Evolutionary processes,dispersal limitation and climatic history shape current diversity patterns of European dragonflies

We investigated the effects of contemporary and historical factors on the spatial variation of European dragonfly diversity. Specifically, we tested to what extent patterns of endemism and phylogenetic diversity of European dragonfly assemblages are structured by 1) phylogenetic conservatism of thermal adaptations and 2) differences in the ability of post‐glacial recolonization by species adapted to running waters (lotic) and still waters (lentic). We investigated patterns of dragonfly diversity using digital distribution maps and a phylogeny of 122 European dragonfly species, which we constructed by combining taxonomic and molecular data. We calculated total taxonomic distinctiveness and mean pairwise distances across 4192 50 × 50 km equal‐area grid cells as measures of phylogenetic diversity. We compared species richness with corrected weighted endemism and standardized effect sizes of mean pairwise distances or residuals of total taxonomic distinctiveness to identify areas with higher or lower phylogenetic diversity than expected by chance. Broken‐line regression was used to detect breakpoints in diversity–latitude relationships. Dragonfly species richness peaked in central Europe, whereas endemism and phylogenetic diversity decreased from warm areas in the south‐west to cold areas in the north‐east and with an increasing proportion of lentic species. Except for species richness, all measures of diversity were consistently higher in formerly unglaciated areas south of the 0°C isotherm during the Last Glacial Maximum than in formerly glaciated areas. These results indicate that the distributions of dragonfly species in Europe were shaped by both phylogenetic conservatism of thermal adaptations and differences between lentic and lotic species in the ability of post‐glacial recolonization/dispersal in concert with the climatic history of the continent. The complex diversity patterns of European dragonflies provide an example of how integrating climatic and evolutionary history with contemporary ecological data can improve our understanding of the processes driving the geographical variation of biological diversity.     

Modifications of membrane phospholipid composition in nisin-resistant Listeria monocytogenes Scott A.

A nisin-resistant (NISr) variant of Listeria monocytogenes Scott A was isolated by stepwise exposure to increasing concentrations of nisin in brain heart infusion (BHI) broth. The NISr strain was about 12 times more resistant to nisin than was the wild-type (WT) strain. Accordingly, higher nisin concentrations were required to dissipate both components of the proton motive force in the NISr strain than in the WT strain. Comparison of the membrane fatty acyl composition of the sensitive strain with that of its NISr derivative revealed no significant differences. From phospholipid head group composition analysis and phospholipid biosynthesis measurements during growth in the absence and presence of nisin, it could be inferred that the NISr strain produces relatively more phosphatidylglycerol (PG) and less diphosphatidylglycerol (DPG) than the parent strain does. Monolayer studies with pure lipid extracts from both strains showed that nisin interacted more efficiently with lipids derived from the WT strain than with those derived from the NISr strain, reflecting qualitative differences in nisin sensitivity. Involvement of the cell wall in acquisition of nisin resistance was excluded, since the WT and NISr strains showed a comparable sensitivity to lysozyme. Recently, it has been demonstrated that nisin penetrates more deeply into lipid monolayers of DPG than those of other lipids including PG, phosphatidylcholine, phosphatidylethanolamine, monogalactosyldiacylglycerol, and digalactosyldiacylglycerol (R.A. Demel, T. Peelen, R.J. Siezen, B. de Kruijff, and O.P. Kuipers, Eur. J.Biochem. 235:267-274, 1996). Collectively, the mechanism of nisin resistance in this L. monocytogenes NISr strain is attributed to a reduction in the DPG content of the cytoplasmic membrane.     

MERISTEMATIC PRECURSORS OF VASCULAR PARENCHYMA DIFFERENTIATE FROM G2 PHASE AFTER REPLICATING DNA DISCONTINUOUSLY

A small population of cells representing 1% or less of those in the root-tip meristem was identified as the precursor of vascular parenchyma and certain root-cap cells in carbohydrate starved cultured pea roots. Autoradiography and cytophotometric measurements of nuclei labeled with [³H]-thymidine showed that in the absence of carbohydrate the precursor cells replicate their DNA discontinuously accumulating temporarily in late S phase prior to differentiating from the G₂ phase. Besides discontinuity of DNA synthesis, the nuclei of precursor cells undergo a change in morphology. The nuclei are shaped round when replicating DNA but later on, while differentiating, they become oblong. This transformation occurs within 72 hr after the starved roots are fed sucrose. Autoradiograms of serial cross-sections of pulse-labeled roots indicate that the cells in late S phase differentiate forming a ring around the stelar cylinder and a ring around the periphery of the root. These observations suggest that during the last half of the final S phase the precursor cells modify their chromosomal DNA and that this modification is associated with the initial steps of differentiation.     

Control of cell progression through the mitotic cycle by carbohydrate provision. I. Regulation of cell division in excised plant tissue

A stationary phase in the root meristem of excised pea roots was established by prolonged carbohydrate deprivation in sterile culture medium. When the stationary phase had been established, cells that had collected in the G1 period of the mitotic cycle were induced to enter the S stage by subjection to relatively short intervals of carbohydrate provision (sucrose spurts). Progression and cycle location of the G1 cells induced to enter S were measured with tritiated thymidine and radioautography. The results indicated that the number of G1 cells induced to enter S increased directly with the spurt duration and that cells could be positioned and retained in the S and/or G2 periods by varying the duration of the spurt. The data support the hypothesis that S and maybe M stages have a relatively larger dependence on carbohydrate availability, and presumably a greater energy requirement, than G1 and G2.     

CELL ARREST IN Gl AND G2 OF THE MITOTIC CYCLE OF VICIA FABA ROOT MERISTEMS

Experiments were performed with cultured excised primary root tips of Vicia faba ‘Longpod’ to determine: (1) the proportion of meristematic cells arrested in Gl and in G2 during carbohydrate starvation, and to determine if the proportion is fixed or can be varied experimentally; (2) the effect of increased starvation on the ability of arrested cells in Gl and G2 to initiate DNA synthesis and mitosis, respectively, when exogenous sucrose was supplied; and (3) whether puromycin, cycloheximide, or actinomycin D prevented the initiation of DNA synthesis and the onset of mitosis. Microspectrophotometry of nuclear DNA and autoradiographic measurements of incorporated ³H-thymidine showed that 72 hr of starvation immediately after excision produced tissue with more than 70 % of the cells arrested in G2 and less than 30 % in Gl. If cultured for three days and then starved for 72 hr, the tissue had nearly equal numbers of cells arrested in Gl and G2. As the duration of starvation increased, the time required to initiate DNA synthesis and to divide when carbohydrate was replenished also increased. Inhibition of protein synthesis by puromycin and cycloheximide prevented the initiation of DNA synthesis and mitosis, but actinomycin D, an inhibitor of RNA synthesis, did not prevent division of cells from G2 nor DNA synthesis by cells from Gl. The experiments demonstrated that the mitotic cycle of Vicia has two major controls, one in Gl and another in G2, and that other factors determine how many cells are affected by either of these cycle controls.     

The use of solvent relaxation technique to investigate headgroup hydration and protein binding of simple and mixed phosphatidylcholine/surfactant bilayer membranes

The subject of this report was to investigate headgroup hydration and mobility of two types of mixed lipid vesicles, containing nonionic surfactants; straight chain Brij 98, and polysorbat Tween 80, with the same number of oxyethylene units as Brij, but attached via a sorbitan ring to oleic acid. We used the fluorescence solvent relaxation (SR) approach for the purpose and revealed differences between the two systems. Fluorescent solvent relaxation probes (Prodan, Laurdan, Patman) were found to be localized in mixed lipid vesicles similarly as in pure phospholipid bilayers. The SR parameters (i.e. dynamic Stokes shift, Deltanu, and the time course of the correlation function, C(t)) of such labels are in the same range in both kinds of systems. Each type of the tested surfactants has its own impact on water organization in the bilayer headgroup region probed by Patman. Brij 98 does not modify the solvation characteristics of the dye. In contrast, Tween 80 apparently dehydrates the headgroup and decreases its mobility. The SR data measured in lipid bilayers in presence of Interferon alfa-2b reveal that this protein, a candidate for non-invasive delivery, affects the bilayer in a different way than the peptide melittin. Interferon alfa-2b binds to mixed lipid bilayers peripherally, whereas melittin is deeply inserted into lipid membranes and affects their headgroup hydration and mobility measurably.     

激光及γ射线对有丝分裂染色体畸变感应现象的比较

波长514nm的激光照射可用于研究激光导致有丝分裂染色体畸变的效应。本文提供了一种新的辐照系统,能用于研究突变的感应现象,并与从γ-线辐射源获得的结果进行了比较。 Abstract:Laser irradiation at wavelength 514 nm was used to study the effect of lasers in inducing chromosomal aberrations at mitosis.This study offers a new radiation system which could be used for the induction of mutations.Results are compared with those obtained from studies using γ-rays as irradiation source.