Bio-availability of phosphorus in sediments of the western Dutch Wadden Sea

The purpose of this study was to make a prognosis of the effects of extended purification of terrestrial waste water, reaching the Wadden Sea by the River Rhine and Lake IJssel, on the phosphate concentration in the western Wadden Sea.The quantities of different phosphorus fractions in intertidal and subtidal sediments of the Marsdiep tidal basin (western Dutch Wadden Sea) were measured. Different methods are applied to determine the amount of phosphorus that can be released from these sediments. The direct bioavailability is determined by inoculating sediment suspensions with a natural mixture of precultured micro-organisms from the sampling area. A second approach is the measurement of the phosphate release under different redox conditions. Sequential extraction of sediment samples with different solvents is also applied. Under the present conditions and compared to the nutrient loads from fresh water (Lake IJssel) and from the North Sea, the phosphorus stored in the sediments of the western Dutch Wadden Sea plays a minor role in the total supply to micro-algae and bacteria. The bulk of the biologically available phosphorus in the sediments originates from the metal-associated fraction. Releasable phosphate may contribute to the local annual primary production to an extent of ca 45 to ca 150 g C m^–2 a^–1. The total amount of phosphorus in the sediment (mainly calcite associated) is twice to 6 times the biologically available amount.     

Anaerobic degradation of dimethylsulfoniopropionate to 3-S-methylmercaptopropionate by a marine Desulfobacterium strain

Dimethylsulfoniopropionate, an osmolyte of marine algae, is thought to be the major precursor of dimethyl sulfide, which plays a dominant role in biogenic sulfur emission. The marine sulfate-reducing bacterium Desulfobacterium strain PM4 was found to degrade dimethylsulfoniopropionate to 3-S-methylmercaptopropionate. The oxidation of one of the methyl groups of dimethylsulfoniopropionate was coupled to the reduction of sulfate; this process is similar to the degradation betaine to dimethylglycine which was described earlier for the same strain. Desulfobacterium PM4 is the first example of an anaerobic marine bacterium that is able to demethylate dimethylsulfoniopropionate.Abbreviations DMSP dimethylsulfoniopropionate - DMS dimethyl sulfide - MMPA 3-S-methylmercaptopropionate     

Direct resolution of enantiomers of basic imidazol-2-yl-substituted alcohols by gas chromatography on chirasil-val

The direct resolution of enantiomers of a series of imidazol-2-yl-substituted alcohols has been achieved by gas chromatography on a well-deactivated fused-silica capillary column, coated with L -Chirasil-Val as the chiral stationary phase. The separation of these basic compounds is accomplished without exaggerated peak tailing. Compared to simpler alcohols the resolution factors (α) observed are extraordinarily large. While the imidazolyl substituent may contribute to the mechanism of the chiral discrimination, the crucial interaction is assumed to be through the hydroxy group, based on the observation that the resolution factors for the corresponding O-acetyl derivatives are markedly reduced. © 1993 Wiley-Liss, Inc.     

EPR Spin Trapping Study of the Decomposition of Azo Compounds in Aqueous Solutions by Ultrasound: Potential for Use as Sonodynamic Sensitizers for Cell Killing

Sonodynamic therapy, a promising new approach to cancer treatment, is based on synergistic cell killing by combination of certain drugs (sonosensitizers) and ultrasound. Although the mechanism of sonodynamic action is not understood, the role of free radicals produced from sonosensitizers by ultrasound is implicated. In this work, we studied formation of free radicals during the decomposition of several water-soluble azo compounds by 50 kHz ultrasound in aqueous solutions. Using the spin trap 3, 5-dibromo-4-nitrosobenzene sulfonate (DBNBS) tertiary carbon-centered radicals from 2, 2'-azobis (N,N'-dimethyl-eneisobutyramidine) dihydrochloride (VA-044), 2-(carbamoylazo)-isobutyronitrile (V-30), and 2, 2'-azobis (2-amidinopropane) dihydrochloride (AAPH) and CH3 radicals from 1, 1'-azobis (N,N'-dimethylformamide) (ADMF) were detected in argonsaturated solutions and the corresponding oxygen-centered radicals (alkoxyl and peroxyl) from VA-044, V-30, and AAPH were identified using the spin trap 5, 5'-dimethyl-l-pyrroline-N-oxide (DMPO) in aerated sonicated solutions. No free radicals from 4, 4'-dihydroxyazobenzene-3, 3'-dicarboxylic acid, disodium salt (DHAB) could be found in either system. While VA-044 and AAPH could also be readily decomposed by heat (42.5°C and 80°C), V-30 decomposition only occurred in the ultrasound-exposed solutions. The most likely mechanism of decomposition of azo compounds by ultrasound is their thermolysis in the heated shell of the liquid surrounding ca vita ting bubbles driven by ultrasound and/or by pyrolysis inside these bubbles. Experiments using scavengers of ·OH and ·H, which are produced by sonolysis in aqueous solutions, demonstrated that these radicals are not involved in the ultrasound-mediated radical production from the azo compounds. Due to the known cytotoxic potential of free radicals produced from azo compounds, the use of these compounds as ultrasound sensitizers appears to be a promising approach for sonodynamic cell killing.     

Drought stress of apple trees alters leaf emissions of volatile compounds

Actively growing potted apple trees ( Malus domestica [L.] Borkh. ev. Delicious) unacclimated to drought stress were subjected to drought to determine changes in emissions of leaf volatile compounds. Drought stress was imposed over a 2-week period by weighing pots every 2 or 3 days and adding water hack to an arbitrary and decreasing traction of the original pot weight. Stem water potential was -2.7. -2.0 and -0.8 MPa for the severely stressed, moderately stressed and control trees, respectively. 13 days alter watering treatments were begun. Water use the last 4 days of the experiment was about one-half for the moderately and severely stressed trees compared to that of the controls Twenty-nine volatile compounds were identified by using gas chromatography and mass spectroscopy. Emission rates of hexanal, (E)-2-hexenal, (E)-2-hexen-1-ol, 1-hexenol, hexyl acetate and (E)-2-hexenyl acetate were 5 to 310 times higher for severely stressed trees compared to those of the controls with the moderately stressed trees intermediate. The large increases in hexanal. (E)-2-hexenal and l-hexanol may be related. In enhanced lipoxygenase activity. Volatile compounds are products of metabolism and measurement of their changes after biotic or abiotic stresses will increase understanding of the relationship of changes in plant metabolism by those stresses.     

Are polyphosphates or phosphate esters prebiotic reagents?

It is widely held that there was a phosphate compound in prebiotic chemistry that played the role of adenosine triphosphate and that the first living organisms had ribose-phosphate in the backbone of their genetic material. However, there are no known efficient prebiotic synthesis of high-energy phosphates or phosphate esters. We review the occurrence of phosphates in Nature, the efficiency of the volcanic synthesis of P₄O₁₀, the efficiency of polyphosphate synthesis by heating phosphate minerals under geological conditions, and the use of high-energy organic compounds such as cyanamide or hydrogen cyanide. These are shown to be inefficient processes especially when the hydrolysis of the polyphosphates is taken into account. For example, if a whole atmosphere of methane or carbon monoxide were converted to cyanide which somehow synthesized polyphosphates quantitatively, the polyphosphate concentration in the ocean would still have been insignificant. We also attempted to find more efficient high-energy polymerizing agents by spark discharge syntheses, but without success. There may still be undiscovered robust prebiotic syntheses of polyphosphates, or mechanisms for concentrating them, but we conclude that phosphate esters may not have been constituents of the first genetic material. Phosphoanhydrides are also unlikely as prebiotic energy sources. Correspondence to: S.L. Miller     

Vanadium derivatives act as growth factor — mimetic compounds upon differentiation and proliferation of osteoblast-like UMR106 cells

The effect of different vanadium compounds on proliferation and differentiation was examined in osteoblast-like UMR106 cells. Vanadate increased the cell growth in a biphasic manner, the higher doses inhibiting cell progression. Vanadyl stimulated cell proliferation in a dose-responsive manner. Similar to vanadate, pervanadate increased osteoblast-like cell proliferation in a biphasic manner but no inhibition of growth was observed. Vanadyl and pervanadate were stronger stimulators of cell growth than vanadate. Only vanadate was able to regulate the cell differentiation as measured by cell alkaline phosphatase activity. These results suggest that vanadium derivatives behave like growth factors on osteoblast-like cells and are potential pharmacological tools in the control of cell growth.     

Biotransformation of diphenyl ether by the yeastTrichosporon beigelii SBUG 752

Trichosporon beigelii SBUG 752 was able to transform diphenyl ether. By TLC, HPLC, GC, GC-MS, NMR- and UV-spectroscopy, several oxidation products were identified. The primary attack was initiated by a monooxygenation step, resulting in the formation of 4-hydroxydiphenyl ether, 2-hydroxydiphenyl ether and 3-hydroxydiphenyl ether (48:47:5). Further oxidation led to 3,4-dihydroxydiphenyl ether. As a characteristic product resulting from the cleavage of an aromatic ring, the lactone of 2-hydroxy-4-phenoxymuconic acid was identified. The possible mechanism of ring cleavage to yield this metabolite is discussed.     

The role of the secondary plant compound 2,5-dihydroxymethyl 3,4-dihydroxypyrrolidine as a feeding inhibitor for insects

The cyclic amino alditol 2,5-dihydroxymethyl 3,4-dihydroxypyrrolidine (DMDP) has recently been shown to be an inhibitor of various glucosidases. We have investigated its role as a plant protective chemical against a range of phytophagous insects by examining its effects on development, feeding behaviour and functioning of taste receptors. We have shown that it can inhibit feeding and can be toxic. The mechanisms by which these effects are achieved are discussed in the context of the molecular structure of the compound.

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Résumé Récemment a été mis en évidence le puissant pouvoir inhibiteur de différents glucosidases. Présenté par l'amino-alditol cyclique, 2,5 dihydroxymethyl 3,4 dihydroxypyrrolidine (DMDP), isolé de graines de la légumineuse Lonchocarpus sericeus. Nous avons examiné le rôle de ce composé secondaire dans la stratégie défensive de la plante contre une gamme d'insectes phytophages, à travers son action sur le développement, le comportement alimentaire et le fonctionnement des récepteurs gustatifs. Nous avons montré que DMDP peut inhiber, suivant la dose, la prise de nourriture et, qu'aprs ingestion (par Spodoptera spp), il peut agir comme une toxine. Par suite de sa structure moléculaire, DMDP peut être considéré, non seulement comme l'analogue d'un sucre, mais aussi comme un alcaloïde. Le bilan des résultats de nos expériences suggère que l'efficacité de DMDP comme phagodissuadant, si elle ne provient pas de sa toxicité, découle principalement de ses propriétés d'alcaloïde.

     

Early metabolic changes in regenerating microfragments of the liverwort Riella helicophylla (Bory et Mont.) Mont.: Protein and RNA synthesis,free α-amino concentration

Microfragments of constant size were isolated from the thallus of Riella by a rapid punching procedure. Thus it was possible to study various metabolic parameters especially during the first hours after fragment isolation. Protein synthesis increases rapidly after a slight decrease at 30 min. The earliest significant increase in RNA synthesis occurs at 8 h, indicating a different activation pattern. The concentration of -amino compounds drops at 30 min and then increases continuously, thus exhibiting a close relationship with the measured alterations in protein synthesis. Another indication of metabolic conversions during regeneration is provided by the changing level of free radioactive leucine, which shows a marked turning point at 24 h after fragmentation. Analysis of free -amino concentrations in small regions of larger fragments also indicates the establishment of new intercellular correlations only a few hours after isolation of the cells from the meristem. Up to the 8th h after fragmentation, the contents of both the adaxial and peripheral fragment regions increase. Thereafter only the adaxial (regenerating) cells continue accumulating; the peripheral (nonregenerating) ones remain at the same level.