共查询到20条相似文献,搜索用时 31 毫秒
1.
A leaf disk assay for photorespiration has been developed based on the rate of release of recently fixed 14CO 2 in light in a rapid stream of CO 2-free air at 30° to 35°. In tobacco leaves (Havana Seed) photorespiration with this assay is 3 to 5 times greater than the 14CO 2 output in the dark. In maize, photorespiration is only 2% of that in tobacco. The importance of open leaf stomata, rapid flow rates of CO2-free air, elevated temperatures, and oxygen in the atmosphere in order to obtain release into the air of a larger portion of the 14CO2 evolved within the tissue in the light was established in tobacco. Photorespiration, but not dark respiration, was inhibited by α-hydroxy-2-pyridinemethanesulfonic acid, an inhibitor of glycolate oxidase, and by 3-(4-chlorophenyl)-1,1-dimethylurea (CMU), an inhibitor of photosynthetic electron transport, under conditions which did not affect the stomata. These experiments show that the substrates of photorespiration and dark respiration differ and also provide additional support for the role of glycolate as a major substrate of photorespiration. It was also shown that at 35° the quantity of 14CO2 released in the assay may represent only 33% of the gross 14CO2 evolved in the light, the remainder being recycled within the tissue. It was concluded that maize does not evolve appreciable quantities of CO2 in the light and that this largely accounts for the greater efficiency of net photosynthesis exhibited by maize. Hence low rates of photorespiration may be expected to be correlated with a high rate of CO2 uptake at the normal concentrations of CO2 found in air and at higher light intensities. 相似文献
2.
Using an open and a closed system of gas analysis, it was found that CO 2 evolution in light and in darkness from plant leaves (sunflower, soybean, watermelon, eggplant, and jackbean) have a different response to temperature. While the rate of CO 2 evolution in light increased with increasing temperature from 17 to 35° and then declined, the rate of CO 2 evolution in darkness increased continuously up to 40°. The rate of CO 2 evolution in light was affected by light intensity. At 1800 ft-c and below 35° the rate of CO 2 evolution in light was greater than in darkness, but above 35° it became lower than in darkness. The Q 10 for CO 2 evolution in light was consistently lower than that in darkness. 相似文献
3.
The total metabolic cost of soybean ( Glycine max L. Mer Clark) nodule nitrogen fixation was empirically separated into respiration associated with electron flow through nitrogenase and respiration associated with maintenance of nodule function. Rates of CO2 evolution and H2 evolution from intact, nodulated root systems under Ar:O2 atmospheres decreased in parallel when plants were maintained in an extended dark period. While H2 evolution approached zero after 36 hours of darkness at 22°C, CO2 evolution rate remained at 38° of the rate measured in light. Of the remaining CO2 evolution, 62% was estimated to originate from the nodules and represents a measure of nodule maintenance respiration. The nodule maintenance requirement was temperature dependent and was estimated at 79 and 137 micromoles CO2 (per gram dry weight nodule) per hour at 22°C and 30°C, respectively. The cost of N2 fixation in terms of CO2 evolved per electron pair utilized by nitrogenase was estimated from the slope of H2 evolution rate versus CO2 evolution rate. The cost was 2 moles CO2 evolved per mole H2 evolved and was independent of temperature. In this symbiosis, nodule maintenance consumed 22% of total respiratory energy while the functioning of nitrogenase consumed a further 52%. The remaining respiratory energy was calculated to be associated with ammonia assimilation, transport of reduced N, and H2 evolution. 相似文献
4.
Summary Evolution of CO 2 into CO 2-free air was measured in the light and in the dark over a range of temperatures from 15 to 50°. Photosynthetic rates were measured in air and O 2-free air over the same range of temperatures. Respiration in the light had a different sensitivity to temperature compared with respiration in the dark. At the lower temperatures the rate of respiration in the light was higher than respiration in the dark, whereas at temperatures above 40° the reverse was observed. For any one species the maximum rates of photosynthesis and photorespiration occur at about the same temperature. The maximum rate for dark respiration generally is found at a temperature about 10° higher. Zea mays and Atriplex nummularia showed no enhancement of photosynthesis in O 2-free air nor any evolution of CO 2 in CO 2-free air at any of the temperatures. 相似文献
5.
The total CO 2 produced by aseptic Drosophila cultures during the entire duration of life has been determined at 15°, 26°, and 30°C. in the dark and at 22–26°C. in the light. The total amount of CO 2 produced is not constant but is greater at 15° than at 26° or 30°, and is much greater in the light than in the dark. The total duration of life, therefore, is not determined by the time required to produce a limiting amount of CO 2. 相似文献
6.
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
7.
Temperature effects on nocturnal carbon gain and nocturnal acid accumulation were studied in three species of plants exhibiting Crassulacean acid metabolism: Mamillaria woodsii, Opuntia vulgaris, and Kalanchoë daigremontiana. Under conditions of high soil moisture, nocturnal CO 2 gain and acid accumulation had temperature optima at 15 to 20°C. Between 5 and 15°C, uptake of atmospheric CO 2 largely accounted for acid accumulation. At higher tissue temperatures, acid accumulation exceeded net carbon gain indicating that acid synthesis was partly due to recycling of respiratory CO 2. When plants were kept in CO 2-free air, acid accumulation based on respiratory CO 2 was highest at 25 to 35°C. Net acid synthesis occurred up to 45°C, although the nocturnal carbon balance became largely negative above 25 to 35°C. Under conditions of water stress, net CO 2 exchange and nocturnal acid accumulation were reduced. Acid accumulation was proportionally more decreased at low than at high temperatures. Acid accumulation was either similar over the whole temperature range (5-45°C) or showed an optimum at high temperatures, although net carbon balance became very negative with increasing tissue temperatures. Conservation of carbon by recycling respiratory CO 2 was temperature dependent. At 30°C, about 80% of the dark respiratory CO 2 was conserved by dark CO 2 fixation, in both well irrigated and water stressed plants. 相似文献
8.
Summary A tracer technique was used to measure photorespiration in Amaranthus lividus, soybean and corn. Under a light intensity of 40 Wm -2 (400–700 nm) efflux of tracer carbon dioxide from Amaranthus into air was comparable to that from soybean over a 30-min period and 10 times that from corn. Initial rates of efflux of tracer into air from Amaranthus were higher than from soybean and 9 times that from corn. Efflux of CO 2 from Amaranthus over 30 min in 120 Wm -2 was only 5 times that of corn and the initial rate was only one third that of soybean. Though total efflux from soybean was similar at the two light intensities, the initial rate was slightly higher under 120 Wm -2. For Amaranthus and soybean, pure oxygen doubled total efflux of CO 2 and substantially increased the initial rate compared with CO 2-free air whereas there was no effect on corn. A comparison of the light and dark curves suggests that light and dark respiration had different substrates. The results are interpreted in terms of the recycling of photorespiratory CO 2. 相似文献
9.
When leaves of a mangrove, Rhizophora mangle, were exposed to an excess of light at chilling temperatures, synthesis of zeaxanthin through violaxanthin de-epoxidation as well as nonphotochemical fluorescence quenching were markedly reduced. The results suggest a protective role of energy dissipation against the adverse effects of high light and chilling temperatures: leaves of R. mangle that had been preilluminated in 2% O 2, 0% CO 2 at low photon flux density and showed a high level of zeaxanthin, and leaves that had been kept in the dark and contained no zeaxanthin, were both exposed to high light and chilling temperatures (5°C leaf temperature) in air and then held under control conditions in low light in air at 25°C. Measurements of chlorophyll a fluorescence at room temperature showed that the photochemical efficiency of PSII and the yield of maximum fluorescence of the preilluminated leaf recovered completely within 1 to 3 hours under the control conditions. In contrast, the fluorescence responses of the predarkened leaf in high light at 5°C did not recover at all. During a dark/light transient in 2% O 2, 0% CO 2 in low light at 5°C, nonphotochemical fluorescence quenching increased linearly with an increase in the zeaxanthin content in leaves of R. mangle. In soybean ( Glycine max) leaves, which contained a background level of zeaxanthin in the dark, a similar treatment with excess light induced a level of nonphotochemical fluorescence quenching that was not paralleled by an increase in the zeaxanthin content. 相似文献
10.
1. Green plants have been found to emit light of approximately the same color as their fluorescent light for several minutes following illumination. This light is about 10 –3 the intensity of the fluorescent light, about one-tenth second after illumination below saturation or 10 –6 of the intensity of the absorbed light. 2. The decay curve follows bimolecular kinetics at 6.5°C. and reaction order 1.6 at 28°C. 3. This light saturates as does photosynthesis at higher light intensities and in about the same intensity range as does photosynthesis. 4. An action spectrum for light emitted as a function of the wave length of exciting light has been determined. It parallels closely the photosynthetic action spectrum. 5. The intensity of light emission was studied as a function of temperature and found to be optimal at about 37°C. with an activation energy of approximately 19,500 calories. Two-temperature studies indicated that the energy may be trapped in the cold, but that temperatures characteristic for enzymatic reactions are necessary for light production. 6. Illumination after varying dark periods showed initial peaks of varying height depending on the preceding dark period. 7. 5 per cent CO 2 reversibly depresses the amount of light emitted by about 30 per cent. About 3 minutes are required for this effect to reach completion at room temperatures. 8. Various inhibitors of photosynthesis were tested for their effect on luminescence and were all inhibitory at appropriate concentrations. 9. Irradiation with ultraviolet light (2537A) inhibits light production at about the same rate as it inhibits photosynthesis. 10. This evidence suggests that early and perhaps later chemical reactions in photosynthesis may be partially reversible. 相似文献
11.
The most heat-sensitive functions of chloroplasts in Spinacia oleracea L. including the stromal carboxylation reaction, the light-induced electrical field gradient across the thylakoid membrane, as well as the overall photosynthetic CO 2 fixation were less affected by heat if chloroplasts were heated in the light: 50% inactivation occurred around 35°C in the dark and around 40°C in the light. Relative low light intensities were sufficient to obtain optimal protection against heat. In contrast, the light-induced ΔpH across the thylakoid membrane, the photophosphorylation, and the photochemical activity of photosystem II which were less sensitive to heat in the dark (50% inactivation above 40°C) were not protected by light. Photosystem II even was destabilized somewhat by light. The effect of light on the heat sensitivity of the water-splitting reaction was dependent on the pH in the medium. Protection by light only occurred at alkaline pH, in which case heat sensitivity was high (50% inactivation at 33°C in the dark and at 38°C in the light). Protection was prevented by uncouplers. At pH 6.8 when the heat sensitivity was low in any case (50% inactivation at 41°C in the dark), light had no further protecting effect. Protection by light has been discussed in terms of light-induced transport of protons from the stroma to the thylakoid space and related ion fluxes. 相似文献
12.
The metabolism of [ 13C]malate was studied in the Crassulacean plant Kalanchoë tubiflora following exposure to 13CO 2 for 2 hour intervals during a 16 hour dark cycle. Nuclear magnetic resonance spectroscopy of [ 13C]malate extracted from labeled tissue revealed that the transient flux of malate to the mitochondria, estimated by the randomization of [4- 13C]malate to [1- 13C]malate by fumarase, varied substantially during the dark period. At both 15 and 25°C, the extent of malate label randomization in the mitochondria was greatest during the early and late parts of the dark period and was least during the middle of the night, when the rate of 13CO 2 uptake was highest. Randomization of labeled malate continued for many hours after malate synthesis had initially occurred. Internally respired 12CO 2 also served as a source of carbon for malate formation. At 15°C, 15% of the total malate was formed from respired 12CO 2, while at 25°C, 49% of the accumulated malate was derived from respired 12CO 2. Some of the malate synthesized from external 13CO 2 was also respired during the night. The proportion of the total [ 13C]malate respired during the dark period was similar at 15 and 25°C, and respiration of newly formed [ 13C]malate increased as the night period progressed. These data are discussed with regard to the relative fluxes of malate to the mitochondria and the vacuole during dark CO 2 fixation. 相似文献
13.
Light integrators with a linear response are not suitable for measuring the light climates of plants because plants are not linear integrators. It should be possible to make a quantitative allowance for this nonlinearity by using the CO 2 uptake curve of the plant. To test this, we have subjected white clover plants to different levels of constant light, comparing the rate of increase of total dry matter with the net rate of uptake of CO 2 per day. Temperature, humidity, daylength and nutrient supply were kept constant. The growth rate calculated from CO 2 uptake agreed well with the observed rate over the light levels tested (3.7-88 w·m −2, 0.4-0.7 micron: 1 w·m −2 = 10 3 erg · sec −1 cm −2). All plants put on weight over the few days of the experiment, even those placed at light levels below their compensation point. The plants adapted their respiration rates to be a constant proportion of their growth rates. Most of the adaptation occurred within 24 hours of the light change. The adaptation of respiration has implications for models of light/growth relations in plant communities, almost all of which assume that respiration is proportional to leaf area and independent of growth rate or light level. The only model which does not is that of de Wit, and this gave good agreement with our results. 相似文献
14.
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
15.
Dewatered sewage sludge was composted in a laboratory-scale autothermal reactor in which a constant temperature of 60°C was kept as long as possible by regulating the air feed rate. The change in CO 2 evolution rate was measured continuously from the start up through the cessation of compositing. The succession of mesophilic bacteria, thermophilic bacteria, and thermophilic actinomycetes was also observed during the composting. Specific CO 2 evolution rates of thermophilic bacteria and actinomycetes in the constant-temperature region of 60°C were assessed quantitatively. It was found that the CO 2 evolution rate was attributed to thermophilic bacteria at the initial stage of 60°C and to thermophilic actinomycetes at the later stage of 60°C. 相似文献
16.
Single clover plants were grown in the vegetative state, at 20 ± 1°, 85 ± 5% relative humidity, 320 ± 10 ppm CO 2, 12-hour day, with Hoagland nutrient in Perlite, and 100 w · m −2 of photosynthetically active radiation (0.4-0.7 μ) from mercury-fluorescent lamps. Each plant was confined within a circle 18 cm in diameter by means of a wire framework. The CO 2 exchange rate of the whole plant was measured every second day for 3 months. There was no optimum leaf area index for the net photosynthesis rate. The respiration rate was determined mainly by the gross photosynthesis rate and only partly by the amount of non-photosynthetic or heavily shaded tissue. At the maximum leaf area index, when leaves were dying as fast as they were being produced, both photosynthesis and respiration remained at or near their maximum rates. At the end of 3 months, the whole plant was harvested and the dry weight and carbon content determined. The measured dry weight was close to that calculated from the total CO 2 uptake and a constant ratio of carbon content to dry weight of 39%. Optimum leaf area indices observed in field experiments are attributed to the failure to include the material which dies between harvests, and to decreases in the gross photosynthesis rate caused by climate changes or lack of nutrient, for example. The difference between production rate and growth rate or yield is emphasized. 相似文献
17.
Differences among species in respiration rates in CO 2-free air, in light and dark, were studied using the standard leaf chamber technique and the infrared carbon dioxide analyzer. Photosynthesis, transpiration and respiration were measured. In all species studied, rates of respiration were considerably higher in dark than in light. This effect was assumed to be due to reassimilation of the respiratory CO 2. A resistance analogy model was derived to account for the apparent differences in internal recycling of CO 2 among species; the differences were correlated with differences in maximum photosynthetic rates in normal air and optimal conditions (P 310) and with internal resistances to CO 2 diffusion (r k). Species with high P 310 and low r k appear to reassimilate all the endogenous CO 2, whereas other species with lower P 310 and higher r k appear to reassimilate only a part of their respiratory CO 2. Experiments with the photosynthetic inhibitor, 3-(3,4-dichlorophcnyl)-l,l-dimethyl urea (DCMU), indicated that species with zero respiration in CO 2-free air and light release respiratory CO 2 when photosynthesis is inhibited. It is concluded that the CO 2 released in the presence of DCMU represents respiratory CO 2 which recycles to photosynthesis under normal conditions. 相似文献
18.
Spinach chloroplasts were used to study the relationship between photosynthetic CO 2 fixation and temperature from 30 to −15°C. In saturating light and high concentrations of CO 2, the temperature coefficients (Q 10) above 20°C were less than 2 in the intact chloroplast. Below 15°C, the Q 10 values were greater than 2 and gradually increased with decreasing (down to 0°C) temperature to approximately 4.4. Photosynthesis responded similarly to temperature in a reconstituted chloroplast preparation fortified with ribose 5-phosphate. In the intact chloroplast, temperature did not alter the Q 10 value in low light and high CO 2. Elevating the temperature to 25°C after photosynthesizing at −15°C (46 minutes) or 0°C (17 minutes) restored the temperature-depressed photosynthetic rate without a lag in the intact chloroplast to the rate of a chloroplast continually at 25°C. At 0°C, the intact chloroplast photosynthetic rate responded slightly to the inorganic phosphate concentration (0.1-1.0 millimolar) and to pH (7.0-8.6). Relative to 25°C, the levels of ribulose 1,5-bisphosphate and glycerate 3-phosphate were increased 1300 and 200%, respectively, whereas glycolate decreased 57% during intact chloroplast photosynthesis at 0°C. Chilling temperature impeded the transport of photosynthetic intermediates from the stromal compartment to the external medium. Ethylene glycol was shown to be an appropriate additive to prevent freezing of the reaction mixture down to −15°C for photosynthetic CO 2 assimilation. 相似文献
19.
In the cyanobacterium Agmenellum quadruplicatum steady-state redox conditions were monitored in vivo for cytochrome ( +c553) and P700 versus intensities of an actinic light 1 or light 2 (mainly absorbed by photosystems, and 2, respectively). Parallel measurements of O 2 evolution were used to calibrate intensities for rates of electron transfer. Results show that the quality of actinic light (as light 1 or light 2) depends on intensity as well as wavelength. The contribution of electron flow from respiration is confirmed by observations of relative rate of photoreaction 1 estimated from Ip (intensity × fraction of P700 reduced). With 3,- (3,4-dichlorophenyl-1, 1-dimethylurea) (DCMU) the rate of photoreaction 1 depends upon, and is sensitive to small changes in, the rate of dark respiration. Very slow transient dark reductions of Cyt ( f+c553) and P700 following any low intensity actinic light 1 are attributed to respiratory electron flow. Cyclic electron flow around photoreaction 1 cannot be large compared to dark respiration and cannot vary significantly with light intensity.This paper is contributed in honor of my longtime friend, L.N.M. Duysens, who has carried still further the eminence of the Dutch tradition in biophysics. 相似文献
20.
The photosynthetic and respiratory rates of 5- to 7-year-old aspen stems ( Populus tremuloides Michx.) were monitored in the field for 1 year to determine the seasonal patterns. The stem was not capable of net photosynthesis, but the respiratory CO 2 loss from the stem was reduced by 0 to 100% depending on the time of year and the level of illumination as a result of bark photosynthesis. The monthly dark respiratory rate ranged from 0.24 mg CO 2/dm 2· hr in January to a maximum 7.4 mg CO 2/dm 2· hr in June. Individual measurements ranged from 0.02 mg CO 2/dm 2· hr in February to 12.3 mg CO 2/dm 2· hr in June. Gross photosynthesis followed a pattern similar to the dark respiratory rate. The mean monthly rate was highest in June (1.65 mg CO 2/dm 2· hr) and lowest in December (0.02 mg CO 2/dm 2· hr). Individual measurements ranged from 0.0 mg CO 2/dm 2· hr in winter to 5.5 mg CO 2/dm 2· hr in July. 相似文献
|