168 research outputs found
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Doubled haploid ramets via embryogenesis of haploid tissue cultures
Tissue culture in the oil palm business is generally concerned with the multiplication
(clonal production) of dura, pisifera and tenera palms. These are all normal diploids
(2n=2x=36). Sumatra Bioscience has pioneered haploid tissue culture of oil palm
(n=x=18). Haploid oil palm is the first step in producing doubled haploid palms
which in turn provide parental lines for F1 hybrid production. Chromosome doubling
is known to occur during embryogenesis in other haploid cultures, e.g. barley anther
culture. Haploid tissue cultures in oil palm were therefore set up to investigate and
exploit spontaneous chromosome doubling during embryogenesis. Flow cytometry of
embryogenic tissue showed the presence of both haploid (n) and doubled haploid (2n)
cells indicating spontaneous doubling. Completely doubled haploid ramets were
regenerated suggesting that doubling occurred during the first mitoses of
embryogenesis. This is the first report of doubled haploid production in oil palm via
haploid tissue culture. The method provides a means of producing a range of doubled
haploids in oil palm from the 1,000 plus haploids available at Sumatra Bioscience, in
addition the method also produced doubled haploid (and haploid) clones.
1
In vitro propagation of cedar (Cedrela odorata L.) from juvenile shoots
Garriga, M (Garriga, Miguel); Caligari, PDS (Caligari, Peter D. S.). Univ Talca, Inst Biol Vegetal & Biotecnol, Talca, ChileCedrela odorata L. is one of the most important timber species currently traded in the Caribbean and Central America; however, it has been intensively exploited. In vitro techniques and clonal propagation can help to develop new plantations and assist in establishing improvement programs for this species. The aim of this study was to develop a protocol to establish in vitro conditions and to micropropagate this species from nodal explants from juvenile cuttings taken from field trees. Disinfection of node explants with 5% propiconazole CE 25 during 3 min resulted in 100% explant disinfection and 60% morphogenic response on those established explants. Shoot development was optimized by cultivating in vitro node explants in Murashige and Skoog basal medium supplemented with 2 mg L(-1) 6-bencilaminopurine and 3 mg L(-1) naphthaleneacetic acid. This medium resulted in 100% shoot development from the in vitro node explants with a 3.93 cm mean height. Rooting was also stimulated 6 wk after individualization of the regenerated plants on the same micropropagation medium with a mean of 3.9 roots per plant. In vitro plants did not show morphologic differences when compared to ex vitro seeds
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Methods of producing haploid and doubled haploid oil palms
The present invention relates to haploid oil palm plants and homozygous doubled haploid oil palm plants. The invention also relates to methods for producing and selecting haploid and doubled haploid plants. More particularly, but not exclusively, the method may be used for selecting haploid and doubled haploid oil palm plants. Haploid and doubled haploid plants are selected by a large-scale screening based on a combination of the phenotype with the use of molecular methods combined with flow cytometry techniques to identify haploid and doubled haploid plants. More particularly, a method for selecting haploid and doubled haploid plants is described comprising: (a) germinating seeds; (b) selecting seedlings with atypical phenotype; (c) assessing heterozygosity using markers; (d) isolating cells from the seedlings and determining the DNA content of the cells; and (e) isolating and purifying the DNA and using defined molecular markers to characterise the genotype of the plant. The haploid oil palm plants may be used for producing homozygous doubled haploid oil palms: doubled haploids may be intercrossed to produce uniform F.sub.1 hybrids of superior properties
Magnetic flux generation and transport in cool stars
The Sun and other cool stars harbouring outer convection zones manifest
magnetic activity in their atmospheres. The connection between this activity
and the properties of a deep-seated dynamo generating the magnetic flux is not
well understood. By employing physical models, we study the spatial and
temporal characteristics of the observable surface field for various stellar
parameters. We combine models for magnetic flux generation, buoyancy
instability, and transport, which encompass the entire convection zone. The
model components are: (1) a thin-layer alpha-Omega dynamo at the base of the
convection zone; (2) buoyancy instabilities and the rise of flux tubes through
the convection zone in 3D, which provides a physically consistent determination
of emergence latitudes and tilt angles; and (3) horizontal flux transport at
the surface. For solar-type stars and rotation periods longer than about 10
days, the latitudinal dynamo waves generated by the deep-seated alpha-Omega
dynamo are faithfully reflected by the surface distribution of magnetic flux.
For rotation periods of the order of two days, however, Coriolis acceleration
of rising flux loops leads to surface flux emergence at much higher latitudes
than the dynamo waves at the bottom of the convection zone reach. A similar
result is found for a K0V star with a rotation period of two days. In the case
of a rapidly rotating K1 subgiant, overlapping dynamo waves lead to noisy
activity cycles and mixed-polarity fields at high latitudes.Comment: 14 pages, 14 figures. Accepted for publication in Astronomy &
Astrophysic
Magnetic flux emergence in granular convection: Radiative MHD simulations and observational signatures
We study the emergence of magnetic flux from the near-surface layers of the
solar convection zone into the photosphere. To model magnetic flux emergence,
we carried out a set of numerical radiative magnetohydrodynamics simulations.
Our simulations take into account the effects of compressibility, energy
exchange via radiative transfer, and partial ionization in the equation of
state. All these physical ingredients are essential for a proper treatment of
the problem. Furthermore, the inclusion of radiative transfer allows us to
directly compare the simulation results with actual observations of emerging
flux. We find that the interaction between the magnetic flux tube and the
external flow field has an important influence on the emergent morphology of
the magnetic field. Depending on the initial properties of the flux tube (e.g.
field strength, twist, entropy etc.), the emergence process can also modify the
local granulation pattern. The emergence of magnetic flux tubes with a flux of
Mx disturbs the granulation and leads to the transient appearance of
a dark lane, which is coincident with upflowing material. These results are
consistent with observed properties of emerging magnetic flux.Comment: To appear in A&
Simulation of the Formation of a Solar Active Region
We present a radiative magnetohydrodynamics simulation of the formation of an
Active Region on the solar surface. The simulation models the rise of a buoyant
magnetic flux bundle from a depth of 7.5 Mm in the convection zone up into the
solar photosphere. The rise of the magnetic plasma in the convection zone is
accompanied by predominantly horizontal expansion. Such an expansion leads to a
scaling relation between the plasma density and the magnetic field strength
such that . The emergence of magnetic flux into the
photosphere appears as a complex magnetic pattern, which results from the
interaction of the rising magnetic field with the turbulent convective flows.
Small-scale magnetic elements at the surface first appear, followed by their
gradual coalescence into larger magnetic concentrations, which eventually
results in the formation of a pair of opposite polarity spots. Although the
mean flow pattern in the vicinity of the developing spots is directed radially
outward, correlations between the magnetic field and velocity field
fluctuations allow the spots to accumulate flux. Such correlations result from
the Lorentz-force driven, counter-streaming motion of opposite-polarity
fragments. The formation of the simulated Active Region is accompanied by
transient light bridges between umbrae and umbral dots. Together with recent
sunspot modeling, this work highlights the common magnetoconvective origin of
umbral dots, light bridges and penumbral filaments.Comment: Accepted for publication in Ap
The dynamical disconnection of sunspots from their magnetic roots
After a dynamically active emergence phase, magnetic flux at the solar
surface soon ceases to show strong signs of the subsurface dynamics of its
parent magnetic structure. This indicates that some kind of disconnection of
the emerged flux from its roots in the deep convection zone should take place.
We propose a mechanism for the dynamical disconnection of the surface flux
based upon the buoyant upflow of plasma along the field lines. Such flows arise
in the upper part of a rising flux loop during the final phases of its buoyant
ascent towards the surface. The combination of the pressure buildup by the
upflow and the cooling of the upper layers of an emerged flux tube by radiative
losses at the surface lead to a progressive weakening of the magnetic field in
several Mm depth. When the field strength has become sufficiently low,
convective motions and the fluting instability disrupt the flux tube into thin,
passively advected flux fragments, thus providing a dynamical disconnection of
the emerged part from its roots. We substantiate this scenario by considering
the quasi-static evolution of a sunspot model under the effects of radiative
cooling, convective energy transport, and pressure buildup by a prescribed
inflow at the bottom of the model. For inflow speeds in the range shown by
simulations of thin flux tubes, we find that the disconnection takes place in a
depth between 2 and 6 Mm for disconnection times up to 3 days.Comment: 11 pages, 5 figures, accepted by A&
Solar Flux Emergence Simulations
We simulate the rise through the upper convection zone and emergence through
the solar surface of initially uniform, untwisted, horizontal magnetic flux
with the same entropy as the non-magnetic plasma that is advected into a domain
48 Mm wide from from 20 Mm deep. The magnetic field is advected upward by the
diverging upflows and pulled down in the downdrafts, which produces a hierarchy
of loop like structures of increasingly smaller scale as the surface is
approached. There are significant differences between the behavior of fields of
10 kG and 20 or 40 kG strength at 20 Mm depth. The 10 kG fields have little
effect on the convective flows and show little magnetic buoyancy effects,
reaching the surface in the typical fluid rise time from 20 Mm depth of 32
hours. 20 and 40 kG fields significantly modify the convective flows, leading
to long thin cells of ascending fluid aligned with the magnetic field and their
magnetic buoyancy makes them rise to the surface faster than the fluid rise
time. The 20 kG field produces a large scale magnetic loop that as it emerges
through the surface leads to the formation of a bipolar pore-like structure.Comment: Solar Physics (in press), 12 pages, 13 figur
A retrospective of the GREGOR solar telescope in scientific literature
In this review, we look back upon the literature, which had the GREGOR solar
telescope project as its subject including science cases, telescope subsystems,
and post-focus instruments. The articles date back to the year 2000, when the
initial concepts for a new solar telescope on Tenerife were first presented at
scientific meetings. This comprehensive bibliography contains literature until
the year 2012, i.e., the final stages of commissioning and science
verification. Taking stock of the various publications in peer-reviewed
journals and conference proceedings also provides the "historical" context for
the reference articles in this special issue of Astronomische
Nachrichten/Astronomical Notes.Comment: 6 pages, 2 color figures, this is the pre-peer reviewed version of
Denker et al. 2012, Astron. Nachr. 333, 81
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