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171.
Walter C. Oechel George L. Vourlitis Joseph Verfaillie Tim Crawford Steve Brooks Edward Dumas Allen Hope Douglas Stow Bill Boynton Viktor Nosov Rommel Zulueta 《Global Change Biology》2000,6(Z1):160-173
Net CO2 flux measurements conducted during the summer and winter of 1994–96 were scaled in space and time to provide estimates of net CO2 exchange during the 1995–96 (9 May 1995–8 May 1996) annual cycle for the Kuparuk River Basin, a 9200 km2 watershed located in NE Alaska. Net CO2 flux was measured using dynamic chambers and eddy covariance in moist‐acidic, nonacidic, wet‐sedge, and shrub tundra, which comprise 95% of the terrestrial landscape of the Kuparuk Basin. CO2 flux data were used as input to multivariate models that calculated instantaneous and daily rates of gross primary production (GPP) and whole‐ecosystem respiration (R) as a function of meteorology and ecosystem development. Net CO2 flux was scaled up to the Kuparuk Basin using a geographical information system (GIS) consisting of a vegetation map, digital terrain map, dynamic temperature and radiation fields, and the models of GPP and R. Basin‐wide estimates of net CO2 exchange for the summer growing season (9 May?5 September 1995) indicate that nonacidic tundra was a net sink of ?31.7 ± 21.3 GgC (1 Gg = 109 g), while shrub tundra lost 32.5 ± 6.3 GgC to the atmosphere (negative values denote net ecosystem CO2 uptake). Acidic and wet sedge tundra were in balance, and when integrated for the entire Kuparuk River Basin (including aquatic surfaces), whole basin summer net CO2 exchange was estimated to be in balance (?0.9 ± 50.3 GgC). Autumn to winter (6 September 1995–8 May 1996) estimates of net CO2 flux indicate that acidic, nonacidic, and shrub tundra landforms were all large sources of CO2 to the atmosphere (75.5 ± 8.3, 96.4 ± 11.4, and 43.3 ± 4.7 GgC for acidic, nonacidic, and shrub tundra, respectively). CO2 loss from wet sedge surfaces was not substantially different from zero, but the large losses from the other terrestrial landforms resulted in a whole basin net CO2 loss of 217.2 ± 24.1 GgC during the 1995–96 cold season. When integrated for the 1995–96 annual cycle, acidic (66.4 + 25.25 GgC), nonacidic (64.7 ± 29.2 GgC), and shrub tundra (75.8 ± 8.4 GgC) were substantial net sources of CO2 to the atmosphere, while wet sedge tundra was in balance (0.4 + 0.8 GgC). The Kuparuk River Basin as a whole was estimated to be a net CO2 source of 218.1 ± 60.6 GgC over the 1995–96 annual cycle. Compared to direct measurements of regional net CO2 flux obtained from aircraft‐based eddy covariance, the scaling procedure provided realistic estimates of CO2 exchange during the summer growing season. Although winter estimates could not be assessed directly using aircraft measurements of net CO2 exchange, the estimates reported here are comparable to measured values reported in the literature. Thus, we have high confidence in the summer estimates of net CO2 exchange and reasonable confidence in the winter net CO2 flux estimates for terrestrial landforms of the Kuparuk river basin. Although there is larger uncertainty in the aquatic estimates, the small surface area of aquatic surfaces in the Kuparuk river basin (≈ 5%) presumably reduces the potential for this uncertainty to result in large errors in basin‐wide CO2 flux estimates. 相似文献
172.
The unexpected mating system of the androdioecious barnacle Chelonibia testudinaria (Linnaeus 1758) 下载免费PDF全文
Androdioecy was first described by Darwin in his seminal work on barnacle diversity; he identified males and hermaphrodites in the same reproductive population. Today, we realize that many androdioecious plants and animals share astonishing similarities, particularly with regard to their evolutionary history and mating system. Notably, these species were ancestrally dioecious, and their mating system has the following characteristics: hermaphrodites self‐fertilize frequently, males are more successful in large mating groups, and males have a mating advantage. A male mating advantage makes androdioecy more likely to persist over evolutionary times. Androdioecious barnacles, however, appear to persist as an outlier with a different evolutionary trajectory: they originate from hermaphroditic species. Although sexual systems of androdioecious barnacles are known, no information on the mating system of androdioecious barnacles is available. This study assessed the mating system of the androdioecious barnacle Chelonibia testudinaria. In contrast to other androdioecious species, C. testudinaria does not self‐fertilize, males do not have a mating advantage over hermaphrodites, and the average mating group is quite small, averaging only three individuals. Mating success is increased by proximity to the mate and penis length. Taken together, the mating system of C. testudinaria is unusual in comparison with other androdioecious plants and animals, and the lack of a male mating advantage suggests that the mating system alone does not provide an explanation for the maintenance of androdioecy in this species. Instead, we propose that sex‐specific life history equalizes male and hermaphroditic overall fitness. 相似文献
173.
174.
Hope A. Cole Feng Cui Josefina Ocampo Tara L. Burke Tatiana Nikitina V. Nagarajavel Naoe Kotomura Victor B. Zhurkin David J. Clark 《Nucleic acids research》2016,44(2):573-581
Eukaryotic chromosomal DNA is assembled into regularly spaced nucleosomes, which play a central role in gene regulation by determining accessibility of control regions. The nucleosome contains ∼147 bp of DNA wrapped ∼1.7 times around a central core histone octamer. The linker histone, H1, binds both to the nucleosome, sealing the DNA coils, and to the linker DNA between nucleosomes, directing chromatin folding. Micrococcal nuclease (MNase) digests the linker to yield the chromatosome, containing H1 and ∼160 bp, and then converts it to a core particle, containing ∼147 bp and no H1. Sequencing of nucleosomal DNA obtained after MNase digestion (MNase-seq) generates genome-wide nucleosome maps that are important for understanding gene regulation. We present an improved MNase-seq method involving simultaneous digestion with exonuclease III, which removes linker DNA. Remarkably, we discovered two novel intermediate particles containing 154 or 161 bp, corresponding to 7 bp protruding from one or both sides of the nucleosome core. These particles are detected in yeast lacking H1 and in H1-depleted mouse chromatin. They can be reconstituted in vitro using purified core histones and DNA. We propose that these ‘proto-chromatosomes’ are fundamental chromatin subunits, which include the H1 binding site and influence nucleosome spacing independently of H1. 相似文献
175.
Anne Fairbrother Brett Hartl Bruce K. Hope Jeffrey J. Jenkins Ya-Wei Li Dwayne R. J. Moore 《人类与生态风险评估》2016,22(2):502-518
Despite data gaps and information shortfalls, government agencies in the United States are expected to produce timely and defensible decisions to regulate pesticide use under the Federal Insecticide, Fungicide, and Rodenticide Act and in compliance with the Endangered Species Act. The decision to register a pesticide is predicated on a conclusion that no unreasonable effects will accrue to the environment, including threatened and endangered species. We recognize that the definition of acceptable risk is a policy judgment stemming from legislative language and judicial interpretation. However, a common risk assessment approach with similar technical underpinnings and a high degree of transparency used by all the agencies would be cost effective and more likely to achieve consensus among interested parties. Quantitative probabilistic risk assessment (PRA) methods can be used to develop risk estimates and to describe the level of confidence in these estimates. PRA methods can also differentiate among the contributions of natural stochasticity, measurement variability, and lack of knowledge. Because this approach enhances transparency and increases understanding of the implications of limited data sets and associated assumptions, we encourage the appropriate agencies to implement PRA methods as a means of reaching common ground when assessing risks of pesticides to listed species. 相似文献
176.
Sodium-1,2-C Acetate Incorporation in Roots of Frost-hardy and Less Hardy Alfalfa Varieties under Hardening Conditions 下载免费PDF全文
When the temperature of incorporation of sodium acetate-1, 2-14C into lipids of alfalfa (Medicago media Pers. var. Rambler and Medicago sativa L. var. Caliverde) roots was lowered from 22 C to 1 C, elongation and desaturation of fatty acids and the labeling of phosphatidylcholine were strongly stimulated. 相似文献
177.
Adenosine triphosphatase activity in the neural lobe of the bovine pituitary gland 总被引:3,自引:3,他引:0 下载免费PDF全文
1. Homogenates of neural lobes of bovine pituitary glands were fractionated by differential and density-gradient ultracentrifugation and the distribution of adenosine triphosphatase (ATPase) activity was studied. It was shown that all the activity was membrane-bound. 2. On the basis of ionic requirements the ATPase activity was grouped into three categories: (a) Mg2+-dependent, (b) Ca2+-dependent and (c) Mg2++Na++K+-dependent (ouabain-sensitive) ATPases. The activity in the absence of bivalent cations was negligible. The ratio between the activities of the three ATPases varied between the different subcellular fractions. 3. Preincubation of the subcellular fractions with deoxycholate increased the activity of the Mg2++Na++K+-dependent enzyme, whereas the Mg2+- and Ca2+-activated ATPases were either unaffected or slightly inhibited. Triton X-100 solubilized the Mg2+- and Ca2+-ATPases; however, the activity of the Mg2++Na++K+-ATPase was abolished by the concentration of Triton X-100 used. 4. All the subfractions displayed unspecific nucleotide triphosphatase activity towards GTP, ITP and UTP. These substrates inhibited the hydrolysis of ATP by all three ATPases. ADP also inhibited the ATPases. 5. Polyacrylamide-gel electrophoresis of extracts containing the Mg2+- and Ca2+-dependent ATPase activity solubilized by Triton X-100 revealed the presence of two enzymes; one activated by either Mg2+ or Ca2+ and the other activated only by Ca2+. 6. In sucrose density gradients the distribution of vasopressin was different from that of all three types of ATPases. It is therefore suggested that the neurosecretory granules do not possess ATPase activity. 相似文献
178.
Roslyn E. Wallace Paul J. Vasington John C. Petricciani Hope E. Hopps Douglas E. Lorenz Zdenek Kadanka 《In vitro cellular & developmental biology. Plant》1973,8(5):333-341
Summary Seven epithelial cell lines derived from kidney and 20 fibroblastic cell lines deriving from lung, heart, muscle, kidney,
and skin tissue of five rhesus and six African green monkey fetuses have been established and propagated in culture. Four
epithelial cell two fibroblastic cell lines resumed cell multiplication after a period of growth decline, and these lines
developed cytogenetic changes and growth characteristics of cells capable of unlimited growth in vitro.
Sixteen of the fibroblastic lines derived from lung, heart, muscle, or skin were characterized by a finite life consisting
of a period of active cell multiplication, followed by growth decline, senescence, and cell death. Fibroblasts derived from
lung appeared to have the greatest growth potential in terms of total population doublings, and fibroblastic lines from rhesus
monkeys were usually capable of more doublings than similar lines from African green monkeys. All fibroblastic lines were
predominantly diploid during active growth from passages 1 to 30, but several lines developed karyological changes preceding
or during growth decline and senescence.
All lines tested were found sensitive to a number of human viruses. All tests on these cells for microbial agents and for
tumorigenicity have been negative, and the have been preserved by freezing without loss of properties.
These cell lines may be useful as standardized substrates in studies requiring nonhuman primate cells.
The research upon which this publication is based was performed pursuant to Contract No. NIH-69-100 with the Division of Biologics
Standards of the National Institutes of Health. 相似文献
179.
Partial Correction of Structural Defects in Alcohol Dehydrogenase through Interallelic Complementation in Drosophila melanogaster 下载免费PDF全文
Alcohol dehydrogenases (ADH) from the F1 progeny of all pairwise crosses between 12 null-activity mutants and crosses between these mutants and four active variants, ADHn5 ADHF, ADHD and ADHS, were analyzed for the presence of active or inactive heterodimers. Gels were stained for ADH enzyme activity, and protein blots of duplicate gels were probed with ADH-specific antibody to detect cross-reacting material. Crosses between the three major electrophoretic variants. ADHF, ADHS and ADHD, all produced active heterodimers. Four mutant proteins (ADHn2, ADHn4, ADHn10 and ADHn13) did not form heterodimers with any other ADH subunit tested. Of the 28 crosses involving the remaining null activity mutants, 22 produce heterodimers. Twelve of these exhibit partial restoration of enzyme activity. In five cases of active heterodimers from null-activity crosses, Adhn11 supplied one of the subunits. In two crosses involving the active variant ADHD, the null activity mutant subunits (ADHn8 and ADHn3) destabilized the heterodimer sufficiently to cause inactivation of the ADHD subunit. In the cross between AdhF and Adhn3, the activity of the ADHF subunit was also greatly reduced in association with the ADHn3 subunit. Two crosses (Adhn1 x Adhn11 and Adhn5 x Adhn12) result in partial restoration of one of the homodimeric proteins (ADH n1 and ADHn12, respectively), as well as forming active heterodimers. 相似文献
180.
The isolation of neurophysin-I and -II from bovine pituitary neurosecretory granules separated on a large scale from other subcellular organelles. Demonstration of slow equilibration of neurosecretory granules during centrifugation in a sucrose density gradient 总被引:12,自引:10,他引:2 下载免费PDF全文
1. An improved procedure for the isolation of neurosecretory granules from the posterior lobe of the bovine pituitary gland is described. 2. Of the total oxytocic and pressor activities present in the original tissue 80% was sedimentable. 3. The granules were separated from mitochondria by prolonged centrifugation in a sucrose density gradient. During a sedimentation period of 5hr. the granules moved progressively into denser regions of the gradient and the mitochondria remained at the top. 4. The biological activities of the granules were measured: the oxytocic activity was 11·56±1·63 and the pressor activity was 15·60±3·91 units/mg. of protein. 5. A protein was isolated from a lysate of granules prepared from 40 pituitary glands. Amino acid analysis showed that it consisted of a mixture of neurophysin-I and neurophysin-II in equal proportions. It accounted for 60% of the soluble granule protein and for 50% of the total granule protein. 6. The neurophysins present in the granules are associated with 19·1 units of oxytocic and 21·1 units of pressor activity/mg. of protein. 7. Starch-gel electrophoresis revealed the presence of both neurophysins in extracts of 15 pituitary glands studied individually. 8. We conclude that the polypeptide hormones, oxytocin and [8-arginine]-vasopressin, are normally closely associated with the two neurophysins within neurosecretory granules of the pituitary gland. 相似文献