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991.
Aggregation of the amyloid-β (Aβ) peptide is considered a central event in the pathogenesis of Alzheimer's disease (AD). In order to bypass methodological bias related to a variety of impurities commonly present in typical preparations of synthetic Aβ, we developed a simple, generally applicable method for recombinant production of human Aβ and Aβ variants in Escherichia coli that provides milligram quantities of Aβ in very high purity and yield. Amyloid fibril formation in vitro by human Aβ1-42, the key amyloidogenic Aβ species in AD, was completed threefold faster with recombinant Aβ1-42 compared to synthetic preparations. In addition, recombinant Aβ1-42 was significantly more toxic to cultured rat primary cortical neurons, and it was more toxic in vivo, as shown by strongly increased induction of abnormal phosphorylation of tau and tau aggregation into neurofibrillary tangles in brains of P301L tau transgenic mice. We conclude that even small amounts of impurities in synthetic Aβ—including a significant fraction of racemized peptides that cannot be avoided due to the technical limitations of peptide synthesis—prevent or slow Aβ incorporation into the regular quaternary structure of growing β-amyloid fibrils. The results validate the use of recombinant Aβ1-42 for both in vitro and in vivo studies addressing the mechanisms underlying Aβ aggregation and its related biological consequences for the pathophysiology, therapy, and prevention of AD. 相似文献
992.
Chandraraj Krishnan Leonardo da Costa Sousa Mingjie Jin Linpei Chang Bruce E. Dale Venkatesh Balan 《Biotechnology and bioengineering》2010,107(3):441-450
Sugarcane is one of the major agricultural crops cultivated in tropical climate regions of the world. Each tonne of raw cane production is associated with the generation of 130 kg dry weight of bagasse after juice extraction and 250 kg dry weight of cane leaf residue postharvest. The annual world production of sugarcane is ~1.6 billion tones, generating 279 MMT tones of biomass residues (bagasse and cane leaf matter) that would be available for cellulosic ethanol production. Here, we investigated the production of cellulosic ethanol from sugar cane bagasse and sugar cane leaf residue using an alkaline pretreatment: ammonia fiber expansion (AFEX). The AFEX pretreatment improved the accessibility of cellulose and hemicelluloses to enzymes during hydrolysis by breaking down the ester linkages and other lignin carbohydrate complex (LCC) bonds and the sugar produced by this process is found to be highly fermentable. The maximum glucan conversion of AFEX pretreated bagasse and cane leaf residue by cellulases was ~85%. Supplementation with hemicellulases during enzymatic hydrolysis improved the xylan conversion up to 95–98%. Xylanase supplementation also contributed to a marginal improvement in the glucan conversion. AFEX‐treated cane leaf residue was found to have a greater enzymatic digestibility compared to AFEX‐treated bagasse. Co‐fermentation of glucose and xylose, produced from high solid loading (6% glucan) hydrolysis of AFEX‐treated bagasse and cane leaf residue, using the recombinant Saccharomyces cerevisiae (424A LNH‐ST) produced 34–36 g/L of ethanol with 92% theoretical yield. These results demonstrate that AFEX pretreatment is a viable process for conversion of bagasse and cane leaf residue into cellulosic ethanol. Biotechnol. Bioeng. 2010;107: 441–450. © 2010 Wiley Periodicals, Inc. 相似文献
993.
Rust diseases cause significant reductions annually in yield of cereal crops worldwide. Traditional monoculture cropping systems apply significant selection pressure on the pathogen to cause rapid shifts in pathotypes. Plant breeders strive to stay ahead of the evolving pathogens by releasing new crop genotypes with new rust resistance genes or gene combinations. Owing to the limited number of known resistance genes and the lack of molecular understanding of the plant-pathogen interaction, rusts remain challenging organisms to study, both at organismal and molecular levels. This review discusses recent progress by a number of laboratories towards better understanding the molecular component of rust disease resistance. 相似文献
994.
Contribution of leaf surface fungi to the air spora 总被引:1,自引:0,他引:1
High concentrations of airborne fungal spores frequently occur from spring through fall in temperate areas of the world. Although
it is generally assumed that fungi on leaf surfaces are contributors to the air spora, little data are available comparing
the types of fungi found on leaf surfaces with those in the atmosphere. Air sampling was carried out with a Burkard Spore
Trap located on the roof of a building on the University of Tulsa campus using standard methods. Leaf samples were aseptically
collected from Ulmus americana and Quercus palustris trees on campus, placed in sterile plastic bags, and brought to the lab. For each leaf, 4 cm2 areas of both upper and lower leaf surfaces were swabbed and plated on malt extract agar with streptomycin. Cultures were
incubated at room temperature for 5–7 days and then examined microscopically. Results were expressed as colony forming units
(CFU)/cm2. Twenty-one fungal taxa were identified from the air samples. The most abundant taxa were Cladosporium, ascospores, basidiospores, and Alternaria; together these four spore types comprised over 90% of the yearly total. Yeasts were the most abundant fungi isolated from
both leaf types. Among the mycelial fungi were Phoma species, followed by Cladosporium and Alternaria. Overall twenty genera of filamentous fungi were identified. Yeasts and Phoma are normally splash dispersed and were not identified in the Burkard air samples. However, 10 taxa isolated from leaf surfaces
were registered in air samples. Crude estimates of the leaf surface area of each tree suggest that the total fungal load was
approximately 5.04×108 CFU for Ulmus and 2.71×108 CFU for Quercus. Of these levels, 19% were from fungi also detected in air samples. The data suggest that some leaf-surface fungi are major
contributors to the air spora. 相似文献
995.
外源SOD和APX基因在转基因烟草中的表达与遗传 总被引:3,自引:0,他引:3
分析转超氧化物歧化酶基因(SOD)或抗坏血酸过氧化物酶基因(APX)烟草及其自交和杂交后代的叶片中超氧化物歧化酶(SOD)和过氧化物酶(POD)活性的结果表明:转基因烟草的SOD和POD活性在终花期最强,不同叶位叶中SOD活性差异不明显,POD活性以下部叶为最高;转基因烟草的SOD或POD活性显著高于近等基因的非转基因品系。杂交后代(F1、F2)的SOD活性能保持稳定,略高于亲本;自交后代(S1~S3)与自交亲本的SOD和POD活性相当。 相似文献
996.
997.
The TTAA-specific lepidopteran transposon piggyBac has already proved useful as a gene-transfer vector for efficient transformation of a wide variety of insects. Transposable element excision and transposition assays are useful indicators of an element's ability to be mobilized in vivo and, thus, potentially serve as a transforming vector. Here, we report that this transposon is capable of excision and transposition in tobacco budworm embryos with relatively low frequency. 相似文献
998.
The calling activity of virgin Phyllonorycter junoniella (Z.) females under a cycling thermal regime differed from that under constant temperature in the following ways: the percentage of females calling at the morning activity peak was increased; the morning period of calling activity was prolonged; the total period of calling activity of an individual female was increased; an extra peak of activity occurred at the end of the photophase, and females changed the calling pattern during the active period. We assume that the occurrence of two calling peaks and the extension of the calling period might be adaptive for a Ph. junoniella species with a sex ratio strongly shifted towards females (8:1 females:males), as it could lead to an increased proportion of females mated. 相似文献
999.
Determinants of Leaf Litter Nutrient Cycling in a Tropical Rain Forest: Soil Fertility Versus Topography 总被引:1,自引:0,他引:1
We investigated the influence of landscape-level variation in soil fertility and topographic position on leaf litter nutrient
dynamics in a tropical rain forest in Costa Rica. We sampled across the three main edaphic conditions (ultisol slope, ultisol
plateau, and inceptisol) to determine the effect of soil nutrients on leaf litter nutrient concentrations while controlling
for topography, and to examine topographic effects while controlling for soil nutrients. Both leaf litter macronutrient [phosphorus
(P), nitrogen (N), sulfur (S), calcium (Ca), potassium (K), magnesium (Mg)] and micronutrient concentrations were quantified
throughout a 4-year period. Leaf litter [P], [N] and [K] varied significantly among soil types. The variation in [P], [N],
and [K] was explained by soil fertility alone. Leaf litter [S], [Ca], and [Mg] did not vary among the three soil types. Macronutrient
(P, K, Mg, S, Ca) concentrations in the leaf litter were much less variable than those of Fe and Al. Lower variability in
essential plant nutrients suggests a great deal of plant control over the amount of nutrients resorbed before senescense.
Leaf litter macronutrient concentrations varied significantly over the 4-year period, but the temporal variation did not differ
among the three edaphic types as anticipated. Hence, although the magnitude of nutrient fluxes may be controlled by local
factors such as soil fertility, temporal patterns are likely regulated by a common environmental variable such as precipitation
or temperature. 相似文献
1000.
Our objective was to determine how varied is the response of C cycling to temperature and irradiance in tundra vegetation. We used a large chamber to measure C exchange
at 23 locations within a small arctic catchment in Alaska during summer 2003 and 2004. At each location, we determined light
response curves of C exchange using shade cloths, twice during a growing season. We used data to fit a simple photosynthesis-irradiance,
respiration-temperature model, with four parameters. We used a maximum likelihood technique to determine the acceptable parameter
space for each light curve, given measurement uncertainty. We then explored which sites and time periods had parameter sets
in common—an indication of functional similarity. We found that seven distinct parameter sets were required to explain observed
C flux responses to temperature and light variation at all sites and time periods. The variation in estimated maximum photosynthetic
rate (Pmax) was strongly correlated with measurements of site leaf area index (LAI). The behavior of tussock tundra sites, the dominant
vegetation of arctic tundra, could largely be described with a single parameter set, with a Pmax of 9.7 μmol m−2 s−1. Tussock tundra sites had, correspondingly, similar LAI (mean = 0.66). Non-tussock sites (for example, sedge and shrub tundras)
had larger spatial and temporal variations in both C dynamic parameters (Pmax varying from 9.7–25.7 μmol m−2 s−1) and LAI (0.6–2.0). There were no clear relationships between dominant non-tussock vegetation types and a particular parameter
set. Our results suggest that C dynamics of the acidic tussock tundra slopes and hilltops in northern Alaska are relatively
simply described during the peak growing season. However, the foot-slopes and water tracks have more variable patterns of
LAI and C exchange, not simply related to the dominant vegetation type. 相似文献