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41.
Intravenous (IV) infusions of neurotensin (NT) in anesthetized guinea pigs elicited dose-dependent pressor effects and tachycardia. Both effects were significantly reduced or abolished in guinea pigs given a chronic treatment with the neurotoxin capsaicin. In guinea pig isolated atria NT evoked a positive inotropic and chronotropic effect. Both effects were completely abolished in atria derived from capsaicin-treated guinea pigs. The positive inotropic and chronotropic effects of NT in guinea pig atria were mimicked by capsaicin and calcitonin gene-related peptide (CGRP). These results were interpreted as an indication that NT produces its cardiovascular effects in guinea pigs by activating capsaicin-sensitive sensory neurons. 相似文献
42.
The highest concentration of neurokinin A-like immunoreactivity and substance P-like immunoreactivity in the guinea pig small intestine was associated with the myenteric plexus-containing longitudinal muscle layer. Chromatographic analysis of extracts of this tissue demonstrated the presence of neurokinin A and neuropeptide K but the probable absence of neurokinin B. A fraction of synaptic vesicles of density 1.133 +/- 0.003 g/ml was prepared from the myenteric plexus-containing tissue by density gradient centrifugation in a zonal rotor and was enriched 29 +/- 12-fold in the concentration of neurokinin A-like immunoreactivity and 43 +/- 13-fold in the concentration of substance P-like immunoreactivity. This fraction was separated from the fraction of vasoactive intestinal peptide-containing vesicles (density, 1.154 +/- 0.009 g/ml). Chromatographic analysis of lysates of the vesicles indicated the presence of neurokinin A but not neuropeptide K. It is postulated that beta-pre-protachykinin is processed to substance P, neurokinin A, and neuropeptide K in the cell bodies of myenteric plexus neurons but that conversion of neuropeptide K to neurokinin A takes place during packaging into storage vesicles for axonal transport. The data are consistent with the proposal that neurokinin A and substance P are stored in the same synaptic vesicle, but the possibility of cosedimentation of different vesicles of very similar density cannot be excluded. 相似文献
43.
Summary Following transduction of exponentially growing cultures of Escherichia coli with phage P1, cells with recombinant phenotype begin to increase in number after an initial lag of about one generation time. We show that transductants for markers located at different positions on the chromosome begin to increse at different times, in reverse order to that in which they are replicated. The period over which this happens is equal in duration to the time taken to replicate the chromosome and we have used this relationship to calculate the C-period of E. coli K12 growing at 30°C. We exclude transduction-induced filamentation as the cause of the initial lag and suggest that the lag may result from the way in which donor DNA is inherited. 相似文献
44.
Emergence and growth of barley was severely decreased by short periods (less than 24 hours) of pre-emergence waterlogging
at 20°C. The extent of damage depended on a combination of duration of waterlogging, soil water potential and aggregate size.
Potentials of less than—4kPa prevented loss of plants developing in aggregates of less than 2 mm diameter after a transitory
period of waterlogging although some shoot and root damage occurred. By comparison seeds growing in soil consisting of aggregates
greater than 2 mm in diameter were not damaged by transitory waterlogging even when drainage only occurred at−0.8kPa. The
severity of damage increased with the period of waterlogging. A criterion obtained as the product of mean size grade and water
potential gave a single value (−4NM−1) below which emergence was satisfactory. Waterlogging halfway through germination gave more severe damage than near sowing
date or near emergence. 相似文献
45.
The fate of15N labeled nitrogen applied to mature citrus trees 总被引:1,自引:0,他引:1
Summary The efficiency and balance of nitrogen from one year's application was studied in a long-term fertigation experiment. Enriched
nitrogen fertilizer, K15NO3, was applied to a 22-year-old Shamouti orange tree with a history of high N applications (N3) and to an N-starved tree (N1). The distribution of N in the different parts of the trees and in the soil was determined after the experimental trees were
excavated.
Similar total recovery of the labeled fertilizer N was found in the trees and soil in both treatments (N1−61.7% N3−56%). However, the distribution between tree and soil was different. The amount of recovered residual fertilizer in the soil
was much larger in the N3 treatment than in N1. The highest percentage of fertilizer N was found in the new organs,i.e. fruits, twigs and leaves. The roots and branches took up only 6–14% from the labeled fertilizer.
Only 20.9% of the leaf N and 23.4% of the fruit N in the N3 tree originated in the labeled fertilizer, indicating translocation of N from older parts of the tree to new growth.
Evidence was found of storage of N in the wooded branches, while the roots contained a surprisingly small part of labeled
fertilizer.
Contribution 1599E. 相似文献
46.
The N2O flux from the surface of grass-covered pots was only significant following grass maturing. Removal of the above-ground plant
material resulted in an immediate and long-lasting increase in N2O production in the soil. The results suggest that easily available organic matter from the roots stimulates the denitrification
when the plants are damaged. Grass cutting might therefore result in a marked nitrogen loss through denitrification. The quantitative
effect was equal in soil with and without succinate added. The size of the anaerobic zone around the roots is therefore sufficient
to allow for denitrification activity mediated by increased organic matter availability because of plant cutting. 相似文献
47.
For three acid soils from Santa Catarina, Brazil, lime application and time of incubation with lime had little effect on the
adsorption of added phosphorus. In two soils with high contents of exchangeable aluminium, solution P and isotopically exchangeable
P were decreased by incubating with lime for 1 month: phosphorus was probably adsorbing on freshly precipitated aluminium
hydrous oxides. In one soil with less exchangeable aluminium, P in solution was increased by liming. After 23 months lime
increased solution and exchangeable P possibly due to crystallization of aluminium hydrous oxides reducing the number of sites
for P adsorption. All these changes were however small.
In a pot experiment, lime and phosphorus markedly increased barley shoot and root dry matter and P uptake. Although liming
reduced P availability measured by solution P, isotopically exchangeable P and resin extractable P, it increased phosphorus
uptake by reducing aluminium toxicity and promoting better root growth. The soil aluminium saturation was reduced by liming,
but the concentration of aluminium in roots changed only slightly. The roots accumulated aluminium without apparently being
damaged. 相似文献
48.
The effects of ethylene oxide (EtO) on survival of soil microflora and on selected chemical properties of a sandy-loam soil
were examined.
Soil sterilization was achieved after 8 hours exposure to EtO. Ethylene oxide treatment increased soil pH and organic matter
content. Extractable Mn and Fe slightly increased whereas P content decreased. Total N was not affected by the treatment. 相似文献
49.
Summary The alder has a perennial nodule cluster. The nodule amount on the roots increases with tree age. The N2-fixing activity of nodules decreases with nodule age. Purple coloured soils with various soil pHs and CaCO3 contents are, in the main, the ones which influence nodulation and N2-fixing. Higher N2-fixing capacity existed in the neutral and low calcium soils. High calcium soils and acid soils can restrain nodulation and
the N2-fixing rate significantly. On the slope, where calcarous light loams are found, the annual nitrogen fixation capacity of
alder and cypress mixed plantations, less than 10 years old, is 16 or 17 kg/ha yr, but in the valley, a pure alder plantation
can reach 40 kg/ha yr. 相似文献
50.
A continuous nutrient flow system has been developed to measure microbial activity in soil with various concentrations of
added substrate. The system consists of a thin soil layer through which substrate was added continuously over periods up to
4.5 days. Substrate utilization was determined by effluent analysis. Respiration was measured manually by injecting a sample
into a gas chromatograph or automatically by coupling the growth chamber to a computer-controlled gas sampling valve. This
permitted respiratory CO2 to be measured by the gas chromatograph at intervals selected by the investigator. Software controlling the valve and gas
chromatograph not only automated gas phase sampling, but also provided a scan of CO2 evolution and a preliminary data summary. This included the date and time of sample, peak height, and percent CO2 in the gas phase. Data for growth on glucose using a microbial population native to a California annual grassland soil demonstrated
that the direct cell count and respiratory techniques for biomass estimation give comparable results. This procedure provides
the potential for detailed analyses of substrate utilization in studies of the growth and maintenance of soil microorganisms. 相似文献