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991.
Curry, Alan; Grayson, Robin F., and Hosey, Geoffrey R. Under the Microscope New York: Van Nostrand Reinhold, 1983 $14.50 Reviewed by Michael E. Somers. Polking, Kirk Oceans of the World: Our Essential Resource New York: Philomel Books (Putnam), 1983 106 pp. $14.95 hardcover Reviewed by Robert E. Knowlton. Nitecki, Matthew H. Coevolution Chicago: University of Chicago Press, 1983 392 pp. $30 hardcover, $17 paper Reviewed by Donald J. Zinn. Garfield, Eugene Essays of an Information Scientist, vol. 5 (1981–82) Philadelphia, Pa.: ISI Press, 1983 850 pp. $25 Reviewed by Judith A. Douville. 相似文献
992.
Watershed land use alters riverine silica cycling 总被引:1,自引:0,他引:1
Recent research has highlighted that humans are perturbing the global silica (Si) cycle through land use change. Here we compare in-stream Si biogeochemistry across four rivers that lie along a gradient of land use change in New England, USA. Differences between basins were most notable during the late winter/early spring period when dissolved Si (DSi) concentrations declined significantly in all but the most urban site. Declines in DSi concentration could not be attributed to volumetric dilution by higher discharges, nor in-stream phytoplankton growth, as biogenic Si concentrations did not increase during this period. We provide evidence that uptake of Si by terrestrial vegetation, specifically trees, is responsible for the observed declines of in-stream DSi concentrations (a loss of 2.7 μM day?1 at the most forested site). We hypothesize that sap flow during this late winter/early spring period is driving this accretion. We estimate that 68 kmol Si km?2 is accreted annually by New England forests, falling well within the range of forest Si accretion rates found in published studies. This analysis increases our understanding of the mechanisms contributing to altered Si biogeochemistry in rivers draining watersheds with different land use. 相似文献
993.
Olke C. Uhlenbeck Jannette Carey Paul J. Romaniuk Peggy T. Lowary Dorothy Beckett 《Journal of biomolecular structure & dynamics》2013,31(2):539-552
Abstract The interaction between bacteriophage R17 coat protein and its RNA binding site for translational repression was studied as an example of a sequence-specific RNA-protein interaction. A nitrocellulose filter retention assay is used to demonstrate equimolar binding between the coat protein and a synthetic 21 nucleotide RNA fragment. The Kj at 2°C in a buffer containing 0.19 M salt is about 1 nM. The relatively weak ionic strength dependence of Ka and a ΔH = ?19 kcal/mole indicates that most of the binding free energy is due to non-electrostatic interactions. Since a variety of RN As failed to compete with the 21 nucleotide fragment for coat protein binding, the interaction appears highly sequence specific. We have synthesized more than 30 different variants of the binding site sequence in order to identify the portions of the RNA molecule which are important for protein binding. Out of the five single stranded residues examined, four were essential for protein binding whereas the fifth could be replaced by any nucleotide. One variant was found to bind better than the wild type sequence. Substitution of nucleotides which disrupted the secondary structure of the binding fragment resulted in very poor binding to the protein. These data indicated that there are several points of contact between the RNA and the protein and the correct hairpin secondary structure of the RNA is essential for protein binding. 相似文献
994.
995.
Carpenter MA Powell JH Ishizuka KJ Palmeri KJ Rendulic S De Tomaso AW 《The Biological bulletin》2011,220(1):57-70
The colonial ascidian Botryllus schlosseri undergoes a histocompatibility reaction that can result in vascular fusion of distinct genotypes, creating a chimera. Chimerism has both potential benefits, such as an immediate increase in size that may enhance growth rates, and costs. For the latter, the presence of multiple genotypes in a chimera can lead to competition between genetically distinct stem cell lineages, resulting in complete replacement of somatic and germline tissues by a single genotype. Although fusion can occur at any point after metamorphosis, previous studies have focused on chimeras created from sexually mature adults, where no benefit to chimerism has been documented. Here we focus on the costs and benefits of fusion between juveniles, characterizing growth rates and patterns of somatic and germline chimerism after natural and controlled fusion events. We also compared outcomes between low- and high-density growth conditions, the latter more likely representative of what occurs in natural populations. We found that growth rates were density-dependent, and that only chimeras grew under high-density conditions. We also observed a positional component to a post-fusion event called resorption, indicating that extrinsic factors were important in this process. Patterns of germline and somatic chimerism and dominance in chimeras made from fused juveniles were equivalent to those after fusion of sexually mature adults, and there were no age-related differences in these processes. Finally, by using genetic markers that could retrospectively assign genotypes, we also found that the majority of individual testes in a chimera were clonally derived. 相似文献
996.
A better understanding of the functionality of probiotics and dietary fibres with prebiotic activity is required for the development of improved synbiotic preparations. In this study, utilization of β(2-1) fructans, galactooligosaccharides, and plant polysaccharides as prebiotics by lactobacilli, bifidobacteria, and pediococci was investigated. Our results demonstrate that prebiotics with linear chains consisting of galactose units are better utilized by probiotics than are those consisting of glucose and fructose units, and the ability of probiotic bacteria to utilize prebiotics is strain-specific. In addition, rye fructooligosaccharides represent a prebiotic fibre that supports the growth of a wide range of probiotic cultures and as such has a potential to improve the successfulness of probiotic treatments. This study also demonstrates dietary fibre utilization by pediococci and provides data supporting the possible use of pediococci as a probiotic in synbiotic combinations. 相似文献
997.
Jason D. Stockwell Jonathan P. Doubek Rita Adrian Orlane Anneville Cayelan C. Carey Laurence Carvalho Lisette N. De Senerpont Domis Gaël Dur Marieke A. Frassl Hans‐Peter Grossart Bas W. Ibelings Marc J. Lajeunesse Aleksandra M. Lewandowska María E. Llames Shin‐Ichiro S. Matsuzaki Emily R. Nodine Peeter Nges Vijay P. Patil Francesco Pomati Karsten Rinke Lars G. Rudstam James A. Rusak Nico Salmaso Christian T. Seltmann Dietmar Straile Stephen J. Thackeray Wim Thiery Pablo Urrutia‐Cordero Patrick Venail Piet Verburg R. Iestyn Woolway Tamar Zohary Mikkel R. Andersen Ruchi Bhattacharya Josef Hejzlar Nasime Janatian Alfred T. N. K. Kpodonu Tanner J. Williamson Harriet L. Wilson 《Global Change Biology》2020,26(5):2756-2784
In many regions across the globe, extreme weather events such as storms have increased in frequency, intensity, and duration due to climate change. Ecological theory predicts that such extreme events should have large impacts on ecosystem structure and function. High winds and precipitation associated with storms can affect lakes via short‐term runoff events from watersheds and physical mixing of the water column. In addition, lakes connected to rivers and streams will also experience flushing due to high flow rates. Although we have a well‐developed understanding of how wind and precipitation events can alter lake physical processes and some aspects of biogeochemical cycling, our mechanistic understanding of the emergent responses of phytoplankton communities is poor. Here we provide a comprehensive synthesis that identifies how storms interact with lake and watershed attributes and their antecedent conditions to generate changes in lake physical and chemical environments. Such changes can restructure phytoplankton communities and their dynamics, as well as result in altered ecological function (e.g., carbon, nutrient and energy cycling) in the short‐ and long‐term. We summarize the current understanding of storm‐induced phytoplankton dynamics, identify knowledge gaps with a systematic review of the literature, and suggest future research directions across a gradient of lake types and environmental conditions. 相似文献
998.
999.
Meredith K. D. Hawking Donna M. Lecky Neville Q. Verlander Cliodna A. M. McNulty 《PloS one》2013,8(10)