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1.
Salvatore Magazù Giacomo Maisano Federica Migliardo Antonio Benedetto 《Biochimica et Biophysica Acta - Proteins and Proteomics》2010,1804(1):49-55
In the present paper a procedure for the biomolecular motion characterization based on the evaluation of the Mean Square Displacement (MSD), through the Self Distribution Function (SDF), is presented. In particular it will be shown how the MSD, which represents a good observable for the characterization of the dynamical properties in disordered systems, can be decomposed into partial contributions associated to the system dynamical processes within a specific spatial scale. It will be shown how the SDF procedure allows to evaluate both the total MSD and the partial MSDs through the total SFD and the partial SDFs. As a result, the total MSD is the weighed sum of the partial MSD contributions in which the weights are obtained by the fitting procedure of measured EINS intensity data. We apply the SDF procedure at EINS data collected, by the IN13 backscattering spectrometer at the Institute Laue-Langevin, Grenoble, on aqueous mixtures of two homologous disaccharides (sucrose and trehalose) and on dry myoglobin in trehalose environment. It emerges that the hydrogen bond imposed network of the water–trehalose mixture appears to be stronger with respect to that of the water–sucrose mixture and this result can justify the highest bioprotectant effectiveness of trehalose in comparison with sucrose. Furthermore it emerges that, the partial MSD behaviours of sucrose and trehalose are equivalent in the low Q domain (0–1.7) Å− 1 whereas they are different in the high Q domain (1.7–4) Å- 1. This circumstance suggests that the higher structure sensitivity of sucrose in respect to trehalose should be related to the small spatial observation windows. 相似文献
2.
Transpiration and whole-tree conductance in ponderosa pine trees of different heights 总被引:17,自引:0,他引:17
M. G. Ryan B. J. Bond B. E. Law R. M. Hubbard D. Woodruff E. Cienciala J. Kucera 《Oecologia》2000,124(4):553-560
Changes in leaf physiology with tree age and size could alter forest growth, water yield, and carbon fluxes. We measured tree
water flux (Q) for 14 ponderosa pine trees in two size classes (12 m tall and ∼40 years old, and 36 m tall and ∼ 290 years old) to determine
if transpiration (E) and whole-tree conductance (g
t) differed between the two sizes of trees. For both size classes, E was approximately equal to Q measured 2 m above the ground: Q was most highly correlated with current, not lagged, water vapor pressure deficit, and night Q was <12% of total daily flux. E for days 165–195 and 240–260 averaged 0.97 mmol m–2 (leaf area, projected) s–1 for the 12-m trees and 0.57 mmol m–2 (leaf area) s–1 for the 36-m trees. When photosynthetically active radiation (I
P) exceeded the light saturation for photosynthesis in ponderosa pine (900 μmol m–2 (ground) s–1), differences in E were more pronounced: 2.4 mmol m–2 (leaf area) s–1 for the 12-m trees and 1.2 mmol m–2 s–1 for the 36-m trees, yielding g
t of 140 mmol m–2 (leaf area) s–1 for the 12-m trees and 72 mmol m–2 s–1 for the 36-m trees. Extrapolated to forests with leaf area index =1, the 36-m trees would transpire 117 mm between 1 June
and 31 August compared to 170 mm for the 12-m trees, a difference of 15% of average annual precipitation. Lower g
t in the taller trees also likely lowers photosynthesis during the growing season.
Received: 19 April 1999 / Accepted: 23 March 2000 相似文献
3.
An effect of desiccation (a decrease of relative water content from 97% to 10% within 35 h) on Photosystem II was studied
in barley leaf segments (Hordeum vulgare L. cv. Akcent) using chlorophyll a fluorescence and thermoluminescence (TL). The O-J-I-P fluorescence induction curve revealed a decrease of FP and a slight shift of the J step to a shorter time with no change in its height. The analysis of the fluorescence decline
after a saturating light flash revealed an increased portion of slow exponential components with increasing desiccation. The
TL bands obtained after excitation by continuous light were situated at about –27°C (Zv band – recombination of P680+QA
−), –14 °C (A band – S3QA
−), +12 °C (B band – S2/3QB
−) and +45 °C (C band – TyrD+QA
−). The bands related to the S-states of oxygen evolving complex (A and B) were reduced by desiccation and shifted to higher
and lower temperatures, respectively. In accordance with this, the band observed at about +27 °C (S2QB
−) after excitation by 1 flash fired at –10 °C and band at about +20 °C (S2/3QB
−) after 2 flashes decreased with increasing water deficit and shifted to lower temperatures. A new band around 5 °C appeared
in both regimes of TL excitation for a relative water content of under 42% and was attributed to the Q band (S2QA
−). It is suggested that under desiccation, an inhibition of the formation of S2- and S3-states in OEC occurred simultaneously with a lowering of electron transport on the acceptor side of PS II. The temperature
down-shift of the TL bands obtained after the flash excitation was induced at the initial phases of water stress, indicating
a decrease of the activation energy for the S2/3QB
−recombination.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
4.
Leaf gas exchange in a clonal eucalypt plantation as related to soil moisture, leaf water potential and microclimate variables 总被引:7,自引:0,他引:7
M. S. Mielke M. A. Oliva N.F. de Barros R. M. Penchel C. A. Martinez S. da Fonseca A.C. de Almeida 《Trees - Structure and Function》2000,14(5):263-270
In order to determine how environmental and physiological factors affect leaf gas exchange in a 9-year-old clonal eucalypt
plantation (Eucalyptus grandis Hill ex. Maiden hybrids) in the State of Espirito Santo, Brazil, the diurnal patterns of predawn leaf water potential (Ψpd), and leaf gas exchange were monitored from November 1995 to August 1996. Soil water content (Θ) and microclimatic variables
were also recorded. Most of the rainfall during the experimental period occurred from October to December 1995 and from March
to April 1996, causing a significant variation in Θ and Ψpd. A high positive correlation (r
2=0.92) was observed between Ψpd and Θ measured at 0.3 m depth from the soil surface. During conditions of high soil water availability, the maximum values
of stomatal conductance for water vapor (g
s) and net photosynthetic rate (A) were over 0.4 mol m–2 s–2 and l5 μmol m–2 s–1, respectively. The results showed that Ψpd and leaf gas exchange of the examined trees were susceptible to changes in the water content of the upper soil layers, where
the major concentration of active roots occur. Multiple linear regression analysis indicated that photosynthetic active radiation
(Q), vapor pressure deficit (VPD), atmospheric CO2 molar fraction (C
a), and Ψpd were the most important factors controlling g
s whereas Q and VPD were the main microclimatic variables controlling A.
Received: 5 November 1998 / Accepted: 10 November 1999 相似文献
5.
Cornicchi E Capponi S Marconi M Onori G Paciaroni A 《European biophysics journal : EBJ》2008,37(5):583-590
Through elastic neutron scattering measurements, we investigated the thermal fluctuations of DNA enclosed by glycerol–water
glassy matrices, at different levels of hydration, over the wide temperature range from 20 to 300 K. For all the samples,
the extracted hydrogen mean square displacements (MSD) show a purely vibrational harmonic trend at very low temperatures,
and a first onset of anharmonic dynamics above ∼100 K. Such onset is consistent with the activation of DNA methyl group rotational
motions. Then, at a certain temperature T
d, the MSD show a second onset of anharmonicity, which corresponds to the DNA dynamical transition. The T
d values vary as a function of the hydration degree of the environment. The crucial role of the solvent mobility to activate
the DNA thermal fluctuations is proposed, together with a preferential hydration effect of the DNA phosphate groups. Finally,
a comparison between the average mobility of homologous samples of DNA and the lysozyme protein is considered.
Advanced neutron scattering and complementary techniques to study biological systems. Contributions from the meetings, “Neutrons
in Biology”, STFC Rutherford Appleton Laboratory, Didcot, UK, 11–13 July and “Proteins At Work 2007”, Perugia, Italy, 28–30
May 2007. 相似文献
6.
Susanne G. L. Quaak John B. A. G. Haanen Jos H. Beijnen Bastiaan Nuijen 《AAPS PharmSciTech》2010,11(1):344-350
Since plasmid DNA (pDNA) is unstable in solution, lyophilisation can be used to increase product shelf life. To prevent stress
on pDNA molecules during lyophilisation, cryo- and lyoprotectants have to be added to the formulation. This study assessed
the effect of disaccharides on naked pDNA stability after lyophilisation using accelerated stability studies. Naked pDNA was
lyophilised with sucrose, trehalose, maltose or lactose in an excipient/DNA w/w ratio of 20. To one part of the vials extra residual moisture was introduced by placing the vials half opened in a 25°C/60%
RH climate chamber, before placing all vials in climate chambers (25°C/60% RH and 40°C/75% RH) for stability studies. An ex vivo human skin model was used to assess the effect of disaccharides on transfection efficiency. Lyophilisation resulted in amorphous
cakes for all disaccharides with a residual water content of 0.8% w/w. Storage at 40°C/75% RH resulted in decreasing supercoiled (SC) purity levels (sucrose and trehalose maintained approximately
80% SC purity), but not in physical collapse. The addition of residual moisture (values between 7.5% and 10% w/w) resulted in rapid collapse except for trehalose and decreasing SC purity for all formulations. In a separate experiment
disaccharide formulation solutions show a slight but significant reduction (<3% with sucrose and maltose) in transfection
efficiency when compared to pDNA dissolved in water. We demonstrate that disaccharides, like sucrose and trehalose, are effective
lyoprotectants for naked pDNA. 相似文献
7.
New insights into the interaction of proteins and disaccharides—The effect of pH and concentration 下载免费PDF全文
To gain new insights into the interaction of proteins and disaccharides, we investigated the hydrodynamic radii, , of lysozyme molecules in solution and in a ternary protein‐sugar‐water system by PFG‐NMR. Our approach is based on the assumption that the anhydrobiotic properties of disaccharides like trehalose are based on aggregation of sugar molecules to the proteins, i.e., accumulation of sugar molecules close to the protein, and that this process can be investigated by the experimentally detectable value of the protein. The Rh values are calculated from the experimentally determined diffusion coefficients and the application of a viscosity correction using the inert molecule dioxane as an internal viscosity reference. The experiments were performed as a function of sugar concentration, the overall particle concentration and the pH value. We investigated the disaccharides trehalose and sucrose, mainly for the reason that trehalose has well know cryptobiotic properties while sucrose, which is similar in size and structure, lacks these properties. The results show the formation of a protective sugar shell around the proteins over a wider range of concentrations and pH values in the case of trehalose. 相似文献
8.
Chlorophyll fluorescence is routinely taken as a quantifiable measure of the redox state of the primary quinone acceptor QA of PSII. The variable fluorescence in thylakoids increases in a single turnover flash (STF) from its low dark level F
o towards a maximum F
mSTF when QA becomes reduced. We found, using twin single turnover flashes (TTFs) that the fluorescence increase induced by the first
twin-partner is followed by a 20–30% increase when the second partner is applied within 20–100 μs after the first one. The
amplitude of the twin response shows a period-of-four oscillation associated with the 4-step oxidation of water in the Kok
cycle (S states) and originates from two different trapped states with a life time of 0.2–0.4 and 2–5 ms, respectively. The
oscillation is supplemented with a binary oscillation associated with the two-electron gate mechanism at the PSII acceptor
side. The F(t) response in high frequency flash trains (1–4 kHz) shows (i) in the first 3–4 flashes a transient overshoot 20–30% above
the F
mSTF = 3*F
o level reached in the 1st flash with a partial decline towards a dip D in the next 2–3 ms, independent of the flash frequency,
and (ii) a frequency independent rise to F
m = 5*F
o in the 3–60 ms time range. The initial overshoot is interpreted to be due to electron trapping in the S0 fraction with QB-nonreducing centers and the dip to the subsequent recovery accompanying the reoxidation of the double reduced acceptor pair
in these RCs after trapping. The rise after the overshoot is, in agreement with earlier findings, interpreted to indicate
a photo-electrochemical control of the chlorophyll fluorescence yield of PSII. It is anticipated that the double exciton and
electron trapping property of PSII is advantageous for the plant. It serves to alleviate the depression of electron transport
in single reduced QB-nonreducing RCs, associated with electrochemically coupled proton transport, by an increased electron trapping efficiency
in these centers. 相似文献
9.
Nitrogen and Phosphorous Excretion Rates by Tubificids from the Prahova River (Romania) 总被引:2,自引:0,他引:2
Nitrogen and phosphorous exchange at the water–sediment interface is controlled both by complex physico-chemical factors and
biological processes. Zoobenthos excretion is one of the most important processes in the mineralization of sedimented organic
mater. In polluted freshwaters, tubificid worms are among the dominant components of the benthic community. Rates of ammonium
and inorganic phosphate excretion by tubificids were experimentally assessed. They were related to the tubificid abundance
in a stream ecosystem polluted with municipal and industrial wastewater. The relationship between these rates and temperature
were investigated within the range of 4–23 °C. Relatively constant excretion rates were obtained for both nutrients in the
first 8 h of excretion, ranging between 0.076 and 0.226 μg N mg d.w.−1 h−1 and 0.0065–0.01 μg P mg d.w.−1 h−1, respectively. Q10 values of 2.52 for ammonium and 1.31 for phosphate were calculated. If we presume that all excreta eventually enters the
water column, then we can calculate that these invertebrates potentially add 39.17 mg N m−2 day−1 and 0.49 mg P m−2 day−1. These values accounts for 17.16 and 7.56% of the nutrient load in the river water, respectively. 相似文献
10.
Salvatore Magazù Emanuele Calabrò Salvatore Campo Salvatore Interdonato 《Journal of biological physics》2012,38(1):61-74
The aim of this study was the investigation of static magnetic field effects on haemoglobin secondary structure and the bioprotective
effectiveness of two disaccharides, sucrose and trehalose. Samples of haemoglobin aqueous solutions, in the absence and in
the presence of sucrose and trehalose, were exposed to a uniform magnetic field at 200 mT, which is the exposure limit established
by the ICNIRP recommendation for occupational exposure. Spectral analysis by FTIR spectroscopy after 3 and 7 h of exposure
revealed a decrease in the amide A vibration band for haemoglobin in bi-distilled water solution. Analogue exposures did not
produce any appreciable change of amide A for haemoglobin in sucrose and trehalose solutions. Otherwise, no relative increase
of
\upbeta \upbeta -sheet contents in amide I and II regions was detected for haemoglobin aqueous solutions, leading us to exclude the hypothesis
that static magnetic fields can induce the formation of aggregates in the protein. In addition, a decrease in CH3 stretching linkages occurred for haemoglobin in bi-distilled water solution after exposure, which was not observed for haemoglobin
in sucrose and trehalose aqueous solutions, providing further evidence of a bioprotective compensatory mechanism of such disaccharides. 相似文献
11.
de Boer AL Neerken S de Wijn R Permentier HP Gast P Vijgenboom E Hoff AJ 《Photosynthesis research》2002,71(3):221-239
Mutants of Rhodobacter (Rba.) sphaeroides are described which were designed to study electron transfer along the so-called B-branch of reaction center (RC) cofactors.
Combining the mutation L(M214)H, which results in the incorporation of a bacteriochlorophyll, β, for HA [Kirmaier et al. (1991) Science 251: 922–927] with two mutations, G(M203)D and Y(M210)W, near BA, we have created a double and a triple mutant with long lifetimes of the excited state P* of the primary donor P, viz. 80 and 160 ps at room temperature, respectively. The yield of P+QA
− formation in these mutants is reduced to 50 and 30%, respectively, of that in wildtype RCs. For both mutants, the quantum
yield of P+HB
− formation was less than 10%, in contrast to the 15% B-branch electron transfer demonstrated in RCs of a similar mutant of
Rba. capsulatus with a P* lifetime of 15 ps [Heller et al. (1995) Science 269: 940–945]. We conclude that the lifetime of P* is not a governing factor in switching to B-branch electron transfer. The direct photoreduction of the secondary quinone,
QB, was studied with a triple mutant combining the G(M203)D, L(M214)H and A(M260)W mutations. In this triple mutant QA does not bind to the reaction center [Ridge et al. (1999) Photosynth Res 59: 9–26]. It is shown that B-branch electron transfer
leading to P+QB
− formation occurs to a minor extent at both room temperature and at cryogenic temperatures (about 3% following a saturating
laser flash at 20 K). In contrast, in wildtype RCs P+QB
− formation involves the A-branch and does not occur at all at cryogenic temperatures. Attempts to accumulate the P+QB
− state under continuous illumination were not successful. Charge recombination of P+QB
− formed by B-branch electron transfer in the new mutant is much faster (seconds) than has been previously reported for charge
recombination of P+QB
− trapped in wildtype RCs (105 s) [Kleinfeld et al. (1984b) Biochemistry 23: 5780–5786]. This difference is discussed in light of the different binding
sites for QB and QB
− that recently have been found by X-ray crystallography at cryogenic temperatures [Stowell et al. (1997) Science 276: 812–816].
We present the first low-temperature absorption difference spectrum due to P+QB
−.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
12.
Ha SJ Kim SY Seo JH Moon HJ Lee KM Lee JK 《Applied microbiology and biotechnology》2007,76(1):109-116
The production yield of Coenzyme Q10 (CoQ10) from the sucrose consumed by Agrobacterium tumefaciens KCCM 10413 decreased, and high levels of exopolysaccharide (EPS) accumulated after switching from batch culture to fed-batch
culture. Therefore, we examined the effect of sucrose concentration on the fermentation profile by A. tumefaciens. In the continuous fed-batch culture with the sucrose concentration maintained constantly at 10, 20, 30, and 40 g l−1, the dry cell weight (DCW), specific CoQ10 content, CoQ10 production, and the production yield of CoQ10 from the sucrose consumed increased, whereas EPS production decreased as maintained sucrose concentration decreased. The
pH-stat fed-batch culture system was adapted for CoQ10 production to minimize the concentration of the carbon source and osmotic stress from sucrose. Using the pH-stat fed-batch
culture system, the DCW, specific CoQ10 content, CoQ10 production, and the product yield of CoQ10 from the sucrose consumed increased by 22.6, 13.7, 39.3, and 39.3%, respectively, whereas EPS production decreased by 30.7%
compared to those of fed-batch culture in the previous report (Ha SJ, Kim SY, Seo JH, Oh DK, Lee JK, Appl Microbiol Biotechnol,
74:974–980, 2007). The pH-stat fed-batch culture system was scaled up to a pilot scale (300 l), and the CoQ10 production results obtained (626.5 mg l−1 of CoQ10 and 9.25 mg g DCW−1 of specific CoQ10 content) were similar to those obtained at the laboratory scale. Thus, an efficient and highly competitive process for microbial
CoQ10 production is available. 相似文献
13.
Keirith A. Snyder Robert Monnar Simon R. Poulson Peter Hartsough Franco Biondi 《Trees - Structure and Function》2010,24(3):585-595
Diurnal fluctuations of leaf water isotope ratios (δ18O and δD) were measured for Jeffrey (Pinus jeffreyi Balf.) and lodgepole (Pinus contorta Douglas ex Louden) pine. Two trees per species were sampled every few hours on 15–16 October 2005 and 19–20 June 2006. Diurnal
gas exchange was measured during the summer sampling. In fall 2005, leaf water δ18O ranged from 0.7 to 9.0‰, and leaf water δD ranged from −70 to −50‰. In summer 2006, leaf water δ18O ranged from 7.7 to 20.7‰, and leaf water δD ranged from −61 to −24‰. Diurnal variation of leaf water isotope values typically
reached a maximum in early afternoon, began decreasing around midnight, and reached a minimum in mid-morning. Both periods
showed a high degree of enrichment relative to source water, with leaf water–source water enrichments ranging up to 37.8‰
for δ18O, and up to 95‰ for δD. Leaf water enrichment varied by season with summer enrichment being greater than fall enrichment.
A steady-state model (i.e., modified Craig–Gordon modeling) for leaf water isotope compositions did not provide a good fit
to measured values of leaf water. In summer, a non-steady state model provided a better fit to the measured data than the
steady-state model. Our findings demonstrate substantial leaf water enrichment above source water and diurnal variations in
the isotopic composition of leaf water, which has application to understanding short-term variability of atmospheric gases
(water vapor, CO2, O2), climate studies based on the isotopic composition of tree rings, and ecosystem water fluxes. 相似文献
14.
Encapsulated cocoa (Theobroma cacao L.) somatic embryos subjected to 0.08–1.25 M sucrose treatments were analyzed for embryo soluble sugar content, non-freezable
water content, moisture level after desiccation and viability after desiccation and freezing. Results indicated that the higher
the sucrose concentration in the treatment medium, the greater was the extent of sucrose accumulation in the embryos. Sucrose
treatment greatly assisted embryo post-desiccation recovery since only 40% of the control embryos survived desiccation, whereas
a survival rate of 60–95% was recorded for embryos exposed to 0.5–1.25 M sucrose. The non-freezable water content of the embryos
was estimated at between 0.26 and 0.61 g H2O g−1dw depending on the sucrose treatment, and no obvious relationship could be found between the endogenous sucrose level and
the amount of non-freezable water in the embryos. Cocoa somatic embryos could withstand the loss of a fraction of their non-freezable
water without losing viability following desiccation. Nevertheless, the complete removal of potentially freezable water was
not sufficient for most embryos to survive freezing. 相似文献
15.
Citric acid production from sucrose using a recombinant strain of the yeast Yarrowia lipolytica 总被引:1,自引:0,他引:1
Förster A Aurich A Mauersberger S Barth G 《Applied microbiology and biotechnology》2007,75(6):1409-1417
The yeast Yarrowia lipolytica is able to secrete high amounts of several organic acids under conditions of growth limitation and carbon source excess.
Here we report the production of citric acid (CA) in a fed-batch cultivation process on sucrose using the recombinant Y. lipolytica strain H222-S4(p67ICL1) T5, harbouring the invertase encoding ScSUC2 gene of Saccharomyces cerevisiae under the inducible XPR2 promoter control and multiple ICL1 copies (10–15). The pH-dependent expression of invertase was low at pH 5.0 and was identified as limiting factor of the CA-production
bioprocess. The invertase expression was sufficiently enhanced at pH 6.0–6.8 and resulted in production of 127–140 g l−1 CA with a yield Y
CA of 0.75–0.82 g g−1, whereas at pH 5.0, 87 g l −1 with a yield Y
CA of 0.51 gg−1 were produced. The CA-productivity Q
CA increased from 0.40 g l −1 h−1 at pH 5.0 up to 0.73 g l −1 h−1 at pH 6.8. Accumulation of glucose and fructose at high invertase expression level at pH 6.8 indicated a limitation of CA
production by sugar uptake. The strain H222-S4(p67ICL1) T5 also exhibited a gene–dose-dependent high isocitrate lyase expression
resulting in strong reduction (<5%) of isocitric acid, a by-product during CA production. 相似文献
16.
Solubilization of enzymes in water-in-oil microemulsions and their rapid and efficient release through use of a pH-degradable surfactant 总被引:3,自引:0,他引:3
α-Chymotrypsin and lysozyme were solubilized in a water/O-[(2-tridecyl, 2-ethyl-1,3-dioxolan-4-yl)methoxy]–O′-methoxy poly(ethylene glycol) (CK-2,13 surfactant)/isooctane water-in-oil microemulsion solution at 1.5–2 and 10 g l−1 for 0.15 and 1.2 M CK-2,13, respectively. Upon contact with an equal volume of 0.1 M NaH2PO4/Na2HPO4 buffer, pH 5, a three-phase system (Winsor-III system) was formed, consisting of a surfactant-rich middle phase and aqueous
and isooctane-rich “excess” phases. Both enzymes were rapidly released into the aqueous excess phase, with 70% recovery of
each in 30 and 60 min for microemulsion solutions containing 0.15 and 1.2 M surfactant, respectively. The recovered enzymes retained >90% of their original specific activity. 相似文献
17.
Sediments from Xuanwu Lake have been dredged in the past 3 years to improve the water quality, but methanogenesis should still
exist in the newly settled sediment. Methane production, methanogens, and physiochemical parameters were detected in the surface
sediments (0–5 cm) and/or vertical sediments (0–21 cm, segmented at interval of 3 cm). Methane flux at water–air interface
varied among five detected sites. Principal component analysis showed that CH4 flux, content of water and the concentration of total nitrogen (TN), CH4 and organic matters (OM) weighed most heavily on the component I in surface sediments while different patterns were observed
for vertical sediments. The copy number of the 16S rRNA gene for bacteria was lower in the surface sediment (0–6 cm) than
that in deeper sediments (12–21 cm), while 16S rRNA genes of Archaea were almost evenly distributed in the vertical sediments.
Representatives belonging to the orders Methanobacteriales, Methanomicrobiales, and Methanosarcinales were detected in all samples of the vertical sediments, except that no members of the Methanococcales were detected in the samples at 0–6 cm. The level of Methanobacteriales reached a highest density at 18.1 × 104 copies g−1 dry weight (dw) at 6–9 cm; for Methanosarcinales (76.89 × 106 copies g−1 dw) and Methanococcales (82.70 × 103 copies g−1 dw) at 12–15 cm, whereas for Methanomicrobiales (43.37 × 106 copies g−1 dw) at 9–12 cm. Methanosarcinaceae and Methanosaetaceae reached to their highest densities at 6–9 and 9–12 cm, respectively. These data provided useful information for better understanding
the methanogenesis in the newly settled sediments of a recently dredged lake. 相似文献
18.
An efficient system for clonal mass propagation in liquid culture was established for the propagation of ornamental gentian.
In a test of the requirements for three cytokinins [6-benzylaminopurine, N-(2-chloro-4-pyridyl)-N′-phenylurea and N-phenyl-N′-1,2,3-thiadiazol-5-yl urea (TDZ)] in combination with 1-naphthaleneacetic acid (NAA), we found that effective propagation
of shoots occurred with 0.01 mg l–1 TDZ in a 300 ml conical flask that contained 100 ml of medium. The propagation of shoots was also affected by the concentrations
of macronutrients (KNO3, NH4NO3 and CaCl2) and sucrose in Murashige and Skoog's (MS) medium, and it was influenced to some extent by the speed of agitation on an orbital
shaker. The most efficient propagation of shoots was achieved in full-strength MS medium supplemented with 0.01 mg l–1 TDZ and 20 g l–1 sucrose with agitation at 150 rpm. The propagation of shoots was maximal after 6 weeks of culture (140 shoots from five nodal
segments in one flask). Large-scale propagation in a 5-l fermenter was attempted using 3 l of MS medium that contained 0.01
mg l–1 TDZ and 20 g l–1 sucrose. More than 2,000 shoots were obtained in the fermenter in 5 weeks following the initial cultivation of five nodal
segments for 6 weeks in one 300-ml flask. The shoots that had propagated in the fermenter were transferred directly to soil
without prior rooting in vitro and were easily acclimatized within 1 month.
Received: 7 October 1997 / Revision received: 16 January 1998 / Accepted: 30 January 1998 相似文献
19.
In an attempt to find superior propellants, 2-diazo-4,6-dinitrophenol (DDNP) and its –NO2, –NH2, –CN, –NC, –ONO2, and –NF2 derivatives were studied at the B3LYP/6-311++G** level of density functional theory (DFT). Sensitivity was evaluated using bond dissociation enthalpies (BDEs) and molecular
surface electrostatic potentials. The C–NO2 bond appears to be the trigger bond during the thermolysis process for these compounds, except for the –ONO2 and –NF2 derivatives. Electrostatic potential results show that electron-withdrawing substituents make the charge imbalance more anomalous,
which may change the strength of the bond, especially the weakest trigger bond. Most of the DDNP derivatives have the impact
sensitivities that are higher than that of DDNP, making them favorable for use as solid propellants in micro-rockets. The
theoretical densities (ρ), heats of formation (HOFs), detonation energies (Q), detonation pressures (P), and detonation velocities (D) of the compounds were estimated. The effects of various substituent groups on ρ, HOF, Q, D, and P were investigated. Some derivatives exhibit perfect detonation properties. The calculated relative specific impulses (I
r,sp) of all compounds except for –NH2 derivatives were higher than that of DDNP, and also meet the requirements of propellants. 相似文献
20.
The rabbit Na+/glucose cotransporter (SGLT1) exhibits a presteady-state current after step changes in membrane voltage in the absence of
sugar. These currents reflect voltage-dependent processes involved in cotransport, and provide insight on the partial reactions
of the transport cycle. SGLT1 presteady-state currents were studied as a function of external Na+, membrane voltage V
m
, phlorizin and temperature. Step changes in membrane voltage—from the holding V
h
to test values, elicited transient currents that rose rapidly to a peak (at 3–4 msec), before decaying to the steady state,
with time constants τ≈4–20 msec, and were blocked by phlorizin (K
i
≈30 μm). The total charge Q was equal for the application of the voltage pulse and the subsequent removal, and was a function of V
m
. The Q-V curves obeyed the Boltzmann relation: the maximal charge Q
max was 4–120 nC; V
0.5, the voltage for 50% Q
max was −5 to +30 mV; and z, the apparent valence of the moveable charge, was 1. Q
max and z were independent of V
h
(between 0 and −100 mV) and temperature (20–30°C), while increasing temperature shifted V
0.5 towards more negative values. Decreasing [Na+]
o
decreased Q
max, and shifted V
0.5 to more negative voltages 9by −100 mV per 10-fold decrease in [Na+]
o
). The time constant τ was voltage dependent: the τ-V relations were bell-shaped, with maximal τmax 8–20 msec. Decreasing [Na+]
o
decreased τmax, and shifted the τ-V curves towards more negative voltages. Increasing temperature also shifted the τ-V curves, but did not affect τmax. The maximum temperature coefficient Q
10 for τ was 3–4, and corresponds to an activation energy of 25 kcal/mole. Simulations of a 6-state ordered kinetic model for
rabbit Na+/glucose cotransport indicate that charge-movements are due to Na+-binding/dissociation and a conformational change of the empty transporter. The model predicts that (i) transient currents
rise to a peak before decay to steady-state; (ii) the τ-V relations are bell-shaped, and shift towards more negative voltages as [Na+]
o
is reduced; (iii) τmax is decreased with decreasing [Na+]
o
; and (iv) the Q-V relations are shifted towards negative voltages as [Na+]
o
is reduced. In general, the kinetic properties of the presteady-state currents are qualitatively predicted by the model.
Received: 12 August 1996/Revised: 30 September 1996 相似文献