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31.
R. A. Pickering P. W. Morgan 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1985,70(2):199-206
Summary Several interspecific and intergeneric crosses involving five Hordeum species, Triticum aestivum and Secale cereale were carried out to investigate the influence of two contrasting temperatures on chromosome elimination during embryo development. In four of the interspecific Hordeum crosses, chromosome elimination was significantly increased at the higher of the two temperatures, resulting in greater proportions of haploid plant progenies. However, there was no significant effect of temperature in the other interspecific cross between H. lechleri x H. bulbosum nor in the two intergeneric crosses between H. vulgare x S. cereale and T. aestivum x H. bulbosum whose progeny were exclusively hybrid and haploid, respectively. 相似文献
32.
P. K. Ponnuswamy 《Journal of biosciences》1985,8(1-2):151-165
The salient features of the differential equation model to study protein dynamics are presented with results for 19 proteins. 相似文献
33.
Temperature Dependence of Catecholamine Secretion from Cultured Bovine Chromaffin Cells 总被引:2,自引:1,他引:1
Abstract: Secretion of both epinephrine and norepinephrine by cultured chromaffin cells was studied at temperatures ranging from 0°C to 37°C. The percentage of epinephrine secreted was always lower than that of norepinephrine when the cells were stimulated with either acetylcholine or high K+ at any temperature. When the cells were stimulated with acetylcholine or carbachol the percentage of catecholamine secreted at 10 min increased with temperature from 4°C to 24°C and then decreased from 24°C to 37°C. Potassium-stimulated cells secreted increasing amounts of catecholamine as the temperature was increased to 37°C. We found, however, that the initial rates of secretion increased continuously as temperature increased throughout the range for both carbachol-and K+ -stimulated cells. The temperature maximum of acetylcholine-stimulated secretion is caused by a faster shut-off of secretion at higher temperature. The Arrhenius plots of initial rates show an inflection point at approximately 17°C for carbachol-stimulated cells. The plot for K+ -stimulated cells is a straight line over the entire temperature range. The transition could be caused by a conformational change in the cholinergic receptor/ion channel molecule. 相似文献
34.
Climate and plant distribution at global and local scales 总被引:12,自引:0,他引:12
This paper investigates, with predictive models, the utility of ecophysiological responses to climate as predictors of plant distribution. At the global scale responses to extreme minimum temperatures and to the hydrological budget effectively predict the distribution limits of the major vegetation types of the World. A minimum temperature of -15°C, for example, appears critical in controlling the poleward spread of vegetation that is dominated by evergreen broadleaved species; however, the presence or absence of more frost resistant species, such as those that are deciduous broadleaved, is not obviously explained in terms of extremes of climate. In such cases, predicting the competitive relationships between species is necessary and dependent on the climatic sensitivity of population dynamics.We are grateful to Hans de Kroon for discussions on the application of matrices to ecology. 相似文献
35.
Single-channel conductance fluctuations are analysed for gramicidin A incorporated into binary-mixed black lipid membranes of charged phosphatidic acid and neutral lecithin in different molar ratios. At very low Ca++ concentrations in the electrolyte (i.e. in the presence of EDTA) homogeneous lipid mixtures are identified through their conductance and life time probability distributions for integral gramicidin pores. As for the pure lipid components, the conductance histograms each show a single maximum with regular width and for all channels a single mean lifetime is found.For Ca++-levels (10-6–10-5
M) that are close to the critical demixing concentration (10-4
M) unusually broad conductance distributions and reduced lifetimes are found provided the PC content, x, of the membrane is close to the critical mixture (x
crit0.5). We interpret this as a first example of the coupling of a membrane function (the transport of ions) to a lipid matrix with locally fluctuating composition close to a critical demixing point.For
the conductance histogram of gramicidin A in an equimolar mixture of PA and PC shows two well-separated maxima. A correlation analysis between conductance and lifetime of the single pores shows that the two channel populations also differ significantly in their mean channel lifetime, *. This finding is interpreted as being direct evidence for Ca++-induced lateral phase separation in black lipid membranes, as has been postulated recently.Abbreviations used HEPES
N-2-hydroxyethyl-piperazine-N-2-ethane-sulfonic acid
- EDTA
ethylenediaminetetraacetic acid 相似文献
36.
Subhash C. Gupta Catherine Potrikus Reese J. Woodland Hastings 《Archives of microbiology》1986,143(4):325-329
A recombinant plasmid which carried a 5 kb fragment of Vibrio harveyi DNA containing the luxA and luxB genes was mobilized from Escherichia coli into luminescence-deficient mutants of V. harveyi. The cloned genes complemented a temperature sensitive luciferase mutation, but failed to complement lesions in two different aldehyde deficient mutants. Expression of the cloned genes was not subject to autoinduction in either E. coli or in V. harveyi. 相似文献
37.
38.
Intra- and interspecific competition between laboratory populations of four green leafhoppers, Nephotettix spp. was studied in the laboratory under three different temperature regimes of 24°C, 27°C and 30°C. For the single-species population of the three tropical species, the equilibrium density increased as the temperature increased. On the other hand, for the temperature species N. cincticeps, the highest equilibrium density was at the intermediate temperature and the lowest at high temperature. Interspecific interactions between two tropical (N. virescens vs. N. nigropictus), a tropical and a temperature (N. virescens vs. N. cincticeps) and a rice-feeding and a grass-inhabiting (N. virescens vs. N. malayanus) Nephotettix species were also studied in the laboratory at the three temperature regimes. Temperature differentially affected the outcome of competition between two Nephotettix species. Between N. virescens and N. nigropictus, the latter was more successful over the former at low and intermediate temperatures, while the former was more successful at high temperature. Between N. virescens and N. cincticeps, the temperate species inhibited the growth of the tropical species at low temperature while the tropical species inhibited the growth of the temperate species at high temperature. At intermediate temperature, the population of N. virescens persisted at a slightly higher density over the population of N. cincticeps. Between the rice-feeding N. virescens and the grass-inhabiting N. malayanus, regardless of temperature the population density of the latter was greatly reduced and later became extinct while the population of the former continued its growth. These consequences of competition between two Nephotettix species conformed fairly well to those predicted by theLotka-Volterra model using demographic parameters specified for each species. 相似文献
39.
Conformational fluctuations in a globular protein, bovine pancreatic trypsin inhibitor, in the time range between picoseconds and nanoseconds are studied by a Monte Carlo simulation method. Multiple energy minima are derived from sampled conformations by minimizing their energy. They are distributed in clusters in the conformational space. A hierarchical structure is observed in the simulated dynamics. In the time range between 10(-14) and 10(-10) seconds dynamics is well represented by a superposition of vibrational motions within an energy well with transitions among minima within each cluster. Transitions among clusters take place in the time range of nanoseconds or longer. 相似文献
40.
Johan U. Grobbelaar 《Journal of applied phycology》1989,1(4):333-340
It has been suggested that turbulence with the resultant light/dark cycle and light gradient through which phytoplankton move,
enhances their productivity. The stationary bottle incubation technique for estimating rates of primary productivity has mainly
been criticized because of bottle effects, the elimination of natural turbulence and the presence of photo-inhibition. In
a series of experiments where productivity was measured over static profiles and compared to the productivity in a mixed system,
no definite conclusion could be reached regarding the effect of varying light/dark cycles of medium frequency (seconds to
minutes). It appeared as though the ratio of the euphotic depth to mixing depth (Z
eu/Z
m) influenced productivity more than the duration of the light/dark cycle. The static bottle incubation method gave higher
integral productivities than the mixed samples at low ratio's ofZ
eu/Z
m. It is suggested that mixing has two separate, but synergistic effects i.e. it not only moves the phytoplankton cells through
a light/dark cycle, but also decreases the boundary layer, which increases the rate of exchange through the cell wall of nutrients
and metabolites. In doing so more nutrients are available and light could be utilized more efficiently and therefore, productivity
is increased. 相似文献