Showing papers by "Martin Luther University of Halle-Wittenberg published in 1986"

Phosphorus requirements of the wheat plant in various stages of its life cycle

Abstract: In pot experiments root growth and P uptake were found to precede shoot growth. The high rate of P uptake in the early stages of the life cycle is not an expression of luxury consumption but reflects a high P requirement in plants. Plants cultivated in nutrient solutions with different P concentrations during various stages of development showed that a high P supply (1 ppm) between Feekes stages 6 and 9 (30 days) caused a higher grain yield than the same P concentration between Feekes stages 11 and 17 (30 days). The early applied P caused a high number of fertile ears per area, a high number of grains per ear, and a high P pool in vegetative parts. The latter could be mobilized during the grain-filling period. Therefore, for high grain yields soil and fertilizers have to meet the high P requirement (about 20 μg P/m root · day) in an early stage of plant growth. During the grain filling period the P supply can be much lower.

Studies on the thermal inactivation of immobilized enzymes

Abstract: The thermal inactivation of a great number of immobilized enzymes shows a biphasic kinetics, which distinctly differs from the first-order inactivation kinetics of the corresponding soluble enzymes. As shown for alpha-amylase, chymotrypsin, and trypsin covalently bound to silica, polystyrene, or polyacrylamide, the dependence of the remaining activities on the heating time can be well described by the sum of two exponential terms. To interpret this mathematical model function, the catalytic properties of immobilized enzymes (number of active sites in silica-bound trypsin, K(M) and E(a) values in silica-bound alpha-amylase and chymotrypsin) at different stages of inactivation and the influence of various factors (coupling conditions, addition of denaturants or stabilizers, etc.) on the thermal inactivation of silica-bound alpha-amylase were studied. Furthermore, conformational alterations in the thermal denaturation of spin-labeled soluble and silica-bound beta-amylase were compared by electron spin resonance (ESR) studies. The results suggest that the biphasic inactivation kinetics reflects two different pathways according to which catalytically identical enzyme molecules are predominantly inactivated.

Report on test matrices for generalized inverses

Abstract: This paper is a comprehensive report on test matrices for the generalized inversion of matrices. Two principles are described how to construct singular square or arbitrary rectangular test matrices and their Moore-Penrose inverses. By prescribing the singular values of the matrices or by suitably choosing the free parameters test matrices with condition numbers of any size can be obtained. We also deal with test matrices which are equal to their Moore-Penrose inverse. In addition to many advices how to construct test matrices the paper presents many test matrices explicitly, in particular singular square matrices of ordern, sets of 7×6 and 7×5 matrices of different rank, a set of 5×5 matrices which are equal to their Moore-Penrose inverse and some special test matrices known from literature. For the set of 7×6 parameter matrices also the singular values corresponding to six values of the parameter are listed. For three simple parameter matrices of order 5×4 and 6×5 even test results obtained by eight different algorithms are quoted.

Third chromosome suppressor of position-effect variegation loci in Drosophila melanogaster

Abstract: As a result of a genetic analysis of 63 third chromosome suppressor mutations of position-effect variegation 12 different loci showing dominant suppression have been identified and their map positions determined. A compilcation of the genetic data available for each suppressor locus is given. The strong suppressor effects of the mutations have been quantified by measurements of white variegation inwm4h/wm4h,wm4h/Y andwm4h/O flies. Mutant alleles of three loci were found in these studies to dominate over the strong enhancer effect of complete loss of the Y chromosome. Most of the identified loci suppressing position-effect variegation represent essential genetic funtions; only three loci represent nonessential functions. Mutations of two loci display recessive butyrate sensitivity and lethal interaction with the heterochromatic Y chromosome suggesting that these genes affect chromosomal condensation. Studies with deficiencies and triploids revealed that most of the loci represent haplo-abnormal suppressor functions. The use of the isolated mutant material for genetic, developmental and molecular studies of processes connected with gene inactivation in position-effect variegation is discussed.

Suppressor mutation of position-effect variegation in Drosophila melanogaster affecting chromatin properties

Abstract: The dominant mutation Su-var(2)1 01 which suppresses position-effect variegation and displays recessive butyrate sensitivity was found to result in significant hyperacetylation of histone H4. This biochemical finding, as well as the genetic properties of this mutation, strongly suggest that the wild-type product of the corresponding locus is involved in histone H4 deacetylation. In larvae containing the suppressor mutation the accessibility of chromatin to endogenous nucleases is significantly increased which might be causally connected with histone H4 hyperacetylation. The suppressor mutation Su-var(2)1 01 has, therefore, to be classified as a chromatin condensation mutation.

Wheat specific repetitive DNA sequences — construction and characterization of four different genomic clones

Abstract: The construction and molecular analysis of four recombinant clones — pTa1, pTa2, pTa7, and pTa8 — is described. The four clones contain different highly repeated sequences of genomic DNA from Triticum aestivum variety ‘Chinese Spring’. The wheat specificity has been determined by colony and dot blot hybridization in comparison with total rye DNA (Secale cereale variety ‘Petka’). The four clones with a variable degree of specificity were compared by sequence analysis after the recloning of wheat DNA inserts into M13 mp8. Within the sequencing data a tendency can be observed that those repeated sequences which show the highest degree of species specificity contain a significantly increased amount of GC residues.

Dielectric dispersion in PZT ceramics

Abstract: The frequency dependence of the complex dielectric constant (DC) of Pb(TixZr1-x)O3 ceramics (x=0.4; 0.48; 0.6) was measured between 10 Hz and 1010 Hz. Only one dispersion region was found with the relaxation frequency being independent of x. The spectral shape function for PZT 0.4, which is independent of the temperature between - 123°C and +239°C, corresponds to the many-body universal response described by Jonscher, Dissado and Hill. Our results scarcely corroborate the common idea of domain-wall and phase boundary contributions to the DC.

Localization of RNA-degrading enzyme activity within vacuoles of cultured tomato cells.

Abstract: Protoplasts were prepared from cells of a tomato (Lycopersicon esculentum Mill. cv. Lukullus) suspension culture and purified to eliminate the highly active exogenous RNase present in the enzyme mixture used for cell wall digestion. The purified protoplasts were used to determine the location of the endogenous RNase activity (measured at pH 5 with yeast RNA as the substrate). Vacuoles were released by shaking the purified protoplasts in alkaline buffer containing EDTA. RNase was unambiguously shown to be located within the vacuoles by (i) its co-purification with the vacuoles in a discontinuous gradient and by (ii) the co-migration of RNase and α-mannosidase (EC 3.2.1.24), a vacuolar marker, during repeated centrifugation of the vacuoles. Vacuolar RNase was insensitive to EDTA, Mg2+, Mn2+ and Ca2+ but was stimulated by citrate or KH2PO4. It exhibited a pH-optimum in the range of pH 5–6. Gel electrophoretic analysis revealed one single band for RNase of isolated vacuoles. This activity co-migrated with an RNase from cells extracted under mild conditions. Thus, it was possible to distinguish the vacuolar RNase from the RNase of extracellular origin. RNA-degrading activity was present in vacuoles throughout the growth of the culture. The activity in vacuoles gradually increased during exponential growth followed by a dramatic increase in the stationary phase.

Degradation of phenolic compounds by the yeast Candida tropicalis HP 15. II. Some properties of the first two enzymes of the degradation pathway.

Abstract: The first two enzymes of the phenol degradation pathway were determined and characterized in crude extracts from Candida tropicalis HP 15. The phenol hydroxylase (EC 1.14.13.7) was a stable NADPH2- and FAD-dependent enzyme with a pH-optimum of 7.6 to 8.0 and a broad substrate specificity. Influence of ultrasound rapidly reduced the enzyme activity. The catechol 1,2-oxygenase (EC 1.13.1.1) had a broad pH-optimum between 7.5 and 9.6 and a limited substrate specificity. Two active protein bands indicating the presence of two isofunctional enzymes were detectable after electrophoretic separation of crude and partially purified extracts on polycrylamide gels and specific staining for catechol 1,2-oxygenase activity.

Study of formation and reversion of Guinier-Preston zones in Al-4.5 at%Zn-x at%Mg alloys by positrons

Abstract: Measurements of the positron lifetime, τ, and the shape parameter,S, of the 2γ-angular correlation curve are reported for the Al-4.5 at%Zn-x at%Mg alloys (0 ⩽x ⩽ 2.5). In the alloys aged at room temperature after quenching two types of Guinier-Preston (GP) zones coexist both of which are able to trap positrons. The first type of zone is rich in zinc and completely free of any vacancy-type defects. The second type contains vacancies surrounded by zinc and magnesium atoms. From the comparison of τ andS, the composition of the surroundings of vacancies as a function of the magnesium concentration of the alloys is concluded. By increasing the magnesium content and the ageing time of the alloys the second type of GP zone increasingly dominates over the first one. The stability of both types of zone are studied in a reversion experiment. In an alloy with 2.5 at%Mg the formation of the η′ and η-phases are observed. The positron annihilation results are compared with the results obtained by calorimetry, small angle X-ray scattering and electron microscopy on the same alloy series.

Abscisic acid metabolism -vacuolar/extravacuolar distribution of metabolites.

Abstract: The biotransformation of abscisic acid (ABA) was studied in cell suspension cultures of Lycopersicon esculentum The ABA was converted by the cells to phaseic acid, nigellic acid, dihydrophaseic acid, abscisic acid-β-D-glucopyranosyl ester (ABA-Glc) and other ABA and phaseic acid conjugates Investigation of their cellular distribution showed that the conjugated forms were located only in the vacuoles whereas ABA and its acidic metabolites were found mainly in the extravacuolar fractions Our results, together with a number of studies on the increase of ABA-Glc as a response to stress, allow us to propose that ABA-Glc is irreversibly compartmented in the vacuoles of plant cells

Comparative study of the blood pressure effects of four different vegetable fats on young, spontaneously hypertensive rats

Abstract: Following the suckling period, four groups of male four-week-old spontaneously hypertensive rats (SHR) were fed semisynthetic diets with 14% (by weight) of either sunflower seed oil [46% 18:2(n-6); linoleic acid (LA)-rich], linseed oil [62.5% 18:3(n-3) + 12.9% 18:2(n-6); alpha-linolenic acid (LNA)-rich], evening primrose oil [9.2% 18:3(n-6) + 71% 18:2(n-6); gamma-linolenic acid (LNA)-rich] or hydrogenated palm kernel fat [1.5% 18:2(n-6); polyunsaturated fatty acid (PUFA)-deficient], respectively, up to an age of 18 wk. All diets enriched with PUFA provoked an attenuation of hypertension development. The effect was lowest in the LA-rich group and highest in the gamma-LNA-rich group. Differences in fatty acid composition of renal phospholipids between groups reflect the fatty acids present in the respective dietary fats. Renomedullary production of PGF2 alpha was significantly reduced in alpha-LNA-rich and slightly diminished in gamma-LNA-rich fed rats. Aortic formation of 6-keto-PGF1 alpha and TXB2 was increased in animals fed the gamma-LNA-rich diet. Thus, the attenuation of hypertension development cannot be explained only by changes in prostanoid formation. Other mechanisms possibly involved should be pursued.

A reduced angular momentum expansion in the multiple‐scattering theory

Abstract: In order to improve the calculations of ARPES, ARAES, and EXAFS a new approximation in the multiple-scattering theory for the excited electrons is introduced, which is called reduced angular momentum expansion (RAME). In the RAME the incoming waves are approximated in the range of the scattering potential by a limited set of spherical waves with low angular momenta. This is a much better description than the plane wave approximation in the often used small scattering-centre approximation. The RAME possesses a high accuracy for energies down to 40 eV and needs a substantially lower numerical effort than the full angular momentum expansion. For higher energies it can be further simplified and it modified small-scattering-centre approximation is obtained, which takes into account the curvature of the waves by means of effective scattering amplitudes. Um die Berechnung von ARPES, ARAES und EXAFS zu verbessern, wird eine neue Naherung in die Vielfachstreutheorie fur die angeregten Elektronen eingefuhrt, die als reduzierte Drehimpulsentwicklung (RAME) bezeichnet werden soll. In der RAME werden die einfallenden Wellen im Bereich des Streupotentials durch einen beschrankten Satz von Kugelwellen mit niedrigen Drehimpulsquantenzahlen approximiert. Das ist eine weitaus bessere Beschreibung als die Approximation durch eine ebene Welle in der oft verwendeten Naherung kleiner Streuzentren. Die RAME besitzt eine hohe Genauigkeit fur Energien bis hinab zu 40 eV und benotigt wesentlich weniger Rechenaufwand als eine vollstandige Drehimpulsentwicklung. Bei hoheren Energien kann sie weiter vereinfacht werden, und man erhalt eine modifizierte Naherung kleiner Streuzentren, die die Krummung der Wellenfronten durch effektive Streuamplituden berucksichtigt.

IR Transmission Investigations of (Bi1−xSbx)2Te3 Single Crystals

Abstract: IR transmission spectra are measured at (Bi1−xSbx)2Te3 single crystals with x = 0.5, 0.7, 0.9 near the absorption edge at 84 and 300 K. For the determination of the optical constants also the reflectivity of polarized infrared light is recorded in the plasma range at 300 K. The dependence of the free carrier part of the dielectric function on the wave number ϵ(v) indicates that acoustic phonon scattering is the dominant mechanism. The interband contribution ϵ(v) is interpreted by indirect allowed band transitions. The energy gap and the phonon energies are calculated and lie in a physically reasonable range.

Generalizations in linear pharmacokinetics using properties of certain classes of residence time distributions. I. Log-convex drug disposition curves

Abstract: Introducing the phenomenoiogical concept of a time-varying fractional rate of elimination kD(t)and applying the theory of lifetime distributions, implications of the log-convexity of drug disposition curves are examined and some important applications are described. Linear pharmacokinetic systems exhibiting a log-convex impulse response and satisfying the basic conditions underlying the noncompartmental approach have the following properties: (1) The time-varying volume of distribution V(t)increases, and consequently the fractional rate of elimination kD(t)=CL/V(t)decreases monotonically. (2) The concentration-time curve and the time course of total amount of drug in the body, respectively, have an exponential tail [where V(t)approaches the equilibrium value VZ].The relative dispersion of residence times (CV D 2 =VDRT/MDRT2)and the ratio Vss/VZ (V ss is the volume of distribution at steady state) act as measures of departure from pure monoexponential decay (one-compartment behaviour). The role of the latter parameters as shape parameters of the curve that characterize the distributional properties of drugs is discussed. Upper and lower bounds of the time course of drug amount in the body are derived using the parameters MDRTand CV D 2 or λz (terminal exponential coefficient), respectively. This approach is also employed to construct upper bounds on the fractional error in AUCdetermination by numerical integration that is due to curve truncation. The significance of the fractional elimination rate concept as a unifying approach in interspecies pharmacokinetic scaling is pointed out. Some applications of the results are demonstrated, using digoxin data from the literature.

Reentrant Nematic phases in Binary Systems of Terminal-Nonpolar Compounds

Abstract: The phase diagrams of nine binary systems containing recentrant nematic phases in the sequence Nre SA N and Sc Nre SA N are presented. In these mixtures both components are of the trminal-nonpolar type. X-ray diffraction studies of three systems were carried out. The relationship between the form of the phase diagrams and the chemical nature and polymorphism of the separate components is discussed.