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1.
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
2.
Concurrent O 2 evolution, O 2 uptake, and CO 2 uptake by illuminated maize ( Zea mays) leaves were measured using 13CO 2 and 18O 2. Considerable O 2 uptake occurred during active photosynthesis. At CO 2 compensation, O 2 uptake increased. Associated with this increase was a decrease in O 2 release such that a stoichiometric exchange of O 2 occurred. The rate of O 2 exchange at CO 2 compensation was directly related to O 2 concentration in the atmosphere at least up to 8% (v/v). 相似文献
3.
Photosynthetic CO 2 and O 2 exchange was studied in two moss species, Hypnum cupressiforme Hedw. and Dicranum scoparium Hedw. Most experiments were made during steady state of photosynthesis, using 18O 2 to trace O 2 uptake. In standard experimental conditions (photoperiod 12 h, 135 micromoles photons per square meter per second, 18°C, 330 microliters per liter CO 2, 21% O 2) the net photosynthetic rate was around 40 micromoles CO 2 per gram dry weight per hour in H. cupressiforme and 50 micromoles CO 2 per gram dry weight per hour in D. scoparium. The CO 2 compensation point lay between 45 and 55 microliters per liter CO 2 and the enhancement of net photosynthesis by 3% O 2versus 21% O 2 was 40 to 45%. The ratio of O 2 uptake to net photosynthesis was 0.8 to 0.9 irrespective of the light intensity. The response of net photosynthesis to CO 2 showed a high apparent Km (CO 2) even in nonsaturating light. On the other hand, O 2 uptake in standard conditions was not far from saturation. It could be enhanced by only 25% by increasing the O 2 concentration (saturating level as low as 30% O 2), and by 65% by decreasing the CO 2 concentration to the compensation point. Although O 2 is a competitive inhibitor of CO 2 uptake it could not replace CO 2 completely as an electron acceptor, and electron flow, expressed as gross O 2 production, was inhibited by both high O 2 and low CO 2 levels. At high CO 2, O 2 uptake was 70% lower than the maximum at the CO 2 compensation point. The remaining activity (30%) can be attributed to dark respiration and the Mehler reaction. 相似文献
4.
A closed system consisting of an assimilation chamber furnished with a membrane inlet from the liquid phase connected to a mass spectrometer was used to measure O 2 evolution and uptake by Chlamydomonas reinhardtii cells grown in ambient (0.034% CO 2) or CO 2-enriched (5% CO 2) air. At pH = 6.9, 28°C and concentrations of dissolved inorganic carbon (DIC) saturating for photosynthesis, O 2 uptake in the light (U o) equaled O 2 production (E o) at the light compensation point (15 micromoles photons per square meter per second). E o and U o increased with increasing photon fluence rate (PFR) but were not rate saturated at 600 micromoles photons per square meter per second, while net O 2 exchange reached a saturation level near 500 micromoles photons per square meter per second which was nearly the same for both, CO 2-grown and air-grown cells. Comparison of the U o/E o ratios between air-grown and CO 2-grown C. reinhardtii showed higher values for air-grown cells at light intensities higher than light compensation. For both, air-grown and CO 2-grown algae the rates of mitochondrial O 2 uptake in the dark measured immediately before and 5 minutes after illumination were much lower than U o at PFR saturating for net photosynthesis. We conclude that noncyclic electron flow from water to NADP + and pseudocyclic electron flow via photosystem I to O 2 both significantly contribute to O 2 exchange in the light. In contrast, mitochondrial respiration and photosynthetic carbon oxidation cycle are regarded as minor O 2 consuming reactions in the light in both, air-grown and CO 2-grown cells. It is suggested that the “extra” O 2 uptake by air-grown algae provides ATP required for the energy dependent CO 2/HCO 3− concentrating mechanism known to be present in these cells. 相似文献
5.
The response of CO 2 fixation to a sudden increase in ambient CO 2 concentration has been investigated in intact leaf tissue from spinach ( Spinacia oleracea) using a dual channel infrared gas analyzer. Simultaneous with these measurements, changes in fluorescence emission associated with a weak, modulated measuring beam were recorded. Application of brief (2-3 seconds) dark intervals enabled estimation of the dark fluorescence level ( Fo) under both steady state and transient conditions. The degree of suppression of Fo level fluorescence in the light was strongly correlated with nonphotochemical quenching under all conditions. During CO 2-induced oscillations in photosynthesis under 2% O 2 the changes in nonphotochemical quenching anticipate changes in the rate of uptake of CO 2. At such low levels of O 2 and constant illumination, changes in the relative quantum efficiency of open photosystem II units were estimated as the ratio of the rate of CO 2 uptake and the photochemical quenching coefficient. Under the same conditions the relative quantum efficiency of photosystem II was found to vary inversely with the degree of nonphotochemical quenching. The relationship between changes in the rate of CO 2 uptake: photochemical quenching coefficient and nonphotochemical quenching was altered somewhat when the same experiment was conducted under 20% O 2. The results suggest that electron transport coupled to reduction of O 2 occurs to varying degrees with time during oscillations, especially when ambient O 2 concentrations are high. 相似文献
6.
The nature of the different processes of O 2 uptake involved in the light in the red macroalga Chondrus crispus Stackhouse ( Rhodophyta, Gigartinales) was investigated. At limiting CO 2, INH (2.5 mM) did not alter the O 2 uptake rate. Glycolate was not excreted and did not accumulate within the cells. KCN reduced the rate of O 2 uptake in the light by 76% at limiting CO 2 and by 43% at saturating CO 2, but caused > 95% inhibition of O 2 evolution. DCMU (5 μM) totally blocked the photosynthetic electron transport chain, but allowed a residual O 2 uptake of 3.0±0.6 μmol O 2 .h ?1.g ?1 FW, irrespective of the CO 2 concentration. In saturating CO 2, a high light intensity pretreatment significantly stimulated the rate of O 2 uptake compared to net O 2 evolution, suggesting the persistence, in the light, of mitochondrial respiration. Irrespective of the CO 2 concentration, the optimum temperature for O 2 evolution was 17°C whereas dark O 2 uptake increased linearly with temperature. In contrast, O 2 uptake in the light showed an optimum at 17°C in limiting CO 2, and 21–25° C in saturating CO 2; its Q 10 was 2.4 at limiting CO 2, a value close to that of RuBP oxygenase, and 3.1 at saturating CO 2, a value close to that of dark respiration. It is concluded that: 1) mitochondrial respiration and Mehler reaction are both involved at all CO 2 concentrations, 2) RuBP oxygenase activity cannot account for more than 45%, and Mehler reaction for less than 20%, of the total O 2 uptake observed in the light at limiting CO 2. 相似文献
7.
The oxyhydrogen reaction in the presence and absence of CO 2 was studied in H 2-adapted Scenedesmus obliquus by monitoring the initial rates of H 2, O 2, and 14CO 2 uptake and the effect of inhibitors on these rates with gas-sensing electrodes and isotopic techniques. In the presence of 0.02 atmosphere O 2, the pH 2 was varied from 0 to 1 atmosphere. Whereas the rate of O 2 uptake increased by only 30%, the rate of H 2 uptake increased severalfold over the range of pH 2 values. At 0.1 atmosphere H 2 and 0.02 atmosphere O 2, rates for H 2 and O 2 uptake were between 15 and 25 micromoles per milligram chlorophyll per hour. As the pH 2 was changed from 0 to 1 atmosphere, the quotient H 2:O 2 changed from 0 to roughly 2. This change may reflect the competition between H 2 and the endogenous respiratory electron donors. Respiration in the presence of glucose and acetate was also competitive with H 2 uptake. KCN inhibited equally respiration (O 2 uptake in the absence of H 2) and the oxyhydrogen reaction in the presence and absence of CO 2. The uncoupler carbonyl cyanide p-trifluoromethoxyphenylhydrazone accelerated the rate of respiration and the oxyhydrogen reaction to a similar extent. It was concluded that the oxyhydrogen reaction both in the presence and absence of CO 2 has properties in common with components of respiration and photosynthesis. Participation of these two processes in the oxyhydrogen reaction would require a closely linked shuttle between mitochondrion and chloroplast. 相似文献
8.
In spinach ( Spinacia oleracea) and barley ( Hordeum vulgare) leaves, chlorophyll a fluorescence and O 2 evolution have been measured simultaneously following re-illumination after a dark interval or when steady state photosynthesis has been perturbed by changes in the gas phase. In high CO 2 concentrations, both O 2 and fluorescence can display marked dampening oscillations that are antiparallel but slightly out of phase (a rise or fall in fluorescence anticipating a corresponding fall or rise in O 2 by about 10 to 15 seconds). Infrared gas analysis measurements showed that CO 2 uptake behaved like O 2 evolution both in the period of oscillation (about 1 minute) and in its relation to fluorescence. In the steady state, oscillations were initiated by increases in CO 2 or by increases or decreases in O 2. Oscillations in O 2 or CO 2 did not occur without associated oscillations in fluorescence and the latter were a sensitive indicator of the former. The relationship between such oscillations in photosynthetic carbon assimilation and chlorophyl a fluorescence is discussed in the context of the effect of ATP or NADPH consumption on known quenching mechanisms. 相似文献
9.
C 4 grasses of the NAD‐ME type ( Astrebla lappacea, Eleusine coracana, Eragrostis superba, Leptochloa dubia, Panicum coloratum, Panicum decompositum) and the NADP‐ME type ( Bothriochloa bladhii, Cenchrus ciliaris, Dichanthium sericeum, Panicum antidotale, Paspalum notatum, Pennisetum alopecuroides, Sorghum bicolor) were used to investigate the role of O 2 as an electron acceptor during C 4 photosynthesis. Mass spectrometric measurements of gross O 2 evolution and uptake were made concurrently with measurements of net CO 2 uptake and chlorophyll fluorescence at different irradiances and leaf temperatures of 30 and 40 °C. In all C 4 grasses gross O 2 uptake increased with increasing irradiance at very high CO 2 partial pressures ( pCO 2) and was on average 18% of gross O 2 evolution. Gross O 2 uptake at high irradiance and high pCO 2 was on average 3.8 times greater than gross O 2 uptake in the dark. Furthermore, gross O 2 uptake in the light increased with O 2 concentration at both high CO 2 and the compensation point, whereas gross O 2 uptake in the dark was insensitive to O 2 concentration. This suggests that a significant amount of O 2 uptake may be associated with the Mehler reaction, and that the Mehler reaction varies with irradiance and O 2 concentration. O 2 exchange characteristics at high pCO 2 were similar for NAD‐ME and NADP‐ME species. NAD‐ME species had significantly greater O 2 uptake and evolution at the compensation point particularly at low irradiance compared to NADP‐ME species, which could be related to different rates of photorespiratory O 2 uptake. There was a good correlation between electron transport rates estimated from chlorophyll fluorescence and gross O 2 evolution at high light and high pCO 2. 相似文献
10.
Unidirectional O 2 fluxes were measured with 18O 2 in a whole plant of wheat cultivated in a controlled environment. At 2 or 21% O 2, O 2 uptake was maximum at 60 microliters per liter CO 2. At lower CO 2 concentrations, it was strongly inhibited, as was photosynthetic O 2 evolution. At 2% O 2, there remained a substantial O 2 uptake, even at high CO 2 level; the O 2 evolution was inhibited at CO 2 concentrations under 330 microliters per liter. The O 2 uptake increased linearly with light intensity, starting from the level of dark respiration. No saturation was observed at high light intensities. No significant change in the gas-exchange patterns occurred during a long period of the plant life. An adaptation to low light intensities was observed after 3 hours illumination. These results are interpreted in relation to the functioning of the photosynthetic apparatus and point to a regulation by the electron acceptors and a specific action of CO 2. The behavior of the O 2 uptake and the study of the CO 2 compensation point seem to indicate the persistence of mitochondrial respiration during photosynthesis. 相似文献
11.
The effect of O 2 on inorganic carbon (C i) transport was studied with a high CO 2-requiring mutant (E 1) of Anacystis nidulans R 2. Oxygen (above 2%) inhibited C i transport by 15–35|X% at CO 2 concentrations above 200 μl/l, but had no apparent effect at low, limiting CO 2 concentration. The action spectra for C i transport measured in the presence or absence of 20% O 2 showed two peaks around 684 and 625 nm, corresponding to chlorophyll a and phycocyanin absorption, respectively. The difference between these two spectra (anaerobic minus aerobic) showed one peak around 625 nm, which indicates that a linear electron transport from water to O 2 is involved in the O 2 inhibition of C i transport. Dithiothreitol could overcome the inhibition by O 2. The results suggested that the O 2 inhibition is a result of inactivation of the C i-transporting system. 相似文献
12.
A mass spectrometric method combining 16O/ 18O and 12C/ 13C isotopes was used to quantify the unidirectional fluxes of O 2 and CO 2 during a dark to light transition for guard cell protoplasts and mesophyll cell protoplasts of Commelina communis L. In darkness, O 2 uptake and CO 2 evolution were similar on a protein basis. Under light, guard cell protoplasts evolved O 2 (61 micromoles of O 2 per milligram of chlorophyll per hour) almost at the same rate as mesophyll cell protoplasts (73 micromoles of O 2 per milligram of chlorophyll per hour). However, carbon assimilation was totally different. In contrast with mesophyll cell protoplasts, guard cell protoplasts were able to fix CO 2 in darkness at a rate of 27 micromoles of CO 2 per milligram of chlorophyll per hour, which was increased by 50% in light. At the onset of light, a delay observed for guard cell protoplasts between O 2 evolution and CO 2 fixation and a time lag before the rate of saturation suggested a carbon metabolism based on phospho enolpyruvate carboxylase activity. Under light, CO 2 evolution by guard cell protoplasts was sharply decreased (37%), while O 2 uptake was slowly inhibited (14%). A control of mitochondrial activity by guard cell chloroplasts under light via redox equivalents and ATP transfer in the cytosol is discussed. From this study on protoplasts, we conclude that the energy produced at the chloroplast level under light is not totally used for CO 2 assimilation and may be dissipated for other purposes such as ion uptake. 相似文献
13.
Glycolate and ammonia excretion plus oxygen exchanges were measured in the light in l-methionine- dl-sulfoximine treated air-grown Chlamydomonas reinhardii. At saturating CO 2 (between 600 and 700 microliters per liter CO 2) neither glycolate nor ammonia were excreted, whereas at the CO 2 compensation concentration (<10 microliters per liter CO 2) treated algae excreted both glycolate and ammonia at rates of 37 and 59 nanomoles per minute per milligram chlorophyll, respectively. From the excretion values we calculate the amount of O 2 consumed through the glycolate pathway. The calculated value was not significantly different from the component of O 2 uptake sensitive to CO 2 obtained from the difference between O 2 uptake of the CO 2 compensation point and at saturating CO 2. This component was about 40% of stationary O 2 uptake measured at the CO 2 compensation point. From these data we conclude that glyoxylate decarboxylation in air-grown Chlamydomonas represents a minor pathway of metabolism even in conditions where amino donors are deficient and that processes other than glycolate pathway are responsible for the O 2 uptake insensitive to CO 2. 相似文献
14.
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
15.
The photoacoustic response of the photosynthetic apparatus to a short light pulse consists of three components: heat evolution, O 2 evolution and CO 2 uptake. Recent attempts of deconvoluting the individual components by curve-fitting by means of model curves [Kolbowski et al. (1990) Photosynth Res 25: 309–316] suffered from the fact that the model curve for CO 2 uptake changed its curve shape with CO 2 concentration. Here, it is shown that good fits can be obtained if a stretching factor is incorporated into the fitting routine which adjusts the shape of the uptake model curve. The relationship between CO 2 uptake und H + transport across the thylakoid membrane was investigated by experiments in different CO 2 concentrations from 0 to 7%. It was found that under limiting conditions (7% CO 2) the flux ratio CO 2: O 2 was close to 4. This was compared with the value expected from the stoichiometries of the linear electron transport chain. 相似文献
16.
An increase of medium NaCl concentration induces Dunaliella cells to evolve O 2 photosynthetically even in the absence of CO 2. This NaCl-induced O 2 evolution may reflect the induced conversion of reserve carbohydrate to glycerol. The quantum yield for the NaCl-induced O 2 evolution, in the absence of CO 2, is 1.5-fold higher than that obtained for CO 2 fixation. Since the synthesis of glycerol from reserve carbohydrate in the absence of CO 2 requires only 0.5 ATP/NADPH, whereas photosynthesis requires at least 1.3 ATP/NADPH, it is concluded that the ATP/2e − ratio coupled to NADP reduction in Dunaliella is lower than required for CO 2 fixation. 相似文献
17.
The specificity factor of Rubisco ( S f) was estimated in intact leaves from the carboxylation of ribulose-1,5-bisphosphate (RuBP) at various CO 2/O 2 ratios. As oxygenation is calculated by the difference of the 14CO 2 uptake by RuBP in the absence and presence of oxygen, it is important to choose the optimum CO 2/O 2 ratios. At high CO 2 concentration (1,000 cm 3 m ?3 and higher) oxygenation consumes less than 50% RuBP but the difference of concentrations of CO 2 at cell walls ( C w) and at the carboxylation centers ( C c) is 2?C5% and the influence of mesophyll resistance ( r md) is of minor importance. To accumulate large endogenous pool of RuBP, the leaves were preilluminated in the CO 2- and O 2-free gas environments for 8 to 10 s. Thereafter the light was switched off and the leaves were flushed with the gas containing different concentrations of 14CO 2 and O 2. The specificity factor of Rubisco was calculated from the amount of the tracer taken up under different 14CO 2/O 2 ratios by the exhaustion of the RuBP pool. Application of 14CO 2 allowed us to discriminate between the CO 2 uptake and the concurrent respiratory CO 2 release which proceeded at the expense of unlabelled intermediates. 相似文献
18.
The effect of O 2 on the CO 2 exchange of detached leaves of corn ( Zea mays), wheat ( Triticum vulgare), oats ( Avena sativa), barley ( Hordeum vulgare), timothy ( Phleum pratense) and cat-tail ( Typha angustifolia) was measured with a Clark oxygen electrode and infrared carbon dioxide analysers in both open and closed systems. Corn leaves did not produce CO2 in the light at any O2 concentration, as was shown by the zero CO2 compensation point and the absence of a CO2 burst in the first minute of darkness. The rate of photosynthesis was inhibited by O2 and the inhibition was not completely reversible. On the other hand, the steady rate of respiration after a few minutes in the dark was not affected by O2. These results were interpreted as indicating the absence of any measurable respiration during photosynthesis. Twelve different varieties of corn studied all responded to O2 in the same way. The other 5 monocotyledons studied did produce CO2 in the light. Moreover, the CO2 compensation point increased linearly with O2 indicating a stimulation of photorespiration. The implications of the lack of photorespiration in studies of primary productivity are discussed. 相似文献
19.
Vacuolated and nonvacuolated root tissues of Zea mays were exposed to low water potentials by addition of mannitol or glycerol. Temporary increases were observed for O 2 uptake, but CO 2 evolution remained steady. This increase in O 2 uptake ceased after 15 minutes. Further treatment induced decreases in respiration, with similar reductions in O 2 uptake and CO 2 evolution. 相似文献
20.
Diurnal time courses of net CO 2 assimilation rates, stomatal conductance and light-driven electron fluxes were measured in situ on attached leaves of 30-year-old Turkey oak trees ( Quercus cerris L.) under natural summer conditions in central Italy. Combined measurements of gas exchange and chlorophyll a fluorescence under low O 2 concentrations allowed the demonstration of a linear relationship between the photochemical efficiency of PSII (fluorescence measurements) and the apparent quantum yield of gross photosynthesis (gas exchange). This relationship was used under normal O 2 to compute total light-driven electron fluxes, and to partition them into fractions used for RuBP carboxylation or RuBP oxygenation. This procedure also yielded an indirect estimate of the rate of photorespiration in vivo. The time courses of light-driven electron flow, net CO 2 assimilation and photorespiration paralleled that of photosynthetic photon flux density, with important afternoon deviations as soon as a severe drought stress occurred, whereas photochemical efficiency and maximal fluorescence underwent large but reversible diurnal decreases. The latter observation indicated the occurrence of a large non-photochemical energy dissipation at PSII. We estimated that less than 60% of the total photosynthetic electron flow was used for carbon assimilation at midday, while about 40% was devoted to photorespiration. The rate of carbon loss by photorespiration ( R1) reached mean levels of 56% of net assimilation rates. The potential application of this technique to analysis of the relative contributions of thermal de-excitation at PSII and photorespiratory carbon recycling in the protection of photosynthesis against stress effects is discussed. 相似文献
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