Identification of methyl (methylO-acetyl-O-methylhexopyranosid)uronates by mass spectrometry

Fragmentation of methyl (methylO-acetyl-O-methyl-α-d-gluco- and -galactopyranosid, uronates has been studied at 70 and 12 eV. At 12 eV, the production of ions resulting from secondary and further processes is greatly diminished and the spectra are simpler and easier to interpret. The energy required for the elimination of acetic acid and ketene has been calculated from the ion-appearance potentials. The number and location of methyl groups in methyl (methylO-acetyl-O-methyl-hexopyranosid)uronates can be determined. The procedure is particularly suitable for g.l.c.-m.s. of the uronic acid portion of methanolysates of methylated biopolymers and other substances containing uronic acids. From the presence or absence of peaks for molecular ions in the 12-eV spectra,gluco andgalacto isomers which do not contain a methoxyl group at C-4 can be distinguished. The synthesis of methyl (methyl 2,3-di-O-methyl-α-d-galactopyranosid)uronate is also described.     

Finding minimal generating set for metabolic network with reversible pathways

Elementary flux modes give a mathematical representation of metabolic pathways in metabolic networks satisfying the constraint of non-decomposability. The large cost of their computation shifts attention to computing a minimal generating set which is a conically independent subset of elementary flux modes. When a metabolic network has reversible reactions and also admits a reversible pathway, the minimal generating set is not unique. A theoretical development and computational framework is provided which outline how to compute the minimal generating set in this case. The method is based on combining existing software to compute the minimal generating set for a “pointed cone” together with standard software to compute the Reduced Row Echelon Form.     

Distending stress of the cytoskeleton is a key determinant of cell rheological behavior

One fundamental question in cell biology is what determines rheological properties of living cells. If the cytoskeletal distending stress is a key determinant of cell rheology, then modulating this stress by cell stretching should have a major effect on cell rheological properties. If not, then other mechanisms must play a major role. We developed a stretchable cell culture device that could rapidly stretch cells and thus generate passive mechanical stress within the cytoskeleton. This device was placed inside a magnetic cytometry system to measure the effect of stretching on rheological properties of cultured human airway smooth muscle cells. A gradual increase in cell distension caused a systematic increase in cell dynamic stiffness in a manner which was consistent with earlier observations where the active component of the distending stress was modulated pharmacologically. These findings provide strong evidence that the cytoskeletal distending stress is a key determinant of cell rheological properties.     

Spore germination of Frankia strains isolated from Colletia hystrix and Retanilla ephedra (Rhamnaceae)

Two Frankia strains, ChI1 from Colletia hystrix and ReI6 from Retanilla ephedra, were assayed to determine the germinability of their spores and the stages of the life cycle in different media. In BAP medium, both strains showed approximately 18% spore germination. However, in BAP medium lacking micronutrients and FeEDTA, strain ChI1 spores exhibited approximately 53% germination and strain ReI6 spores about 42%. The survey also showed that the spores were not heat-resistant, the ReI6 spores being more sensitive than ChI1 spores. Both strains exhibited a small increase in their percentage of germination with a 15-pulse ultrasonic treatment.     

Production of indole-3-acetic acid by several wild-type strains of Ustilago maydis

Indole-3-acetic acid (IAA) was identified and quantitated in spent media from cultures of ten Ustilago maydis strains. IAA was identified by thin-layer chromatography, high performance liquid chromatography (HPLC) and u.v. spectroscopy, and was quantitated by HPLC. All strains produced IAA in a tryptophan (Trp)-supplemented minimal medium at levels of 0.1 to 4.0 g IAA/ml of spent medium as assessed by HPLC. The highest levels of IAA were found in strains I2 and P2. The latter was also capable of producing IAA without addition of Trp to the medium.     

Local biodiversity and multi-habitat use in empidoid flies (Insecta: Diptera, Empidoidea)

The empidid fauna of four small adjacent biotopes bordering a pond was investigated for 2 consecutive years in Brittany (France). Adult activity was studied using yellow water traps, whereas suitable larval habitats were determined using emergence traps. While 24 species emerged from the soils, 45 flew above the four sites. The number of species emerging from each site was nearly identical. However, the highest number of individuals emerged from the heathland and numbers rapidly declined towards the pond banks. On the contrary, the greatest aerial activity occurred in the woodlot and near the pond banks. Fourteen times less flying activity was found above the dry heathland. The latter appeared to be a site of larval growth but mating and feeding of the adults took place in the woodlot. Reproduction sites and space used by the adults differed among the dominant species. The species assemblage could not be fully explained within the spatial limits of the four sites. Considering the species'behaviour, it is suggested that immigration of species and individuals from other sites should explain these differences. The study, which is supported by four other research works, emphasizes the role of key resource played by ecotonal zones between aquatic and terrestrial ecosystems in the persistence of species over a larger set of habitats. Considering the complementarity of habitats is essential to explain diversity patterns in species which need different space units to complete their life-cycle.     

The conservation of agrobiodiversity on-farm: questioning the emerging paradigm

The genetic diversity of traditional varieties of crops is the most economically valuable part of global biodiversity and is of paramount importance for future world crop production. The Biodiversity Convention has given a clear mandate for on-farm conservation. However, very little formal research has been done and no agreed set of scientific principles yet exists for on-farm conservation of genetic resources. This lack of scientific knowledge has not prevented an explosion of recommendations on how to conserve agrobiodiversity on-farm and it is possible to identify an emerging paradigm. Through a review of some of the assumptions on which this paradigm is based, we clearly show that if attempts to conserve agrobiodiversity on-farm are based on these misconceptions, they are likely to fail. By assessing the present activities of farmers, we propose a research agenda to increase the diversity available to farmers and to enhance farmers' capacity to manage this diversity dynamically. Increasing genetic diversification, combined with farmers' experimental abilities, and underpinned by the formal system, will ensure greater on-farm conservation of more useful genetic resources.     

New differences between isoenzymes A and B from Candida rugosa lipase

Water adsorption isotherms of pure lipases A and B from Candida rugosa are different and can be used to distinguish between the isoenzymes. The maximum esterification yield (50%, 20h) can be achieved at initial 0.9<1.0. Lipase B is more stereoselective (49% yield, 98% enantiomeri excess) than lipase A (47% yield, 72% enantiomerci excess) but both isoenzymes mainly esterify the (S) 2(4-isobutylphenyl)propionic acid (Ibuprofen).