Galactitol accumulation by glucose-6-phosphate deficient fibroblasts: a cellular model for resistance to the complications of diabetes mellitus

When incubated in high galactose media, fibroblasts from individuals with the severe (Mediterranean) variety of glucose-6-phosphate dehydrogenase (G6PD) deficiency accumulate significantly less galactitol than do fibroblasts from matched control subjects. The effect is not observed in fibroblasts from black subjects with the more common, and milder, A- variant of G6PD deficiency. Since aldose reductase and sorbitol dehydrogenase activities in experimental and control fibroblasts are identical, the effect is most likely due to the substantial reduction in NADPH levels in severely G6PD-deficient cells. Sorbitol does not accumulate either in control or in G6PD deficient fibroblasts incubated in high glucose medium, most likely because of the action of sorbitol dehydrogenase, and the presence of a carrier-mediated glucose transport system in the cell membrane which limits the concentration of glucose that can accumulate in these cells.     

Plant clonality: Biology and diversity

The current approaches to the study of clonal plants are reviewed. Most studies concentrate at the level of the ramet and clonal fragment exploring the “microscopic” view of clonal plants, dealing with the translocation of resources, clonal integration, plasticity of growth etc. The information gained, by this approach can be used in the understanding of higher levels of organization within the clonal system either with the help of spatially explicit modelling techniques, or by using means and distributions of size within a population instead of studying individual ramets separately. Plant scientists use the term clone with two meanings, viz. (a) a set of physiologically connected, but potentially independent ramets, and (b) a set of genetically identical, but potentially physically separated individuals. The overlap of these terms differs between individual plant species, depending on the extent of physical separation of the ramets and the degree of physiological integration between the ramets; the lower the frequency of ramet separation, the closer are the physiological and genetic concepts of the clone. Three critical areas seem to be neglected in clonal plant research: (a) the interrelationship between hierarchical levels in clonal plants, (b) the particular spatial structure of their environment, and (c) the importance of clonal plants in different ecological communities.     

Characterization of a cDNA encoding the protein moiety of a putative arabinogalactan protein from Lycopersicon esculentum

The nucleotide sequence of a cDNA prepared from poly(A)⁺ RNA from Lycopersicon esculentum fruit codes for a protein, M _r 20812, with features representative of the protein core of arabinogalactan proteins. The deduced amino acid sequence resembles that of peptides of arabinogalactan proteins isolated from carrot and rose and is most similar to the sequence of tryptic peptides from Lolium multiflorum (Gleeson et al., Biochem J 264 (1989) 857–862). The similar sequences include a number of Ala-Pro repeats, a feature considered distinctive of arabinogalactan proteins. The amino acid composition is similar to that of the peptide core of the Lolium multiflorum arabinogalactan protein; alanine, serine and proline account for 57% of the polypeptide. The mRNA corresponding to the cDNA sequence was detected in roots, leaves and fruit. The levels of mRNA are reduced in older leaves, in fruit that have commenced ripening and in leaves and fruit that have been wounded.     

Parametric sensitivity of stoichiometric flux balance models applied to wild-type Escherichia coli metabolism

The esterification of lauric acid with geraniol catalyzed by the commercially immobilized lipase preparation from Mucor miehei, Lipozyme(R), was studied in well-stirred flasks. The enzyme support was characterized in terms of its internal and external surface area, protein location, and protein content. It was found that the enzyme was mainly located on the external surface of the support, therefore, internal diffusional limitations were not important. It was also shown that the protein content of the support depends on the size of the particle, with smaller particles containing higher amounts of protein per unit weight. Under the conditions studied, the reaction was not under external mass transfer limitations, and the initial reaction rate depended on the size of the support particles. This was mainly due to the different protein contents on the support as a function of particle size and not to internal or external mass transfer limitations. Also, it was found that the inhibition exerted by water was predominantly a physical effect due to its accumulation around the enzyme. It was also found that the reaction was substrate inhibited by lauric acid, but not by geraniol. (c) 1995 John Wiley & Sons, Inc.     

Chilling-sensitive mutants of arabidopsis

Twenty-one mutants ofArabidopsis thaliana were isolated that developed chlorosis or necrosis upon incubation at low temperature (10°C to 15°C). Crosses among mutants in different phenotypic classes showed that mutants in three of four classes were found in a small number of loci. This article is reproduced fromWeeds World, vol. 1. For electronic access toWeeds World, see PMBR 12(4):302–303.     

Transmission Studies with Cucumber Green Mottle Mosaic Virus

Cucumber green mottle mosaic virus may spread in bottlegourd under field conditions through soil contaminated with infected plant debris followed by contact. No seed transmission was noticed in bottlegourd (Lagenaria siceraria) or vegetable marrow (Cucurbita pepo) although pollen grains and cotyledons from infected bottlegourd flowers or seeds, respectively, contained negliginle amounts of virus. Cucumber leaf beerles (Raphidopalpa fevicollis) are probable vectors since their regurgitated fluid and excretes contained infective virus particles. No vector fungi were found in the soil around infected bottlegourd plants.     

Location and orientation relative to the micelle surface for glucagon in mixed micelles with dodecylphosphocholine EPR and NMR studies

The spin labels, 5-doxylstearate, 12-doxylstearate, 16-doxylstearate and 1-oxyl-2,2,6,6-tetramethyl-4-dodecylphospiperidine, have been incorporated into dodecylphospocholine micelles and mixed dodecylphosphocholine/ glucagon micelles. The EPR spectral parameters for the different spin labels and the ¹H- and ¹³C-NMR relaxation rates for nuclei of the detergent molecules indicated that inclusion of up to one spin label molecule per micelle had little influence on the spatial organization of the micelles. Furthermore, the location and environment of the spin labels in the dodecylphosphocholine micelles were not noticeably affected by the addition of glucagon and the ¹H-NMR spectra observed for glucagon in mixed spin label/deuterated dodecylphosphocholine/glucagon micelles showed that the different spin labels had essentially no effect on the conformation of glucagon. Approximate spatial locations within the micelle for the nitroxide moieties of the different spin labels were determined from the NMR relaxation rates observed for different nuclei of dodecylphosphocholine. On this basis, the line broadening of individually assigned glucagon ¹H-NMR lines by the different spin labels was used to determine the approximate orientation of the polypeptide chain with respect to the micelle surface. Overall, the data indicate that the glucagon backbone runs roughly parallel to the micelle surface, with the depth of immersion adjusted so that polar and apolar side chains can be oriented towards the surface or interior of the micelle, respectively.     

On the study of two interacting populations one of which acts independently of the other

Many ecological and biological systems can be studied in terms of a bivariate stochastic branching process, {X ₁ (t), X ₂ (t)}, each of whose components (or populations) varies in magnitude according to the laws of a generalized birth-death process. Of particular interest is such a model in which the birth and death rates of the first population,X ₁, are constant while those of the second population,X ₂, exhibit a functional dependence upon the magnitude of the first. It is shown, first, that the existence of the stochastic mean of a birth death process implies the existence of all higher moments. The values of all the factorial moments of such a process are then determined. The moments of the dependent population of the bivariate process are given in terms of its expectation and the joint probability density function of the process is determined. It is possible, therefore, to use Bayesian techniques to infer conclusions about the independent population, given information about the variation of the dependent one.