Tree resistance to Lymantria dispar caterpillars: importance and limitations of foliar tannin composition

The ability of foliar tannins to increase plant resistance to herbivores is potentially determined by the composition of the tannins; hydrolyzable tannins are much more active as prooxidants in the guts of caterpillars than are condensed tannins. By manipulating the tannin compositions of two contrasting tree species, this work examined: (1) whether increased levels of hydrolyzable tannins increase the resistance of red oak (Quercus rubra L.), a tree with low resistance that produces mainly condensed tannins, and (2) whether increased levels of condensed tannins decrease the resistance of sugar maple (Acer saccharum Marsh.), a tree with relatively high resistance that produces high levels of hydrolyzable tannins. As expected, when Lymantria dispar L. caterpillars ingested oak leaves coated with hydrolyzable tannins, levels of hydrolyzable tannin oxidation increased in their midgut contents. However, increased tannin oxidation had no significant impact on oxidative stress in the surrounding midgut tissues. Although growth efficiencies were decreased by hydrolyzable tannins, growth rates remained unchanged, suggesting that additional hydrolyzable tannins are not sufficient to increase the resistance of oak. In larvae on condensed tannin-coated maple, no antioxidant effects were observed in the midgut, and levels of tannin oxidation remained high. Consequently, neither oxidative stress in midgut tissues nor larval performance were significantly affected by high levels of condensed tannins. Post hoc comparisons of physiological mechanisms related to tree resistance revealed that maple produced not only higher levels of oxidative stress in the midgut lumen and midgut tissues of L. dispar, but also decreased protein utilization efficiency compared with oak. Our results suggest that high levels of hydrolyzable tannins are important for producing oxidative stress, but increased tree resistance to caterpillars may require additional factors, such as those that produce nutritional stress.     

Integrating multiple data sources to assess the distribution and abundance of bottlenose dolphins Tursiops truncatus in Scottish waters

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Negative Effects of Sample Pooling on PCR-Based Estimates of Soil Microbial Richness and Community Structure

In this study, we examined the effect of various pooling strategies on the characterization of soil microbial community composition and phylotype richness estimates. Automated ribosomal intergenic spacer analysis (ARISA) profiles were determined from soil samples that were (i) unpooled (extracted and amplified individually), (ii) pooled prior to PCR amplification, or (iii) pooled prior to DNA extraction. Regression analyses suggest that the less even the soil microbial community (i.e., low Shannon equitability, E_H), the greater was the impact of either pooling strategy on microbial detection (R² = 0.766). For example, at a tropical rainforest site, which had the most uneven fungal (E_H of 0.597) and bacterial communities (E_H of 0.822), the unpooled procedure detected an additional 67 fungal and 115 bacterial phylotypes relative to either of the pooled procedures. Phylotype rarity, resulting in missed detection upon pooling, differed between the fungal and bacterial communities. Fungi were typified by locally abundant but spatially rare phylotypes, and the bacteria were typified by locally rare but spatially ubiquitous phylotypes. As a result, pooling differentially influenced plot comparisons, leading to an increase in similarity for the bacterial community and a decrease in the fungal community. In conclusion, although pooling reduces sample numbers and variability, it could mask a significant portion of the detectable microbial community, particularly for fungi due to their higher spatial heterogeneity.Microbial communities in soils are extremely complex, with heterogeneity expressed on a wide variety of scales (6-9, 16). Therefore, soil sampling strategies typically combine multiple small samples, obtained from various locations within the area of interest, into a single homogenized sample that is then subsampled for analysis. Previous studies (5, 11, 15) have compared the sizes of the subsamples to best represent the microbial diversity in the pooled samples. Larger sample sizes are typically recommended for community profiling (5, 11, 15) because they can reduce variability in the subsample and appear to adequately capture the dominant members of the community (3, 11). Conversely, multiple small subsamples have been proposed to be better suited for identifying rare community members and estimating species richness (10-11). While previous studies have largely been conducted to determine the variability of the subsample—and, hence, its ability to represent the larger, homogenized sample—the impact of soil sample size and pooling to best represent the site of interest and its influence on plot comparisons has not been adequately explored. For example, “rare” species in the pooled, homogenized sample may arise from two different scenarios: (i) species are found in high abundance at fine scales but are heterogeneously spaced, and (ii) species are found in low abundance but are ubiquitously distributed. Furthermore, detection of rare species could be problematic with molecular approaches that rely on PCR for amplification and detection.Although molecular techniques can detect many microbial species missed by traditional culturing (20), they suffer from several potential biases (14, 17) that may limit successful PCR amplification and detection. For example, because PCR is a competitive process, species with a low relative abundance will be amplified to a lesser degree and may not reach detection threshold levels. This process is routinely utilized in competitive PCR to analyze starting template concentrations in mixed nucleic acid samples (17, 19). Furthermore, this effect would be seen by any process that could dilute rare phylotypes, such as pooling DNA extracts prior to amplification. Therefore, if the microbial community in the starting template is too complex, reducing the soil sample size will increase the likelihood that less abundant species are successfully amplified and detected.In this study, we analyzed the influence of three different sampling strategies on microbial community profiling using automated ribosomal intergenic spacer analysis (ARISA) and the following types of samples: (i) unpooled, (ii) pooled prior to PCR amplification, or (iii) pooled prior to DNA extraction. This sampling scheme was designed to test the effects of different common sampling strategies on microbial community profiles of samples containing equal soil volumes. Studies were conducted at three different field sites with various types of plant overstory complexity: an agricultural corn field, a ponderosa pine forest, and a tropical rainforest.     

Loss of ATRX, genome instability, and an altered DNA damage response are hallmarks of the alternative lengthening of telomeres pathway

The Alternative Lengthening of Telomeres (ALT) pathway is a telomerase-independent pathway for telomere maintenance that is active in a significant subset of human cancers and in vitro immortalized cell lines. ALT is thought to involve templated extension of telomeres through homologous recombination, but the genetic or epigenetic changes that unleash ALT are not known. Recently, mutations in the ATRX/DAXX chromatin remodeling complex and histone H3.3 were found to correlate with features of ALT in pancreatic neuroendocrine cancers, pediatric glioblastomas, and other tumors of the central nervous system, suggesting that these mutations might contribute to the activation of the ALT pathway in these cancers. We have taken a comprehensive approach to deciphering ALT by applying genomic, molecular biological, and cell biological approaches to a panel of 22 ALT cell lines, including cell lines derived in vitro. Here we show that loss of ATRX protein and mutations in the ATRX gene are hallmarks of ALT-immortalized cell lines. In addition, ALT is associated with extensive genome rearrangements, marked micronucleation, defects in the G2/M checkpoint, and altered double-strand break (DSB) repair. These attributes will facilitate the diagnosis and treatment of ALT positive human cancers.     

Effect of fatigue on hamstring coactivation during isokinetic knee extensions

We examined the effect of fatigue of the quadriceps muscles on coactivation of the hamstring muscles and determined if the response is different between two isokinetic speeds in ten males and ten females with no history of knee pathology. Electromyographic data were recorded from the vastus lateralis and biceps femoris muscles during 50 maximal knee extensions at isokinetic speeds of 1.75 rad · s⁻¹ (100° · s⁻¹) and 4.36 rad · s⁻¹ (250° · s⁻¹). A greater degree of coactivation was apparent at the higher speed, but the increase in coactivation of the hamstring muscles was similar at both speeds. The results revealed that: (1) coactivation is greater at a higher isokinetic speed, and (2) coactivation increases during fatigue, but the rate of increase is independent of contraction velocity. Accepted: 15 June 1998     

Evidence for the role of glycoprotein G of respiratory syncytial virus in binding of Neisseria meningitidis to HEp-2 cells

Abstract Viral glycoproteins G and F are expressed on the surface of cells infected with respiratory syncytial virus (RSV). We investigated the role of these proteins in the previously reported enhanced binding of Neisseria meningitidis to RSV-infected HEp-2 cells. Virus particles attached to bacteria were detected by immunofluorescence with flow cytometry. Binding of FITC-labelled bacteria to RSV-infected cells was significantly inhibited by monoclonal antibody against glycoprotein G. Unlabelled bacteria interfered with binding of the anti-G monoclonal antibody to these cells. These interactions were not found with a monoclonal antibody against glycoprotein F. We propose that glycoprotein G of RSV expressed on the surface of infected cells might act as an additional receptor for meningococci.     

Comparison of the structure of the immunoglobulins from horse serum

A study of the chemical structure of the horse immunoglobulins IgG and IgA(T) has shown that the amino acid contents of the peptide chains are very similar. These globulins differ most markedly in the products of papain digestion. IgG gives 3.5s products, whereas IgA(T) gives a 5s fraction and smaller components. This difference appears to be associated with the presence of an additional easily reducible disulphide bond in the Fd fragment of the heavy chain. There is two to three times as much carbohydrate in IgA(T) as in IgG. In both, this is in the heavy chain and in IgA(T) more than half is covalently bound to the Fd fragment. The differences in antigenic specificity between horse IgG and IgA(T) appear to be due to structural differences in the Fc fragment.     

The Effect of pH on the Covalent Complexes of Thymidylate Synthase

Abstract

The objective of this investigation was to study the effect of pH on the dissociation constants and binding ratios of covalent complexes of thymidylate synthases from Escherichia coli and Lactobacillus casei.