survive through periods or seasons of less favourable conditions. In agriculture tomato is an important crop and seed companies go through big efforts to deliver uniformly germinating seed batches. Uniform germination of a seed lot does not often come naturally. Seed to seed variation in timing of germination and also dormancy cause non-uniform germination of seed batches. This variation and dormancy of tomato seeds is the subject of the experimental work presented in this thesis. Several molecular and biophysical techniques have been used to expand our knowledge of tomato seed physiology.The firefly luciferase-luciferin system has been used in two distinct techniques to study single tomato seeds. A reporter gene construct consisting of a CaMV 35S promoter and the luciferase gene was introduced in tomato by Agrobacterium mediated transformation (Chapter 2). Transgenic seeds were obtained and imbibed in 0.1 mM luciferin solutions. The expression of the luciferase gene was linked with photon emission from the seeds during germination. Luciferase was expressed in a developmental pattern during germination in all germinating seeds. Luciferase expression increased during germination. Although the expression pattern of luciferase was intrinsically linked with the completion of germination, the luciferase activity of a single seed could not be used as a prediction of the time point of visible germination or of the germination rate of a single seed. This was due to the combination of both a time component and an intrinsic variation in the level of expression.Both primarily and secondarily dormant tomato seeds did not show luciferase activity. This enabled us to distinguish, non destructively, dormant from germinating tomato seeds prior to radicle protrusion and, hence, separation of those seeds for future experiments.Luciferase was also used to visualize distribution of ATP in sections of tomato seeds during dormancy and germination (Chapter 3). It was shown that not the overall ATP level or concentration of a seed was related to germination or dormancy per se , but merely the localised increase of ATP levels in the radicle. Dormant tomato seeds did not show an increase in the level of ATP in the radicle.Germination of seeds starts with the uptake of water and finishes by water uptake by the radicle at the initiation of seedling growth. Water uptake by tomato seeds was studied with the use of NMR-imaging (Chapter 4) . Water uptake resulted in an uneven distribution of water over the seed tissues. The endosperm had higher water content during germination. Radicle protrusion was accompanied by an uptake of extra water, thereby stretching the endosperm outward which resulted in rupture of the endosperm cap, which marked the end of germination. In contrast with the commonly adopted model in which seeds take up extra water only after germination, tomato seeds showed this extra water uptake prior to germination.Linker histones play an important role in the regulation of gene expression by remodelling DNA architecture. Distinct linker histones are thereby under control of different developmental processes in plants. With this in mind we have studied the expression of two different linker histones in tomato, which were originally believed to be under control of either GA or ABA, by the use of reverse-transciptase PCR. ABA and GA are antagonists in the regulation of seed germination and this makes both linker histones excellent candidates to play a role in the regulation of germination and dormancy of tomato seeds (Chapter 5). It was shown that the two different linker histones were differentially expressed in seeds, in relation with dormancy or germination. The linker histones also appeared not to be necessarily under direct control of either GA or ABA. A model is presented in which dormancy and germination are controlled by the linker histones, which, on their turn, are under direct control of phytochrome signal transduction. Expression of the histones may be stimulated or accompanied by ABA or GA
On the Exchange of Kinetic and Magnetic Energy Between Clouds and the Interstellar Medium
We investigate, through 2D MHD numerical simulations, the interaction of a
uniform magnetic field oblique to a moving interstellar cloud. In particular we
explore the transformation of cloud kinetic energy into magnetic energy as a
result of field line stretching. Some previous simulations have emphasized the
possible dynamical importance of a ``magnetic shield'' formed around clouds
when the magnetic field is perpendicular to the cloud motion (Jones et al.
1996, Miniati et al. 1998). It was not clear, however, how dependent those
findings were to the assumed field configuration and cloud properties. To
expand our understanding of this effect, we examine several new cases by varing
the magnetic field orientation angle with respect to the cloud motion (\theta),
the cloud-background density contrast, and the cloud Mach number.
We show that in 2D and with \theta large enough, the magnetic field tension
can become dominant in the dynamics of the motion of high density contrast, low
Mach number clouds. In such cases a significant fraction of cloud kinetic
energy can be transformed into magnetic energy with the magnetic pressure at
the cloud nose exceeding the ram pressure of the impinging flow. We derive a
characteristic timescale for this process of energy ``conversion''. We find
also that unless the cloud motion is highly aligned to the magnetic field,
reconnection through tearing mode instabilities in the cloud wake limit the
formation of a strong flux rope feature following the cloud. Finally we attempt
to interpret some observational properties of the magnetic field in view of our
results.Comment: 24 pages in aaspp4 Latex and 7 figures. Accepted for publication in
The Astrophysical Journa
Isotopic Production Cross Sections in Proton-Nucleus Collisions at 200 MeV
Intermediate mass fragments (IMF) from the interaction of Al,
Co and Au with 200 MeV protons were measured in an angular range
from 20 degree to 120 degree in the laboratory system. The fragments, ranging
from isotopes of helium up to isotopes of carbon, were isotopically resolved.
Double differential cross sections, energy differential cross sections and
total cross sections were extracted.Comment: accepted by Phys. Rev.
GMRT Observations of the 2006 outburst of the Nova RS Ophiuchi: First detection of emission at radio frequencies < 1.4 GHz
The first low radio frequency (<1.4 GHz) detection of the outburst of the
recurrent nova RS Ophiuchi is presented in this letter. Radio emission was
detected at 0.61 GHz on day 20 with a flux density of ~48 mJy and at 0.325 GHz
on day 38 with a flux density of ~ 44 mJy. This is in contrast with the 1985
outburst when it was not detected at 0.327 GHz even on day 66. The emission at
low radio frequencies is clearly non-thermal and is well-explained by a
synchrotron spectrum of index alpha ~ -0.8 (S propto nu^alpha) suffering
foreground absorption due to the pre-existing, ionized, warm, clumpy red giant
wind. The absence of low frequency radio emission in 1985 and the earlier
turn-on of the radio flux in the current outburst are interpreted as being due
to higher foreground absorption in 1985 compared to that in 2006, suggesting
that the overlying wind densities in 2006 are only ~30% of those in 1985.Comment: 14 pages, 1 figure. Accepted for publication in ApJ
TRIS III: the diffuse galactic radio emission at
We present values of temperature and spectral index of the galactic diffuse
radiation measured at 600 and 820 MHz along a 24 hours right ascension circle
at declination . They have been obtained from a subset of
absolute measurements of the sky temperature made with TRIS, an experiment
devoted to the measurement of the Cosmic Microwave Background temperature at
decimetric-wavelengths with an angular resolution of about .
Our analysis confirms the preexisting picture of the galactic diffuse
emission at decimetric wavelength and improves the accuracy of the measurable
quantities. In particular, the signal coming from the halo has a spectral index
in the range above 600 MHz, depending on the sky position. In the
disk, at TRIS angular resolution, the free-free emission accounts for the 11%
of the overall signal at 600 MHz and 21% at 1420 MHz. The polarized component
of the galactic emission, evaluated from the survey by Brouw and Spoelstra,
affects the observations at TRIS angular resolution by less than 3% at 820 MHz
and less than 2% at 600 MHz. Within the uncertainties, our determination of the
galactic spectral index is practically unaffected by the correction for
polarization.
Since the overall error budget of the sky temperatures measured by TRIS at
600 MHz, that is 66 mK(systematic)18 mK (statistical), is definitely smaller
than those reported in previous measurements at the same frequency, our data
have been used to discuss the zero levels of the sky maps at 150, 408, 820 and
1420 MHz in literature. Concerning the 408 MHz survey, limiting our attention
to the patch of sky corresponding to the region observed by TRIS, we suggest a
correction of the base-level of K.Comment: Accepted for publication in the Astrophysical Journa
Properties of the warm magnetized ISM, as inferred from WSRT polarimetric imaging
We describe a first attempt to derive properties of the regular and turbulent
Galactic magnetic field from multi-frequency polarimetric observations of the
diffuse Galactic synchrotron background. A single-cell-size model of the thin
Galactic disk is constructed which includes random and regular magnetic fields
and thermal and relativistic electrons. The disk is irradiated from behind with
a uniform partially polarized background. Radiation from the background and
from the thin disk is Faraday rotated and depolarized while propagating through
the medium. The model parameters are estimated from a comparison with 350 MHz
observations in two regions at intermediate latitudes done with the Westerbork
Synthesis Radio Telescope. We obtain good consistency between the estimates for
the random and regular magnetic field strengths and typical scales of structure
in the two regions. The regular magnetic field strength found is a few
microGauss, and the ratio of random to regular magnetic field strength is 0.7
+/- 0.5, for a typical scale of the random component of 15 +/- 10 pc.
Furthermore, the regular magnetic field is directed almost perpendicular to the
line of sight. This modeling is a potentially powerful method to estimate the
structure of the Galactic magnetic field, especially when more polarimetric
observations of the diffuse synchrotron background at intermediate latitudes
become available.Comment: 12 pages, 6 figures, accepted by A&
A Sino-German 6\ cm polarization survey of the Galactic plane VI. Discovery of supernova remnants G178.2-4.2 and G25.1-2.3
Supernova remnants (SNRs) were often discovered in radio surveys of the
Galactic plane. Because of the surface-brightness limit of previous surveys,
more faint or confused SNRs await discovery. The Sino-German 6\ cm
Galactic plane survey is a sensitive survey with the potential to detect new
low surface-brightness SNRs. We want to identify new SNRs from the 6\
cm survey map of the Galactic plane. We searched for new shell-like objects in
the 6\ cm survey maps, and studied their radio emission, polarization,
and spectra using the 6\ cm maps together with the 11\ cm and
21\ cm Effelsberg observations. Extended polarized objects with
non-thermal spectra were identified as SNRs. We have discovered two new, large,
faint SNRs, G178.2-4.2 and G25.1-2.3, both of which show shell structure.
G178.2-4.2 has a size of 72 arcmin x 62 arcmin with strongly polarized emission
being detected along its northern shell. The spectrum of G178.2-4.2 is
non-thermal, with an integrated spectral index of . Its
surface brightness is , which makes G178.2-4.2 the second faintest known Galactic SNR.
G25.1-2.3 is revealed by its strong southern shell which has a size of 80
arcmin x 30\arcmin. It has a non-thermal radio spectrum with a spectral index
of . Two new large shell-type SNRs have been detected at
6\ cm in an area of 2200 deg^2 along the the Galactic plane. This
demonstrates that more large and faint SNRs exist, but are very difficult to
detect.Comment: 8 pages, 8 figures, accepted by Astronomy and Astrophysics. For the
version with high resolution figures, please go to
http://zmtt.bao.ac.cn/6cm/papers/2newSNR.pd
Detection of continuum radio emission associated with Geminga
A deep Very Large Array observation of the Geminga pulsar field led to the
discovery, at a higher than 10 sigma significance level, of radio emission
trailing the neutron star proper motion. This 10-arcsec-long radio feature,
detected with a flux of 0.4 mJy at 4.8 GHz, is marginally displaced (2.7\pm1.8
arcsec) from the pulsar (which, at any rate, is unlikely to contribute with
magnetospheric pulsed emission more than 15% to the total observed radio
luminosity, about 1E26 erg/s) and positionally coincident with the X-ray axial
tail recently discovered by Chandra and ascribed to the pulsar wind nebula
(PWN). Overall, the Geminga radio tail is compatible with the scenario of a
synchrotron-emitting PWN, but the present data do not allow us to discriminate
between different (and not always necessarily mutually exclusive) possible
processes for producing that. If this radio feature does not result from
intrinsic peculiarities of Geminga, but its proximity and radio-quiet nature
(both helping in not hindering the faint diffuse radio emission), other
relatively near and energetic radio-quiet pulsars could show similar structures
in dedicated interferometric observations.Comment: Version accepted by MNRAS Letters (new title and substantial changes
in response to referees reports); 5 pages, 2 colour figure
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