The interaction of homologous series of alkanols with sodium channels in nerve membrane vesicles

Summary The potency of members of the homologous series of alkanols to block²²Na uptake through sodium channels stimulated by veratridine was studied in membrane vesicles obtained from lobster walking leg nerves. A cut-off was revealed at the level of 1-undecanol. However, secondary isomers of inactive primary homologues, such as 5-dodecanol and 5-tridecanol, were able to block ion flux. From the concentration required for an equipotent effect, it was calculated that the standard free energy for adsorption of primary alkanols is –725 cal/mol CH₂. Furthermore, since the concentration required for an equipotent effect for primary isomer was found to be lower than that obtained for secondary isomers, it is concluded that the latter are less potent than the former. The similarity between this set of results and those obtained in intact frog sciatic nerve (J. Requena et al.,J. Membrane Biol. 84:229–238, 1985) offers further support to the notion that the procedure employed to isolate the membrane vesicles does preserve the Na channels. However, the mechanism of alcohol inhibition of the Na channel in isolated membrane vesicles would seem to be somewhat different from that preferred in axons. While in vesicles the block needs to be thought in terms of a reduction in the number of conducting Na channel, in axons this is considered to be the less likely mode of action, mainly because under veratridine it is not possible to invoke a shift in the steady-state activation or inactivation.     

Similarities of adenosine uptake systems in astrocytes and neurons in primary cultures

Uptake of extracellular adenosine was studied in primary cultures of astrocytes or neurons. Both cell types showed a high affinity uptake. TheK _m values were not significantly different (6.5±3.75 M in astrocytes and 6.1±1.86 M in neurons), but the intensity of the uptake was higher in astrocytes than in neurons (V _max values of 0.16±0.030 and 0.105±0.010 nmol×min^–1×mg^–1 protein, respectively). The temperature sensitivity was similar in the two cell types. Adenosine uptake inhibitors and benzodiazepines inhibited the adenosine uptake systems in both astrocytes and neurons with IC₅₀ values in the high nanomolar or the micromolar range and the rank order of potency was similar in the two cell types. In both cell types the (–) isomers of two sets of benzodiazepine stereoisomers were more potent than the (+) isomers. Dixon analysis showed that dipyridamole, papaverine, hexobendine and chlordiazepoxide inhibited the adenosine uptake competitively and clonazepam noncompetitively in both cell types.     

Biotic and abiotic methane releases from Lake Biwa sediment slurry

To determine the rate and mechanism of CH₄ production in Lake Biwa sediment, slurry was prepared and incubated. Surface sediment (sed) slurry (1.5–6cm) showed a CH₄ release rate (4.9–9.5nmolg-dry-sed^–1 day^–1) higher than that observed in the 5- to 10-cm sediment slurry (0.2–2nmolg-dry-sed^–1 day^–1). Methane release from the surface (1.5–6cm) sediment slurry was biotic and was inhibited by addition of 2-bromoethanesulfonate (BES, an inhibitor of CH₄ production), whereas that from 5- to 10-cm sediment slurry was abiotic. The addition of BES, HNO₃, and O₂ showed no effect on the CH₄ release rate from the 5- to 10-cm sediment slurry. In addition, tracers (NaH¹³CO₃, ¹³CH₃COONa) were not incorporated into the released CH₄. However, ¹³C of CH₄ released from the 5- to 10-cm sediment slurry (–74.0 ± 0.6) indicated that this CH₄ was produced by bacterial metabolism in the past, stored by adsorption on the surface of clay minerals in the sediment, and then released abiotically by desorption from the sediment slurry as a result of a decrease in hydraulic pressure and CH₄ concentration in the pore water. This CH₄ stored by adsorption could be extracted by autoclaving. In the sediment below 5cm, bacterial activity for CH₄ production ceased, possibly because of the limitated availability of H₂. To clarify the mechanism of CH₄ production in the sediment, biotic CH₄ production and the abiotic CH₄ release found here should be estimated separately.     

Effect of tree distance on N2O and CH4-fluxes from soils in temperate forest ecosystems

Complete annual cycles of N₂O and CH₄ flux in forest soils at a beech and at a spruce site at the Höglwald Forest were followed in 1997 by use of fully automatic measuring systems. In order to test if on a microsite scale differences in the magnitude of trace gas exchange between e.g. areas in direct vicinity of stems and areas in the interstem region at both sites exist, tree chambers and gradient chambers were installed in addition to the already existing interstem chambers at our sites. N₂O fluxes were in a range of –4.6–473.3 g N₂O-N m^–2 h^–1 at the beech site and in a range of –3.7–167.2 g N₂O-N m^–2 h^–1 at the spruce site, respectively. Highest N₂O emissions were observed during and at the end of a prolonged frost period, thereby further supporting previous findings that frost periods are of crucial importance for controlling annual N₂O losses from temperate forests. Fluxes of CH₄ were in a range of +10.4––194.0 g CH₄ m^–2 h^–1 at the beech site and in a range of –4.4––83.5 g CH₄ m^–2 h^–1 at the spruce site. In general, both N₂O-fluxes as well as CH₄-fluxes were higher at the beech site. On a microsite scale, N₂O and CH₄ fluxes at the beech site were highest within the stem area (annual mean: 49.6±3.3 g N₂O-N m^–2 h^–1; –77.2±3.1 g CH₄ m^–2 h^–1), and significantly lower within interstem areas (18.5±1.4 g N₂O-N m^–2 h^–1; –60.2±1.8 g CH₄ m^–2 h^–1). Significantly higher values of total N, C and pH in the organic layer, as well as increased soil moisture, especially in spring, in the stem areas, are likely to contribute to the higher N₂O fluxes within the stem area of the beech. Also for the spruce site, such differences in trace gas fluxes could be demonstrated to exist (mean annual N₂O emission within (a) stem areas: 9.7±0.9 g N₂O-N m^–2 h^–1 and (b) interstem areas: 6.2±0.6 g N₂O-N m^–2 h^–1; mean annual CH₄ uptake within (a) stem areas: –26.1±0.6 g CH₄ m^–2 h^–1 and (b) interstem areas: –38.4±0.8 g CH₄ m^–2 h^–1), though they were not as pronounced as at the beech site.     

Carbon isotope fractionation of methyl bromideduring agricultural soil fumigations

The isotopic composition ofmethyl bromide (CH₃Br) has been suggestedto be a potentially useful tracer forconstraining the global CH₃Br budget. Inorder to determine the carbon isotopiccomposition of CH₃Br emitted from the mostsignificant anthropogenic application(pre-plant fumigation) we directly measured the¹³C of CH₃Br released duringcommercial fumigation. We also measured theisotopic fractionation associated withdegradation in agricultural soil under typicalfield fumigation conditions. The isotopiccomposition of CH₃Br collected in soilseveral hours after injection of the fumigantwas –44.5 and this value increased to –20.7over the following three days. The mean kineticisotope effect (KIE) associated withdegradation of CH₃Br in agricultural soil(12) was smaller than the reported value formethylotrophic bacterial strain IMB-1, isolatedfrom previously fumigated agricultural soil,but was similar to methylotrophic bacterialstrain CC495, isolated from a pristine forestlitter zone. Using this fractionationassociated with the degradation of CH₃Brin agricultural soil and the mean¹³C of the industriallymanufactured CH₃Br (–54.4), we calculatethat the agricultural soil fumigation sourcehas a carbon isotope signature that ranges from–52.8 to –42.0. Roughly 65% ofindustrially manufactured CH₃Br is usedfor field fumigations. The remaining 35% isused for structural and post-harvestfumigations with a minor amount used duringindustrial chemical manufacturing. Assumingthat the structural and post-harvest fumigationsources of CH₃Br are emitted withoutsubstantial fractionation, we calculate thatthe ¹³C of anthropogenicallyemitted CH₃Br ranges from –53.2 to –47.5.     

Four years continuous record of CH4-exchange between the atmosphere and untreated and limed soil of a N-saturated spruce and beech forest ecosystem in Germany

In order to gain information about seasonal and interannual variations of CH₄-fluxes at a spruce control site, a limed spruce site and a beech site of the Höglwald Forest, Bavaria, Germany, complete annual cycles of CH₄-exchange between the soil and the atmosphere with 2-hourly resolution were followed for 4 consecutive years. The ranges of CH₄ fluxes observed for the different sites were: +12.4 to –69.4 g CH₄ m^–2 h^–1 (spruce control site), +11.7 to –51.4 g CH₄ m^–2 h^–1 (limed spruce site), and –4.4 to –167.3 g CH₄ m^–2 h^–1 (beech site). Lowest rates of atmospheric CH₄-uptake or even a weak net-emission of CH₄ by the soils were observed during winter/spring times, whereas highest rates of CH₄-uptake were always found in summer/spring. Over the entire observation period of 4 years, mean CH₄-uptake rates were –1.82 kg CH₄-C ha^–1 yr^–1 at the spruce control site, –1.31 kg CH₄-C ha^–1 yr^–1 at the limed spruce site, and –4.84 kg CH₄-C ha^–1 yr^–1 at the beech site. The results obtained in this study demonstrate that in view of the huge interannual variations in CH₄-fluxes of approx. 1 kg CH₄-C ha^–1 yr^–1, multiple year measurements of CH₄-fluxes are necessary to accurately characterize the sink strength of temperate forest for atmospheric CH₄. By comparison of CH₄-fluxes measured at the spruce control site and the limed spruce site, a significant negative effect of forest floor liming on CH₄-uptake could be demonstrated. Compared to the spruce stand, the beech stand showed on average approx. 3 times higher rates of atmospheric CH₄-uptake, most likely due to pronounced differences between both sites with regard to the organic layer structure and bulk density of the mineral soil. Regression analysis between CH₄-fluxes and environmental parameters revealed that at all sites the dominating factors regulating temporal variations of CH₄ fluxes were soil moisture and soil temperature. Field measurements of CH₄ concentrations in the soil profile and laboratory measurements of CH₄-oxidation and CH₄-production activity on soil samples taken from different soil depths showed that the CH₄-flux at the Höglwald Forest sites is the net-result of simultaneous occurring production and consumption of CH₄ within the soil. Highest CH₄-oxidation activity was found in the uppermost centimeters of the mineral soil, whereas highest potential CH₄-production activity was found in the organic layer.     

Influence of glycosylation inhibitors on dihydropyridine binding to cardiac cells

In primary cultures of neonatal rat heart cells we found a linear correlation between the number of L-type calcium channel-specific dihydropyridine (DHP) binding sites and spontaneous beating frequency (v).Formation of glycoproteins in tissue culture was suppressed by different inhibitors of N-glycosylation. This inhibition alters to a different extent the binding of the DHP ligand (+)-[methyl-³H]PN 200-110 and v. The most severe but reversible effect occurs at 6 g/ml tunicamycin (B_max 45% and v 6%, resp., of control), a slight increase in B_max at 0.1–0.5 mM castanospermine and 0.05–2.5 mM deoxymannojirimycin. The other inhibitors gave no significant alterations of B_max.     

N 5-Methyltetrahydromethanopterin: coenzyme M methyltransferase in methanogenic archaebacteria is a membrane protein

An assay is described that allows the direct measurement of the enzyme activity catalyzing the transfer of the methyl group from N ⁵-methyltetrahydromethanopterin (CH₃–H₄MPT) to coenzyme M (H–S–CoM) in methanogenic archaebacteria. With this method the topology, the partial purification, and the catalytic properties of the methyltransferase in methanol- and acetate-grown Methanosarcina barkeri and in H₂/CO₂-grown Methanobacterium thermoautotrophicum were studied. The enzyme activity was found to be associated almost completely with the membrane fraction and to require detergents for solubilization. The transferase activity in methanol-grown M. barkeri was studied in detail. The membrane fraction exhibited a specific activity of CH₃–S–CoM formation from CH₃–H₄MPT (apparent K _m=50 M) and H–S–CoM (apparent K _m=250 M) of approximately 0.6 mol·min^-1·mg protein^-1. For activity the presence of Ti(III) citrate (apparent K _m=15 M) and of ATP (apparent K _m=30 M) were required in catalytic amounts. Ti(III) could be substituted by reduced ferredoxin. ATP could not be substituted by AMP, CTP, GTP, S-adenosylmethionine, or by ATP analogues. The membrane fraction was methylated by CH₃–H₄MPT in the absence of H–S–CoM. This methylation was dependent on Ti(III) and ATP. The methylated membrane fraction catalyzed the methyltransfer from CH₃–H₄MPT to H–S–CoM in the absence of ATP and Ti(III). Demethylation in the presence of H–S–CoM also did not require Ti(III) or ATP. Based on these findings a mechanism for the methyltransfer reaction and for the activation of the enzyme is proposed.Abbreviations H₄MPT tetrahydromethanopterin - CH₃–H₄MPT N ⁵-methyl-H₄MPT - H–S–CoM 2-mercaptoethanesulfonate or coenzyme M - CH₃–S–CoM 2(methylthio)ethanesulfonate or methylcoenzyme M - SDS-PAGE sodium dodecylsulfate polyacrylamide gel electrophoresis - DTT dithiothreitol - MOPS morpholinopropanesulfonate - CHAPS 3-[(3-cholamidopropyl)-dimethylammonio]-1-propane-sulfonate - 1 U = 1 mol/min     

Analogs of thyrotropin-releasing hormone (TRH): Receptor affinities in brains,spinal cords,and pituitaries of different species

[³H](3-Me-His²) thyrotropin-releasing hormone ([³H]MeTRH) bound to TRH receptors in rodent, rabbit and dog brain and spinal cord (SC), and in rat, sheep, bovine and dog anterior pituitary (PIT) glands, with high affinity (dissociation constants, K_ds=5–9 nM; n=3–4) but to different densities of these sites (B _max range 6–145 fmol/mg protein) (rabbit SC>sheep PITG.pig brain>dog brain>rat brain>bovine and dog PIT). Various TRH analogs competitively inhibited [³H]MeTRH binding in these tissues with a similar rank order of potency: MeTRH>TRH> CG3703RX77368MK-771>TRH Glycinamide>Glu¹-TRHCG3509NVal²-TRH>>>TRH free acid>>>and cyclo-His-Pro, indicating a pharmacological similarity of CNS and pituitary TRH receptors. While most TRH analogs displaced [³H]MeTRH binding with a similar potency in the different species, TRH exhibited a 2-fold lower affinity in the rat and G.pig brain than in other tissues of other species. Similarly, CG3703 was 2.4–4.5 times more active in the rabbit brain than in the rodent and dog brain, and also more potent in the rabbit brain as compared to the sheep PIT. However, MK-771 and RX77368 had a similar affinity for the brain TRH receptors in the different species but RX77368 was 2-fold more active in the SC preparations and 3–4-fold less active in the sheep PIT when compared to the brain homogenates. RX 77368 exhibited the highest affinity for the dog PIT TRH receptor. In contrast, MK-771 showed a similar affinity for the brain, SC and PIT TRH receptor apart from in the rat PIT where it had the highest affinity. Similarly, TRH glycinamide was more active in the dog brain than rodent and rabbit brain. These data suggest that while the rank order of potency of TRH analogs is similar in the species examined, certain analogs appear to be more potent in certain tissues of some species than in others. In addition, the current results have shown that CG3703 is almost equipotent with RX77368 and MK-771 in most species but is substantially more active than its related analog, CG3509 in the brain, SC and PIT. Taken together, these observations may have some relevance to the future clinical applications of these metabolically stabilized TRH analogs.     

Experimental and computational study of the radiation-induced decomposition of formaldehyde. Implications to cometary nuclei

The radiation-induced decomposition of aqueous solutions of formaldehyde was studied at 298 and 77 K in order to obtain an insight into the possible role of ionizing radiation on cometary chemistry. Aqueous solutions of 1.0 mol dm^–3 formaldehyde were exposed to -radiation in the dose range from 0.01 kGy to 1.2 MGy. The radiation chemical yield of decomposition of formaldehyde was determined to be: G(–CH₂(OH)₂)=26.3±1.2 at 298 K and G0.48 at 77 K.Based on previous estimates of the total dose of ionizing radiation that comets have accumulated over 4.6 billion years, we predict a radiation-induced depletion of formaldehyde as a function of depth in comet nuclei: 100% destruction in the outer layers (0–20 m) and 10% destruction in the interior layers.A Portion of this work was presented at the XXVIII COSPAR Plenary Meeting (MF. 7) held at the Hague, The Netherlands on June 25–26, 1990.     

Control of carbon mineralization to CH4 and CO2 in anaerobic,Sphagnum-derived peat from Big Run Bog,West Virginia

The mineralization of organic carbon to CH₄ and CO₂ inSphagnum-derived peat from Big Run Bog, West Virginia, was measured at 4 times in the year (February, May, September, and November) using anaerobic, peat-slurry incubations. Rates of both CH₄ production and CO₂ production changed seasonally in surface peat (0–25 cm depth), but were the same on each collection date in deep peat (30–45 cm depth). Methane production in surface peat ranged from 0.2 to 18.8 mol mol(C)^–1 hr^–1 (or 0.07 to 10.4 g(CH₄) g^–1 hr^–1) between the February and September collections, respectively, and was approximately 1 mol mol(C)^–1 hr^–1 in deep peat. Carbon dioxide production in surface peat ranged from 3.2 to 20 mol mol(C)^–1 hr^–1 (or 4.8 to 30.3 g(CO₂) g^–1 hr^–1) between the February and September collections, respectively, and was about 4 mol mol(C)^–1 hr^–1 in deep peat. In surface peat, temperature the master variable controlling the seasonal pattern in CO₂ production, but the rate of CH₄ production still had the lowest values in the February collection even when the peat was incubated at 19°C. The addition of glucose, acetate, and H₂ to the peat-slurry did not stimulate CH₄ production in surface peat, indicating that CH₄ production in the winter was limited by factors other than glucose degradation products. The low rate of carbon mineralization in deep peat was due, in part, to poor chemical quality of the peat, because adding glucose and hydrogen directly stimulated CH₄ production, and CO₂ production to a lesser extent. Acetate was utilized in the peat by methanogens, but became a toxin at low pH values. The addition of SO₄ ^2– to the peat-slurry inhibited CH4 production in surface peat, as expected, but surprisingly increased carbon mineralization through CH4 production in deep peat. Carbon mineralization under anaerobic conditions is of sufficient magnitude to have a major influence on peat accumulation and helps to explain the thin (< 2 m deep), old (> 13,000 yr) peat deposit found in Big Run Bog.     

Methane emissions from wet grasslands on peat soil in a nature preserve

The area of wet grasslands on peat soil in the Netherlands is slowly increasing at the expense of drained, agriculturally used grasslands. This study aimed (i) to assess the contribution of wet grasslands on peat soil to methane (CH₄) emissions, and (ii) to explain differences among sites and between years in order to improve our understanding of controlling factors. For these purposes, a field study was conducted in the period 1994–1996 in the nature preserve Nieuwkoopse Plassen, which is a former peat mining and agricultural area. Net CH₄ emissions were measured weekly to monthly with vented closed flux chambers at three representative sites, and at ditches near these sites. Three-years average of CH₄ emissions was 7.9 g CH₄ m^–2 yr^–1 for Drie Berken Zudde, 13.3 for Koole, and 20.4 for Brampjesgat. Ditches near the sites emitted 4.2–22.5 g CH₄ m^–2 yr^–1. The time-course of CH₄ emissions for all experimental sites and years was fit with a multiple linear regression model with ground water level and soil temperature as independent variables. Lowering or raising the ground water level by 5 cm could decrease or increase CH₄ emissions by 30–50%. Therefore, ground water level management of these grasslands should be done with care.     

Effect of urea fertilizer and environmental factors on CH4 emissions from a Louisiana,USA rice field

Methane emissions from a flooded Louisiana, USA, rice field were measured over the first cropgrowing season. Microplots contained the semidwarf Lemont rice cultivar drill seeded into a Crowley silt loam soil (Typic Albaqualfs). Urea fertilizer was applied preflood at rates of 0, 100, 200 and 300 kg N ha^–1. Emissions of CH₄ from the plots to the atmosphere were measured over a 86-d sampling period until harvest. Methane samples were collected in the morning hours (0730–0930) using a closed-chamber technique. Emissions of CH₄ were highly variable over the first cropping season and a significant urea fertilizer effect was observed. Two peak CH₄ emission periods were observed and occurred about 11 d after panicle differentiation and during the ripening stages. Maximum CH₄ emmissions from the 0, 100, 200 and 300 urea-N treatments were 6.0, 8.9, 9.8 and 11.2 kg CH₄ ha^–1 d^–1, respectively. These flux measurements corresponded to approximately 210, 300, 310 and 360 kg CH₄ evolved ha^–1 over the 86-d sampling period for the 4 treatments.     

Contribution of methanol to the production of methane and its <Superscript>13</Superscript>C-isotopic signature in anoxic rice field soil

Conversion of methanol to CH₄ has a large isotope effect so that a small contribution of methanol-dependent CH₄ production may decrease the ¹³CH₄ of total CH₄ production. Therefore, we investigated the role of methanol for CH₄ production. Methanol was not detectable above 10 M in anoxic methanogenic rice field soil. Nevertheless, addition of ¹³C-labeled methanol (99% enriched) resulted in immediate accumulation of ¹³CH₄. Addition of 0.1 M ¹³C-methanol resulted in increase of the ¹³CH₄ from –47 to –6 within 2 h, followed by a slow decrease. Addition of 1 M ¹³C-methanol increased ¹³CH₄ to +500 within 4 h, whereas 10 M increased ¹³CH₄ to +2500 and continued to increase. These results indicate that the methanol concentrations in situ, which diluted the ¹³C-methanol added, were 0.1 M and that the turnover of methanol contributed only about 2% to total CH₄ production at 0.1 M. However, contribution increased up to 5 and 17% when 1 and 10 M methanol were added, respectively. Anoxic rice soil that was incubated at different temperatures between 10 and 37 °C exhibited maximally 2–6% methanol-dependent methanogenesis about 1–2 h after addition of 1 M ¹³C-methanol. Only at 50 °C, contribution of methanol to CH₄ production reached a maximum of 10%. After longer (7–10 h) incubation, however, contribution generally was only 2–4%. Methanol accumulated in the soil when CH₄ production was inhibited by chloroform. However, the accumulated methanol accounted for only up to 0.7 and 1.2% of total CH₄ production at 37 and 50 °C, respectively. Collectively, our results show that methanol-dependent methanogenesis was operating in anoxic rice field soil but contributed only marginally to total CH₄ production and the isotope effect observed at both low and high temperature.     

Determinants of spatial variability of methane emissions from wet grasslands on peat soil

Methane (CH₄) emissions from soils, representing the consequence of CH₄ production, CH₄ consumption and CH₄ transport, are poorly characterised and show a large spatial variability. This study aimed to assess the determinants of field-scale spatial variability of CH₄ emissions from wet grasslands on peat soil. Mean CH₄ emission rates of a three-year experiment at 18 plots distributed over three sites in the nature preserve Nieuwkoopse Plassen on peat soil in the Netherlands were related to CH₄ production and CH₄ consumption capacities of soil layers, and to soil and vegetation characteristics. Spatial variability of CH₄ emissions and possible determining factors was high. Annual CH₄ emissions ranged from 3 to 37 g CH₄ m^–2 yr^–1. Coefficients of variation (CV) of CH₄ emissions were on average 37% among sites and 83% within sites. Most important determinants of spatial variability were CH₄ production capacity (average: 211 ng CH₄ g^–1 dry soil h^–1; CV: 131%) and aboveground biomass of sedges (Carex spp.) (average: 0.45 g dm^–2; CV: 127%) (P<0.01). Sedges may affect CH₄ emissions by stimulating CH₄ transport from anaerobic layers to the surface via their vascular system and/or by serving as substrate for methanogens. For extrapolation of CH₄ emissions to larger areas, best results will be obtained by using factors that are easy to determine, like vegetation.     

Effect of microrelief and vegetation on methane emission from wet polygonal tundra, Lena Delta, Northern Siberia

The effect of microrelief and vegetation on methane (CH₄) emission was investigated in a wet polygonal tundra of the Lena Delta, Northern Siberia (72.37N, 126.47E). Total and plant-mediated CH₄ fluxes were measured by closed-chamber techniques at two typical sites within a low-centred polygon. During the study period, total CH₄ flux averaged 28.0±5.4mgm^–2d^–1 in the depressed polygon centre and only 4.3±0.8mgm^–2d^–1 at the elevated polygon rim. This substantial small-scale spatial variability of CH₄ emission was caused by strong differences of hydrologic conditions within the microrelief of the polygon, which affected aeration status and organic matter content of the soils as well as the vegetation cover. Beside water table position, the vegetation cover was a major factor controlling CH₄ emission from polygonal tundra. It was shown that the dominant vascular plant of the study area, Carex aquatilis, possesses large aerenchyma, which serve as pathways for substantial plant-mediated CH₄ transport. The importance of plant-mediated CH₄ flux was strongly influenced by the position of the water table relative to the main root horizon. Plant-mediated CH₄ transport accounted for about two-thirds of the total flux in the wet polygon centre and for less than one-third of the total flux at the moist polygon rim. A clipping experiment and microscopic-anatomical studies suggested that plant-mediated CH₄ transport via C. aquatilis plants is driven only by diffusion and is limited by the high diffusion resistance of the dense root exodermes.     

Biosynthetic relationships between β-diketones and esterified alkan-2-ols deduced from epicuticular wax of barley mutants

Summary The synthesis and deposition of the epicuticular waxes in barley are determined by the eceriferum (cer) loci. On the uppermost internodes, leaf sheaths and spikes of the wild type Bonus, the -diketones and hydroxy--diketones (almost entirely hentriacontan-14,16-dione and 25-hydroxyhentriacontan-14,16-dione, respectively) are the predominating wax classes. In these same waxes esters containing alkan-2-ols (primarily tridecan-2-ol and pentadecan-2-ol) are present. Analyses of the -diketone content and ester composition of waxes from Bonus and eight cer mutants led to the hypothesis that these two wax classes are synthesized from common precursors, namely C₁₄ and C₁₆ chain elongation intermediates. Subsequently, decarboxylation with a simultaneous retention of the carbonyl groups in the -position would lead to the esterified alkan-2-ols while retention of two carbonyl groups plus further elongation would lead to the -diketones. This closer biosynthetic relationship of the -diketones to the esterified alkan-2-ols than to the other lipid classes-hydrocarbons, alkan-1-ol containing esters, aldehydes, alkan-1-ols and free acids—found in all barley waxes is illustrated schematically and the approximate sites of action of the cer loci indicated.     

Methane and nitrous oxide exchange in differently fertilised grassland in southern Germany

We examined the effect of fertilisation (200 kg cattle slurry-N ha^–1 year^–1) on the exchange of N₂O and CH₄ in the soil–plant system of meadow agroecosystems in southern Germany. From 1996 to 1998, we regularly determined the gas fluxes (closed chamber method) and associated environmental parameters. N₂O and CH₄ fluxes were not significantly affected by fertilisation. N₂O fluxes at the unfertilised and fertilised plots were small, generally between 50 and –20 g N m^–2 h^–1. We identified some incidents of N₂O uptake. CH₄-C fluxes ranged from 1.3 to –0.2 mg m^–2 h^–1 and were not significantly different from 0 at both plots. We budgeted an annual net emission of 15.5 and 29.6 mg m^–2 N₂O-N and an annual CH₄-C net emission of 184.2 and 122.7 mg m^–2 at the unfertilised and fertilised plots, respectively. Apparently, rapid N mineralization and uptake in the densely rooted topsoil prevents N losses and the inhibition of CH₄ oxidation.     

Bacterial Processes of the Methane Cycle in Bottom Sediments of Lake Baikal

The activity of methanogenic and methanotrophic bacteria was evaluated in bottom sediments of Lake Baikal. Methane concentration in Baikal bottom sediments varied from 0.0053 to 81.7 ml/dm³. Bacterial methane was produced at rates of 0.0004–534.7 l CH₄/(dm³ day) and oxidized at rates of 0.005–1180 l CH₄/(dm³ day). Peak methane production and oxidation were observed in Frolikha Bay near a methane vent. Methane was emitted into water at rates of 49.2–4340 l CH₄/(m² day). Rates of bacterial methane oxidation in near-bottom water layers ranged from 0.002 to 1.78 l/(l day). Methanogens and methanotrophs were found to play an important role in the carbon cycle through all layers of sediments, particularly in the areas of methane vent and gas-hydrate occurrence.     

Unique transglycosylation potential of extracellular α-d-galactosidase from Talaromyces flavus

The transglycosylation potential of the extracellular α-d-galactosidase from the filamentous fungus Talaromyces flavus CCF 2686, chosen as the best enzyme from the screening, was investigated using a series of sterically hindered alcohols (primary, secondary and tertiary) as galactosyl acceptors. Nine alkyl α-d-galactopyranosides derived from the following alcohols – tert-butyl alcohol, 2-methyl-2-butyl alcohol, 2-methyl-1-propyl alcohol, 2,2,2-trifluoroethyl alcohol, 2-propyn-1-ol, n-pentyl alcohol, 3,5-dihydroxybenzyl alcohol, 1-phenylethyl alcohol and 1,4-dithio-dl-threitol – were prepared on a semi-preparative scale. This demonstrates a broad synthetic potential of the T. flavus α-d-galactosidase that has not been observed with another enzyme tested. Moreover, this enzyme exhibits good transglycosylation yields (6–34%). The enzymatic synthesis of tert-butyl α-d-galactopyranoside by transglycosylation was studied in detail.