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1.
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
2.
The rate of CO 2 assimilation and levels of metabolites of the C 4 cycle and reductive pentose phosphate pathway in attached leaves of maize ( Zea mays L.) were measured over a range of light intensity from 0 to 1,900 microEinsteins per square meter per second under a saturated CO 2 concentration of 350 microliters per liter and a limiting CO 2 concentration of 133 microliters per liter. The level of ribulose 1,5-bisphosphate (RuBP) stayed almost constant (around 60 nanomoles per milligram chlorophyll [Chl]) from low to high light intensities under 350 microliters per liter. Levels of 3-phosphoglycerate (PGA) increased from 100 to 650 nanomoles per milligram Chl under 350 microliters per liter CO 2 with increasing light intensity. The calculated RuBP concentration of 6 millimolar (corresponded to 60 nanomoles per milligram Chl) was about two times above the estimated RuBP binding-site concentration on ribulose bisphosphate carboxylase-oxygenase (Rubisco) of ~2.6 millimolar in maize bundle sheath chloroplasts in the light. The ratio of RuBP/PGA increased with decreasing light intensity under 350 microliters per liter CO 2. These results suggest that RuBP carboxylation is under control of light intensity possibly due to a limited supply of CO 2 to Rubisco through the C 4 cycle whose activity is highly dependent on light intensity. Pyruvate level increased with increasing light intensity as long as photosynthesis rate increased. A positive relationship between levels of PGA and those of pyruvate during steady-state photosynthesis under various conditions suggests that an elevated concentration of PGA increases the carbon input into the C 4 cycle through the conversion of PGA to PEP and consequently the level of total intermediates of the C 4 cycle can be raised to mediate higher photosynthesis rate. 相似文献
3.
Preincubation of illuminated tobacco ( Nicotiana tabacum L.) leaf disks in glycidate (2,3-epoxypropionate) or glyoxylate inhibited photorespiration by about 40% as determined by the ratio of 14CO 2 evolved into CO 2-free air in light and in darkness. However, under identical preincubation conditions used for the light/dark 14C assays, the compounds failed to reduce photorespiration or stimulate net photosynthesis in tobacco leaf disks based on other CO 2 exchange parameters, including the CO 2 compensation concentration in 21% O 2, the inhibitory effect of 21% O 2 on net photosynthesis in 360 microliters per liter of CO 2 and the rate of net photosynthetic 14CO 2 uptake in air. The effects of both glycidate and glyoxylate on the 14C assay are inconsistent with other measures of photorespiratory CO2 exchange in tobacco leaf disks, and thus these data question the validity of the light to dark ratio of 14CO2 efflux as an assay for relative rates of photorespiration (Zelitch 1968, Plant Physiol 43: 1829-1837). The results of this study specifically indicate that neither glycidate nor glyoxylate reduces photorespiration or stimulates net photosynthesis by tobacco leaf disks under physiological conditions of pO2 and pCO2, contrary to previous reports. 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.
Exposure of ferredoxin-dependent glutamate synthase (EC 1.4.7.1) mutants of Arabidopsis thaliana to photorespiratory conditions resulted in the accumulation of NH 4+ and the inhibition of photosynthesis. However, upon transfer from 2% O 2, 350 microliters per liter CO 2, to 21% O 2, 350 microliters per liter CO 2, net photosynthesis declined at a slower rate in methionine sulfoximine treated leaf discs relative to controls. The recovery of photosynthesis was also more rapid in MSO-treated leaf discs although ammonia levels were more than threefold higher. Photosynthesis in leaf discs treated with azaserine was inhibited more than controls when transferred to 21% O 2 and recovered less than controls when returned to 2% O 2 although NH 4+ levels were not significantly different. The results obtained are consistent with the view that the rapid inhibition of photosynthesis in the glutamate synthase mutants in photorespiratory conditions is not due to the accumulation of NH 4+ but rather to the depletion of amino donors for glyoxylate and the consequent effects of glyoxylate on the lack of return of carbon to the chloroplast. 相似文献
6.
Experiments are described further indicating that O 2-resistant photosynthesis observed in a tobacco ( Nicotiana tabacum) mutant with enhanced catalase activity is associated with decreased photorespiration under conditions of high photorespiration relative to net photosynthesis. The effects on net photosynthesis of (a) increasing O 2 concentrations from 1% to 42% at low CO 2 (250 microliters CO 2 per liter), and (b) of increasing O 2 concentrations from 21% to 42% at high CO 2 (500 microliters CO 2 per liter) were investigated in M 6 progeny of mutant and wild-type leaf discs. The mutant displayed a progressive increase in net photosynthesis relative to wild type with increasing O 2 and the faster rate at 42% O 2 was completely reversed on returning to 21% O 2. The photosynthetic rate by the mutant was similar to wild type in 21% and 42% O 2 at 500 microliters CO 2 per liter, and a faster rate by the mutant was restored on returning to 250 microliters CO 2 per liter. The results are consistent with a lowered release of photorespiratory CO 2 by the mutant because greater catalase activity inhibits the chemical decarboxylation of α-keto acids by peroxisomal H 2O 2. Higher catalase activity was observed in the tip and middle regions of expanding leaves than in the basal area. On successive selfing of mutant plants with enhanced catalase activity, the percent of plants with this phenotype increased from 60% in M 4 progeny to 85% in M 6 progeny. An increase was also observed in the percent of plants with especially high catalase activity (averaging 1.54 times wild type) on successive selfings suggesting that homozygosity for enhanced catalase activity was being approached. 相似文献
7.
Two naturally occurring species of the genus Alternanthera, namely A. ficoides and A. tenella, were identified as C 3-C 4 intermediates based on leaf anatomy, photosynthetic CO 2 compensation point (Γ), O 2 response of г, light intensity response of г, and the activities of key enzymes of photosynthesis. A. ficoides and A. tenella exhibited a less distinct Kranz-like leaf anatomy with substantial accumulation of starch both in mesophyll and bundle sheath cells. Photosynthetic CO 2 compensation points of these two intermediate species at 29°C were much lower than in C 3 plants and ranged from 18 to 22 microliters per liter. Although A. ficoides and A. tenella exhibited similar intermediacy in г, the apparent photorespiratory component of O 2 inhibition in A. ficoides is lower than in A. tenella. The г progressively decreases from 35 microliters per liter at lowest light intensity to 18 microliters per liter at highest light intensity in A. tenella. It was, however, constant in A. ficoides at 20 to 25 microliters per liter between light intensities measured. The rates of net photosynthesis at 21% O 2 and 29°C by A. ficoides and A. tenella were 25 to 28 milligrams CO 2 per square decimeter per hour which are intermediate between values obtained for Tridax procumbens and A. pungens, C 3 and C 4 species, respectively. The activities of key enzymes of C 4 photosynthesis, phosphoenolpyruvate carboxylase, pyruvate Pi dikinase, NAD malic enzyme, NADP malic enzyme and phosphoenolpyruvate carboxykinase in the two intermediates, A. ficoides and A. tenella are very low or insignificant. Results indicated that the relatively low apparent photorespiratory component in these two species is presumably the basis for the C 3-C 4 intermediate photosynthesis. 相似文献
8.
Greenhouse-grown plants of Xanthium strumarium L. were exposed in a growth cabinet to 10 C during days and 5 C during nights for periods of up to 120 hours. Subsequently, CO 2 exchange, transpiration, and leaf temperature were measured on attached leaves and in leaf sections at 25 or 30 C, 19 C dew point of the air, 61 milliwatts per square centimeter irradiance, and CO 2 concentrations between 0 and 1000 microliters per liter ambient air. Net photosynthesis and stomatal conductance decreased and dark respiration increased with increasing duration of prechilling. The reduction in net photosynthesis was not a consequence of decreased stomatal conductance because the intercellular CO 2 concentration in prechilled leaves was equal to or greater than that in greenhouse-grown controls. The intercellular CO 2 concentration at which one-half maximum net photosynthesis occurred remained the same in prechilled leaves and controls (175 to 190 microliters per liter). Stomata of the control plants responded to changes in the CO 2 concentration of the air only slightly. Prechilling for 24 hours or more sensitized stomata to CO 2; they responded to changes in CO 2 concentration in the range from 100 to 1000 microliters per liter. 相似文献
9.
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
10.
Needles from phosphorus deficient seedlings of Pinus radiata D. Don grown for 8 weeks at either 330 or 660 microliters CO 2 per liter displayed chlorophyll a fluorescence induction kinetics characteristic of structural changes within the thylakoid chloroplast membrane, i.e. constant yield fluorescence (F O) was increased and induced fluorescence ([F P-F I]/F O) was reduced. The effect was greatest in the undroughted plants grown at 660 μl CO 2 L −1. By week 22 at 330 μl CO 2 L −1 acclimation to P deficiency had occurred as shown by the similarity in the fluorescence characteristics and maximum rates of photosynthesis of the needles from the two P treatments. However, acclimation did not occur in the plants grown at 660 μl CO 2 L −1. The light saturated rate of photosynthesis of needles with adequate P was higher at 660 μl CO 2 L −1 than at 330 μl CO 2 L −1, whereas photosynthesis of P deficient plants showed no increase when grown at the higher CO 2 concentration. The average growth increase due to CO 2 enrichment was 14% in P deficient plants and 32% when P was adequate. In drought stressed plants grown at 330 μl CO 2 L −1, there was a reduction in the maximal rate of quenching of fluorescence (R Q) after the major peak. Constant yield fluorescence was unaffected but induced fluorescence was lower. These results indicate that electron flow subsequent to photosystem II was affected by drought stress. At 660 μl CO 2 L −1 this response was eliminated showing that CO 2 enrichment improved the ability of the seedlings to acclimate to drought stress. The average growth increase with CO 2 enrichment was 37% in drought stressed plants and 19% in unstressed plants. 相似文献
11.
The effect of pH, O 2 concentration, and temperature on the CO 2 compensation point (Г[CO 2]) of isolated Asparagus sprengeri Regel mesophyll cells has been determined in a closed, aqueous environment by a sensitive gas-chromatographic technique. Measured values range between 10 and 100 microliters per liter CO 2 depending upon experimental conditions. The Г(CO 2) increases with increasing temperature. The rate of increase is dependent upon the O 2 concentration and is more rapid at high (250-300 micromolar), than at low (30-60 micromolar), O 2 concentrations. The differential effect of temperature on Г(CO 2) is more pronounced at pH 6.2 than at pH 8.0, but this pH-dependence is not attributable to a direct, differential effect of pH on the relative rates of photosynthesis and photorespiration, as the O 2-sensitive component of Г(CO 2) remains constant over this range. The Г(CO 2) of Asparagus cells at 25°C decreases by 50 microliters per liter when the pH is raised from 6.2 to 8.0, regardless of the prevailing O 2 concentration. It is suggested that the pH-dependence of Г(CO 2) is related to the ability of the cell to take up CO 2 from the aqueous environment. The correlation between high HCO 3− concentrations and low Г(CO 2) at alkaline pH indicates that extracellular HCO 3− facilitates the uptake of CO 2, possibly by increasing the flux of inorganic carbon from the bulk medium to the cell surface. The strong O 2− and temperature-dependence of Г(CO 2) indicates that isolated Asparagus mesophyll cells lack an efficient means for concentrating intracellular CO 2 to a level sufficient to reduce or suppress photorespiration. 相似文献
12.
Numerous net photosynthetic and dark respiratory measurements were made over a period of 4 years on leaves of 24 sour orange ( Citrus aurantium) trees; 8 of them growing in ambient air at a mean CO 2 concentration of 400 microliters per liter, and 16 growing in air enriched with CO 2 to concentrations approaching 1000 microliters per liter. Over this CO 2 concentration range, net photosynthesis increased linearly with CO 2 by more than 200%, whereas dark respiration decreased linearly to only 20% of its initial value. These results, together with those of a comprehensive fine-root biomass determination and two independent aboveground trunk and branch volume inventories, suggest that a doubling of the air's current mean CO 2 concentration of 360 microliters per liter would enhance the growth of the trees by a factor of 3.8. 相似文献
13.
A series of laboratory exposures of two varieties of bush bean ( Phaseolus vulgaris L., var 274 and var 290) was conducted to determine the sensitivity of [ 14C]photosynthate allocation patterns to alteration by SO 2 and O 3. Experiments with the pollution-resistant 274 variety demonstrated short-term changes in both 14C and biomass allocation to roots of 14CO 2-labeled plants but no significant effect on yield by up to 40 hours of exposure to SO 2 at 0.50 microliters per liter or 4 hours of O 3 at 0.40 microliters per liter. Subsequent experiments with the more sensitive 290 variety demonstrated significant alteration of photosynthesis, translocation, and partitioning of photosynthate between plant parts including developing pods. Significant increases in foliar retention of photosynthate (+40%) occurred after 8 hours of exposure to SO 2 at 0.75 microliters per liter (6.0 microliters per liter-hour) and 11 hours of exposure to O 3 at 0.30 microliters per liter-hour (3.3 microliters-hours). Time series sampling of labeled tissues after 14CO 2 uptake showed that the disruption of translocation patterns was persistent for at least 1 week after exposures ceased. Subsequent longer-term exposures at lower concentrations of both O 3 (0.0, 0.10, 0.15, and 0.20 microliters per liter) and SO 2 (0.0, 0.20, and 0.40 microliters per liter) demonstrated that O 3 more effectively altered allocation than SO 2, that primary leaves were generally more sensitive than trifoliates, and that responses of trifoliate leaves varied with plant growth stage. Altered rates of allocation of photosynthate by leaves were generally associated with alterations of similar magnitude and opposite direction in developing pods. Collectively, these experiments suggest that allocation patterns can provide sensitive indices of incipient growth responses of pollution-stressed vegetation. 相似文献
14.
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
15.
The effect of sink strength on photosynthetic rates under conditions of long-term exposure to high CO 2 has been investigated in soybean. Soybean plants (Merr. cv. Fiskeby V) were grown in growth chambers containing 350 microliters CO 2 per liter air until pod set. At that time, plants were trimmed to three trifoliolate leaves and either 21 pods (high sink treatment) or 6 pods (low sink treatment). Trimmed plants were either left in 350 microliters CO 2 per liter of air or placed in 1000 microliters CO 2 per liter of air (high CO 2 treatment) until pod maturity. Whole plant net photosynthetic rates of all plants were measured twice weekly, both at 350 microliters CO 2 per liter of air and 1000 microliters CO 2 per liter of air. Plants were also harvested at this time for dry weight measurements. Photosynthetic rates of high sink plants at both measurement CO 2 concentrations were consistently higher than those of low sink plants, and those of plants given the 350 microliter CO 2 per liter of air treatment were higher at both measurement CO 2 concentrations than those of plants given the 1000 microliters CO 2 per liter of air treatment. When plants were measured under treatment CO 2 levels, however, rates were higher in 1,000 microliter plants than 350 microliter CO 2 plants. Dry weights of all plant parts were higher in the 1,000 microliters CO 2 per liter air treatment than in the 350 microliters CO 2 per liter air treatment, and were higher in the low sink than in the high sink treatments. 相似文献
16.
The inhibition of photosynthesis at low leaf water potentials was studied in soil-grown sunflower to determine the degree to which photosynthesis under high light was affected by stomatal and nonstomatal factors. Below leaf water potentials of −11 to −12 bars, rates of photosynthesis at high light intensities were insensitive to external concentrations of CO 2 between 200 and 400 microliters per liter. Photosynthesis also was largely insensitive to leaf temperature between 10 and 30 C. Changes in CO 2 concentration and temperature had negligible effect on leaf diffusive resistance. The lack of CO 2 and temperature response for both photosynthesis and leaf diffuse resistance indicates that rates of photosynthesis were not limited by either CO 2 diffusion or a photosynthetic enzyme. It was concluded that photosynthesis under high light was probably limited by reduced photochemical activity of the leaves at water potentials below −11 to −12 bars. 相似文献
17.
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
18.
Wheat was cultivated in a small phytotronic chamber. 18O 2 was used to measure the O 2 uptake by the plant, which was recorded simultaneously with the O 2 evolution, net CO 2 uptake, and transpiration. At normal atmospheric CO 2 concentration, photorespiration, measured as O 2 uptake, was as important as the net photosynthesis. The level of true O 2 evolution was independent of CO 2 concentration and stayed nearly equal to the sum of net CO 2 photosynthesis and O 2 uptake. We conclude that at a given light intensity, O 2 and CO 2 compete for the reducing power produced at constant rate by the light reactions of photosynthesis. 相似文献
19.
A leaf chamber has been designed which allows the measurement of both CO 2 and water vapor exchange in Spinacia oleracea leaf discs. The center of the disc lies within a cylindrical gas chamber and its margins are enclosed within a cavity through which water or various metabolites can be pumped. In saturating light and normal atmospheres, the leaf discs have a relatively low resistance to H 2O vapor transfer ( rw = 1.87 seconds per centimeter) and can support high rates of photosynthesis for several hours. The abaxial surface of a disc had a higher resistance to water vapor transfer ( rw = 3.22 seconds per centimeter) than the adaxial ( rw = 2.45 seconds per centimeter) despite having a higher stomatal frequency (abaxial, 105/square millimeter; adaxial, 58/square millimeter). In 2% O 2, the discs required an internal concentration of CO 2 of 115 microliters per liter to support one-half of the maximal velocity of apparent photosynthesis (average value, 66 milligrams CO 2 per square decimeter per hour). In 20% O 2, the comparable values are 156 microliters per liter and 56 milligrams CO 2 per square decimeter per hour. In air, apparent photosynthesis saturated at intensities (750 microeinsteins per square meter per second) well below that of daylight but, when the internal CO 2 was raised to 700 to 900 microliters per liter, photosynthesis was not saturated even at daylight intensities (2025 microeinsteins per square meter per second). The distribution of Prussian blue crystals, formed after ferrocyanide feeding, showed that water entered the disc via the vasculature. When 25-minute pulses of orthophosphate were provided in the feeding solution, there were concentration-dependent increases in both rw and rm leading to inhibition of photosynthesis. The orthophosphate-dependent inhibitions were reversible. 相似文献
20.
The relationship between net photosynthesis and CO 2 concentration was investigated for four species of lichen using an infrared gas analyzer operating in a closed loop system. All species showed a linear relationship at low CO 2 levels (100 microliters per liter) with CO 2 saturation levels being in excess of 400 microliters per liter. Detailed studies of Sticta latifrons showed a strong influence of thallus water content which resulted in the net photosynthetic response at high water contents still being nearly linear at 1000 microliters per liter CO 2. Very low CO 2 compensation values (5 microliters per liter) were obtained under some conditions but the value varied between thalli and with thallus water content. The results differ from previous studies which reported low CO 2 saturation levels (200 microliters per liter) and no apparent effect of water content. It is suggested that some of these differences may result from the use of a discrete sampling injection infrared gas analyzer system in the earlier studies and an assessment is made of the influence of nonsaturating CO 2 levels, lack of cuvette ventilation, and data presentation for this technique. 相似文献
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