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1.
Rates of inorganic nitrogen uptake by three Northeast US and three Asian species of Porphyra were compared in short-term incubations to evaluate potential for longer term and larger scale examination of bioremediation of nutrient-loaded effluents from finfish aquaculture facilities. The effects of nitrogen (N) species and concentration, temperature, acclimation history, and irradiance were investigated. Uptake rates increased ca. nine-fold from 20 to 150 μM N. Nitrate and ammonium uptake occurred at similar rates. Irradiance had a strong effect, with uptake at 40 μmol photons m−2 s−1only 55% of uptake at 150 μmol photons m−2 s−1. N-replete tissue took up inorganic nitrogen at rates that averaged only 60% of nutrient-deprived tissue. Although there were species (P. amplissima > (P. purpurea = P. umbilicalis)) and temperature effects (10 °C>5 °C>15 °C), interactions among factors indicated that individual species be considered separately. Overall, P. amplissima was the best Northeast US candidate. It took up ammonium at faster rates than other local species at 10 and 15 °C, two temperatures that fall within the expected range of industrial conditions for finfish operations. 相似文献
2.
The nitrogen uptake and growth capabilities of the potentially harmful, raphidophycean flagellate Heterosigma akashiwo (Hada) Sournia were examined in unialgal batch cultures (strain CCMP 1912). Growth rates as a function of three nitrogen substrates (ammonium, nitrate and urea) were determined at saturating and sub-saturating photosynthetic photon flux densities (PPFDs). At saturating PPFD (110 μE m−2 s−1), the growth rate of H. akashiwo was slightly greater for cells grown on NH4+ (0.89 d−1) compared to cells grown on NO3− or urea, which had identical growth rates (0.82 d−1). At sub-saturating PPFD (40 μE m−2 s−1), both urea- and NH4+-grown cells grew faster than NO3−-grown cells (0.61, 0.57 and 0.46 d−1, respectively). The N uptake kinetic parameters were investigated using exponentially growing batch cultures of H. akashiwo and the 15N-tracer technique. Maximum specific uptake rates (Vmax) for unialgal cultures grown at 15 °C and saturating PPFD (110 μE m−2 s−1) were 28.0, 18.0 and 2.89 × 10−3 h−1 for NH4+, NO3− and urea, respectively. The traditional measure of nutrient affinity—the half saturation constants (Ks) were similar for NH4+ and NO3− (1.44 and 1.47 μg-at N L−1), but substantially lower for urea (0.42 μg-at N L−1). Whereas the α parameter (α = Vmax/Ks), which is considered a more robust indicator for substrate affinity when substrate concentrations are low (<Ks), were 19.4, 12.2 and 6.88 × 10−3 h−1/(μg-at N L−1) for NH4+, NO3− and urea, respectively. These laboratory results demonstrate that at both saturating and sub-saturating N concentrations, N uptake preference follows the order: NH4+ > NO3− > urea, and suggests that natural blooms of H. akashiwo may be initiated or maintained by any of the three nitrogen substrates examined. 相似文献
3.
The kinetics of formation of the complex ion, μ-carbonato-di-μ-hydroxo-bis((1,5-diamino-3-aza-pentane) cobalt(III), from the tri-μ-hydroxo-bis((1,5-diamino-3-aza-pentane(III)cobalt(III)) ion in aqueous buffered carbonate solution have been studied spectrophotometrically at 295 nm over the ranges 20.0θ°C34.8, 8.03pH9.44, 5 mM [CO32−35 mM and at an ionic strength of 0.1 M (LiClO4). On the basis of the kinetic results a mechanism, involving rapid cleavage of an hydroxo bridge followed by carbon dioxide uptake with subsequent bridge formation, has been proposed. At 25 °C, the rate of the carbon dioxide uptake is 0.58 M−1 s−1 with ΔH≠ = (13.2±0.7) kcal mol−1 and ΔS≠ = (−15.1 ± 0.7) cal deg−1 mol−1. The results are composed with those obtained for several mononuclear cobalt(III) and one dinuclear cobalt(III) complexes. 相似文献
4.
Garber SS Messerli MA Hubert M Lewis R Hammar K Indyk E Smith PJ 《The Journal of membrane biology》2005,203(2):101-110
Self-referencing ion - selective electrodes (ISEs), made with Chloride Ionophore I-Cocktail A (Fluka), were positioned 1–3 μm from human embryonic kidney cells (tsA201a) and used to record chloride flux during a sustained hyposmotic challenge. The ISE response was close to Nernstian when comparing potentials (VN) measured in 100 and 10 mM NaCl (ΔVN = 57 ± 2 mV), but was slightly greater than ideal when comparing 1 and 10 mm NaCl (ΔVN = 70 ± 3 mV). The response was also linear in the presence of 1 mm glutamate, gluconate, or acetate, 10 μm tamoxifen, or 0.1, 1, or 10 mm HEPES at pH 7.0. The ISE was ∼3 orders of magnitude more selective for Cl− over glutamate or gluconate but less than 2 orders of magnitude move selective for Cl− over bicarbonate, acetate, citrate or thiosulfate. As a result this ISE is best described as an anion sensor. The ISE was ‘poisoned’ by 50 μm 5−nitro-2-(3phenylpropyl-amino)-benzoic acid (NPPB), but not by tamoxifen. An outward anion efflux was recorded from cells challenged with hypotonic (250 ± 5 mOsm) solution. The increase in efflux peaked 7–8 min before decreasing, consistent with regulatory volume decreases observed in separate experiments using a similar osmotic protocol. This anion efflux was blocked by 10 μm tamoxifen. These results establish the feasibility of using the modulation of electrochemical, anion-selective, electrodes to monitor anions and, in this case, chloride movement during volume regulatory events. The approach provides a real-time measure of anion movement during regulated volume decrease at the single-cell level. 相似文献
5.
Cultures of the obligate psychrophilic diatom Fragilariopsis cylindrus (Grunow) were grown for 4 months under steady-state conditions at −1 °C and +7 °C (50 μmol photons m−2 s−1) prior to measurements in order to investigate long-term acclimation of photosynthesis to both temperatures. No differences in maximum intrinsic quantum yield of PS II (FV/FM) and relative electron transport rates could be detected at either temperature after 4 months of acclimation. Measurements of photosynthesis (relative electron transport rates) vs. irradiance (P vs. E curves) revealed similar values for relative light utilization efficiency (α = 0.57 at −1 °C, α = 0.60 at +7 °C) but higher values for irradiance levels at which photosynthesis saturates (EK) at −1 °C and, therefore, higher maximum photosynthesis (PMAX = 54 (relative units) at −1 °C, PMAX = 49 at +7 °C). Nonphotochemical quenching (NPQ) measurements at 385 μmol photons m−2 s−1 indicated higher (37%) NPQ for diatoms grown at −1 °C compared to +7 °C, which was possibly related to a 2-fold increase in the concentration of the pigment diatoxanthin and a 9-fold up-regulation of a gene encoding a fucoxanthin chlorophyll a,c-binding protein. Expression of the D1 protein encoding gene psbA was ca. 1.5-fold up-regulated at −1 °C, whereas expression levels of other genes from Photosystem II (psbC, psbU, psbO), as well as rbcL, the gene encoding the Rubisco large subunit were similar at both temperatures. However, a 2-fold up-regulation of a plastid glyceraldehyde-P dehydrogenase at −1 °C indicated enhanced Calvin cycle activity. This study revealed for the first time that a polar diatom could efficiently acclimate photosynthesis over a wide range of polar temperatures given enough time. Acclimation of photosynthesis at −1 °C was probably regulated similarly to high light acclimation. 相似文献
6.
Miniature heat balance-sap flow gauges were used to measure water flows in small-diameter roots (3–4 mm) in the undisturbed soil of a mature beech–oak–spruce mixed stand. By relating sap flow to the surface area of all branch fine roots distal to the gauge, we were able to calculate real time water uptake rates per root surface area (Js) for individual fine root systems of 0.5–1.0 m in length. Study aims were (i) to quantify root water uptake of mature trees under field conditions with respect to average rates, and diurnal and seasonal changes of Js, and (ii) to investigate the relationship between uptake and soil moisture θ, atmospheric saturation deficit D, and radiation I. On most days, water uptake followed the diurnal course of D with a mid-day peak and low night flow. Neighbouring roots of the same species differed up to 10-fold in their daily totals of Js (<100–2000 g m−2 d−1) indicating a large spatial heterogeneity in uptake. Beech, oak and spruce roots revealed different seasonal patterns of water uptake although they were extracting water from the same soil volume. Multiple regression analyses on the influence of D, I and θ on root water uptake showed that D was the single most influential environmental factor in beech and oak (variable selection in 77% and 79% of the investigated roots), whereas D was less important in spruce roots (50% variable selection). A comparison of root water uptake with synchronous leaf transpiration (porometer data) indicated that average water fluxes per surface area in the beech and oak trees were about 2.5 and 5.5 times smaller on the uptake side (roots) than on the loss side (leaves) given that all branch roots <2 mm were equally participating in uptake. Beech fine roots showed maximal uptake rates on mid-summer days in the range of 48–205 g m−2 h−1 (i.e. 0.7–3.2 mmol m−2 s−1), oak of 12–160 g m−2 h−1 (0.2–2.5 mmol m−2 s−1). Maximal transpiration rates ranged from 3 to 5 and from 5 to 6 mmol m−2 s−1 for sun canopy leaves of beech and oak, respectively. We conclude that instantaneous rates of root water uptake in beech, oak and spruce trees are above all controlled by atmospheric factors. The effects of different root conductivities, soil moisture, and soil hydraulic properties become increasingly important if time spans longer than a week are considered. 相似文献
7.
Q. Chen L. F. Wang N. Su H. D. Qin H. B. Niu J. L. Wang H. Q. Zhai J. M. Wan 《Photosynthetica》2008,46(1):35-39
A yellow leaf colouration mutant (named ycm) generated from rice T-DNA insertion lines was identified with less grana lamellae and low thylakoid membrane protein contents.
At weak irradiance [50 μmol(photon) m−2 s−1], chlorophyll (Chl) contents of ycm were ≈20 % of those of WT and Chl a/b ratios were 3-fold that of wild type (WT). The leaf of ycm showed lower values in the actual photosystem 2 (PS2) efficiency (ΦPS2), photochemical quenching (qP), and the efficiency of excitation capture by open PS2 centres 1 (Fv′/Fm′) than those of WT, except no difference in the maximal efficiency of PS2 photochemistry (Fv/Fm). With progress in irradiance [100 and 200 μmol(photon) m−2 s−1], there was a change in the photosynthetic pigment stoichiometry. In ycm, the increase of total Chl contents and the decrease in Chl a/b ratio were observed. ΦPS2, qP, and Fv′/Fm′ of ycm increased gradually along with the increase of irradiance but still much less than in WT. The increase of xanthophyll ratio
[(Z+A)/(V+A+Z)] associated with non-photochemical quenching (qN) was found in ycm which suggested that ycm dissipated excess energy through the turnover of xanthophylls. No significant differences in pigment composition were observed
in WT under various irradiances, except Chl a/b ratio that gradually decreased. Hence the ycm mutant developed much more tardily than WT, which was caused by low photon energy utilization independent of irradiance. 相似文献
8.
Kinetics of ammonium, nitrate and phosphorus uptake by Canna indica and Schoenoplectus validus 总被引:1,自引:0,他引:1
Canna indica L. is an upright perennial rhizomatous herb, and Schoenoplectus validus (Vahl) A. Löve and D. Löve is a tall, perennial, herbaceous sedge. The nutrient uptake kinetics of C. indica and S. validus were investigated using the modified depletion method after plants were grown for 4 weeks in simulated secondary-treated wastewater. The maximum uptake rate (Imax) and Michaelis–Menten constant (Km) were estimated by iterative curve fitting. The Imax for NH4N (623 μmol g−1 dry root weight h−1) was significantly higher than that for NO3N (338 μmol g−1 dry root weight h−1) in S. validus. In contrast, no difference was observed in C. indica. The Imax values for NO3N and NH4N were higher in S. validus than in C. indica. A significantly lower Km was detected for NO3N uptake in C. indica (385 μmol L−1) compared to that in S. validus (1908 μmol L−1). The Imax for PO4P did not differ between the plant species. The Km for PO4P was significantly higher in C. indica (157 μmol L−1) than in S. validus (60 μmol L−1). In conclusion, we found that S. validus preferred NH4N over NO3N, had greater capacity for N uptake and higher affinity for PO4P, but C. indica had greater affinity for NO3N. Nutrient uptake capacity is likely related to habitat preference, and is influenced by the structure of roots and rhizomes. 相似文献
9.
Jeffrey J. Springer JoAnn M. Burkholder Patricia M. Glibert Robert E. Reed 《Harmful algae》2005,4(3):533-551
The spatial-temporal distribution of a dinoflagellate bloom dominated or co-dominated by Prorocentrum minimum was examined during autumn through early spring in a warm temperate, eutrophic estuary. The developing bloom was first detected from a web-based alert provided by a network of real-time remote monitoring (RTRM) platforms indicating elevated dissolved oxygen and pH levels in upper reaches of the estuary. RTRM data were used to augment shipboard sampling, allowing for an in-depth characterization of bloom initiation, development, movement, and dissipation. Prolonged drought conditions leading to elevated salinities, and relatively high nutrient concentrations from upstream inputs and other sources, likely pre-disposed the upper estuary for bloom development. Over a 7-month period (October 2001–April 2002), the bloom moved toward the northern shore of the mesohaline estuary, intensified under favorable conditions, and finally dissipated after a major storm. Bloom location and transport were influenced by prevailing wind structure and periods of elevated rainfall. Chlorophyll a within bloom areas averaged 106 ± 13 μg L−1 (mean ± 1 S.E.; maximum, 803 μg L−1), in comparison to 20 ± 1 μg L−1 outside the bloom. There were significant positive relationships between dinoflagellate abundance and TN and TP. Ammonium, NO3−, and SRP concentrations did not decrease within the main bloom, suggesting that upstream inputs and other sources provided nutrient-replete conditions. In addition, PAM fluorometric measurements (09:00–13:00 h) of maximal PSII quantum yield (Fv/Fm) were consistently 0.6–0.8 within the bloom until late March, providing little evidence of photo-physiological stress as would have been expected under nutrient-limiting conditions. Nitrogen uptake kinetics were estimated for P. minimum during the period when that species was dominant (October–December 2001), based on literature values for N uptake by an earlier P. minimum bloom (winter 1999) in the Neuse Estuary. The analysis suggests that NH4+ was the major N species that supported the bloom. Considering the chlorophyll a concentrations during October and December and the estimated N uptake rates, phytoplankton biomass was estimated to have doubled once per day. Bloom displacement (January–February) coincided with higher diversity of heterotrophic dinoflagellate species as P. minimum abundance decreased. This research shows the value of RTRM in bloom detection and tracking, and advances understanding of dinoflagellate bloom dynamics in eutrophic estuaries. 相似文献
10.
Here we characterized transepithelial taurine transport in monolayers of cultured human intestinal Caco-2 cells by analyzing kinetic apical and basolateral uptake and efflux parameters. Basolateral uptake was Na+- and Cl−- dependent and was inhibited by β-amino acids. Uptake by this membrane showed properties similar to those of the apical TauT system. In both membranes, taurine uptake fitted a model consisting of a non-saturable plus a saturable component, with a higher half-saturation constant and transport capacity at the apical membrane (Km, 17.1 μmol/L; Vmax, 28.4 pmol·cm−2·5 min−1) than in the basolateral domain (Km, 9.46 μmol/L; Vmax, 5.59 pmol·cm−2·5 min−1). The non-saturable influx component, estimated in the absence of Na+ and Cl−, showed no significant differences between apical and basolateral membranes (KD, 89.2 and 114.7 nL·cm−2 · 5 min−1, respectively). Taurine efflux from the cells is a diffusive process, as shown in experiments using preloaded cells and in trans-stimulation studies (apical KD,72.7 and basolateral KD, 50.1 nL·cm−2·5 min−1). Basolateral efflux rates were significantly lower than passive influx rates. We conclude that basolateral taurine uptake in Caco-2 cells is mediated by a transport mechanism that shares some properties with the apical system TauT. Moreover, calculation of unidirectional and transepithelial taurine fluxes reveals that apical influx of this amino acid is higher than basolateral efflux rates, thereby enabling epithelial cells to accumulate taurine against a concentration gradient. 相似文献
11.
Involvement of betacyanin in chilling-induced photoinhibition in leaves of <Emphasis Type="Italic">Suaeda salsa</Emphasis> 总被引:1,自引:0,他引:1
Seeds of Suaeda salsa were cultured in dark for 3 d and betacyanin accumulation in seedlings was promoted significantly. Then the seedlings with
accumulated betacyanin (C+B) were transferred to 14/10 h light/dark and used for chilling treatment 15 d later. Photosystem
2 (PS2) photochemistry, D1 protein content, and xanthophyll cycle during the chilling-induced photoinhibition (exposed to
5 °C at a moderate photon flux density of 500 μmol m−2 s−1 for 3 h) and the subsequent restoration were compared between the C+B seedlings and the control (C) ones. The maximal efficiency
of PS2 photochemistry (Fv/Fm), the efficiency of excitation energy capture by open PS2 centres (Fv′/Fm′), and the yield of PS2 electron transport (ΦPS2) of the C+B and C leaves both decreased during photoinhibition. However, smaller decreases in Fv/Fm, Fv′/Fm′, and ΦPS2 were observed in the C+B leaves than in C ones. At the same time, the deepoxidation state of xanthophyll cycle, indicated
by (A+Z)/(V+A+Z) ratio, increased rapidly but the D1 protein content decreased considerably during the photoinhibition. The
increase in rate of (A+Z)/(V+A+Z) was higher but the D1 protein turnover was slower in C+B than C leaves. After photoinhibition
treatment, the plants were transferred to a dim irradiation (10 μmol m−2 s−1) at 25 °C for restoration. During restoration, the chlorophyll (Chl) fluorescence parameters, D1 protein content, and xanthophyll
cycle components relaxed gradually, but the rate and level of restoration in the C+B leaves was greater than those in the
C leaves. The addition of betacyanins to the thylakoid solution in vitro resulted in similar changes of Fv/Fm, D1 protein content, and (A+Z)/(V+A+Z) ratio during the chilling process. Therefore, betacyanin accumulation in S. salsa seedlings may result in higher resistance to photoinhibition, larger slowing down of D1 protein turnover, and enhancement
of non-radiative energy dissipation associated with xanthophyll cycle, as well as in greater restoration after photoinhibition
than in the control when subjected to chilling at moderate irradiance. 相似文献
12.
The microalga Pavlova lutheri is a potential source of economically valuable docosahexaenoic and eicosapentaenoic acids. Specific chemical and physical culture conditions may enhance their biochemical synthesis. There are studies relating the effect of CO2 on growth; however, this parameter should not be assessed independently, as its effect strongly depends on the light intensity available. In this research, the combined effects of light intensity and CO2 content on growth and fatty acid profile in P. lutheri were ascertained, in order to optimize polyunsaturated fatty acid production. The influence of the operation mode was also tested via growing the cultures by batch and by continuous cultivation. Higher light intensities associated with lower dilution rates promoted increases in both cell population and weight per cell. Increased levels of CO2 favored the total lipid content, but decreased the amounts of polyunsaturated fatty acids. Mass productivities of eicosapentaenoic acid (3.61 ± 0.04 mg · L−1 · d−1) and docosahexaenoic acid (1.29 ± 0.01 mg · L−1 · d−1) were obtained in cultures supplied with 0.5% (v/v) CO2, at a dilution rate of 0.297 d−1 and a light intensity of 120 μE · m−2 · s−1. 相似文献
13.
Observations of near-bottom populations of Karenia brevis suggest that these cells may derive nutrients from the sediment–water interface. Cells undergoing a metabolic-mediated migration may be in close proximity to enhanced concentrations of nutrients associated with the sediment during at least a fraction of their diel cycle. In this study, the growth, uptake and assimilation rates of ammonium, nitrate, and urea by K. brevis were examined on a diel basis to better understand the potential role of these nutrients in the near-bottom ecology of this species. Three strains of K. brevis, C6, C3, and CCMP 2229, were grown under 12:12 light dark cycle under 30 μmol photons m−2 s−1 delivered to the surface plain of batch cultures. Nitrogen uptake was evaluated using 15N tracer techniques and trichloroacetic acid extraction was used to evaluate the quantity of nitrogen (N) assimilated into cell protein. Growth rates ranged from a low of 0.12 divisions day−1 for C6 and C3 grown on nitrate to a high of 0.18 divisions day−1 for C3 grown on urea. Diurnal maximum uptake rates, ρmax, varied from 0.41 pmol-N cell−1 h−1 for CCMP 2229 grown on nitrate, to 1.29 pmol-N cell−1 h−1 for CCMP 2229 grown on urea. Average nocturnal uptake rates were 29% of diurnal rates for nitrate, 103% of diurnal uptake rates for ammonium and 56% of diurnal uptake rates for urea. Uptake kinetic parameters varied between substrates, between strains and between day and night measurements. Highest maximum uptake rates were found for urea for strains CCMP2229 and C3 and for ammonium for strain C6. Rates of asmilation into protein also varied day and night, but overall were highest for urea. The comparison of maximal uptake rates as well as assimilation efficiencies indicate that ammonium and urea are utilized (taken up and assimilated) more than twice was fast as nitrate on a diel basis. 相似文献
14.
Prostaglandins A2, B1, E1, E2, F1α and F2α were added to cultures of human epidermal cells (keratinocytes) for 24 hours at 37°C, and the effects on 3H-thymidine uptake into DNA was measured. At 70 μg/ml all prostaglandins tested except PGF2α inhibited the uptake of 3H-thymidine greater than 50%. However, at 35 μg/ml, PGA2 and PGB1 were the only two prostaglandins to show significant inhibition, 96% and 51% respectively. At 17.5 μg/ml only PGA2 caused substantial inhibition, 68%. In order to determine if the PGA2 action was mediated by membrane receptors propranolol, phentolamine, metiamide and prostynoic acid were added in conjunction with PGA2. None of the above receptor antagonists were able to reduce the PGA2-induced inhibition of 3H-thymidine uptake. These results indicate that the pre-incubation of human keratinocytes with prostaglandins for 24 hours results in a decrease of 3H-thymidine incorporation in DNA. The precise mechanism of action is unknown at this time. 相似文献
15.
Sinan Akgl Yasemin Kaar Serpil
zkara Handan Yavuz Adil Denizli M. Yakup Arica 《Journal of Molecular Catalysis .B, Enzymatic》2001,15(4-6)
Poly(2-hydroxyethylmethacrylate) (pHEMA) based flat sheet membrane was prepared by UV-initiated photopolymerization technique. The membrane was then grafted with
-histidine. Catalase immobilization onto the membrane from aqueous solutions containing different amounts of catalase at different pH was investigated in a batch system. The maximum catalase immobilization capacity of the pHEMA–histidine membrane was 86 μg cm−2. The activity yield was decreased with the increase of the enzyme loading. It was observed that there was a significant change between Vmax value of the free catalase and Vmax value of the adsorbed catalase on the pHEMA–histidine membrane. The Km value of the immobilized enzyme was higher 1.5 times than that of the free enzyme. Optimum operational temperature was 5°C higher than that of the free enzyme and was significantly broader. It was observed that enzyme could be repeatedly adsorbed and desorbed without loss of adsorption capacity or enzyme activity. 相似文献
16.
Uptake of testosterone was demonstrated in membrane vesicles prepared from Pseudomonas testosteroni grown on testosterone. In contrast, membrane vesicles from uninduced cultures revealed no significant transport activity for steroids. The Km of the reaction was 2 · 10−6M and the V 28.5 nmoles/min per mg protein. Steroid uptake was maximal within the pH range of 8 to 9 and at incubation temperatures between 30 and 37 °C. Transport of steroid was dependent upon NAD+ and was reduced by NADH, dinitrophenol, and inhibitors of electron transport, such as N3− · CN− and amytal. The intravesicular steroid concentration was approx. 800 times the steroid concentration present in the medium at the start of the incubation. 相似文献
17.
Overexpression of Iron Superoxide Dismutase in Transformed Poplar
Modifies the Regulation of Photosynthesis at Low CO2
Partial Pressures or Following Exposure to the Prooxidant Herbicide
Methyl Viologen 总被引:1,自引:0,他引:1
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Ana-Carolina M. Arisi Gabriel Cornic Lise Jouanin Christine H. Foyer 《Plant physiology》1998,117(2):565-574
Chloroplast-targeted overexpression of an Fe superoxide dismutase (SOD) from Arabidopsis thaliana resulted in substantially increased foliar SOD activities. Ascorbate peroxidase, glutathione reductase, and monodehydroascorbate reductase activities were similar in the leaves from all of the lines, but dehydroascorbate reductase activity was increased in the leaves of the FeSOD transformants relative to untransformed controls. Foliar H2O2, ascorbate, and glutathione contents were comparable in all lines of plants. Irradiance-dependent changes in net CO2 assimilation and chlorophyll a fluorescence quenching parameters were similar in all lines both in air (21% O2) and at low (1%) O2. CO2-response curves for photosynthesis showed similar net CO2-exchange characteristics in all lines. In contrast, values of photochemical quenching declined in leaves from untransformed controls at intercellular CO2 (Ci) values below 200 μL L−1 but remained constant with decreasing Ci in leaves of FeSOD transformants. When the O2 concentration was decreased from 21 to 1%, the effect of FeSOD overexpression on photochemical quenching at limiting Ci was abolished. At high light (1000 μmol m−2 s−1) a progressive decrease in the ratio of variable (Fv) to maximal (Fm) fluorescence was observed with decreasing temperature. At 6oC the high-light-induced decrease in the Fv/Fm ratio was partially prevented by low O2 but values were comparable in all lines. Methyl viologen caused decreased Fv/Fm ratios, but this was less marked in the FeSOD transformants than in the untransformed controls. These observations suggest that the rate of superoxide dismutation limits flux through the Mehler-peroxidase cycle in certain conditions. 相似文献
18.
Peter Strlfors Per Belfrage 《Biochimica et Biophysica Acta (BBA)/Molecular Cell Research》1982,721(4):434-440
The catalytic subunit of cAMP-dependent protein kinase from rat adipose tissue was purified to apparent homogeneity by making use of the differential binding of the holoenzyme and the free catalytic subunit to CM-Sephadex and by gel chromatography. Stability and yield was improved by inclusion of nonionic detergent in all steps after dissociation of the holoenzyme. Isoelectric focusing separated enzyme species with pI values of 7.8 and 8.6–8.8. The amino acid composition was similar to the enzyme purified from other tissues. Enzyme activity was markedly unstable in dilute solutions (<5 μg/ml). Additions of nonionic detergent, glycerol, bovine serum albumin and, especially, histones stabilized the enzyme. With protamine, the catalytic subunit had an apparent Km of 60 μM and Vmax of 20 μmol·min−1·mg−1, corresponding values with mixed histones were 12 μM and 1.2 μmol·min−1·mg−1. With both protein substrates the apparent Km for ATP was 11 μM. Concentrations of Mg2+ above 10 mM were inhibitory. Histone phosphorylation was inhibited by NaCl (50% at 0.5 M NaCl) while protamine phosphorylation was stimulated (4-fold at 1 M NaCl). Inorganic phosphate inhibited both substrates (histones: 50% at 0.3 M, and protamine: 50% at 0.5 M). pH optimum was around pH 9 with both substrates. The catalytic subunit contained 2.0 (range of three determinations, 1.7–2.3) mol phosphate/mol protein. It was autophosphorylated and incorporated 32Pi from [γ-32P]ATP in a time-dependent process, reaching saturation when approx. 0.1 mol phosphate/mol catalytic subunit was incorporated. 相似文献
19.
Gonzalo Izaguirre Alexandra Kikonyogo Regina Pietruszko 《Comparative biochemistry and physiology. Part B, Biochemistry & molecular biology》1998,119(4):747-754
Methylglyoxal was demonstrated to be a substrate for the isozymes E1, E2 and E3 of human aldehyde dehydrogenase. Pyruvate was the product from the oxidation of methylglyoxal by the three isozymes. At pH 7.4 and 25oC, the major and minor components of the E3 isozyme catalyzed the reaction with Vmax of 1.1 and 0.8 μmol NADH min−1 mg−1 protein, respectively, compared to 0.067 and 0.060 μmol NADH min−1 mg−1 protein for the E1 and E2 isozymes, respectively. The E2 isozyme had a Km for methylglyoxal of 8.6 μM, the lowest compared to 46 μM for E1 and 586 and 552 μM for the major and minor components of the E3 isozyme, respectively. Both components of the E3 isozyme showed substrate inhibition by methylglyoxal, with Ki values of 2.0 mM for the major component and 12 mM for the minor component at pH 9.0. Substrate inhibition by methylglyoxal was not observed with the E1 and E2 isozymes. Methylglyoxal strongly inhibited the glycolaldehyde activity of the E1 and E2 isozymes. Mixed-type models of inhibition were employed as an approach to calculate the inhibition constants, 44 and 10.6 μM for E1 and E2 isozymes, respectively. 相似文献
20.
Net ecosystem exchange of CO2 (NEE) was measured during 2005 using the eddy covariance (EC) technique over a reed (Phragmites australis (Cav.) Trin. ex Steud.) wetland in Northeast China (121°54′E, 41°08′N). Diurnal NEE patterns varied markedly among months. Outside the growing season, NEE lacked a diurnal pattern and it fluctuated above zero with an average value of 0.07 mg CO2 m−2 s−1 resulting from soil microbial activity. During the growing season, NEE showed a distinct V-like diel course, and the mean daily NEE was −7.48 ± 2.74 g CO2 m−2 day−1, ranging from −13.58 g CO2 m−2 day−1 (July) to −0.10 g CO2 m−2 day−1 (October). An annual cycle was also apparent, with CO2 uptake increasing rapidly in May, peaking in July, and decreasing from August. Monthly cumulative NEE ranged from −115 ± 24 g C m−2 month−1 (the reed wetland was a CO2 sink) in July to 75 ± 16 g C m−2 month−1 (CO2 source) in November. The annual CO2 balance suggests a net uptake of −65 ± 14 g C m−2 year−1, mainly due to the gains in June and July. Cumulative CO2 emission during the non-growing season was 327 g C m−2, much greater than the absolute value of the annual CO2 balance, which proves the importance of the wintertime CO2 efflux at the study site. The ratio of ecosystem respiration (Reco) to gross primary productivity (GPP) for this reed ecosystem was 0.95, indicating that 95% of plant assimilation was consumed by the reed plant or supported the activities of heterotrophs in the soil. Daytime NEE values during the growing season were closely related to photosynthetically active radiation (PAR) (r2 > 0.63, p < 0.01). Both maximum ecosystem photosynthesis rate (Amax) and apparent quantum yield (α) were season-dependent, and reached their peak values in July (1.28 ± 0.11 mg CO2 m−2 s−1, 0.098 ± 0.027 μmol CO2 μmol−1 photon, respectively), corresponding to the observed maximum NEE in July. Ecosystem respiration (Reco) relied on temperature and soil water content, and the mean value of Q10 was about 2.4 with monthly variation ranging from 1.8 to 4.1 during 2005. Annual methane emission from this reed ecosystem was estimated to be about 3 g C m−2 year−1, and about 5% of the net carbon fixed by the reed wetland was released to the atmosphere as CH4. 相似文献