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1.
The effect of 21% O 2 and 3% O 2 on the CO 2 exchange of detached wheat leaves was measured in a closed system with an infrared carbon dioxide analyzer. Temperature was varied between 2° and 43°, CO 2 concentration between 0.000% and 0.050% and light intensity between 40 ft-c and 1000 ft-c. In most conditions, the apparent rate of photosynthesis was inhibited in 21% O 2 compared to 3% O 2. The degree of inhibition increased with increasing temperature and decreasing CO 2 concentration. Light intensity did not alter the effect of O 2 except at light intensities or CO 2 concentrations near the compensation point. At high CO 2 concentrations and low temperature, O 2 inhibition of apparent photosynthesis was absent. At 3% O 2, wheat resembled tropical grasses in possessing a high rate of photosynthesis, a temperature optimum for photosynthesis above 30°, and a CO 2 compensation point of less than 0.0005% CO 2. The effect of O 2 on apparent photosynthesis could be ascribed to a combination of stimulation of CO 2 production during photosynthesis, and inhibition of photosynthesis itself. 相似文献
2.
14CO 2 assimilation, 14C incorporation into glycolate and glycolate accumulation in -HPMS treated bean leaves at various O 2 and CO 2 concentrations were studied. In 1% CO 2 oxygen concentration had no significant effect on glycolate accumulation and 14C incorporation into glycolate. In the CO 2 concentration range of 0.03% to 0.01%, increased oxygen concentration decreased not only 14CO 2 assimilation but also glycolate accumulation and 14C incorporation into glycolate. In 1% and 0.1% CO 2, no matter what O 2 concentration was supplied, and in 0.03% CO 2 with 2% and 21% O 2, all of the glycolate accumulated was formed from newly assimilated carbon. In 0.01% CO 2 and 2%, 21% and 100% O 2, and in 0.03% CO 2 with 100% O 2, a substantial portion of the glycolic acid that accumulated in leaves originated from endogenous unlabelled substrates. These findings are discussed in terms of possible changes in the ratio of RuBP carboxylation to RuBP oxygenation and of changes of RuBP pool size, induced by changing O 2 and CO 2 concentrations.This work was supported by the Polish Academy of Sciences, Contract No. 10.2.10. 相似文献
3.
Two cultivars of wheat ( Triticum aestivum L. cvs Sonoita and Yecora Rojo) were grown to maturity in a growth chamber within four sub-chambers under two CO 2 levels (350 or 1000 microliters per liter) at either ambient (21%) or low O 2 (5%). Growth analysis was used to characterize changes in plant carbon budgets imposed by the gas regimes. Large increases in leaf areas were seen in the low O 2 treatments, due primarily to a stimulation of tillering. Roots developed normally at 5% O 2. Seed development was inhibited by the subambient O 2 treatment, but this effect was overcome by CO 2 enrichment at 1000 microliters per liter. Dry matter accumulation and seed number responded differently to the gas treatments. The greatest dry matter production occurred in the low O 2, high CO 2 treatment, while the greatest seed production occurred in the ambient O 2, high CO 2 treatment. Growth and assimilation were stimulated more by either CO 2 enrichment or low O 2 in cv Yecora Rojo than in Sonoita. These experiments are the first to explore the effect of whole plant low O 2 treatments on growth and reproduction. The finding that CO 2 enrichment overcomes low O 2-induced sterility may help elucidate the nature of this effect. 相似文献
4.
An open system associated with an infrared gas analyzer was employed to study transients in CO 2 exchange generated upon darkening preilluminated leaf discs of tobacco ( Nicotiana tabacum vars John Williams Broadleaf and Havana Seed). An empirical formula presented previously enabled prediction of the analyzer response under nonsteady state conditions as a function of time and of the leaf CO 2 exchange rate. A computer was used to evaluate parameters of the leaf CO 2 release rate to provide an estimate of the initial rate of postillumination CO 2 evolution and to produce maximal agreement between predicted and observed analyzer responses. In 21% O 2, the decline in rate of CO 2 evolution upon darkening followed first order kinetics. Initial rates of CO 2 evolution following darkening were relatively independent of the prior ambient CO 2 concentrations. However, rates of photorespiration expressed as a fraction of net photosynthesis declined rapidly with increasing external CO 2 concentration at 21% O 2. Under normal atmospheric conditions, photorespiration was 45 to 50% of the net CO 2 fixation rate at 32°C and high irradiance. The rapid initial CO 2 evolution observed upon darkening at 21% O 2 was absent in 3% O 2. Rates of photorespiration under normal atmospheric concentrations of CO 2 and O 2 as measured by the postillumination burst were highly dependent upon temperature (observed activation energy = 30.1 kilocalories per mole). The results are discussed with respect to previously published estimates of photorespiration in C 3 leaf tissue. 相似文献
5.
Intact spinach ( Spinacia oleracea L.) chloroplasts, when pre-illuminated at 4 millimoles quanta per square meter per second for 8 minutes in a CO 2-free buffer at 21% O 2, showed a decrease (30-70%) in CO 2-dependent O 2 evolution and 14CO 2 uptake. This photoinhibition was observed only when the O 2 concentration and the quantum fluence rate were higher than 4% and 1 millimole per square meter per second, respectively. There was only a small decrease in the extent of photoinhibition when the CO 2 concentration was increased from 0 to 25 micromolar during the treatment, but photoinhibition was abolished when the CO 2 concentration was increased to 30 micromolar. Addition of small quantities of P-glycerate (40-200 micromolar) or glycerate (160 micromolar) was found to prevent photoinhibition. Other intermediates of the Calvin cycle (fructose-6-P, fructose-1,6-P, ribose-5-P, ribulose-5-P) also prevented photoinhibition to various extents. Oxaloacetate was not effective in preventing photoinhibition in these chloroplasts. The amount of O 2 evolved during treatments with 3-P-glycerate or glycerate was no more than 65% of that measured in the presence of low CO 2 concentrations (9-12 micromolar) which did not prevent photoinhibition. In all cases, the extent to which photoinhibition was prevented by these metabolites was not correlated to the amount of O 2 evolved during the photoinhibitory treatment. It is concluded that in these chloroplasts the prevention of the O 2-dependent photoinhibition of light saturated CO 2 fixation capacity is not linked to the dissipation of excitation energy via the photosynthetic electron transport nor to ATP utilization. The requirement of O 2 for photoinhibition of CO 2 fixation capacity in isolated chloroplasts may be explained by an effect of O 2 in allowing metabolic depletion of Calvin cycle intermediates. 相似文献
6.
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
7.
Through use of a recently developed technique that can measure CO 2 exchange by individual attached roots, the influences of soil O 2 and CO 2 concentrations on root respiration were determined for two species of shallow-rooted cacti that typically occur in porous,
well-drained soils. Although soil O 2 concentrations in the rooting zone in the field were indistinguishable from that in the ambient air (21% by volume), the
CO 2 concentrations 10 cm below the soil surface averaged 540 μLL −1 for the barrel cactus Ferocactus acanthodes under dry conditions and 2400 μLL −1 under wet conditions in a loamy sand. For the widely cultivated platyopuntia Opuntia ficus-indica in a sandy clay loam, the CO 2 concentration at 10 cm averaged 1080 μLL −1 under dry conditions and 4170 μLL −1 under wet conditions. For both species, the respiration rate in the laboratory was zero at 0% O 2 and increased to its maximum value at 5% O 2 for rain roots (roots induced by watering) and 16% O 2 for established roots. Established roots of O. ficus-indica were slightly more tolerant of elevated CO 2 than were those of F. acanthodes, 5000 μLL −1 inhibiting respiration by 35% and 46%, respectively. For both species, root respiration was reduced to zero at 20,000 μLL −1 (2%) CO 2. In contrast to the reversible effects of 0% O 2, inhibition by 2% CO 2 was irreversible and led to the death of cortical cells in established roots in 6 h. Although the restriction of various
cacti and other CAM plants to porous soils has generally been attributed to their requirement for high O 2 concentrations, the present results indicate that susceptibility of root respiration to elevated soil CO 2 concentrations may be more important. 相似文献
8.
Dry matter accumulation, nitrogen content and N 2 fixation rates of soybean ( Glycine max [L.] Merr. cv. Wye) plants grown in chambers in which the aerial portion was exposed to a pO 2 of 5, 10, 21, or 30% and a pCO 2 of 300 μl CO 2/l or a pO 2 of 21% and a pCO 2 of 1200 μl CO 2/l during the complete growth cycle were measured. Total N 2[C 2H 2] fixed was increased by CO 2/O 2 ratios greater than those in air and was decreased by ratios smaller than those in air; the effects on N 2 fixation of decreased pO 2 or elevated pCO 2 were quantitatively similar during the period of vegetative growth. Decreased pO 2 produced a smaller increase then elevated pCO 2 during the reproductive period, presumably because of the decreased sink activity of the arrested reproductive growth under subambient pO 2. At a pO 2 of 5% and a pCO 2 of 300 μl CO 2/l total N 2 fixed was increased 125% and per cent nitrogen content in the vegetative parts was increased relative to air while that in the seed was decreased. Dry matter production was increased and reproductive growth was arrested as previously reported for plants receiving only fertilizer nitrogen. At a pO 2 of 30% and a pCO 2 of 300 μl CO 2/l total N 2 fixed was decreased 50% and per cent nitrogen content in the vegetative part was increased relative to air while that in the reproductive structures was unaffected. Dry matter production was similarly decreased in both vegetative and reproductive structures. These effects of altered pO 2 in the aerial part on N 2 fixation are consistent with the hypothesis that the amount of photosynthate available to the nodule may be the most significant primary factor limiting N 2 fixation while sink activity of the reproductive structures may be a secondary factor. 相似文献
9.
Four species of the genus Flaveria, namely F. anomala, F. linearis, F. pubescens, and F. ramosissima, were identified as intermediate C 3-C 4 plants based on leaf anatomy, photosynthetic CO 2 compensation point, O 2 inhibition of photosynthesis, and activities of C 4 enzymes. F. anomala and F. ramosissima exhibit a distinct Kranz-like leaf anatomy, similar to that of the C 4 species F. trinervia, while the other C 3-C 4 intermediate Flaveria species possess a less differentiated Kranz-like leaf anatomy. Photosynthetic CO 2 compensation points of these intermediates at 30°C were very low relative to those of C 3 plants, ranging from 7 to 14 microliters per liter. In contrast to C 3 plants, net photosynthesis by the intermediates was not sensitive to O 2 concentrations below 5% and decreased relatively slowly with increasing O 2 concentration. Under similar conditions, the percentage inhibition of photosynthesis by 21% O 2 varied from 20% to 25% in the intermediates compared with 28% in Lycopersicon esculentum, a typical C 3 species. The inhibition of carboxylation efficiency by 21% O 2 varied from 17% for F. ramosissima to 46% for F. anomala and were intermediate between the C 4 (2% for F. trinervia) and C 3 (53% for L. esculentum) values. The intermediate Flaveria species, especially F. ramosissima, have substantial activities of the C 4 enzymes, phosphoenolpyruvate carboxylase, pyruvate, orthophosphate dikinase, NADP-malic enzyme, and NADP-malate dehydrogenase, indicating potential for C 4 photosynthesis. It appears that these Flaveria species may be true biochemical C 3-C 4 intermediates. 相似文献
10.
The weedy species Parthenium hysterophorus (Asteraceae) possesses a Kranz-like leaf anatomy. The bundle sheath cells are thick-walled and contain numerous granal chloroplasts, prominent mitochondria, and peroxisomes, all largely arranged in a centripetal position. Both mesophyll and bundle sheath chloroplasts accumulate starch. P. hysterophorus exhibits reduced photorespiration as indicated by a moderately low CO 2 compensation concentration (20-25 microliters per liter at 30°C and 21% O 2) and by a reduced sensitivity of net photosynthesis to 21% O 2. In contrast, the related C 3 species P. incanum and P. argentatum (guayule) lack Kranz anatomy, have higher CO 2 compensation concentrations (about 55 microliters per liter), and show a greater inhibition of photosynthesis by 21% O 2. Furthermore, in P. hysterophorus the CO 2 compensation concentration is relatively less sensitive to changes in O 2 concentrations and shows a biphasic response to changing O 2, with a transition point at about 11% O 2. Based on these results, P. hysterophorus is classified as a C 3-C 4 intermediate. The activities of diagnostic enzymes of C 4 photosynthesis in P. hysterophorus were very low, comparable to those observed in the C 3 species P. incanum ( e.g. phosphoenolpyruvate carboxylase activity of 10-29 micromoles per milligram of chlorophyll per hour). Exposures of leaves of each species to 14CO 2 (for 8 seconds) in the light resulted in 3-phosphoglycerate and sugar phosphates being the predominant initial 14C products (77-84%), with ≤4% of the 14C-label in malate plus aspartate. These results indicate that in the C 3-C 4 intermediate P. hysterophorus, the reduction in leaf photorespiration cannot be attributed to C 4 photosynthesis. 相似文献
11.
The quantum yields of C 3 and C 4 plants from a number of genera and families as well as from ecologically diverse habitats were measured in normal air of 21% O 2 and in 2% O 2. At 30 C, the quantum yields of C 3 plants averaged 0.0524 ± 0.0014 mol CO 2/absorbed einstein and 0.0733 ± 0.0008 mol CO 2/absorbed einstein under 21 and 2% O 2. At 30 C, the quantum yields of C 4 plants averaged 0.0534 ± 0.0009 mol CO 2/absorbed einstein and 0.0538 ± 0.0011 mol CO 2/absorbed einstein under 21 and 2% O 2. At 21% O 2, the quantum yield of a C 3 plant is shown to be strongly dependent on both the intercellular CO 2 concentration and leaf temperature. The quantum yield of a C 4 plant, which is independent of the intercellular CO 2 concentration, is shown to be independent of leaf temperature over the ranges measured. The changes in the quantum yields of C 3 plants are due to changes in the O 2 inhibition. The evolutionary significance of the CO 2 dependence of the quantum yield in C 3 plants and the ecological significance of the temperature effects on the quantum yields of C 3 and C 4 plants are discussed. 相似文献
12.
Spatial and temporal variations in the concentrations of dissolved gases (CH 4, CO 2, and O 2) in peat cores were studied using membrane inlet mass spectrometry (MIMS). Variations in vertical gas profiles were observed between random peat cores taken from hollows on the same peat bog. Methane concentrations in profiles (0–30 cm) generally increased with depth and reached maximum values in the range of 200–450 m CH 4 below about 13-cm depth. In some profiles, a peak of dissolved methane was observed at 7-cm depth. Oxygen penetrated to approximately 2-cm depth in the hollows. The sampling probe was used to continuously monitor CH 4, CO 2, and O 2 concentrations at fixed depths in peat cores over periods of several days. The concentration of dissolved CO 2 and O 2 at 1-cm depth oscillated over a 24-h period with the maximum of CO 2 concentration corresponding with the minimum of 0 2. Diurnal variations in CO 2 but not CH 4 were measured at 15-cm depth; dissolved CO 2 levels decreased during daylight hours to a constant minimum concentration of 4.85 mm. This report also describes the application of MIMS for the measurement of gaseous diffusion rates in peat using an inert gas (argon); the value of D, the diffusion coefficient, was 2.07 × 10 –8 m 2 s –1.
Correspondence to: D. Lloyd 相似文献
13.
Plants were obtained with novel O 2-resistant photosynthetic characteristics. At low CO 2 (250-350 μL CO 2 L −1) and 30°C when O 2 was increased from 1% to 21% to 42%, the ratio of net CO 2 uptake in O 2-resistant whole plants or leaf discs compared to wild type increased progressively, and this was not related to stomatal opening. Dihaploid plantlets regenerated from anther culture were initially screened and selected for O 2-resistant growth in 42% O 2/160 μL CO 2 L −1 and 0.18% of the plantlets showed O 2-resistant photosynthesis. About 30% of the progeny (6 of 19 plants) of the first selfing of a fertile plant derived from a resistant dihaploid plant had O 2-resistant photosynthesis, and after a second selfing this increased to 50% (6 of 12 plants). In 21% O 2 and low CO 2, net photosynthesis of the resistant plants was about 15% greater on a leaf area basis than wild type. Net photosynthesis was compared in leaf discs at 30 and 38°C in 21% O 2, and at the higher temperature O 2-resistant plants showed still greater photosynthesis than wild type. The results suggest that the O 2-resistant photosynthesis described here is associated with a decreased stoichiometry of CO 2 release under conditions of rapid photorespiration. This view was supported by the finding that leaves of O 2-resistant plants averaged 40% greater catalase activity than wild type. 相似文献
14.
Photorespiration in Chlorella pyrenoidosa Chick. was assayed by measuring 18O-labeled intermediates of the glycolate pathway. Glycolate, glycine, serine, and excreted glycolate were isolated and analyzed on a gas chromatograph/mass spectrometer to determine isotopic enrichment. Rates of glycolate synthesis were determined from 18O-labeling kinetics of the intermediates, pool sizes, derived rate equations, and nonlinear regression techniques. Glycolate synthesis was higher in high CO 2-grown cells than in air-grown cells when both were assayed under the same O 2 and CO 2 concentrations. Synthesis of glycolate, for both types of cells, was stimulated by high O 2 levels and inhibited by high CO 2 levels. Glycolate synthesis in 1.5% CO 2-grown Chlorella, when exposed to a 0.035% CO 2 atmosphere, increased from about 41 to 86 nanomoles per milligram chlorophyll per minute when the O 2 concentration was increased from 21% to 40%. Glycolate synthesis in air-grown cells increased from 2 to 6 nanomoles per milligram chlorophyll per minute under the same gas levels. Synthesis was undetectable when either the O 2 concentration was lowered to 2% or the CO 2 concentration was raised to 1.5%. Glycolate excretion was also sensitive to O 2 and CO 2 concentrations in 1.5% CO 2-grown cells and the glycolate that was excreted was 18O-labeled. Air-grown cells did not excrete glycolate under any experimental condition. Indirect evidence indicated that glycolate may be excreted as a lactone in Chlorella. Photorespiratory 18O-labeling kinetics were determined for Pavlova lutheri, which unlike Chlorella and higher plants did not directly synthesize glycine and serine from glycolate. This alga did excrete a significant proportion of newly synthesized glycolate into the media. 相似文献
15.
Amount and products of photosynthesis during 10 minutes were measured at different 14CO 2 concentrations in air. With tobacco ( Nicotiana tabacum L. cv. Maryland Mammoth) leaves the percentage of 14C in glycine plus serine was highest (42%) at 0.005% CO 2, and decreased with increasing CO 2 concentration to 7% of the total at 1% CO 2 in air. However, above 0.03% CO 2 the total amount of 14C incorporated into the glycine and serine pool was about constant. At 0.005% or 0.03% CO 2 the percentage and amount of 14C in sucrose was small but increased greatly at higher CO 2 levels as sucrose accumulated as an end product. Relatively similar data were obtained with sugar beet ( Beta vulgaris L. cv. US H20) leaves. The results suggest that photorespiration at high CO 2 concentration is not inhibited but that CO 2 loss from it becomes less significant. 相似文献
16.
The dependence of alfalfa ( Medicago sativa L.) root and nodule nonphotosynthetic CO 2 fixation on the supply of currently produced photosynthate and nodule nitrogenase activity was examined at various times after phloem-girdling and exposure of nodules to Ar:O 2. Phloemgirdling was effected 20 hours and exposure to Ar:O 2 was effected 2 to 3 hours before initiation of experiments. Nodule and root CO 2 fixation rates of phloem-girdled plants were reduced to 38 and 50%, respectively, of those of control plants. Exposure to Ar:O 2 decreased nodule CO 2 fixation rates to 45%, respiration rates to 55%, and nitrogenase activities to 51% of those of the controls. The products of nodule CO 2 fixation were exported through the xylem to the shoot mainly as amino acids within 30 to 60 minutes after exposure to 14CO 2. In contrast to nodules, roots exported very little radioactivity, and most of the 14C was exported as organic acids. The nonphotosynthetic CO 2 fixation rate of roots and nodules averaged 26% of the gross respiration rate, i.e. the sum of net respiration and nonphotosynthetic CO 2 assimilation. Nodules fixed CO 2 at a rate 5.6 times that of roots, but since nodules comprised a small portion of root system mass, roots accounted for 76% of the nodulated root system CO 2 fixation. The results of this study showed that exposure of nodules to Ar:O 2 reduced nodule-specific respiration and nitrogenase activity by similar amounts, and that phloem-girdling significantly reduced nodule CO 2 fixation, nitrogenase activity, nodule-specific respiration, and transport of 14C photoassimilate to nodules. These results indicate that nodule CO 2 fixation in alfalfa is associated with N assimilation. 相似文献
17.
Etiolated rice seedlings ( Oryza sativa L.) exhibited marked morphological differences when grown in sealed containers or in containers through which air was passed continuously. Enhancement of coleoptile and mesocotyl growth and inhibition of leaf and root growth in the sealed containers (enclosure syndrome) were accompanied by accumulation of CO 2 and C 2H 4 in and depletion of O 2 from the atmosphere. Ethylene (1 l 1 –1), high levels of CO 2, and reduced levels of O 2 contributed equally to the increase in coleoptile and mesocotyl growth. The effect of enclosure could be mimicked by passing a gas mixture of 3% O 2, 82% N 2, 15% CO 2 (all v/v), and 1 l l –1) C 2H 4 through the vials containing the etiolated seedlings. The effects of high CO 2 and low O 2 concentrations were not mediated through increased C 2H 4 production. The enclosure syndrome was also observed in rice seedlings grown under water either in darkness or in light. The length of the rice coleoptile was positively correlated with the depth of planting in water-saturated vermiculite. The length of coleoptiles of wheat, barley, and oats was not affected by the depth of planting. In rice, the length of coleoptile was determined by the levels of O 2, CO 2, and ethylene, rather than by light. This regulatory mechanism allows rice seedlings to grow out of shallow water in which the concentration of O 2 is limiting. 相似文献
18.
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
19.
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
20.
An apparatus to produce continuous gas mixtures for use in measurements of plant gas exchange is described. A wide range of CO 2 and water vapor concentrations can be provided and O 2 concentration can be varied from 0 to 21%. Changes in the concentrations of the components are accomplished conveniently, rapidly, and independently. With occasional adjustments, CO 2 and O 2 concentrations can be maintained to within ± 1 μl/l and ± 0.1%, respectively. Dew point of the gas mixture can be maintained to within ± 0.05 C. 相似文献
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