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81.
Razet R Thomet U Furtmüller R Jursky F Sigel E Sieghart W Dodd RH 《Bioorganic & medicinal chemistry letters》2000,10(22):2579-2583
Analogues of bicuculline devoid of the benzo ring fused to the lactone moiety were prepared by reacting 2-(tert-butyl-dimethylsiloxy)furans with 3,4-dihydroisoquinolinium salts. Some of these compounds (e.g., ROD185, 8) acted as modulators of the GABAA receptor, displacing ligands of the benzodiazepine binding site. They also strongly stimulated GABA currents mediated by recombinant GABA(A) receptors expressed in Xenopus oocytes. 相似文献
82.
83.
Area per lipid and acyl length distributions in fluid phosphatidylcholines determined by (2)H NMR spectroscopy 下载免费PDF全文
Deuterium ((2)H) NMR spectroscopy provides detailed information regarding the structural fluctuations of lipid bilayers, including both the equilibrium properties and dynamics. Experimental (2)H NMR measurements for the homologous series of 1, 2-diacyl-sn-glycero-3-phosphocholines with perdeuterated saturated chains (from C12:0 to C18:0) have been performed on randomly oriented, fully hydrated multilamellar samples. For each lipid, the C-D bond order parameters have been calculated from de-Paked (2)H NMR spectra as a function of temperature. The experimental order parameters were analyzed using a mean-torque potential model for the acyl chain segment distributions, and comparison was made with the conventional diamond lattice approach. Statistical mechanical principles were used to relate the measured order parameters to the lipid bilayer structural parameters: the hydrocarbon thickness and the mean interfacial area per lipid. At fixed temperature, the area decreases with increasing acyl length, indicating increased van der Waals attraction for longer lipid chains. However, the main effect of increasing the acyl chain length is on the hydrocarbon thickness rather than on the area per lipid. Expansion coefficients of the structural parameters are reported and interpreted using an empirical free energy function that describes the force balance in fluid bilayers. At the same absolute temperature, the phosphatidylcholine (PC) series exhibits a universal chain packing profile that differs from that of phosphatidylethanolamines (PE). Hence, the lateral packing of phospholipids is more sensitive to the headgroup methylation than to the acyl chain length. A fit to the area per lipid for the PC series using the empirical free energy function shows that the PE area represents a limiting value for the packing of fluid acyl chains. 相似文献
84.
Photoinhibition, as measured by the dark-adapted chlorophyll
a fluorescence ratio
Fv/Fm, was assessed in
Syzygium moorei, a species with dark green juvenile
leaves, Syzygium corynanthum, which has light green
juvenile leaves, and two species with pink-red juvenile leaves
(Syzygium wilsonii and Syzygium
luehmannii). All plants were glasshouse-grown (maximum
PPFD 1500 mol
m-2 s-1) under optimum
nutrition and water.When measured at midday, dark-adapted
Fv/Fm ratios of juvenile leaves
gradually increased in all species as percentage of full leaf expansion (%
FLE) increased. Fluorescence measurement 3h after
sunset or pre-dawn also showed a developmental effect on
Fv/Fm, with juvenile leaves of
S. luehmannii and S. wilsonii
showing much lower Fv/Fm at all
stages of development. Dark-adapted
Fv/Fm, values in both juvenile
and mature leaves generally never exceeded 0.8 at any stage in any of the
species.Courses of Fv/Fm on sunny
days showed greater diurnal photoinhibition in green juvenile
(c. 50% FLE) leaves of
S. moorei (24%) and S.
corynanthum (36%) than in mature leaves of the previous flush in
these species (<10%). Diurnal photoinhibition was statistically
similar (18-24%) in pink-red juvenile and green mature leaves of
S. luehmannii and S. wilsonii.
Re-positioning juvenile leaves of S. wilsonii
horizontally increased diurnal photoinhibition.Exposure of leaves to a
standard mild photoinhibitory light treatment (30 min at 1000 mol
m-2s-1) showed that juvenile
leaves of all species had a lower percentage of high energy state quenching
(qE) and a higher percentage of photoinhibitory
quenching (qI) than mature
leaves. 相似文献
85.
Two glasshouse experiments were done to assess the development and metabolic activity of mycorrhizas formed by isolates of
arbuscular mycorrhizal fungi (AMF) from three different genera, Acaulospora, Gigaspora and Glomus on either Pueraria phaseoloides L. or Desmodium ovalifolium L. plants. The second of the two experiments included three levels of a localised phosphate source in the pots. Alkaline
phosphatase (ALP), stained histochemically in the intra-radical mycelium (IRM) of AMF over sequential harvests, did not provide
a direct marker for the efficiency of AMF in mobilising phosphorus (P) for plant growth and development. The ability of the
extra-radical mycelium (ERM) to scavenge a localised phosphate source, determined by its extraction from buried 35-μm mesh
pouches, was dependent on the species of AMF tested. This work indicates that AMF from different genera have unique patterns
of mycelial development when forming mycorrhizas with tropical hosts in the presence of a localised phosphate source. AMF
also appear to have different mechanisms for the control of P transfer, within the mycelium, to the host. The significance
of the architecture of the ERM is discussed as well as the localisation of ALP in the IRM in determining the efficiency of
AMF in terms of P accumulation in planta and subsequent growth of plants.
Accepted: 19 August 1998 相似文献
86.
Sara Dodd Graham A. Place R. L. Hall Stephen E. Harding 《European biophysics journal : EBJ》1998,28(1):38-47
We have used two different approaches to determine hydrodynamic parameters for mucins secreted by guinea-pig tracheal epithelial
cells in primary culture. Cells were cultured under conditions that promote mucous cell differentiation. Secreted mucins were
isolated as the excluded fraction from a Sepharose CL-4B gel filtration column run under strongly dissociating conditions.
Biochemical analysis confirmed the identity of the high molecular weight material as mucins. Analytical ultracentrifugation
was used to study the physical properties of the purified mucins. The weight average molecular mass (M
w
) for three different preparations ranged from 3.3×106 to 4.7×106 g/mol (corresponding to an average structure of 1 – 2 subunits), and the sedimentation coefficient from 25.5 to 35 S. Diffusion
coefficients ranging from 4.5×10–8 to 6.4×10–8 cm2/s were calculated using the Svedberg equation. A polydispersity index (M
z
/M
w
) of ∼1.4 was obtained. Diffusivity values were also determined by image analysis of mucin granule exocytosis captured by
videomicroscopy. The time course of hydration and dissolution of mucin was measured and a relationship is presented which
models both phases, each with first order kinetics, in terms of a maximum radius and rate constants for hydration and dissolution.
A median diffusivity value of 8.05×10–8 cm2/s (inter-quartile range = 1.11×10–7 to 6.08×10–8 cm2/sec) was determined for the hydration phase. For the dissolution phase, a median diffusivity value of 6.98×10–9 cm2/s (inter-quartile range = 1.47×10–8 to 3.25×10–9 cm2/sec) was determined. These values were compared with the macromolecular diffusion coefficients (D
20,w
) obtained by analytical ultracentrifugation. When differences in temperature and viscosity were taken into account, the resulting
D
37,g
was within the range of diffusivity values for dissolution. Our findings show that the physicochemical properties of mucins
secreted by cultured guinea-pig tracheal epithelial cells are similar to those of mucins of the single or double subunit type
purified from respiratory mucus or sputum. These data also suggest that measurement of the diffusivity of dissolution may
be a useful means to estimate the diffusion coefficient of mucins in mucus gel at the time of exocytosis from a secretory
cell.
Received: 10 March 1998 / Accepted: 27 March 1998 相似文献
87.
Two experiments were conducted to determine the establishment success of reintroducing Microlaena stipoides (pātītī, weeping rice grass) into existing high‐fertility grassland on the volcanic cones of the Auckland Isthmus. The first experiment monitored the survival and development of juveniles planted in a factorial design including two planting densities, two slope classes and two aspects across three cones. Plant survival during establishment was consistently over 90%. Maximum M. stipoides cover after 2 years (>80%) was achieved on north‐facing steep slopes (>25°) at the greater planting density (40 plants/m2). However, results were particularly idiosyncratic to specific cone/topographical combinations. The second experiment, on a flat site on one cone, monitored the survival and development of juveniles planted across four post‐planting treatments designed to suppress resident vegetation recovery. Plant survival after 6 months was relatively low (50%), and none of the treatments achieved greater than 5% cover of M. stipoides after 1 year. The chosen post‐planting treatments were unable to suppress vigorous recovery of competitive exotic grasses on a moist fertile site. Overall, juvenile planting was shown to be a potentially successful method of Microlaena establishment and could restore indigenous dominance to exotic grassland in this environment, but individual site factors and the high cost of establishment must be considered. 相似文献
88.
Rui S. Oliveira Paula M. L. Castro John C. Dodd Miroslav Vosátka 《Plant and Soil》2006,287(1-2):209-221
Different species of arbuscular mycorrhizal fungi (AMF) can produce different amounts of extraradical mycelium (ERM) with differing architectures. They also have different efficiencies in gathering phosphate from the soil. These differences in phosphate uptake and ERM length or architecture may contribute to differential growth responses of plants and this may be an important contributor to plant species coexistence. The effects of the development of the ERM of AMF on the coexistence of two co-occurring plant species were investigated in root-free hyphal chambers in a rhizobox experimental unit. The dominant shrub (Salix atrocinerea Brot.) and herbaceous (Conyza bilbaoana J. Rémy) plant species found in a highly alkaline anthropogenic sediment were studied in symbiosis with four native AMF species (Glomus intraradices BEG163, Glomus mosseae BEG198, Glomus geosporum BEG199 and Glomus claroideum BEG210) that were the most abundant members of the AMF community found in the sediment. Different AMF species did not influence total plant productivity (sum of the biomass of C. bilbaoana and S. atrocinerea), but had a great impact on the individual biomass of each plant species. The AMF species with greater extracted ERM lengths (G. mosseae BEG198, G. claroideum BEG210 and the four mixed AMF) preferentially benefited the plant species with a high mycorrhizal dependency (C. bilbaoana), while the AMF species with the smallest ERM length (G. geosporum BEG199) benefited the plant species with a low mycorrhizal dependency (S. atrocinerea). Seed production of C. bilbaoana was only observed in plants inoculated with G. mosseae BEG198, G. claroideum BEG210 or the mixture of the four AMF. Our results show that AMF play an important role in the reproduction of C. bilbaoana coexisting with S. atrocinerea in the alkaline sediment and have the potential to stimulate or completely inhibit seed production. The community composition of native AMF and the length of the mycelium they produce spreading from roots into the surrounding soil can be determinant of the coexistence of naturally co-occurring plant species. 相似文献
89.
Two glasshouse experiments were performed to assess the development and metabolic activity of mycorrhizas formed by isolates
of arbuscular mycorrhizal fungi (AMF) from three different genera, Acaulospora, Gigaspora and Glomus on Desmodium ovalifolium L. plants. In the first experiment the effect of disturbance of a pre-established extra-radical mycelium (ERM) was studied.
In the second experiment the effect of phosphate addition as either organic matter (OM) or fertiliser was studied. Disturbance
of a pre-established ERM reduced the formation of mycorrhizas by Gigaspora rosea (BEG111) and increased that by Glomus manihotis (BEG112) on D. ovalifolium plants. Acaulospora tuberculata (BEG41) failed to form mycorrhizas in the experiment. Either Gi. rosea (BEG111) or G. manihotis (BEG112) appeared to be the major component of the colonisation resulting from treatments with combinations of two or three
of the AMF and determined the sensitivity of these treatments to disturbance of a pre-established ERM. The addition of phosphate
fertiliser (10 mg P kg-1) reduced mycorrhiza formation by each species of AMF compared with the addition of OM (10 mg P kg-1). This work indicates that AMF from different genera respond differently to management by agricultural practices when in
association with a tropical legume. Clearly, there is potential to alter the formation of mycorrhizas of AMF from different
genera, through the use of agricultural practices. The significance of the development and metabolic activity of mycorrhizas
formed by AMF from different genera for plant growth is discussed.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
90.
Wang YS Russell WK Wang Z Wan W Dodd LE Pai PJ Russell DH Liu WR 《Molecular bioSystems》2011,7(3):714-717
Using evolved pyrrolysyl-tRNA synthetase-tRNA(CUA)(Pyl) pairs, L-phenylalanine, p-iodo-L-phenylalanine and p-bromo-L-phenylalanine have been genetically incorporated into proteins at amber mutation sites in E. coli. 相似文献