Inhibition of tetrachloromethane-induced cross-linking of microsomal fatty acids by the spin-trap α-phenyl- N - t -butylnitrone

The effect of the spin-trap α-phenyl-N-t-butylnitrone (PBN) on the formation of fatty acid dimers induced by the anoxic microsomal metabolism of tetrachloromethane was investigated in vitro, in particular, with respect to cross-linking of arachidonic acid with a second one (C₂₀–C₂₀) and of arachidonic acid with docosahexaenoic acid (C₂₀–C₂₂). PBN exerted no effect on anaerobic tetrachloromethane metabolism but inhibited dimer formation, half-maximally at a concentration of 0.1 mmol L^?1. Trichloromethyl octadecenoic acid was also found, but at levels 10-fold lower than the fatty acid dimers. The data suggest that the hepato-protective effect of PBN against tetrachloromethane-toxicity may be due to its ability to scavenge fatty acid radicals, resulting in stable, non-reactive entities, which do not undergo secondary reactions such as cross-linking. The data confirm and extend previous findings that crosslinking plays an important role in tetrachloromethane toxicity and similar cases of metabolic radical-induced toxicity.     

Grassland root communities: species distributions and how they are linked to aboveground abundance

There is little comprehensive information on the distribution of root systems among coexisting species, despite the expected importance of those distributions in determining the composition and diversity of plant communities. This gap in knowledge is particularly acute for grasslands, which possess large numbers of species with morphologically indistinguishable roots. In this study we adapted a molecular method, fluorescent fragment length polymorphism, to identify root fragments and determine species root distributions in two grasslands in Yellowstone National Park (YNP). Aboveground biomass was measured, and soil cores (2 cm in diameter) were collected to depths of 40 cm and 90 cm in an upland, dry grassland and a mesic, slope-bottom grassland, respectively, at peak foliar expansion. Cores were subdivided, and species that occurred in each 10-cm interval were identified. The results indicated that the average number of species in 10-cm intervals (31 cm3) throughout the sampled soil profile was 3.9 and 2.8 species at a dry grassland and a mesic grassland, respectively. By contrast, there was an average of 6.7 and 14.1 species per 0.5 m2, determined by the presence of shoot material, at dry and mesic sites, respectively. There was no relationship between soil depth and number of species per 10-cm interval in either grassland, despite the exponential decline of root biomass with soil depth at both sites. There also was no relationship between root frequency (i.e., the percentage of samples in which a species occurred) and soil depth for the vast majority of species at both sites. The preponderance of species were distributed throughout the soil profile at both sites. Assembly analyses indicated that species root occurrences were randomly assorted in all soil intervals at both sites, with the exception that Festuca idahoensis segregated from Artemisia tridentata and Pseudoroegnaria spicata in 10-20 cm soil at the dry grassland. Root frequency throughout the entire sampled soil profile was positively associated with shoot biomass among species. Together these results indicated the importance of large, well-proliferated root systems in establishing aboveground dominance. The findings suggest that spatial belowground segregation of species probably plays a minor role in fostering resource partitioning and species coexistence in these YNP grasslands.     

使用安捷伦7000A三重串联四极杆GC/MS/MS系统测定大气颗粒物中的硝基多环芳烃

采用毛细管GC 结合安捷伦7000A 三重串联四极杆GC/MS（G7010AA）系统的多反应监测（MRM）模式分析了大气颗粒物中的硝基多环芳烃（nitro-PAHs）.传统硝基多环芳烃的分析方法是在样品前处理之后,使用单四极杆GC/MS 的选择离子监测SIM 模式或者多维GC/MS,但基于MS/MS 检测模式超强的选择性,可直接分析大气颗粒物的粗提物.实际样品中的硝基多环芳烃可以检测到pg·μL-1 的级别,相对应于大气样品中pg·m-3级的含量.     

Nitrogen cycling during seven years of atmospheric CO2 enrichment in a scrub oak woodland

Experimentally increasing atmospheric CO2 often stimulates plant growth and ecosystem carbon (C) uptake. Biogeochemical theory predicts that these initial responses will immobilize nitrogen (N) in plant biomass and soil organic matter, causing N availability to plants to decline, and reducing the long-term CO2-stimulation of C storage in N limited ecosystems. While many experiments have examined changes in N cycling in response to elevated CO2, empirical tests of this theoretical prediction are scarce. During seven years of postfire recovery in a scrub oak ecosystem, elevated CO2 initially increased plant N accumulation and plant uptake of tracer 15N, peaking after four years of CO2 enrichment. Between years four and seven, these responses to CO2 declined. Elevated CO2 also increased N and tracer 15N accumulation in the O horizon, and reduced 15N recovery in underlying mineral soil. These responses are consistent with progressive N limitation: the initial CO2 stimulation of plant growth immobilized N in plant biomass and in the O horizon, progressively reducing N availability to plants. Litterfall production (one measure of aboveground primary productivity) increased initially in response to elevated CO2, but the CO2 stimulation declined during years five through seven, concurrent with the accumulation of N in the O horizon and the apparent restriction of plant N availability. Yet, at the level of aboveground plant biomass (estimated by allometry), progressive N limitation was less apparent, initially because of increased N acquisition from soil and later because of reduced N concentration in biomass as N availability declined. Over this seven-year period, elevated CO2 caused a redistribution of N within the ecosystem, from mineral soils, to plants, to surface organic matter. In N limited ecosystems, such changes in N cycling are likely to reduce the response of plant production to elevated CO2.     

Combination of two indication systems in pre-alpine lakes — diatom index and macrophyte index

Since the climax of eutrophication in the early 1980s mainly greater lakes have been investigated and monitored in terms of their nutrient charge. In the future there will still be a need to develop guidelines for monitoring the trophic status of smaller lakes. Four small lakes were investigated by the author in the years 1996 and 1997. In order to define the nutrient charge of those lakes more precisely, special emphasis has been put upon the two criteria diatoms and macrophytes. Eventually an evaluation of the lakes' catchment areas will also be an important component of these studies. Benthic diatoms are the main part of periphyton. As unicellular fast reproducing organisms they are excellent indicators for trophic situations in lakes. The diatom index denotes the trophic status of the littoral zone during the last few weeks before sampling. The macrophytes, however, reflect the nutrient charge over a longer period, i.e. several years. The macrophyte index is based on the fact that some species are most prevalent at certain nutrient loads. The effort to combine these two indication systems carries a high resolution of spatial nutrient changes as well as in temporally changes.     

In vitro establishment of continuous cell cultures and cell lines from ten colonial cnidarians

Continuous cell cultures from the ten taxa of sedentary colonial marine cnidariansStylophora pistillata, Porites lutea, Favia favus (Anthozoa, Hexacorallia, Madeporaria),Parerythropodium fulvum fulvum, Dendronephthya hemprichi, Nephthya sp.Heteroxenia fuscescence (Anthozoa, Octocorallia, Alcyonacea),Clathraria rubrinoides, Plexaura A (Anthozoa, Octocorallia, Gorgonacea) andMillepora dichotoma (Hydrozoa) were established in vitro. Primary cultures of various cell types (5 to 20 m) were obtained from colony fragments and/or planula larvae (collected in 1993 from coral reefs at Eilat, Red Sea and from the San Blas islands, Panama) using three dissociation approaches: a mechanical approach, chemical approach and a novel approach, spontaneous dissociation. Cells were cultured in a modified Leibowitz L15 medium, with 5 to 10% heat-inactivated fetal bovine serum, diluted in seawater. Cell proliferation was observed in primary cultures within 7 to 20 d following dissociation. When developed to secondary cultures, spindle-shaped cells (5 to 10 m) gradually replaced all other cell types seen in primary cultures ofS. pistillata, C. rubrinoides, P.f. fulvum andM. dichotoma. The spindle-shaped cells differentiated to several cell types when the diluted medium was replaced with a concentrated one, or when microbial contamination occurred. Secondary cultures of spindle-shaped cells from three species (S. pistillata, C. rubrinoides andM. dichotoma) were cloned. They gave rise to continuously proliferating cell lines (NIO-SPP-1, NIO-CR-1 and NIO-MD-1, respectively). A clone fromPlexaura planula, originated from one rounded cell, started to differentiate and gave rise to a heterogeneous culture. Samples of the above four cultures were frozen for future work. Rounded cells of various sizes (5 to 30 m) dominated secondary cell cultures ofH. fuscescence, D. hemprichi, Nephthya sp.,P. f. fulvum andF. favus. Several cell cultures fromP. lutea developed flattened cell interconnected by ectoplasmic networks characteristic of the eukaryotic unicellular organisms of the phylum Labyrinthulomycota. We propose that this culture methodology may be used as a ubiquitous protocol for producing tissue cultures from other cnidarians. The established cell lines may be used in a variety of disciplines in cnidarian biology and ecology.     

Influence of emergence success on the annual reproductive output of leatherback turtles

Reproductive output of leatherback turtles (Dermochelys coriacea) is affected by the stochastic nature of emergence success. Average emergence success of nests at Playa Grande, Costa Rica was 0.38 ± 0.27. Incubation temperature affected development of leatherback turtle eggs and emergence of hatchlings from the nest. We found that high temperatures reduced hatching success and emergence rate and increased embryonic mortality both early and late during incubation at Playa Grande. There was a temporal effect on emergence success that resulted in more hatchlings being produced at the beginning of the season, because of higher emergence success, than toward the end. Likewise, production of hatchlings varied from year to year. The average annual reproductive output was 252 ± 141 hatchlings per female. The 2005–2006 nesting season had the highest emergence success and produced the greatest number of hatchlings per female compared to the 2004–2005 (+120%) and 2006–2007 (+41%) seasons. However, average clutch size (62 ± 10) and clutch frequency (9.45 ± 1.63), were not different among years. Turtles that had nested a high number of years exhibited greater clutch frequency and arrived earlier to nest than turtles that had nested in fewer numbers of years. Nesting when environmental conditions favor high developmental success and emergence rate may constitute an advantageous reproductive strategy.     

Effect of selenium on the growth of Lemna minor

The effect of selenium on the vegetative reproduction of cultured Lemna minor was investigated. Cultures were grown for 28 days at a temperature of 23 ± 3°C and under a constant (24 h) light cycle. Growth was monitored every seven days. The growth of L. minor was inhibited at high concentrations (>5mg/L [Se]), but stimulated at low concentrations (0.2—2mg/L [Se]). This stimulation of growth at low selenium concentrations has significant implications for the use of selenium enriched superphosphate fertilisers on selenium deficient pastures.