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131.
Dissolved organic carbon (DOC) in Lake Fryxell, 10 streams flowing into the lake, and the moat surrounding the lake was studied to determine the influence of sources and biogeochemical processes on its distribution and chemical nature. Lake Fryxell is an amictic, permanently ice-covered lake in the McMurdo Dry Valleys which contains benthic and planktonic microbial populations, but receives essentially no input of organic material from the ahumic soils of the watershed. Biological activity in the water column does not appear to influence the DOC depth profile, which is similar to the profiles for conservative inorganic constituents. DOC values for the streams varied with biomass in the stream channel, and ranged from 0.2 to 9.7 mg C/L. Fulvic acids in the streams were a lower percentage of the total DOC than in the lake. These samples contain recent carbon and appear to be simpler mixtures of compounds than the lake samples, indicating that they have undergone less humification. The fulvic acids from just above the sediments of the lake have a high sulfur content and are highly aliphatic. The main transformations occurring as these fractions diffuse upward in the water column are 1) loss of sulfur groups through the oxycline and 2) decrease in aliphatic carbon and increase in the heterogeneity of aliphatic moieties. The fraction of modem14C content of the lake fulvic acids range from a minimum of 0.68 (approximately 3000 years old) at 15m depth to 0.997 (recent material) just under the ice. The major processes controlling the DOC in the lake appear to be: 1) The transport of organic matter by the inflow streams resulting in the addition of recent organic material to the moat and upper waters of the lake; 2) The diffusion of organic matter composed of relict organic material and organic carbon resulting from the degradation of algae and bacteria from the bottom waters or sediments of the lake into overlying glacial melt water, 3) The addition of recent organic matter to the bottom waters of the lake from the moat. 相似文献
132.
Uncultivated plants growing on disturbed sites may be useful for assessing the bioavailability of some metals in soils, and thus the potential for metal mobilization up the terrestrial food chain, an important element in ecological risk assessment. A planted chicory cultivar (Cichorium intybus L. var. foliosum Hegi.) and the uncultivated plants horseweed (Canada fleabane) (Erigeron canadensis L.) and dogfennel (Eupatorium capillifolium (Lam.) Small) were evaluated for their ability to act as index plant species for soil Cd, Cr, Ni, and V at two field sites where these metals had been applied five yr previously to two highly weathered sandy Ultisols. Soil Cd was available to all analyzed plant tissues of all three plant species at both sites, particularly on the sandier Blanton soil. Chicory was an effective index plant for Cd on the finer textured Orangeburg soil but functioned as an indicator plant (toxicity symptoms were observed) on the sandier Blanton soil. Horseweed and dogfennel were effective index plants for Cd in both contaminated soils. Soil Cr, Ni, and V were less bioavailable than soil Cd and plant metal uptake was more sensitive to residual soil Cr, Ni, and V than was soil extraction with double acid. Horseweed and chicory may have potential as index plants for soil Cr. Chicory may have potential as a Ni index plant. Chicory and dogfennel may have potential as V index plants. 相似文献
133.
134.
Pei-Wen Chiang SuQing Wang Paul Smithivas Woo-Joo Song Saravanan Ramamoorthy Joseph Hillman Sheryl Puett Margaret L. Van Keuren Eric Crombez Arun Kumar Thomas W. Glover Diane E. Miller Chun-Hui Tsai C.Clare Blackburn Xiao-Ning Chen Zhiguang Sun Jan-Fang Cheng Julie R. Korenberg David M. Kurnit 《Genomics》1996,34(3):328
135.
Hillard S. Kaplan Jane B. Lancaster Sara E. Johnson John A. Bock 《Human nature (Hawthorne, N.Y.)》1995,6(4):325-360
Our objective is to test an optimality model of human fertility that specifies the behavioral requirements for fitness maximization
in order (a) to determine whether current behavior does maximize fitness and, if not, (b) to use the specific nature of the behavioral deviations from fitness maximization towards the development of models of evolved
proximate mechanisms that may have maximized fitness in the past but lead to deviations under present conditions. To test
the model we use data from a representative sample of 7,107 men living in Albuquerque, New Mexico, between 1990 and 1993.
The model we test proposes that low fertility in modern settings maximizes number of grandchildren as a result of a trade-off
between parental fertility and next generation fertility. Results do not show the optimization, although the data do reveal
a trade-off between parental fertility and offspring education and income.
We propose that two characteristics of modern economies have led to a period of sustained fertility reduction and to a corresponding
lack of association between income and fertility. The first is the direct link between costs of investment and wage rates
due to the forces of supply and demand for labor in competitive economies. The second is the increasing emphasis on cumulative
knowledge, skills, and technologies in the production of resources. Together they produce historically novel conditions. These
two features of modern economies may interact with evolved psychological and physiological mechanisms governing fertility
and parental investment to produce behavior that maximizes the economic productivity of lineages at the expense of fitness.
If cognitive processes evolved to track diminishing returns to parental investment and if physiological processes evolved
to regulate fertility in response to nutritional state and patterns of breast feeding, we might expect non-adaptive responses
when returns from parental investment do not diminish until extremely high levels are reached. With high economic payoffs
from parental investment, people have begun to exercise cognitive regulation of fertility through contraception and family
planning practices. Those cognitive processes maynot have evolved to handle fitness trade-offs between fertility and parental investment.
A preliminary presentation of this data was published in R. I. M. Dunbar, ed.,Human Reproduction Decisions: Biological and Social Perspectives. New York: St. Martin’s Press, 1995. Support for the research project, “Male Fertility and Parenting in New Mexico,” began
with two seed grants from the University of New Mexico’s Biomedical Research Grants Program, 1988 and 1989, and one from the
University of New Mexico Research Allocations Committee, 1988. Further seed money as well as interim funding came from the
William T. Grant Foundation (#89130589 and #91130501). The major support for the project came from the National Science Foundation
from 1990 to 1993 (#BNS-9011723 and #DBS-911552). Both National Science Foundation grants included Research Experience for
Undergraduates supplements.
Hillard S. Kaplan is an Associate Professor of Anthropology at the University of New Mexico. His earlier research and publications
focused on food sharing, time allocation, parental investment, and reproductive strategies among Ache hunter-gatherers in
Paraguay, Machiguenga and Piro forager-horticulturalists in Peru, and villagers of several ethnicities in Botswana. New research
and theory concern fertility, parental investment, and mating strategies in developed and developing nations. This research
formulates a new theory of reproductive decision-making and the demographic transition, integrating human capital and parental
investment theory in a synthesis of economic and evolutionary approaches.
Jane B. Lancaster is a Professor of Anthropology at the University of New Mexico. Her research and publications are on human
reproductive biology and behavior, especially human parental investment; women’s reproductive biology of pregnancy, lactation,
and child-spacing; and male fertility and investment in children. Current research with Hillard S. Kaplan is on male life
history strategies among a large sample of men in New Mexico. She has coedited three books on human parental investment:School-Age Pregnancy and Parenthood (with B. Hamburg),Parenting across the Life Span (with J. Altmann, A. Rossi, and L. Sherrod), andOffspring Abuse and Neglect (with R. Gelles). She is scientific editor of a quarterly journal,Human Nature: An Interdisciplinary, Biosocial Perspective published by Aldine de Gruyter. She is also a council member of the newly formed Human Behavior and Evolution Society.
John A. Bock is Andrew W. Mellon Post-Doctoral Fellow in Epidemiology and Population Health at the National Centre for Epidemiology
and Population Health, The Australian National University. His research focuses on the allocation of parental investment and
the determinants of children’s activities, integrating aspects of economic and evolutionary theory. He has ongoing field research
with Bantu and Bushmen agro-pastoralists and forager-horticulturalists in the Okavango Delta, Botswana. He is also collaborating
with Lancaster and Kaplan on the determinants of progeny distribution and homosexuality among New Mexican men.
Sara E. Johnson is a Ph.D. candidate at the University of New Mexico. Her major research trajectory focuses on trade-offs
in life history characters. Her research experience includes participation in a study of variation in growth and development
among children in a multi-ethnic community in the Okavango Delta, Botswana, in addition to her dissertation work on individual
variation in growth and mortality among juvenile baboons. She is collaborating with Lancaster and Kaplan on the association
between survival and fertility among Albuquerque men. 相似文献
136.
Timothy A. McCaffrey Domenick J. Falcone Diane Vicente Baoheng Du Seth Consigli Wolfgang Borth 《Journal of cellular physiology》1994,159(1):51-59
The transforming growth factor-β (TGF-β) family of proteins exert diverse and potent effects on proliferation, differentiation, and extracellular matrix synthesis. However, relatively little is known about the stability or processing of endogenous TGF-β activity in vitro or in vivo. Our previous work indicated that (1) TGF-β1 has strong heparin-binding properties that were not previously recognized because of neutralization by iodination, and (2) heparin, and certain other polyanions, could block the binding of TGF-β1 to α2-macroglobulin (α2-M). The present studies investigated the influence of heparin-like molecules on the stability of the TGF-β1 signal in the pericellular environment. The results indicate that heparin and fucoidan, a naturally occurring sulfated L-fucose polymer, suppress the formation of an initial non-covalent interaction between 125I-TGF-β1 and activated α2-M. Electrophoresis of 125I-TGF-β1 showed that fucoidan protects TGF-β1 from proteolytic degradation by plasmin and trypsin. While plasmin caused little, if any, activation of latent TGF-β derived from vascular smooth muscle cells (SMC), plasmin degraded acid-activated TGF-β, and purified TGF-β1, and this degradation was inhibited by fucoidan. In vitro, heparin and fucoidan tripled the half-life of 125I-TGF-β1 and doubled the amount of cell-associated 125I-TGF-β1. Consistent with this protective effect, heparin- and fucoidan-treated SMC demonstrated elevated levels of active, but not latent, TGF-β activity. © 1994 wiley-Liss, Inc. 相似文献
137.
138.
Beverly K. Pierson Diane Valdez Mark Larsen Elizabeth Morgan E. Erin Mack 《Photosynthesis research》1994,41(1):35-52
We report the presence of a diverse number ofChloroflexus-like organisms in intertidal marine and submerged hypersaline microbial mats using light, infrared fluorescence, and electron microscopy. The intertidal organisms appear morphologically very similar to thermophilicC. aurantiacus while the 2 hypersaline strains are larger and have a more complex ultrastructure composed of chlorosome-bearing internal membranes that appear to arise as invaginations of the cell membrane. By comparing spectroradiometry of microbial mat layers with microscopic observations, we have confirmed that theChloroflexus-like organisms are major constituents of the hypersaline microbial mat communities. In situ studies on mat layers dominated byChloroflexus-like organisms showed that sulfide-dependent photoautotrophic activity sustained by near infrared radiation prevailed. Autoradiographic analyses revealed that autotrophy was sustained in the filaments by 750 nm radiation. Three morphologically distinct strains are now maintained in mixed culture. One of these appears to be growing photoautotrophically. 相似文献
139.
Gang Fang K. Venkateswarlu Diane E. Kelly Steven L. Kelly 《Biotechnology letters》1994,16(12):1253-1258
The Saccharomyces cerevisiae strain AH22 was capable of human P4501A1 expression without detectable background of yeast P450, unlike ATCC44773. Repeated backcrossing to AH22 produced a strain allowing transformation by vectors carrying various common selectable markers. Background yeast xenobiotic metabolism was observed only with growth on complex medium. 相似文献
140.
Bioluminescent Salmonella typhimurium provides a rapid assay for measuring the efficacy of freeze-drying suspension media 总被引:1,自引:1,他引:0
A strain of Salmonella typhimurium , transformed to a bioluminescent phenotype, was used to compare three freeze-drying suspension media: inositol serum broth with and without added gelatin and sterile skimmed milk. Recovery and growth studies performed by measuring changes in bioluminescence demonstrated that of the three media tested, the routinely used inositol serum broth was the most effective freeze-drying suspension medium. 相似文献