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11.
Z. Rengel 《Plant and Soil》1990,128(2):185-189
Ammonium acetate and BaCl2-triethanolamine were used to desorb Mg2+ from the root Donnan free space (DFS) of 23-d-old ryegrass (Lolium multiflorum Lam. cvs. Gulf and Wilo). Amounts of desorbed Mg2+ increased with the increase in Mg2+ activity of the nutrient solution. Slightly less Mg2+ was desorbed by Ba2+ than by NH4
+. Previously published data on short-term net Mg2+ uptake by intact 23-d-old ryegrass plants of the two cultivars were linearly related to the amount of exchangeable Mg+ desorbed from the root DFS (r2=0.90 and 0.81 for the desorption by NH4
+ and Ba2+, respectively). A sward of Mg2+ ions attracted to the negative charges of the cell surface is suggested to represent a part of a pool of Mg2+ available for active transport through the plasmalemma. 相似文献
12.
B. Rasnow 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1996,178(3):397-411
How might electric fish determine, from patterns of transdermal voltage changes, the size, shape, location, and impedance of a nearby object? I have investigated this question by measuring and simulating electric images of spheres and ellipsoids near an Apteronotus leptorhynchus. Previous studies have shown that this fish's electric field magnitude, and perturbations of the field due to objects, are complicated nonliner functions of distance from the fish. These functions become much simpler when distance is measured from the axes of symmetry of the fish and the object, instead of their respective edges. My analysis suggests the following characteristics of high frequency electric sense and electric images. 1. The shape of electric images on the fish's body is relatively independent of a spherical object's radius, conductivity, and rostrocaudal location. 2. An image's relative width increases linearly with lateral distance, and might therefore unambiguously encode object distance. 3. Only objects with very large dielectric constants cause appreciable phase shifts, and the degree of shift depends strongly on water conductivity. 4. Several parameters, such as the range of electric sense, may depend on the rostrocaudal location of an object. Large objects may be detectable further from the head than the tail, and conversely, small objects may be detectable further from the tail than head. 5. Asymmetrical objects produce different electric images, correlated with their cross-sections, for different orientations and phases of the electric field. 6. The steep attenuation with distance of the field magnitude causes spatial distortions in electric images, somewhat analogous to the perspective distortion inherent in wide angle optical lenses. 相似文献
13.
A combinatorial sequence space (CSS) model was introduced to represent sequences as a set of overlapping k-tuples of some fixed length which correspond to points in the CSS. The aim was to analyze clusterization of protein sequences in the CSS and to test various hypotheses about the possible evolutionary basis of this clusterization. The authors developed an easy-to-use technique which can reveal and analyze such a clusterization in a multidimensional CSS. Application of the technique led to an unexpectedly high clusterization of points in the CSS corresponding to k-tuples from known proteins. The clusterization could not be inferred from nonuniform amino acid frequencies or be explained by the influence of homologous data. None of the tested possible evolutionary and structural factors could explain the clusterization observed either. It looked as if certain protein sequence variations occurred and were fixed in the early course of evolution. Subsequent evolution (predominantly neutral) allowed only a limited number of changes and permitted new variants which led to preservation of certain k-tuples during the course of evolution. This was consistent with the theory of exon shuffling and protein block structure evolution. Possible applications of sequence space features found were also discussed.Correspondence to: H.A. Lim 相似文献
14.
David K. Chapman ers Johnsson Christina Karlsson Allan Brown David Heathcote 《Physiologia plantarum》1994,90(1):157-162
In a spaceflight experiment, autotropism by oat ( Avena sativa L.) coleoptiles following gravitropic responses was prominent in weightlessness: counter-reactions led to the straightening of the curved coleoptiles. This was not the case during clinorotation on earth. The autotropic reactions appeared to be related to the stimulus received during the stimulus period, i.e. the greater the response the greater the autotropic counter-reaction. Previous models of the gravitropic system which predicted that coleoptiles would not straighten in weightlessness are disproved. A modification to one of the models is proposed which includes the autotropic response observed in spaceflight. The nature of the counter-reactions in the absence of gravitropic stimulation is discussed. 相似文献
15.
T. Jermy 《Entomologia Experimentalis et Applicata》1993,66(1):3-12
Most hypotheses concerning the evolution of insect-plant relationships are based on the assumptions that, (1) phytophagous
insects reduce plant fitness, and that (2) insect-plant relationships are the result of unconstrained selection. It can be
shown, however, that there is little evidence to support these assumptions. As an alternative, it is proposed that the evolution
of insect-plant relationships results primarily from autonomous evolutionary events; namely from heritable functional changes
within the insects' nervous system that determine plant recognition and ultimately host plant specificity. These changes cannot
be evoked by selective ecological agents. They originate from intrinsic changes (mutationssensu lato) within the insect genome. Ecological factors play a secondary role: by either supporting or preventing the establishment
of the new genotype with the novel food preference.
This paper has been dedicated in warm friendship to Professor Louis M. Schoonhoven, the leading scientist in sensory physiology
of phytophagous insects, on the occasion of his 60th birthday. 相似文献
16.
Maarten Jaap Erik Broekman Selwyn Hoeks Rosa Freriks Merel M. Langendoen Katharina M. Runge Ecaterina Savenco Ruben ter Harmsel Mark A. J. Huijbregts Marlee A. Tucker 《Global Ecology and Biogeography》2023,32(2):198-205
Motivation
Home range is a common measure of use of space by animals because it provides ecological information that is useful for conservation applications. In macroecological studies, values are typically aggregated to species means to examine general patterns of use of space by animals. However, this ignores the environmental context in which the home range was estimated and does not account for intraspecific variation in home range size. In addition, the focus of macroecological studies on home ranges has historically been biased towards terrestrial mammals. The use of aggregated numbers and the terrestrial focus limit our ability to examine home-range patterns across different environments, their variation in time and variation between different levels of organization. Here, we introduce HomeRange, a global database with 75,611 home-range values across 960 different species of mammals, including terrestrial, aquatic and aerial species.Main types of variables contained
The dataset contains estimates of home ranges of mammals, species names, methodological information on data collection, method of home-range estimation, period of data collection, study coordinates and name of location, in addition to species traits derived from the studies, such as body mass, life stage, reproductive status and locomotor habit.Spatial location and grain
The collected data are distributed globally. Across studies, the spatial accuracy varies, with the coarsest resolution being 1°.Time period and grain
The data represent information published between 1939 and 2022. Across studies, the temporal accuracy varies; some studies report start and end dates specific to the day, whereas for other studies only the month or year is reported.Major taxa and level of measurement
Mammalian species from 24 of the 27 different taxonomic orders. Home-range estimates range from individual-level values to population-level averages.Software format
Data are supplied as a comma-delimited text file (.csv) and can be loaded directly into R using the “HomeRange” R package ( https://github.com/SHoeks/HomeRange ). 相似文献17.
Allyson Tucker Dilks Joanne Gilchrist Yik Lam Nathan Nicholes Brad Stanley 《Biotechnology progress》2023,39(4):e3351
No-salt flowthrough hydrophobic interaction chromatography (HIC) has been shown to effectively remove process and product-related impurities from bioprocess streams. In this publication, a panel of six antibodies has been used to demonstrate operating principles for the application of no-salt flowthrough HIC in antibody purification processes. The results indicate that no-salt flowthrough HIC provides robust aggregate clearance across operating conditions including flow rate, and variations in resin ligand density. Additionally, HMW reduction has an optimal pH range relative to the isoelectric point of each molecule and high molecular weight (HMW) reduction can be improved by altering the total protein load and/or HMW concentration to drive binding of high molecular weight species to the resin. 相似文献
18.
实验分别在出生后4周龄的幼年和成年鲁氏菊头蝠(Rhinolophusrouxi)上进行。使用移动声刺激装置,高频喇叭可在动物头部前方水平方向180度、垂直方向60度的范围内移动。玻璃微电极记录单个神经元的听反应。实验考察了幼年和成年动物下丘神经元的听空间特性,共观察了301个神经元,其中幼年动物148个,成年动物153个。结果表明,4周龄的幼年动物下丘听神经元已表现出方向敏感性,即每个听神经元均有一个特定的最佳反应中心和反应域。但神经元听反应中心在听空间的分布相当弥散,大多数位于对侧水平方向20—80度、垂直方向上下15度范围内。而成年动物听神经元反应中心的分布则相当集中,局限地分布于对侧水平方向28-50度,垂直方向0—10度范围内,两者构成明显差异。 相似文献
19.
Alexander Tschopp Augusto Cogoli Marian L. Lewis Dennis R. Morrison 《Journal of biotechnology》1984,1(5-6)
Attachment to a substrate and survival of human embryonic kidney (HEK) cells have been tested in an incubator installed in the flight-deck of the Space Shuttle ‘Challenger’ during its eighth mission.HEK cells are producing the enzyme urokinase and are presently investigated as candidates for electrophoretic separation in an apparatus developed and manufactured by McDonnell Douglas.Attachment of HEK cells to a substrate is mandatory for survival and production of urokinase after electrophoretic separation.Analysis of the samples shows that cells adhere, spread and survive in microgravity (< 10−3 ×g) conditions as well as the ground controls at 1 × g. This result represents an important step towards further bioprocessing in space. 相似文献
20.
Activation of microcarrier-attached lymphocytes in microgravity 总被引:1,自引:0,他引:1
Bechler B Cogoli A Cogoli-Greuter M Müller O Hunzinger E Criswell SB 《Biotechnology and bioengineering》1992,40(8):991-996
A technology has been developed to achieve optimal attachment of adhesion-independent lymphocytes to microcarrier beads. The activation of T-lymphocytes by concanavalin A was tested under microgravity conditions in an experiment carried out in space during the first Spacelab Life Science Mission. Activation, measured as the synthesis of deoxyribonucleic acid (DNA) and the production of interferon-gamma, more than doubled in attached lymphocytes in microgravity. The depression of the activation discovered in previous space experiments is due to an impairment not of the lymphocyte but of the macrophage function. The system described here may be useful for radiobiological investigations on the effect of high-energy particles and for testing the efficiency of the immune system in humans during the long-duration space flight planned in the future. The biotechnological significance of the increased lymphokine production in space remains to be assessed. 相似文献