The influence of the cytosolic oncotic pressure on the permeability of the mitochondrial outer membrane for ADP: implications for the kinetic properties of mitochondrial creatine kinase and for ADP channelling into the intermembrane space

Summary Cytosolic proteins as components of the physiological mitochondrial environment were substituted by dextrans added to media normally used for incubation of isolated mitochondria. Under these conditions the volume of the intermembrane space decreases and the contact sites between the both mitochondrial membranes increase drastically. These morphological changes are accompanied by a reduced permeability of the mitochondrial outer compartment for adenine nucleotides as it was shown by extensive kinetic studies of mitochondrial enzymes (oxidative phosphorylation, mi-creatine kinase, mi-adenylate kinase). The decreased permeability of the mitochondrial outer membrane causes increased rate dependent concentration gradients in the micromolar range for adenine nucleotides between the intermembrane space and the extramitochondrial space. Although all metabolites crossing the outer membrane exhibit the same concentration gradients, considerable compartmentations are detectable for ADP only due to its low extramitochondrial concentration. The consequences of ADP-compartmentation in the mitochondrial intermembrane space for ADP-channelling into the mitochondria are discussed.     

An NADH nitrate reductase gene copy appears to have been deleted in barley

Cultivated barley,Hordeum vulgare L., has a single NADH nitrate reductase (NR) gene while diploid wheat,Triticum monococcum, and cultivated hexaploid wheat,Triticum aestivum L., have two NADH NR genes. To determine whether the NADH NR gene was duplicated since the divergence ofTriticum fromHordeum or was deleted from barley, theT. Monococcum NADH NR gene heme-hinge regions were sequenced and compared with the barley NADH NR gene sequence. Sequence identity and phylogenetic analyses showed that one of theT. Monococcum NADH NR genes is more-closely related to the barley NADH NR gene than to the otherT. Monococcum NADH NR gene. The heme-hinge region of all three NR genes appeared to have evolved at a constant rate. These results suggest that the NADH NR gene duplicated before the divergence ofTriticum andHordeum and that a deletion resulted in the loss of one NADH NR gene from cultivated barley.     

A phloem-specific sucrose-H+ symporter from Plantago major L. supports the model of apoplastic phloem loading

In this paper the cloning of a full-length cDNA clone encoding the PmSUC2 sucrose-H⁺ symporter from Plantago major is described. This plant allows the simple preparation of vascular bundles from the basal regions of fully developed source leaves and thus a separation of vascular and non-vascular tissue. A cDNA library was constructed from poly(A)⁺ RNA isolated from vascular bundles and used for the subsequent cloning of cDNAs. The respective mRNA is specifically expressed in the vascular bundles as shown on Northern blots of total RNA from vascular and non-vascular tissues. The PmSUC2 protein has 12 putative transmembrane helices and is highly homologous to other plant sucrose transporters. Substrate specificity and energy dependence of the transporter encoded by this cDNA were determined by expression in baker's yeast Saccharomyces cerevisiae. The PmSUC2 protein catalyses the transport of sucrose into transgenic yeast cells. Invertase null mutants of yeast expressing PmSUC2 accumulate sucrose more than 200-fold. This transport was sensitive to uncouplers or SH-group inhibitors. Plasma membranes from yeast cells expressing the PmSUC2 protein were purified and fused to proteoliposomes containing cytochrome-c-oxidase. In this system sucrose is accumulated only when proton motive force is generated, indicating that PmSUC2 is a sucrose-H⁺ symporter. The apparent molecular weight of the PmSUC2 protein is 35 kDa on 10% SDS-polyacrylamide gels. The presented data strongly support the theory of phloem loading from the apoplastic space by a sucrose-H⁺ symporter.     

Separation of the enantiomers of coumarinic anticoagulant drugs by capillary electrophoresis using maltodextrins as chiral modifiers

The separation and quantitation of coumarinic anticoagulant drug enantiomers were achieved by direct chiral capillary electrophoresis using complex maltooligosaccharide mixtures as stereoselective electrolyte modifiers. Chiral separations were characterized by a high selectivity and efficiency, enabling enantiomeric excess determinations. In addition, preliminary results indicate the applicability of the method for the determination of individual enantiomers in biological samples. So the method can be used to perform stereoselective pharmacokinetic studies. © 1994 Wiley-Liss, Inc.     

CAPITULUM PHYLLOTAXIS AND NUMERICAL CANALIZATION IN MICROSERIS PYGMAEA (ASTERACEAE: LACTUCEAE)

The positions at which floret primordia arise in developing capitulum buds of Microseris pygmaea D. Don have been mapped by computer-assisted light microscopy. The primordia can be assigned positions along a basic phyllotactic spiral with a divergence angle of about 137.5°. In addition, there are regular deviations from a spiral arrangement. Typically, the first 26 primordia in phyllotactic sequence are arranged in two concentric circles of 13 primordia with considerable deviations in the divergence angle and in the distances between primordia along a parastichy at positions 13 and 26. This arrangement can be simulated by geometric models that include nearest neighbor packing, together with spiral phyllotaxis. The circular arrangement of peripheral primordia at nearly equal radial distances from the center of the developing capitulum helps to explain the numerical constancy (canalization) of peripheral structures, especially the constant number of 13 inner phyllaries on heads with very different numbers of florets.     

A molecular,isozyme and morphological map of the barley (Hordeum vulgare) genome

A map of the barley genome consisting of 295 loci was constructed. These loci include 152 cDNA restriction fragment length polymorphism (RFLP), 114 genomic DNA RFLP, 14 random amplified polymorphic DNA (RAPD), five isozyme, two morphological, one disease resistance and seven specific amplicon polymorphism (SAP) markers. The RFLP-identified loci include 63 that were detected using cloned known function genes as probes. The map covers 1,250 centiMorgans (cM) with a 4.2 cM average distance between markers. The genetic lengths of the chromosomes range from 124 to 223 cM and are in approximate agreement with their physical lengths. The centromeres were localized to within a few markers on all of the barley chromosomes except chromosome 5. Telomeric regions were mapped for the short (plus) arms of chromosomes 1, 2 and 3 and the long (minus) arm of chromosomes 7.This research was also supported by other members of the NABGMP: K. Kasha, Department of Crop Science, University of Guelph, Guelph, Ontario, Canada NIG 2W1; W. Kim, Agriculture Canada Research Station, 195 Dafoe Road, Winnipeg, Manitoba, Canada R3T 2M9; A. Laroche, Agriculture Canada Research Station, P.O. Box 3000 Main, Lethbridge, Alberta, Canada,TU 4B1; S. Molnar, Plant Research Centre Agriculture Canada, Central Experimental farm, Ottawa, Ontario, Canada K1A 0C6; G. Scoles, Department of Crop Science, University of Saskatchewan, Saskatoon, Saskatchewan, Canada S7N OWOThis research is part of the North American Barley Genome Mapping Project, R. A. Nilan and K. Kasha, Coordinator and Associate Coordinator, respectively Permanent address: Department of Plant Genetics, NI Vavilov Institute of General Genetics, Russian Academy of Sciences, Moscow     

Climate–ecosystem modelling made easy: The Land Sites Platform

Dynamic Global Vegetation Models (DGVMs) provide a state-of-the-art process-based approach to study the complex interplay between vegetation and its physical environment. For example, they help to predict how terrestrial plants interact with climate, soils, disturbance and competition for resources. We argue that there is untapped potential for the use of DGVMs in ecological and ecophysiological research. One fundamental barrier to realize this potential is that many researchers with relevant expertize (ecology, plant physiology, soil science, etc.) lack access to the technical resources or awareness of the research potential of DGVMs. Here we present the Land Sites Platform (LSP): new software that facilitates single-site simulations with the Functionally Assembled Terrestrial Ecosystem Simulator, an advanced DGVM coupled with the Community Land Model. The LSP includes a Graphical User Interface and an Application Programming Interface, which improve the user experience and lower the technical thresholds for installing these model architectures and setting up model experiments. The software is distributed via version-controlled containers; researchers and students can run simulations directly on their personal computers or servers, with relatively low hardware requirements, and on different operating systems. Version 1.0 of the LSP supports site-level simulations. We provide input data for 20 established geo-ecological observation sites in Norway and workflows to add generic sites from public global datasets. The LSP makes standard model experiments with default data easily achievable (e.g., for educational or introductory purposes) while retaining flexibility for more advanced scientific uses. We further provide tools to visualize the model input and output, including simple examples to relate predictions to local observations. The LSP improves access to land surface and DGVM modelling as a building block of community cyberinfrastructure that may inspire new avenues for mechanistic ecosystem research across disciplines.     

Effects of nitrite-induced methaemoglobinaemia on oxygen affinity of carp blood

Synopsis The oxygen transport characteristics and the acid-base status of carp blood was studied in vitro by equilibration of blood samples with and without addition of 5mmol l^–1 of nitrite for 30 min at various Po₂ values in combination with Pco₂ of 1.5 and 5.7mmHg (0.2 and 0.76kPa). After equilibration pH, Po₂, Pco₂, and Co₂ as well as methaemoglobin and HCO₃ ^– concentration were determined and oxygen dissociation curves established. At Pco₂ of 1.5mmHg (0.2kPa) oxygen affinity, expressed by a normal P₅₀ of 3.3mmHg (0.44kPa) was unaffected by nitrite exposure, whereas at Pco₂ 5.7 (0.76kPa), nitrite exposure shifted P₅₀ from 7.59mmHg (1.01kPa) to 21.9mmHg (2.92kPa). Methaemoglobin formation was greater at the higher Pco₂ and increased with falling Po₂. Erythrocyte shrinkage and rising plasma [HC0₃ ^–] during nitrite exposure indicated that the erythrocyte osmoregulation was significantly affected. The present results indicate significantly reduced oxygen affinity upon exposure of carp blood to nitrite. This result contrasts with findings in mammalian blood, where oxygen affinity is greatly enhanced.     

The kinetics and regulation of M-xylose transport in Candida utilis

Low-affinity (K _m=67.6±3.2 mM) and high-affinity (K _m=1.9±1.2 mM) D-xylose transport occur in Candida utilis grown, respectively, on D-glucose or D-xylose. Starvation of glucose-grown cells decreases the K _m value (10.5±2.6 mm). The high-affinity system appearing during starvation required protein synthesis and it was inactivated when cells were exposed to glucose, by a process independent of protein synthesis. High-affinity transport was accompanied by transient alkalinization of yeast suspensions, indicating that it is a proton symport, whereas low-affinity transport was not. Both systems, however, were inhibited by metabolic inhibitors and by replacing H₂O in the transport assay with D₂O, indicating that both may be proton symports. Glucose and acetic acid also inhibited both high-and low-affinity xylose transport.S.G. Kilian, B.A. Prior and J.C. du Preez are with the Department of Microbiology and Biochemistry, University of the Orange Free State, P.O. Box 339, Bloemfontein 9300, Republic of South Africa