共查询到20条相似文献,搜索用时 46 毫秒
1.
Fei Ma Xiao-Bo Chen Min Sang Peng Wang Jian-Ping Zhang Liang-Bi Li Ting-Yun Kuang 《Photosynthesis research》2009,100(1):19-28
We have attempted to investigate the correlation between the detergent-perturbed structural integrity of the Cyt b
6
f complex from the marine green alga Bryopsis corticulans and its photo-protective properties, for which the nonionic detergents n-octyl-β-d-glucopyranoside (β-OG) and n-dodecyl-β-d-maltoside (β-DM), respectively, were used for the preparation of Cyt b
6
f, and the singlet oxygen (1O2*) production as well as the triplet excited-state chlorophyll a (3Chl a*) formation and deactivation were examined by spectroscopic means. Near-infrared luminescence of 1O2
* (~1,270 nm) on photo-irradiation was detected for the β-OG preparation where the complex is mainly in oligomeric state, but
not for the β-DM one in which the complex exists in dimeric form. Under anaerobic condition, photo-excitation of Chl a in the β-DM preparation generated 3Chl a* with a lower quantum yield of ΦT ~ 0.02 and a longer lifetime of ~600 μs with respect to those as in the case of β-OG preparation, ΦT ~ 0.12 and 200–300 μs. These results prove that the enzymatically active and intact Cyt b
6
f complex on photo-excitation tends to produce little 3Chl a* or 1O2
*, which implies that the pigment–protein assembly of Cyt b
6
f complex per se is crucial for photo-protection.
F. Ma and X.-B. Chen contributed equally to this work. 相似文献
2.
Two approaches to determine the fraction (μ) of mitochondrial respiration sustained during illumination by measuring CO2 gas exchange are compared. In single leaves, the respiration rate in the light (`day respiration' rate Rd) is determined as the ordinate of the intersection point of A–ci curves at various photon flux densities and compared with the CO2 evolution rate in darkness (`night respiration' rate Rn). Alternatively, using leaves with varying values of CO2 compensation concentration (Γ), intracellular resistance (ri) and Rn, an average number for μ can be derived from the linear regression between Γ and the product riċRn. Both methods also result in a number c* for that intercellular CO2 concentration at which net CO2 uptake rate is equal to –Rd. c* is an approximate value of the photocompensation point Γ* (Γ in the absence of mitochondrial respiration), which is related
to the CO2/O2 specificity factor of Rubisco Sc/o. The presuppositions and limitations for application of both approaches are discussed. In leaves of Nicotiana tabacum, at 22 °C, single leaf measurements resulted in mean values of μ = 0.71 and c* = 34 μmol mol−1. At the photosynthetically active photon flux density of 960 μmol quanta m−2 s−1, nearly the same numbers were derived from the linear relationship between Γ and riċRn. c* and Rd determined by single leaf measurements varied between 31 and 41 μmol mol−1 and between 0.37 and 1.22 μmol m−2 s−1, respectively. A highly significant negative correlation between c* and Rd was found. From the regression equation we obtained estimates for Γ* (39 μmol mol−1), Sc/o (96.5 mol mol−1) and the mesophyll CO2 transfer resistance (7.0 mol−1 m2 s).
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
3.
Streptococcus mutans OMZ 176 was grown in a sucrose-free medium containing fructose as a carbohydrate source. Dextransucrase was precipitated from the culture supernatant with 40% saturated ammonium sulfate. The activity of dextransucrase was shown to be stimulated by exogenous dextran. Maximum activity was reached when the concentration of exogenous dextran was 2 mg/ml. Dextrans modified at the nonreducing ends by reaction with tripsyl chloride and/or by hydrolysis with an exodextranase also activated dextransucrase four to six times over that of a control. The exodextranasemodified dextrans have nonreducing chains that are very short in comparison with unmodified dextran and the tripsyl-modified dextrans have chains that are blocked at the nonreducing ends with a triisopropylbenzenesulfonyl group on the C6 hydroxyl group. Because the nonreducing ends of the modified dextrans are not available for reaction, the activation of dextransucrase by these modified dextrans cannot be due to primer reactions with the nonreducing ends. The activation of dextransucrase, thus, must be by an alternate mechanism. Two alternative mechanisms discussed are an allosteric effect and nucleophilic displacement reactions by the added dextran. It was also found that the addition of increasing amounts of dextran shifted the synthesis from an insoluble dextran to a soluble dextran. 相似文献
4.
A controlled growth chamber experiment was conducted to investigate the short-term water use and photosynthetic responses
of 30-d-old carrot seedlings to the combined effects of CO2 concentration (50–1 050 μmol mol−1) and moisture deficits (−5, −30, −55, and −70 kPa). The photosynthetic response data was fitted to a non-rectangular hyperbola
model. The estimated parameters were compared for effects of moisture deficit and elevated CO2 concentration (EC). The carboxylation efficiency (α) increased in response to mild moisture stress (−30 kPa) under EC when
compared to the unstressed control. However, moderate (−55 kPa) and extreme (−70 kPa) moisture deficits reduced α under EC.
Maximum net photosynthetic rate (P
Nmax) did not differ between mild water deficit and unstressed controls under EC. Moderate and extreme moisture deficits reduced
P
Nmax by nearly 85 % compared to controls. Dark respiration rate (R
D) showed no consistent response to moisture deficit. The CO2 compensation concentration (Γ) was 324 μmol mol−1 for −75 kPa and ranged 63–93 μmol mol−1 for other moisture regimes. Interaction between moisture deficit and EC was noticed for P
N, ratio of intercellular and ambient CO2 concentration (C
i/C
a), stomatal conductance (g
s
), and transpiration rate (E). P
N was maximum and C
i/C
a was minimum at −30 kPa moisture deficit and at C
a of 350 μmol mol−1. The g
s and E showed an inverse relationship at all moisture deficit regimes and EC. Water use efficiency (WUE) increased with moisture
deficit up to −55 kPa and declined thereafter. EC showed a positive influence towards sustaining P
N and increasing WUE only under mild moisture stress, and no beneficial effects of EC were noticed at moderate or extreme moisture
deficits. 相似文献
5.
Earlier works demonstrated theoretically and experimentally that during gel electrophoresis the mobility μ and the dispersion coefficient Dx [reflecting band broadening; G. W. Slater and J. Noolandi (1985) Physics Review Letters, Vol. 55, pp. 1579–1582; T. A. Duke, A. N. Semenov, and J. L. Viovy (1992) Physics Review Letters, Vol. 69, pp. 3260–3263] depend on the chain length, the electric field, and on the gel concentration. Using a Fluorescence Recovery After Photobleaching setup coupled with an electrophoretic cell, we show that they also depend of the DNA concentrationC. Two regimes are observed. The first is analogous to a “dilute” regime in the gel where μ and Dx are DNA concentration independent. In the second regime, μ and Dx decrease when C increases. These results are explained by DNA-DNA interactions. As expected the C* concentration, under which measurements must be carried out to avoid this effect, is found to be the same as the overlap concentration C* determined in solution. Using concentrations of the studied DNA lower than its C*, μ and Dx show a field dependence in good agreement with the predictions of the Biased Reptation model with Fluctuations. © 1997 John Wiley & Sons, Inc. Biopoly 42: 471–478, 1997 相似文献
6.
Leaf senescence of Quercus myrtifolia as affected by long-term CO2 enrichment in its native environment 总被引:1,自引:0,他引:1
J. -H. Li P. Dijkstra § G. J. Hymus § R. M. Wheeler † W. C. Piastuch ‡ C. R. Hinkle‡ B. G. Drake§ 《Global Change Biology》2000,6(7):727-733
The long‐term effects of elevated (ambient plus 350 μmol mol?1) atmospheric CO2 concentration (Ca) on the leaf senescence of Quercus myrtifolia Willd was studied in a scrub‐oak community during the transition from autumn (December 1997) to spring (April 1998). Plants were grown in large open‐top chambers at the Smithsonian CO2 Research Site, Merritt Island Wildlife Refuge, Cape Canaveral, Florida. Chlorophyll (a + b) concentration, Rubisco activity and N concentration decreased by 75%, 82%, and 52%, respectively, from December (1997) to April (1998) in the leaves grown at ambient Ca. In contrast, the leaves of plants grown at elevated Ca showed no significant decrease in chlorophyll (a + b) concentration or Rubisco activity, and only a 25% reduction in nitrogen. These results indicate that leaf senescence was delayed during this period at elevated Ca. Delayed leaf senescence in elevated Ca had important consequences for leaf photosynthesis. In elevated Ca the net photosynthetic rate of leaves that flushed in Spring 1997 (last year's leaves) and were 13 months old was not different from fully‐expanded leaves that flushed in 1998, and were approximately 1 month old (current year's leaves). In ambient Ca the net photosynthetic rate of last year's leaves was 54% lower than for current year's leaves. When leaves were fully senesced, nitrogen concentration decreased to about 40% of the concentration in non‐senesced leaves, in both CO2 treatments. In April, net photosynthesis was 97% greater in leaves grown in elevated Ca than in those grown at ambient. During the period when elevated Ca delayed leaf senescence, more leaves operating at higher photosynthetic rate would allow the ecosystem dominated by Q. myrtifolia to gain more carbon at elevated Ca than at ambient Ca. 相似文献
7.
This work aimed to evaluate if gas exchange and PSII photochemical activity in maize are affected by different irradiance
levels during short-term exposure to elevated CO2. For this purpose gas exchange and chlorophyll a fluorescence were measured on maize plants grown at ambient CO2 concentration (control CO2) and exposed for 4 h to short-term treatments at 800 μmol(CO2) mol−1 (high CO2) at a photosynthetic photon flux density (PPFD) of either 1,000 μmol m−2 s−1 (control light) or 1,900 μmol m−2 s−1 (high light). At control light, high-CO2 leaves showed a significant decrease of net photosynthetic rate (P
N) and a rise in the ratio of intercellular to ambient CO2 concentration (C
i/C
a) and water-use efficiency (WUE) compared to control CO2 leaves. No difference between CO2 concentrations for PSII effective photochemistry (ΦPSII), photochemical quenching (qp) and nonphotochemical quenching (NPQ) was detected. Under high light, high-CO2 leaves did not differ in P
N, C
i/C
a, ΦPSII and NPQ, but showed an increase of WUE. These results suggest that at control light photosynthetic apparatus is negatively
affected by high CO2 concentration in terms of carbon gain by limitations in photosynthetic dark reaction rather than in photochemistry. At high
light, the elevated CO2 concentration did not promote an increase of photosynthesis and photochemistry but only an improvement of water balance due
to increased WUE. 相似文献
8.
Andreas Janshoff Claudia Steinem Manfred Sieber A. el Bayâ Marcus Alexander Schmidt H.-J. Galla 《European biophysics journal : EBJ》1997,26(3):261-270
The binding of cholera toxin, tetanus toxin and pertussis toxin to ganglioside containing solid supported membranes has been
investigated by quartz crystal microbalance measurements. The bilayers were prepared by fusion of phospholipid-vesicles on
a hydrophobic monolayer of octanethiol chemisorbed on one gold electrode placed on the 5 MHz AT-cut quartz crystal. The ability
of the gangliosides GM1, GM3, GD1a, GD1b, GT1b and asialo-GM1 to act as suitable receptors for the different toxins was tested by measuring the changes of quartz resonance frequencies.
To obtain the binding constants of each ligand-receptor-couple Langmuir-isotherms were successfully fitted to the experimental
adsorption isotherms. Cholera toxin shows a high affinity for GM1 (Ka = 1.8 ⋅ 108M–1), a lower one for asialo-GM1 (Ka = 1.0 ⋅ 107 M–1) and no affinity for GM3. The C-fragment of tetanus toxin binds to ganglioside GD1a, GD1b and GT1b containing membranes with similar affinity (Ka∼106 M–1), while no binding was observed with GM3. Pertussis toxin binds to membranes containing the ganglioside GD1a with a binding constant of Ka = 1.6 ⋅ 106 M–1, but only if large amounts (40 mol%) of GD1a are present. The maximum frequency shift caused by the protein adsorption depends strongly on the molecular structure of
the receptor. This is clearly demonstrated by an observed maximum frequency decrease of 99 Hz for the adsorption of the C-fragment
of tetanus toxin to GD1b. In contrast to this large frequency decrease, which was unexpectedly high with respect to Sauerbrey's equation, implying
pure mass loading, a maximum shift of only 28 Hz was detected after adsorption of the C-fragment of tetanus toxin to GD1a.
Received: 14 January 1997 / Accepted: 15 April 1997 相似文献
9.
Min Sang Fei Ma Jie Xie Xiao-Bo Chen Ke-Bin Wang Xiao-Chun Qin Wen-Da Wang Jing-Quan Zhao Liang-Bi Li Jian-Ping Zhang Ting-Yun Kuang 《Biophysical chemistry》2010
Electron paramagnetic resonance (EPR) spectroscopy was used to detect the light-induced formation of singlet oxygen (1O2*) in the intact and the Rieske-depleted cytochrome b6f complexes (Cyt b6f) from Bryopsis corticulans, as well as in the isolated Rieske Fe–S protein. It is shown that, under white-light illumination and aerobic conditions, chlorophyll a (Chl a) bound in the intact Cyt b6f can be bleached by light-induced 1O2*, and that the 1O2* production can be promoted by D2O or scavenged by extraneous antioxidants such as l-histidine, ascorbate, β-carotene and glutathione. Under similar experimental conditions, 1O2* was also detected in the Rieske-depleted Cyt b6f complex, but not in the isolated Rieske Fe–S protein. The results prove that Chl a cofactor, rather than Rieske Fe–S protein, is the specific site of 1O2* formation, a conclusion which draws further support from the generation of 1O2* with selective excitation of Chl a using monocolor red light. 相似文献
10.
R. Candau A. Belli G. Y. Millet D. Georges B. Barbier J. D. Rouillon 《European journal of applied physiology and occupational physiology》1998,77(6):479-485
The aim of the present study was to examine the physiological and mechanical factors which may be concerned in the increase
in energy cost during running in a fatigued state. A group of 15 trained triathletes ran on a treadmill at velocities corresponding
to their personal records over 3000m [mean 4.53 (SD 0.28) m · s−1] until they felt exhausted. The energy cost of running (C
R) was quantified from the net O2 uptake and the elevation of blood lactate concentration. Gas exchange was measured over 1 min firstly during the 3rd–4th min
and secondly during the last minute of the run. Blood samples were collected before and after the completion of the run. Mechanical
changes of the centre of mass were quantified using a kinematic arm. A significant mean increase [6.9 (SD 3.5)%, P < 0.001] in C
R from a mean of 4.4 (SD 0.4) J · kg−1 · m−1 to a mean of 4.7 (SD 0.4) J · kg−1 · m−1 was observed. The increase in the O2 demand of the respiratory muscles estimated from the increase in ventilation accounted for a considerable proportion [mean
25.2 (SD 10.4)%] of the increase in CR. A mean increase [17.0 (SD 26.0)%, P < 0.05] in the mechanical cost (C
M) from a mean of 2.36 (SD 0.23) J · kg−1 · m−1 to a mean of 2.74 (SD 0.55) J · kg−1 · m−1 was also noted. A significant correlation was found between C
R and C
M in the non-fatigued state (r = 0.68, P < 0.01), but not in the fatigued state (r = 0.25, NS). Furthermore, no correlations were found between the changes (from non-fatigued to fatigued state) in C
R and the changes in C
M suggesting that the increase in C
R is not solely dependent on the external work done per unit of distance. Since step frequency decreased slightly in the fatigued
state, the internal work would have tended to decrease slightly which would not be compatible with an increase in C
R. A stepwise regressions showed that the changes in C
R were linked (r = 0.77, P < 0.01) to the changes in the variability of step frequency and in the variability of potential cost suggesting that a large
proportion of the increase in C
R was due to an increase in the step variability. The underlying mechanisms of the relationship between C
R and step variability remains unclear.
Accepted: 15 September 1997 相似文献
11.
N. Rashevsky 《Bulletin of mathematical biology》1962,24(3):319-325
The driver tries to keep the car in the center of the lane. If the car is too near the left edge, this causes the driver to
make a “corrective” right turn. If the car is near the right edge, a “corrective” left turn is made. Therefore, a quantity
which decreases with increasing distance Δ
L
from the left edge may be considered as a stimulusS
R producing the reactionR
R of turning to the right. A similar situation holds for the distance Δ
R
from the right edge. When the car is in the center of the lane, Δ
L
= Δ
R
andS
R
=S
L
, the stimuli are equal. We thus have here a situation analogous to the one studied by H. D. Landahl in his theory of psychophysical
discrimination. In general a reactionR
R
(resp.R
L
) will occur only ifR
R
−R
L
≥h
* (resp.R
L
−R
R
≥h
*) whereh
* is a threshold. Applying Landahl’s theory to this situation, we find thath
* determines the distance from the edge, at which a corrective turn is made. This distance is not constant, but a function
of the speedv of the car. The requirement that a corrective turn should be madebeforre the car runs off the road leads to an expression for the maximum safe speed. Because of the transcendency of the equations
involved, closed solutions cannot be obtained. It is, however, shown that the expression for maximum safe speed, given in
a previous paper (Bull. Math. Biophysics,21, 299–308, 1959), is a rough first approximation to the expressions found now. 相似文献
12.
The transverse relaxation rate, R2, measured as a function of the effective field (R2 dispersion) using a Carr-Purcell-Meiboom-Gill (CPMG) pulse train, is well suited to detect conformational exchange in proteins.
The dispersion data are commonly fitted by a two-site (sites a and b) exchange model with four parameters: the relative population,
pa, the difference in chemical shifts of the two sites, δω, the correlation time for exchange, τex, and the intrinsic relaxation rate (i.e., transverse relaxation rate in the absence of chemical exchange), R20. Although the intrinsic relaxation rates of the two sites, R20a and R20b, can differ, they are normally assumed to be the same (i.e., R20a = R20b = R20) when fitting dispersion data. The purpose of this investigation is to determine the magnitudes of the errors in the optimized
exchange parameters that are introduced by the assumption that R20a = R20b. In order to accomplish this goal, we first generated synthetic constant-time CPMG R2 dispersion data assuming two-site exchange with R20a ≠ R20b, and then fitted the synthetic data assuming two-site exchange with R20 = R20a = R20b. Although all the synthetic data generated assuming R20a ≠ R20b were well fitted (assuming R20a = R20b), the optimized values of pa and τ ex differed from their true values, whereas the optimized values of δω values did not. A theoretical analysis using the Carver–Richards
equation explains these results, and yields simple, general equations for estimating the magnitudes of the errors in the optimized
parameters, as a function of ( R20a − R20b). 相似文献
13.
The sesquiterpene lactone, 2-methyl-2-butenoic acid dodecahydro-4-(hydroxymethyl)-10a-methyl-8-methylene-3,7-dioxooxineno[5,6]cyclodeca[1,2-b]furan-9-yl ester [1aR*-[1aS*,4R*,5aS*,8aR*,9R*(E)]], argophyllone-B, was isolated from acetone extracts from the leaves of Helianthus argophyllus. Its structure has been determined by single crystal X-ray analysis. Complete 1H NMR and 13C NMR assignments have been made. 相似文献
14.
The dynamics of the nucleobase and the ribose moieties in a 14-nt RNA cUUCGg hairpin-loop uniformly labeled with 13C and 15N were studied by 13C spin relaxation experiments. R1, R1ρ and the 13C-{1H} steady-state NOE of C6 and C1′ in pyrimidine and C8 and C1′ in purine residues were obtained at 298 K. The relaxation data were analyzed by the model-free formalism to yield dynamic
information on timescales of pico-, nano- and milli-seconds. An axially symmetric diffusion tensor with an overall rotational
correlation time τc of 2.31±0.13 ns and an axial ratio of 1.35±0.02 were determined. Both findings are in agreement with hydrodynamic calculations.
For the nucleobase carbons, the validity of different reported 13C chemical shift anisotropy values (Stueber, D. and Grant, D. M., 2002 J. Am. Chem. Soc. 124, 10539–10551; Fiala et al., 2000 J. Biomol. NMR 16, 291–302; Sitkoff, D. and Case, D. A., 1998 Prog. NMR Spectroscopy 32, 165–190) is discussed. The resulting dynamics are in agreement with the structural features of the cUUCGg motif in that
all residues are mostly rigid (0.82 < S2 < 0.96) in both the nucleobase and the ribose moiety except for the nucleobase of U7, which is protruding into solution (S2 = 0.76). In general, ribose mobility follows nucleobase dynamics, but is less pronounced. Nucleobase dynamics resulting from
the analysis of 13C relaxation rates were found to be in agreement with 15N relaxation data derived dynamic information (Akke et al., 1997 RNA 3, 702–709).
Electronic supplementary material Electronic supplementary material is available for this article at
and accessible for authorised users. 相似文献
15.
Xiahong Feng 《Oecologia》1998,117(1-2):19-25
To evaluate how the land carbon reservoir has been responding to the rising CO2 concentration of the atmosphere, it is important to study how plants in natural forests adjust physiologically to the changing
atmospheric conditions. Many experimental studies have addressed this issue, but it has been difficult to scale short-term
experimental observations to long-term ecosystem-level responses. This paper derives carbon-isotope-related variables for
the past 100–200 years from measurements on trees from natural forests. Calculations show that the c
i/c
a ratios [c
i/c
a is the ratio of the CO2 concentration (μmol mol−1) in the intercellular space of leaves to that in the atmosphere] of the trees were constant or increased slightly before
the 20th century, but changed more rapidly in the 20th century; some increased, some decreased, and some stayed constant.
In contrast, the CO2 concentration inside plant leaves increased monotonically for all trees.
Received: 12 June 1997 / Accepted: 29 June 1998 相似文献
16.
Translational Diffusion of Macromolecule-sized Solutes in Cytoplasm and Nucleus 总被引:26,自引:3,他引:23 下载免费PDF全文
Fluorescence recovery after photobleaching (FRAP) was used to quantify the translational diffusion of microinjected FITC-dextrans and Ficolls in the cytoplasm and nucleus of MDCK epithelial cells and Swiss 3T3 fibroblasts. Absolute diffusion coefficients (D) were measured using a microsecond-resolution FRAP apparatus and solution standards. In aqueous media (viscosity 1 cP), D for the FITC-dextrans decreased from 75 to 8.4 × 10−7 cm2/s with increasing dextran size (4–2,000 kD). D in cytoplasm relative to that in water (D/Do) was 0.26 ± 0.01 (MDCK) and 0.27 ± 0.01 (fibroblasts), and independent of FITC-dextran and Ficoll size (gyration radii [RG] 40–300 Å). The fraction of mobile FITC-dextran molecules (fmob), determined by the extent of fluorescence recovery after spot photobleaching, was >0.75 for RG < 200 Å, but decreased to <0.5 for RG > 300 Å. The independence of D/Do on FITC-dextran and Ficoll size does not support the concept of solute “sieving” (size-dependent diffusion) in cytoplasm. Photobleaching measurements using different spot diameters (1.5–4 μm) gave similar D/Do, indicating that microcompartments, if present, are of submicron size. Measurements of D/Do and fmob in concentrated dextran solutions, as well as in swollen and shrunken cells, suggested that the low fmob for very large macromolecules might be related to restrictions imposed by immobile obstacles (such as microcompartments) or to anomalous diffusion (such as percolation). In nucleus, D/Do was 0.25 ± 0.02 (MDCK) and 0.27 ± 0.03 (fibroblasts), and independent of solute size (RG 40–300 Å). Our results indicate relatively free and rapid diffusion of macromolecule-sized solutes up to approximately 500 kD in cytoplasm and nucleus. 相似文献
17.
Carbon isotopes and water use efficiency: sense and sensitivity 总被引:1,自引:0,他引:1
We revisit the relationship between plant water use efficiency and carbon isotope signatures (δ13C) of plant material. Based on the definitions of intrinsic, instantaneous and integrated water use efficiency, we discuss
the implications for interpreting δ13C data from leaf to landscape levels, and across diurnal to decadal timescales. Previous studies have often applied a simplified,
linear relationship between δ13C, ratios of intercellular to ambient CO2 mole fraction (C
i/C
a), and water use efficiency. In contrast, photosynthetic 13C discrimination (Δ) is sensitive to the ratio of the chloroplast to ambient CO2 mole fraction, C
c/C
a (rather than C
i/C
a) and, consequently, to mesophyll conductance. Because mesophyll conductance may differ between species and over time, it
is not possible to determine C
c/C
a from the same gas exchange measurements as C
i/C
a. On the other hand, water use efficiency at the leaf level depends on evaporative demand, which does not directly affect
Δ. Water use efficiency and Δ can thus vary independently, making it difficult to obtain trends in water use efficiency from
δ13C data. As an alternative approach, we offer a model available at to explore how water use efficiency and 13C discrimination are related across leaf and canopy scales. The model provides a tool to investigate whether trends in Δ indicate
changes in leaf functional traits and/or environmental conditions during leaf growth, and how they are associated with trends
in plant water use efficiency. The model can be used, for example, to examine whether trends in δ13C signatures obtained from tree rings imply changes in tree water use efficiency in response to atmospheric CO2 increase. This is crucial for predicting how plants may respond to future climate change.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
18.
Subashini M. Devarajan Padma V. Sonavane Ganeshchandra S. Doble Mukesh 《Journal of molecular modeling》2011,17(5):1141-1147
Drug uptake by polymer was modeled using a molecular dynamics (MD) simulation technique. Three drugs—doxorubicin (water soluble),
silymarin (sparingly water soluble) and gliclazide (water insoluble)—and six polymers with varied functional groups—alginic
acid, sodium alginate, chitosan, Gantrez AN119 (methyl-vinyl–ether-co-malic acid based), Eudragit L100 and Eudragit RSPO (both
acrylic acid based)—were selected for the study. The structures were modeled and minimized using molecular mechanics force
field (MM+). MD simulation (Gromacs-forcefield, 300 ps, 300 K) of the drug in the vicinity of the polymer molecule in the
presence of water molecules was performed, and the interaction energy (IE) between them was calculated. This energy was evaluated
with respect to electric-dipole, van der Waals and hydrogen bond forces. A good linear correlation was observed between IE
and our own previous data on drug uptake* [R
2 = 0.65, Radj2 = 0.65,Rpre2 = 0.56, {\hbox{R}}_{\rm{adj}}^2 = 0.65,{\hbox{R}}_{\rm{pre}}^2 = 0.56, and a F ratio of 30.25, P < 0.001; Devarajan et al. (2005) J Biomed Nanotechnol 1:1–9]. Maximum drug uptake by the polymeric nanoparticles (NP) was
achieved in water as the solvent environment. Hydrophilic interaction between NP and water was inversely correlated with drug
uptake. The MD simulation method provides a reasonable approximation of drug uptake that will be useful in developing polymer-based
drug delivery systems. 相似文献
19.
Summary The cell is considered to be divided into nucleic acids, proteinaceous material and storage compounds. The enzyme is believed to be constitutive but repressed by the rate of catabolism. A structured model is developed to describe the growth, amylase production and dissolved oxygen profile in the batch culture ofAspergillus oryzae.Nomenclature CA
Conc. of enzyme SKB units/m3
- CD,CE,CG,CO,CS
Conc. of D.E.G. mass, oxygen, substrate kg/m3
- CO*
Mean oxygen conc. in gas-liquid interface kg/m3
- CX
Total cell conc. kg/m3
- D
D-mass (proteins) kg
- E
E-mass (storage carbon) kg
- G
G-mass (necleic acids) kg
- KE
Rate of usage of E-mass kg/m3/h
- KEO
KE with oxygen limitation kg/m3/h
- Q
Active fraction of promotor genes -
- RD,RE,RG
Rate of production of D,E,G-mass kg/m3/h
- RO,RS
Rate of usage of oxygen, substrate kg/m3/h
- RDO,REO,RGO
RD,RE and RG with oxygen limitation kg/m3/h
- S
Substrate (carbon) concentration kg/m3
- t
Time h
- to
Time at which CS = 0 h
- K1,K2,K3,K24,K25
Stoichiometric constants -
- K4,K5,K6,K7
Rate constants h–1
- K8-K12,K18,K20-K23
Michaelis-Menten constants kg/m3
- K26,K26
Absorption coefficient, K26 at CX = 0 h–1
- K27
Empirical constant kg/m3
- K15
Rate of enzyme formation SKB units/kg
- K16,K17
Equilibrium constants m3/kg
- K19
Decay constant for mRNA h–1 相似文献
20.
A range of fluorescently labelled probes of increasing molecular weight was used to monitor diffusion via the symplast in
regenerating thin cell layer (TCL) explants of Torenia fournieri. An increase in intercellular movement of these molecules was associated with the earliest stages of vegetative shoot regeneration,
with the movement of a 10 kDa dextran (FD 10000) observed between epidermal cells prior to the appearance of the first cell
divisions. A low frequency of dextran movement in thin cell layers maintained under non-regenerating conditions was also observed,
indicating a possible wound induced increase in intercellular movement. Dextran movement between epidermal cells reached a
peak by day 4 of culture and then declined as cell division centres (CDCs) formed, became meristematic regions and finally
emerged as adventitious shoots. Within CDCs, testing with small fluorescent probes (CF: carboxyfluorescein, mw 376 Da and
F(Glu)3: fluorescein-triglutamic acid, mw 799 Da) revealed a mosaic of cell isolation and regions of maintained symplastic linkage.
Within shoots, surface cells of the presumptive apical meristem permitted the intercellular movement of 10 kDa dextrans but
epidermal cells of the surrounding leaf primordia did not permit dextran movement. In some cases, intercellular movement of
CF was maintained within leaf primordia. Symplastic movement of labelled dextrans during regeneration in Torenia thin cell layers represents a significant increase in the basal size exclusion limit (SEL) of this tissue and reveals the
potential for intercellular trafficking of developmentally related endogenous macromolecules. 相似文献