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Krystyna Kozŀowska Barbara Żurawska-Czupa Jerzy Krupa 《Histochemistry and cell biology》1977,54(2):149-157
Summary The avoid the effect of enzymes on the cell surface during the isolation procedure, in the present work isolation of cells from solid tissues by means of a chelating agent was attempted. Cell coat of hepatocytes and thymocytes was stained with ruthenium red and examined with the electron microscope. Adequacy of the isolation methods employed for studies of cell surface glycoproteins was tested by treating with trypsin. Reaggregation of isolated hepatocytes was performed too. The above results allow the suggestion that the use of EDTA for isolation of liver cells is suitable for the study of surface material of cells. 相似文献
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Toshihiko Hara 《植被学杂志》1993,4(3):409-416
Abstract. Both size structure and variability (spatial heterogeneity, disturbance, stochasticity, variation in species attributes, etc.) are regarded as regulatory mechanisms of species coexistence. However, none of the models so far proposed consider both size structure and variability simultaneously. A size-structured variation model for plant-community dynamics is proposed, which is based on the diffusion model for growth dynamics of plant populations. This model has four functions: (1) mean growth rate of individuals of size x at time t, G(t, x) (species-specific mean traits, e.g. competitive ability); (2) variance in growth rate of individuals of size x at time t, D(t, x) (stochastic factors due to genetic variation, environmental heterogeneity, spatial variation of individuals, etc.); (3) mortality rate of individuals of size x at time t, M(t, x); and (4) recruitment rate at time t, R(t), as a boundary condition. The interference function for individuals of size x at time t, C(t, x), is introduced, which expresses the degree of interactions between individuals and hence averaged effects of local neighbourhood competition; the G(t, x), D(t, x), M(t, x) and R(t) functions are given in terms of C(t, x). These four functions describe the growth dynamics of individuals of each species in the plant community. Effects of the G(t, x), D(t, x), M(t, x) and R(t) functions on species coexistence in plant communities were evaluated by simulation and the relative importance of the D(t, x) function as well as size structure was shown for species coexistence especially in plant communities where competition among species is non-transitive or niche limitation does not work. 相似文献
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The avoid the effect of enzymes on the cell surface during the isolation procedure, in the present work isolation of cells from solid tissues by means of a chelating agent was attempted. Cell coat of hepatocytes and thymocytes was stained with ruthenium red and examined with the electron microscope. Adequacy of the isolation methods employed for studies of cell surface glycoproteins was tested by treating with trypsin. Reaggregation of isolated hepatocytes was performed too. The above results allow the suggestion that the use of EDTA for isolation of liver cells is suitable for the study of surface material of cells. 相似文献
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Aurélien Roger Alexandre Colard Caroline Angelard Ian R Sanders 《The ISME journal》2013,7(11):2137-2146
Arbuscular mycorrhizal fungi (AMF) form symbioses with most plant species. They are ecologically important determinants of plant growth and diversity. Considerable genetic variation occurs in AMF populations. Thus, plants are exposed to AMF of varying relatedness to each other. Very little is known about either the effects of coexisting AMF on plant growth or which factors influence intraspecific AMF coexistence within roots. No studies have addressed whether the genetics of coexisting AMF, and more specifically their relatedness, influences plant growth and AMF coexistence. Relatedness is expected to influence coexistence between individuals, and it has been suggested that decreasing ability of symbionts to coexist can have negative effects on the growth of the host. We tested the effect of a gradient of AMF genetic relatedness on the growth of two plant species. Increasing relatedness between AMFs lead to markedly greater plant growth (27% biomass increase with closely related compared to distantly related AMF). In one plant species, closely related AMF coexisted in fairly equal proportions but decreasing relatedness lead to a very strong disequilibrium between AMF in roots, indicating much stronger competition. Given the strength of the effects with such a shallow relatedness gradient and the fact that in the field plants are exposed to a steeper gradient, we consider that AMF relatedness can have a strong role in plant growth and the ability of AMF to coexist. We conclude that AMF relatedness is a driver of plant growth and that relatedness is also a strong driver of intraspecific coexistence of these ecologically important symbionts. 相似文献
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Immunocytochemistry revealed growth hormone-releasing hormone (GRF)-containing cells (4-10/50 microns thick coronal sections) in the ventral portion of the medial parvicellular subdivision of the paraventricular nucleus (PVN) in the rat. In the same region we also detected about the same number of neurons containing the mRNA that encodes GRF using in situ hybridization histochemistry. Fluorescence double labelling immunohistochemistry showed the presence of GRF and tyrosine hydroxylase (TH) in the same PVN neurons. The overlap between the two populations of cells is only partial: less than half of TH-positive cells contain GRF and vice versa. 相似文献
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Plant species vary in their growth response to arbuscular mycorrhizal (AM) fungi, with responses ranging from negative to positive. Differences in response to AM fungi may affect competition between plant species, influencing their ability to coexist. We hypothesized that positively responding species, whose growth is stimulated by AM fungi, will experience stronger intraspecific competition and weaker interspecific competition in soil containing AM fungi, while neutrally or negatively responding species should experience weaker intraspecific and stronger interspecific competition. We grew Plantago lanceolata, which responds positively to AM fungi, and Bromus inermis, which responds negatively to AM fungi, in an additive response surface competition experiment that varied the total density and relative frequency of each species. Plants were grown in sterilized background soil that had been inoculated with whole soil biota, which includes AM fungi, or a microbial wash, that contained other soil microbes but no AM fungi, or in sterilized soil that contained no biota. The positively responding P. lanceolata was more strongly limited by intraspecific than interspecific competition when AM fungi were present. By contrast, the presence of AM fungi decreased the strength of intraspecific competition experienced by the negatively responding B. inermis. Because AM fungi are almost always present in soil, strong intraspecific competition in positively responding species would prevent them from outcompeting species that respond neutrally or negatively to AM fungi. The potential for increased intraspecific competition to offset growth benefits of AM fungi could, therefore, be a stabilizing mechanism that promotes coexistence among plant species. 相似文献
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The effect of the structure of the community matrix, i.e. its covariance, and the average strength of competition on the number of alternative stable subsets of species (domains of attraction) and the number of species per domain are explored by computer simulation. Communities with negative covariance of the competitive interaction coefficients tend to have fewer domains and fewer species per domain. Regardless of the covariance, more domains of attraction and fewer species per domain of attraction occur with increasing average competition among community members. 相似文献
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Annett Nold 《Theoretical population biology》1979,15(2):232-245
The possibility of equilibrium is studied for model assemblages of competing species and their resources. The “assemblage niche” is defined as the set of resource productivities which yields an equilibrium population exceeding zero for all species. A radius of this set, which is a measure of the ability of the assemblage to have equilibrium states, is defined and estimated. This radius decreases as resource utilization overlap increases; the behavior is compared with known results concerning response to rapid resource fluctuations. A system of ordinary differential equations having such an equilibrium is studied. It is shown that a global asymptotic stability property holds in regions with boundaries defined by a certain scalar function, if the specific productivity satisfies a monotonicity condition. This generalizes known results, which have been obtained for antisymmetric Lotka-Volterra systems. 相似文献
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Yurewicz KL 《Oecologia》2004,138(1):102-111
Behavioral and morphological traits often influence a key trade-off between resource acquisition and vulnerability to predation, and understanding trait differences between species can provide critical insight into their interactions with other species and their distributions. Such an approach should enhance our understanding of the criteria for coexistence between species that can interact through both competition and predation (i.e. intraguild predators and prey). I conducted a common garden experiment that revealed strong differences between three guild members (larval salamanders Ambystoma laterale, A. maculatum, and A. tigrinum) in behavior, morphology, and growth in the presence and absence of a shared top predator (the larval dragonfly Anax longipes). All three species also reduced their activity and modified their tail fin depth, tail muscle length, and body length in response to non-lethal Anax. Species that act as intraguild predators were more active and could grow faster than their intraguild prey species, but they also suffered higher mortality in laboratory predation trials with Anax. I also used survey data from natural communities to compare the distribution of Ambystoma species between ponds differing in abiotic characteristics and predatory invertebrate assemblages. An intraguild prey species (A. maculatum) was found more reliably, occurred at higher densities, and was more likely to persist late into the larval period in ponds with more diverse invertebrate predator assemblages. Taken together, these results indicate that top predators such as Anax may play an important role in influencing intraguild interactions among Ambystoma and ultimately their local distribution patterns. 相似文献
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Sedimentation coefficients of replicating and crosslinked DNA 总被引:1,自引:0,他引:1
V A Bloomfield 《Biopolymers》1968,6(3):285-292
The sedimentation coefficients of branched and cyclic replicating DNA structures have been calculated taking into account both chain stiffness and excluded volume effects. For branched DNA, the calculated ratio S0(α)/S0(0) of the sedimentation coefficient at degree of replication α to that at α = 0 increases from 1.000 to 1.331 as α goes from 0 to 1. For cyclic replicating DNA, S0(1)/S0(0) = 1.517. The considerable difference between these two ratios for α = 1 suggests that the two types of replicating structures may feasibly be distinguished by sedimentation velocity studies, A similar calculation has been made of the sedimentation coefficient of singly cross-linked DNA under denaturing conditions, as a function of placement of the crosslink. In 0.195M Na+, the ratio S0(α)/S0(0) varies from 1.000 at α = 0 to 1.124 at α = 0.5, where α is the fractional distance of the crosslink from the end of the chain. 相似文献
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Bex3 expression and possible function in growth control were studied. It was expressed in a limited number of organs, including gonads and hippocampal regions of the brain. Visualized by deconvolution microscopy as a GFP-fusion protein in F9 teratocarcinoma cells, Bex3 localized, along with concentrations of actin, at perinuclear mitochondria that were undergoing active DNA replication. Bex3 association with mitochondria required a nuclear export signal (NES) and the C-terminal four amino acids (CaaX box), and siRNA reduction of Bex3 levels led to slow or negligible growth rates of the F9 cells. Thus, Bex3 may be required in target tissues for mitochondrial function at a distinct phase of the cellular growth cycle. 相似文献
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Kao RH 《The New phytologist》2007,175(4):764-772
Reproductive isolation via apomixis is one way for newly created cytotypes to persist and coexist with other cytotypes. Arnica cordifolia (Asteraceae) has both triploid and tetraploid cytotypes co-occurring in many locations. The rate of apomixis in each cytotype was explored as a mechanism for the maintenance of sympatric cytotypes. Flow cytometry was used on both adults and seeds from mixed cytotype populations to estimate reproductive mode and to evaluate the relationship between cytotype frequency and reproductive success. Flowering time was surveyed to look for temporal reproductive isolation between cytotypes. Both triploids and tetraploids can be asexual. Apomixis in A. cordifolia is usually autonomous, not pseudogamous as previously thought. Sexual reproduction appears to be uncommon. The minority cytotype in each population does not produce fewer seeds, confirming that minority cytotype exclusion is unlikely to occur via reproductive disadvantage. Triploids flowered earlier than tetraploids, but with much overlap. Asexual reproduction is an important factor promoting the coexistence of cytotypes in this system. Other mechanisms maintaining populations of sympatric cytotypes are not well studied or understood and warrant further investigation. 相似文献
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Non-enzymatic glycosylation of collagen occurs both in vivo during diabetes and in vitro after incubation with glucose. Glycosylated collagen exhibits altered physicochemical and biological properties which could explain some of the complications of diabetes. To provide a mechanistic explanation of this modification the localization of bound glucose was investigated using NaB[3H]H4 reduction and CNBr cleavage. Glucose fixation is distributed mainly on the alpha 1CB6 peptide after in vitro glycosylation whereas this distribution occurs less specifically during diabetes. It is concluded that fibrillogenesis alteration of in vitro glycosylated collagen is related to glucose fixation on free epsilon NH2 sites normally implied in intermolecular interactions. 相似文献
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We investigated whether the specific localization of DNA replicator sites at the nuclear membrane at the end of the S phase,
found in dividing animal cells and in the plantHaplopappus gracilis, applied also to other plants. We found that nuclei labelled at the nuclear periphery were observed in plants where the chromocenters
are localized at the nuclear membrane. In other plants, where the chromocenters are scattered throughout the nucleus, a different
pattern of labelling is observed where the silver grains are restricted to a number of distinct sites, distributed in a fashion
similar to that of the chromocenters. We believe that these nuclei were replicating the chromocentric heterochromatin and
so were therefore at the end of the S phase. The specific patterns of the distribution of DNA replicator sites at the end
of the S phase make it possible to distinguish nuclei which are in the late S phase and thus define a specific stage of the
S phase, during which only heterochromatin replication occurs. 相似文献
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Amarasekare P 《Proceedings. Biological sciences / The Royal Society》2002,269(1509):2541-2550
Interference competition is ubiquitous in nature. Yet its effects on resource exploitation remain largely unexplored for species that compete for dynamic resources. Here, I present a model of exploitative and interference competition with explicit resource dynamics. The model incorporates both biotic and abiotic resources. It considers interference competition both in the classical sense (i.e. each species suffers a net reduction in per capita growth rate via interference from, and interference on, the other species) and in the broad sense (i.e. each species suffers a net reduction in per capita growth rate via interference from, but can experience an increase in growth rate via interference on, the other species). Coexistence cannot occur under classical interference competition even when the species inferior at resource exploitation is superior at interference. Such a trade-off can, however, change the mechanism of competitive exclusion from dominance by the superior resource exploiter to a priority effect. Now the inferior resource exploiter can exclude the superior resource exploiter provided it has a higher initial abundance. By contrast, when interference is beneficial to the interacting species, coexistence is possible via a trade-off between exploitation and interference. These results hold regardless of whether the resource is biotic or abiotic, indicating that the outcome of exploitative and interference competition does not depend on the exact nature of resource dynamics. The model makes two key predictions. First, species that engage in costly interference mechanisms (e.g. territoriality, overgrowth or undercutting, allelopathy and other forms of chemical competition) should not be able to coexist unless they also engage in beneficial interference mechanisms (e.g. predation or parasitism). Second, exotic invasive species that displace native biota should be superior resource exploiters that have strong interference effects on native species with little or negative cost. The first prediction provides a potential explanation for patterns observed in several natural systems, including plants, aquatic invertebrates and insects. The second prediction is supported by data on invasive plants and vertebrates. 相似文献
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Baculoviruses, and in particular, the nucleopolyhedroviruses infect a wide range of arthropod hosts and have the potential to be used as biopesticides. However, one of the major drawbacks with these pathogens as biocontrol agents is that they have a slow response time. Alterations to the speed of kill and pathogen life history characteristics can influence the competitive outcome and persistence between wildtype and modified strains. Here, we explore, theoretically, how life-history modifications of pathogens can affect the epidemiology and ecology of strain coexistence. In particular, we show how under simple mass action disease transmission, life-history difference between strains are insufficient to allow coexistence. Additional heterogeneities in transmission are shown to be necessary to facilitate coexistence of wildtype and modified pathogen strains. We also illustrate how the patterns of infectivity of wildtype and modified strains can also affect long-term coexistence, and argue that appropriate assessment of genetic modifications must be presented in terms of relevant ecological theory. 相似文献