Showing papers by "Leibniz Association published in 1998"

Extended Electrokinetic Characterization of Flat Solid Surfaces

Abstract: An experimental setup has been developed and applied for the combined determination of the electrokinetic potential and the surface conductivity of flat surfaces. The key feature of the new device (designated as microslit electrokinetic setup) is the variability of the distance between two parallel flat sample surfaces (10 mm x 20 mm) forming a slit channel. The setup allows us to decrease this distance down to about 1 µm keeping the surfaces parallel. In consequence, streaming potential measurements can be performed at a given solid/liquid interface both at conditions where surface conductivity is negligible and at conditions where surface conductivity significantly contributes to the total channel conductivity. The zeta potential is calculated at different channel geometries based on streaming potential and channel conductivity data and, alternatively, based on streaming current measurements and the dimensions of the cross section of the slit channel. The results obtained were found to agree well if correct conductivity values for the calculation of the zeta potential based on the streaming potential data are used. The surface conductivity is determined from the extrapolation of the channel conductance values gained at a number of sufficiently small distances between the parallel sample surfaces to the distance zero. An additional feature of the developed microslit electrokinetic setup is the assessability of the hydrodynamic thickness of adsorbed layers of macromolecules or particles at the investigated flat surface. In a series of measurements a plasma-deposited fluoropolymer (PDFP) layer on top of a glass carrier and an adsorption layer of the blood protein fibrinogen on top of the PDFP layer were characterized by zeta potential and surface conductivity measurements in different aqueous electrolyte solutions (KCl, KOH, HCl). For the PDFP/solution interfaces zeta potential up to -100 mV were obtained in solutions of neutral pH exclusively due to preferential ion adsorption. After adsorption of fibrinogen the zeta potential is considerably reduced. For the PDFP/solution interfaces surface conductivities were determined in the range of (1-2) x 10(-9) S. The contribution of the diffuse layer to the surface conductivity has been calculated from the zeta potential according to the approach of Bikerman (Kolloid Z. 72, 100 (1935)) and compared with the experimentally determined surface conductivity. Based on this comparison ions in hydrodynamically immobile interfacial layers were concluded to contribute considerably to the surface conductivity in all investigated cases. This so-called additional surface conductivity is attributed to the accumulation of hydroxide and hydronium ions in the Stern layer. Both the high specific mobility of these ions (as compared to the potassium and the chloride ions) and the conductivity of the charge determining species may contribute to the experimental observations. After adsorption of fibrinogen onto the PDFP surface the additional surface conductivity is increased by about an order of magnitude. The latter fact is assumed to be caused by the presence of mobile ions in the interfacial volume of the adsorbed protein layer. In addition to the electrochemical characterization of the adsorbed protein layer its hydrodynamic thickness has been determined by means of liquid flow measurements with the microslit electrokinetic setup. The obtained value of 48 +/- 5 nm correlates well with the protein dimensions given in the literature and is in the order of magnitude of the optical layer extension determined by ellipsometry. Copyright 1998 Academic Press.

Microsatellite Enrichment in Organisms with Large Genomes (Allium cepa L.)

Abstract: To exploit the polymorphism of repeat numbers in short tandem repeat (STR) sequences (microsatellites) as molecular markers, STRs must be isolated and PCR primers must be developed in flanking sequences. In species with large genomes such as Allium cepa L. (onion and shallot), an efficient selection procedure for genomic fragments containing STRs is a crucial step. Here we describe a nonradioactive method for microsatellite isolation based on affinity capture of single-stranded restriction fragments annealed to biotinylated microsatellite oligonucleotides (CA)10, (GAA)8 and (AAC)8 followed by adapter-mediated genomic PCR. Cloning of the products in E. coli and plasmid sequencing revealed more than 60% positive clones. Primers were designed in STR-flanking regions, and one or two bands were amplified in 13 diploid onion and five shallot accessions. Allelism of the bands was confirmed by product sequencing.

The use of microsatellite markers for detection of genetic diversity in barley populations

Abstract: A barley lambda-phage library was screened with (GA)n and (GT)n probes for developing microsatellite markers. The number of repeats ranged from 2 to 58 for GA and from 2 to 24 for GT. Fifteen selected microsatellite markers were highly polymorphic for barley. These microsatellite markers were used to estimate the genetic diversity among 163 barley genotypes chosen from the collection of the IPK Genebank, Germany. A total of 130 alleles were detected by 15 barley microsatellite markers. The number of alleles per microsatellite marker varied from 5 to 15. On average 8.6 alleles per locus were observed. Except for GMS004 all other barley microsatellite markers showed on average a high value of gene diversity ranging from 0.64 to 0.88. The mean value of gene diversity in the wild forms and landraces was 0.74, and even among the cultivars the gene diversity ranged from 0.30 to 0.86 with a mean of 0.72. No significant differences in polymorphism were detected by the GA and GT microsatellite markers. The estimated genetic distances revealed by the microsatellite markers were, on average , 0.75 for the wild forms, 0.72 for landraces and 0.70 among cultivars. The microsatellite markers were able to distinguish between different barley genotypes. The high degree of polymorphisms of microsatellite markers allows a rapid and efficient identification of barley genotypes.

A Ty3/gypsy retrotransposon-like sequence localizes to the centromeric regions of cereal chromosomes.

Abstract: A 745 bp sequence (pSau3A9) located at the centromeres of several cereal species was isolated from a sorghum BAC library by Jiang et al. (1996, Proc. Natl Acad. Sci. USA, 93, 14210-14213). We have amplified a partially homologous 809 bp sequence from barely genomic DNA by PCR and localized it to the centromeres of barley, wheat and rye chromosomes by fluorescent in situ hybridization (FISH). Sequence analysis showed this barley homolog of pSau3A9 to have high similarity to the integrase region of the polyprotein gene of Ty3/gypsy group retrotransposons. Using this integrase sequence as a probe, several clones were isolated from a lambda library constructed of genomic barley DNA. One of the lambda clones contained coding regions for all five catalytic sites characteristic of the retrotransposon polyprotein. Two direct repeats flanking the polyprotein gene are homologous to the cereal centromeric sequence described by Aragon-Alcaide et al. (1996, Chromosoma, 105, 261-268) and may represent all or part of the long-terminal repeats (LTRs). Different plasmid subclones containing various regions of the lambda clone were used in FISH to show that the entire polyprotein gene and upstream flanking sequences, including the presumed LTR, are present at barley centromeres. The preferential (or exclusive) localization of an apparently complete retroelement within the centromeric regions of several cereal species raises interesting questions about its role in karyotype evolution and centromere function.

Phosphorus availability, root exudates, and microbial activity in the rhizosphere

Abstract: Field and pot experiments showed that the P demand of wheat is highest in early stages of growth (up to 1.67 μg P per cm2 root surface and day). The needed orthophosphate ions H2PO4− and HPO42-move from soil to the root by diffusion. This process is controlled by the concentration gradient of the diffusible phosphate and the effective diffusion coefficient according to Pick's first law. Root excretions (rhizodeposition) are able to affect both characteristics. The water soluble portion of rhizodeposition contains more than 50% of up to 8 different sugars, 10–40% carboxylic acids and 10–15 amino acids and amides. The composition varies in dependence on the age of the root parts and on nutrition (Zea mays L., Brassica napus L., Pisum sativum L.). Diffusion experiments using small soil blocks showed that 50–75% of the root exudates were decomposed by respiration within 3 days. The rest was largely chemically converted. Originally present sugars disappeared. Due to the biosynthesis of different organic acids from the individual sugars the mobilisation of Ca3(PO4)2 by Pantoea agglomerans increased when the sugar mixture was derived from the rhizodeposition of P deficient plants with more pentoses instead of glucose and fructose (mainly effect of anions). In the rhizosphere therefore a mixture of rhizodeposition and its conversion products exists which affects the binding of phosphorus in soil and the P transport to the root. This should be considered both for the development of new soil extractants and for modelling the P supply to plants. Phosphorverfugbarkeit, Wurzelexsudate und mikrobielle Aktivitat in der Rhizosphare Vegetationsversuche zeigten, das der P-Bedarf des Weizens im Jugendstadium besonders hoch ist (bis 1.67 μg P je cm2 Wurzeloberflache und Tag). Die Anlieferung der hierfur benotigten Orthophosphationen (HPO42−, H2PO4−) erfolgt durch Diffusion, die vom Konzentrationsgradienten diffusiblen Phosphates sowie vom effektiven Diffusionskoeffizienten abhangt. Wurzelabscheidungen (Rhizodeposition) konnen beide Faktoren beeinflussen. Deren losliche Anteile bestehen meist zu mehr als 50% aus bis zu 8 Zuckern, zu 10–40% aus Carbonsauren sowie aus etwa 10–15 Aminosauren und Amiden. Ihre Zusammensetzung wechselt u. a. mit dem Alter der Wurzelteile und der Ernahrung (Zea mays L., Brassica napus L., Pisum sativum L.). Diffusionsversuche unter Verwendung kleiner Bodenblocke (30 mm × 20 mm × 10 mm) zeigten, das 50–75% der loslichen Verbindungen innerhalb von 3 d durch Mikroben veratmet werden. Der Rest ist weitgehend chemisch verandert. Ursprunglich vorhandene Zucker finden sich nicht mehr. Auf Grund der Bildung unterschiedlicher Sauren aus den einzelnen Zuckern erhoht sich beispielsweise bei Pantoea agglomerans das Losungsvermogen fur Ca3(PO4)2, wenn die Zuckermischung aus der Rhizodeposition von P-Mangelpflanzen stammt und dadurch mehr Pentosen auf Kosten eines Teils der Glucose und Fructose enthalt (vor allem Anioneneffekt). In der Rhizosphare greift also eine Mischung aus Rhizodeposition und ihren Umwandlungsprodukten in die P-Bindung und den P-Transport zur Wurzel ein, was bei der Entwicklung neuer Bodenextraktionsmittel wie bei der Modellbildung zu berucksichtigen ist.

Antibiotic activity of new cyanobacterial isolates from Australia and Asia against green algae and cyanobacteria

Abstract: One hundred and ninety-eight cyanobacterial strains, newly isolated mainly from samples collected from diverse habitats in Australia, Indonesia, Nepal, Thailand and Vietnam, were screened from their antibiotic activity against green algal species of the genera Coelastrum, Scenedesmus and Monoraphidium. We report the discovery of ten strains of Fischerella, seven of Nostoc and three of Calothrix that produce antialgal compounds with a broad activity spectrum. Some of these bioactive cyanobacteria inhibited all three algae, whereas others inhibited only two, and some only one. In addition, the 20 active strains were tested against other selected cyanobacteria, including Anabaena doliolum which grows well both photoautotrophically in light and heterotrophically in darkness, and three toxic species, Microcytis aeruginosa, Anabaena circinalis and Nodularia spumigena, which are problems in Australia and other parts of the world. At least one Fischerella strain had bioactivity directed against photosynthetic electron transport of algal chloroplasts, whereas others had no effect on photosynthesis. In most cases the growth inhibitory effects were also tested in the presence of a proteinase. The results are discussed in the light of the possible nature of the chemical inhibition and also in relationship to competition and allelopathy in algal populations.

The Role of Proteolysis in the Processing and Assembly of 11S Seed Globulins

Abstract: 11S seed storage proteins are synthesized as precursors that are cleaved post-translationally in storage vacuoles by an asparaginyl endopeptidase. To study the specificity of the reaction catalyzed by this asparaginyl endopeptidase, we prepared a series of octapeptides and mutant legumin B and G4 glycinin subunits. These contained amino acid mutations in the region surrounding the cleavage site. The endopeptidase had an absolute specificity for Asn on the N-terminal side of the severed peptide bond but exhibited little specificity for amino acids on the C-terminal side. The ability of unmodified and modified subunits to assemble into hexamers after post-translational modification was evaluated. Cleavage of subunits in trimers is required for hexamer assembly in vitro. Products from a mutant gene encoding a noncleavable prolegumin subunit (LeBΔN 281 ) accumulated as trimers in seed of transgenic tobacco, but products from the unmodified prolegumin B gene accumulated as hexamers. Therefore, the asparaginyl endopeptidase is required for hexamer assembly.

Characterization of aroma volatiles in tomatoes by sensory analyses

Abstract: Using gas chromatography-olfactometry and aroma extract dilution analysis 34 aroma compounds were found with flavour dilution factors > or = 4. (Z)-3-hexenal, hexanal, 1-octen-3-one, methional, 1-penten-3-one and 3-methylbutanal belonged to the most odour-active aroma volatiles in fresh tomatoes. Smell, taste and aftertaste of different tomato cultivars were evaluated by quantitative descriptive analysis. By applying principal component analysis to both sensory attributes and chemical compounds (odour-active aroma volatiles, titratable acid and reducing sugars) the first three components explained 70% of the total variance. The data set was reduced to the sensory attributes intensive, tomato, sour, fruity, sweet and bitter as well as to important chemical compounds. Relations between chemical compounds and sensory attributes were found.

Interphase characterization in composites with new non-destructive methods

Abstract: Results of single-fibre pull-out tests reflect a combination of adhesive, cohesive and frictional phenomena that complicate micromechanical modelling and the relation to composite properties. SEM images of fracture surfaces detected cohesive fracture and unstable crack propagation during pull-out of well sized fibres out of both ductile and brittle matrices. New non-destructive methods have been used to characterize the physical properties of interphases. Atomic force microscopy in force modulation mode has visualized interphases of 1 to 3 μm thickness and gradients depending on the fibre–matrix model composite. The single fibre dynamic load test has been shown to be a feasible tool for determination of fibre–matrix adhesion or friction and ductility of matrix.

Extrinsic giant magnetoresistance in chromium (IV) oxide, CrO2

Abstract: Polycrystalline CrO2 is shown to exhibit a giant magnetoresistance (GMR) at low temperatures. A rapid decrease in the GMR with increasing temperature is correlated with a decrease in the intergranular resistance. Single-crystal CrO2 is a half-metallic ferromagnet, as the data are interpreted to reflect two types of charge carriers, crossing a grain boundary: those that tunnel between conduction bands of adjacent grains and those that hop after residing at a localized state for a time long compared to a spin relaxation time.

Electron beam facility in polymer research: radiation induced functionalization of polytetrafluoroethylene

Abstract: The main field of electron irradiation processing applications is polymeric material. A universal electron beam irradiation facility for research and service in the institute of polymer research was demonstrated. The industrial electron beam accelerator works in the medium energy range from 0.6 to 1.5 MeV. One of our research activities using the electron beam accelerator is the radiation-induced functionalization of polytetrafluoroethylene (PTFE). The changes in chemical structure of PTFE irradiated in ammonia, air, and vacuum were investigated by infrared spectrometry.

Characterization of bovine Sarcocystis species by analysis of their 18S ribosomal DNA sequences.

Abstract: Two Sarcocystis hirsuta isolates from 2 cattle (Bos taurus), 2 Sarcocystis hominis-like isolates from 2 cattle, 1 each Sarcocystis hominis-like isolate from a zoo-born dwarf zebu (B. taurus) and from a zoo-born bison (Bison bison), and 1 each Sarcocystis cruzi isolate from the dwarf zebu and the bison have been characterized by comparing the directly sequenced polymerase chain reaction products of their 18S rRNA genes. Sequences of 2 different isolates from the same species always showed a very high, nearly complete identity to each other both within all or only the conserved overlapping nucleotides. Thus, the 18S rDNA sequences of both S. hirsuta isolates proved to belong to a single species. The same is true for all 3 S. cruzi sequences. The 4 S. hominis-like isolates could not be placed within a single species using these criteria. They formed 2 separate groups (1 cattle isolate and the bison isolate, and the other cattle isolate and the dwarf zebu isolate). The results suggest that zoo-born large mammals do serve as intermediate hosts for Sarcocystis species known from indigenous herbivores, and that there might be another species found in cattle that is morphologically very similar to S. hominis.

Tailored Fiber Placement-Mechanical Properties and Applications

Abstract: Tailored Fiber Placement (TFP) is a new automated textile process for the production of reinforcing structures. This process allows the consistent transfer of calculated locally optimum fiber quantities and orientations into fiber preforms. The mechanical properties achieved with TFP reinforced carbon fiber/epoxy and glass fiber/epoxy are compared with tape and fabric reinforced composites. Generally, static mechanical properties of TFP-laminates are better than fabric laminates and close to tapes. However, the ultimate compression strength of carbon/epoxy TFP is lower than comparable tape composites. Fatigue behaviour of a cross-ply carbon/epoxy TFP is compared with a fabric reinforced laminate. The advantages and possibilities of TFP are demonstrated by means of typical applications like bicycle components.

Viability of small preantral ovarian follicles from domestic cats after cryoprotectant exposure and cryopreservation.

Abstract: About 1500 preantral follicles can be recovered from a single cat ovary by mechanical dissection This is a potentially rich source of genetic material if ova could be preserved and grown in vitro, especially from rare or endangered species that die abruptly or are ovariectomized for medical reasons The aims of this study were to examine cryoprotectant toxicity and then the potential of successfully cryopreserving preantral cat follicles In the initial toxicity trial, isolated cat follicles (40-90 micron) were exposed to dimethylsulfoxide, glycerol, 1,2-propandiol or ethylene glycol at 0 degrees C for 15 min Follicle viability was assessed by supravital staining using a combination of Trypan blue and Hoechst 33258 at O h, and after 18 h and 1 week of culture Percentages of follicles with intact oocytes and granulosa cells were similar (P > 005) among control (no cryoprotectant), dimethylsulfoxide, 1,2-propandiol and ethylene glycol treatments at all time points, but were reduced (P < 005) after glycerol exposure On the basis of this finding, dimethylsulfoxide and 1,2-propandiol were used to cryopreserve intact follicles, and post-thaw viability was assessed by supravital staining and 5-bromo-2'-deoxyuridine uptake into oocytes and granulosa cells during culture Of control (noncryopreserved) follicles, 314% +/- 29%, 188% +/- 19% and 162% +/- 16% were intact after O h, 18 h and 1 week of culture, respectively Uptake of 5-bromo-2'-deoxyuridine occurred in approximately 20% of follicles at all time points On the basis of the presence of both a healthy oocyte and granulosa cells, cryopreservation in dimethylsulfoxide or 1,2-propandiol allowed approximately 19% of follicles to survive Approximately 10% demonstrated clear evidence of cell activity that was sustainable for 1 week In conclusion, the cat ovary contains a population of preantral follicles that are not adversely affected by short-term exposure to most conventional cryoprotectants Furthermore, there is a subpopulation of these follicles capable of surviving cryopreservation, remaining structurally intact and physiologically active after thawing

Two novel MYB homologues with changed expression in late embryogenesis-defective Arabidopsis mutants.

Abstract: Two novel MYB genes (ATMYBR1 and ATMYBR2) were isolated from Arabidopsis thaliana. Binding to a conserved MYB recognition sequence is demonstrated for the ATMYBR1 protein. The expression of both genes is affected by the fus3, lec1 and abi3 mutations causing pleiotropic defects during late embryogenesis and seed maturation including the loss of dormancy and desiccation tolerance. The strong increase of the transcript levels of both MYB genes during very late stages of embryogenesis typically found in wild type is missing in the mutants. Furthermore, the expression of both MYB genes is developmentally regulated in vegetative tissues. The highly conserved repeats (R2 and R3) of the DNA binding MYB domain of both proteins represent chimeric structures combining features typical of plant and animal derived proteins. This demonstrates the existence of a distinct subfamily of animal-like MYB factors in plant genomes.

An in‐situ ATR‐FTIR study on polyelectrolyte multilayer assemblies on solid surfaces and their susceptibility to fouling

Abstract: In-situ attenuated total reflection (ATR)-FTIR spectroscopy was used to monitor the consecutively alternating adsorption of polyethylenimine (PEI) and poly(acrylic acid) (PAC) onto both Si crystals (SiO) and CO2 plasma-treated polypropylene (PP) films. The vibration band vas(COO−) and v(CO) of PAC are diagnostic for the polyelectrolyte layer build-up and sensitive to protonation changes. Human serum albumine (HSA) adsorption experiments revealed a strong decrease of fouling for the PP films, which were modified with polyelectrolyte multilayers, in comparison to the unmodified ones.

Preconditioning of Rat Heart with Monophosphoryl Lipid A: A Role for Nitric Oxide

Abstract: Preconditioning with monophosphoryl lipid A (MLA) protects rabbit hearts from prolonged ischemic reperfusion injury by a mechanism involving inducible nitric oxide synthase (iNOS) activation. This study was undertaken to determine whether MLA also could precondition rat hearts in a similar manner. Rats were injected with two different doses of MLA (300 microg/kg or 450 microg/kg i.v.) or vehicle (control), and after 24 hr the animals were sacrificed for preparation of isolated perfused rat hearts. Hearts were then perfused by working mode, and then made ischemic for 30 min followed by 30 min of reperfusion. Another group of hearts were treated simultaneously with a nitric oxide (NO) blocker, L-nitro-arginine-methyl-ester (L-NAME) (10 mg/kg) and MLA (450 microg/kg). For arrhythmia studies, 12 hearts were used in each group (total, 48 hearts). Cardiac functions were examined in a separate group of 24 hearts (n = 6/group). MLA-treated hearts (either dose) were tolerant to ischemic reperfusion injury as evidenced by improved postischemic ventricular recovery [coronary flow (ml/min) 19.1 +/- 0.8 (300 microg/kg MLA), 22.6 +/- 1.0 (450 microg/kg MLA) vs. 15.9 +/- 0.7 (control); aortic flow (ml/min) 20.7 +/- 1.8 (300 microg/kg MLA), 25.8 +/- 1.4 (450 microg/kg MLA) vs. 11. 0 +/- 0.8 (control); left ventricular developed pressure (kPa) 13.3 +/- 0.6 (300 microg/kg MLA), 14.6 +/- 0.2 (450 microg/kg MLA) vs. 10. 3 +/- 0.7 (control)]. Incidences of ventricular fibrillation and ventricular tachycardia were decreased compared with the control group only in the 450 microg/kg dose of MLA-treated hearts (92% to 33%). Pretreatment of the hearts with L-NAME inhibited the preconditioning effect of MLA. To examine the induction of the iNOS expression, RNAs were extracted from the control and MLA-treated hearts (after 2, 4,6, 8, 12 and 24 hr of treatment) and Northern blot analyses were performed with a specific cDNA probe for iNOS. A single band of approximately 4.6 kb corresponding to iNOS mRNA was detected after 4 hr of MLA treatment, whereas the maximal iNOS expression was found between 6 and 8 hr of MLA treatment. The results of this study demonstrated that MLA induced the expression of iNOS and protected the myocardium from ischemic reperfusion injury which is blocked by an inhibitor of NO synthesis, which suggests a role of NO in MLA-mediated cardioprotection.

Movement and pattern of activity of the roach in the River Spree, Germany

Abstract: Water body and bank structure use of adult roach Rutilus rutilus were examined to increase the knowledge of the most abundant species in the River Spree, Germany. Six tracking series were conducted between 1994 and 1995 to analyse the seasonal and diel movements of the fish. In each series, four to 12 roach were tagged externally and located every 2 h for up to 14 days using radiotelemetry. Roach were highly active, moving up to 10 km downstream to Lake Dameritzsee, and up to 6 km upstream from their release site. The fish, which mostly swam greater distances upstream during the day and downstream at night, were most active during the spawning season. Their habitat range varied greatly. Close-range habitat, based on 50% of all radiolocations, varied between 5 and 1350 m (mean, X=296 m). Wide-range habitat, based on 90% of all radiolocations, varied between 75 and 3820 m (X=1006 m). The fish preferred different sections of water at different times of year, casting doubt on the relevance of the term home range. Generally, roach stayed close to the bank structures of the main channel during the day and moved to the stagnant waters at night. Consequently, they were most active at dawn and dusk.

Effect of hybrid yarn structure on the delamination behaviour of thermoplastic composites

Abstract: Continuous-glass-fibre-reinforced polyamide-matrix composites have been manufactured on the basis of hybrid yarns with different arrangements of the reinforcing glass and polyamide matrix fibres. In addition, glass fibres with different sizings were used. To characterize the delamination behaviour of composites made with these semi-finished products, mechanical and fracture mechanical tests were performed, including longitudinal and transverse tensile, compression shear, double cantilever beam, single-edge notched and end-notched flexure tests. The results demonstrate the significant influence of the different hybrid yarn structures and glass fibre coatings on fracture toughness. The best mechanical and fracture mechanical properties have been obtained for composites manufactured with air-textured commingled yarns containing glass fibres only with aminosilane as coupling agent.

Microbial Food Webs in an Artificially Divided Acidic Bog Lake

Abstract: The microbial loop of a naturally acidic bog lake, Grosse Fuchskuhle (Northeastern Germany), that had been artificially divided into 4 basins, was investigated. In the northeast (NE) and southwest (SW) basins, which differ strongly in chemistry and primary production, we conducted intensive studies of the main carbon fluxes through microbial food webs. In the less acidic, NE basin, much higher phytoplankton as well as bacterial biomass and production were found in parallel with negligible numbers of larger zooplankters. Weakly top-down controlled populations of protists were characterized by an exceptionally low numerical proportion of heterotrophic nanoflagellates (HNF) to ciliates (-1.5-3.5). The ciliate community was dominated by a scuticociliate, Cyclidium sp. (>95% of total ciliates), with an estimated grazing rate equal to 46-80% of heterotrophic bacterial production. In contrast, in the more humic, SW basin, both phyto- and bacterioplankton dynamics seemed to be top-down controlled by abundant populations of small fine-filter feeding cladocerans, Ceriodaphnia quadrangula and Diaphanosoma brachyurum. Consequently, ciliates disappeared from the food web structure of the SW basin, HNF dropped to negligible numbers and bacteria showed very uniform morphology, dominated by small cocci or short rods. Our investigations have shown that the division of the lake into separate compartments can lead to very different microbial food web structures with extreme species compositions.

Drop size distribution and LWC in Po valley fog

Abstract: In this paper results are presented of ground-based fog microphysical measurements obtained during the CHEMDROP experiment in the Po Valley (Northern Italy) in November 1994. Altogether about 85 hours of drop microphysical data are analyzed. At the beginning of the experiment a comparison of some of the different microphysical instruments, operated during the experiment, was performed. It has revealed some differences between the Liquid Water Content LWC measured by Particle Volume Monitors (PVMs), and by several Forward Scattering Spectrometer Probes (FSSPs). Possible explanations for the discrepancies are discussed. The FSSP derived drop size distributions (number and mass) were parameterized in terms of log-normal distributions. The statistical analysis of the fittings has shown that the overwhelming majority of the drop mass size distributions was characterized by a bimodal shape. The most frequent values of the mode parameters (median diameter, geometric standard deviation) are given in Table 3 of this paper. An investigation of the temporal evolution of the drop size distribution revealed two typical phases of fog formation. In the first step both modes of the drop mass size distribution increase more or less uniform, whereas in the second phase the large drop mode drastically rises. Furthermore, the second phase is characterized by quasi-periodic oscillations in nearly all mode parameters of the drop size distribution with a period between ten and 15 minutes. In the last part of the paper the frequent occurrence of drizzle within the fog was studied by comparing the measurements with respective model calculations.

4-Hydroxy-1-(3-pyridyl)-1-butanone-hemoglobin adducts as biomarkers of exposure to tobacco smoke: validation of a method to be used in multicenter studies.

Abstract: Hemoglobin (Hb) adducts of 4-hydroxy-1-(3-pyridyl)-1-butanone (HPB), a metabolite of two tobacco-specific nitrosamines [4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone and N'-nitrosonornicotine], were measured as biomarkers of exposure to tobacco smoke as part of a study on genetic alterations and susceptibility to lung cancer among nonsmokers. HPB-Hb adducts were measured after collection of RBCs by Ficoll gradient in six collaborating centers, release of HPB by alkaline hydrolysis from Hb, clean-up by solid-phase extraction, and analysis of an electron-capturing derivative by gas chromatography-electron capture mass spectrometry. Prior to analysis of samples from study subjects, the reproducibility of this approach was validated in blood from donors. The coefficient of variation of reproducibility of paired aliquots from five samples ranged from 7 to 25%; the within-sample reproducibilities of four and eight aliquots were 4 and 16%, respectively. The study subjects consisted of 18 smokers and 52 never-smokers. HPB-Hb adduct levels were significantly higher (P = 0.02) in smokers (26 +/- 13 fmol HPB/g Hb) than in never-smokers (20 +/- 8 fmol HPB/g Hb). There was no difference between sexes. These results suggest that the level of HPB-Hb adducts, measured using a method modified to facilitate use in multicenter studies, can be a useful biomarker of exposure to tobacco smoke.