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1.
The time course of O 2 consumption after acute salinity exposure (1, 3, 6, 12, and 24 h to 0, 7, 14, 21, 28, and 35 S) was examined in isolated supraesophageal ganglia, gills, and intact Macrobrachium olfersii (Wiegmann), a hyperosmoregulating freshwater palaemonid shrimp, to establish patterns of metabolic adjustment during salinity adaptation. In whole shrimps, O 2 uptake rates decline with salinity increase to 21 S, subsequently increasing with further salinity increase. The rates increase to maxima after 6–12-h exposure in low salinities, decreasing steadily with time in high salinities. In gill preparations, O 2 consumption rates increase to a maximum in 14 S, then decline; they are maximal after 3–6-h exposure to low salinities and diminish with time in high salinities. In the supraesophageal ganglion, rates of O 2 uptake, always measured in seawater of 18 S, are also maximal when shrimps are exposed to 14 S, subsequently declining or levelling off. Rates decrease with time in shrimps exposed to very low salinities, and are stable in 21 S, reaching maxima after 3–6-h exposure of shrimps to all other media. Both tissues thus exhibit characteristic response patterns of O 2 consumption rate which appear to depend on their functional significance within the context of the whole organism. Such data are interpreted to indicate an interrelationship between O 2 consumption and osmoregulatory capability. 相似文献
2.
The sites and rates of mitochondrial production of superoxide and H 2O 2
in vivo are not yet defined. At least 10 different mitochondrial sites can generate these species. Each site has a different maximum capacity ( e.g. the outer quinol site in complex III (site III Qo) has a very high capacity in rat skeletal muscle mitochondria, whereas the flavin site in complex I (site I F) has a very low capacity). The maximum capacities can greatly exceed the actual rates observed in the absence of electron transport chain inhibitors, so maximum capacities are a poor guide to actual rates. Here, we use new approaches to measure the rates at which different mitochondrial sites produce superoxide/H 2O 2 using isolated muscle mitochondria incubated in media mimicking the cytoplasmic substrate and effector mix of skeletal muscle during rest and exercise. We find that four or five sites dominate during rest in this ex vivo system. Remarkably, the quinol site in complex I (site I Q) and the flavin site in complex II (site II F) each account for about a quarter of the total measured rate of H 2O 2 production. Site I F, site III Qo, and perhaps site E F in the β-oxidation pathway account for most of the remainder. Under conditions mimicking mild and intense aerobic exercise, total production is much less, and the low capacity site I F dominates. These results give novel insights into which mitochondrial sites may produce superoxide/H 2O 2
in vivo. 相似文献
3.
Vesicles prepared with the French press from membranes of cyanelles of Cyanophora paradoxa retain O 2 evolution activity with rates up to 500 micromoles 2,6-dichlorophenolindophenol reduced per hour per milligram chlorophyll. This activity is immediately lost when the vesicles are transferred from the sucrose-phosphate-citrate preparation buffer into dilute phosphate buffer. Similar preparations from Phormidium laminosum, a thermophilic cyanobacterium retain activity under such conditions. Photosystem I activities of both cyanobacterial vesicle preparations were determined by direct spectrophotometric measurement of N,N,N′,N′-tetramethyl- p-phenylenediamine photooxidation in the presence of anthraquinone-2-sulfonate. The rates so determined were compared with rates of O 2 taken up in the presence of methyl viologen or anthraquinone-2-sulfonate as electron acceptors. The predicted stoichiometry of two was observed for moles of N,N,N′,N′-tetramethyl- p-phenylenediamine oxidized per mole of oxygen taken up. Anthraquinone-2-sulfonate was the better electron acceptor, and maximal rates of 943 micromoles per hour per milligram chlorophyll for O 2 uptake were observed for Phormidium laminosum preparations in the presence of superoxide dismutase. For purposes of comparison, spinach chloroplasts were assayed for similar activities. All preparations were readily assayed for photosystem I activity by the direct spectrophotometric method, which has advantages of simplicity and freedom from errors introduced by photoxidation of other substrates by photosystem I when O 2 uptake is measured. 相似文献
4.
The pathways through which NADPH, NADH and H 2 provide electrons to nitrogenase were examined in anaerobically isolated heterocysts. Electron donation in freeze-thawed heterocysts and in heterocyst fractions was studied by measuring O 2 uptake, acetylene reduction and reduction of horse heart cytochrome c. In freeze-thawed heterocysts and membrane fractions, NADH and H 2 supported cyanide-sensitive, respiratory O 2 uptake and light-enhanced, cyanide-insensitive uptake of O 2 resulting from electron donation to O 2 at the reducing side of Photosystem I. Membrane fractions also catalyzed NADH-dependent reduction of cytochrome c. In freeze-thawed heterocysts and soluble fractions from heterocysts, NADPH donated electrons in dark reactions to O 2 or cytochrome c through a pathway involving ferredoxin:NADP reductase; these reactions were only slightly influenced by cyanide or illumination. In freeze-thawed heterocysts provided with an ATP-generating system, NADH or H 2 supported slow acetylene reduction in the dark through uncoupler-sensitive reverse electron flow. Upon illumination, enhanced rates of acetylene reduction requiring the participation of Photosystem I were observed with NADH and H 2 as electron donors. Rapid NADPH-dependent acetylene reduction occurred in the dark and this activity was not influenced by illumination or uncoupler. A scheme summarizing electron-transfer pathways between soluble and membrane components is presented. 相似文献
5.
Several flavin-dependent enzymes of the mitochondrial matrix utilize NAD + or NADH at about the same operating redox potential as the NADH/NAD + pool and comprise the NADH/NAD + isopotential enzyme group. Complex I (specifically the flavin, site I F) is often regarded as the major source of matrix superoxide/H 2O 2 production at this redox potential. However, the 2-oxoglutarate dehydrogenase (OGDH), branched-chain 2-oxoacid dehydrogenase (BCKDH), and pyruvate dehydrogenase (PDH) complexes are also capable of considerable superoxide/H 2O 2 production. To differentiate the superoxide/H 2O 2-producing capacities of these different mitochondrial sites in situ, we compared the observed rates of H 2O 2 production over a range of different NAD(P)H reduction levels in isolated skeletal muscle mitochondria under conditions that favored superoxide/H 2O 2 production from complex I, the OGDH complex, the BCKDH complex, or the PDH complex. The rates from all four complexes increased at higher NAD(P)H/NAD(P) + ratios, although the 2-oxoacid dehydrogenase complexes produced superoxide/H 2O 2 at high rates only when oxidizing their specific 2-oxoacid substrates and not in the reverse reaction from NADH. At optimal conditions for each system, superoxide/H 2O 2 was produced by the OGDH complex at about twice the rate from the PDH complex, four times the rate from the BCKDH complex, and eight times the rate from site I F of complex I. Depending on the substrates present, the dominant sites of superoxide/H 2O 2 production at the level of NADH may be the OGDH and PDH complexes, but these activities may often be misattributed to complex I. 相似文献
6.
The growth rates of Pseudomonas putida KT2442 and mt-2 on benzoate, 4-hydroxybenzoate, or 4-methylbenzoate showed an exponential decrease with decreasing oxygen tensions (partial O 2 tension [pO 2] values). The oxygen tensions resulting in half-maximal growth rates were in the range of 7 to 8 mbar of O 2 (corresponding to 7 to 8 μM O 2) (1 bar = 10 5 Pa) for aromatic compounds, compared to 1 to 2 mbar for nonaromatic compounds like glucose or succinate. The decrease in the growth rates coincided with excretion of catechol or protocatechuate, suggesting that the activity of the corresponding oxygenases became limiting. The experiments directly establish that under aerobic and microaerobic conditions (about 10 mbar of O 2), the diffusion of O 2 into the cytoplasm occurs at high rates sufficient for catabolic processes. This is in agreement with calculated O 2 diffusion rates. Below 10 mbar of O 2, oxygen became limiting for the oxygenases, probably due to their high Km values, but the diffusion of O 2 into the cytoplasm presumably should be sufficiently rapid to maintain ambient oxygen concentrations at oxygen tensions as low as 1 mbar of O 2. The consequences of this finding for the availability of O 2 as a substrate or as a regulatory signal in the cytoplasm of bacterial cells are discussed. 相似文献
7.
Two Clark-type polarographic electrodes were used to measure simultaneous H 2 and O 2 exchange from three species of the blue-green alga Anabaena. Maximum H 2 photoevolution from N 2-fixing cultures of Anabaena required only the removal of dissolved O 2 and N 2; no adaptation period was necessary. No correlation of H 2 photoproduction with photosynthetic O 2 evolution, beyond their mutual light requirement, was found. Hydrogen photoevolution has the following characteristics in common with N 2 fixation in these organisms: DCMU insensitivity; similar white light dependency with very low dark production rates; maximum efficiency in photosystem I light; inhibition by N 2, O 2 and acetylene; and an apparent requirement for the presence of heterocysts. Growth on nitrate medium reduces, and on ammonium medium obliterates, both reactions. Cultures grown under limiting CO 2 conditions have H 2 photoproduction rates proportional to their growth rates. Hydrogenase activity is inferred from H 2 uptake in the dark, but this activity apparently is independent of the photoevolution of H 2 which is ascribed strictly to the nitrogenase system. 相似文献
8.
Light-dependent O 2 exchange was measured in intact, isolated soybean ( Glycine max. var. Williams) cells using isotopically labeled O 2 and a mass spectrometer. The dependence of O 2 exchange on O 2 and CO 2 was investigated at high light in coupled and uncoupled cells. With coupled cells at high O 2, O 2 evolution followed similar kinetics at high and low CO 2. Steady-state rates of O 2 uptake were insignificant at high CO 2, but progressively increased with decreasing CO 2. At low CO 2, steady-state rates of O 2 uptake were 50% to 70% of the maximum CO 2-supported rates of O 2 evolution. These high rates of O 2 uptake exceeded the maximum rate of O 2 reduction determined in uncoupled cells, suggesting the occurrence of another light-induced O 2-uptake process ( i.e. photorespiration). Rates of O2 exchange in uncoupled cells were half-saturated at 7% to 8% O2. Initial rates (during induction) of O2 exchange in uninhibited cells were also half-saturated at 7% to 8% O2. In contrast, steady-state rates of O2 evolution and O2 uptake (at low CO2) were half-saturated at 18% to 20% O2. O2 uptake was significantly suppressed in the presence of nitrate, suggesting that nitrate and/or nitrite can compete with O2 for photoreductant. These results suggest that two mechanisms (O2 reduction and photorespiration) are responsible for the light-dependent O2 uptake observed in uninhibited cells under CO2-limiting conditions. The relative contribution of each process to the rate of O2 uptake appears to be dependent on the O2 level. At high O2 concentrations (≥40%), photorespiration is the major O2-consuming process. At lower (ambient) O2 concentrations (≤20%), O2 reduction accounts for a significant portion of the total light-dependent O2 uptake. 相似文献
9.
Irpex lacteus is a white rot basidiomycete proposed for a wide spectrum of biotechnological applications which presents an interesting, but still scarcely known, enzymatic oxidative system. Among these enzymes, the production, purification, and identification of a new dye-decolorizing peroxidase (DyP)-type enzyme, as well as its physico-chemical, spectroscopic, and catalytic properties, are described in the current work. According to its N-terminal sequence and peptide mass fingerprinting analyses, I. lacteus DyP showed high homology (>95%) with the hypothetical (not isolated or characterized) protein cpop21 from an unidentified species of the family Polyporaceae. The enzyme had a low optimal pH, was very stable to acid pH and temperature, and showed improved activity and stability at high H 2O 2 concentrations compared to other peroxidases. Other attractive features of I. lacteus DyP were its high catalytic efficiency oxidizing the recalcitrant anthraquinone and azo dyes assayed ( kcat/ Km of 1.6 × 10 6 s -1 M -1) and its ability to oxidize nonphenolic aromatic compounds like veratryl alcohol. In addition, the effect of this DyP during the enzymatic hydrolysis of wheat straw was checked. The results suggest that I. lacteus DyP displayed a synergistic action with cellulases during the hydrolysis of wheat straw, increasing significantly the fermentable glucose recoveries from this substrate. These data show a promising biotechnological potential for this enzyme. 相似文献
10.
Complex I (NADH-ubiquinone reductase) and Complex III (ubiquinol-cytochrome c reductase) supplemented with NADH generated O 2? at maximum rates of 9.8 and 6.5 nmol/min/mg of protein, respectively, while, in the presence of superoxide dismutase, the same systems generated H 2O 2 at maximum rates of 5.1 and 4.2 nmol/min/mg of protein, respectively. H 2O 2 was essentially produced by disproportionation of O 2?, which constitutes the precursor of H 2O 2. The effectiveness of the generation of oxygen intermediates by Complex I in the absence of other specific electron acceptors was 0.95 mol of O 2? and 0.63 mol of H 2O 2/mol of NADH. A reduced form of ubiquinone appeared to be responsible for the reduction of O 2 to O 2?, since (a) ubiquinone constituted the sole common major component of Complexes I and III, (b) H 2O 2 generation by Complex I was inhibited by rotenone, and (c) supplementation of Complex I with exogenous ubiquinones increased the rate of H 2O 2 generation. The efficiency of added quinones as peroxide generators decreased in the order Q 1 > Q 0 > Q 2 > Q 6 = Q 10, in agreement with the quinone capacity of acting as electron acceptor for Complex I. In the supplemented systems, the exogenous quinone was reduced by Complex I and oxidized nonenzymatically by molecular oxygen. Additional evidence for the role of ubiquinone as peroxide generator is provided by the generation of O 2? and H 2O 2 during autoxidation of quinols. In oxygenated buffers, ubiquinol (Q 0H 2), benzoquinol, duroquinol and menadiol generated O 2? with k3 values of 0.1 to 1.4 m ? · s ?1 and H 2O 2 with k4 values of 0.009 to 4.3 m ?1 · s ?1. 相似文献
11.
Fluorescence time curves (Kautsky effect) were studied in anaerobic Scenedesmus obliquus, with an apparatus capable of simultaneous recording of O 2 exchange, and far-red actinic illumination. Results, as interpreted in terms of electron transport reactions, suggest: In the course of becoming anaerobic, fluorescence induction undergoes a series of changes, indicating at least three different effects of the absence of O 2 on electron transport. (1) Immediately on removal of O 2, once the pool of intermediates between the two photo-systems is reduced by light reaction II, electron flow stops, resulting in high fluorescence yield and a cessation of O 2 evolution. O 2 appears to regulate linear electron flow and cyclic feedback of electrons to the intermediate pool. (2) An endogenous reductant formed anaerobically reduces the System II acceptors in the dark. The time course of this reduction is at least biphasic, indicative of inhomogeneity of the primary acceptor pool. Prolonged dark anaerobic treatment induces maximal initial fluorescence which decays rapidly in light and with a System I action spectrum. (3) Anaerobic treatment eventually results in deactivation of the oxidizing side of System II, limiting System II even when the acceptors are oxidized by System I pre-illumination. 相似文献
12.
Excitation with short actinic flashes (2 μs) of oxygenated dark-adapted Chlamydomonas cells deposited on a bare O 2 platinum electrode induces an increase of the amperometric signal after the first two flashes. Mass spectrometer experiments performed in the presence of 18O 2 showed that this signal was not due to the photolysis of water (H 216O). The insensitivity of this signal to 10 μM DCMU (3-(3,4-dichlorophenyl)-1,1-dimethylurea), its stimulation by acetate or high O 2 concentration as well as its inhibition by cyanide indicate that these flash-induced changes in O 2 concentration were related to the inhibition of a respiratory process. Because this rather fast inhibition of respiration is insensitive to antimycin A and to salicyl hydroxamic acid, inhibitors of mitochondrial respiration, and because it occurs on a single flash illumination, we conclude that the related respiratory activity takes place inside the chloroplast (chlororespiration) and not in the mitochondria. This interpretation is confirmed by the quite high Km(O2) of this process (about 23 μM) compared to those measured for the mitochondrial reactions (0.2 μM for the cytochrome oxidase pathway and 5.5 μM for the alternative pathway). In a mutant lacking Photosystem I activity, no photoinhibition of respiration was observed. We conclude from the above results that the light-induced inhibition of chlororespiration is due to the oxidation by Photosystem I activity of electron carriers common to both photosynthetic and chlororespiratory chains. 相似文献
13.
Polyethylene glycol (PEG), which is often used to impose low water potentials (ψ w) in solution culture, decreases O 2 movement by increasing solution viscosity. We investigated whether this property causes O 2 deficiency that affects the elongation or metabolism of maize ( Zea mays L.) primary roots. Seedlings grown in vigorously aerated PEG solutions at ambient solution O 2 partial pressure ( pO 2) had decreased steady-state root elongation rates, increased root-tip alanine concentrations, and decreased root-tip proline concentrations relative to seedlings grown in PEG solutions of above-ambient pO 2 (alanine and proline accumulation are responses to hypoxia and low ψ w, respectively). Measurements of root pO 2 were made using an O 2 microsensor to ensure that increased solution pO 2 did not increase root pO 2 above physiological levels. In oxygenated PEG solutions that gave maximal root elongation rates, root pO 2 was similar to or less than (depending on depth in the tissue) pO 2 of roots growing in vermiculite at the same ψ w. Even without PEG, high solution pO 2 was necessary to raise root pO 2 to the levels found in vermiculite-grown roots. Vermiculite was used for comparison because it has large air spaces that allow free movement of O 2 to the root surface. The results show that supplemental oxygenation is required to avoid hypoxia in PEG solutions. Also, the data suggest that the O 2 demand of the root elongation zone may be greater at low relative to high ψ w, compounding the effect of PEG on O 2 supply. Under O 2-sufficient conditions root elongation was substantially less sensitive to the low ψ w imposed by PEG than that imposed by dry vermiculite. 相似文献
14.
O 2 reduction was investigated in photosystem I (PS I) complexes isolated from cyanobacteria Synechocystis sp. PCC 6803 wild type (WT) and menB mutant strain, which is unable to synthesize phylloquinone and contains plastoquinone at the quinone-binding site A 1. PS I complexes from WT and menB mutant exhibited different dependencies of O 2 reduction on light intensity, namely, the values of O 2 reduction rate in WT did not reach saturation at high intensities, in contrast to the values in menB mutant. The obtained results suggest the immediate phylloquinone involvement in the light-induced O 2 reduction by PS I. 相似文献
15.
The unicellular blue-green bacterium Agmenellum quadruplicatum strain BG-1 was found to be capable of rapid photoheterotrophic growth but unable to grow in the dark on a variety of reduced organic substrates. The generation time on glycerol was 12 h, and on CO 2, 3 h. Glycerol carbon was converted into cellular carbon with a very high efficiency. This high efficiency of carbon conversion, the action spectrum for growth on glycerol, cell pigmentation, gas exchange measurements, and immediate ability of photoheterotrophically grown cells to evolve O 2 (upon the addition of CO 2) suggest the involvement of both photosystems I and II of photosynthesis during photoheterotrophic growth. 相似文献
16.
The clam Lucina pectinalis supports its symbiotic bacteria by H 2S transport in the open and accessible heme pocket of Lucina Hb I and by O 2 transport in the narrow and crowded heme pocket of Lucina Hb II. Remarkably, air-equilibrated samples of Lucina Hb I were found to be more rapidly oxidized by nitrite than any previously studied Hb, while those of Lucina Hb II showed an unprecedented resistance to oxidation induced by nitrite. Nitrite-induced oxidation of Lucina Hb II was enabled only when O 2 was removed from its active site. Structural analysis revealed that O 2 “clams up” the active site by hydrogen bond formation to B10Tyr and other distal-side residues. Quaternary effects further restrict nitrite entry into the active site and stabilize the hydrogen-bonding network in oxygenated Lucina Hb II dimers. The dramatic differences in nitrite reactivities of the Lucina Hbs are not related to their O 2 affinities or anaerobic redox potentials, which were found to be similar, but are instead a result of differences in accessibility of nitrite to their active sites; i.e. these differences are due to a kinetic rather than thermodynamic effect. Comparative studies revealed heme accessibility to be a factor in human Hb oxidation by nitrite as well, as evidenced by variations of rates of nitrite-induced oxidation that do not correlate with R and T state differences and inhibition of oxidation rate in the presence of O 2. These results provide a dramatic illustration of how evolution of active sites with varied heme accessibility can moderate the rates of inner-sphere oxidative reactions of Hb and other heme proteins. 相似文献
17.
The action spectrum of apparent photosynthesis for attached radish ( Raphanus sativus L. var. Early Scarlet Globe) and corn ( Zea mays L. var. Pride V.) leaves was measured at 300 μl/l CO 2 and both 21% and 2% O 2. The spectra were measured at light intensities where apparent photosynthesis was proportional to intensity. For radish, a high compensation point plant, oxygen had an inhibiting effect on photosynthesis at all wavelengths from 402 to 694 mμ. If a constant rate of photosynthesis at 21% O 2 for the different wavelengths was chosen, then the percent increase in net CO 2 fixation at 2% O 2 was constant. For corn, a low compensation point plant, no inhibitory effect of oxygen concentration from 2% to 21% O 2 was found over the visible spectrum. The CO 2 compensation point for light intensities greater than the light compensation point was found to be constant and independent of wavelength for both radish and corn leaves. For radish, the lowering of the oxygen concentration from 21% to 2% at these intensities was found to reduce the CO 2 compensation point by the same amount for the wavelengths studied. 相似文献
18.
Lactic acid bacteria (LAB) show anti-inflammatory effects, and their genomic DNA was identified as one of the anti-inflammatory components. Despite the differences in anti-inflammatory effects between live LAB dependent not only on genus but also species, this effect has not been compared at the genomic DNA level. We compared the anti-inflammatory effects of the genomic DNA from five Lactobacillus species— Lactobacillus acidophilus, Lactobacillus casei, Lactobacillus gasseri, Lactobacillus plantarum, and Lactobacillus reuteri—using Caco-2 cells. To evaluate anti-inflammatory effects, decreases in H 2O 2-induced IL-8 secretion and inhibition of H 2O 2-induced NF-κB/IκB-α system activation were examined. All LAB genomic DNAs dose-dependently decreased H 2O 2-induced IL-8 secretion and inhibited H 2O 2-induced NF-κB/IκB-α system activation. Comparison of these effects between Lactobacillus species showed that the anti-inflammatory effects of L. acidophilus genomic DNA are lower than those of the other species. Furthermore, suppression of Toll-like receptor 9 (TLR9), a specific receptor of bacterial DNA, expression by RNAi abolished the decrease of H 2O 2-induced IL-8 secretion and inhibition of H 2O 2-induced NF-κB/IκB-α system activation by LAB genomic DNA. Our results demonstrated that the anti-inflammatory effects of genomic DNA differ between Lactobacillus species and TLR9 is one of the major pathways responsible for the anti-inflammatory effect of LAB genomic DNA. 相似文献
19.
FabF elongation condensing enzyme is a critical factor in determining the spectrum of products produced by the FASII pathway. Its active site contains a critical cysteine-thiol residue, which is a plausible target for oxidation by H 2O 2. Streptococcus pneumoniae produces exceptionally high levels of H 2O 2, mainly through the conversion of pyruvate to acetyl-P via pyruvate oxidase (SpxB). We present evidence showing that endogenous H 2O 2 inhibits FabF activity by specifically oxidizing its active site cysteine-thiol residue. Thiol trapping methods revealed that one of the three FabF cysteines in the wild-type strain was oxidized, whereas in an spxB mutant, defective in H 2O 2 production, none of the cysteines was oxidized, indicating that the difference in FabF redox state originated from endogenous H 2O 2. In vitro exposure of the spxB mutant to various H 2O 2 concentrations further confirmed that only one cysteine residue was susceptible to oxidation. By blocking FabF active site cysteine with cerulenin we show that the oxidized cysteine was the catalytic one. Inhibition of FabF activity by either H 2O 2 or cerulenin resulted in altered membrane fatty acid composition. We conclude that FabF activity is inhibited by H 2O 2 produced by S. pneumoniae. 相似文献
20.
We found similarities between the effects of low night temperatures (5°C–10°C) and slowly imposed water stress on photosynthesis in grapevine ( Vitis vinifera L.) leaves. Exposure of plants growing outdoors to successive chilling nights caused light- and CO 2-saturated photosynthetic O 2 evolution to decline to zero within 5 d. Plants recovered after four warm nights. These photosynthetic responses were confirmed in potted plants, even when roots were heated. The inhibitory effects of chilling were greater after a period of illumination, probably because transpiration induced higher water deficit. Stomatal closure only accounted for part of the inhibition of photosynthesis. Fluorescence measurements showed no evidence of photoinhibition, but nonphotochemical quenching increased in stressed plants. The most characteristic response to both stresses was an increase in the ratio of electron transport to net O 2 evolution, even at high external CO 2 concentrations. Oxygen isotope exchange revealed that this imbalance was due to increased O 2 uptake, which probably has two components: photorespiration and the Mehler reaction. Chilling- and drought-induced water stress enhanced both O 2 uptake processes, and both processes maintained relatively high rates of electron flow as CO 2 exchange approached zero in stressed leaves. Presumably, high electron transport associated with O 2 uptake processes also maintained a high ΔpH, thus affording photoprotection. 相似文献
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