A new null hypothesis for measuring the degree of plant community organization

An attempt is made to derive a measure for the degree of plant community organization, which would not be based on species co-occurrence and co-abundance. The use of the independent random distribution hypothesis (IRDH) is suggested for this purpose. The hypothesis is expected to be valid, if no deterministic phytosociological-structure-generating mechanism is present. If structural variability is used as a statistic for testing the hypothesis, deviances from the conditions of IRDH (species distributions are independent from each other, environmental gradients are lacking) will be attributable either to species interactions (smaller structural variability than expected), or to environmental heterogeneity (greater structural variability than expected). Structural variability is evaluated as the variance of species diversity, the indexN=exp(H') is used for measuring diversity. The precise measure of the degree of community organizationW is computed as the shift between two empirical distributions:D ^* (VN) or Bootstrap distribution of variance of diversity in the community, andD ^o (VN) or the random community variability distribution, which is evaluated after simulating the IRDH conditions.A satisfactory interpretation can be given to the results of evaluatingW for 11 data sets of 10 relevés each.Abbreviation IRDH Independent random distribution hypothesis     

Involvement of Escherichia coli DNA polymerase II in response to oxidative damage and adaptive mutation.

DNA polymerase II (Pol II) is regulated as part of the SOS response to DNA damage in Escherichia coli. We examined the participation of Pol II in the response to oxidative damage, adaptive mutation, and recombination. Cells lacking Pol II activity (polB delta 1 mutants) exhibited 5- to 10-fold-greater sensitivity to mode 1 killing by H2O2 compared with isogenic polB+ cells. Survival decreased by about 15-fold when polB mutants containing defective superoxide dismutase genes, sodA and sodB, were compared with polB+ sodA sodB mutants. Resistance to peroxide killing was restored following P1 transduction of polB cells to polB+ or by conjugation of polB cells with an F' plasmid carrying a copy of polB+. The rate at which Lac+ mutations arose in Lac- cells subjected to selection for lactose utilization, a phenomenon known as adaptive mutation, was increased threefold in polB backgrounds and returned to wild-type rates when polB cells were transduced to polB+. Following multiple passages of polB cells or prolonged starvation, a progressive loss of sensitivity to killing by peroxide was observed, suggesting that second-site suppressor mutations may be occurring with relatively high frequencies. The presence of suppressor mutations may account for the apparent lack of a mutant phenotype in earlier studies. A well-established polB strain, a dinA Mu d(Apr lac) fusion (GW1010), exhibited wild-type (Pol II+) sensitivity to killing by peroxide, consistent with the accumulation of second-site suppressor mutations. A high titer anti-Pol II polyclonal antibody was used to screen for the presence of Pol II in other bacteria and in the yeast Saccharomyces cerevisiae. Cross-reacting material was found in all gram-negative strains tested but was not detected in gram-positive strains or in S. cerevisiae. Induction of Pol II by nalidixic acid was observed in E. coli K-12, B, and C, in Shigella flexneri, and in Salmonella typhimurium.     

A highly repetitive, mariner-like element in the genome of Hyalophora cecropia.

A highly repetitive DNA element, homologous to the mariner transposon of Drosophila mauritiana was found in the intron of the gene for cecropin A, an antibacterial peptide from the Cecropia moth. The mariner-like elements (MLE) represent a homogeneous population with a copy number of about 1000/genome. Sequencing analysis showed it to be 1255 base pairs long, including 38-base pair terminal inverted repeats. The MLE contains a defective reading frame. Nevertheless, the putative product is clearly homologous to the predicted translation product encoded by mariner. In consonance is also the fact that the inverted repeats are highly conserved between the two elements and that the overall DNA homology is 48%. Since the mariner element is present in several Drosophila species closely related to Drosophila melanogaster and since MLE is present in the lepidopteran Cecropia, a route of horizontal transfer is indicated rather than vertical transmission from a common ancestor. This suggests the possible use of mariner for the construction of an interspecies vector.     

Clinical assessment of rheumatic diseases using viscoelastic parameters for synovial fluid

For the first time it is clearly exhibited that synovial fluid (SF) is thixotropic. Although no hysteresis loops were observed for SF, not even at high shear rates, thixotropy may be exhibited by measuring the rate of recovery after extensive shearing. The rebuilding of the structure in a small-amplitude oscillatory state following the high-shear-rate state reveals the thixotropic behaviour. Five different viscoelastic parameters for various synovial fluids (SF) were obtained using oscillatory rheometry. It was also shown that for SF in the low frequency range, corresponding to a knee joint almost at rest, the shear loss modulus G" is greater than the shear storage modulus G', since the system is allowed to dissipate energy at rest. However, with movement, G' increases and eventually becomes greater than G" at a characteristic frequency above which the system has insufficient time to dissipate energy and hence responds as an elastic body. This functional behaviour, characteristic for normal SF, broke down in the SF of rheumatoid arthritis. It was also absent in the SF of knee joints with meniscus lesions and ligament defects.     

The space-use strategy of plants with different growth forms,in a field experiment with manipulated nutrients and light

The biomass allocation pattern in plants is known to depend on the below and above-ground resource availabilities. In a herbaceous multi-species stand, it can be expected that the effects of nutrient and light availability on plants’ general space-use strategy are fundamentally different. We hypothesized that nutrient status alters the amount of biomass produced per unit canopy volume (biomass density), but not so much the biomass vertical distribution pattern. Changes in light availability, in contrast, should affect the vertical distribution pattern of biomass but not biomass density. We were also interested in whether the effect of resource manipulation on a plant’s space-use strategy depends on its basic morphological characteristics (growth form). The results from a four-year permanent plot experiment in a species-rich grassland, with fertilization and additional illumination from mirrors applied to 40 × 40 cm plots, showed that our main hypothesis was correct. Fertilization significantly affected biomass density above as well as below-ground, while additional illumination generally did not. Light addition altered the vertical distribution pattern of above-ground biomass, which remained unaffected by the fertilizer treatment.     

Phosphoramidate protides of carbocyclic 2',3'-dideoxy-2',3'-didehydro-7-deazaadenosine with potent activity against HIV and HBV

Synthesis of phosphoramidate protides of carbocyclic D- and L-2',3'-dideoxy-2',3'-didehydro-7-deazaadenosine by treatment of the nucleoside with phosphorochloridates in the presence of pyridine and t-BuMgCl is described. Several of these protides showed significantly improved antiviral potency over the parent nucleosides against both HIV and HBV.     

Characterization of glucose oxidase immobilization onto mica carrier by atomic force microscopy and kinetic studies

Glucose oxidase (E.C 1.1.3.4) immobilized onto activated surface of mica was analyzed by enzymatic kinetics and visualization with atomic force microscopy (AFM). The activity of the immobilized enzyme decreased with the decrease of concentration of gamma-aminopropyltrimethoxysilane used for the first step of activation of mica, while AFM analysis showed similar homogeneous filling of the surface with the enzyme. The comparison of enzyme activity with its surface filling revealed that there has to be additional vertical structures, which cannot be visualized by the methods of AFM. The simultaneous decrease of the silanizing agent and the concentration of the enzyme led to molecular resolution for the enzyme on the surface of mica. This allows to propose the described method also for analyzing other surfaces of solid materials with coupled biomolecules.