Showing papers by "Leibniz University of Hanover published in 1995"

The role of the apoplast in aluminium toxicity and resistance of higher plants: A review†

Abstract: In acid mineral soils excess of aluminium ions (AI) is one of the most important factors determining plant species and ecotype distribution, and limiting growth and yield of crops. Aluminium preferentially accumulates in the root tips as sites of cell division and cell elongation. Whether inhibition of cell-division rate is due to direct interaction of Al with the chromatin in the nuclei is rather questionable because of the low radial mobility of Al in the root and the rapidity of cessation of root elongation after Al addition to the growth medium. Externally applied Al instantaneously binds to binding sites in the apoplast. Cross binding of pectates by Al may affect extensibility and water permeability of the cell wall. Interaction of Al with other cell-wall constituents is most likely but needs clarification. Aluminium also affects plasma-membrane characteristics. Ca2+ influx and K+ efflux are inhibited, and synthesis of callose is induced. Induction of callose suggests an increase rather than a decrease in cytosolic Ca2+ as initial response to Al. There is little evidence suggesting major disruption of plasma membrane and cytoplasmic functions by AI. K+ uptake, H+ extrusion, Fe(III) reducing capacity and lipid peroxidation are hardly affected even in roots severely inhibited in elongation by Al. Al uptake and physiological/biochemical effects of Al on intact plant roots can be mimicked even more sensitively using cell suspension cultures which, therefore, represent a powerful tool for the study of Al toxicity. Large differences in Al resistance exist between plant species and cultivars of a species. Root elongation-rate and callose formation can be used as indicators for Al injury. Since short term Al injury is mainly expressed in the apoplast. Al resistance requires exclusion of Al from or/and inactivation of Al in the apoplast. Generally, Al-resistant genotypes are characterized by lower Al accumulation of the root apical meristems. This is achieved by a lower cation-exchange capacity/surface negativity or complexation of Al through root exudates (mucilage, organic acids). Long term exposure of plants to Al also inhibits shoot growth via induction of nutrient (Mg, Ca, P) deficiencies, drought stress and phytohormone imbalances. Such longer term effects have to be taken into consideration when selecting genotypes for high yielding capacity on acid soils high in available Al. Die Bedeutung des Apoplasten fur Aluminium-Toxizitat und Aluminium-Resistenz hoherer Pflanzen: Ein Uberblick In sauren Mineralboden bestimmen Aluminium (Al)-Ionen masgeblich die Verbreitung von Pflanzenarten und Okotypen und begrenzen Wachstum und Ertrag von Nutzpflanzen. Aluminium wird vor allem in der Wurzelspitze akkumuliert, dem Ort der Zellteilung und der Zellstreckung. Angesichts der geringen radialen Beweglichkeit von Al in der Wurzel und der Schnelligkeit, mit der eine Hemmung des Wurzelwachstums nach Zusatz von Al zur Nahrlosung einsetzt, ist es allerdings fraglich, ob dies durch eine direkte Interaktion von Al mit dem Chromatin bewirkt wird. Extern zugesetztes Al wird sofort im Apoplasten gebunden. Eine Vernetzung von Pektinen durch Al kann grundlegende Zellwandeigenschaften wie Ausdehnbarkeit und Permeabilitat fur Wasser beeinflussen. Interaktionen von Al mit anderen Zellwandkomponenten sind sehr wahrscheinlich. Eine grundliche Charakterisierung dieser Inter-aktionen ist dringend notwendig. Aluminium beeinflust auch Plasmamembraneigenschaften. So hemmt Al den Ca2+ Influx und den K+ Efflux und induziert die Bildung von Callose. Die Induktion der Callosesynthese weist auf eine Erhohung und nicht auf eine haufig vermutete Erniedrigung der cytosolischen Ca2+ Aktivitat hin. Es existieren keine deutlichen Hinweise darauf, das Al die Integritat der Plasmamembran zerstort oder cytosolische Funktionen wesentlich beeintrachtigt. Selbst bei stark durch Al geschadigten Wurzeln sind K+ Aufnahme und H+ Abgabe, Fe(III) Reduktionskapazitat und die Lipidperoxidation kaum beeinflust. Aluminium-Aufnahme und physiologische/biochemische Effekte von Al bei intakten Pflanzen konnen - wesentlich empfindlicher - auch an Suspensionszellkulturen demonstriert werden. Zellkulturen stellen daher ein sehr empfindliches, geeignetes System zur Untersuchung von Al-Wirkungen dar. Es existieren grose Unterschiede in der Al-Resistenz zwischen verschiedenen Pflanzenarten und zwischen Genotypen innerhalb einer Art. Die Hemmung des Wurzellangenwachstums und die. Bildung von Callose stellen empfindliche Indikatoren fur Al-Schadigung dar. Da Kurzzeit-effekte von Al vor allem im Apoplasten exprimiert werden, erfordert Al-Resistenz den Ausschlus von Al vom oder Inaktivierung im Apoplasten. Im allgemeinen zeichnen sich resistente Genotypen durch eine geringere Akkumulation von Al im apikalen Wurzelmeristem aus. Hierzu tragt eine geringere Kationenaustauschkapazitat/Oberflachennegativitat oder eine Komplexierung von Al durch Wurzelexsudate (Mucigel, organische Sauren) bei. Langfristige Einwirkung von Al auf Pflanzen hemmt auch das Sproswachstum durch Induktion von Nahrstoff- (Mg, Ca, P) oder Wassermangel und Storungen des Phytohormonhaushaltes. Bei der Selektion von Genotypen mit hohem Ertragspotential auf sauren Boden mit hohem Al-Angebot, mussen auch diese Langzeiteffekte berucksichtigt werden.

Polarization-dependent high-order two-color mixing.

Abstract: High-order frequency mixing experiments using the radiation of a high-power Ti:sapphire laser and its second harmonic are described and discussed. Linearly and circularly polarized light fields with comparable intensities have been used. For the theoretical description a three-dimensional quantum-mechanical calculation with a \ensuremath{\delta}-function potential has been applied, showing quite good agreement with the experiments.

Clonal growth in Ailanthus altissima on a natural site in West Virginia

Abstract: The exotic tree Ailanthus altissima is usually con- fined to open sites. As an exception, Ailanthus established in a densely closed forest in West Virginia, which was analyzed with the aim to elucidate possible pathways of persistence in forest succession of this light-demanding pioneer species. Demographic analysis revealed a seedling mortality of 100 %. Instead, the understory is populated by clonal ramets, ranging from one to more than 19 yr of age, with a mean of 5 yr. Growth averages only 0.11 m/yr, and height is correlated with age. This clonal growth contrasts with the performance of Ailanthus on open sites. The possible ecological benefits of establishing a ramet bank in a resource-poor habitat are con- sidered in terms of space occupation of a pioneer species.

Antioxidative constituents of Rosmarinus officinalis and Salvia officinalis

Abstract: The determination of carnosic acid in different foodstuffs is reported. The recovery efficiencies for carnosic acid ranged from 68.1% to 96.2% depending on the food matrices. Highest recoveries were found in mayonnaise and egg yolk. After acidification of milk, phenolic diterpenes were found almost exclusively in the casein fraction obtaining the lowest recovery rate. Although carnosic acid is considered to be unstable, particularly in solvents, considerable amounts were present following the ripening period of raw sausage. In lyophilized chicken meat carnosic acid degrades slowly and decreases storagedependent degradation of α- and γ-tocopherol.

Action spectrum for erythema in humans investigated with dye lasers

Abstract: — Erythema reactions of human skin were reevaluated with improved experimental methods: a tunable, highly monochromatic irradiation source as well as an instrumental measurement of skin reactions were used. The irradiation system consisted of an excimer laser pumped dye laser and a U V fiber optic system. The skin color after irradiation was determined with a colorimeter in the three-dimensional norm system of the Commission Internationale d'Eclairage (CIE). The wavelength dependence for delayed erythema was investigated in the UVB and UVA region from 294 nm to 374 nm in skin type II and III individuals. The maximum of the action spectrum in the UVB range was measured at 298.5 nm and an additional maximum was found at 362 nm in the UVA range. The action spectrum is compared with previous spectra from the literature and with the current standard erythema curve of the CIE as well as with other photobiological action spectra. Our results suggest a UVA/UVB boundary at 330 nm.

In situ microscopy for on-line characterization of cell-populations in bioreactors, including cell-concentration measurements by depth from focus.

Abstract: A new technique is presented which allows the use of a front-end sensor head for in situ and on-line characterization of cell concentration and cell size during fermentation. An epifluorescence microscope is mounted in a port of a bioreactor viewing directly into the agitated broth. Still images from cells are generated using pulsed illumination. They are directly visualized on a monitor and used for automatic image analysis. The cell concentration and morphological information are determined by counting and evaluating the cell images with respect to their depth from focus characteristic. An in situ microscope was successfully tested during yeast fermentations and yielded results which correlated well with results from a hemocytometer. (c) 1995 John Wiley & Sons, Inc.

Nonstandard relaxation behavior in ionically conducting materials.

Abstract: We investigate by Monte Carlo simulations the diffusion of ions in ordered and structurally disordered lattices, where the Coulomb interaction between the mobile ions is explicitly taken into account. Results for tracer diffusion, conductivity, the diffusion-induced spin-lattice relaxation rate, and the incoherent intermediate scattering function are discussed in detail. It is shown that the presence of both disorder and Coulomb interactions leads to the typical deviations from the standard behavior of the relevant transport quantities (non-BPP, where BPP indicates Bloembergen, Purcell, and Pound behavior of the spin-lattice relaxation rate, strong dispersion of the conductivity, nonexponential decay of relaxation functions, etc.) that are experimentally observed in a wide class of ion-conducting materials.

Dynamical behaviour of a friction oscillator with simultaneous self and external excitation

Abstract: Friction-induced self-sustained oscillations, also known as stick-slip vibrations, occur in mechanical systems as well as in everyday life. In engineering applications these vibrations are undesirable and should be avoided. In the present paper it is shown how the very robust limit cycles of stick-slip vibrations can be broken up by a harmonic disturbance. Based on a simple model of a friction oscillator with simultaneous self and external excitation the resulting bifurcation behaviour and the routes to chaos are investigated for a wide range of system parameters. The influence of different types of friction characteristics is elaborated and the admissibility of smoothing procedures is examined by comparing results gained for non-smooth and smoothed friction characteristics.

Adsorption of Water Vapor on the MgO(100) Single Crystal Surface

Abstract: The adsorption of H 2 O on the MgO(100) surface prepared by cleaving a single crystal in situ under ultrahigh vacuum has been studied. For the first time Low Energy Electron Diffraction (LEED) has revealed an ordering of the H 2 O monolayer with a c(4x2) translational symmetry at 150 K, highly sensitive Polarization Fourier Transform Infrared Spectroscopy (PIR) has shown a strong, very broad polarized absorption from ∼ 3050-3500 cm -1 in the spectral range of the symmetric and antisymmetric H 2 O stretching vibration ν 1 and ν 3 . The peak absorption is less than 0.1%, the integrated absorption 0.07 cm -1 and 0.11 cm -1 for p- and s-polarization, respectively, indicating that the molecular plane is nearly parallel to the surface. This broad polarized band is assigned to the ordered, nearly planar H 2 O monolayer with all OH groups participating in strong O-H...O bonds between nearest neighbor H 2 O molecules. In the ordered monolayer no dangling OH groups have been found. Additionally a sharp, p-polarized absorption at 3680 cm -1 has been observed, attributed to dangling OH bonds of the adsorbate on steps. At temperatures above 190K three sharp, polarized absorptions at 3672, 3626 and 3513 cm -1 with integrated absorptions in the range from 4.10 -4 to 5.10 -3 cm -1 and their disappearance above 240 K have been detected. They are ascribed to isolated H 2 O molecules on steps (3672 cm -1 ) and terraces, respectively. For D 2 O on MgO(100) all corresponding absorptions have been measured.

Randomized trial with early-stage Hodgkin's disease testing 30 Gy vs. 40 Gy extended field radiotherapy alone

Abstract: Purpose : To evaluate whether or not a total dose (TD) of 30 Gy is sufficient for treatment of assumed subclinical Hodgkin's Disease compared to 40 Gy TD with early stage Hodgkin's Disease (ESHD). Methods and Materials : In a prospective multicenter trial, 376 patients with laparotomy-proven ESHD stages PS IA to PS IIB without risk factors such as large mediastinum, massive splenic involvement, extranodal disease, elevated erythrocyte sedimentation rate (ESR), and/or three or more involved lymphnode areas were randomly allocated either to receive (ARM A) 40 Gy TD extended field-radiotherapy (EF-RT) or (ARM B) 30 Gy TD EF-RT plus 10 Gy TD involved field-radiotherapy (IF-RT), both arms without any chemotherapy. Three hundred sixty-six of these patients were evaluable for early and long-term response, such as remission status, freedom from treatment failure (FFTF), and overall survival (OAS). For quality control, all planning and verification films as well as dose charts were prospectively reviewed by a panel of four experts, all heads of a radiotherapy department, where protocol violations (PV) were seen either with regard to errors in treatment technique, treatment volume, in TD and/or in dose/time-relationship. Results : Treatment resulted in a complete remission (CR) of 98% ; in a 5-year FFTF of 76%, and a 5-year OAS of 97%. There was no difference between the two arms in favor of 40 Gy EF compared to 30 Gy EF regarding FFTF and OAS, without any in field relapse throughout the EF volumes. Expectedly, 5-years FFTF was significantly influenced by the quality of radiotherapeutical procedures : 70% with protocol violations (PV) vs. 82% without PV. Conclusion : Subclinical involvement in ESHD without risk factors is sufficiently treated by a TD of 30 Gy without chemotherapy, leading to a 5-years FFTF of 82% and a 5-year OAS of 97% in a multicenter treatment setting, where quality assurance is mandatory.

Verification of a three-dimensional numerical model simulation of the flow in the vicinity of spur dikes

Abstract: The objective of this paper is to show the results of simulations of the flow near spur dikes using a three dimensional numerical model. Special attention was given to the simulation of the wake formed downstream of the dyke and the influence of the eddy viscosity field on velocities, flow depths and reattachment lengths. The most important features of the model are described. Comparisons with flume measurements conducted at the Franzius Institute in Hannover, Germany are also presented.

Delay-induced chaos in catalytic surface reactions : no reduction on pt(100)

Abstract: Deterministic chaos has been observed in the $\mathrm{NO}+\mathrm{CO}$ and $\mathrm{NO}+{\mathrm{H}}_{2}$ reactions on Pt(100). A mathematical model is proposed that explains the origin as being due to delays in the response of a population of reacting adsorbate islands globally coupled via the gas phase. The dynamical equations of this model yield a sequence of period-doubling bifurcations resulting in chaos.

Electrical tomography techniques for process engineering applications

Abstract: This paper summarizes the characteristics of electrical tomography techniques, highlights their current applications and gives an indication of their future applications in the chemical process engineering environment.

Degradation of 4-chloro-2-methylphenol by an activated sludge isolate and its taxonomic description.

Abstract: The Gram-negative strain S1, isolated from activated sludge, metabolized 4-chloro-2-methylphenol by an inducible pathway via a modifiedortho-cleavage route as indicated by a transiently secreted intermediate, identified as 2-methyl-4-carboxymethylenebut-2-en-4-olide by gas chromatography/mass spectrometry. Beside 4-chloro-2-methylphenol only 2,4-dichlorophenol and 4-chlorophenol were totally degraded, without an accumulation of intermediates. The chlorinated phenols tested induced activities of 2,4-dichlorophenol hydroxylase and catechol 1,2-dioxygenase type II. Phenol itself appeared to be degraded more efficiently via a separate, inducibleortho-cleavage pathway. The strain was characterized with respect to its physiological and chemotaxonomic properties. The fatty acid profile, the presence of spermidine as main polyamine, and of ubiquinone Q-10 allowed the allocation of the strain into the α-2 subclass of theProteobacteria. Ochrobactrum anthropi was indicated by fatty acid analysis as the most similar organism, however, differences in a number of physiological features (e.g. absence of nitrate reduction) and pattern of soluble proteins distinguished strain S1 from this species.

Sexual risk behaviour reduction associated with voluntary HIV counselling and testing in HIV infected patients in Thailand

Abstract: Sexual risk behaviour, measured by anonymously self-reported sexual activity, number of sexual partners, and condom use rates, was studied in age- and gender-matched HIV-1 positive consecutive patients from the Thai Red Cross Immune Clinic (IC) (study group, questioned after voluntary HIV counselling and testing) and the Thai Red Cross Anonymous Clinic (AC) (control group, questioned before voluntary HIV counselling and testing) in Bangkok, Thailand in 1993/94. More than 80% of study patients reported having decreased their sexual activity and their number of sexual partners since receipt of the positive HIV test result. Compared to control patients, study patients reported more often abstaining from sex (42% vs 14%), and more often using condoms during all their last three incidences of sexual intercourse (44% vs 14%). These findings give evidence for the value of voluntary HIV counselling and testing in contributing to the reduction of HIV transmission in Asia.

A formal approach to nonlinear analog circuit verification

Abstract: This contribution presents an approach to nonlinear dynamic analog circuit verification. The input-output behavior of two systems is analyzed to check whether they are functionally similar. The algorithm compares the implicit nonlinear state space descriptions of the two systems on the same or on different levels of abstraction by sampling the state spaces and by building a nonlinear one-to-one mapping of the state spaces. Some examples demonstrate the feasibility of our approach.

Effect of aluminium on membrane properties of soybean (Glycine max) cells in suspension culture

Abstract: Short-term responses of soybean (Glycine max) cells to aluminium (Al) were studied in suspension culture. Formation of callose was the most sensitive indicator of Al effects. As low as 5 μM Al induced callose formation and an increase in callose concentration could be measured as early as 15 min after beginning the Al treatment. Also membrane permeability was rapidly affected by Al. Potassium net-efflux was reduced by increasing Al concentrations up to 300 μM Al. Increasing the pH of the external solution from 4.3 to 5.3 enhanced callose formation, indicating more severe Al damage at pH 5.3, which is in agreement with a model on H+ amelioration of Al toxicity. Al did not initiate or enhance ferrous sulfate (FeSO4)-promoted lipid peroxidation. The results indicate hat the plasma membrane is a primary target of Al and that cell suspension culture is a powerful tool to study effects of Al on plant roots.

Multiresidue analysis of polar pesticides in surface and drinking water by on-line enrichment and thermospray LC-MS

Abstract: In the search for a fast and robust sample handling and preparation step to analyse various pesticides at trace levels in aqueous samples, an on-line trace enrichment has been combined with our thermospray LC-MS method [1] allowing both selective identification and a quantification down to the lower ng/L level. 51 polar pesticides were investigated by applying solid phase extraction to 50–100 ml aqueous samples using small cartridges filled with 40 mg adsorbent. Prior to their liquid chromatographic separation, the enriched analytes were eluted from the solid phase with the initial methanol/water gradient composition of the HPLC onto the analytical column using column switching techniques. A base-deactivated C18 material and the two styrene-divinylbenzene copolymers PLRP-S and PRP-1 were tested for enrichment in combination with a C8-bonded silica analytical column. The method developed was evaluated with respect to recoveries, precision, limits of detection and linearity. Furthermore, it was applied to various environmental samples. Apart from a few compounds of higher polarity, most of the pesticides show recoveries >60% (often >80%) with relative standard deviations between 1–15%. Overall method detection limits are in the range of 1–100 ng/L allowing, with one exception, a ready verification of the pesticide limit of 100 ng/L set in the EU drinking water guideline [2].