Spatial patterns in a two-tiered semi-arid shrubland in southeastern Spain

Abstract. Single species and bivariate distribution patterns in a semi-arid shrubland in southeastern Spain, dominated by the tall leguminous shrub Retama sphaerocarpa, were investigated by second-order spatial analysis based on Ripley's K-function. Shrubs were significantly clumped because of a strong association of dwarf shrubs, mostly Artemisia barrelieri, under the canopy of Retama. Retama shrubs were randomly distributed, but when different size-classes were analysed separately, the pattern changed from significantly clumped to random and then to regular with increasing canopy diameter, suggesting increasing intraspecific competition with shrub size. Artemisia was significantly clumped at all scales because of aggregation under the canopy of large Retama shrubs. The association between the species became stronger with increasing canopy diameter of Retama shrubs, suggesting that facilitation prevailed over interspecific competition because of niche separation in different tiers, both above and below ground. Retama shrub size thus determined both the type of pattern for its own size class and tier, and the scale and intensity of the association with its understorey shrubs.     

Enlarged Similarity of Nucleic Acid Sequences

The concept of nucleic acid sequence base alternations is presented.The number of base alterations for the sequences of differentlength is established. The definition of "enlarged similarity"of nucleic acids sequences on the basis of sequence base alterationsis introduced. Mutual information between sequences is usedas a quantitative measure of enlarged similarity for two comparedsequences. The method of mutual information calculation is developedconsidering the correlation of bases in compared sequences.The definitions of correlated similarity and evolution similaritybetween compared sequences are given. Results of the use ofenlarged similarity approach for DNA sequences analysis arediscussed.     

OPTIMIZATION OF AN IMMUNOFLUORESCENT ASSAY OF THE INTERNAL ENZYME RIBULOSE-1,5-BISPHOSPHATE CARBOXYLASE (RUBISCO) IN SINGLE PHYTOPLANKTON CELLS1

Immunochemical probes are widely used to identih different species and to quantify and understand the role that different antigens play within cells. We optimized a single-cell immunofluorescent assay for the carbon fixation enzyme ribulose-1,5-bisphosphate carboxylase (Rubisco) in order to quantify the enzyme by flow cytometry in phytoplankton cells. The criteria for optimization of the immunofluorescent assay for Rubisco in single cells included maximization of Rubisco immunogenicity, minimization of Rubisco diffusion out of the cells, minimization of cell breakage, and maximization of the cell labeling. Several fixatives (cross-linkers and denaturing) and permeabilizing agents were tested on 26 species of phytoplankton. The only fixative / permeabilizing agent that fulfilled the criteria established for the assay was 96% ethanol. Phytoplankton cells collected from the field needed further treatment with a strong oxidant to permeabilize ethanolfixed cells and thus allow the antibody probe to access the Rubisco antigen. This study should have a general applicability to the study of other soluble photosynthetic antigens in single phytoplankton cells.     

Analysis of spatial and semporal organization in a salmonid brook in relation to physical factors and macrophytic vegetation

Four compartments of a salmonid brook were studied in consecutive sections either at sector scale or at facies scale: physical features, water quality, macrophytes and salmonids. The most important factor in the spatial and temporal organisation was the longitudinal zonation assessed by the four compartments. It was mainly shown by a gradient of the length of the morphodynamic sequence and of the facies width, of the pH and the conductivity and of macrophyte cover. It induced a colonisation by older trout in the downstream part of the brook where growth was better and shelter given by the bankside vegetation was more abundant. There were also greater densities of other age-classes upstream, with a correlation between salmon and rock shelter. Furthermore, the second factor corresponded to the flow characteristics and a granulometry gradient. The third factor corresponded chiefly to lighting, salmon numbers and densities. Salmonids showed a temporal stability from spring to autumn,and an opposition between growth and density. Six clusters of sectors defined functional entities. With regard to the 3—dimensitnal structure of the brook, the special pattern of each compartment shows its contribution to the functioning of the whole. Taking into account the scale of the study, the coexistence between trout and salmon did not show a competition between the two species, but rather a spatial partition, thanks to thehheterogenity inside each sector. We concluded on the necessity of studying sympatry at the facies scale to assess the role of habitat factors as regulators of carrying capacity.     

Parametric sensitivity of stoichiometric flux balance models applied to wild-type Escherichia coli metabolism

The esterification of lauric acid with geraniol catalyzed by the commercially immobilized lipase preparation from Mucor miehei, Lipozyme(R), was studied in well-stirred flasks. The enzyme support was characterized in terms of its internal and external surface area, protein location, and protein content. It was found that the enzyme was mainly located on the external surface of the support, therefore, internal diffusional limitations were not important. It was also shown that the protein content of the support depends on the size of the particle, with smaller particles containing higher amounts of protein per unit weight. Under the conditions studied, the reaction was not under external mass transfer limitations, and the initial reaction rate depended on the size of the support particles. This was mainly due to the different protein contents on the support as a function of particle size and not to internal or external mass transfer limitations. Also, it was found that the inhibition exerted by water was predominantly a physical effect due to its accumulation around the enzyme. It was also found that the reaction was substrate inhibited by lauric acid, but not by geraniol. (c) 1995 John Wiley & Sons, Inc.     

Effects of asexual reproduction on the neighborhood area of cyclical parthenogens

The habitat occupied by a subpopulation and withinwhich there is random mating is known as itsneighborhood area. Neighborhood area is dependenton dispersal rates and organisms with low rates ofdispersal are expected to have small neighborhoodareas. In the absence of evolutionary forces,neighborhood areas under sexual reproduction will beconstant in size as long as dispersal patterns do notchange. This scenario differs when reproduction is bycyclical parthenogenesis since recombination anddispersal may occur in different generations. Ingeneral, dispersal distances increase with the numberof parthenogenetic generations. We show that cyclicalparthenogenesis increases neighborhood area which,concomitantly, decreases the potential for geneticsubdivision. It is noteworthy, however, that theincrease in neighborhood area is a decreasing functionof the number of parthenogenetic generations.This mechanism may have important implications for thepopulation structure of planktonic rotifers living ina horizontally undifferentiated habitat. In suchhabitats organisms are effectively unrestricted intheir lateral movements. Because rotifers typicallyhave low dispersal rates spatial geneticdiscontinuities may develop that divide the populationinto genetically distinct subpopulations. Counteringthis tendency is the increased neighborhood areaproduced by dispersal during the parthenogeneticphase. Thus cyclical parthenogenesis in organismslike rotifers may have important and previouslyunreported effects on the population's geneticstructure.     

Influence of muscle activity on the forces in the femur: An in vivo study

Experiments were performed on two patients with custom-made instrumented massive proximal femoral prostheses implanted after tumour resection. In vivo axial forces transmitted along the prostheses were telemetered during level walking, single- and double-leg stance, and isometric exercises of the hip muscles. These activities varied the lever arms available to the external loads: minimum for double-leg stance and maximum for hip isometric exercises. Kinematic, force plate, EMG and telemetered force data were recorded simultaneously. The force magnification ration (FMR; the ratio of the telemetered axial force to the external force) was calculated. The FMRs ranged from 1.3 (during double-leg stance) to 29.8 (during abductors test), indicating that a major part of the axial force in the long bones is a response to muscle activity, the strength of which depends on the lever arms available to the external loads. From these results, it was shown that the bulk of the bending moment along limbs is transmitted by a combination of tensile forces in muscles and compressive forces in bones, so moments transmitted by the bones are smaller than the limb moments. It was concluded that appropriate simulation of muscle forces is important in experimental or theoretical studies of load transmission along bones.     

Energy-dispersive X-ray analysis of the extracellular cadmium sulfide crystallites of Klebsiella aerogenes

Klebsiella aerogenes forms electron-dense partieles on the cell surface in response to the presence of cadmium ions in the growth medium. These particles ranged from 20 to 200 nm in size, and quantitative energy dispersive X-ray analysis established that they comprise cadmium and sulfur in a 1:1 ratio. This observation leads to the conclusion that the particles are cadmium sulfide crystallites. A combination of atomic absorption spectroscopy, inductively coupled plasma mass spectrometry, and acid-labile sulfide analysis revealed that the total intracellular and bound extracellular cadmium:sulfur ratio is also 1:1, which suggests that the bulk of the cadmium is fixed as extracellular cadmium sulfide. The tolerance of K. acrogenes to cadmium ions and the formation of the cadmium sulfide crystallites were dependent on the buffer composition of the growth medium. The addition of cadmium ions to phosphate-buffered media resulted in cadmium phosphate precipitates that remove the potentially toxic cadmium ions from the growth medium. Electrondense particles formed on the surfaces of bacteria grown under these conditions were a combination of cadmium sulfide and cadmium phosphates. The specific bacterial growth rate in the exponential phase of batch cultures was not affected by up to 2mM cadmium in Tricine-buffered medium, but formation of cadmium sulfide crystallites was maximal during the stationary phase of batch culture. Cadmium tolerance was much lower (10 to 150 M) in growth media buffered with Tris, Bistris propane, Bes, Tes, or Hepes. These results illustrate the importance of considering medium composition when comparing levels of bacterial cadmium tolerance.Abbreviations EDXA Energy dispersive X-ray analysis - AAS Atomic absorption spectroscopy - TEM Transmission electron microscopy - SEM Scanning electron microscopy - ICP-MS Inductively coupled plasma mass spectrometry - ALSA Acid-labile sulfide analysis     

Analysis of viability and cell types of macroalgal protoplasts using flow cytometry

The ability to rapidly distinguish viable sub-populations of cells within populations of macroalgal protoplast isolations was demonstrated using flow cytometry. Viable protoplasts from Ulva sp. and Porphyra perforata J. Ag. were distinguished from non-viable protoplasts based on differential fluorescein accumulation. The identities of cortical and epidermal protoplasts from Macrocystis pyrifera (L.) C. Ag. were inferred based on light-scattering and chlorophyll a autofluorescence. Three cell types could be distinguished among protoplasts released from thalli of P. perforata based on chlorophyll a and phycoerythrin autofluorescence. Mixed protoplast populations of Ulva sp. and P. perforata were also discernable based on relative chlorophyll a and phycoerythrin autofluorescence. The ability to screen heterogenous protoplast populations rapidly, combined with the cell sorting capabilities of many flow cytometers, should prove valuable for seaweed biotechnology.     

A procedure for detecting structural domains in proteins.

A procedure is described for detecting domains in proteins of known structure. The method is based on the intuitively simple idea that each domain should contain an identifiable hydrophobic core. By applying the algorithm described in the companion paper (Swindells MB, 1995, Protein Sci 4:93-102) to identify distinct cores in multi-domain proteins, one can use this information to determine both the number and the location of the constituent domains. Tests have shown the procedure to be effective on a number of examples, even when the domains are discontinuous along the sequence. However, deficiencies also occur when hydrophobic cores from different domains continue through the interface region and join one another.