Substrate and Donor Specificity of Glycosyl Transferases

It has been shown that all selectins recognize the carbohydrate epitopes sialyl Lewis^x and sialyl Lewis^a. For the establishment of the structure-activity relationship, the efficient synthesis of these tetrasaccharides and derivatives is therefore of vital interest. The glycosyl transferase-mediated approach is summarized with emphasis on the use of modified acceptors and modified sugar-nucleotide donors. A survey of the involved enzymes: (1-3) and (1-4)galactosyl transferases, (2-3)sialyl transferase, FucT III and FucT VI reveals that the enzymatic synthesis is highly efficient for the rapid preparation of sialyl Lewis^x- and sialyl Lewis^a-derivatives.     

Effect of chemical modifiers of amino acid residues on proton conduction by the H+-ATPase of mitochondria

The effect of chemical modifiers of amino acid residues on the proton conductivity of H⁺-ATPase in inside out submitochondrial particles has been studied. Treatment of submitochondrial particles prepared in the presence of EDTA (ESMP) with the arginine modifiers, phenylglyoxal or butanedione, or the tyrosine modifier, tetranitromethane, caused inhibition of the ATPase activity. Phenylglyoxal and tetranitromethane also caused inhibition of the anaerobic release of respiratory H⁺ in ESMP as well as in particles deprived of F₁ (USMP). Butanedione treatment caused, on the contrary, acceleration of anaerobic proton release in both particles. The inhibition of proton release caused by phenylglyoxal and tetranitromethane exhibited in USMP a sigmoidal titration curve. The same inhibitory pattern was observed with oligomycin and withN,N-dicyclohexylcarbodiimide. In ESMP, relaxation of H⁺ exhibited two first-order phases, both an expression of the H⁺ conductivity of the ATPase complex. The rapid phase results from transient enhancement of H⁺ conduction caused by respiratory H⁺ itself. Oligomycin,N,N-dicyclohexylcarbodiimide, and tetranitromethane inhibited both phases of H⁺ release, and butanedione accelerated both. Phenylglyoxal inhibited principally the slow phase of H⁺ conduction. In USMP, H⁺ release followed simple first-order kinetics. Oligomycin depressed H⁺ release, enhanced respiratory H⁺, and restored the biphasicity of H⁺ release. Phenylglyoxal and tetranitromethane inhibited H⁺ release in USMP without modifying its first-order kinetics. Butanedione treatment caused biphasicity of H⁺ release from USMP, introducing a very rapid phase of H⁺ release. Addition of soluble F₁ to USMP also restored biphasicity of H⁺ release. A mechanism of proton conduction by F _o is discussed based on involvement of tyrosine or other hydroxyl residues, in series with the DCCD-reactive acid residue. There are apparently two functionally different species of arginine or other basic residues: those modified by phenylglyoxal, which facilitate H⁺ conduction, and those modified by butanedione, which retard H⁺ diffusion.     

Negative-ion fast atom bombardment and electrospray ionization tandem mass spectrometry for characterization of sulfated and sialyl Lewis-type glycosphingolipids

Structural characterization of sulfated and sialyl Lewis (Le)-type glycosphingolipids performed by fast atom bombardment (FAB) and electrospray ionization (ESI) mass spectrometry is described. Both FAB and ESI collision-induced dissociation tandem mass spectrometry (CID-MS/MS) of acidic glycosphingolipids allowed identification of the sulfated or sialyl sugar, and provided information on the saccharide chain sequence. The negative-ion tandem FABMS of sulfated Le-type glycosphingolipids having the non-reducing end trisaccharide ion as the precursor can be used to differentiate the Le^a- and Le^X-type oligosaccharides. The ESI CID-MS/MS of multiple-charged ions provided even more detailed structural information, and some of the useful daughter ions appeared with higherm/z values than the precusor because of a lower charge-state. These methodologies can be applied to the structural analyses of glycoconjugates with much larger molecular masses and higher polarity, such as the poly-sulfated and sialyl analogues.Abbreviations CID collision-induced dissociation - ESI electrospray ionization - FABMS fast atom bombardment mass spectrometry - Fuc fucose - Gal galactose - GlcNAc N-acetylglucosamine - Le Lewis - Le^a Lewis^a - Le^X Lewis^X - MS/MS mass spectrometry/mass spectrometry - NeuAc N-acetylneuraminic acid - 3-SO₄-Le^a 3-sulfated Le^a pentaosyl ceramide - 3-SO₄-Le^X 3-sulfated Le^X pentaosyl ceramide - 2,3-SO₄-Le^X 2,3-disulfated Le^X pentaosyl ceramide - 3-S-Le^a 3-sialyl Le^a pentaosyl ceramide - 3-S-Le^x 3-sialyl Le^X heptaosyl ceramide - 3-S-Le^X-Le^X 3-sialyl-Le^x-Le^x octaosyl ceramide.     

Enzymic synthesis,chemical characterisation and Sda activity of GalNAcß1-4[NeuAcα2-3]Galß1-4GlcNAc and GalNAcß1-4[NeuAcα2-3]Galß1-4Glc

The tetrasaccharides GalNAcß1-4[NeuAc2-3]Galß1-4Glc and GalNAcß1-4[NeuAc2-3]Galß1-4GlcNAc were synthesised by enzymic transfer of GalNAc from UDP-GalNAc to 3-sialyllactose (NeuAc2-3Galß1-4Glc) and 3-sialyl-N-acetyllactosamine (NeuAc2-3Galß1-4GlcNAc). The structures of the products were established by methylation and¹H-500 MHz NMR spectroscopy. In Sd^a serological tests the product formed with 3-sialyl-N-acetyllactosamine was highly active whereas that formed with 3-sialyllactose had only weak activity.     

Endogenous abscisic acid and 2-trans-abscisic acid in alternate bearing ‘Wilking’ mandarin trees

The relationship of abscisic acid (ABA) and 2-trans-abscisic acid (t-ABA) to alternate bearing has been examined in Wilking mandarin (Citrus reticulata Blanco) trees. Leaves, stems and buds of trees loaded with fruit (on trees) had 4.3, 6.0 and 2.2 fold higher ABA levels than the corresponding organs from off trees. Leaves had higher ABA levels than stems and buds in both on and off trees. t-ABA was non-detectable in Wilking leaf, stem and bud tissue. Amounts of t-ABA not exceeding 40% of the ABA content, were found in Shamouti and Valencia orange buds and in Wilking fruit peel.The elevated levels of ABA in on tree organs may reflect a stress imposed by the fruit overload.     

Growth,acetylene reduction activity and localization of nitrogenase in relation to vesicle formation in Frankia strains Cc1.17 and Cp1.2

A comparative study was conducted on the effect of NH₄Cl on growth, vesicle formation and formation of nitrogenase of Frankia strains Cc1.17 and Cp1.2, derived from root nodules of Colletia cruciata and Comptonia peregrina, respectively. On a medium without combined nitrogen (P-N), both strains formed spherical cells, called vesicles, like many other Frankia strains. Data are presented on the number of vesicles per mg protein, after cultivation in media with sodium propionate as C-source without combined nitrogen (P-N) or with 0.2 g NH₄Cl/l (P+N). Strain Cp1.2 as may other Frankia strains, showed on P+N medium a very strong reduction of vesicle formation of 99% relative to the number of vesicles formed on P-N medium, after 11 days growth. However, in strain Cc11.17 this reduction was only 70%. The occurence of relatively large numbers of vesicles in P+N media has not yet been reported for other Frankia strains. No acetylene reduction activity was found in NH ₄ ⁺ -grown cells. The regulation of induction of nitrogenase in Frankia by NH₄Cl was tested by immuno-gelectrophoresis using antisera against nitrogenase of Rhizobium leguminosarum PRE. The component I of the enzyme showed crossreactivity while the component II had only a weak crossreaction. The experiments indicated that no nitrogenase was detectable in the NH ₄ ⁺ -grown cells. For the localization of nitrogenase, relative amounts of the enzyme were compared in whole cells and vesicle-enriched fractions. Western blots showed a significant enrichment of nitrogenase in the vesicle fractions, which indicated that most of the nitrogenase was localized in the vesicle.     

Net N input and riverine N export from Illinois agricultural watersheds with and without extensive tile drainage

Some of the largest riverine N fluxes in the continental USA have been observed in agricultural regions with extensive artificial subsurface drainage, commonly called tile drainage. The degree to which high riverine N fluxes in these settings are due to high net N inputs (NNI), greater transport efficiency caused by the drainage systems, or other factors is not known. The objective of this study was to evaluate the role of tile drainage by comparing NNI and riverine N fluxes in regions of Illinois with similar climate and crop production practices but with different intensities of tile drainage. Annual values of NNI between 1940 and 1999 were estimated from county level agricultural production statistics and census estimates of human population. During 1945–1961, riverine nitrate flux in the extensively tile drained region averaged 6.6kgNha^–1year^–1 compared to 1.3 to 3.1kgNha^–1 for the non-tile drained region, even though NNI was greater in the non-tile drained region. During 1977–1997, NNI to the tile-drained region had increased to 27kgNha^–1year^–1 and riverine N flux was approximately 100% of this value. In the non-tile-drained region, NNI was approximately 23kgNha^–1year^–1 and riverine N flux was between 25% and 37% of this value (5 to 9kgNha^–1year^–1). Denitrification is not included in NNI and, therefore, any denitrification losses from tile-drained watersheds must be balanced by other N sources, such as depletion of soil organic N or underestimation of biological N fixation. If denitrification and depletion of soil organic N are significant in these basins, marginal reductions in NNI may have little influence on riverine N flux. If tile drained cropland in Illinois is representative of the estimated 11 million ha of tile drained cropland throughout the Mississippi River Basin, this 16% of the drainage area contributed approximately 30% of the increased nitrate N flux in the Lower Mississippi River that occurred between 1955 and the 1990s.     

Structure of a new nonasaccharide isolated from human milk: VI2Fuc,V4Fuc,III3Fuc-p-lacto-N-hexaose

The structure of a new nonasaccharide isolated from human milk has been investigated. By using methylation analysis, FAB-MS and¹H-and¹³C-NMR spectroscopy as basic methods of structural investigation, this oligosaccharide was identified as VI²--Fuc,V⁴-Fuc,III³--Fuc-p-lacto-n-hexaose: Fuc1-2Gal1-3[Fuc1-4]GlcNAc1-3Gal1-4[Fuc1-3]GlcNAc1-3Gal1-4Glc.Abbreviations COSY correlation spectroscope - DP degree of polymerisation - FAB-MS fast atom bombardment-mass spectrometry - HPLC high performance liquid chromatography - NMR nuclear magnetic resonance - GLC gas-liquid chromatography     

1H and13C-NMR analysis of four pentasaccharides from urine of blood-group A and B,Leb adults. Confirmation of the structure of two new oligosaccharides: Fuc(α1–2)[GalNAc(α1–3)]Gal(β1–3)[Fuc(α1–4)]Glc and Fuc(α1–2)[Gal(α1–3)]Gal(β1–3)[Fuc(α1–4)]Glc

The major pentasaccharides Fuc(1-2)[GalNAc(1-3)]Gal(1-4)[Fuc(1-3)]Glc and Fuc(1-2) [Gal(1-3)]Gal(1-4)[Fuc(1-3)]Glc, which are normally present in the urine of bloodgroup A Le^b and B Le^b healthy subjects, were each found to be contaminated by a minor component when analysed by¹H-NMR. The determination of these structures, Fuc(1-2) [GalNAc(1-3)]Gal(1-3)[Fuc(1-4)]Glc and Fuc(1-2) [Gal(1-3)]Gal(1-3)[Fuc(1-4)]Glc, was based on the results of methylation analysis and¹H/¹³C-NMR spectroscopy.Abbreviations HPLC high performance liquid chromatography - GLC gas liquid chromatography - NMR nuclear magnetic resonance - COSY correlation spectroscopy - Gal d-galactopyranose - GalNAc 2-acetamido-2-deoxy-d-galactopyranose - Glc d-glucopyranose - Fuc l-fucopyranose - LNDFH I lacto-N-difucohexaose I (Le^b determinant     

Effect of oxygen on growth and respiration of potato tuber callus

Growth and oxygen uptake of potato callus is faster in an oxygen-enriched atmosphere (70% oxygen, v/v; oxygen-callus) than in air (20% oxygen, v/v; air-callus). Especially the non-mitochondrial, so-called residual respiration is increased in oxygen-callus. The capacities of the mitochondrial respiratory pathways (cytochrome pathway, V_cyt and alternative pathway, V_alt) are also higher in this callus. In both callus types only a small part of the alternative pathway capacity is used in uninhibited respiration. The lower oxygen uptake of air-callus at normal air oxygen pressures is partially due to diffusional impedance. Measurement of the respiratory parameters of air-callus in oxygen-saturated medium leads to higher values than measurement in air-saturated medium, although these values are still lower than those of oxygen-callus.ATP-production was calculated from the oxygen-uptake data and compared with the dry weight production of the callus to give values of 10.0 and 10.8 g dry weight produced.-mol ATP^-1, for air-callus and oxygen-callus respectively. As no harmful side-effects are observed, cultivation of callus under elevated oxygen pressures may be useful, when rapid callus-growth is necessary.Abbreviations AA antimycin A; A; - BHAM benzohydroxamate - DW dry weight - FW fresh weight - 8-OHQ 8-hydroxyquinolin - RC respiratory control - SHAM salicylhydroxamate     

Opioid and Cannabinoid Receptors Share a Common Pool of GTP-Binding Proteins in Cotransfected Cells, But Not in Cells Which Endogenously Coexpress the Receptors

1. Opioid (, , ) and cannabinoid (CB1, CB2) receptors are coupled mainly toG_i/G_o GTP-binding proteins. The goal of the present study was to determine whether different subtypes of opioid and cannabinoid receptors, when coexpressed in the same cell, share a common reservoir, or utilize different pools, of G proteins.2. The stimulation of [³⁵S]GTPS binding by selective opioid and cannabinoid agonists was tested in transiently transfected COS-7 cells, as well as in neuroblastoma cell lines. In COS-7 cells, cotransfection of - and -opioid receptors led to stimulation of [³⁵S]GTPS binding by either -selective (DAMGO) or -selective (DPDPE) agonists. The combined effect of the two agonists was similar to the effect of either DAMGO or DPDPE alone, suggesting the activation of a common G-protein reservoir by the two receptor subtypes.3. The same phenomenon was observed when COS-7 cells were cotransfected with CB1 cannabinoid receptors and either - or -opioid receptors.4. On the other hand, in N18TG2 neuroblastoma cells, which endogenously coexpress CB1 and -opioid receptors, as well as in SK-N-SH neuroblastoma cells, which coexpress - and -opioid receptors, the combined effects of the various agonists (the selective cannabinoid DALN and the selective opioids DPDPE and DAMGO) were additive, implying the activation of different pools of G proteins by each receptorsubtype.5. These results suggest a fundamental difference between native and artificially transfected cells regarding the compartmentalization of receptors and GTP-binding proteins.     

Formation of the imidazolides of dinucleotides under potentially prebiotic conditions

Summary Imidazolides of dinucleotides such as ImpApA can be formed from the corresponding dinucleotides in a two-stage process, which gives up to 15% yields under potentially prebiotic conditions. First a solution of the dinucleotide and sodium trimetaphosphate is dried out at constant temperature and humidity. This produces polyphosphates such as pnApA in excellent yield (80%). The products are dissolved in water, imidazole is added, and the solution is dried out again. This yields the 5-phosphorimidazolides.Abbreviations P₃! trimetaphosphate - A adenosine - U uridine - EDTA ethylenediaminetetraacetic acid - Ap adenosine 2(3)-phosphate - Ap! adenosine cyclic 2:3-phosphate - pA adenosine 5-phosphate - pA²p adenosine 2, 5-diphosphate - pA³p adenosine 3, 5-diphosphate - pAp! 5-phospho-adenosine cyclic 2:3-phosphate - ATP adenosine 5-triphosphate - ImpA adenosine 5-phosphorimidazolide - A²pA adenylyl-[25]-adenosine - A³pA adenylyl-[35]-adenosine - A²pU adenylyl-[25]-uridine - A³pU adenylyl-[35]-uridine - pA²pA 5-phosphoadenylyl-[25]-adenosine - pA³pA 5-phospho-adenylyl-[35]-adenosine - pA²pU 5-phospho-adenylyl-[25]-uridine - pA³pU 5-phospho-adenylyl-[35]-uridine - pApN (N= A, U) 5-phosphate of a dinucleoside phosphate - p_nApN (N = A, U; n = 2, 3, 4.) 5-polyphosphate of a dinucleoside phosphate - ImpA²pA imidazolide of pA²pA - ImpA³pA imidazolide of pA³pA - ImpA²pU imidazolide of pA²pU - ImpA³pU imidazolide of pA³pU - ImpApN imidazolide of pApN     

Action of rat liver Galβ1-4GlcNAc α(2-6)-sialyltransferase on Manβ1-4GlcNAcβ-OMe,GalNAcβ1-4GlcNAcβ-OMe,Glcβ1-4GlcNAcβ-OMe and GlcNAcβ1-4GlcNAcβ-OMe as synthetic substrates

Incubation of synthetic Man\1-4GlcNAc-OMe, GalNAc1-4GlcNAc-OMe, Glc1-4GlcNAc-OMe, and GlcNAc1-4GlcNac-OMe with CMP-Neu5Ac and rat liver Gal1-4GlcNAc (2-6)-sialyltransferase resulted in the formation of Neu5Ac2-6Man1-4GlcNAc-OMe, Neu5Ac2-6GalNAc1-4GlcNAc-OMe, Neu5Ac2-6Glc1-4GlcNAc-OMe and Neu5Ac2-6GlcNAc1-4GlcNAc-OMe, respectively. Under conditions which led to quantitative conversion of Gal1-4GlcNAc-OEt into Neu5Ac2-6Gal1-4GlcNAc-OEt, the aforementioned products were obtained in yields of 4%, 48%, 16% and 8%, respectively. HPLC on Partisil 10 SAX was used to isolate the various sialyltrisaccharides, and identification was carried out using 1- and 2-dimensional 500-MHz¹H-NMR spectroscopy.Abbreviations 2D 2-dimensional - CMP cytidine 5-monophosphate - CMP-Neu5Ac cytidine 5-monophospho--N-acetylneuraminic acid - COSY correlation spectroscopy - DQF double quantum filtered - HOHAHA homonuclear Hartmann-Hahn - MLEV composite pulse devised by M. Levitt - Neu5Ac N-acetylneuraminic acid - Neu5Ac2en 2-deoxy-2,3-didehydro-N-acetylneuraminic acid     

Voltage clamping with single microelectrodes: Comparison of the discontinuous mode and continuous mode using the Axoclamp 2A amplifier

Summary The voltage clamp technique is a powerful method for studying the physiology of excitable membrane. This technique has made possible the determination of ionic responses generated by activation of either receptor-mediated or voltage-dependent processes. The development of the whole-cell, tight-seal voltage clamp method has allowed the analysis and examination of membrane physiology at the single cell level. The method allows the characterization of voltage-dependent ionic conductances both at the macroscopic (whole-cell) and at the microscopic (unitary conductance or single channel) level in cells less than 10 µm in diameter, a feat difficult to achieve with conventional fine-tipped micropipettes.In this paper, several methologies used for culturing neuronal and non-neuronal cells in the laboratory are described. A comparison between the two modes of voltage clamp using blunt-tipped patch-microelectrodes, the switching (discontinuous) and the non-switching (continuous) modes, of the Axoclamp-2A amplifier is made. Some results on membrane currents obtained from neuronal and non-neuronal cells using the single electrode whole-cell tight-seal voltage clamp is illustrated. The possible existence of two inactivating K⁺ currents, one dependent on Ca⁺⁺ the other is not, is discussed.     

Cajaflavanone and cajanone released from Cajanus cajan (L. Millsp.) roots induce nod genes of Bradyrhizobium sp.

A broad-host-range plasmid (pEA2-21) containing a Bradyrhizobium sp (F-4) nod DABC-lacZ translation fusion was constructed and used to monitor nod gene expression in response to pigeonpea root exudate. Two nod-inducing compounds were isolated and identified. Spectral analysis using ultraviolet absorption, infrared spectra, proton nuclear magnetic resonance, and mass spectrometry showed that the two inducers were 5,4-dihydroxy-6-(3-methyl-2-butenyl)-2, 2-dimethyl pyrano-[5, 6:7, 8]-flavanone (cajaflavanone) and 2,4,5-trihydroxy-5-isopentenyl-6, 7-dimethylchromene iso-flavanone (cajanone). When pEA2-21 was introduced into Rhizobium trifolii and R. meliloti cajanone and cajaflavanone did not induce nod gene indicating that specificity of induction appears to be influenced by the host-strain genome.     

α-Thalassemia and the production of different α chain variants in heterozygotes

The production of five chain variants (Hb G-Georgia, Hb St. Luke's, Hb Lloyd, Hb Montgomery, and Hb G-Philadelphia) in heterozygotes was evaluated through hematological observations, hemoglobin quantification, and biosynthetic studies. All heterozygotes for Hb St. Luke's and Hb Lloyd and most heterozygotes with Hb G-Georgia and Hb Montgomery had normal hematology and average / values of about 1.1. They were assigned a normal genotype (^G/), although the proportions of Hb St. Luke's and Hb G-Georgia were low (10 to 13%) and those of Hb Lloyd and Hb Montgomery twice as high (20%). Data from short-term incubations confirmed this genotype for some of these heterozygotes. Isolated Hb St. Luke's and Hb G-Georgia gave low ^G/ values (0.2 and 0.3) indicating that these Hb variants were defective at the level of Hb assembly. Isolated Hb Montgomery and Hb G-Philadelphia, however, gave higher ^G/ values of 0.6 and 0.8, respectively. A second type of variability existed among Hb G-Georgia (20 vs. 13%), Hb Montgomery (28 vs. 20%), and Hb G-Philadelphia (47 vs. 34%) heterozygotes, in whom the levels of Hb G differed. The occurrence of higher levels of these three chain heterozygosities was associated with hematological or biosynthetic evidence of a mild or moderate chain deficiency due to an -thalassemia-2 heterozygosity (^G/⁰ or ^0G/) or a homozygosity (^0G/⁰), respectively.This study was supported in part by USPHS Research Grants HLB-05168 and HLB-15158.     

Potent,extra-channel influence of several calcium-channel modulators on striatal binding of [3H]tyramine

A number of Ca²⁺-, K⁺-, and Na⁺-channel modulators has been tested with respect to their effects on [³H]tyramine (TY) binding, as a putative marker for the vesicular dopamine (DA) transporter in striatal membrane preparations containing vesicle ghosts. Among organic Ca²⁺-channel modulators, the diphenylalkylamines tested consistently inhibited TY binding: the order of potency was prenylamine>lidoflazine>flunarizine>cinnarizine, with K_i values of 0.1, 0.2, 0.5 and 1.2 M, respectively. Low (up to 100 nM) concentrations of prenylamine did competitively inhibit TY binding, and higher concentrations provoked a mixed-type inhibition. Furthermore, LIGAND-analysis of competition curves revealed a high- and a low-affinity binding site for prenylamine and flunarizine. The TY binding process was also sensitive to selected K⁺- and Na⁺-channel modulators. Since several Ca²⁺-antagonists are known to affect H⁺-ATPase and the bioenergetics of catecholamine storage vesicles in chromaffin granules, thus affecting monoamine storage, the energy requirements for the formation of the TY/carrier complex were here assessed, assuming similarity between chromaffin granules and synaptic vesicles. TY binding, though not reflecting endovesicle-sequestered TY, was indeed strongly sensitive (with K_i coefficients in the fM or low nM range) to the dissipation of the vesicular transmembrane proton concentration ( pH), electrical ( ), and proton electrochemical ( H⁺) gradients, provoked by a number of specifically targeted agents. It is concluded that Ca²⁺-channel agents of the diphenylalkylamine group may directly affect striatal TY binding due to an extrachannel-regulated competition with TY for the vesicular carrier of DA, as well indirectly, by disruption of the transmembrane energization of the reserpine-sensitive carrier.     

Analysis of primary food sources and trophic relationships of aquatic animals in a mangrove-fringed estuary,Khung Krabaen Bay (Thailand) using dual stable isotope techniques

Stable carbon (¹³C) and nitrogen (¹⁵N) isotopes were used to elucidate primary food sources and trophic relationships of organisms in Khung Krabaen Bay and adjacent offshore waters. The three separate sampling sites were mangroves, inner bay and offshore. The ¹³C values of mangrove leaves were –28.2 to –29.4, seagrass –10.5, macroalgae –14.9 to –18.2, plankton –20.0 to –21.8, benthic detritus –15.1 to –26.3, invertebrates –16.5 to –26.0, and fishes –13.4 to –26.3. The ¹⁵N values of mangrove leaves were 4.3 to 5.7, seagrass 4.3, macroalgae 2.2 to 4.4, plankton 5.7 to 6.4 , benthic detritus 5.1 to 5.3, invertebrates 7.2 to 12.2 , and fishes 6.3 to 15.9. The primary producers had distinct ¹³C values. The ¹³C values of animals collected from mangroves were more negative than those of animals collected far from shore. The primary carbon sources that support food webs clearly depended on location. The contribution of mangroves to food webs was confined only to mangroves, but a mixture of macroalgae and plankton was a major carbon source for organisms in the inner bay area. Offshore organisms clearly derived their carbon through the planktonic food web. The ¹⁵N values of consumers were enriched by 3–4 relative to their diets. The ¹⁵N data suggests that some of aquatic animals had capacity to change their feeding habits according to places and availability of foods and as a result, individuals of the same species could be assigned to different trophic levels at different places.     

Identification of two RAPD markers tightly linked with the Nicotiana debneyi gene for resistance to black root rot of tobacco

Linkage of randomly amplified polymorphic DNA (RAPD) markers with a single dominant gene for resistance to black root rot (Chalara elegans Nag Raj and Kendrick; Syn. Thielaviopsis basicola [Berk. and Broome] Ferraris) of tobacco (Nicotiana tabacum L.), which was transferred from N. debneyi Domin, was investigated in this study. There were 2594 repeatable RAPD fragments generated by 441 primers on DNAs of Delgold tobacco, a BC₅F₈ near isogenic line (NIL) carrying the resistance gene in a Delgold background, and PB19, the donor parent of the resistance gene. Only 7 of these primers produced eight RAPD markers polymorphic between Delgold and PB19, indicating there are few RAPD polymorphisms between them despite relatively dissimilar pedigrees. Five of the eight RAPD markers were not polymorphic between Delgold and the NIL. All of these markers proved to be unlinked with the resistance gene in F₂ linkage tests. Of the remaining three RAPD markers polymorphic between Delgold and the NIL, two were shown to be strongly linked with the resistance gene; one in coupling and the other in repulsion. Application of the two RAPDs in the elimination of linkage drag associated with the N. debneyi resistance gene and marker-assisted selection for the breeding of new tobacco cultivars with the resistance gene is discussed.     

Aspects of carbon and nitrogen cycling in soils of the Bornhöved Lake district II. Modelling the influence of temperature increase on soil respiration and organic carbon content in arable soils under different managements

Based on field measurements in two agriculturalecosystems, soil respiration and long-term response ofsoil organic carbon content (SOC) was modelled. Themodel predicts the influence of temperature increaseas well as the effects of land-use over a period ofthirty years in a northern German glacial morainelandscape. One of the fields carried a maizemonoculture treated with cattle slurry in addition tomineral fertilizer (maize monoculture), the otherwas managed by crop rotation and recieved organicmanure (crop rotation). The soils of both fieldswere classified as cambic Arenosols. The soilrespiration was measured in the fields by means of theopen dynamic inverted-box method and an infrared gasanalyser. The mean annual soil respiration rates were 268 (maizemonoculture) and 287 mg CO₂ m^-2 h^-1(crop rotation). Factors controlling soil respirationwere soil temperature, soil moisture, root respirationand carbon input into the soil. Q₁₀-valuesof soil respiration were generally higher in winterthan in summer. This trend is interpreted as anadaptive response of the soil microbial communities.In the model a novel mathematical approach withvariable Q₁₀-values as a result oftemperature and moisture adjustment is proposed. Withthe calibrated model soil respiration and SOC werecalculated for both fields and simulations over aperiod of thirty years were established. Simulationswere based on (1) local climatic data, 1961 until1990, and (2) a regional climate scenario for northernGermany with an average temperature increase of 2.1 K.Over the thirty years period with present climateconditions, the SOC pool under crop rotation wasnearly stable due to the higher carbon inputs, whereasabout 16 t C ha^-1 were lost under maizemonoculture. Under global warming the mean annualsoil respiration for both fields increased and SOCdecreased by ca. 10 t C ha^-1 under croprotation and by more than 20 t C ha^-1 undermaize monoculture. It was shown that overestimationof carbon losses in long-term prognoses can be avoidedby including a Q₁₀-adjustment in soilrespiration models.