Xanchryones I−N,Six Unusual Phloroglucinol-Amino Acid Hybrids from the Leaves of Xanthostemon chrysanthus

Six new phloroglucinol derivatives, xanchryones I−N ( 1 – 6 ), were isolated from the leaves of Xanthostemon chrysanthus. Compounds 1 – 6 are unusual phloroglucinol-amino acid hybrids constructed through C₂−N and O−C₁′ bonds forming a peculiar oxazole ring. The structures and absolute configurations of compounds 1 – 6 were determined by MS, NMR, and single-crystal X-ray diffraction. Moreover, the anti-inflammatory and antibacterial activities of these compounds were evaluated.     

Prototropic tautomerism and basic molecular principles of hypoxanthine mutagenicity: an exhaustive quantum-chemical analysis

The molecular structures, relative stability order, and dipole moments of a complete family of 21 planar hypoxanthine (Hyp) prototropic molecular–zwitterionic tautomers including ylidic forms were computationally investigated at the MP2/6–311++G(2df,pd)//B3LYP/6–311++G(d,p) level of theory in vacuum and in three different surrounding environments: continuum with a low dielectric constant (??=?4) corresponding to a hydrophobic interface of protein–nucleic acid interactions, dimethylsulfoxide (DMSO), and water. The keto-N1HN7H tautomer was established to be the global minimum in vacuum and in continuum with ??=?4, while Hyp molecule exists as a mixture of the keto-N1HN9H and keto-N1HN7H tautomers in approximately equal amounts in DMSO and in water at T?=?298.15?K. We found out that neither intramolecular tautomerization by single proton transfer in the Hyp base, nor intermolecular tautomerization by double proton transfer in the most energetically favorable Hyp·Hyp homodimer (symmetry C _2h ), stabilized by two equivalent N1H…O6 H-bonds, induces the formation of the enol tautomer (marked with an asterisk) of Hyp with cis-oriented O6H hydroxyl group relative to neighboring N1C6 bond. We first discovered a new scenario of the keto–enol tautomerization of Hyp?·?Hyp homodimer (C _2h ) via zwitterionic near-orthogonal transition state (TS), stabilized by N1⁺H…N1^? and O6⁺H…N1^? H-bonds, to heterodimer Hyp^??·?Hyp (C _s ), stabilized by O6H…O6 and N1H…N1 H-bonds. We first showed that Hyp^??·?Thy mispair (C _s ), stabilized by O6H…O4, N3H…N1, and C2H…O2 H-bonds, mimicking Watson–Crick base pairing, converts to the wobble Hyp?·?Thy base pair (C _s ), stabilized by N3H…O6 and N1H…O2 H-bonds, via high- and low-energy TSs and intermediate Hyp?·?Thy^?, stabilized by O4H…O6, N1H…N3, and C2H…O2 H-bonds. The most energetically favorable TS is the zwitterionic pair Hyp⁺?·?Thy^? (C _s ), stabilized by O6⁺H…O4^?, O6⁺H…N3^?, N1⁺H…N3^?, and N1⁺H…O2^? H-bonds. The authors expressed and substantiated the hypothesis, that the keto tautomer of Hyp is a mutagenic compound, while enol tautomer Hyp^? does not possess mutagenic properties. The lifetime of the nonmutagenic tautomer Hyp^? exceeds by many orders the time needed to complete a round of DNA replication in the cell. For the first time purine–purine planar H-bonded mispairs containing Hyp in the anti-orientation with respect to the sugar moiety – Hyp?·?Ade _syn , Hyp?·?Gua^? _syn , and Hyp?·?Gua _syn , that closely resembles the geometry of the Watson–Crick base pairs, have been suggested as the source of transversions. An influence of the surrounding environment (??=?4) on the stability of studied complexes and corresponding TSs was estimated by means of the conductor-like polarizable continuum model. Electron-topological, structural, vibrational, and energetic characterictics of all conventional and nonconventional H-bonds in the investigated structures are presented. Presented data are key to understanding elementary molecular mechanisms of mutagenic action of Hyp as a product of the adenine deamination in DNA.     

Analysis of the interacting surface of maurotoxin with the voltage‐gated Shaker B K+ channel

Maurotoxin (MTX) is a 34‐residue toxin that was isolated initially from the venom of the scorpion Scorpio maurus palmatus. Unlike the other toxins of the α‐KTx6 family (Pi1, Pi4, Pi7, and HsTx1), MTX exhibits a unique disulfide bridge organization of the type C₁? C₅, C₂? C₆, C₃? C₄, and C₇? C₈ (instead of the conventional C₁? C₅, C₂? C₆, C₃? C₇, and C₄? C₈, herein referred to as Pi1‐like) that does not prevent its folding along the classic α/β scaffold of scorpion toxins. MTX_Pi1 is an MTX variant with a conventional pattern of disulfide bridging without any primary structure alteration of the toxin. Here, using MTX and/or MTX_Pi1 as models, we investigated how the type of folding influences toxin recognition of the Shaker B potassium channel. Amino acid residues of MTX that were studied for Shaker B recognition were selected on the basis of their homologous position in charybdotoxin, a three disulfide‐bridged scorpion toxin also active on this channel type. These residues favored either an MTX‐ or MTX_Pi1‐like folding. Our data indicate clearly that Lys²³ and Tyr³² (two out of ten amino acid residues studied) are the most important residues for Shaker B channel blockage by MTX. For activity on SKCa channels, the same amino acid residues also affect, directly or indirectly, the recognition of SK channels. The molecular modeling technique and computed docking indicate the existence of a correlation between the half cystine pairings of the mutated analogs and their activity on the Shaker B K⁺ channel. Overall, mutations in MTX could, or could not, change the reorganization of disulfide bridges of this molecule without affecting its α/β scaffold. However, changing of the peptide backbone (cross linking disulfide bridges from MTX‐like type vs MTX_Pi1‐like type) appears to have less impact on the molecule activity than mutation of certain key amino acids such as Lys²³ and Tyr³² in this toxin. Copyright © 2011 European Peptide Society and John Wiley & Sons, Ltd.     

Five New C21-Steroidal Sapogenins from the Acid Hydrolysate of Cynanchum otophyllum Roots

Five new C₂₁-steroidal sapogenins ( 1 – 5 ) named cynotogenins J−N, were isolated from the acid hydrolysate of Cynanchum otophyllum roots. Their structures were established by extensive spectroscopic analysis (UV, IR, HR-ESI-MS, and NMR). Most notably, compounds 1 – 3 harboring a rare 5β,6β-epoxy group in the C₂₁-steroidal skeleton of Cynanchum plants. All compounds were evaluated for their cytotoxicities against multiple cancer cell lines, in which compounds 5 showed weak cytotoxicity against HepG2 cancer cells with IC₅₀ values of 44.90 μM.     

Lycopodium Alkaloids from Huperzia serrata and Their Anti-acetylcholinesterase Activities

One new fawcettimine-type alkaloid ( 1 ), one new miscellaneous-type alkaloid ( 2 ), four new lycodine-type alkaloids ( 3 – 6 ), and eight known ones ( 7 – 14 ) were isolated from the whole plants of Huperzia serrata. Their structures and absolute configurations were elucidated based on spectroscopic data, X-ray diffraction, ECD calculation and Mosher's method. Compound 1 was a rare C₁₈N₂-type Lycopodium alkaloid, possessing serratinine skeleton with an amide side chain in C-5. The absolute configuration of the 18-OH of compounds 4 – 6 were first determined by Mosher's method. Moreover, compounds 1 – 14 were assayed anti-acetylcholinesterase effect in vitro, and compound 7 showed significant anti-acetylcholinesterase activity with an IC₅₀ value of 16.18±1.64 μM.     

Interactions of tropospheric CO2 and O3 enrichments and moisture variations on microbial biomass and respiration in soil

Soil microbial biomass C (C_mic) is a sensitive indicator of trends in organic matter dynamics in terrestrial ecosystems. This study was conducted to determine the effects of tropospheric CO₂ or O₃ enrichments and moisture variations on total soil organic C (C_org), mineralizable C fraction (C_Min), C_mic, maintenance respiratory (qCO₂) or C_mic death (qD) quotients, and their relationship with basal respiration (BR) rates and field respiration (FR) fluxes in wheat‐soybean agroecosystems. Wheat (Triticum aestivum L.) and soybean (Glycine max. L. Merr) plants were grown to maturity in 3‐m dia open‐top field chambers and exposed to charcoal‐filtered (CF) air at 350 μL CO₂ L^?1; CF air + 150 μL CO₂ L^?1; nonfiltered (NF) air + 35 nL O₃ L^?1; and NF air + 35 nL O₃ L^?1 + 150 μL CO₂ L^?1 at optimum (? 0.05 MPa) and restricted soil moisture (? 1.0 ± 0.05 MPa) regimes. The + 150 μL CO₂ L^?1 additions were 18 h d^?1 and the + 35 nL O₃ L^?1 treatments were 7 h d^?1 from April until late October. While C_org did not vary consistently, C_Min, C_mic and C_mic fractions increased in soils under tropospheric CO₂ enrichment (500 μL CO₂ L^?1) and decreased under high O₃ exposures (55 ± 6 nL O₃ L^?1 for wheat; 60 ± 5 nL O₃ L^?1 for soybean) compared to the CF treatments (25 ± 5 nL O₃ L^?1). The qCO₂ or qD quotients of C_mic were also significantly decreased in soils under high CO₂ but increased under high O₃ exposures compared to the CF control. The BR rates did not vary consistently but they were higher in well‐watered soils. The FR fluxes were lower under high O₃ exposures compared to soils under the CF control. An increase in C_mic or C_mic fractions and decrease in qCO₂ or qD observed under high CO₂ treatment suggest that these soils were acting as C sinks whereas, reductions in C_mic or C_mic fractions and increase in qCO₂ or qD in soils under elevated tropospheric O₃ exposures suggest the soils were serving as a source of CO₂.     

Two New C19-Diterpenoid Alkaloids from Delphinium shawurense

Shawurenine C ( 1a ) and D ( 1b ), a new pair of regioisomeric C₁₉-diterpenoid alkaloids, and five known C₁₉-diterpenoid alkaloids ( 2 – 6 ) were isolated from the aerial part of Delphinium shawurense W. T. Wang. The chemical structures of new compounds were established based on spectroscopic analyses: HR-ESI-MS, and 1D, 2D NMR spectroscopic data. The anti-inflammatory and cytotoxic activities of these diterpenoid alkaloids were also evaluated.     

Diterpenoids from Euphorbia neriifolia and Their Related Anti‐HIV and Cytotoxic Activity

Fifteen diterpenoids ( 1 – 15 ), including three undescribed ones with ent‐atisane skeleton, eupnerias G–I ( 1 – 3 ), were obtained from Euphorbia neriifolia. Compounds 1 – 3 were established through comprehensive spectroscopic analysis. Compounds 4 and 5 exhibited obvious anti‐HIV‐1 effect, and their EC₅₀ were 6.6±3.2 and 6.4±2.5 μg mL^?1, respectively. Compound 6 exhibited moderate cytotoxicity on HepG2 and HepG2/Adr cells with IC₅₀ at 13.70 and 15.57 μm , respectively. In addition, compound 15 exhibited significant cytotoxicity on HepG2 cell lines (IC₅₀=0.01 μm ), while it did not show any cytotoxicity against HepG2/Adr cell lines.     

Characterization and properties of steroid binding protein in Bufo arenarum serum

Serum steroid binding properties of mature Bufo arenarum females were studied. Binding data obtained using charcoal adsorption assay and equilibrium dialysis methods indicates a single protein, named Bufo arenarum sex binding protein (Ba SBP), which binds 5 α-dihydrotestosterone (DHT), testosterone (T), and estradiol-17β (E₂) with high affinity (10⁷ M^?1 – 10⁸ M^?1) and fair capacity (10^?6 M). Scatchard plot analysis demonstrated the coexistence of two binding sites. Ba SBP has a sedimentation coefficient of 5.2 S in sucrose gradient centrifugation in low salt and under steady-state conditions. The specificity of this protein, determined by competitive binding experiments, is comparable to human SBP. DHT and T bind with higher affinity than E₂. Estriol and estrone competed poorly, while diethylstilbestrol and C₂₁ steroids did not compete. The binding capacity of this protein is under estrogenic control. © 1994 Wiley-Liss, Inc.     

Direct and indirect effects of elevated atmospheric CO2 on net ecosystem production in a Chesapeake Bay tidal wetland

The rapid increase in atmospheric CO₂ concentrations (C_a) has resulted in extensive research efforts to understand its impact on terrestrial ecosystems, especially carbon balance. Despite these efforts, there are relatively few data comparing net ecosystem exchange of CO₂ between the atmosphere and the biosphere (NEE), under both ambient and elevated C_a. Here we report data on annual sums of CO₂ (NEE_net) for 19 years on a Chesapeake Bay tidal wetland for Scirpus olneyi (C₃ photosynthetic pathway)‐ and Spartina patens (C₄ photosynthetic pathway)‐dominated high marsh communities exposed to ambient and elevated C_a (ambient + 340 ppm). Our objectives were to (i) quantify effects of elevated C_a on seasonally integrated CO₂ assimilation (NEE_net = NEE_day + NEE_night, kg C m^?2 y^?1) for the two communities; and (ii) quantify effects of altered canopy N content on ecosystem photosynthesis and respiration. Across all years, NEE_net averaged 1.9 kg m^?2 y^?1 in ambient C_a and 2.5 kg m^?2 y^?1 in elevated C_a, for the C₃‐dominated community. Similarly, elevated C_a significantly (P < 0.01) increased carbon uptake in the C₄‐dominated community, as NEE_net averaged 1.5 kg m^?2 y^?1 in ambient C_a and 1.7 kg m^?2 y^?1 in elevated C_a. This resulted in an average CO₂ stimulation of 32% and 13% of seasonally integrated NEE_net for the C₃‐ and C₄‐dominated communities, respectively. Increased NEE_day was correlated with increased efficiencies of light and nitrogen use for net carbon assimilation under elevated C_a, while decreased NEE_night was associated with lower canopy nitrogen content. These results suggest that rising C_a may increase carbon assimilation in both C₃‐ and C₄‐dominated wetland communities. The challenge remains to identify the fate of the assimilated carbon.     

The effect of bacterial strain and temperature changes on the nitrogenase activity of Lotus pedunculatus root nodules

After 40 days of growth at 25°C, Lotus pedunculatus cav., cv. Maku plants infected with Rhizobium loti strain NZP2037 displayed similar relative growth rates but had twice the nodule mass and only one third the whole plant dry weight of plants infected with Bradyrhizobium sp. (Lotus) strain CC814s. In the NZP2037 symbiosis, the rate of CO₂ evolution (per g dry weight of nodulated root) was 1.6 times as high as that in the CC814s symbiosis while the rate of C₂H₂ reduction (per g dry weight of nodule) was only 48% of that in the CC814s symbiosis. Studies of the effect of short term temperature changes on the gas exchange characteristics (CO₂ and H₂ evolution, C₂H₂ reduction) of these symbioses revealed wide differences in the optima for C₂H₂ reduction. Nodules infected with NZP2037 displayed maximal C₂H₂ reduction rates [157 μmol (g dry weight nodule)^?1 h^?1] at 12°C, whereas nodules infected with CC814s were optimal at 30°C [208 μmol (g dry weight nodule)^?1 h^?1]. These short term studies suggested that differences in temperature optima for N₂ may have partially accounted for the poorer effectivity, at 25°C, of strain NZP2037 when compared with strain CC-814s. The relative efficiency [RE = 1 – (H₂ evolution/C₂H₂ reduction)] of N₂ fixation varied widely with temperature in the two symbioses, but there was a general trend toward higher RE with lower temperatures. The ratio of CO₂ evolution: C₂H₂ reduction (mol/mol) in nodulated roots infected with CC814s was constant (ca 10 CO₂/C₂H₂) between 5°C and 30°C, whereas in plants infected with NZP2037 it reached a minimal value of 3.3 CO₂/C₂H₂ at 10°C and was 19 CO₂/C₂H₂ at the growing temperature (25°C).     

Thermal denaturation of Na- and Li-DNA in salt-free solutions

Thermal denaturation of Na- and Li-DNA from chicken erythrocytes was studied by means of scanning microcalorimetry in salt-free solutions at DNA concentrations (C_p) from 4.5 · 10^?2 to 1 · 10^?3 moles of nucleotides/liter (M). Linear dependencies of DNA melting temperature (T_m) vs lgC_p were obtained: ((1)) ((2)) for Na- and Li-DNA, respectively. Microcalorimetry data were compared with the results of spectrophotometric studies at 260 nm of DNA thermal denaturation in Me-DNA + MeCl solutions at C_p ? (6–8) · 10^?5 M and C_s = 0–40 mM (Me is Na or Li, C_s is salt concentration). It was found that Eqs. (1) and (2) are valid in DNA salt-free solutions over the C_p range 6 · 10^?5?4.5 · 10^?2M. Protonation of DNA bases due to the absorption of CO₂ from air in Na-DNA + NaCl solutions affects DNA melting parameters at C_s < 4 mM. Linear dependence of T_m on lga₊ is found in Na-DNA + NaCl at C_s > 0.4 mMin the absence of contact of solutions with CO₂ from air (a₊ is cation activity). A dependence of [dT_m/dlga₊] on Li⁺ activity was observed in Li-DNA + LiCl solutions at C_s < 10 mM: [dT_m/dlga₊] increases from 17°–18° at C_s > 10 mM to 28°–30° at C_s ? 0.2–0.4 mM. Spectrophotometric measurements at 282 nm show that this effect was caused by protonation of bases in fragments of denatured DNA in neutral solutions. The Poisson–Boltzmann (PB) equation was solved for salt-free DNA at the melting point. The linear dependence of T_m vs lgC_p was interpreted in terms of Manning's condensation theory. PB and Manning's theories fit the experimental data if charge density parameter (ξ) of denatured DNA is in the range 1.8–2.1 (assuming for native DNA ξ = 4.2). Specificity of Li ions in interactions with DNA is discussed. © 1994 John Wiley & Sons, Inc.     

Conformational transitions of a dipeptide in water: Effects of imposed pathways using umbrella sampling techniques

The free energy difference between two states of a molecular system separated by an energy barrier can generally be computed using the technique of umbrella sampling along a chosen reaction coordinate or pathway. The effect of a particular choice of pathway upon the obtained free energy difference is investigated by molecular dynamics simulation of a model system consisting of a glycine dipeptide in aqueous solution. Two different reaction coordinates connecting the so-called C₅ and C₇ conformations, one involving intramolecular hydrogen bonds and the other involving the peptide ?, ψ angles, are considered. The Gibbs free energy differences ΔG(C₅ – C₇) are small in both cases, 1.5 ± 1 kJ mol^?1 and 2.2 ± 1 kJ mol ^?1, respectively. The two different reaction coordinates yield free energy differences that are identical to within their statistical error. It is found that the exchange of solute–solute, solute–water, and water–water hydrogen bonds involves free energy changes of less than k_BT, which points at the existence of a multitutde of low free energy pathways connecting the C₅ and C₇ dipeptide conformations. © 1994 John Wiley & Sons, Inc.     

Julichrome Monomers from Marine Gastropod Mollusk‐Associated Streptomyces and Stereochemical Revision of Julichromes Q3 ⋅ 5 and Q3 ⋅ 3

Two julichrome monomers, julichromes Q₁₁ ( 1 ) and Q₁₂ ( 2 ), along with five known julichromes (Q₁₀, Q_{3 ? 5}, Q_{3 ? 3}, Q_{6 ? 6}, Q₆, 3 – 7 ) and four known anthraquinones (chrysophanol, 4‐acetylchrysophanol, islandicin, huanglongmycin A, 8 – 11 ), were isolated from the marine gastropod mollusk Batillaria zonalis‐associated Streptomyces sampsonii SCSIO 054. This is the first report of julichromes isolated from a marine source. Extensive dissection of 1D and 2D NMR datasets combined with X‐ray crystallography enabled rigorous elucidation of the previously reported configurations of julichrome Q_{3 ? 5} ( 4 ) and related julichrome Q_{3 ? 3} ( 5 ); both of the configuration at C(9) needs to be revised. In addition, julichrome Q₁₂ ( 2 ) was found to display antibacterial activity against Micrococcus luteus and Bacillus subtilis with MICs of 2.0 and 8.0 μg mL^?1; four compounds ( 1 , 3 , 6 , 7 ) also showed inhibitory activities against an array of methicillin‐resistant Staphylococcus aureus, S. aureus and S. simulans AKA1 with MIC values ranging from 8 to 64 μg mL^?1.     

Atmospheric CO2 concentration does not directly affect leaf respiration in bean or poplar

It is a matter of debate if there is a direct (short‐term) effect of elevated atmospheric CO₂ concentration (C_a) on plant respiration in the dark. When C_a doubles, some authors found no (or only minor) changes in dark respiration, whereas most studies suggest a respiratory inhibition of 15–20%. The present study shows that the measurement artefacts – particularly leaks between leaf chamber gaskets and leaf surface, CO₂ memory and leakage effects of gas exchange systems as well as the water vapour (‘water dilution’) effect on DCO₂ measurement caused by transpiration – may result in larger errors than generally discussed. A gas exchange system that was used in three different ways – as a closed system in which C_a increased continuously from 200 to 4200 mmol (CO₂) mol^‐1 (air) due to respiration of the enclosed leaf; as an intermittently closed system that was repeatedly closed and opened during C_a periods of either 350 or 2000 mmol mol^‐1, and as an open system in which C_a varied between 350 and 2000 mmol mol^‐1– is described. In control experiments (with an empty leaf chamber), the respective system characteristics were evaluated carefully. When all relevant system parameters were taken into account, no effects of short‐term changes in CO₂ on dark CO₂ efflux of bean and poplar leaves were found, even when C_a increased to 4200 mmol mol^‐1. It is concluded that the leaf respiration of bean and poplar is not directly inhibited by elevated atmospheric CO₂.     

Occurrence of Melibiose‐Containing Glycosphingolipids in a Sample of a Sponge‐Coral Association (Desmapsamma anchorata/Carijoa riisei)

In our research on biologically active compounds from Vietnamese marine invertebrates, rare melibiose‐containing glycosphingolipids were found in a sample of a sponge‐coral association (Desmapsamma anchorata/Carijoa riisei). Melibiosylceramides were analyzed as constituents of some multi‐component RP‐HPLC fractions, and the structures of 14 new ( 1b , 3b , 4a – 4c , 6a – 6c , 8b , 9a , 9b , 10b , 11a , 11b ) and five known ( 2b , 5a – 5c , 7b ) natural compounds were elucidated using NMR, mass spectrometry, optical rotation, and chemical transformations. These α‐d ‐Galp‐(1→6)‐β‐d ‐Glcp‐(1 1)‐ceramides (presumably sponge‐derived compounds) were shown to contain phytosphingosine‐type n‐t17:0 ( 1 ), (6E)‐n‐t17:1 ( 2 ), i‐t17:0 ( 3 ), n‐t18:0 ( 4 ), (6E)‐n‐t18:1 ( 5 ), i‐t18:0 ( 6 ), (6E)‐i‐t18:1 ( 7 ), i‐t19:0 ( 8 ), (6E)‐i‐t19:1 ( 9 ), ai‐t19:0 ( 10 ), and (6E)‐ai‐t19:1 ( 11 ) backbones N‐acylated with saturated straight‐chain (2R)‐2‐hydroxy C₂₁ ( a ), C₂₂ ( b ), and C₂₃ ( c ) acids. Characteristic trends in the fragmentations of the terminal parts of tetraacetylated normal‐chain and iso‐ and anteiso‐branched sphingoid bases were observed using GC/MS. The total sum of melibiosylceramides and compound 5b caused a reduction in colony formation of human melanoma cells.     

The family 6 carbohydrate-binding module (CtCBM6B) of Clostridium thermocellum alpha-L-arabinofuranosidase binds xylans and thermally stabilized by Ca2+ ions

Abstract

The gene encoding CtCBM6B of Clostridium thermocellum α-L-arabinofuranosidase (Ct43Araf) was cloned in pET-21a(+) vector, over-expressed using Escherichia coli BL-21(DE3) cells and purified by immobilized metal-ion affinity chromatography (IMAC). The recombinant CtCBM6B showed a molecular size close to 15 kDa by SDS-PAGE analysis, which was close to the expected size of 14.74 kDa. The ligand-binding affinity of CtCBM6B was assessed against ligands for which the catalytic enzyme, Ct43Araf showed maximum activity. The affinity-gel electrophoresis of CtCBM6B with rye arabinoxylan showed lower equilibrium association constant (K_a, 4.0% C^{? 1}), whereas, it exhibited higher affinity (K_a, 19.6% C^{? 1}) with oat spelt xylan. The ligand-binding analysis of CtCBM6B by fluorescence spectroscopy also revealed similar results with low K_a (3.26% C^{? 1}) with rye arabinoxylan and higher affinity for oat spelt xylan (K_a, 17.9% C^{? 1}) which was corroborated by greater blue-shift in case of oat spelt xylan binding. The CtCBM6B binding with insoluble wheat arabinoxylan by adsorption isotherm analysis showed significant binding affinity as reflected by the equilibrium association constant (K_a), 9.4 × 10³ M^{? 1}. The qualitative analysis by SDS-PAGE also corroborated the CtCBM6B binding with insoluble wheat arabinoxylan. The protein-melting curve of CtCBM6B displayed the peak shift from 53°C to 59°C in the presence of Ca²⁺ ions indicating that Ca²⁺ ions impart thermal stability to the CtCBM6B structure.     

Dynamic changes of canopy-scale mesophyll conductance to CO₂ diffusion of sunflower as affected by CO₂ concentration and abscisic acid

Leaf‐level measurements have shown that mesophyll conductance (g_m) can vary rapidly in response to CO₂ and other environmental factors, but similar studies at the canopy‐scale are missing. Here, we report the effect of short‐term variation of CO₂ concentration on canopy‐scale g_m and other CO₂ exchange parameters of sunflower (Helianthus annuus L.) stands in the presence and absence of abscisic acid (ABA) in their nutrient solution. g_m was estimated from gas exchange and on‐line carbon isotope discrimination (Δ_obs) in a ¹³CO₂/¹²CO₂ gas exchange mesocosm. The isotopic contribution of (photo)respiration to stand‐scale Δ_obs was determined with the experimental approach of Tcherkez et al. Without ABA, short‐term exposures to different CO₂ concentrations (C_a 100 to 900 µmol mol^?1) had little effect on canopy‐scale g_m. But, addition of ABA strongly altered the CO₂‐response: g_m was high (approx. 0.5 mol CO₂ m^?2 s^?1) at C_a < 200 µmol mol^?1 and decreased to <0.1 mol CO₂ m^?2 s^?1 at C_a >400 µmol mol^?1. In the absence of ABA, the contribution of (photo)respiration to stand‐scale Δ_obs was high at low C_a (7.2‰) and decreased to <2‰ at C_a > 400 µmol mol^?1. Treatment with ABA halved this effect at all C_a.     

Electric‐induced mortality of newly transformed juvenile fishes in waters of different conductivity

In three experiments, each with three species of newly transformed juvenile fishes, the immediate mortality was determined after electrical exposure to 60 Hz pulsed DC in waters of different conductivity (C_w). With a constant applied power density (D_a; 1·0–4·9 mW cm^?3 depending on species) over a range of C_w(10–1020 μS cm^?1), the results predicted that the highest fish mortality would occur at C_w of 65 μS cm^?1 for bluegill Lepomis macrochirus, 74 μS cm^?1 for largemouth bass Micropterus salmoides and at 140–175 μS cm^?1 for channel catfish Ictalurus punctatus. In experiment 2, the voltage gradient (E) was maintained constant (2·5–8·0 peak V cm^?1 depending on species) over the same range of C_w, and fish mortality increased with current density (J) or D_a, which are directly related to C_w. In experiment 3, fish mortality did not differ when peak E(3 or 8 V cm^?1 depending on species) and mean J(0·09 or 0·24 mA cm^?2 depending on species) were held constant by changing pulse width in waters with different C_w(99, 165 or 495 μS cm^?1). Fish mortality in this experiment was not significantly related to peak or mean transferred power density, and the ‘power transfer theory for electrofishing’ was not useful for predicting electrofishing mortality. Overall, the results of the present study indicated that mortality caused by exposure to electricity can be predicted more accurately with the variables peak E and mean J than with models requiring determination of effective conductivity of the fish.     

Interaction between atmospheric CO2 concentration and water deficit on gas exchange and crop growth: testing of ecosys with data from the Free Air CO2 Enrichment (FACE) experiment

Soil water deficits are likely to influence the response of crop growth and yield to changes in atmospheric CO₂ concentrations (C_a), but the extent of this influence is uncertain. To study the interaction of water deficits and C_a on crop growth, the ecosystem simulation model ecosys was tested with data for diurnal gas exchange and seasonal wheat growth measured during 1993 under high and low irrigation at C_a= 370 and 550 μmol mol^?1 in the Free Air CO₂ Enrichment (FACE) experiment near Phoenix, AZ. The model, supported by the data from canopy gas exchange enclosures, indicated that under high irrigation canopy conductance (g_c) at C_a= 550 μmol mol^?1 was reduced to about 0.75 that at C_a= 370 μmol mol^?1, but that under low irrigation, g_c was reduced less. Consequently when C_a was increased from 370 to 550 μmol mol^?1, canopy transpiration was reduced less, and net CO₂ fixation was increased more, under low irrigation than under high irrigation. The simulated effects of C_a and irrigation on diurnal gas exchange were also apparent on seasonal water use and grain yield. Simulated vs. measured seasonal water use by wheat under high irrigation was reduced by 6% vs. 4% at C_a= 550 vs. 370 μmol mol^?1 but that under low irrigation was increased by 3% vs. 5%. Simulated vs. measured grain yield of wheat under high irrigation was increased by 16% vs. 8%, but that under low irrigation was increased by 38% vs. 21%. In ecosys, the interaction between C_a and irrigation on diurnal gas exchange, and hence on seasonal crop growth and water use, was attributed to a convergence of simulated g_c towards common values under both C_a as canopy turgor declined. This convergence caused transpiration to decrease comparatively less, but CO₂ fixation to increase comparatively more, under high vs. low C_a. Convergence of g_c was in turn attributed to improved turgor maintenance under elevated C_a caused by greater storage C concentrations in the leaves, and by greater rooting density in the soil.