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1.
The response of whole leaf photosynthesis of wheat ( Triticum aestivum L.) in relation to soluble CO 2 available to the mesophyll cells, under low (1.5%) O 2 at 25, 30, and 35 C, followed Michaelis-Menten kinetics up to saturating CO 2 but deviated at high CO 2 levels where the experimental Vmax is considerably less than the calculated Vmax. The affinity of the leaves for CO 2 during photosynthesis was similar from 25 to 35 C with K m (CO 2) values of approximately 3.5 to 5 μM. 相似文献
2.
The inhibition of photosynthesis by O 2 in air-grown Chlorella pyrenoidosa was investigated using three experimental techniques (artificial leaf, aqueous method, and O 2 electrode) to measure carbon assimilation. CO 2 response curves were determined under different O 2, pH, and temperature conditions. Regardless of the experimental technique and condition, O 2 inhibition was not evident until a concentration of 50% was reached; Vmax values were reduced whereas Km (CO 2) values were unaffected by the increasing O 2 concentration. The response of photosynthesis to O 2 was independent of CO 2 and HCO 3− concentrations as well as temperature. Relative rates of photosynthesis showed a 4 to 5% stimulation in 2% O 2, a 12% inhibition in 50% O 2, and a 24% inhibition in 100% O 2. The inhibition by 50% O 2 was still reversible after 20 minutes exposure whereas 100% O 2 caused irreversible inhibition after only 4 minutes. 相似文献
3.
The occurrence of photorespiration in soybean ( Glycine max [L.] Merr.) leaf cells was demonstrated by the presence of an O 2-dependent CO 2 compensation concentration, a nonlinear time course for photosynthetic 14CO 2 uptake at low CO 2 and high O 2 concentrations, and an O 2 stimulation of glycine and serine synthesis which was reversed by high CO 2 concentration. The compensation concentration was a linear function of O 2 concentration and increased as temperature increased. At atmospheric CO 2 concentration, 21% O 2 inhibited photosynthesis at 25 C by 27%. Oxygen inhibition of photosynthesis was competitive with respect to CO 2 and increased with increasing temperature. The K m (CO 2) of photosynthesis was also temperature-dependent, increasing from 12 μ m CO 2 at 15 C to 38 μ m at 35 C. In contrast, the K i (O 2) was similar at all temperatures. Oxygen inhibition of photosynthesis was independent of irradiance except at 10 m m bicarbonate and 100% O 2, where inhibition decreased with increasing irradiance up to the point of light saturation of photosynthesis. Concomitant with increasing O 2 inhibition of photosynthesis was an increased incorporation of carbon into glycine and serine, intermediates of the photorespiratory pathway, and a decreased incorporation into starch. The effects of CO 2 and O 2 concentration and temperature on soybean cell photosynthesis and photorespiration provide further evidence that these processes are regulated by the kinetic properties of ribulose-1,5-diphosphate carboxylase with respect to CO 2 and O 2. 相似文献
4.
With an experimental system using mass spectrometry techniques and infra-red gas analysis of CO 2 developed for aquatic plants, we studied the responses to various light intensities and CO 2 concentrations of photosynthesis and O 2 uptake of the red macroalga Chondrus crispus S. The CO 2 exchange resistance at air-water interface which could limit the photosynthesis was experimentally measured. It allowed the calculation of the free dissolved CO 2 concentration. The response to light showed a small O 2 uptake (37% of net photosynthesis in standard conditions) compared to C 3 plants; it was always higher than dark respiration and probably included a photoindependent part. The response to CO 2 showed: (a) an O 2 uptake relatively insensitive to CO 2 concentration and not completely inhibited with high CO 2, (b) a general inhibition of gas exchanges below 130 microliters CO 2 per liter (gas phase), (c) an absence of an inverse relationship between O 2 and CO 2 uptakes, and (d) a low apparent Km of photosynthesis for free CO 2 (1 micromolar). These results suggest that O 2 uptake in the light is the sum of different oxidation processes such as the glycolate pathway, the Mehler reaction, and mitochondrial respiration. The high affinity for CO 2 is discussed in relation to the use of HCO 3− and/or the internal CO 2 accumulation. 相似文献
5.
The carbon dioxide compensation concentration of Panicum milioides was less than that of soybean over the range of 15 to 35 C. In soybean ( Glycine max [L.] Merr. cv. Wayne), the compensation concentration was directly proportional to O 2 concentration. In P. milioides, the compensation concentration was near zero up to 10% O 2 and then increased linearly with higher O 2, although the slope of the response was less than that in soybean. Leaf extracts of P. milioides contained 3-fold higher phosphoenolpyruvate carboxylase activity than soybean leaf extracts. Oxygen inhibition of photosynthesis and carboxy-lation efficiency was less in P. milioides than that observed in soybean. The affinity of P. millioides ribulose-1,5-di-P carboxylase for CO 2 appeared to be slightly greater than that of soybean. The affinity of both enzymes for O 2 was similar. The reduced response of the compensation concentration and photosynthesis to O 2 in P. milioides may be explained by photosynthetic phosphoenolpyruvate carboxylase fixation and by an apparent increased affinity of ribulose-1,5-di-P carboxylase for CO 2. 相似文献
6.
The regulation of ribulose-1,5-bisphosphate (RuBP) carboxylase (rubisco) activity in Phaseolus vulgaris was studied under moderate CO 2 and high light, conditions in which photosynthesis in C 3 plants can be insensitive to changes in O 2 partial pressure. Steady state RuBP concentrations were higher, the calculated rate of RuBP use was lower and the activation state of rubisco was lower in low O 2 relative to values observed in normal O 2. It is suggested that the reduced activity of rubisco observed here is related to feedback effects which occur when the rate of net CO 2 assimilation approaches the maximum capacity for starch and sucrose synthesis (triose phosphate utilization). The activation state of rubisco was independent of O 2 partial pressure when light or CO 2 was limiting for photosynthesis. Reduced activity of rubisco was also observed at limiting light. However, in this species light dependent changes in the concentration of an inhibitor of rubisco controlled the apparent Vmax of rubisco in low light while changes in the CO 2-Mg 2+ dependent activation of rubisco controlled the apparent Vmax in high light. 相似文献
7.
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
8.
The effects of elevated atmospheric CO 2 concentration on growth of forest tree species are difficult to predict because practical limitations restrict experiments to much shorter than the average life-span of a tree. Long-term, process-based computer models must be used to extrapolate from shorter-term experiments. A key problem is to ensure a strong flow of information between experiments and models. In this study, meta-analysis techniques were used to summarize a suite of photosynthetic model parameters obtained from 15 field-based elevated [CO 2] experiments on European forest tree species. The parameters studied are commonly used in modelling photosynthesis, and include observed light-saturated photosynthetic rates ( Amax), the potential electron transport rate ( Jmax), the maximum Rubisco activity ( Vcmax) and leaf nitrogen concentration on mass ( Nm) and area ( Na) bases. Across all experiments, light-saturated photosynthesis was strongly stimulated by growth in elevated [CO 2]. However, significant down-regulation of photosynthesis was also observed; when measured at the same CO 2 concentration, photosynthesis was reduced by 10–20%. The underlying biochemistry of photosynthesis was affected, as shown by a down-regulation of the parameters Jmax and Vcmax of the order of 10%. This reduction in Jmax and Vcmax was linked to the effects of elevated [CO 2] on leaf nitrogen concentration. It was concluded that the current model is adequate to model photosynthesis in elevated [CO 2]. Tables of model parameter values for different European forest species are given. 相似文献
9.
When intact nodulated roots of soybean ( Glycine max L. Merr. nodulated with Bradyrhizobium japonicum strain USDA 16) were exposed to an atmosphere lacking N 2 gas (Ar:O 2 80:20), total nitrogenase activity (measured as H 2 evolution) and respiration (CO 2 evolution) declined with time of exposure. In Ar-inhibited nodules, when the O 2 concentration in the rhizosphere was increased in a linear `ramp' of 2.7% per minute, 93% of the original H 2 evolution and 99% of the CO 2 evolution could be recovered. The internal nodule O 2 concentration (estimated from leghemoglobin oxygenation) declined to 56% of its initial value after 60 minutes of Ar:O 2 exposure and could be partially recovered by the linear increases in O 2 concentration. Nodule gas permeability, as estimated from the lag in ethylene production following exposure of nodules to acetylene, decreased to 26% of its initial value during the Ar-induced decline. Collectively, the results provide direct evidence that the Ar-induced decline results from decreased nodule gas permeability and indicate that the decline in permeability, rather than being immediate, occurs gradually over the period of Ar:O 2 exposure. 相似文献
10.
A mass spectrometer with a membrane inlet was used to monitor light-driven O 2 evolution, O 2 uptake, and CO 2 uptake in suspensions of algae ( Scenedesmus obliquus). We observed the following. ( a) The rate of O 2 uptake, which, in the presence of iodoacetamide, replaces the uptake of CO 2, showed a distinct plateau (V max) beyond ~30% O 2 and was half-maximal at ~8% O 2. We concluded that this light-driven O 2 uptake process, which does not involve carbon compounds, is saturated at lower O 2 concentrations than are photorespiration and glycolate formation. ( b) In the absence of inhibitor, O 2 evolution was relatively unaffected by the presence or absence of CO 2. During the course of CO 2 depletion, electron flow to CO 2 was replaced by an equivalent flow to O 2. ( c) There was a distinct delay between the cessation of CO 2 uptake and the increase in O 2 uptake. We ascribe this delay to the transient utilization of another electron acceptor—possibly bicarbonate or another bound form of CO 2. 相似文献
11.
The magnitude of the percentage inhibition of photosynthesis by atmospheric levels of O 2 in the C 3 species Solanum tuberosum L., Medicago sativa L., Phaseolus vulgaris L., Glycine max L., and Triticum aestivum L. increases in a similar manner with an increase in the apparent solubility ratio of O 2/CO 2 in the leaf over a range of solubility ratios from 25 to 45. The solubility ratio is based on calculated levels of O 2 and CO 2 in the intercellular spaces of leaves as derived from whole leaf measurements of photosynthesis and transpiration. The solubility ratio of O 2/CO 2 can be increased by increased leaf temperature under constant atmospheric levels of O 2 and CO 2 (since O 2 is relatively more soluble than CO 2 with increasing temperature); by increasing the relative levels of O 2/CO 2 in the atmosphere at a given leaf temperature, or by increased stomatal resistance. If the solubility ratio of O 2/CO 2 is kept constant, as leaf temperature is increased, by varying the levels of O 2 or CO 2 in the atmosphere, then the percentage inhibition of photosynthesis by O 2 is similar. The decreased solubility of CO 2 relative to O 2 (decreased CO 2/O 2 ratio) may be partly responsible for the increased percentage inhibition of photosynthesis by O 2 under atmospheric conditions with increasing temperature. 相似文献
12.
Gas exchange measurements and noninvasive leghemoglobin (Lb) spectrophotometry (nodule oximetry) were used to monitor nodule responses to shoot removal in alfalfa ( Medicago sativa L. cv Weevlchek) and birdsfoot trefoil ( Lotus corniculatus L. cv Fergus). In each species, total nitrogenase activity, measured as H 2 evolution in Ar:O 2 (80:20), decreased to <50% of the initial rate within 1 hour after detopping, and net CO 2 production decreased to about 65% of the initial value. In a separate experiment in which nodule oximetry was used, nodule O 2 permeability decreased 50% within 5 hours in each species. A similar decrease in the O 2-saturated respiration rate ( Vmax) for the nodule central zone occurred within 5 hours in birdsfoot trefoil, but only after 24 hours in alfalfa. Lb concentration, also measured by oximetry, decreased after 48 to 72 hours. The decrease in permeability preceded the decrease in Vmax in each species. Vmax may depend mainly on carbohydrate availability in the nodule. If so, then the decrease in permeability could not have been triggered by decreasing carbohydrate availability. Both oximetry and gas exchange data were consistent with the hypothesis that, for the cultivars tested, carbohydrate availability decreased more rapidly in birdsfoot trefoil than in alfalfa nodules. Fractional Lb oxygenation (initially about 0.15) decreased during the first 24 hours after detopping but subsequently increased to >0.65 for a majority of nodules of each species. This increase could lead to O 2 inactivation of nitrogenase. 相似文献
13.
Application of the widely used Farquhar model of photosynthesis in interpretation of gas exchange data assumes that photosynthetic properties are homogeneous throughout the leaf. Previous studies showed that heterogeneity in stomatal conductance ( gs) across a leaf could affect the shape of the measured leaf photosynthetic CO 2 uptake rate ( A) versus intercellular CO 2 concentration ( Ci) response curve and, in turn, estimation of the critical biochemical parameters of this model. These are the maximum rates of carboxylation ( Vc,max), whole-chain electron transport ( Jmax), and triose-P utilization ( VTPU). The effects of spatial variation in Vc,max, Jmax, and VTPU on estimation of leaf averages of these parameters from A-Ci curves measured on a whole leaf have not been investigated. A mathematical model incorporating defined degrees of spatial variability in Vc,max and Jmax was constructed. One hundred and ten theoretical leaves were simulated, each with the same average Vc,max and Jmax, but different coefficients of variation of the mean (CV VJ) and varying correlation between Vc,max and Jmax (Ω). Additionally, the interaction of variation in Vc,max and Jmax with heterogeneity in VTPU, gs, and light gradients within the leaf was also investigated. Transition from Vc,max- to Jmax-limited photosynthesis in the A-Ci curve was smooth in the most heterogeneous leaves, in contrast to a distinct inflection in the absence of heterogeneity. Spatial variability had little effect on the accuracy of estimation of Vc,max and Jmax from A-Ci curves when the two varied in concert (Ω = 1.0), but resulted in underestimation of both parameters when they varied independently (up to 12.5% in Vc,max and 17.7% in Jmax at CV VJ = 50%; Ω = 0.3). Heterogeneity in VTPU also significantly affected parameter estimates, but effects of heterogeneity in gs or light gradients were comparatively small. If Vc,max and Jmax derived from such heterogeneous leaves are used in models to project leaf photosynthesis, actual A is overestimated by up to 12% at the transition between Vc,max- and Jmax-limited photosynthesis. This could have implications for both crop production and Earth system models, including projections of the effects of atmospheric change. 相似文献
14.
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
15.
A plant was found in the C 3-C 4 intermediate species, Flaveria linearis, in which apparent photosynthesis is stimulated by atmospheric O 2 concentrations. A survey of 44 selfed progeny of the plant showed that the O 2 stimulation of apparent photosynthesis was passed on to the progeny. When leaves equilibrated at 210 milliliters per liter O 2 were transferred to 20 milliliters per liter O 2 apparent photosynthesis was initially stimulated, but gradually declined so that at 30 to 40 minutes the rate was only about 80 to 85% of that at 210 milliliters per liter O 2. Switching from 20 to 210 milliliters per liter caused the opposite transition in apparent photosynthesis. All other plants of F. linearis reached steady rates within 5 minutes after switching O 2 that were 20 to 24% lower in 210 than in 20 milliliters per liter O 2. At low intercellular CO 2 concentrations and low irradiances, O 2 inhibition of apparent photosynthesis of the aberrant plant was similar to that in normal plants, but at an irradiance of 2 millimoles quanta per square meter per second and near 300 microliters per liter CO 2 apparent photosynthesis was consistently higher at 210 than at 20 milliliters per liter O 2. In morphology and leaf anatomy, the aberrant plant is like the normal plants in F. linearis. The stimulation of apparent photosynthesis at air levels of O 2 in the aberrant plant is similar to other literature reports on observations with C 3 plants at high CO 2 concentrations, high irradiance and/or low temperatures, and may be related to limitation of photosynthesis by triose phosphate utilization. 相似文献
16.
Physiological regulation of nodule gas permeability has a central role in the response of legumes to such diverse factors as drought, defoliation, and soil nitrate. A new method for quantifying nodule respiration and O 2 permeability, based on noninvasive spectrophotometry of leghemoglobin, was evaluated using intact, attached nodules of Lotus corniculatus. First, the relationship between nodule respiration (O 2 consumption) rate and internal O 2 concentration was determined from the rate of decrease in fractional oxygenation of leghemoglobin (FOL) under N 2. The rate of increase of FOL under 100% O 2 was then used to calculate nodule O 2 permeability, after correcting for respiration. Inactivation of nitrogenase by exposure to 100% O 2 for 15 minutes led to decreases in both permeability and O 2-saturated respiration ( Vmax), but the brief (<15 seconds) exposures to 100% O 2 required by the assay itself had little effect on either parameter. A gradual increase in external O 2 concentration from 20 to 40% resulted in a reversible decrease in permeability, but no change in Vmax. The new method is likely to be useful for research on nodule physiology and might also be applicable to agronomic research and crop improvement programs. 相似文献
17.
Oxygen inhibition of photosynthesis was studied with intact spinach ( Spinacia oleracea L.) chloroplasts which exhibited very high rates of photosynthetic CO 2 reduction and were insensitive to additions of photosynthetic intermediates when CO 2 was available at saturating concentrations. Photosynthetic rates were measured polarographically as O 2 evolution, and the extent of the reduction of substrate was estimated from the amount of O 2 evolved. With CO 2 as substrate, inhibition of photosynthesis by O 2 was dependent on pH. At pH values above 8, rates of O 2 evolution were strongly inhibited by O 2 and only a fraction of the added bicarbonate was reduced before O 2 evolution ceased. The extent of O 2 evolution declined with increasing O 2 concentration and decreasing initial bicarbonate concentration. At pH 7.2, the initial photosynthetic rate was inhibited about 30% at high O 2 levels, but the extent of O 2 evolution was unaffected and most of the added bicarbonate was reduced. Photosynthetic O 2 evolution with 3-phosphoglycerate as substrate was similarly dependent on pH and O 2 concentration. In contrast, there was little effect of O 2 and pH on oxaloacetate-dependent oxygen evolution. Acid-base shift experiments with osmotically shocked chloroplasts showed that ATP formation was not affected by O 2. The results are discussed in terms of a balance between photosynthetic O 2 evolution and O 2 consumption by the ribulose diphosphate oxygenase reaction. 相似文献
18.
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
19.
The effects of aminoacetonitrile (a competitive inhibitor of glycine oxidation) on net photosynthesis, glycolate pathway intermediates, and ribulose-1,5-bisphosphate (RuBP) levels have been investigated at different O 2 and CO 2 concentrations with soybean ( Glycine max)[L] Merr. cv Pioneer 1677) leaf discs floated on 25 millimolar aminoacetonitrile (AAN) for 50 minutes prior to assay. At 2% O2 and 200 or 330 microliters per liter CO2, the inhibitor had no effect on the rate of net photosynthesis and RuBP levels when compared with the control levels. At 11% to 60% O2, AAN caused a decrease in net photosynthesis in addition to the inhibition by O2. This extra inhibition ranged from 22% to 59% depending on the O2 and CO2 concentrations. The levels of RuBP, however, were 1.3 to 2.7 times higher than in the control plants at the same O2 concentrations. At 40% O2 and 200 microliters per liter CO2, the inhibitor caused a 6-fold increase in glycine and more than 2-fold increase in glyoxylate levels, whereas those of glycolate decreased by approximately one-half. The decrease in net photosynthesis observed with AAN is not the result of the depletion of the RuBP pool due to the lack of recycling of carbon from the glycolate pathway to the Calvin cycle. The higher levels of RuBP caused by AAN in photorespiratory conditions, suggest that RuBP carboxylase was inhibited. Glyoxylate could be a possible candidate for the inhibition of the enzyme but what is known so far about its inhibitory properties in vitro may not fit the existing in vivo conditions. An alternative explanation for the inhibition is proposed. 相似文献
20.
There has been much interest in the chloroplast-encoded large subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) as a target for engineering an increase in net CO 2 fixation in photosynthesis. Improvements in the enzyme would lead to an increase in the production of food, fiber, and renewable energy. Although the large subunit contains the active site, a family of rbcS nuclear genes encodes the Rubisco small subunits, which can also influence the carboxylation catalytic efficiency and CO 2/O 2 specificity of the enzyme. To further define the role of the small subunit in Rubisco function, small subunits from spinach, Arabidopsis, and sunflower were assembled with algal large subunits by transformation of a Chlamydomonas reinhardtii mutant that lacks the rbcS gene family. Foreign rbcS cDNAs were successfully expressed in Chlamydomonas by fusing them to a Chlamydomonas rbcS transit peptide sequence engineered to contain rbcS introns. Although plant Rubisco generally has greater CO 2/O 2 specificity but a lower carboxylation Vmax than Chlamydomonas Rubisco, the hybrid enzymes have 3–11% increases in CO 2/O 2 specificity and retain near normal Vmax values. Thus, small subunits may make a significant contribution to the overall catalytic performance of Rubisco. Despite having normal amounts of catalytically proficient Rubisco, the hybrid mutant strains display reduced levels of photosynthetic growth and lack chloroplast pyrenoids. It appears that small subunits contain the structural elements responsible for targeting Rubisco to the algal pyrenoid, which is the site where CO 2 is concentrated for optimal photosynthesis. 相似文献
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