1,864 research outputs found

    Interactions among biotic and abiotic controls of carbon dynamics in a global change field experiment

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    Climate warming and increased atmospheric nitrogen deposition may substantially influence biosphere C cycling over the next century by altering ecosystem processes such as productivity and decomposition. Field studies are commonly used to explore plant responses to global change, although the underlying mechanisms can be difficult to isolate owing to the lack of control of factors such as plant-animal interactions. Ultimately, indirect effects via herbivore and detritivore responses may feedback to influence plant responses to the experimental treatments. The goal of this thesis was to explore interactions among biotic and abiotic drivers of carbon dynamics within the context of experimental warming and nitrogen addition in the field. Evidence from a herbivore exclusion experiment revealed that mollusc effects on net primary productivity were more pronounced in warmed plots than in ambient temperature plots, likely as a result of temperature-related increases in mollusc metabolic activity and plant consumption rate. Furthermore, the effects of rodent exclusion on grass biomass were significantly greater in N-fertilized plots than non-fertilized plots. Feeding experiments suggested that this finding is likely attributed to increased grass palatability in response to N addition. Results from a litter decomposition experiment indicated that warming impeded the contribution of detritivores to carbon turnover, though this effect was transient. Increased precipitation over the course of the experiment may have promoted recovery of the detritivore community, and could also account for the significant detritivore effects observed following one year of incubation. Reciprocal litter transplants between the treatments plots and untreated areas of the field indicated that the observed responses from the main experiment were unlikely to be accounted for by the individual effects of litter quality or microenvironment alone. Overall, the influence of global change factors such as warming and increased atmospheric nitrogen deposition on carbon-related processes such as productivity can be substantially modified by indirect effects on herbivore dynamics, with consumer-specific treatment effects suggesting that this relationship is complex and can depend on both diet quality and microclimate. Though detritivores were relatively insensitive to warming and N addition as decomposition progressed, they likely play an important role in the overall magnitude of ecosystem C turnover

    Metabolism and transactivation activity of 13,14-dihydroretinoic acid

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    Journal ArticleThe metabolism of vitamin A is a highly regulated process that generates essential mediators involved in the development, cellular differentiation, immunity, and vision of vertebrates. Retinol saturase converts all-trans-retinol to all-trans-13,14-dihydroretinol (Moise, A. R., Kuksa, V., Imanishi, Y., and Palczewski, K. (2004) J. Biol. Chem. 279, 50230-50242). Here we demonstrate that the enzymes involved in oxidation of retinol to retinoic acid and then to oxidized retinoic acid metabolites are also involved in the synthesis and oxidation of all-trans-13,14-dihydroretinoic acid. All-trans-13,14-dihydroretinoic acid can activate retinoic acid receptor/retinoid X receptor heterodimers but not retinoid X receptor homodimers in reporter cell assays. All-trans-13,14-dihydroretinoic acid was detected in vivo in Lrat-/- mice supplemented with retinyl palmitate. Thus, all-trans-13,14-dihydroretinoic acid is a naturally occurring retinoid and a potential ligand for nuclear receptors. This new metabolite can also be an intermediate in a retinol degradation pathway or it can serve as a precursor for the synthesis of bioactive 13,14-dihydroretinoid metabolites

    Endothelial dysfunction in adolescents and young adults with nonalcoholic liver disease

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    Nonalcoholic liver disease is a global public health problem that increases cardiovascular morbidity and mortality in these patients. This paper discusses endothelial dysfunction among patients (adolescents and young adults) with nonalcoholic liver disease. On the one hand, evidence suggests that cardiovascular disease is the leading cause of mortality in patients with advanced nonalcoholic liver disease and that nonalcoholic fatty liver is associated with an increased risk of cardiovascular disease independent of the presence of cardiovascular risk factors and metabolic syndrome components. On the other hand, nonalcoholic liver disease, especially the non-inflammatory form of nonalcoholic steatohepatitis, may not only be a marker of cardiovascular damage but also a factor involved in its pathogenesis. Such patients are candidates not only for the treatment of liver disease but also for the early treatment of cardiovascular risk factors because many of them, especially those with severe nonalcoholic liver disease, will develop major cardiovascular events and may eventually die of cardiovascular disease before the advanced liver disease occurs

    MECHANISTIC ASPECTS OF CAROTENOID BIOSYNTHESIS

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    This document is the Accepted Manuscript version of a Published Work that appeared in final form in Chemical Reviews, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see http://pubs.acs.org/doi/abs/10.1021/cr400106
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