Molecular Marker-Facilitated Investigations of Quantitative Trait Loci in Maize. II. Factors Influencing Yield and Its Component Traits

Because traits such as grain yield are polygenically inherited and strongly influenced by environment, determination of genotypic values from phenotypic expression is not precise and improvement strategies are frequently based on low heritabilities. Increased knowledge of the genetic factors involved in the expression of yield should enhance the improvement of this trait. The objectives of this study were to identify and locate genetic factors (i.e., quantitative trait loci, QTL\u27s) associated with grain yield and 24 yield-related traits in two F2populations of maize (Zea mays L.) using isozyme marker loci. (The populations were generated by selfing the F1, hybrids CO159 ✕ Tx303 and T232 ✕ CM37.) In addition, assessments of the types and magnitudes of gene effects expressed by these QTL\u27s were made. About two-thirds of the associations among 17 to 20 marker loci and the 25 quantitative traits were significant with a large proportion of these at P \u3c 0.001. Proportions of variation accounted for by genetic factors associated with individual marker loci varied from less than 1% to more than 11%. Although individual marker loci accounted for relatively small proportions of the phenotypic variation for these yield-related traits, differences between mean phenotypic values of the two homozygous classes at certain loci were occasionally more than 16% of the population mean. Also, different genomic regions contributed to yield through different subsets of the yield-related traits. Predominant types of gene action varied among loci and among the 25 quantitative traits. For plant grain yield, top ear grain weight, and ear length, the gene action was primarily dominant or overdominant. However, mainly additive gene action was implicated for ear number, kernel row number, and second ear grain weight. Results from these studies should prove to be useful for manipulating QTL\u27s in marker-facilitated selection program

Duplicated Chromosome Segments in Maize (Zea mays L.): Further Evidence from Hexokinase Isozymes

The genetic control of hexokinase isozymes (ATP: d-hexose-6-phosphotransferase, E.C. 2.7.7.1, HEX) in maize (Zea mays L.) was studied by starch gel electrophoresis. Genetic analysis of a large number of inbred lines and crosses indicates that the major isozymes observed are encoded by two nuclear loci, designated Hexl and Hex2. Five active allozymes and one null variant are associated with Hexl, while Hex2 has nine active alleles in addition to a null variant. Alleles at both loci govern the presence of single bands, with no intragenic or intergenic heteromers visible, suggesting that maize HEX\u27s are active as monomers. Organelle preparations demonstrate that the products of both loci are cytosolic. All alleles, including the nulls, segregate normally in crosses. Vigorous and fertile plants were synthesized that were homozygous for null alleles at both loci, suggesting that other hexosephosphorylating enzymes exist in maize that are undetected with our assay conditions. Linkage analyses and crosses with B-A translocation stocks place Hexl on the short arm of chromosome 3, 27 centimorgans from Pgd2 (phosphogluconate dehydrogenase) and Hex2 on the long arm of chromosome 6, approximately 45 centimorgans from Pgdl. It is suggested that the parallel linkages among these two pairs of duplicated genes reflects an evolutionary history involving chromosome segment duplication or polyploidy

Bursty, Broadband Electromagnetic Waves Associated with Thin Current Layers and Turbulent Magnetosheath Reconnection

We investigate observations of intense bursts of electromagnetic wave energy in association with the thin current layers of turbulent magnetosheath reconnection. These observed emissions form two distinct types: (i) broadband emissions that extend continuously to lOs of Hertz; and (ii) structured bursts of emitted energy that occur above 80-Hz, often displaying features reminiscent of absorption bands and are observed at local minima in the magnetic field. We present detailed analyses of these intense bursts of electromagnetic energy and quantify their proximity to X- and O-nulls, as well as their correlation to the amount of magnetic energy converted by the process of magnetic reconnection

Examination of Bursty Electromagnetic Waves Observed During Intervals of Turbulent Magnetosheath Reconnection

We investigate observations of intense bursts of electromagnetic waves in association with magnetic reconnection in the turbulent magnetosheath. These structured, broadband bursts occur above 80-Hz, often displaying features reminiscent of absorption bands and are observed at local minima in the magnetic field. We present detailed analyses of these intense bursts of electromagnetic waves and quantify their proximity to X- and O-nulls

Source of the Bursty Bulk Flow Diffuse Aurora: Electrostatic Cyclotron Harmonic and Whistler Waves in the Coupling of Bursty Bulk Flows to Auroral Precipitation

Electron cyclotron harmonic (ECH) and whistler chorus waves are recognized as the two mechanisms responsible for the resonant waveparticle interactions necessary to precipitate plasma sheet electrons into the ionosphere, producing the diffuse Aurora. Previous work has demonstrated ECH waves dominate electron scattering at L shells >8, while whistler chorus dominates scattering at L shells L 1, consistent with electron betatron acceleration. Here, however, we nd whistler chorus emissions throughout an interval of fast ows where Te,/Te,||< 1. Parallel electron beams account for the enhanced parallel electron temperature and serve as the instability mechanism for the whistler chorus. The parallel electron beams and associated cigarshaped distributions are consistent with Fermi acceleration at dipolarizations in fast ows. We demonstrate that the scattering efciency of the whistler chorus exceeds that of ECH waves, which THEMIS also detects during the fast ows. The obliquity of the whistler waves permits efcient scattering of lowerenergy electrons into the diffuse aurora. We conclude that Fermi acceleration of electrons provides one important freeenergy source for the waveparticle interactions responsible for coupling plasma sheet electrons into the diffuse aurora during substorm conditions

Quenched and Negative Hall Effect in Periodic Media: Application to Antidot Superlattices

We find the counterintuitive result that electrons move in OPPOSITE direction to the free electron E x B - drift when subject to a two-dimensional periodic potential. We show that this phenomenon arises from chaotic channeling trajectories and by a subtle mechanism leads to a NEGATIVE value of the Hall resistivity for small magnetic fields. The effect is present also in experimentally recorded Hall curves in antidot arrays on semiconductor heterojunctions but so far has remained unexplained.Comment: 10 pages, 4 figs on request, RevTeX3.0, Europhysics Letters, in pres

Bursty, Broadband Electromagnetic Waves Associated with Three-Dimensional Nulls Observed in Turbulent Magnetosheath Reconnection

We investigate observations of intense bursts of electromagnetic wave energy in association with the thin current layers of turbulent magnetosheath reconnection. These observed emissions - typically detected in the layers immediately outside of the current layer proper - form two distinct types: (i) broadband emissions that extend continuously to lOs of Hertz; and (ii) structured bursts of emitted energy that occur above 80-Hz, often displaying features reminiscent of absorption bands and are observed near the local minima in the magnetic field. We present detailed analyses of these intense bursts of electromagnetic energy and quantify their proximity to X-IO-nulls and magnetic spine connected null pairs, as well as their correlation - if any - to the amount of magnetic energy converted by the process of magnetic reconnection

Transplacental passage of vancomycin in the ex vivo human perfusion model.

OBJECTIVES: To determine maternal-fetal transplacental passage of vancomycin in the ex vivo human placental perfusion model. METHODS: Six term placentas were collected immediately after delivery and perfused with physiologic medium using the single cotyledon perfusion system. Vancomycin was added to the maternal medium and perfused through the maternal circulation of the cotyledon. Over a 1-h period in an open system, samples of the perfusate were collected at defined intervals from the fetal venous catheter and from the maternal effluence to assess vancomycin transfer. Thereafter, the system was closed for 1-5 h to establish accumulation. Transport fraction and clearance indexes were calculated by perfusing antipyrine 14C (positive control). Vancomycin was estimated by high pressure liquid chromatography and antipyrine 14C concentration was determined by liquid scintillation. RESULTS: Mean vancomycin maternal peak and trough concentrations ranged from 30.0 to 51.5 microg/ml and 7.7 to 16.4 microg/ml, respectively. Clearance indexes were minimal with a mean peak range of 0.000-0.080 and a mean trough range of 0.00-0.17. For each placenta, transport fraction for antipyrine 14C was > 1.85 with a single pass of > 40%. No accumulation of vancomycin was noted when the system was closed for 1-5 h. The mean peak clearance index was zero after perfusing the placenta for up to 5 h with 35.8 microg/ml of vancomycin. CONCLUSION: Transplacental passage of vancomycin was minimal in the ex vivo human placental perfusion model, with no detectable accumulation