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1.
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
2.
Open flow-through systems coupled to infrared gas analyzers have been frequently employed in the study of CO 2 exchange transients such as the postillumination burst observed in leaves of C 3 plants. A major limitation associated with use of such systems is their non-steady state response to rapid changes in leaf CO 2 exchange rate. A previous publication outlined a numerical approach to model the analyzer response as a function of CO 2 exchange rate and thus permit estimation of the postillumination burst (Peterson 1983 Plant Physiol 73: 978-982). The model is critically analyzed within the framework of the physics of solute dispersion as previously described for linear flow systems. Thus, the numerical simulation is validated on the basis of physical principle. Additional improvements to the previous model are described which enhance the accuracy and efficiency of use of this technique for estimation of photorespiration. 相似文献
3.
The postillumination transient of CO 2 exchange and its relation to photorespiration has been examined in leaf discs from tobacco ( Nicotiana tabacum) and maize ( Zea mays). Studies of the transients observed by infrared gas analysis at 1, 21, and 43% O 2 in an open system were extended using the nonsteady state model described previously (Peterson and Ferrandino 1984 Plant Physiol 76: 976-978). Cumulative CO 2 exchange equivalents ( i.e. nanomoles CO 2) versus time were derived from the analyzer responses of individual transients. In tobacco (C 3), subtraction of the time course of cumulative CO 2 exchange under photorespiratory conditions (21 or 43% O 2) from that obtained under nonphotorespiratory conditions (1% O 2) revealed the presence of an O 2-dependent and CO 2-reversible component within the first 60 seconds following darkening. This component was absent in maize (C 4) and at low external O 2:CO 2 ratios ( i.e. <100) in tobacco. The size of the component in tobacco increased with net photosynthesis as irradiance was increased and was positively associated with inhibition of net photosynthesis by O 2. This relatively simple and rapid method of analysis of the transient is introduced to eliminate some uncertainties associated with estimation of photorespiration based on the maximal rate of postillumination CO 2 evolution. This method also provides a useful and complementary tool for detecting variation in photorespiration. 相似文献
4.
Gas exchange responses to rapid changes in light were studied in a C 3 tree, Claoxylon sandwicense Muell-Arg and a C 4 tree, Euphorbia forbesii Sherff that are native to the understory of a mesic Hawaiian forest. When light was increased to 500 micromoles per meter per second following a 2 hour preexposure at 22 micromoles per meter per second, net CO 2 uptake rates and stomatal conductance gradually increased for over 1 hour in C. sandwicense but reached maximum values within 30 minutes in E. forbesii. Calculation of the intercellular CO 2 pressures indicated that the primary limitation to CO 2 uptake during this induction was nonstomatal in both species. The photosynthetic response to simulated sunflecks (lightflecks) was strongly dependent on the induction state of the leaf. Total CO 2 uptake during a lightfleck was greater and the response was faster after exposure of the leaf to high light than when the leaf had been exposed only to low light for the previous 2 hours. During a series of lightflecks, induction resulted in increased CO 2 uptake in successive lightflecks. Significant postillumination CO 2 fixation was evident and contributed substantially to the total carbon gain, especially for lightflecks of 5 to 20 seconds' duration. 相似文献
5.
In the shade plant Alocasia macrorrhiza grown in low light, photosynthetic CO 2 assimilation during a 5 second lightfleck plus postillumination CO 2 assimilation can allow up to 60% more photosynthesis than that which occurs during 5 seconds of steady state light of the same intensity (RL Chazdon, RW Pearcy 1986 Oecologia. 69: 524-531). Metabolites of photosynthesis were measured to determine if the pool of ribulose 1,5-bisphosphate (RuBP) could account for all of the postillumination CO 2 assimilation following a lightfleck in Alocasia. It was found that the pool of triose-P was much larger than that of RuBP and could account for five times more postillumination CO 2 assimilation than could RuBP. The same trend was seen in the sun plant Phaseolus vulgaris when it was grown in the shade. In contrast, sun-grown Alocasia and Phasiolus did not have a large pool of triose-P relative to RuBP following a lightfleck. In sun plants, carbon may rapidly be converted to RuBP in the light whereas in shade plants there may be a restriction in the path between the triose-P and RuBP pools. It is hypothesized that in shade plants the buildup of triose-P rather than RuBP during the lightfleck prevents inhibition of electron transport which may otherwise occur because of competition for ATP between the two kinases of the photosynthetic carbon reduction cycle. Utilization of the triose-P for postillumination CO 2 fixation would require the capacity for significant postillumination ATP synthesis. The extensive grana stacking and large intrathylakoid space which accompanies the high level of chlorophyll in low-light-grown Alocasia could be an important contributing factor to postillumination ATP formation. 相似文献
6.
Immediately following exposure to light, a postillumination burst of CO 2 has been detected in Crassulacean acid metabolism plants. A detailed study with pineapple ( Ananas comosus) leaves indicates that the postillumination burst changes its amplitude and kinetics during the course of a day. In air, the postillumination burst in pineapple leaves generally is exhibited as two peaks. The postillumination burst is sensitive to atmospheric CO 2 and O 2 concentrations as well as to the light intensity under which plants are grown. We propose that the CO 2 released in the first postillumination burst peak is indicative of photorespiration since it is sensitive to either O 2 or CO 2 concentration while the second CO 2 evolution peak is likely due to decarboxylation of organic acids involved in Crassulacean acid metabolism. 相似文献
7.
A transient CO 2 burst is exhibited by irradiated leaves of the C 3 plant geranium ( Pelargonium X hortorum, Bailey) after the irradiance is quickly lowered. The light CO 2 burst appears to be related to photorespiration because of its irradiance dependency and its sensitivity to other environmental components such as CO 2 and O 2 concentration. The term post-lower-irradiance CO 2 burst or PLIB is used to describe the phenomenon. The PLIB appears to be a quantitative measurement of photorespiration with intact geranium leaves. The PLIB has been observed with intact leaves of other C 3 plants but not with C 4 leaves. Therefore, it is proposed that, after maximizing intact leaf photosynthetic rates and leaf chamber gas measuring conditions, photorespiration can be measured with intact C 3 leaves such as geranium as a transient post-lower-irradiance CO 2 burst. 相似文献
8.
A computer controlled semiclosed net CO 2 exchange measurement system, employing an infrared gas analyzer and mass flow controllers to inject pure CO 2 at preset rates, has been developed for measuring whole plant net CO 2 exchange and net C gain in a controlled environment ( i.e. CO 2, light, and temperature). Data for tomato ( Lycoperscicon esculentum cv Campbell 19 VF) and rose ( Rosa hybrida cv Samantha) plants grown for 4 and 17 day periods, respectively, clearly show that net C gain measured and computed using nondestructive CO 2 analysis equaled the increase in C content determined by chemical analysis following destruction of the test plants. The analysis of C gain based on CO 2 exchange allows estimation of biomass production and growth of a single population of plants under varying light and CO 2 conditions without physically handling the test plants. 相似文献
9.
In Anabaena variabilis, a postillumination CO 2 burst originating from a pool of HCO 3? is described here. This burst is insensitive to the electron-transport inhibitor, 3-(3,4-dichlorophenyl)-1,1-dimethylurea, but is abolished by carbonyl cyanide p-trifluoromethoxyphenylhydrazone and N, N′-dicyclohexylcarbodiimide (inhibitors of photophosphorylation). The action spectrum for the burst shows that only Photosystem I is involved. 相似文献
10.
A role of the guard cell chloroplasts in the CO 2 response of stomata was investigated through a comparison of the leaf gas exchange characteristics of two closely related orchids: Paphiopedilum harrisianum, which lacks guard cell chloroplasts and Phragmipedium longifolium, which has chlorophyllous guard cells. Leaves of both species had an apparent quantum yield for assimilation of about 0.05, with photosynthesis saturating at 0.300 to 0.400 millimoles per square meter per second. CO 2 curves were obtained by measuring steady-state assimilation and stomatal conductance under 0.180 or 0.053 millimoles per square meter per second white light, or darkness, at 0 to 400 microliters per liter ambient CO 2. The response of assimilation to changes in CO 2 was similar in the two species, but the response of conductance was consistently weaker in Paphiopedilum than in Phragmipedium. The data suggest involvement of guard cell chloroplasts in the stomatal response to CO 2 and in the coupling of assimilation and conductance in the intact leaf. 相似文献
11.
To assess the variability of net photosynthetic CO 2 exchange per unit leaf area and to construct budgets for stands of field-grown tobacco ( Nicotiana tabacum, Connecticut Broadleaf), a number of short-time measurements were made on all available leaf positions on two varieties using a hand-held transparent chamber for conducting gas exchange measurements on leaves. Measurements of net CO 2 exchange were carried out on 18 separate days during a 35-day period, beginning 22 days after the seedlings were transplanted to the field. Gas exchange assays on leaves were conducted under ambient conditions of temperature and light intensity at all times of day. Solar radiation was monitored throughout the period, and losses of respiratory CO 2 from stems, roots, and leaves (in the dark) were estimated. A simple model was proposed to relate daily total CO 2 input to irradiance and total leaf area. The total leaf area was assumed to be a function of day number. Dark respiratory losses accounted for 41% to 47% of total CO 2 assimilation. Analysis of variance indicated that the two varieties were not significantly different in whole plant rate of CO 2 fixation per unit of leaf area. CO 2 input was closely associated with leaf area within each variety. Throughout the experiment, the difference between the two varieties in total leaf area per plant was the largest single factor in determining net CO 2 inputs. The cumulative dry weight increase for each variety was similar to the prediction of net dry matter input obtained by gas exchange measurements, thus confirming the close relationship between total plant net CO 2 assimilation and dry weight yield. 相似文献
12.
Nonautotrophic CO 2 metabolism in Opuntia echinocarpa roots was studied with techniques of manometry and radiometry. The roots were grown in a one-quarter strength nutrient solution for several days; the distal 2 cm was used for physiological studies. The roots assimilated significant quantities of 14CO 2 and appeared to show a crassulacean-type acid metabolism with respect to quality and quantity. Most of the 14C activity was associated with the distal portion of the elongating root indicating correlation with metabolic activity. The 14CO 2 assimilation was comparable to a crassulacean leaf succulent, but 3 times greater than that found for stem tissue of the same Opuntia species. The rates of O2 and CO2 exchange and estimated CO2 fixation were 180, 123, and 57 μl/g per hour. A respiratory quotient of 0.66 was found. The products of 14CO2 fixation were similar in most respects to reported experiments with leaf succulents. Equilibration of the predominant malic acid with isocitric, succinic, and fumaric acids was not evident. The latter observation was interpreted as metabolic isolation of the fixation products rather than poor citric acid cycle activity. A rapid turnover of the fixed 14CO2 was measured by following decarboxlyation kinetics and by product analysis after a postincubation period. The first order rate constant for the steady state release was 4.4 × 10−3 min−1 with a half-time of 157.5 minutes. Amino acids decayed at a more rapid rate than organic acids. 相似文献
13.
The partial pressure of CO 2 inside leaves of several species was measured directly. Small gas exchange chambers were clamped above and below the same section of an amphistomatous leaf. A flowing gas stream through one chamber allowed normal CO 2 and water vapor exchange. The other chamber was in a closed circuit consisting of the chamber, an infrared gas analyzer, and a peristaltic pump. The CO 2 in the closed system rapidly reached a steady pressure which it is believed was identical to the CO 2 pressure inside the leaf, because there was no flux of CO 2 across the epidermis. This measured partial pressure was in close agreement with that estimated from a consideration of the fluxes of CO 2 and vapor at the other surface. 相似文献
14.
The effect of long-term (weeks to months) CO 2 enhancement on (a) the gas-exchange characteristics, (b) the content and activation state of ribulose-1,5-bisphosphate carboxylase (rubisco), and (c) leaf nitrogen, chlorophyll, and dry weight per area were studied in five C 3 species ( Chenopodium album, Phaseolus vulgaris, Solanum tuberosum, Solanum melongena, and Brassica oleracea) grown at CO 2 partial pressures of 300 or 900 to 1000 microbars. Long-term exposure to elevated CO 2 affected the CO 2 response of photosynthesis in one of three ways: (a) the initial slope of the CO 2 response was unaffected, but the photosynthetic rate at high CO 2 increased ( S. tuberosum); (b) the initial slope decreased but the CO 2-saturated rate of photosynthesis was little affected ( C. album, P. vulgaris); (c) both the initial slope and the CO 2-saturated rate of photosynthesis decreased ( B. oleracea, S. melongena). In all five species, growth at high CO 2 increased the extent to which photosynthesis was stimulated following a decrease in the partial pressure of O 2 or an increase in measurement CO 2 above 600 microbars. This stimulation indicates that a limitation on photosynthesis by the capacity to regenerate orthophosphate was reduced or absent after acclimation to high CO 2. Leaf nitrogen per area either increased ( S. tuberosum, S. melongena) or was little changed by CO 2 enhancement. The content of rubisco was lower in only two of the five species, yet its activation state was 19% to 48% lower in all five species following long-term exposure to high CO 2. These results indicate that during growth in CO 2-enriched air, leaf rubisco content remains in excess of that required to support the observed photosynthetic rates. 相似文献
15.
As leaf irradiance is decreased in increments, a single transient CO 2 burst is exhibited by C 3 plant leaves. This post-lower illumination CO 2 burst (PLIB) is sensitive to changes in irradiance, to changes in the concentrations of O 2 and CO 2, and to temperature. Increasing O 2 concentrations above ambient produces a progressively larger PLIB while increasing CO 2 concentrations above ambient produces a progressively smaller PLIB. The PLIB, which exhibits many responses to environment common with other methods for measuring photorespiration and photosynthesis, is proposed as a measure of photorespiration in illuminated leaves of C 3 plants. Although the PLIB cannot be used as a quantitative measurement of photorespiration, we propose that the PLIB is a rapid, easy, relatively inexpensive, nondestructive method for evaluating photorespiration in intact illuminated C 3 leaves in air. 相似文献
16.
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
17.
The exchange properties of the activator CO 2 of spinach ribulose-1,5-bisphosphate carboxylase/oxygenase were characterized both in vitro with the purified enzyme, and in situ within isolated chloroplasts. Carboxyarabinitol-1,5-bisphosphate, a proposed reaction intermediate analog for the carboxylase activity of the enzyme, was used to trap the activator CO 2 on the enzyme both in vitro and in situ. Modulation of ribulose-1,5-bisphosphate carboxylase/oxygenase activity in intact chloroplasts during a light/dark cycle was associated with a similar modulation in carboxyarabinitol-1,5-bisphosphate-trapped CO 2. The exchange kinetics of the activator CO 2 were monitored by activation of the enzyme to steady state in the presence of 12CO 2, followed by addition of 14CO 2 and determination of the amount of labeled CO 2 trapped on the enzyme by carboxyarabinitol-1,5-bisphosphate. Rate constants ( Kobs) for exchange with both the purified enzyme (0.45 min −1) and in illuminated chloroplasts (0.18 min −1) were comparable to the observed rate constants for enzyme activation under the two conditions. A similar exchange of the activator CO 2 was not observed in chloroplasts in the dark. Kinetic analysis of the exchange properties of the purified enzyme were consistent with an equilibrium between active and inactive forms of the enzyme during steady state activation. 相似文献
18.
Most current photosynthesis models, and interpretations of many wholeleaf CO 2 gas exchange measurements, are based on the often unstated assumption that the partial pressure of CO 2 is nearly uniform throughout the airspaces of the leaf mesophyll. Here we present measurements of CO 2 gradients across amphistomatous leaves allowed to assimilate CO 2 through only one surface, thus simulating hypostomatous leaves. We studied five species: Eucalyptus pauciflora Sieb. ex Spreng., Brassica chinensis L., Gossypium hirsutum L., Phaseolus vulgaris L., and Spinacia oleracea L. For Eucalyptus, maximum CO 2 pressure differences across the leaf mesophyll were 73 and 160 microbar when the pressures outside the lower leaf surface were 310 and 590 microbar, respectively. Using an approximate theoretical calculation, we infer that if the CO 2 had been supplied equally at both surfaces then the respective mean intercellular CO 2 pressures would have been roughly 12 and 27 microbar less than the pressures in the substomatal cavities in these cases. For ambient CO 2 pressures near 320 microbar, the average and minimum pressure differences across the mesophyll were 45 and 13 microbar. The corresponding mean intercellular CO 2 pressures would then be roughly 8 and 2 microbar less than those in the substomatal cavities. Pressure differences were generally smaller for the four agricultural species than for Eucalyptus, but they were nevertheless larger than previously reported values. 相似文献
19.
Four self-pollinated, doubled-haploid tobacco, ( Nicotiana tabacum L.) lines (SP422, SP432, SP435, and SP451), selected as haploids by survival in a low CO 2 atmosphere, and the parental cv Wisconsin-38 were grown from seed in a growth room kept at high CO 2 levels (600-700 parts per million). The selected plants were much larger (especially SP422, SP432, and SP451) than Wisconsin-38 nine weeks after planting. The specific leaf dry weight and the carbon (but not nitrogen and sulfur) content per unit area were also higher in the selected plants. However, the chlorophyll, carotenoid, and alkaloid contents and the chlorophyll a/b ratio varied little. The net CO 2 assimilation rate per unit area measured in the growth room at high CO 2 was not higher in the selected plants. The CO 2 assimilation rate versus intercellular CO 2 curve and the CO 2 compensation point showed no substantial differences among the different lines, even though these plants were selected for survival under CO 2 compensation point conditions. Adult leaf respiration rates were similar when expressed per unit area but were lower in the selected lines when expressed per unit dry weight. Leaf respiration rates were negatively correlated with specific leaf dry weight and with the carbon content per unit area and were positively correlated with nitrogen and sulfur content of the dry matter. The alternative pathway was not involved in respiration in the dark in these leaves. The better carbon economy of tobacco lines selected for low CO 2 survival was not apparently related to an improvement of photosynthesis rate but could be related, at least partially, to a significantly reduced respiration (mainly cytochrome pathway) rate per unit carbon. 相似文献
20.
The possibility that differences in stomatal conductance between upper and lower surfaces of amphistomatous leaves are adaptations to differences in CO 2 exchange characteristics for the two surfaces was investigated. The ratio of upper to lower stomatal conductance was found to change little in response to light and humidity for well-watered sunflower ( Helianthus annuus L.) plants. Stressing the plants (ψ = −17 bars) and rewatering 1 day before gas exchange measurements reduced upper conductance more severely than lower in both indoor- and outdoor-grown plants, and caused small changes in conductance ratio with light and humidity. A similar pattern was found using outdoor grown sunflower and cocklebur ( Xanthium strumarium L.) plants. Calculated intercellular CO 2 concentrations for upper and lower surfaces were always close to identical for a particular set of environmental conditions for both sunflower and cocklebur, indicating that no differences in CO 2 exchange characteristics exist between the two surfaces. By artificially creating a CO 2 gradient across the leaf, the resistance to CO 2 diffusion through the mesophyll was estimated and found to be so low that despite possible nonhomogeneity of the mesophyll, differences in CO 2 exchange characteristics for the two surfaces are unlikely. It is concluded that differences in conductance between upper and lower stomates are not adaptations to differences in CO 2 exchange characteristics. 相似文献
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