1,354,135 research outputs found
Plastid Genotyping Reveals the Uniformity of Cytoplasmic Male Sterile-T Maize Cytoplasms
No full textCytoplasmic male-sterile (CMS) lines in maize (Zea mays) have been classified by their response to specific restorer genes into three categories: cms-C, cms-S, and cms-T. A mitochondrial genome representing each of the CMS cytotypes has been sequenced, and male sterility in the cms-S and cms-T cytotypes is linked to chimeric mitochondrial genes. To identify markers for plastid genotyping, we sequenced the plastid genomes of three fertile maize lines (B37, B73, and A188) and the B37 cms-C, cms-S, and cms-T cytoplasmic substitution lines. We found that the plastid genomes of B37 and B73 lines are identical. Furthermore, the fertile and CMS plastid genomes are conserved, differing only by zero to three single-nucleotide polymorphisms (SNPs) in coding regions and by eight to 22 SNPs and 10 to 21 short insertions/deletions in noncoding regions. To gain insight into the origin and transmission of the cms-T trait, we identified three SNPs unique to the cms-T plastids and tested the three diagnostic SNPs in 27 cms-T lines, representing the HA, I, Q, RS, and T male-sterile cytoplasms. We report that each of the tested 27 cms-T group accessions have the same three diagnostic plastid SNPs, indicating a single origin and maternal cotransmission of the cms-T mitochondria and plastids to the seed progeny. Our data exclude exceptional pollen transmission of organelles or multiple horizontal gene transfer events as the source of the mitochondrial urf13-T (unidentified reading frame encoding 13-kD cms-T protein) gene in the cms-T cytoplasms. Plastid genotyping enables a reassessment of the evolutionary relationships of cytoplasms in cultivated maize.Peer reviewe
Selective plant growth using D-amino acids
No full textSelectable marker genes are essential for the efficient selection of transgenic plants. Heterologous genes used as markers typically encode enzymes that neutralize a toxic compound, allowing for positive selection of plants containing the marker. We report on the efficacy of a novel marker gene system that exploits the varying phytotoxicity of D-amino acids and their oxidative deamination products. Our investigation of a putative DAAO gene from Schizosaccharomyces pombe reveals sufficient oxidative deaminase activity to confer D-alanine and D-serine tolerance to transgenic Arabidopsis thaliana plants carrying the heterologous spDAAO gene. We have demonstrated that the spDAAO, when used in conjunction with D-alanine, allows for the positive selection of primary transformants at levels comparable to hygromycin. Additionally, our selection scheme carries the potential for negative selection in the presence of different selection substrates, such as D-valine or D-isoleucine. This attribute, known as conditional selection would provide particular utility to applications involving site-specific recombinase mediated marker gene removal.M.S.Includes bibliographical references (p. 42-46)
Analysis of electron mobility versus temperature after photoexcitation in Si-doped AlxGa1-xAs
No full textOptical characterization of Al(X)Ga(1-x)Sb/GaSb epitaxial heterostructures
No full textThe complex refractive index n+ik and the dielectric function e1+ie2 at room temperature
of AlxGa12xSb films with 0<x<0.5, grown by molecular beam epitaxy on a GaSb substrate, were
determined from 0.02 to 6 eV by using the complementary data from fast Fourier transform
far-infrared, dispersive, and ellipsometric spectrometry. The effect of the native oxide was
accounted for and the self-consistency of the optical functions was checked in the framework of the
Kramers–Kronig causality relations. In the restrahlen region the dielectric function was well fitted
by classical Lorentz oscillators; in the transparent region below the fundamental gap E0, the
refractive index was modeled by a Sellmeier dispersion relation, and in the interband region the
dielectric function near the critical points was analyzed through standard line shapes. Interpolating
the fitting parameters or the interband dielectric spectra, it was possible to obtain the optical
functions for any concentration x between 0.0 and 0.5
PHOTOREFLECTANCE VERSUS PHOTOLUMINESCENCE IN STRAIN INDUCED QUANTUM WELL WIRES
No full textPhotoreflectance vs photoluminescence measurements of stress-induced quantum wires, obtained by patterning an InGaAs layer pseudomorphic grown on a GaAs well in wire-shaped stressors, are presented and compared. An excellent agreement was found between the experimental results obtained with the two techniques about the lateral confinement of the carriers and evidence is given at room temperature of quantization in two directions by means of photoreflectance
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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