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81.
本文采用苏制核微孔滤膜进行了除菌、除支原体实验研究,核孔膜孔径分别为0.07、0.1、0.5、0.7及1.5微米,采用的菌种为白色葡萄球菌、链球菌和大肠杆菌,支原体为解脲脲原体,实验结果表明:0.07及0.1微米的核孔膜可完全滤除细菌及支原体,0.5微米的核孔膜可滤除绝大部分细菌,不能滤除支原体,1.5微米的核孔膜只能滤除少量细菌。 相似文献
82.
Abstract: A novel fluorescent Na+ indicator, Na+ -binding benzofuran isophthalate (SBFI), was used to follow changes in the intracellular free Na+ concentration ([Na+ ]1 ) of synaptosomes. The dye, when loaded into synapto- somes in the form of its acetoxymethyl ester, was responsive to changes of [Na+ ]1 . Calibration was made using the 340/380 nm excitation ratio when the cytoplasmic Na+ concentration was equilibrated with different concentrations of extracellular Na+ in the presence of 2 μ M gramicidin D. The basal value of [Na+ ]1 in synaptosomes in the presence of 140 m M extracellular Na+ was found to be 10.9 ± 1.8 m M. Veratridine, which opens potential-dependent Na+ channels, caused a sudden increase in [Na+ ]1 in a concentration-dependent manner (1 -20 μ M ), whereas the effect of ouabain (20 and 50 μ M ), the inhibitor of the plasma membrane Na+ ,K+ -ATPase, was more gradual. The rise in the fluorescence intensity upon addition of veratridine was prevented completely by 2 μ M tetrodotoxin. α-Latrotoxin, the black widow spider toxin, caused an increase in the fluorescence intensity, which became evident 1 min after the addition of the toxin. The rate of increase was proportional to the concentration of the toxin (0.19–1.5 n M ). This report confirms our earlier finding demonstrating a Na+ -dependent component in the action of α-Iatrotoxin, and shows that changes in [Na+ ]1 in synaptosomes can be followed by SBFI. 相似文献
83.
Kinetics of microbial growth with mixtures of carbon sources 总被引:11,自引:0,他引:11
84.
This article demonstrates the successful in situ real-time monitoring of the cell concentration of Perilla frutescens in a bioreactor by using a laser turbidimeter. It was found that turbidity measurements at 780 nm with the laser sensor were hardly affected by the red color of the anthocyanin produced by P. frutescens cells, nor by the aeration rate or agitation speed within the ranges investigated. There was an excellent linear relationship, with a correlation coefficient (r(2)) higher than 0.99, between the sensor's response and the cell concentration. The whole growth stage of the cells, i.e., lag, logarithmic, and stationary phases, in bioreactor cultivations, could be satisfactorily estimated on-line by means of the in situ turbidimeter. However, during the declining phase of the cells, an apparent deviation was observed between the on-line estimations and off-line measurements of cell concentrations by dry cell weight, while the wet cell weight could be estimated by the same turbidimeter system. We found that this deviation was caused by a decrease in the cell density due to an increase of the individual cell volume and a decrease of the cell dry weight during the declining phase. (c) 1993 John Wiley & Sons, Inc. 相似文献
85.
Hydrobiologia - In 1988–89 a 200 m core was drilled down to granite bedrock in the Pretoria Saltpan as part of a project to ascertain the origin of this unusual feature. The top 90 m of the... 相似文献
86.
The characteristics of sulphate uptake into right-side-out plasma-membrane vesicles isolated from roots of Brassica napus L., Metzger, cv. Drakkar, and purified by aqueous polymer two-phase partitioning, were investigated. Sulphate uptake into the vesicles was driven by an artificially imposed pH gradient (acid outside), and could be observed for 5–10 min before a plateau was reached and no further net uptake occurred. The uptake was partially inhibited in the presence of depolarizing agents and little uptake was observed in the absence of an imposed pH gradient. Uptake was strongly pH-dependent, being greatest at more acidic pH. After imposition of a pH gradient, the capacity for uptake decreased slowly (t1/2>10 min). The uptake had a high-affinity component which was strongly dependent on the external proton concentration (K m=10μM at pH 5.0, 64 μM at pH 6.5). The K m for protons varied from 0.4–1.9 μM as the sulphate concentration was reduced from 33 to 1 μM. A low-affinity component was observed which could be resolved at low temperatures (0 °C). Microsomal membranes that partitioned into the lower phase of the two-phase system gave no indication of high-affinity sulphate transport. Sulphate uptake into plasma-membrane vesicles isolated from sulphur-starved plant material was approximately twofold greater than that observed in those isolated from sulphate-fed plant material. Isolated vesicles therefore mirror the well-known in-vivo response of roots, indicating an increase in the number of transporters to be, at least in part, the underlying cause of derepression. 相似文献
87.
The activation by abscisic acid (ABA) of current through outward-rectifying K+ channels and its dependence on cytoplasmic pH (pHi) was examined in stomatal guard cells of Vicia faba L. Intact guard cells were impaled with multibarrelled and H+-selective microelectrodes to record membrane potentials and pHi during exposures to ABA and the weak acid butyrate. Potassium channel currents were monitored under voltage clamp and, in some experiments, guard cells were loaded with pH buffers by iontophoresis to suppress changes in pHi. Following impalements, stable pHi values ranged between 7.53 and 7.81 (7.67±0.04, n = 17). On adding 20 M ABA, pHi rose over periods of 5–8 min to values 0.27±0.03 pH units above the pHi before ABA addition, and declined slowly thereafter. Concurrent voltage-clamp measurements showed a parallel rise in the outward-rectifying K+ channel current (IK, out) and, once evoked, both pHi and IK, out responses were unaffected by ABA washout. Acid loads, imposed with external butyrate, abolished the ABA-evoked rise in IK, out. Butyrate concentrations of 10 and 30 mM (pH0 6.1) caused pHi to fall to values near 7.0 and below, both before and after adding ABA, consistent with a cytoplasmic buffer capacity of 128±12 mM per pH unit (n = 10) near neutrality. Butyrate washout was characterised by an appreciable alkaline overshoot in pHi and concomitant swell in the steady-state conductance of IK, out. The rise in pHi and iK, out in ABA were also virtually eliminated when guard cells were first loaded with pH buffers to raise the cytoplasmic buffer capacity four- to sixfold; however, buffer loading was without appreciable effect on the ABA-evoked inactivation of a second, inward-rectifying class of K+ channels (IK, in). The pHi dependence of IK, out was consistent with a cooperative binding of at least 2H+ (apparent pKa = 8.3) to achieve a voltage-independent block of the channel. These results establish a causal link previously implicated between cytoplasmic alkalinisation and the activation of IK, out in ABA and, thus, affirm a role for H+ in signalling and transport control in plants distinct from its function as a substrate in H+-coupled transport. Additional evidence implicates a coordinate control of IK, in by cytoplasmic-free [Ca2+] and pHi.Abbreviations ABA
abscisic acid
- [Ca2+]i
cytoplasmic free [Ca2+]i
- EK
K+ equilibrium potential
- IK, out, IK, in
outward-, inward-rectifying K+ channel (current)
- I-V
current-voltage (relation)
- Mes
2-(N-morpholino)ethanesulfonic acid
- pHi
cytoplasmic pH
- Tes
2-{[2-hydroxy-1,1-bis(hydroxymethyl)ethyl]-amino}ethanesulfonic acid
- Vm
membrane potential
We are grateful to G. Thiel (Pflanzenphysiologisches Institut, Universität Göttingen, Germany) for helpful discussions. This work was possible with equipment grants-in-aid from the Gatsby Charitable Foundation, the Royal Society and the University of London Central Research Fund. F.A. holds a Sainsbury Studentship. 相似文献
88.
Dennis A. Bazylinski Anthony J. Garratt-Reed Afshin Abedi Richard B. Frankel 《Archives of microbiology》1993,160(1):35-42
Greigite (Fe3S4) and pyrite (FeS2) particles in the magnetosomes of a many-celled, magnetotactic prokaryote (MMP), common in brackish-to-marine, sulfidic, aquatic habitats, contained relatively high concentrations of copper which ranged from about 0.1 to 10 atomic per cent relative to iron. In contrast, the greigite particles in the magnetosomes of a curved magnetotactic bacterium collected from the same sampling site did not contain significant levels of copper. The ability of the MMP to biomineralize copper within its magnetosomes appeared to be limited to that organism and dependent upon the site from which it was collected. Although the chemical mechanism and physiological function of copper accumulation in the magnetosomes of the MMP is unclear, the presence of copper is the first evidence that another transition metal ion could be incorporated in the mineral phase of the magnetosomes of a magnetotactic bacterium.Abbreviation MMP
many-celled magnetotactic prokaryote 相似文献
89.
Effect of winter fire on primary productivity and nutrient concentration of a dry tropical savanna 总被引:1,自引:0,他引:1
R. S. Singh 《Plant Ecology》1993,106(1):63-71
Burning increased the mean annual canopy and belowground biomass of a dry tropical savanna by 40% and 12%, respectively, while littermass was reduced by 85% in comparison to control savanna. Mean annual aboveground and belowground net primary production were 471 and 631 g m-2 in control, and 584 and 688 g m-2 in burned savanna, respectively. Fire caused an increase in mean aboveground net production of 24% and in belowground net production of 9%.Concentration of carbon, nitrogen and phosphorus in vegetation of unburned plots ranged between 34.01–38.59%, 0.85–1.53% and 0.04–0.11% and in soil from 0.95–1%, 0.011–0.13% and 0.017–0.02%, respectively. Fire increased the mean concentrations of N and P by 16% and 42% in vegetation and 18.18% and 17.65% in soil, respectively. Thus winter fire can be an important tool for the management of dry tropical savanna with respect to biomass production and nutritive quality. 相似文献
90.
Examination of the method for measuring soil respiration in cultivated land: Effect of carbon dioxide concentration on soil respiration 总被引:7,自引:1,他引:6
Toshie Nakadai Hiroshi Koizumi Youzou Usami Mitsumasa Satoh Takehisa Oikawa 《Ecological Research》1993,8(1):65-71
An acceleration of soil respiration with decreasing CO2 concentration was suggested in the field measurements. The result supporrs that obtained in laboratory experiments in our
previous study. The CO2 concentrations in a chamber of the alkali absorption method (the AA-method) were about 150–250 parts/106 lower than that in the atmosphere (about 350 parts/106), while those observed in the open-flow IRGA method (the OF-method) were nearly equal to the soil surface CO2 levels. The AA-method at such low CO2 levels in the chamber appears to overestimate the soil respiration. Our results showed that the rates obtained by the AA-method
were about twice as large as those by the OF-method in field and laboratory measurements. This finding has important consequences
with respect to the validity of the existing data obtained by the AA-method and the estimation of changes in the terrestrial
carbon flow with elevated CO2 相似文献