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131.
The contribution of sediment interstitial water and the water column to the transpiration stream of Myriophyllum aquaticum (Vellozo) Verdcourt was determined to estimate the significance of mass flow in supply of sediment nutrients for plant growth.
Sediment interstitial water accounted for about 2% of the water transpired over a 37 day period. Because of the small volume
of water that originated in the sediment we concluded that mass flow did not significantly enhance nutrient supply to the
roots of M. aquaticum. Relative growth rate (RGR) of adventitious, water roots was greater than whole plant RGR, and RGR of sediment roots was
not significantly different from zero, indicating a shift in the biomass allocation after emergence of the apical meristem
into the air. Water use, measured by the transpiration coefficient, averaged 260 ml H2O mg DW-1, which is similar to C-4 terrestrial plants. M. aquaticum has leaf characteristics commonly associated with xerophytic habitats. These characteristics may be necessary if a high transpiration
rate and a mechanical requirement for high cell turgor pressure, required by a reliance upon hydrostatic pressure for support
of the aerial stems, are mutually exclusive because of morphological constraints on hydraulic conductivity. 相似文献
132.
Linkage analysis of schizophrenia with five dopamine receptor genes in nine pedigrees 总被引:2,自引:0,他引:2
Hilary Coon William Byerley John Holik Mark Hoff Marina Myles-Worsley Lars Lannfelt Pierre Sokoloff Jean-Charles Schwartz Merilyne Waldo Robert Freedman Rosemarie Plaetke 《American journal of human genetics》1993,52(2):327-334
Alterations in dopamine neurotransmission have been strongly implicated in the pathogenesis of schizophrenia for nearly 2 decades. Recently, the genes for five dopamine receptors have been cloned and characterized, and genetic and physical map information has become available. Using these five loci as candidate genes, we have tested for genetic linkage to schizophrenia in nine multigenerational families which include multiple affected individuals. In addition to testing conservative disease models, we have used a neurophysiological indicator variable, the P50 auditory evoked response. Deficits in gating of the P50 response have been shown to segregate with schizophrenia in this sample and may identify carriers of gene(s) predisposing for schizophrenia. Linkage results were consistently negative, indicating that a defect at any of the actual receptor sites is unlikely to be a major contributor to schizophrenia in the nine families studied. 相似文献
133.
Jo Smith Lars Mc Naughton 《European journal of applied physiology and occupational physiology》1993,67(5):420-425
This experiment investigated the effects of intensity of exercise on excess postexercise oxygen consumption (EPOC) in eight trained men and eight women. Three exercise intensities were employed 40%, 50%, and 70% of the predetermined maximal oxygen consumption (VO2max). All ventilation measured was undertaken with a standard, calibrated, open circuit spirometry system. No differences in the 40%, 50% and 70% VO2max trials were observed among resting levels of oxygen consumption (V02) for either the men or the women. The men had significantly higher resting VO2 values being 0.31 (SEM 0.01) 1·min–1 than did the women, 0.26 (SEM 0.01) 1·min–1 (P < 0.05). The results indicated that there were highly significant EPOC for both the men and the women during the 3-h postexercise period when compared with resting levels and that these were dependent upon the exercise intensity employed. The duration of EPOC differed between the men and the women but increased with exercise intensity: for the men 40% – 31.2 min; 50% – 42.1 min; and 70% – 47.6 min and for the women, 40% – 26.9 min; 50% – 35.6 min; and 70% – 39.1 min. The highest EPOC, in terms of both time and energy utilised was at 70% VO2max. The regression equation for the men, where y=O2 in litres, and x=exercise intensity as a percentage of maximum was y=0.380x + 1.9 (r
2=0.968) and for the women is y=0.374x–0.857 (r
2=0.825). These findings would indicate that the men and the women had to exercise at the same percentage of their VO2max to achieve the maximal benefits in terms of energy expenditure and hence body mass loss. However, it was shown that a significant EPOC can be achieved at moderate to low exercise intensities but without the same body mass loss and energy expenditure. 相似文献
134.
Donatella Zona Peter M. Lafleur Koen Hufkens Beniamino Gioli Barbara Bailey George Burba Eugénie S. Euskirchen Jennifer D. Watts Kyle A. Arndt Mary Farina John S. Kimball Martin Heimann Mathias Göckede Martijn Pallandt Torben R. Christensen Mikhail Mastepanov Efrén López-Blanco Albertus J. Dolman Roisin Commane Charles E. Miller Josh Hashemi Lars Kutzbach David Holl Julia Boike Christian Wille Torsten Sachs Aram Kalhori Elyn R. Humphreys Oliver Sonnentag Gesa Meyer Gabriel H. Gosselin Philip Marsh Walter C. Oechel 《Global Change Biology》2023,29(5):1267-1281
Long-term atmospheric CO2 concentration records have suggested a reduction in the positive effect of warming on high-latitude carbon uptake since the 1990s. A variety of mechanisms have been proposed to explain the reduced net carbon sink of northern ecosystems with increased air temperature, including water stress on vegetation and increased respiration over recent decades. However, the lack of consistent long-term carbon flux and in situ soil moisture data has severely limited our ability to identify the mechanisms responsible for the recent reduced carbon sink strength. In this study, we used a record of nearly 100 site-years of eddy covariance data from 11 continuous permafrost tundra sites distributed across the circumpolar Arctic to test the temperature (expressed as growing degree days, GDD) responses of gross primary production (GPP), net ecosystem exchange (NEE), and ecosystem respiration (ER) at different periods of the summer (early, peak, and late summer) including dominant tundra vegetation classes (graminoids and mosses, and shrubs). We further tested GPP, NEE, and ER relationships with soil moisture and vapor pressure deficit to identify potential moisture limitations on plant productivity and net carbon exchange. Our results show a decrease in GPP with rising GDD during the peak summer (July) for both vegetation classes, and a significant relationship between the peak summer GPP and soil moisture after statistically controlling for GDD in a partial correlation analysis. These results suggest that tundra ecosystems might not benefit from increased temperature as much as suggested by several terrestrial biosphere models, if decreased soil moisture limits the peak summer plant productivity, reducing the ability of these ecosystems to sequester carbon during the summer. 相似文献
135.
Barbara Dod Lars S. Jermiin Pierre Boursot Verne H. Chapman J. Tnnes Nielsen Franois Bonhomme 《Journal of evolutionary biology》1993,6(4):529-546
The extent to which alleles can disperse across a hybrid zone depends on the selection they are subjected to in the hybrid genetic background or, for those that are selectively neutral, on their ability to escape from the unfavourable environment by recombination. Three markers spanning a 45 cM segment in the center of the X chromosome were used to investigate the degree to which selection against X chromosome linked genes helps to maintain the barrier to gene flow in the hybrid zone between Mus musculus domesticus and M. m. musculus in Denmark. The introgression of all the sex chromosome specific markers was more limited than that of the autosomal enzymes (Idh1, Amy, Gpd1, Pgm1, Es1, Es2, Mpi, Np1, Es10, Sod1) and the mitochondrial DNA. The cline for DXPas2, which is in the center of the X chromosome, is extremely steep and shows that certain genes located in this region are strongly selected against in the hybrid background. The clines of the other two X-linked markers, Hprt and DXPas1, and of the Y chromosome are not as abrupt and all three have similar asymmetric introgression patterns. Although the musculus variants appear to behave in much the same way as those of the autosomal genes, the domesticus variants do not introgress. The results show that X-linked and to a lesser extent Y-linked genes are more strongly selected against in the hybrid genome than the mitochondrial genome or the different autosomal loci. This suggests that co-adapted gene systems involving the sex chromosomes may play an important role in the hybrid breakdown between the two subspecies. 相似文献
136.
Terje Kalland Mikael Dohlsten Lars Abrahmsén Gunnar Hedlund Per Björk Peter A. Lando Anette Sundstedt Eva Åkerblom Peter Lind 《Cell biochemistry and biophysics》1993,22(1-3):147-164
The bacterial superantigen staphylococcal enterotoxin A (SEA) is an extremely potent activator of T lymphocytes when presented on MHC class II antigens. In order to induce T lymphocytes to reject a tumor, we substituted the specificity of SEA for MHC class II molecules with specificity for tumor cells by combining SEA with a MAb recognizing colon carcinomas. Chemical conjugates or recombinant fusion proteins of the MAb C215 and SEA retained excellent antigen binding properties whereas the binding to MHC class II was markedly reduced. The hybrid proteins directed SEA responsive T cells to tumors with specificity determined by the specificity of the MAb. Significant tumor cell killing was obtained at picomolar concentrations of the hybrid proteins and was the result of direct cell mediated by cytotoxicity as well as production of tumoricidal cytokines by T cells. Targeting of superantigens represents a novel approach to specific immunomodulation and deserves further study as a potential therapy for malignant disease. 相似文献
137.
Michael D. Browning Shuichi Endo Geoffrey B. Smith Ellen M. Dudek Richard W. Olsen 《Neurochemical research》1993,18(1):95-100
Previous work has shown that the GABAA-receptor (GABAA-R) could be phosphorylated by cAMP-dependent protein kinase (PKA), protein kinase C (PKC), and a receptor associated kinase. However, no clear picture has yet emerged concerning the particular subunit subtypes of the GABAA-R that were phosphorylated by PKA and PKC. In the present report we show that an antibody raised against a 23 amino acid polypeptide corresponding to a sequence in the putative intracellular loop of the 1 subunit of the receptor blocks the in vitro phosphorylation of the purified receptor by PKA and PKC. Moreover, N-terminal sequence analysis of the principal phosphopeptide fragment obtained after proteolysis of the receptor yielded a sequence that corresponds to the 3 subunit of the receptor. Such data provide additional support for our hypothesis (Browning et al., 1990, Proc. Natl. Acad. Sci. USA 87:1315–1317) that both PKA and PKC phosphorylate the -subunit of the GABAA-R.Special issue dedicated to Dr. Paul Greengard. 相似文献
138.
Margaret B. Fleming Lauren Stanley Robyn Zallen Matthew T. Chansler Lars A. Brudvig David B. Lowry Marjorie Weber Frank W. Telewski 《American journal of botany》2023,110(11):e16250
Premise
In 1879, Dr. William Beal buried 20 glass bottles filled with seeds and sand at a single site at Michigan State University. The goal of the experiment was to understand seed longevity in the soil, a topic of general importance in ecology, restoration, conservation, and agriculture, by periodically assaying germinability of these seeds over 100 years. The interval between germination assays has been extended and the experiment will now end after 221 years, in 2100.Methods
We dug up the 16th bottle in April 2021 and attempted to germinate the 141-year-old seeds it contained. We grew germinants to maturity and identified these to species by vegetative and reproductive phenotypes. For the first time in the history of this experiment, genomic DNA was sequenced to confirm species identities.Results
Twenty seeds germinated over the 244-day assay. Eight germinated in the first 11 days. All 20 belonged to the Verbascum genus: Nineteen were V. blattaria according to phenotype and ITS2 genotype; and one had a hybrid V. blattaria × V. thapsus phenotype and ITS2 genotype. In total, 20/50 (40%) of the original Verbascum seeds in the bottle germinated in year 141.Conclusions
While most species in the Beal experiment lost all seed viability in the first 60 years, a high percentage of Verbascum seeds can still germinate after 141 years in the soil. Long-term experiments such as this one are rare and invaluable for studying seed viability in natural soil conditions. 相似文献139.
Trine Bottos Olsen Daniel García-Martínez Chiara Villa 《American journal of physical anthropology》2023,180(1):224-234
This study aimed to test the performance of 3D digitizer, CT scanner, and surface scanner in detecting cranial fluctuating asymmetry. Sets of 32 landmarks (6 in the midline and 13 bilateral) were acquired from 14 archeological crania using a 3D digitizer, and from 3D models generated from a CT scanner and surface scanner using Viewbox 4. Levels of shape variation were analyzed in MorphoJ using Procrustes analysis of variance and Principal component analysis. Intra-observer error accounted for 1.7%, 1.8%, and 4.5% of total shape variation for 3D digitizer, CT scanner, and surface scanner respectively. Fluctuating asymmetry accounted for 15%–16% of total shape variation. Variation between techniques accounted for 18% of total shape variation. We found a higher level of missing landmarks in our surface scan data than for both 3D digitizer and CT scanner data, and both 3D model-based techniques sometimes obscured taphonomic damage. All three 3D techniques are appropriate for measuring cranial fluctuating asymmetry. We advise against combining data collected with different techniques. 相似文献
140.
Thelma Panaïotis Marcel Babin Tristan Biard François Carlotti Laurent Coppola Lionel Guidi Helena Hauss Lee Karp-Boss Rainer Kiko Fabien Lombard Andrew M. P. McDonnell Marc Picheral Andreas Rogge Anya M. Waite Lars Stemmann Jean-Olivier Irisson 《Global Ecology and Biogeography》2023,32(11):1991-2005