Moderate impacts of plant invasion and management regimes in coastal hind dune seed banks

Plant invaders may directly or indirectly affect ecosystem resilience through their impact on soil seed banks. The invaders, and the application of control measures, change seed bank dynamics by altering the number of seeds entering and leaving the seed bank. We tested the impact of bitou bush (Chrysanthemoides monilifera ssp. rotundata), on the seed bank. We examined seed banks in heavily-invaded, sparsely-invaded and managed dunes, where bitou bush biomass had been controlled. While management of bitou bush may have reduced the density of bitou bush seeds in the soil, it did not reduce the richness of other weed species. Native tree species richness was significantly higher in seed banks of sparsely-invaded than either heavily-invaded or managed sites, perhaps indicating a permanent shift in community structure following invasion. However, remaining indices of native seed bank diversity were similar across all invasion categories, indicating that seed banks of many native species were unaffected by both invasion and management. While examination of seed banks is informative in assessing past and potential community dynamics, low similarity between the standing vegetation and seed bank at all sites indicated that many hind dune species had other storage or regeneration modes and seed banks cannot be relied upon for comprehensive dune restoration.     

Genetic loci linking improved heat tolerance in wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.) to lower leaf and spike temperatures under controlled conditions

Heat stress adversely affects wheat production in many regions of the world and is particularly detrimental during reproductive development. The objective of this study was to identify novel quantitative trait loci (QTL) associated with improved heat tolerance in wheat (Triticum aestivum L.) and to confirm previous QTL results. To accomplish this, a recombinant inbred line (RIL) population was subjected to a three-day 38°C daytime heat stress treatment during early grain-filling. At maturity, a heat susceptibility index (HSI) was calculated from the reduction of three main spike yield components; kernel number, total kernel weight, and single kernel weight. The HSI, as well as temperature depression (TD) of the main spike and main flag leaf during heat stress were used as phenotypic measures of heat tolerance. QTL analysis identified 14 QTL for HSI, with individual QTL explaining from 4.5 to 19.3% of the phenotypic variance. Seven of these QTL co-localized for both TD and HSI. At all seven loci, the allele for a cooler flag leaf or spike temperature (up to 0.81°C) was associated with greater heat tolerance, indicated by a lower HSI. In a comparison to previous QTL results in a RIL population utilizing the same source of heat tolerance, seven genome regions for heat tolerance were consistently detected across populations. The genetic effect of combining three of these QTL, located on chromosomes 1B, 5A, and 6D, demonstrate the potential benefit of selecting for multiple heat tolerance alleles simultaneously. The genome regions identified in this study serve as potential target regions for fine-mapping and development of molecular markers for more rapid development of heat tolerant germplasm.     

Requirement for activin A and transforming growth factor--beta 1 pro-regions in homodimer assembly

Many proteins are initially synthesized as part of a large precursor. The role of the pro-region in the biosynthesis of transforming growth factor--beta 1 (TGF-beta 1) and activin A, two structurally related disulfide-linked homodimers synthesized as large precursors, was studied. Vectors that expressed either the pro-region or the mature regions of these molecules were used in complementation experiments, only when the pro-region was coexpressed with the mature region did intracellular dimerization and secretion of biologically active homodimers occur. The pro-regions of activin A and TGF-beta 1, therefore, aid the folding, disulfide bond formation, and export of their respective homodimers.     

Light-enhanced free radical formation and trypanocidal action of gentian violet (crystal violet)

Transmission of Chagas' disease by transfusion of blood containing Trypanosoma cruzi has often been reported, and gentian violet, a triarylmethane dye, is widely used by blood banks in attempts to eliminate such transmission. In a study of intact trypanosomes, gentian violet was found to undergo a one-electron reduction to produce a carbon-centered free radical as demonstrated by electron spin resonance spectroscopy. Either reduced nicotinamide adenine dinucleotide or the reduced dinucleotide phosphate could serve as a source of reducing equivalents for the production of this free radical by homogenates of Trypanosoma cruzi. The formation of this free radical, and the trypanocidal action of gentian violet, were enhanced by light. The enhanced free radical formation may be the basic cause of the selective toxicity of gentian violet to Trypanosoma cruzi.     

持续、低剂量金霉素对肉仔鸡免疫机能的抑制作用研究

270只Abore Acre商品代肉用公鸡随机分成3组，金霉素在饲料中添加水平分别为0、50只和150mg/kg，研究饲用金霉素对肉仔鸡法氏囊、脾脏和胸腺等免疫器官发育、以及免疫反应的影响。结果表明50mg/kg的金霉素对肉仔鸡脾脏和21日龄的胸腺无明显抑制作用，对T、B淋巴细胞转化率也无明显抑制作用（P＜0.05），而且显著促进法氏囊的萎缩（P＜0.05）。金霉素对T淋巴细胞转化率有明显的直接抑制作用；50mg/kg和150mg/kg的金素对BAS特异性抗体的产生均有显著的抑制作用（P＜0.01）。研究结果表明，持续、低剂量和金霉素对肉 鸡免疫器官发育和免疫应答具有显著的抑制作用，抑制作用随剂量增加而加强，150mg/kg的金霉素对肉仔鸡具有显著促生长作用。     

Quantum-confined stark effect in single CdSe nanocrystallite quantum dots

The quantum-confined Stark effect in single cadmium selenide (CdSe) nanocrystallite quantum dots was studied. The electric field dependence of the single-dot spectrum is characterized by a highly polarizable excited state ( approximately 10(5) cubic angstroms, compared to typical molecular values of order 10 to 100 cubic angstroms), in the presence of randomly oriented local electric fields that change over time. These local fields result in spontaneous spectral diffusion and contribute to ensemble inhomogeneous broadening. Stark shifts of the lowest excited state more than two orders of magnitude larger than the linewidth were observed, suggesting the potential use of these dots in electro-optic modulation devices.