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1.
The flux of glycolate through the C 2 pathway in Chlamydomonas reinhardtii was estimated after inhibition of the pathway with aminooxyacetate (AOA) or aminoacetonitrile (AAN) by measurement of the accumulation of glycolate and glycine. Cells grown photoautotrophically in air excreted little glycolate except in the presence of 2 m m AOA when they excreted 5 micromoles glycolate per hour per milligram clorophyll. Cells grown on high CO 2 (1-5%) when transferred to air produced three times as much glycolate, with half of the glycolate metabolized and half excreted. The lower amount of glycolate produced by the air-grown cells reflects the presence of a CO 2 concentrating mechanism which raises the internal CO 2 level and decreases the ribulose-1,5-bisP oxygenase reaction for glycolate production. Despite the presence of the CO 2 concentrating mechanism, there was still a significant amount of glycolate produced and metabolized by air-grown Chlamydomonas. The capacity of these cells to metabolize between 5 and 10 micromoles of glycolate per hour per milligram chlorophyll was confirmed by measuring the biphasic uptake of added labeled glycolate. The initial rapid (<10 seconds) phase represented uptake of glycolate; the slow phase represented the metabolism of glycolate. The rates of glycolate metabolism were in agreement with those determined using the C 2-cycle inhibitors during CO 2 fixation. 相似文献
2.
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
3.
The photorespiratory activity of mesophyll protoplasts of Nicotiana plumbaginifolia has been clearly demonstrated by the presence of a Warburg-effect, the occurrence of an important CO 2-sensitive O 2 uptake and the effect of some photorespiratory inhibitors on photosynthetic activity. At a nonsaturating dissolved inorganic carbon (DIC) concentration (0.1 millimolar), we observed that the rate of CO 2 fixation was 60% lower at 50% O 2 compared to that measured at 2% O 2. Using 18O 2 and mass spectrometry, we measured O 2 exchange as a function of light intensity and of DIC concentration. Oxygen uptake measured at the CO 2 compensation point (47.4 micromoles O 2 per hour per milligram chlorophyll) was three-fold higher than that measured at a saturating CO 2 concentration. Cyanide or iodoacetamide, inhibitors of the Calvin cycle, were found to reduce the O 2 uptake to the same extent as CO 2 saturation. We conclude from these results that the major part of the CO 2-sensitive O 2 uptake is due to photorespiration. Further, we investigated the effect on net photosynthesis of some inhibitors of the glycolate pathway. At CO 2 saturation (10 millimolar DIC), 5 millimolar aminoacetonitrile (AAN), and 1 millimolar aminooxyacetate (AOA) did not cause any significant decrease in net photosynthesis. However, when these two inhibitors were added under a period of active photorespiration (10 minutes at the CO 2 compensation point at 20% O 2), we observed a decrease in the rate of net photosynthesis at 10 millimolar DIC measured afterward (respectively, 18 and 29%). This inhibition did not appear at 2% O 2, but was stronger at 50% O 2 (40% for AAN and 47% for AOA). With 0.05 millimolar butyl 2-hydroxy-3-butynoate (BHB) or 0.5 millimolar l-methionine- dl-sulfoximine ( l-MSO), rates of net photosynthesis at 10 millimolar DIC were decreased by 10 to 15%. Additional decreases were observed after a period at the CO 2 compensation point at 20% O 2 (30% for BHB and 20% for l-MSO). From the sites of action of the four inhibitors tested, we suggest the inhibition of photosynthesis occurring after a period of active photorespiration to be due to the toxic accumulation of nonmetabolized phosphoglycolate. 相似文献
4.
Wheat ( Triticum aestivum L. cv Albis) was grown in open-top chambers in the field and fumigated daily with charcoal-filtered air (0.015 microliters per liter O 3), nonfiltered air (0.03 microliters per liter O 3), and air enriched with either 0.07 or 0.10 microliters per liter ozone (seasonal 8 hour/day [9 am-5 pm] mean ozone concentration from June 1 until July 10, 1987). Photosynthetic 14CO 2 uptake was measured in situ. Net photosynthesis, dark respiration, and CO 2 compensation concentration at 2 and 21% O 2 were measured in the laboratory. Leaf segments were freeze-clamped in situ for the determination of the steady state levels of ribulose 1,5-bisphosphate, 3-phosphoglycerate, triose-phosphate, ATP, ADP, AMP, and activity of ribulose, 1,5-bisphosphate carboxylase/oxygenase. Photosynthesis of flag leaves was highest in filtered air and decreased in response to increasing mean ozone concentration. CO 2 compensation concentration and the ratio of dark respiration to net photosynthesis increased with ozone concentration. The decrease in photosynthesis was associated with a decrease in chlorophyll, soluble protein, ribulose bisphosphate carboxylase/oxygenase activity, ribulose bisphosphate, and adenylates. No decrease was found for triose-phosphate and 3-phosphoglycerate. The ratio of ATP to ADP and of triosephosphate to 3-phosphoglycerate were increased suggesting that photosynthesis was limited by pentose phosphate reductive cycle activity. No limitation occurred due to decreased access of CO 2 to photosynthetic cells since the decrease in stomatal conductance with increasing ozone concentration did not account for the decrease in photosynthesis. Ozonestressed leaves showed an increased degree of activation of ribulose bisphosphate carboxylase/oxygenase and a decreased ratio of ribulose bisphosphate to initial activity of ribulose bisphosphate carboxylase/oxygenase. Nevertheless, it is suggested that photosynthesis in ozone stressed leaves is limited by ribulose bisphosphate carboxylation possibly due to an effect of ozone on the catalysis by ribulose bisphosphate carboxylase/oxygenase. 相似文献
5.
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
6.
Two hours after the addition of l-methionine- dl-sulfoximine to the cell suspension, glutamine synthetase activity was inhibited by more than 90% in air-grown Chlamydomonas reinhardii. Cells continued to take up NH 3 from the medium provided that the concentration of dissolved CO 2 was high (equilibrated with 4% CO 2 in air). This NH 3 uptake, about 30% of the control, is discussed in terms of glutamate dehydrogenase activity. Without CO 2, or with a low CO 2 level, a NH 3 excretion was observed, the rate of which depended on the actual concentration of the dissolved CO 2. Experiments with 15NH 3 demonstrated that no NH 3 uptake was masked by this excretion and inversely that no excretion occurred during the uptake in the conditions where it took place. Furthermore, the NH 3 excretion observed in the absence of CO 2 increased when O 2 concentration rose to 15% and was inhibited when 10 millimolar isonicotinic acid hydrazide was supplied to the algal suspension. Thus, NH 3 excretion in the presence of l-methionine- dl-sulfoximine seems to be related to a photorespiratory process inasmuch as it presents the same properties with regard to the O 2 and the isonicotinic acid hydrazide effects. These results favor the hypothesis that NH 3 produced in the medium originates from the glycine to serine reaction. On the other hand, partial inhibition (50%) of photosynthesis by l-methionine- dl-sulfoximine was attributed to uncoupling between electron transfer and photophosphorylation due to NH 3 accumulation into the cell. 相似文献
7.
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
8.
Glycolate was excreted from the 5% CO 2-grown cells of Euglena gracilis Z when placed in an atmosphere of 100% O 2 under illumination at 20,000 lux. The amount of excreted glycolate reached 30% of the dry weight of the cells during incubation for 12 hours. The content of paramylon, the reserve polysaccharide of E. gracilis, was decreased during the glycolate excretion, and of the depleted paramylon carbon, two-thirds was excreted to the outside of cells and the remaining metabolized to other compounds, both as glycolate. The paramylon carbon entered Calvin cycle probably as triose phosphate or 3-phosphoglycerate, but not as CO 2 after the complete oxidation through the tricarboxylic acid cycle. The glycolate pathway was partially operative and the activity of the pathway was much less than the rate of the synthesis of glycolate in the cells under 100% O 2 and 20,000 lux; this led the cells to excrete glycolate outside the cells. Exogenous glycolate was metabolized only to CO 2 but not to glycine and serine. The physiologic role of the glycolate metabolism and excretion under such conditions is discussed. 相似文献
9.
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
10.
The claim that Chlorella sp. (CCAP 211/8p), sometimes referred to as C. fusca, Shihira and Krauss, does not excrete glycolate has been reexamined. Chlorella sp. grown on 5% CO2in air, excreted glycolate when incubated in light in 10 mM bicarbonate. Excretion ceased 30–60 min after transfer of the cells to air and no excretion could be detected with air-grown cells or with cells grown on 5% CO2in media buffered at pH 8.0. Incubation with 10 mM isonicotinyl hydrazide, a glycolate pathway inhibitor, caused excretion in air-grown cells and stimulated excretion in CO2-grown cells indicating that both the rate of glycolate synthesis and metabolism is higher in CO2grown cells than in air-grown cells. Enhanced glycolate synthesis and excretion in CO2-grown cells is correlated with law photosynthetic rate in 10 mM bicarbonate, and the photosynthetic rate of these cells doubles over a period of 2–2.5 h after initial transfer from high CO2to bicarbonate. This correlation of photosynthetic induction with cessation of glycolate excretion is similar to that reported in a bluegreen alga and thought to occur in other green algae. These results indicate that glycolate excretion and its regulation in this species of Chlorella is not different from that in other algae. 相似文献
11.
For the leaf succulent Agave deserti and the stem succulent Ferocactus acanthodes, increasing the ambient CO 2 level from 350 microliters per liter to 650 microliters per liter immediately increased daytime net CO 2 uptake about 30% while leaving nighttime net CO 2 uptake of these Crassulacean acid metabolism (CAM) plants approximately unchanged. A similar enhancement of about 30% was found in dry weight gain over 1 year when the plants were grown at 650 microliters CO 2 per liter compared with 350 microliters per liter. Based on these results plus those at 500 microliters per liter, net CO 2 uptake over 24-hour periods and dry weight productivity of these two CAM succulents is predicted to increase an average of about 1% for each 10 microliters per liter rise in ambient CO 2 level up to 650 microliters per liter. 相似文献
12.
Photoautotrophic calli of Nicotiana plumbaginifolia were grown for 3 weeks under two CO 2 concentrations (500 and 20,000 microliters of CO 2 per liter). Calli cultured at high CO 2 exhibited a two-fold higher rate of growth. At CO 2 test levels, these calli were characterized by a lower net photosynthetic capacity than calli cultured at low CO 2. This diminution due to CO 2 adaptation could be ascribed to a 170% stimulation of dark respiration, a 40% decrease in total ribulose-1,5-bisphosphate carboxylase (Rubisco) activity, and also to a feedback inhibition of photosynthesis: high CO 2 grown calli contained about 5.5-fold more sucrose and three-fold less orthophosphate (Pi) than low CO 2 grown calli. Whether the decrease in Rubisco activity is related to the accumulation of sucrose and to the Pi limitation is discussed. Both calli exhibited a Warburg-effect showing the existence of active photorespiration at low CO 2. In calli grown at low CO 2 with 5 millimolar aminoacetonitrile (AAN), an inhibitor of the glycolate pathway, fresh weight decreased by 25% and chlorophyll content by 40%, dark respiration increased by 50% and net CO 2 uptake decreased by about 60% at 340 microliters of CO 2 per liter and 35% at 10,000 microliters of CO 2 per liter. In these calli, glutamine and glutamate contents were half of control calli. In contrast, AAN did not provoke any noticeable effect in calli grown at high CO 2. In photoautotrophic calli, the inhibition of the glycolate pathway by AAN results in severe perturbations in glutamate metabolism and in chlorophyll biosynthesis. 相似文献
13.
Greenhouse-grown pigeonpea ( Cajanus cajan, [L.] Millsp.; cultivar UW-10) and cowpea ( Vigna unguiculata, [L.] Walp.; cultivar California No. 5) were well-watered (control) or subjected to low water potential by withholding water to compare their modes of adaptation to water-limited conditions. Leaf CO 2 exchange rate (CER), leaf diffusive conductance to CO 2 ( gl), and CO 2 concentration in the leaf intercellular air space (C i) were determined at various CO 2 concentrations and photon flux densities (PFD) of photosynthetically active radiation (400 to 700 nanometer). In cowpea, gl declined to less than 15% of controls and total water potential (ψ w) at midafternoon declined to −0.8 megapascal after 5 days of withholding water, whereas gl in pigeonpea was about 40% of controls even though midafternoon ψ w was −1.9 megapascal. After 8 days of withholding water, ψ w at midafternoon declined to −0.9 and −2.4 megapascals in cowpea and pigeonpea, respectively. The solute component of water potential (ψ s) decreased substantially less in cowpea than pigeonpea. Photosynthetic CER at saturation photon flux density (PFD) and ambient external CO 2 concentration (360 microliters per liter) on day 5 of withholding decreased by 83 and 55% in cowpea and pigeonpea, respectively. When measured at external, CO 2 concentration in bulk air of 360 microliters per liter, the CER of cowpea had fully recovered to control levels 3 days after rewatering; however, at 970 microliters per liter the PFD-saturated CERs of both species were substantially lower than in controls, indicating residual impairment. In stressed plants of both species the CER responses to C i from 250 to 600 microliters per liter indicated that a substantial nonstomatal inhibition of CER had occurred. Although the sensitivity of gl to water limitation in cowpea suggested a dehydration avoidance response, parallel measurements of CER at various C i and PFD indicated that photosynthetic activity of cowpea mesophyll was substantially inhibited by the water-limited treatment. 相似文献
14.
Photosynthetic O 2 production and photorespiratory O 2 uptake were measured using isotopic techniques, in the C 3 species Hirschfeldia incana Lowe., Helianthus annuus L., and Phaseolus vulgaris L. At high CO 2 and normal O 2, O 2 production increased linearly with light intensity. At low O 2 or low CO 2, O 2 production was suppressed, indicating that increased concentrations of both O 2 and CO 2 can stimulate O 2 production. At the CO 2 compensation point, O 2 uptake equaled O 2 production over a wide range of O 2 concentrations. O 2 uptake increased with light intensity and O 2 concentration. At low light intensities, O 2 uptake was suppressed by increased CO 2 concentrations so that O 2 uptake at 1,000 microliters per liter CO 2 was 28 to 35% of the uptake at the CO 2 compensation point. At high light intensities, O 2 uptake was stimulated by low concentrations of CO 2 and suppressed by higher concentrations of CO 2. O 2 uptake at high light intensity and 1000 microliters per liter CO 2 was 75% or more of the rate of O 2 uptake at the compensation point. The response of O 2 uptake to light intensity extrapolated to zero in darkness, suggesting that O 2 uptake via dark respiration may be suppressed in the light. The response of O 2 uptake to O 2 concentration saturated at about 30% O 2 in high light and at a lower O 2 concentration in low light. O 2 uptake was also observed with the C 4 plant Amaranthus edulis; the rate of uptake at the CO 2 compensation point was 20% of that observed at the same light intensity with the C 3 species, and this rate was not influenced by the CO 2 concentration. The results are discussed and interpreted in terms of the ribulose-1,5-bisphosphate oxygenase reaction, the associated metabolism of the photorespiratory pathway, and direct photosynthetic reduction of O 2. 相似文献
15.
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
16.
Homogenates of various lower land plants, aquatic angiosperms, and green algae were assayed for glycolate oxidase, a peroxisomal enzyme present in green leaves of higher plants, and for glycolate dehydrogenase, a functionally analogous enzyme characteristic of certain green algae. Green tissues of all lower land plants examined (including mosses, liverworts, ferns, and fern allies), as well as three freshwater aquatic angiosperms, contained an enzyme resembling glycolate oxidase, in that it oxidized l- but not d-lactate in addition to glycolate, and was insensitive to 2 m m cyanide. Many of the green algae (including Chlorella vulgaris, previously claimed to have glycolate oxidase) contained an enzyme resembling glycolate dehydrogenase, in that it oxidized d- but not l-lactate, and was inhibited by 2 m m cyanide. Other green algae had activity characteristic of glycolate oxidase and, accordingly, showed a substantial glycolate-dependent O 2 uptake. It is pointed out that this distribution pattern of glycolate oxidase and glycolate dehydrogenase among the green plants may have phylogenetic significance. 相似文献
17.
The submerged aquatic plant Isoetes howellii Engelmann possesses Crassulacean acid metabolism (CAM) comparable to that known from terrestrial CAM plants. Infrared gas analysis of submerged leaves showed Isoetes was capable of net CO 2 uptake in both light and dark. CO 2 uptake rates were a function of CO 2 levels in the medium. At 2,500 microliters CO 2 per liter (gas phase, equivalent to 1.79 milligrams per liter aqueous phase), Isoetes leaves showed continuous uptake in both the light and dark. At this CO 2 level, photosynthetic rates were light saturated at about 10% full sunlight and were about 3-fold greater than dark CO 2 uptake rates. In the dark, CO 2 uptake rates were also a function of length of time in the night period. Measurements of dark CO 2 uptake showed that, at both 2,500 and 500 microliters CO 2 per liter, rates declined during the night period. At the higher CO 2 level, dark CO 2 uptake rates at 0600 h were 75% less than at 1800 h. At 500 microliters CO 2 per liter, net CO 2 uptake in the dark at 1800 h was replaced by net CO 2 evolution in the dark at 0600 h. At both CO 2 levels, the overnight decline in net CO 2 uptake was marked by periodic bursts of accelerated CO 2 uptake. CO 2 uptake in the light was similar at 1% and 21% O 2, and this held for leaves intact as well as leaves split longitudinally. Estimating the contribution of light versus dark CO 2 uptake to the total carbon gain is complicated by the diurnal flux in CO 2 availability under field conditions. 相似文献
18.
The short term effects of increased levels of CO 2 on gas exchange of leaves of bigtooth aspen ( Populus grandidentata Michx.) were studied at the University of Michigan Biological Station, Pellston, MI. Leaf gas exchange was measured in situ in the upper half of the canopy, 12 to 14 meters above ground. In 1900 microliters per liter CO 2, maximum CO 2 exchange rate (CER) in saturating light was increased by 151% relative to CER in 320 microliters per liter CO 2. The temperature optimum for CER shifted from 25°C in 320 microliters per liter CO 2 to 37°C in 1900 microliters per liter CO 2. In saturating light, increasing CO 2 level over the range 60 to 1900 microliters per liter increased CER, decreased stomatal conductance, and increased leaf water use efficiency. The initial slope of the CO 2 response curve of CER was not significantly different at 20 and 30°C leaf temperatures, although the slope did decline significantly during leaf senescence. In 1900 microliters per liter CO 2, CER increased with increasing light. The light saturation point and maximum CER were higher in 30°C than in 20°C, although there was little effect of temperature in low light. The experimental results are consistent with patterns seen in laboratory studies of other C 3 species and define the parameters required by some models of aspen CER in the field. 相似文献
19.
A technique is described for the measurement of total dissolved inorganic carbon by acid release as CO 2 followed by its conversion to methane and detection by flame ionization in a modified gas chromatograph. This method was used to determine the dissolved inorganic carbon concentration reached at compensation point when algae were allowed to photosynthesize in a closed system in a buffer at known pH, and the CO 2 compensation point was calculated from this concentration. The CO 2 compensation points of 16 freshwater algae were measured at acid and alkaline pH in air-saturated medium: at acid pH the CO 2 compensation points ranged from 4.8 to 41.5 microliters per liter while at alkaline pH they ranged from 0.2 to 7.2 microliters per liter. Removal of O 2 from the medium caused a slight lowering of compensation point at acid pH but had little effect at alkaline pH. These low, O 2-insensitive compensation points are characteristic of C 4 plants. It is suggested that these low CO 2 compensation points are maintained by an active bicarbonate uptake by algae especially at alkaline pH. 相似文献
20.
Conditions are described whereby suspensions of Chlorella pyrenoidosa and Netrium digitus photosynthetically biosynthesize and excrete glycolate continuously in high yields. Aminooxyacetic acid, an inhibitor of pyridoxal phosphate-linked enzymes, increased the excretion of glycolate approximately 4-fold in 1 hour (8 millimolar) and 20-fold in 4 hours (40 millimolar) in the presence of 0.2% CO 2 in air. The amount of glycolate excreted in the presence of aminooxyacetate and an atmosphere of 0.2% CO 2 in air equaled or exceeded the amount excreted in 0.2% CO 2 in O 2 minus aminooxyacetate. CO 2 and light were required for glycolate excretion. Aminooxyacetate also stimulated photosynthetic glycolate excretion in an atmosphere of 0.2% CO 2 in nitrogen or helium, although the stimulation was not as great as when air or O 2 was present. The excreted glycolate was converted to H2 and CO2 by the combined action of glycolic oxidase and the formic hydrogenlyase complex found in Escherichia coli in total conversion yields of 80%. 相似文献
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