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91.
K. THOMPSON P. R. SHEWRY H. W. WOOLHOUSE 《Botanical journal of the Linnean Society. Linnean Society of London》1979,78(4):299-316
The ecology and distribution of papyrus swamps are briefly reviewed together with the ecology, distribution structure and growth characteristics of Cyperus papyrus.
Three age-classes of culm are recognized and girth and density of each are recorded along transects through mree swamps in the Upemba Basin of Zaïre. A regression of culm-unit biomass on culm girth, developed for Ugandan swamps, is used to convert Upemba measurements into biomasses. It is shown that simple measurements, taken at only a single point in time, yield much information on both the structure and the dynamics of papyrus populations.
It is suggested that the standing-crops of such populations are determined by available light, and by local temperature regimes, and are therefore constant, irrespective of site quality (nutrient status), for any particular climatic zone. Culm-duration (life-time) is not significantly influenced by climate and the ratio culms/rhizomes provides a useful indicator of comparative productivity. Unlike community biomass, productivity can be limited by site quality. 相似文献
Three age-classes of culm are recognized and girth and density of each are recorded along transects through mree swamps in the Upemba Basin of Zaïre. A regression of culm-unit biomass on culm girth, developed for Ugandan swamps, is used to convert Upemba measurements into biomasses. It is shown that simple measurements, taken at only a single point in time, yield much information on both the structure and the dynamics of papyrus populations.
It is suggested that the standing-crops of such populations are determined by available light, and by local temperature regimes, and are therefore constant, irrespective of site quality (nutrient status), for any particular climatic zone. Culm-duration (life-time) is not significantly influenced by climate and the ratio culms/rhizomes provides a useful indicator of comparative productivity. Unlike community biomass, productivity can be limited by site quality. 相似文献
92.
Through a systematic reduction of peptide structure, a series of 25 tripeptide and 5 dipeptide amide and alcohol analogs of enkephalin were synthesized and assayed in vitro on the stimulated guinea pig ileum. Tyr-Pro-Phe-NH2, Tyr-D-Ala-Phe-NH2, Tyr-D-Ala-Phe-ol and Tyr-D-Phe-Phe-NH2 had 20-25% the potency of Met-enkephalin. Four aromatic alkylamides of the dipeptide Tyr-D-Ala were made with benzylamine, phenethylamine, phenylpropylamine and phenylbutylamine. All had full naloxone reversible enkephalin-like activity in the ileum assay. Tyr-D-Ala-phenylpropylamide has about 80% the potency of Met-enkephalin in vitro, and is equipotent with Tyr-D-Ala-Gly-Phe-Met-NH2 in producing analgesia in mice after intraventricular administration. Tyr-D-Phe-NH2 is the smallest peptide to show full intrinsic enkephalin-like activity in vitro, although its potency is very low. 相似文献
93.
Roger Wigren Hans Elwing Ragnar Erlandsson Stefan Welin Ingemar Lundstrm 《FEBS letters》1991,280(2):225-228
It is shown that scanning force microscopy (SFM), operated in the attractive mode, can be used to obtain high resolution pictures of adsorbed fibrinogen molecules on solid surfaces, without the need for staining or special microscope grids. SFM also reveals the three-dimensional structure of the adsorbed molecules. Two forms of adsorbed fibrinogen are demonstrated on hydrophobic silicone dioxide surfaces; a trinodular about 60 nm long and a globular with about a 40 nm diameter. Polymeric networks formed after storage of the surface with adsorbed fibrinogen in PBS for 11 days are also shown. The SFM-results for the trinodular structure suggest the existence of loops or peptide chains extending outside the basic structure of the fibrinogen molecule. 相似文献
94.
Hans Holtschmidt Konrad Sandhoff Werner Fürst Hae Young Kwon Doris Schnabel Kunihiko Suzuki 《FEBS letters》1991,280(2):267-270
The organization of 14 exons covering 97% of the cDNA sequence of human cerebroside sulfate activator protein precursor has been determined from two overlapping EMBL-4 human genomic clones extending over 17kb. All exons and exon/intron splice junctions and five introns were sequenced. Exon 8 consists of only 9 bp and is involved in alternative splicing which generates three different mRNAs of cerebroside sulfate activator precursor. 相似文献
95.
Structural properties of two types of mangrove stands on the northwestern coast of Sri Lanka 总被引:2,自引:1,他引:1
Mangrove stands in Puttalam lagoon and Dutch bay, two interconnected lagoons situated on the northwestern coast of Sri Lanka have been classified broadly into two groups, i.e., estuarine and island/mainland-fringing stands. Structural diversity of six mangrove stands, representing the two types was studied in terms of floristic composition, density, basal area, mean stand diameter, tree height, standing above-ground biomass and leaf-area index.Rhizophora mucronata andAvicennia marina were the dominant species. Higher mean stand diameters for the mangrove stands in Puttalam lagoon indicated greater maturity than the estuarine mangrove stands in Dutch bay. Nevertheless, estuarine stands in Dutch bay were structurally more complex (complexity indices 8.11–22.7) than the island/mainland-fringing mangrove stands (complexity indices 1.38–6.78). Higher number of species present in the estuarine mangrove stands is the major element that contributes to the higher values for the complexity indices for those stands. This appears to mask the contribution of stand-age to the complexity of a mangrove stand. Therefore complexity indices alone may not be used to explain adequately the structural diversity among mangrove stands. 相似文献
96.
Summary There is a long-standing dispute over whether the analysis of species co-occurrence data, typically on islands in an archipelago, can disclose the forces at work in structuring a community. Here we present and utilise three scores S, C and T. S gives the mean number of islands shared by a species pair in the presence/absence data under study. The scores C and T are based on the way that a pair of species occurs on a pair of islands. When each species occurs on a different island, this adds to the checkerboard score C; if they occupy the same island, this increases the togetherness score T.In judging whether observed values of S, C and T are compatible with a null hypothesis assuming no species interaction, we follow Connor and Simberloff (1979) in generating a control group of (constrained) simulated incidence patterns.Presence/absence matrices can have paradoxical features, in combining a high mutual exclusion by species (checkerboardedness) with a degree of species aggregation that is also high. We show that this is in fact inevitable — that, given the usual contraints, C and T can differ only by a constant. This means that extreme checkerboardedness can be produced by forces making for species aggregation, just as well as by those making for avoidance.If we restrict our attention to a subset of species, the constraints are less rigid and the S, C and T scores are somewhat freer to vary. We consider the confamilial subsets in the Vanuatu archipelago as likely candidates for revealing any competition forces at work. Calculating the actual S, C and T scores for these subsets, we compare them with the corresponding scores in a sample of simulated colonization patterns.The actual species-distributions differ significantly from what we would expect if the colonization choices of different species were uncorrelated (save for some biological constraints). The confamilial species of the real world share more islands, and occur in a pattern less checkerboarded, and more aggregated, than their simulation counterparts. This suggests that competition pressures, if they exist, are overcome by countervailing factors.The method used is applicable in other ways, and to a wider class of problems, in analysing the forces behind community structure. 相似文献
97.
G. Binelli L. Gianfranceschi M. E. Pè G. Taramino C. Busso J. Stenhouse E. Ottaviano 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1992,84(1-2):10-16
Summary Densely saturated genetic maps of neutral genetic markers are a prerequisite either for plant breeding programs to improve quantitative traits in crops or for evolutionary studies. cDNA and genomic clones from maize were utilized to initiate the construction of a RFLP linkage map in Sorghum bicolor. To this purpose, an F2 population was produced from starting parental lines IS 18729 (USA) and IS 24756 (Nigeria) that were differentiated with regard to many morphological and agronomical traits. A total of 159 maize clones were hybridized to the genomic DNA of the two parents in order to detect polymorphism: 154 probes hybridized to sorghum and 58 out of these were polymorphic. In almost all of the cases hybridization patterns were similar between maize and sorghum. The analysis of the segregation of 35 polymorphic clones in an F2 population of 149 individuals yielded five linkage groups. The three principal ones recall regions of maize chromosomes 1, 3 and 5: in general, colinearity was maintained. A possible inversion, involving a long region of maize chromosome 3, was detected. Simulations were also performed to empirically obtain a value for the lowest number of individuals of the F2 population needed to obtain the same linkage data.Prof. E. Ottaviano, to whom this paper is dedicated, suddenly died on June 7th, 1991 相似文献
98.
X-ray absorption fine structure experiments were performed to study structural and dynamic aspects of the active site of various forms of myoglobin. The structures determined for deoxyMb, MbCO, and MbO2 are consistent with the structure established by X-ray absorption fine structure experiment and X-ray crystallography. The first shell of ferrous MbNO determined contains 5 nitrogens located at 2.02 A and a short NO bond length of 1.76 A. This study focuses on the change of the XAFS Debye-Waller factor with temperature, which is a measure of thermal and static disorder. It was found that the changes of Debye-Waller factor with temperature for the Mb proteins, except deoxyMb, are consistent with a simple Einstein model, in which a single frequency was assumed for the bond stretching modes. In contrast, the temperature dependence of deoxyMb cannot be fitted to the Einstein model and a large disorder was found at low temperatures, which indicates the existence of conformational substates of the active site. 相似文献
99.
It was recently found that some short peptides (including C- and S-peptide fragments of RNase A) can have considerable helicity in solution, 1–12 which was considered to be surprising. Does the observed helicity require a new explanation, or is it consistent with previous understanding? In this work we show that this helicity is consistent with the physical theory of secondary structure12–19 based on an extension of the conventional Zimm-Bragg model.20 Without any special modifications, this theory explains reasonably well almost all the experimentally observed dependencies of helicity on pH, temperature, and amino acid replacements. We conclude that the observed “general level” of helicity of C- and S-peptides (5–30% at room temperature and 10–50% near 0°C) is “normal” for short peptides consisting mainly of helix-forming and helix-indifferent residues. The helicity is modified by a multitude of weak specific side chain interactions, many of which are taken into account by the present theory;13–19 some discrepancies between the theory and experiment can be explained by weak side-chain-side chain interactions that were neglected. A reasonable coincidence of the theory with experiment suggests that it had been used to investigate the role of local interactions in the formation of α-helical “embryos” in unfolded protein chains. 相似文献
100.
Yuri Gamalei 《Trees - Structure and Function》1991,5(1):50-64
Summary Minor vein structure in various taxonomic groups was described in a previous paper (Gamalei 1989). Here, these results are used to correlate minor vein structure with plant evolutionary, ecological and growth form schemes. The following pattern emerges: reductive evolution from evergreen trees to annual herbs is accompanied by gradually increasing symplastic isolation of the mesophyll and the phloem. This evolutionary tendency is confirmed by the ecological spreading and life-form distribution of modern plants with different types of minor vein structure. The meaning of this phenomenon is discussed. Chilling sensitivity of plasmodesmal translocation is considered to be the main reason. It is suggested that phloem loading for assimilate transport is double-routed. The symplastic route is more ancient and more economical for loading. The apoplastic pathway becomes the main or the only route under unfavorable conditions. The existence of a symplast/apoplast regulatory loading mechanism is suggested. The two loading routes differ in their selectivity for products of photosynthesis which changes their symplast/apoplast ratio which, in turn, determines the composition of the sieve tube exudate. The latter will influence growth and morphogenesis. Correlated changes of structure and function related to photosynthesis, loading, translocation and growth, are analysed with respect to life-form evolution. The influence of the pathway of loading on other processes is discussed. 相似文献