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1.
The stability and, consequently, the lifetime of immobilized enzymes (IME) are important factors in practical applications of IME, especially so far as design and operation of the enzyme reactors are concerned. In this paper a model is presented which describes the effect of intraparticle diffusion on time stability behaviour of IME, and which has been verified experimentally by the two-substrate enzymic reaction. As a model reaction the ethanol oxidation catalysed by immobilized yeast alcohol dehydrogenase was chosen. The reaction was performed in the batch-recycle reactor at 303 K and pH-value 8.9, under the conditions of high ethanol concentration and low coenzyme (NAD+) concentration, so that NAD+ was the limiting substrate. The values of the apparent and intrinsic deactivation constant as well as the apparent relative lifetime of the enzyme were calculated.The results show that the diffusional resistance influences the time stability of the IME catalyst and that IME appears to be more stabilized under the larger diffusion resistance.List of Symbols
C
A, CB, CE mol · m–3
concentration of coenzyme NAD+, ethanol and enzyme, respectively
-
C
p mol · m3
concentration of reaction product NADH
-
d
p mm
particle diameter
-
D
eff m2 · s–1
effective volume diffusivity of NAD+ within porous matrix
-
k
d s–1
intrinsic deactivation constant
-
K
A, KA, KB mol · m–3
kinetic constant defined by Eq. (1)
-
K
A
x
mol · m–3
kinetic constant defined by Eq. (5)
-
r
A mol · m–3 · s–1
intrinsic reaction rate
-
R m
particle radius
-
R
v mol · m–3 · s–1
observed reaction rate per unit volume of immobilized enzyme
-
t
E s
enzyme deactivation time
-
t
r s
reaction time
-
V mol · m–3 · s–1
maximum reaction rate in Eq. (1)
-
V
x mol · m–3 · s–1
parameter defined by Eq. (4)
-
V
f m3
total volume of fluid in reactor
-
w
s kg
mass of immobilized enzyme bed
-
factor defined by Eqs. (19) and (20)
-
kg · m–3
density of immobilized enzyme bed
-
unstableness factor
-
effectiveness factor
-
Thiele modulus
-
relative half-lifetime of immobilized enzyme
Index
o
values obtained with fresh immobilized enzyme 相似文献
2.
F. X. Malcata 《Bioprocess and biosystems engineering》1995,13(1):51-55
The balance equations pertaining to the modelling of a CSTR performing an enzyme-catalyzed reaction in the presence of enzyme deactivation are developed. Combination of heuristic correlations for the size-dependent cost of equipment and the purification-dependent cost of recovery of product with the mass balances was used as a basis for the development of expressions relating a (suitably defined) dimensionless economic parameter with the optimal outlet substrate concentration under the assumption that overall production costs per unit mass of product were to be minimized. The situation of Michaelis-Menten kinetics for the substrate depletion and first order kinetics for the deactivation of enzyme (considering that the free enzyme and the enzyme in the enzyme/substrate complex deactivate at different rates) was explored, and plots for several values of the parameters germane to the analysis are included.List of Symbols
C
E
mol m–3
concentration of active enzyme
-
C
E,0
mol m–3
initial concentration of active enzyme
-
C
p
mol m–3
concentration of product of interest
-
C
s
mol m–3
concentration of substrate
-
C
s,0
mol m–3
initial concentration of substrate
-
I $
capital cost of equipment
-
k
d
s–1
deactivation constant of free enzyme
-
k
d
s–1
deactivation constant of enzyme in enzyme/substrate complex
-
K
m
mol m–3
Michaelis-Menten constant
-
K
m
dimensionless counterpart of K
m
-
k
r
s–1
rate constant associated with conversion of enzyme/substrate complex into product
-
M
w
kg mol–1
molecular weight of product of interest
-
P $ kg–1
cost of recovery of product of interest in pure form
-
Q m3s–1
volumetric flow rate
-
V m3
volume of reactor
-
X $ kg–1
global manufacture cost of product of interest in pure form
-
X
dimensionless counterpart of X
Greek Symbols
1 $ m–1.8
constant
-
2 $ m–3
constant
-
t s
useful life of CSTR
-
0
ratio of initial concentrations of enzyme and substrate
-
ratio of deactivation constant of free enzyme to rate constant of depletion of substrate
-
ratio of deactivation constants
-
univariate function expressing the dependence of the rate of enzyme deactivation on C
S
-
univariate function expressing the dependence of the rate of substrate depletion on C
S
-
dimensionless economic parameter 相似文献
3.
The responses to irradiance of photosynthetic CO2 assimilation and photosystem 2 (PS2) electron transport were simultaneously studied by gas exchange and chlorophyll (Chl) fluorescence measurement in two-year-old apple tree leaves (Malus pumila Mill. cv. Tengmu No.1/Malus hupehensis Rehd). Net photosynthetic rate (P
N) was saturated at photosynthetic photon flux density (PPFD) 600-1 100 (mol m-2 s-1, while the PS2 non-cyclic electron transport (P-rate) showed a maximum at PPFD 800 mol m-2 s-1. With PPFD increasing, either leaf potential photosynthetic CO2 assimilation activity (Fd/Fs) and PS2 maximal photochemical activity (Fv/Fm) decreased or the ratio of the inactive PS2 reaction centres (RC) [(Fi – Fo)/(Fm – Fo)] and the slow relaxing non-photochemical Chl fluorescence quenching (qs) increased from PPFD 1 200 mol m-2 s-1, but cyclic electron transport around photosystem 1 (RFp), irradiance induced PS2 RC closure [(Fs – Fo)/Fm – Fo)], and the fast and medium relaxing non-photochemical Chl fluorescence quenching (qf and qm) increased remarkably from PPFD 900 (mol m-2 s-1. Hence leaf photosynthesis of young apple leaves saturated at PPFD 800 mol m-2 s-1 and photoinhibition occurred above PPFD 900 mol m-2 s-1. During the photoinhibition at different irradiances, young apple tree leaves could dissipate excess photons mainly by energy quenching and state transition mechanisms at PPFD 900-1 100 mol m-2 s-1, but photosynthetic apparatus damage was unavoidable from PPFD 1 200 mol m-2 s-1. We propose that Chl fluorescence parameter P-rate is superior to the gas exchange parameter P
N and the Chl fluorescence parameter Fv/Fm as a definition of saturation irradiance and photoinhibition of plant leaves. 相似文献
4.
Interrelationships Between Nitrogen Supply and Photosynthetic Parameters in Vicia faba L. 总被引:2,自引:2,他引:0
We determined for Vicia faba L the influence of nitrogen uptake and accumulation on the values of photon saturated net photosynthetic rate (P
Nmax), quantum yield efficiency (), intercellular CO2 concentration (C
i), and carboxylation efficiency (C
e). As leaf nitrogen content (NL) increased, the converged onto a maximum asymptotic value of 0.0664±0.0049 mol(CO2) mol(quantum)–1. Also, as NL increased the C
i value fell to an asymptotic minimum of 115.80±1.59 mol mol–1, and C
e converged onto a maximum asymptotic value of 1.645±0.054 mol(CO2) m–2 s–1 Pa–1 and declined to zero at a NL-intercept equal to 0.596±0.096 g(N) m–2. fell to zero for an NL-intercept of 0.660±0.052 g(N) m–2. As NL increased, the value of P
Nmax converged onto a maximum asymptotic value of 33.400±2.563 mol(CO2) m–2 s–1. P
N fell to zero for an NL-intercept of 0.710±0.035 g(N) m–2. Under variable daily meteorological conditions the values for NL, specific leaf area (L), root mass fraction (Rf), P
Nmax, and remained constant for a given N supply. A monotonic decline in the steady-state value of Rf occurred with increasing N supply. L increased with increasing N supply or with increasing NL. 相似文献
5.
S. A. M. van Stroe-Biezen J. M. H. van der Loo L. J. J. Janssen F. M. Everaerts 《Bioprocess and biosystems engineering》1996,15(2):87-94
The enzyme glucose oxidase (GO) was covalently immobilized onto a poly(vinyl alcohol) hydrogel, cross-linked with glutardialdehyde and a polyazonium salt. To compare the kinetic parameters of immobilized GO with the known kinetic parameters of soluble GO, the diffusion cell method was used.Between two compartments, containing solutions with different glucose concentrations, a GO-containing hydrogel membrane was placed. Simultaneous diffusion through and enzymatic reaction in the membrane occurred. In this way diffusional effects of the membrane could be eliminated from the effective kinetic parameters to yield the inherent kinetic parameters.It appeared that the enzymatic reaction is independent of the oxygen concentration at oxygen concentrations 0.22 mol m–3 (Michaelis constant for oxygen < 0.22 mol m–3). Further, the Michaelis constant for glucose does not change dramatically after immobilizing the enzyme. The maximal reaction rate is depending on the enzyme concentration. As the enzyme concentration in the membrane is not exactly known (mainly due to leakage of enzyme out of the membrane during membrane preparation), only an estimation of the turnover number can be made.The diffusion cell method is easy to carry out. Still, some recommendations can be made on the performance.List of Symbols
g
,
0x
partition coefficient of glucose and oxygen, respectively
-
thickness of the wetted membrane (m)
-
A
m
surface area of membrane (m–2)
-
C
constant (mol2 m–3)
-
c
g
, c
0x
concentration of glucose and oxygen, respectively (mol m–3)
-
c
g,0
c
g,
glucose concentration at the filter-paper/membrane interface next to compartment A and B, respectively (mol m–3)
-
c
g, A
c
g, B
glucose concentration in compartment A and B, respectively (mol m–3)
-
c
GO
glucose oxidase concentration (mol m–3)
-
D
eff
effective diffusion coefficient (m2 s–1)
-
D
m
, D
sl
diffusion coefficient in, respectively, the membrane and the solution layer (m2 s–1)
-
d
dl
, d
df
, d
sl
thickness of, respectively, the diffusion layer, the filter-paper and the solution layer (m)
-
h
B
initial slope of concentration versus time curve of compartment B (mol m–3 s–1)
-
J
flux (mol m–2 s–1)
-
J
0
flux in the membrane at membrane/filter-paper interface next to compartment A and B, respectively (mol m–2 s–1)
-
J
A
, J
B
flux leaving compartment A and entering compartment B, respectively (mol m–2 s–1)
-
J
m
flux through the membrane (mol m–2 s–1)
-
k
total mass transfer coefficient (m s–1)
-
k
1
, k
2
rate constant of a particular reaction step (m3 mol–1 s–1)
- k–1, k–2
rate constant of a particular reaction step (s–1)
-
k
cat
(intrinsic) catalytic constant of turnover number (s–1)
-
k
cat
*
inherent catalytic constant, determined by inserting D
m
(s–1)
-
k
cat
**
inherent catalytic constant, determined by inserting D
eff (s–1)
-
k
m
(g)
(intrinsic) Michaelis constant for glucose (mol m–3)
-
k
m
(o)
(intrinsic) Michaelis constant for oxygen (mol m–3)
-
k
m
*
(g)
inherent Michaelis constant for glucose (mol m–3)
-
k
m
*
(o)
inherent Michaelis constant for oxygen (mol m–3)
-
m
GO
number of moles of GO present (mol)
-
P
m
permeability of glucose in the mebrane (m s–1)
-
P
eff
effective permeability (m s–1)
-
V
volume (m3)
-
v
0
initial reaction velocity (mol m–3 s–1)
-
V
max
**
inherent maximal reaction velocity, determined by inserting Deff (mol m–3 s–1)
-
x
distance (m) 相似文献
6.
In Evernia prunastri, photosynthetic gas exchange was saturated with yellow radiation (SOX) at 400 mol m–2s–1, and then red (R), far-red (FR), or blue (B) radiations at irradiance of 15 mol m–2s–1 were added. Because of photosynthesis saturation, any stimulation or decay in CO2 assimilation by any radiation quality could be attributed to the involvement of a non-photosynthetic photoreceptor. Thus CO2 assimilation, effective quantum yield, and photochemical quenching were enhanced when R was included, and decreased with FR. Blue radiation completely abolished CO2 fixation. Hence different spectral radiation qualities may activate non-photosynthetic photoreceptors such as phytochrome and blue photoreceptors, which are involved in regulating the photosynthetic activity in E. prunastri. 相似文献
7.
Three Bromeliaceae species of the medium Orinoco basin, Venezuela, were compared in their light-use characteristics. The bromeliads studied were two species of pineapple, i.e. the wild species Ananas ananassoides originating from the floor of covered moist forest, and the primitive cultivar Panare of Ananas comosus mostly cultivated in semi-shaded palm swamps, and Pitcairnia pruinosa, a species abundant in highly sun exposed sites on rock outcrops. Ananas species are Crassulacean acid metabolism (CAM) plants, P. pruinosa is C3 plant. Plants were grown at low daily irradiance (LL = 1.3 mol m–2 d–1 corresponding to an incident irradiance of 30 mol m–2 s–1) and at high irradiance (HL = 14.7 mol m–2 d–1 or 340 mol m–2 s–1), and CO2 and H2O-vapour gas exchange and photochemical (qP) and non-photochemical quenching (qNP) of chlorophyll a fluorescence of photosystem 2 (PS2) were measured after transfer to LL, medium irradiance (ML = 4.1 mol m–2 d–1 or 95 mol m–2 s–1) and HL. All plants showed flexible light-use, and qP was kept high under all conditions. LL-grown plants of Ananas showed particularly high rates of CAM-photosynthesis when transferred to HL and were not photoinhibited. 相似文献
8.
Total stem, branch, twig, and coarse root respiration (Rt) of an adult Pinus cembra tree at the alpine timberline was measured continuously at ten positions from 7 October 2001 to 21 January 2003 with an automated multiplexing gas exchange system. There was a significant spatial variability in woody tissue respiration when expressed per unit surface area or per unit sapwood volume. Surface area related maintenance (Rm) respiration at 0°C ranged between 0.109 and 0.643 mol m–2 s–1 and there was no clear trend with respect to tissue type and diameter. Sapwood volume based Rm at 0°C by contrast, varied between 2.5 mol m–3 s–1 in the stem and 193.2 mol m–3 s–1 in thin twigs in the upper crown. Estimated Q10 values ranged from 1.7 to 3.1. These Q10 values were used along with Rm at 0°C and annual woody tissue temperature records to predict annual total Rm. Annual total Rm accounted for 73±6% of annual Rt in 2002. 相似文献
9.
Understanding how photosynthetic capacity acclimatises when plants are grown in an atmosphere of rising CO2 concentrations will be vital to the development of mechanistic models of the response of plant productivity to global environmental change. A limitation to the study of acclimatisation is the small amount of material that may be destructively harvested from long-term studies of the effects of elevation of CO2 concentration. Technological developments in the measurement of gas exchange, fluorescence and absorption spectroscopy, coupled with theoretical developments in the interpretation of measured values now allow detailed analyses of limitations to photosynthesisin vivo. The use of leaf chambers with Ulbricht integrating spheres allows separation of change in the maximum efficiency of energy transduction in the assimilation of CO2 from changes in tissue absorptance. Analysis of the response of CO2 assimilation to intercellular CO2 concentration allows quantitative determination of the limitation imposed by stomata, carboxylation efficiency, and the rate of regeneration of ribulose 1:5 bisphosphate. Chlorophyll fluorescence provides a rapid method for detecting photoinhibition in heterogeneously illuminated leaves within canopies in the field. Modulated fluorescence and absorption spectroscopy allow parallel measurements of the efficiency of light utilisation in electron transport through photosystems I and IIin situ.Abbreviations A
net rate of CO2 uptke per unit leaf area (µmol m–2 s–1)
- Asat
light-saturated A
- A820
change in absorptance of PSI on removal of illumination (OD)
- c
CO2 concentration in air (µmol mol–1)
- ca
c in the bulk air; ci, c in the intercellular spaces
- ce
carboxylation efficiency (mol m–2 s–1)
- E
transpiration per unit leaf area (mol m–2 s–1)
- F
fluorescence emission of PSII (relative units)
- Fm
maximal level of F
- Fo
minimal level of F upon illumination when PSII is maximally oxidised
- Fs
the steady-state F following the m peak
- Fv
the difference between Fm and Fo
- F'm
maximal F' generated after the m peak by addition of a saturating light pulse
- F'o
the minimal level of F' after the m peak determined by re-oxidising PSII by far-red light
- g1
leaf conductance to CO2 diffusion in the gas phase (mol m–2 s–1)
- g'1
leaf conductance to water vapour diffusion in the gas phase (mol m–2 s–1)
- kc and ko
the Michaelis constants for CO2 and O2, respectively, (µmol mol–1);
- Jmax
the maximum rate of regeneration of rubP (µmol m–2 s–1)
- l
stomatal limitation to CO2 uptake (dimensionless, 0–1)
- LCP
light compensation point of photosynthesis (µmol m–2 s–1)
- oi
the intercellular O2 concentration (mmol mol–1)
- Pi
cytosol inorganic phosphate concentration
- PSI
photosystem I
- PSII
photosystem II
- Q
photon flux (µmol m–2 s–1)
- Qabs
Q absorbed by the leaf
- rubisCO
ribulose 1:5 bisphosphate carboxylase/oxygenase; rubP, ribulose 1:5 bisphosphate; s, projected surface area of a leaf (m2)
- Vc,max
is the maximum rate of carboxylation (µmol m–2 s–1)
- Wc
the rubisCO limited rate of carboxylation (µmol m–2 s1)
- Wj
the electron transport limited rate of regeneration of rubP (µmol m–2 s–1)
- Wp
the inorganic phosphate limited rate of regeneration of rubP (µmol m–2 s–1)
-
absorptance of light (dimensionless, 0–1)
- a
of standard black absorber 1, of leaf
- s
of integrating sphere walls
- , CO2
compensation point of photosynthesis (µmol mol–1)
-
the specificity factor for rubisCO carboxylation (dimensionless)
- ,
convexity of the response of A to Q (dimensionless 0–1)
-
the quantum yield of photosynthesis on an absorbed light basis (A/Qabs; dimensionless)
-
the quantum yield of photosynthesis on an incident light basis (A/Q; dimensionless)
- app
the maximum
- m
the maximum
- m,app
the photochemical efficiency of PSII (dimensionless, 0–1)
- PSII,m
the maximum 相似文献
10.
Photosystem 2 (PS2)-driven electron transfer was studied in primary leaves of barley (Hordeum vulgare L.) seedlings grown under various photon fluxes (0.3–170.0 mol m–2 s–1) of blue (BR) or red (RR) radiation using modulated chlorophyll fluorescence. The Fv/Fm ratio was 0.78–0.79 in leaves of all radiation variants, except in seedlings grown under BR or RR of 0.3 mol m–2 s–1. The extent of the photochemical phase of the polyphasic Fv rise induced by very strong white light was similar in leaves of all radiation treatments. Neither radiation quality nor photon flux under plant cultivation influenced the amount of non QB-transferring centres of PS2 except in leaves of seedlings grown under BR of 0.3 mol m–2 s–1, in which the amount of such centres increased threefold. Both BR and RR stimulated the development of photochemically competent PS2 at photon fluxes as low as 3 mol m–2 s–1. Three exponential components with highly different half times were distinguished in the kinetics of Fv dark decay. This indicates different pathways of electron transfer from QA
–, the reduced primary acceptor of PS2, to other acceptors. Relative magnitudes of the individual decay components did not depend on the radiation quality or the photon flux during plant cultivation. Significant differences were found, however, between plants grown under BR or RR in the rate of the middle and fast components of Fv dark decay, which showed 1.5-times faster intersystem linear electron transport in BR-grown leaves. 相似文献
11.
Photosynthesis and Water Use Efficiency in Twenty Tropical Tree Species of Differing Succession Status in a Brazilian Reforestation 总被引:10,自引:1,他引:9
Leaf gas exchange characteristics were measured in twenty woody species that differ in succession status ranging from pioneer species (PS) to late succession species (LS) in a Brazilian rain-reforestation ecosystem. Photon-saturated photosynthetic rate, calculated per either a leaf area (P
NA) or a dry mass (P
NM) basis, differed among species. P
NA and P
NM were highest in PS and lowest in LS. Variation among species was 3-fold (from 7 to 23 mol m–2 s–1) for P
NA, and 5-fold (from 50 to 275 mol kg–2 s–1) for P
NM. The highest P
NA (23 mol m–2 s–1) and P
NM (275 mol kg–2 s–1) values were recorded in PS Croton urucurana, while the lowest P
NA (7 mol m–2 s–1) and P
NM (50 mol kg–2 s–1) values were recorded in LS Aspidosperma cylindrocarpon. A considerable overlap was recorded between PS and LS in values of stomatal conductance (g
s), transpiration rate (E), and leaf mass to area ratio (ALM). However, C. urucurana also showed highest g
s and E. P
NM was highly correlated with ALM in both PS and LS (r=–0.75 and –0.90, respectively). The high values of instantaneous transpiration efficiency (ITE) and intrinsic water use efficiency (WUEi) were also observed in the PS when compared with the LS. 相似文献
12.
Dr. D. Vasić-Rački N. Pavlović S. Čižmek M. Dražić B. Husadžić 《Bioprocess and biosystems engineering》1991,7(4):183-187
Based on the kinetic constants determined and the mathematical model of the reactor system developed, the performance of axial flow packed bed continuous enzyme reactor system was studied experimentally and also simulated with the aid of a computer for ultimate objective of optimization of the glucose isomerase reactor system.A reactor model was established analogous to heterogeneous catalytic reactor model taking into account the effect of fluid mass transfer and reversible kinetics. The investigated catalyst system consists of immobilized Streptomyces bambergiensis cells containing the enzyme glucose isomerase, which catalyzes the isomerization of glucose to fructose.List of Symbols
A
0, A
1, A
2
parameters in axial dispersion reactor model
-
c
go, cg, cgemol m–3
glucose concentration at time t=0, at any time and at equilibrium conditions
-
c
gsmol m–3
glucose concentration at particle surface
-
C
dimensionless glucose concentration
-
d
pm
particle diameter
-
d
rm
diameter of reactor tube
-
Da
Damkohler number
-
D
eff m2 s–1
effective glucose diffusion coefficient in Ca-alginate gel beads
-
k
fm s–1
film transfer coefficient
-
K
e
equilibrium constant
-
K
mg, Kmfmol m–3
Michaelis-Menten constant for glucose and fructose, respectively
-
K
mmol m–3
modified Michaelis-Menten constant
-
K
dimensionless parameter
-
K
*
dimensionless parameter
-
L m
length of reactor tube
-
Pe
Peclet number
-
Pe
p
particle Peclet number
-
Q m3 s–1
volumetric flow rate
- (-r
g) mol m–3 s–1
reaction rate
-
Re
p
Reynolds particle number
-
Sc
Schmidt number
-
Sh
Sherwood number
-
t s
time
-
v
0 m s–1
linear superficial fluid velocity
-
V
mg, Vmfmol g–1 s–1
maximal reaction rate for glucose and fructose, respectively
-
V
mmol m–3 s–1
modified maximal reaction rate for glucose
-
V
mg
x
mol m–2 s–1
maximal reaction rate for glucose
-
X
g, Xge
glucose conversion and glucose conversion at equilibrium conditions
-
X
normalized conversion
-
Y
dimensionless glucose concentration
-
void fraction of fixed bed
-
effectiveness factor of biocatalyst
-
Pa s
kinematic viscosity of substrate
-
1 s
first absolute weighted moment
- 2 s2
second central weighted moment
-
gkg m–3
substrate density
-
pkg m–3
particle density
-
2
dimensionless variance of RTD curve
-
s
residence time 相似文献
13.
Photoinhibition and pigment composition of green stem tissues of field-grown adult Eucalyptus nitens were measured on clear spring days with low morning temperatures—conditions that cause photoinhibition in leaves of many plant species. The sun-exposed (north-facing) bark contained less chlorophyll a+b (531 vs 748 mol m–2), neoxanthin (29 vs 41), and -carotene (54 vs 73), more xanthophyll cycle pigments per unit surface area and per unit chlorophyll (71 vs 53 mol m–2 and 141 vs 66 mmol mol–1 chlorophyll), and less lutein per unit chlorophyll (239 vs 190) than the shaded (southern) side. Maximum electron flow rates were 60 mol m–2 s–1 on the sun-exposed side, and about 10 mol m–2 s–1 on the shaded side. Fv/Fm was always lower than 0.8 on the sun-exposed side and the de-epoxidation state (DEPS) of the xanthophyll cycle was dominated by zeaxanthin in midday samples. Fv/Fm increased quickly after darkening, but DEPS recovered more slowly to 40% overnight. This suggested that rapidly reversible pH-dependent quenching was responsible for the bulk of changes in PS II efficiency. Fv/Fm remained below 0.8 overnight, which may well be indicative of photo-damage to PSII. In contrast, DEPS of the shaded side was lower, and Fv/Fm was higher, than for the sun-exposed side. We conclude that E. nitens chlorenchyma on the sun-exposed stem side has a photosynthetic pigment composition similar to sun leaves and it experiences significant photoinhibition in the field. 相似文献
14.
Grain sorghum [Sorghum bicolor (L.) Moench. cvs. TX430 and KS82] was grown in a Haynie very fine sandy loam (coarse-silty, mixed, superactive, calcareous, mesic Mollic Udifluvents) under constant 47 % shade or full irradiance in a greenhouse under two watering regimes to see the combined and individual effects of low irradiance (LI) and low water (LW) on the sorghum genotypes. Under the high-irradiance (HI) and high-water (HW) treatment (control) and the LI-HW treatment, TX430 grew taller than KS82. Both LI and LW reduced several times the fresh and dry masses. Under the control conditions, TX430 reached its maximum net photosynthetic rate (P
Nmax) of 28.93 mol m–2 s–1 at a photosynthetic photon flux density (PPFD) of 1 707 mol m–2 s–1, and KS82 reached its P
Nmax of 28.32 mol m–2 s–1 at a PPFD of 2 973 mol m–2 s–1. The fact that TX430 had P
Nmax under a lower PPFD than KS82 may relate to its taller growth under LI conditions. Hence genotypes of sorghum might be selected for low irradiance using curves relating P
N to PPFD. 相似文献
15.
Summary CO2 assimilation in relation to light intensity and the relationship between leaf nitrogen and phosphorus concentrations and CO2 assimilation in 14 species of ecologically important Zimbabwean trees were examined. Eight of the species are members of the Fabaceae (Leguminosae). In the majority of Zimbabwean climax woodlands, the dominant trees are non-nodulating members of the sub-family Caesalpinioideae. The species examined have higher light saturation points (>700 mol m–2 s–1) than woody species from temperate areas; one species, Acacia nigrescens, did not reach saturation at photon fluxes greater than 1500 mol m–2 sec–1. Higher leaf nitrogen content was found to correlate positively with higher CO2 assimilation rates (r=0.85; P0.0003); there was no correlation between leaf phosphorus content and CO2 uptake rates. There were no significant differences between sites in terms of leaf nitrogen or phosphorus content, but the mean photosynthetic rate at one of the sites (Chizedzi) was lower. Taxa from the nodulating legumes were found to have higher leaf nitrogen contents (309.1±SD 22 mmol m–2) than those of the non-nodulating species (239±33); the lowest nitrogen contents were found in nonleguminous trees (179±42), with the exception of Ziziphus mucronata. This species may form an association with an N2-fixing actinomycete. 相似文献
16.
Photosynthesis and growth rates of Laurencia brongniartii J. Agardh (Rhodophyta, Ceramiales) in preparation for cultivation 总被引:2,自引:1,他引:1
Laurencia brongniartii is usually found at depths below 4 m, but can be found in shallow subtidal areas in crevices and on the walls of a coral reef in Amami Oshima Island, Kagoshima Prefecture, Japan, where irradiances were significantly lower than those at similar depths in open water. In preparation for the possible cultivation of this species for its antibiotic compounds, the effects of temperature and irradiance on photosynthesis and growth were measured. Photosynthesis and growth rates of L. brongniartii explants were highest at 26 and 28 °C, which closely corresponded to temperatures found during August to late December when it was most abundant. The estimated maximum photosynthesis rate (P
max) was 4.41 mol photon m–2 s–1 at 26 °C and 4.07 mol photon m–2 s–1 at 28 °C. Saturating irradiance occurred at 95 mol photon m–2 s–1 at 26 °C and 65 mol photon m–2 s–1 at 28 °C. In contrast, growth experiments at 41.7 mol photon m–2 s–1 caused bleaching of explants and the maximum growth rate observed during the study was 3.02 ± 0.75% day–1 at 28 °C and 25 mol photon m–2 s–1. The difference in the saturating irradiance for photosynthesis and the irradiance that caused bleaching in growth experiments suggests that long-term exposure to high irradiance was detrimental and should be addressed before the initiation of large scale cultivation. 相似文献
17.
Hydrogenase was solubilized from the membrane of acetate-grown Methanosarcina barkeri MS and purification was carried out under aerobic conditions. The enzyme was reactivated under reducing conditions in the presence of H2. The enzyme showed a maximal activity of 120±40 mol H2 oxidized · min–1 · min–1 with methyl viologen as an electron acceptor, a maximal hydrogen production rate of 45±4 mol H2 · min–1 · mg–1 with methyl viologen as electron donor, and an apparent K
m for hydrogen oxidation of 5.6±1.7 M. The molecular weight estimated by gel filtration was 98,000. SDS-PAGE showed the enzyme to consist of two polypeptides of 57,000 and 35,000 present in a 1:1 ratio. The native protein contained 8±2 mol Fe, 8±2 mol S2–, and 0.5 mol Ni/mol enzyme. Cytochrome b was reduced by hydrogen in a solubilized membrane preparation. The hydrogenase did not couple with autologous F420 or ferredoxin, nor with FAD, FMN, or NAD(P)+. The physiological function of the membrane-bound hydrogenase in hydrogen consumption is discussed.Abbreviation CoM-S-S-HTP
the heterodisulfide of 7-mercaptoheptanoylthrconine phosphate and coenzyme M (mercaptoethanesulfonic acid) 相似文献
18.
Avigad Vonshak Lakkana Chanawongse Boosya Bunnag Morakot Tanticharoen 《Journal of applied phycology》1996,8(1):35-40
Three isolates ofSpirulina platensis (Norst) Geitler marked BP, P4P and Z19/2 were compared with respect to their response and acclimation capability to high photon flux densities (HPFD). Cultures exposed to HPFD (1500–3500 mol photon m–2 s–1) exhibited a marked decrease in light-dependent O2 evolution rate. P4P was more sensitive to HPFD than the two other isolates. All three isolates recovered from photoinhibition when placed under low PFD. The BP isolate was able to recover also in the dark but to a lower extent and at a lower rate, while no recovery was observed in the other two isolates under dark conditions. No recovery was observed when protein synthesis was inhibited using chloramphenicol. Cultures grown at 200 mol photon m–2 s–1 differed from cultures grown at 120 mol photon m 2 s-1 by their lower maximal photosynthetic rate (P
max
) and higher light saturation (I
k
) value, while being more resistant to HPFD stress. The ability ofSpirulina isolates to acclimate and withstand HPFD may provide useful information for the selection of strains useful for outdoor mass cultivation.Author for correspondence 相似文献
19.
We studied the export of inorganic carbon and nitrous oxide (N2O) from a Danish freshwater wetland. The wetland is situated in an agricultural catchment area and is recharged by groundwater enriched with nitrate (NO3
–) (1000 M). NO3
– in recharging groundwater was reduced (57.5 mol NO3
– m–2 yr–) within a narrow zone of the wetland. Congruently, the annual efflux of carbon dioxide (CO2) from the sediment was 19.1 mol C m–2 when estimated from monthly in situ measurements. In comparison the CO2 efflux was 4.8 mol C m–2 yr–1 further out in the wetland, where no NO3
– reduction occurred. Annual exports of inorganic carbon in groundwater and surface water was 78.4 mol C m–2 and 6.1 mol C m–2 at the two sites, respectively. N2O efflux from the sedimenst was detectable on five out of twelve sampling dates and was significantly (P < 0.0001) higher in the NO3
– reduction zone (0.35–9.40 mol m–2 h–1, range of monthly means) than in the zone without NO3
– reduction (0.21–0.41 mol m–2 h–1). No loss of dissolved N2O could be measured. Total annual export of N2O was not estimated. The reduction of oxygen (O2) in groundwater was minor throughout the wetland and did not exceed 0.2 mol 02 m–2yr–1. Sulfate (SO4
––) was reduced in groundwater (2.1 mol SO4
–– m–2 yr–1) in the zone without NO3
– reduction. Although the NO3
– in our wetland can be reduced along several pathways our results strongly suggest that NO3
– loading of freshwater wetlands disturb the carbon balance of such areas, resulting in an accelerated loss of inorganic carbon in gaseous and dissolved forms. 相似文献
20.
Protistan community grazing rates upon both bacterioplankton and autotrophic picoplankton were estimated using fluorescently-labeled prey and by measurement of extracellular hydrolysis of 4-methylumbelliferyl (MUF) -N-acetylglucosaminide in a eutrophic reservoir and an oligo-mesotrophic lake during phytoplankton blooms. In addition, enzyme methods were optimized in bacterivorous flagellate cultures by two enzyme assays, based on fluorometric detection of protistan digestive activity, which were compared and calibrated independently against flagellate bacterivory. Enzymatic hydrolyses of MUF -N,N,N-triacetylchitotriose and MUF -N-acetylglucosaminide were measured in cell-free (sonicated) and whole-cell (unsonicated) samples. The hydrolysis of both substrates, using the whole-cell enzyme assay at in situ pH, was correlated significantly with total grazing rate of Bodo saltans. Thus the whole-cell enzyme assay with MUF -N-acetylglucosaminide was used for freshwater samples. High-affinity (K
m
< 1 mol 1–1) and low-affinity (K
m
> 100 mol 1–1) enzymes were distinguished kinetically in most samples from both systems studied. Activities (V
max
) of the high-affinity enzyme varied from 0.24 to 1.43 nmol 1–1 h–1. Protistan community grazing on bacterioplankton was in the range of 0.15–1.36 g C 1–1 h–1. both for lake and reservoir, the differences being observed in grazing on picocyanobacteria (lake, 0.03-0.22 g C 1–1 h–1. reservoir, 0.35–1.56 g C 1–1) h–1. The enzyme activities were correlated significantly with the protistan grazing both on bacterioplakton (r
s
= 0.62, P < 0.001) and total procaryotic picoplankton (the sum of organic carbon grazed from bacteria and picocyanobacteria, r
s
= 0.73, P < 0.001) in the eutrophic reservoir. Weaker relationships (r
s
= 0.42) with a lower slope were found for the oligo-mesotrophic lake. Ingestion rate studies are time-consuming and the digestive enzyme assay with MUF -N-acetylglucosaminide presents a rapid alternative for estimating total protistan prokaryotic picoplanktivory in freshwaters. 相似文献