共查询到20条相似文献,搜索用时 15 毫秒
1.
Repair effects of rutin and quercetin on purine deoxynucleotide radical cations were studied using pulse radiolysis technique. On electron pulse irradiation of N2 saturated deoxynucleotide aqueous solution containing 20 mmol/L K2S2O8, 200 mmol/Lt-BuOH and rutin or quercetin, the transient absorption spectra of the deoxynucleotide radical cations decayed quickly. At the same time, the spectra of flavonoid phenoxyl radicals formed within several dozen microseconds. The results indicated that deoxynucleotide radical cations can be repaired by flavonoids. The rate constants of the repair reactions were 3.8 ×108-4.4 ×108 mol−1 · L · s−1 and 1.3×108-1.8×108 mol−1 · L · s−1 for dAMP and dGMP radical cations, respectively. 相似文献
2.
Repair effects of rutin and quercetin on purine deoxynucleotide radical cations were studied using pulse radiolysis technique. On electron pulse irradiation of N2 saturated deoxynucleotide aqueous solution containing 20 mmol/L K2S2O8, 200 mmol/L f-BuOH and rutin or quercetin, the transient absorption spectra of the deoxynucleotide radical cations decayed quickly. At the same time, the spectra of flavonoid phenoxyl radicals formed within several dozen microseconds. The results indicated that deoxynucleotide radical cations can be repaired by flavonoids. The rate constants of the repair reactions were 3.8 × 108-4.4×108 mol-1 · L · s-1 and 1.3×108-1.8×108 mol-1 · L · s-1 for dAMP and dGMP radical cations, respectively. 相似文献
3.
M. R. de la Peña 《Journal of applied phycology》2007,19(6):647-655
Two series of experiments were conducted to determine suitable growth factors for the mass propagation of the local algal
isolate Amphora sp. A higher growth rate of 0.2 doubling (μ) day−1 was attained at a lower photosynthetic photon flux density (PPFD; 11.4 μmol photon m−2s−1) compared to cultures exposed to higher levels of PPFD (16.1 μmol photon m−2s−1, −0.1 μ day −1; 31.3 μmol photon m−2s−1, 0.0 μ day−1). Cultures located inside the laboratory had a significantly higher cell density (133 × 104 cells cm−2) and growth rate (0.3 μ day−1) compared to those located outdoors (100 × 104 cells cm−2, 0.2 μ day−1). A comparison of nutrient medium across two locations showed that lipid content was significantly higher in cultures enriched
with F/2MTM (macronutrients + trace metals) and F/2MV (macronutrients + vitamins). Saturated fatty acids were also present
in high concentrations in cultures enriched with F/2M (macronutrients only). Significantly higher amounts of saturated fatty
acids were observed in cultures located outdoors (33.1%) compared to those located indoors (26.6%). The protein, carbohydrates
and n-6 fatty acid content of Amphora sp. were influenced by the location and enrichment of the cultures. This study has identified growth conditions for mass
culture of Amphora sp. and determined biochemical composition under those culture conditions.
Presented at the 6th Meeting of the Asian Pacific Society of Applied Phycology, Manila, Philippines. 相似文献
4.
The study of the isotherms desorption of olive mill wastewater (OMW) was investigated to describe its water activity under
different saturated environments. The microbial biodegradation of OMW during its storage in 5 evaporation ponds located in
Agareb (Sfax-Tunisia) was carried out during the oil-harvesting year held 105 days in 2004. Gravimetric static method using
saturated salt solutions was used and OMW as placed at 30°C and under different water activities ranging from 0.11 to 0.90.
Eight models were taken from the literature to describe experimental desorption isotherms. During storage, the evolution of
physico-chemical parameters including pH, temperature, evaporation, humidity, total phosphorus, chemical oxygen demand (COD),
biological oxygen demand (BOD) and phenols and three microbiological flora (aerobic mesophilic bacteria, yeasts and moulds)
were considered. At 30°C, when relative humidity increased in the experimented ponds of 69, 84 and 90%, the evaporation speed
decreased from 1.24 × 10−5 to 5 × 10−6 cm3 s−1, from 6 × 10−5 to 7 × 10−6 cm3 s−1 and from 5 × 10−6 to 1.1 × 10−7 cm3 s−1 respectively. The desorption isotherm exhibited a sigmoidal curve corresponding to type II, typical of many organic material.
The GAB and Peleg models gave the best fit for describing the relationship between the equilibrium moisture content and water
activity in OMW (R
2 = 0.998). During the storage period, the analysis showed an increase of all the physico-chemical parameters studied, except
phenols and total phosphorus concentrations. The microbiological study showed the predominance of yeasts and moulds and the
decrease of bacteria population after 75 days reflecting both effect of recalcitrant compounds and the water activity on microbial
growth. 相似文献
5.
Cappenberg Thom E. Hordijk Kees A. Jonkheer Gert J. Lauwen Jos P. M. 《Hydrobiologia》1982,91(1):161-168
The turnover and exchange rates, as well as the diffusion processes, concerning the input and output of carbon compounds at
the mud-water interface, were studied. The carbon input rates were derived from the annual sedimentation rates of particulate
organic matter (about 1 100 kg C · yr−1). The nature of the sedimented POC, and its breakdown pathways and turnover rates towards important metabolic intermediates
in methanogenesis, were examined. The breakdown kinetics ofChlorella cell walls, a dominant green alga in Lake Vechten, was studied using U-14C-labelled cell walls. The breakdown of the cell walls appears to the rate-limiting step in anaerobic mineralization.
Using first order kinetic equations, and HPLC and GLC and radio-chemical methods, turnover rate constants (k-values) of between
0.18 and 0.32 day−1 and pool sizes of algal cell walls of 37 to 80 μg · g−1 wet mud were found, giving turnover rates of 7.7 to 25.6 μg · g−1 · day−1 of cell wall material. The turnover rates (k-values between 0.07 and 0.31 h−1) of acetate, the most important breakdown product, and its concentration gradients (between 5 and 30 μmol) and diffusion
coefficient (Ds = 2.2 × 10−6 cm2 · s−1) just in and above mud-water interface, was quantified. The diffusion of acetate, within the sediments, could not account
for the turnover rates observed.
Finally, from acetate flux data and from those on the rates of formation of carbon dioxide and methane, the output of carbon
and its cycling in Lake Vechten are discussed. 相似文献
6.
Elongation growth of plant cells occurs by stretching of cell walls under turgor pressure when intermolecular bonds in the
walls are temporarily loosened. The acid-growth theory predicts that wall loosening is the result of wall acidification because
treatments (including IAA and fusicoccin) that cause lowered wall pH cause elongation. However, conclusive evidence that IAA
primarily reduces wall pH has been lacking. Calcium has been reported to stiffen the cell walls. We have used a microelectrode
ion-flux measuring technique to observe directly, and non-invasively, the net fluxes of protons and calcium from split coleoptiles
of oats (Avena sativa L.) in unbuffered solution. Normal net fluxes are 10 nmol · m−2 · s−1 proton efflux and zero calcium flux. The toxin fusicoccin (1 μM) causes immediate efflux from tissue not only of protons,
but also of calcium, about 110 nmol · m−2 · s−1 in each case. The data fit the “weak acid Donnan Manning” model for ion exchange in the cell wall. Thus we associate the
known “acid-growth” effect of fusicoccin with the displacement of calcium from the wall by exchange for protons extruded from
the cytoplasm. Application of 10 μM IAA causes proton efflux to increase transiently by about 15 nmol · m−2 · s−1 with a lag of about 10 min. The calcium influx decreases immediately to an efflux of about 20 nmol · m−2 · s−1. It appears that auxin too causes an “acid-growth” effect, with extruded protons exchanging for calcium in the cell walls.
I. Arif is currently recieving an AIDAB scholarship. This work was supported by an Australian Research Council grant to I.A.
Newman. 相似文献
7.
The bioelectrochemistry of the blue copper protein, pseudoazurin, at glassy carbon and platinum electrodes that were modified
with single-wall carbon nanotubes (SWNTs) was investigated by multiple scan rate cyclic voltammetry. The protein showed reversible
electrochemical behavior at both bare glassy carbon electrodes (GCEs) and SWNT-modified GCEs (SWNT|GCEs); however, direct
electrochemistry was not observed at any of the platinum electrodes. The effect of the carbon nanotubes at the GCE was to
amplify the current response 1000-fold (nA at bare GCE to μA at SWNT|GCE), increase the apparent diffusion coefficient D
app of the solution-borne protein by three orders of magnitude, from 1.35 × 10−11 at bare GCE to 7.06 × 10−8 cm2 s-1 at SWNT|GCE, and increase the heterogeneous electron transfer rate constant k
s threefold, from 1.7 × 10−2 cm s−1 at bare GCE to 5.3 × 10−2 cm s−1 at SWNT|GCE. Pseudoazurin was also found to spontaneously adsorb onto the nanotube-modified GCE surface. Well-resolved voltammograms
indicating quasi-reversible faradaic responses were obtained for the adsorbed protein in phosphate buffer, with I
pc
and I
pa
values now greater than corresponding values for solution-borne pseudoazurin at SWNT|GCEs and with significantly reduced
ΔE
p
values. The largest electron transfer rate constant of 1.7 × 10−1 cm s−1 was achieved with adsorbed pseudoazurin at the SWNT|GCE surface in deaerated buffer solution consistent with its presumed
role in anaerobic respiration of some bacteria. 相似文献
8.
Alfonso Gautieri Simone Vesentini Alberto Redaelli 《Journal of molecular modeling》2010,16(12):1845-1851
The normal diffusion regime of many small and medium-sized molecules occurs on a time scale that is too long to be studied
by atomistic simulations. Coarse-grained (CG) molecular simulations allow to investigate length and time scales that are orders
of magnitude larger compared to classical molecular dynamics simulations, hence providing a valuable approach to span time
and length scales where normal diffusion occurs. Here we develop a novel multi-scale method for the prediction of diffusivity
in polymer matrices which combines classical and CG molecular simulations. We applied an atomistic-based method in order to
parameterize the CG MARTINI force field, providing an extension for the study of diffusion behavior of penetrant molecules
in polymer matrices. As a case study, we found the parameters for benzene (as medium sized penetrant molecule whose diffusivity
cannot be determined through atomistic models) and Poly (vinyl alcohol) (PVA) as polymer matrix. We validated our extended
MARTINI force field determining the self diffusion coefficient of benzene (2.27·10−9 m2 s−1) and the diffusion coefficient of benzene in PVA (0.263·10−12 m2 s−1). The obtained diffusion coefficients are in remarkable agreement with experimental data (2.20·10−9 m2 s−1 and 0.25·10−12 m2 s−1, respectively). We believe that this method can extend the application range of computational modeling, providing modeling
tools to study the diffusion of larger molecules and complex polymeric materials. 相似文献
9.
Hiroshi Takashima Ayako Araki Keiko Takemoto Naokazu Yoshikawa Keiichi Tsukahara 《Journal of biological inorganic chemistry》2006,11(3):316-324
In order to understand the detailed mechanism of the stereoselective photoinduced electron-transfer (ET) reactions of zinc-substituted
myoglobin (ZnMb) with optically active molecules by flash photolysis, we designed and prepared new optically active agents,
such as N,N′-dimethylcinchoninium diiodide ([MCN]I2) and N,N′-dimethylcinchonidinium diiodide ([MCD]I2). The photoexcited triplet state of ZnMb, 3(ZnMb)*, was successfully quenched by [MCN]2+ and [MCD]2+ ions to form the radical pair of ZnMb cation (ZnMb·+) and reduced [MCN]·+ and [MCD]·+, followed by a thermal back ET reaction to the ground state. The rate constants (k
q) for the ET quenching at 25 °C were obtained as k
q(MCN)=(1.9±0.1)×106 M−1 s−1 and k
q(MCD)=(3.0±0.2)×106 M−1 s−1, respectively. The ratio of k
q(MCD)/k
q(MCN)=1.6 indicates that the [MCD]2+ preferentially quenches 3(ZnMb)*. The second-order rate constants (k
b) for the thermal back ET reaction from [MCN]·+ and [MCD]·+ to ZnMb·+ at 25 °C were k
b(MCN)=(0.79±0.04)×108 M−1 s−1 and k
b(MCD)=(1.0±0.1)×108 M−1 s−1, respectively, and the selectivity was k
q(MCD)/k
q(MCN)=1.3. Both quenching and thermal back ET reactions are controlled by the ET step. In the quenching reaction, the energy
differences of ΔΔH
≠(MCD–MCN) and ΔΔS
≠(MCD–MCN) at 25 °C were obtained as −1.1 and 0 kJ mol−1, respectively. On the other hand, ΔΔH
≠(MCD–MCN)=11±2 kJ mol−1 and TΔΔS
≠(MCD–MCN)=−10±2 kJ mol−1 were given in the thermal back ET reaction. The highest stereoselectivity of 1.7 for [MCD]·+ found at low temperature (10 °C) was due to the ΔΔS
≠ value obtained in the thermal back ET reaction.
Electronic Supplementary Material Supplementary material is available for this article at and is accessible for authorized users. 相似文献
10.
Seasonal dynamics of fine root biomass, root length density, specific root length, and soil resource availability in a Larix gmelinii plantation 总被引:1,自引:0,他引:1
Cheng Yunhuan Han Youzhi Wang Qingcheng Wang Zhengquan 《Frontiers of Biology in China》2006,1(3):310-317
Fine root turnover is a major pathway for carbon and nutrient cycling in terrestrial ecosystems and is most likely sensitive
to many global change factors. Despite the importance of fine root turnover in plant C allocation and nutrient cycling dynamics
and the tremendous research efforts in the past, our understanding of it remains limited. This is because the dynamics processes
associated with soil resources availability are still poorly understood. Soil moisture, temperature, and available nitrogen
are the most important soil characteristics that impact fine root growth and mortality at both the individual root branch
and at the ecosystem level. In temperate forest ecosystems, seasonal changes of soil resource availability will alter the
pattern of carbon allocation to belowground. Therefore, fine root biomass, root length density (RLD) and specific root length
(SRL) vary during the growing season. Studying seasonal changes of fine root biomass, RLD, and SRL associated with soil resource
availability will help us understand the mechanistic controls of carbon to fine root longevity and turnover. The objective
of this study was to understand whether seasonal variations of fine root biomass, RLD and SRL were associated with soil resource
availability, such as moisture, temperature, and nitrogen, and to understand how these soil components impact fine root dynamics
in Larix gmelinii plantation. We used a soil coring method to obtain fine root samples (⩽2 mm in diameter) every month from May to October
in 2002 from a 17-year-old L. gmelinii plantation in Maoershan Experiment Station, Northeast Forestry University, China. Seventy-two soil cores (inside diameter
60 mm; depth intervals: 0–10 cm, 10–20 cm, 20–30 cm) were sampled randomly from three replicates 25 m × 30 m plots to estimate
fine root biomass (live and dead), and calculate RLD and SRL. Soil moisture, temperature, and nitrogen (ammonia and nitrates)
at three depth intervals were also analyzed in these plots. Results showed that the average standing fine root biomass (live
and dead) was 189.1 g·m−2·a−1, 50% (95.4 g·m−2·a−1) in the surface soil layer (0–10 cm), 33% (61.5 g·m−2·a−1), 17% (32.2 g·m−2·a−1) in the middle (10–20 cm) and deep layer (20–30cm), respectively. Live and dead fine root biomass was the highest from May
to July and in September, but lower in August and October. The live fine root biomass decreased and dead biomass increased
during the growing season. Mean RLD (7,411.56 m·m−3·a−1) and SRL (10.83 m·g−1·a−1) in the surface layer were higher than RLD (1 474.68 m·m−3·a−1) and SRL (8.56 m·g−1·a−1) in the deep soil layer. RLD and SRL in May were the highest (10 621.45 m·m−3 and 14.83m·g−1) compared with those in the other months, and RLD was the lowest in September (2 198.20 m·m−3) and SRL in October (3.77 m·g−1). Seasonal dynamics of fine root biomass, RLD, and SRL showed a close relationship with changes in soil moisture, temperature,
and nitrogen availability. To a lesser extent, the temperature could be determined by regression analysis. Fine roots in the
upper soil layer have a function of absorbing moisture and nutrients, while the main function of deeper soil may be moisture
uptake rather than nutrient acquisition. Therefore, carbon allocation to roots in the upper soil layer and deeper soil layer
was different. Multiple regression analysis showed that variation in soil resource availability could explain 71–73% of the
seasonal variation of RLD and SRL and 58% of the variation in fine root biomass. These results suggested a greater metabolic
activity of fine roots living in soil with higher resource availability, which resulted in an increased allocation of carbohydrate
to these roots, but a lower allocation of carbohydrate to those in soil with lower resource availability.
__________
Translated from Acta Phytoecologica Sinica, 2005, 29(3): 403–410 [译自: 植物生态学报, 2005, 29(3): 403–410] 相似文献
11.
Light response characteristics of a morphologically diverse group of southern hemisphere conifers as measured by chlorophyll fluorescence 总被引:5,自引:0,他引:5
Unlike northern hemisphere conifer families, the southern family, Podocarpaceae, produces a great variety of foliage forms
ranging from functionally broad-, to needle-leaved. The production of broad photosynthetic surfaces in podocarps has been
linked qualitatively to low-light-environments, and we undertook to assess the validity of this assumption by measuring the
light response of a morphologically diverse group of podocarps. The light response, as apparent photochemical electron transport
rate (ETR), was measured by modulated fluorescence in ten species of this family and six associated species (including five
Cupressaceae and one functionally needle-leaved angiosperm) all grown under identical glasshouse conditions. In all species,
ETR was found to increase as light intensity increased, reaching a peak value (ETRmax) at saturating quantum flux (PPFDsat), and decreasing thereafter. ETRmax ranged from 217 μmol electrons · m−2 · s−1 at a PPFDsat of 1725 μmol photons · m−2 · s−1 in Actinostrobus acuminatus to an ETR of 60 μmol electrons · m−2 · s−1 at a PPFDsat of 745 μmol electrons · m−2 · s−1 in Podocarpus dispermis. Good correlations were observed between ETRmax and both PPFDsat and maximum assimilation rate measured by gas-exchange analysis. The effective quantum yield at light saturation remained
constant in all species with an average value of 0.278 ± 0.0035 determined for all 16 species. Differences in the shapes of
light response curves were related to differences in the response of non-photochemical quenching (q
n), with q
n saturating faster in species with low PPFDsat. Amongst the species of Podocarpaceae, the log of average shoot width was well correlated with PPFDsat, wider leaves saturating at lower light intensities. This suggests that broadly flattened shoots in the Podocarpaceae are
an adaptation to low light intensity.
Received: 15 April 1996 / Accepted: 30 September 1996 相似文献
12.
The aim of this work was to obtain experimental data depending on the properties of calcium stores and SERCAs, to analyse
these data in terms of the models based on simulation of the cellular compartments as communicating vessels, and to relate
this way the data to the above properties. The main characteristics of the stores and corresponding SERCAs have been estimated.
Calcium content in the DTS is ∼1.5 × 106 ions per cell, that in the acidic stores, ∼0.64 × 106 ions per cell. The rate constant of background calcium leakage from the DTS is ∼0.0033 s−1, that from the acidic stores, ∼0.1 s−1. The background activity of SERCA2b is ∼0.22 × 106 s−1 ions per cell, that of SERCA3, ∼2.5 × 106 s−1 ions per cell. The properties of both calcium stores and the SERCAs and the characteristics found might be related to physiological
or pathological state of the cells. 相似文献
13.
Submerged aquatic higher plants maintain acropetal water transport to the young leaves in active growth to satisfy their
demand for nutrients and hormones derived from the roots. We here present the first measurements of hydraulic properties for
a submerged plant, the monocotyledon Sparganium emersum Rehman. The hydraulic conductance per unit length, Kh, was measured in leaf segments without the leaf tip and shown to be greater in old, fully developed leaves (1.5 · 10−10 · m4 · MPa−1 · s−1) than in young leaves (1.0 · 10−10 · m4 · MPa−1 · s−1). In leaves with intact leaf tips, however, Kh was significantly greater in the youngest leaves, which suggests that the leaf tip with the hydathode influences resistance
and thus flow. Microscopy confirmed that the hydathodal area, which is an apical opening, undergoes structural changes with
leaf age; a matrix of microorganisms develops in the older leaves and probably restricts water flow by clogging the hydathodes.
The leaf specific conductivity expressing transport capacity relative to the leaf area supplied, of S. emersum (0.1 · 10−8 to 9 · 10−8 · m2 MPa−1· s−1) was within the same range as for various species of terrestrial ferns, vines and trees. This finding does not support the
traditional concept of functionally reduced vascular transport in
Received: 15 July 1996 / Accepted: 30 November 1996 相似文献
14.
N. Rashevsky 《Protoplasma》1933,20(1):125-130
Summary A mathematical analysis of the diffusion of oxygen into a cell is made, under the assumption, that the true rate of consumption
of oxygen by protoplasm is constant and independent on the oxygen pressure. The results are compared with experimental data.
For unfertilizedArbacia eggs and for bacteria the experimental curves cannot be represented by the theory. Some additional assumptions, like those
proposed byGerard, seem unavoidable. For fertilizedArbacia eggs a good agreement may however be obtained, by taking for the diffusion coefficient of oxygen trough the protoplasm 7×10−7 cm2·min−1, and for the permeability of the cell surface to oxygen 4.25×10−4cm·min−1.
With 1 Text-figure 相似文献
15.
Emile Bol Nicolette J. Broers Wilfred R. Hagen 《Journal of biological inorganic chemistry》2008,13(1):75-84
Formaldehyde ferredoxin oxidoreductase from Pyrococcus furiosus is a homotetrameric protein with one tungstodipterin and one [4Fe–4S] cubane per 69-kDa subunit. The enzyme kinetics have
been studied under steady-state conditions at 80 °C and pre-steady state conditions at 50 °C, in the latter case via monitoring
of the relatively weak (ε ≈ 2 mM−1 cm−1) optical spectrum of the tungsten cofactor. The steady-state data are consistent with a substrate substituted-enzyme mechanism
for three substrates (formaldehyde plus two ferredoxin molecules). The K
M value for free formaldehyde (21 μM) with ferredoxin as an electron acceptor is approximately 3 times lower than the value
measured when benzyl viologen is used as an acceptor. The K
M of ferredoxin (14 μM) is an order of magnitude less than previously reported values. An explanation for this discrepancy
may be the fact that high concentrations of substrate are inhibitory and denaturing to the enzyme. Pre-steady-state difference
spectra reveal peak shifts and a lack of isosbestic points, an indication that several processes happen in the first seconds
of the reaction. Two fast processes (k
obs1 = 4.7 s−1, k
obs2 = 1.9 s−1) are interpreted as oxidation of the substrate followed by rearrangement of the active site. Alternatively, these processes
could be the entry/binding of the substrate followed by its oxidation. The release of the product and the electron shuffling
over the tungsten and iron–sulfur center in the absence of an external electron acceptor are slower (k
obs3 = 6.10 × 10−2 s−1, k
obs4 = 2.18 × 10−2 s−1). On the basis of these results in combination with results from previous electron paramagnetic resonance studies an activation
route plus catalytic redox cycle is proposed. 相似文献
16.
Joseph P. Weir Dennis A. Keefe Jason F. Eaton Robert T. Augustine Dawn M. Tobin 《European journal of applied physiology and occupational physiology》1998,78(6):555-559
We examined the effect of fatigue of the quadriceps muscles on coactivation of the hamstring muscles and determined if the
response is different between two isokinetic speeds in ten males and ten females with no history of knee pathology. Electromyographic
data were recorded from the vastus lateralis and biceps femoris muscles during 50 maximal knee extensions at isokinetic speeds
of 1.75 rad · s−1 (100° · s−1) and 4.36 rad · s−1 (250° · s−1). A greater degree of coactivation was apparent at the higher speed, but the increase in coactivation of the hamstring muscles
was similar at both speeds. The results revealed that: (1) coactivation is greater at a higher isokinetic speed, and (2) coactivation
increases during fatigue, but the rate of increase is independent of contraction velocity.
Accepted: 15 June 1998 相似文献
17.
Leaf photosynthesis, plant growth and nitrogen allocation in rice under different irradiances 总被引:6,自引:0,他引:6
The photosynthetic rates and various components of photosynthesis including ribulose-1,5-bisphosphate carboxylase (Rubisco;
EC 4.1.1.39), chlorophyll (Chl), cytochrome (Cyt) f, and coupling factor 1 (CF1) contents, and sucrose-phosphate synthase (SPS; EC 2.4.1.14) activity were examined in young, fully expanded leaves of rice
(Oryza sativa L.) grown hydroponically under two irradiances, namely, 1000 and 350 μmol quanta · m−2 · s−1, at three N concentrations. The light-saturated rate of photosynthesis measured at 1800 μmol · m−2 · s−1 was almost the same for a given leaf N content irrespective of growth irradiance. Similarly, Rubisco content and SPS activity
were not different for the same leaf N content between irradiance treatments. In contrast, Chl content was significantly greater
in the plants grown at 350 μmol · m−2 · s−1, whereas Cyt f and CF1 contents tended to be slightly smaller. However, these changes were not substantial, as shown by the fact that the light-limited
rate of photosynthesis measured at 350 μmol · m−2 · s−1 was the same or only a little higher in the plants grown at 350 μmol · m−2 · s−1 and that CO2-saturated photosynthesis did not differ between irradiance treatments. These results indicate that growth-irradiance-dependent
changes in N partitioning in a leaf were far from optimal with respect to N-use efficiency of photosynthesis. In spite of
the difference in growth irradiance, the relative growth rate of the whole plant did not differ between the treatments because
there was an increase in the leaf area ratio in the low-irradiance-grown plants. This increase was associated with the preferential
N-investment in leaf blades and the extremely low accumulation of starch and sucrose in leaf blades and sheaths, allowing
a more efficient use of the fixed carbon. Thus, morphogenic responses at the whole-plant level may be more important for plants
as an adaptation strategy to light environments than a response of N partitioning at the level of a single leaf.
Received: 23 February 1997 / Accepted: 8 May 1997 相似文献
18.
The influence of ultraviolet-B radiation on the growth, pigment production and chlorophyll fluorescence of Norway spruce seedlings 总被引:3,自引:0,他引:3
Norway spruce (Picea abies (L.)Karst.) from seven seed sources was grown in a greenhouse with 8.3 and 14.7 kJ·m−2·d−1 m UV-BBE (biologically effective UV-B: 280–320 nm) irradiation, and with no supplemental irradiation as control. The seedlings total
biomass (dry weight) and shoot growth decreased with high UV-B treatment but spruce from low elevation seed sources were more
affected. The seedlings grown at the highest UV-B irradiance (14.7 kJ·m−2·d−1) showed from 5 to 38% inhibition of total biomass and 15 to 70 % shoot growth inhibition. Norway spruce populations from
higher altitude seed sources manifested greater tolerance to UV-B radiation compared to plants from low altitudes. Changes
in phospholipids and protective pigments were also determined. The plants grown at the lower UV-B irradiance (8.3 kJ·m−2·d−1) showed greater ability to concentrations UV-B-absorbing pigments then control plants. Chlorophyll a fluorescence parameter
Rfd, (Rfd=(Fm-Fs)/Fs) showed a significant decrease in needles of UV-B treated plants and this correlated with the altitude of seed source. Exposure
to UV-B affect levels of the ratio of variable to maximum fluorescence (Fv/Fm). Results from this study suggest that the response to increased levels of UV-B radiation is depended upon the ecotypic differentiation
of Norway spruce and involved changes in metabolites in plant tissues. 相似文献
19.
Laccase-catalyzed oxidation of N-substituted phenothiazines and N-substituted phenoxazines was investigated at pH 5.5 and
25°C. The recombinant laccase from Polyporus pinsitus (rPpL) and the laccase from Myceliophthora thermophila (rMtL) were used. The dependence of initial reaction rate on substrate concentration was analyzed by applying the laccase
action scheme in which the laccase native intermediate (NI) reacts with a substrate forming reduced enzyme. The reduced laccase
produces peroxide intermediate (PI) which in turn decays to the NI. The calculated constant (kox) values of the PI formation are (6.1±3.1)×105 M−1s−1 for rPpL and (2.5±0.9)×104 M−1s−1 for rMtL. The bimolecular constants of the reaction of the native intermediate with electron donor (kred) vary in the interval
from 2.2×105 to 2.1×107 M−1s−1 for rPpL and from 1.3×102 to 1.8×105 M-1s−1 for rMtL. The larger reactivity of rPpL in comparison to rMtL is associated with the higher redox potential of type I Cu
of rPpL. The variation of kred values for both laccases correlates with the change of the redox potential of substrates. Following outer sphere (Marcus)
electron transfer mechanism the calculated activationless electron transfer rate and the apparent reorganization energy are
5.0×107 M−1s−1 and 0.29 eV, respectively. 相似文献
20.
Juozas Kulys Kastis Krikstopaitis Arturas Ziemys 《Journal of biological inorganic chemistry》2000,5(3):333-340
N -substituted phenothiazines (PTs) and phenoxazines (POs) catalyzed by fungal Coprinus cinereus peroxidase and Polyporus pinsitus laccase were investigated at pH 4–10. In the case of peroxidase, an apparent bimolecular rate constant (expressed as k
cat/K
m) varied from 1 ×107 M−1 s−1to 2.6×108 M−1 s−1 at pH 7.0. The constants for PO oxidation were higher in comparison to PT. pH dependence revealed two or three ionizable
groups with pK
a values of 4.9–5.7 and 7.7–9.7 that significantly affected the activity of peroxidase. Single-turnover experiments showed
that the limiting step of PT oxidation was reduction of compound II and second-order rate constants were obtained which were
consistent with the constants at steady-state conditions. Laccase-catalyzed PT and PO oxidation rates were lower; apparent
bimolecular rate constants varied from 1.8×105 M−1 s−1 to 2.0×107 M−1 s−1 at pH 5.3. PO constants were higher in comparison to PT, as was the case with peroxidase. The dependence of the apparent
bimolecular constants of compound II or copper type 1 reduction, in the case of peroxidase or laccase, respectively, was analyzed
in the framework of the Marcus outer-sphere electron-transfer theory. Peroxidase-catalyzed reactions with PT, as well as PO,
fitted the same hyperbolic dependence with a maximal oxidation rate of 1.6×108 M−1 s−1 and a reorganization energy of 0.30 eV. The respective parameters for laccase were 5.0×107 M−1 s−1 and 0.29 eV.
Received: 20 September 1999 / Accepted: 24 February 2000 相似文献