共查询到20条相似文献,搜索用时 46 毫秒
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.
Leaf photosynthesis of the sensitive plant Mimosa pudica displays a transient knockout in response to electrical signals induced by heat stimulation. This study aims at clarifying the underlying mechanisms, in particular, the involvement of respiration. To this end, leaf gas exchange and light reactions of photosynthesis were assessed under atmospheric conditions largely eliminating photorespiration by either elevated atmospheric CO 2 or lowered O 2 concentration (i.e. 2000 μmol mol ?1 or 1%, respectively). In addition, leaf gas exchange was studied in the absence of light. Under darkness, heat stimulation caused a transient increase of respiratory CO 2 release simultaneously with stomatal opening, hence reflecting direct involvement of respiratory stimulation in the drop of the net CO 2 uptake rate. However, persistence of the transient decline in net CO 2 uptake rate under illumination and elevated CO 2 or 1% O 2 makes it unlikely that photorespiration is the metabolic origin of the respiratory CO 2 release. In conclusion, the transient knockout of net CO 2 uptake is at least partially attributed to an increased CO 2 release through mitochondrial respiration as stimulated by electrical signals. Putative CO 2 limitation of Rubisco due to decreased activity of carbonic anhydrase was ruled out as the photosynthesis effect was not prevented by elevated CO 2. 相似文献
3.
The mass transfer rate of 14C-sucrose translocation from sugar beet ( Beta vulgaris, L.) leaves was measured over a range of net photosynthesis rates from 0 to 60 milligrams of CO 2 decimeters −2 hour −1 under varying conditions of light intensity, CO 2 concentration, and O 2 concentration. The resulting rate of translocation of labeled photosynthate into total sink tissue was a linear function (slope = 0.18) of the net photosynthesis rate of the source leaf regardless of light intensity (2000, 3700, or 7200 foot-candles), O 2 concentration (21% or 1% O 2), or CO 2 concentration (900 microliters/liter of CO 2 to compensation concentration). These data support the theory that the mass transfer rate of translocation under conditions of sufficient sink demand is limited by the net photosynthesis rate or more specifically by sucrose synthesis and this limitation is independent of light intensity per se. The rate of translocation was not saturated even at net photosynthesis rates four times greater than the rate occurring at 300 microliters/liter of CO 2, 21% O 2, and saturating light intensity. 相似文献
4.
This study examines the effect of antimycin A and nitrite on 14CO 2 fixation in intact chloroplasts isolated from spinach ( Spinacia oleracea L.) leaves. Antimycin A (2 micromolar) strongly inhibited CO 2 fixation but did not appear to inhibit or uncouple linear electron transport in intact chloroplasts. The addition of small quantities (40-100 micromolar) of nitrite or oxaloacetate, but not NH 4Cl, in the presence of antimycin A restored photosynthesis. Antimycin A inhibition, and the subsequent restoration of photosynthetic activities by nitrite or oxaloacetate, was observed over a wide range of CO 2 concentration, light intensity, and temperature. High O 2 concentration (up to 240 micromolar) did not appear to influence the extent of the inhibition by antimycin A, nor the subsequent restoration of photosynthetic activity by nitrite or oxaloacetate. Studies of O 2 exchanges during photosynthesis in cells and chloroplasts indicated that 2 micromolar antimycin A stimulated O 2 uptake by about 25% while net O 2 evolution was inhibited by 76%. O 2 uptake in chloroplasts in the presence of 2 micromolar antimycin A was 67% of total O 2 evolution. These results suggest that only a small proportion of the O 2 uptake measured was directly linked to ATP generation. The above evidence indicates that cyclic photophosphorylation is the predominant energy-balancing reaction during photosynthesis in intact chloroplasts. On the other hand, pseudocyclic O 2 uptake appears to play only a minimal role. 相似文献
5.
The effect of leaf dehydration on photosynthetic O 2 exchange of potato ( Solanum tuberosum L., cv. Haig) leaf discs was examined using 18O 2 as a tracer and mass spectrometry. In normal air (350 μl·l ?1CO 2) and under an irradiance of 390 μmol photons·m ?2·s 1, a relative water deficit (RWD) of about 30% severely decreased net O 2 evolution and increased O 2 uptake by about 50%, thus indicating an enhancement of photorespiration. Increasing CO 2 concentrations diminished O 2 uptake and stimulated net O 2 evolution both in well-hydrated and in dehydrated (RWD of about 30%) leaves. Much higher CO 2 concentrations (up to 4%) were required to observe a complete effect of CO 2 in dehydrated leaves. The chloroplastic CO 2 concentration at the ribulose-1,5-bisphosphate carboxylase-oxygenase (Rubisco) level (C c) was calculated from O 2-exchange data in both well-hydrated and dehydrated leaves, assuming that the specificity factor of Rubisco was unaffected by desiccation. When plotting net O 2 photosynthesis as a function of C c, a similar relationship was obtained for well-hydrated and waterstressed leaf discs, thus showing that the main effect of water deficit is a decrease of the chloroplastic CO 2 concentration. At saturating CO 2 levels, the non-cyclic electron-transport rate, measured either as gross O 2 photosynthesis or as the chlorophyll fluorescence ratio (F m -F s)/F m, was insensitive to water deficit, provided RWD was below 40%. In this range of RWD, the decrease in gross O 2 photosynthesis observed in normal air was attributed to the inability of oxidative processes to sustain the maximal electron-flow rate at low chloroplastic CO 2 concentration. The maximal efficiency of photosystem II, estimated as the chlorophyll fluorescence ratio (F m -F 0)/F m measured in dark-adapted leaves, was not affected by water deficits up to 60%. 相似文献
6.
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
7.
Abstract. It has been shown that atmospheric O 2 can either depress or stimulate the rate of apparent photosynthesis of white mustard depending on the environmental conditions: CO 2 concentration, light intensity and temperature. Stimulation by O 2 was observed only under high photon fluence rate and at high CO 2 concentrations. The critical CO 2 concentration below which O 2 was inhibiting and above which it was stimulating was dependent on the temperature of the assay: for plants grown at 12°C the critical CO 2 concentration was 13.35 mmol at 5° C and 21.92 mmol at 10° C. Stimulation by O 2 depended also on the growth temperature: for measurements at 26.31 mmol m ?3 CO 2, O 2 was stimulating at temperatures less than 12°C for plants grown at 12°C and less than 19°C for plants grown at 27°C. The efficiency of the O 2-dependent stimulation of net photosynthesis was maximum at 9.21 mol m ?3 O 2 at 26.31 mmol m ?3 CO 2. Oxygen-stimulation of net photosynthesis was detected in Nicotiana tabacum L. var Samsun, Lycopersicum esculentum L. and Chenopodium album L. At 5°C and under high photon fluence rate, O 2 increased the carboxylation capacity of the photosynthetic apparatus of mustard and decreased its affinity for CO 2. The O 2 inhibition of the net CO 2 uptake observed at low CO 2 concentrations was the result of a decrease in the affinity for carbon dioxide. The nature of the mechanism which causes the stimulation of photosynthesis is discussed. 相似文献
8.
Summary Crassulacean acid metabolism (CAM) was studied in a tropical epiphytic fern, Pyrrosia longifolia, from a fully sun-exposed and from a very shaded site in Northern Queensland, Australia. Measurements of instantaneous net CO 2 exchange showed carbon gain via CO 2 dark fixation with some net CO 2 uptake also occuring during late afternoon, in both sun and shade fronds. Maximum rates of net CO 2 uptake and the nocturnal increase in titratable acidity were lower in shade than in sun fronds. 13C values of sun and shade fronds were not significantly different, and ranged between-14 and-15 suggesting that, in the long term, carbon gain was mainly via CO 2 dark fixation. Sun fronds had a higher light compensation point of photosynthesis than shade fronds but the same quantum yield. Yet there was no acclimation of photosynthetic O 2 evolution, (measured at 5% CO 2) in sun and shade fronds and photosynthesis saturated at between 200 and 400 mol quanta m -2 s -1. Use of higher light intensities for photosynthesis of sun fronds was probably precluded by low nutrient availability. Total nitrogen was less than 1% of dry weight in fully expanded sun and shade fronds. Exposure of shade fronds to full sunlight for 6 h led to a 60% decline in the quantum yield of photosynthesis and to a decline in variable fluorescence measured at room temperature. Photoinhibition by high light was also observed in Hoya nicholsoniae, a rainforest climber growing in deep shade. This species also exhibited CAM as demonstrated by nocturnal net CO 2 uptake, nocturnal acidification and a 13C value of-14. Photosynthetic O 2 evolution in this species was saturated at 2.5% of full sunlight. Two species of Dendrobium (Orchidaceae) from sun-exposed sites, one species exhibiting CAM and the other one exhibiting net CO 2 uptake exclusively during daytime via conventional C 3 photosynthesis, showed similar light response curves and the same quantum yield for photosynthetic O 2 evolution. 相似文献
9.
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
10.
The nature of the different processes of O 2 uptake involved in the light in the red macroalga Chondrus crispus Stackhouse ( Rhodophyta, Gigartinales) was investigated. At limiting CO 2, INH (2.5 mM) did not alter the O 2 uptake rate. Glycolate was not excreted and did not accumulate within the cells. KCN reduced the rate of O 2 uptake in the light by 76% at limiting CO 2 and by 43% at saturating CO 2, but caused > 95% inhibition of O 2 evolution. DCMU (5 μM) totally blocked the photosynthetic electron transport chain, but allowed a residual O 2 uptake of 3.0±0.6 μmol O 2 .h ?1.g ?1 FW, irrespective of the CO 2 concentration. In saturating CO 2, a high light intensity pretreatment significantly stimulated the rate of O 2 uptake compared to net O 2 evolution, suggesting the persistence, in the light, of mitochondrial respiration. Irrespective of the CO 2 concentration, the optimum temperature for O 2 evolution was 17°C whereas dark O 2 uptake increased linearly with temperature. In contrast, O 2 uptake in the light showed an optimum at 17°C in limiting CO 2, and 21–25° C in saturating CO 2; its Q 10 was 2.4 at limiting CO 2, a value close to that of RuBP oxygenase, and 3.1 at saturating CO 2, a value close to that of dark respiration. It is concluded that: 1) mitochondrial respiration and Mehler reaction are both involved at all CO 2 concentrations, 2) RuBP oxygenase activity cannot account for more than 45%, and Mehler reaction for less than 20%, of the total O 2 uptake observed in the light at limiting CO 2. 相似文献
11.
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
12.
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
13.
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
14.
A mass spectrometric 16O 2/ 18O 2-isotope technique was used to analyse the rates of gross O 2 evolution, net O 2 evolution and gross O 2 uptake in relation to photon fluence rate by Dunaliella tertiolecta adapted to 0.5, 1.0, 1.5, 2.0 and 2.5 M NaCl at 25°C and pH 7.0.At concentrations of dissolved inorganic carbon saturating for photosynthesis (200 M) gross O 2 evolution and net O 2 evolution increased with increasing salinity as well as with photon fluence rate. Light compensation was also enhanced with increased salinities. Light saturation of net O 2 evolution was reached at about 1000 mol m -2s -1 for all salt concentrations tested. Gross O 2 uptake in the light was increased in relation to the NaCl concentration but it was decreased with increasing photon fluence rate for almost all salinities, although an enhanced flow of light generated electrons was simultaneously observed. In addition, a comparison between gross O 2 uptake at 1000 mol photons m -2s -1, dark respiration before illumination and immediately after darkening of each experiment showed that gross O 2 uptake in the light paralleled but was lower than mitochondrial O 2 consumption in the dark.From these results it is suggested that O 2 uptake by Dunaliella tertiolecta in the light is mainly influenced by mitochondrial O 2 uptake. Therefore, it appears that the light dependent inhibition of gross O 2 uptake is caused by a reduction in mitochondrial O 2 consumption by light.Abbreviations DCMU
3-(3, 4-dichlorophenyl)-1, 1-dimethylurea
- DHAP
dihydroxy-acetonephosphate
- DIC
dissolved inorganic carbon
- DR a
rate of dark respiration immediately after illumination
- DR b
rate of dark respiration before illumination
- E 0
rate of gross oxygen evolution in the light
- NET
rate of net oxygen evolution in the light
- PFR
photon fluence rate
- RubP
rubulose-1,5-bisphosphate
- SHAM
salicyl hydroxamic acid
- U 0
rate of gross oxygen uptake in the light 相似文献
15.
The response of net photosynthesis and apparent light respiration to changes in [O 2], light intensity, and drought stress was determined by analysis of net photosynthetic CO 2 response curves. Low [O 2] treatment resulted in a large reduction in the rate of photorespiratory CO 2 evolution. Lightintensity levels influenced the maximum net photosynthetic rate at saturating [CO 2]. These results indicate that [CO 2], [O 2] and light intensity affect the levels of substrates involved in the enzymatic reactions of photosynthesis and photorespiration. Intracellular resistance to CO 2 uptake decreased in low [O 2] and increased at low leaf water potentials. This response reflects changes in the efficiency with which photosynthetic and photorespiratory substrates are formed and utilized. Water stress had no effect on the CO 2 compensation point or the [CO 2] at which net photosynthesis began to saturate at high light intensity. The relationship between these data and recently published in-vitro kinetic measurements with ribulose-diphosphate carboxylase is discussed.Abbreviations
C
w
intracellular CO 2 concentration
-
F
gross
gross photosynthesis
-
F
net
net photosynthesis
-
I
light intensity
-
R
L
light respiration rate
-
r
c
carboxylation resistance
-
r
8
leaf gas-phase resistance
-
r
i
intracellular resistance; to CO 2 uptake
-
r
t
resistance to CO 2 flux between the intercellular spaces and the carboxylation sites
-
T
L
leaf temperature
-
t
leaf water potential
-
CO 2 compensation point 相似文献
16.
Using an open gas-exchange system, apparent photosynthesis, true photosynthesis (TPS), photorespiration (PR) and dark respiration of sunflower ( Helianthus annuus L.) leaves were determined at three temperatures and between 50 and 400 l/l external CO 2. The ratio of PR/TPS and the solubility ratio of O 2/CO 2 in the intercellular spaces both decreased with increasing CO 2. The rate of PR was not affected by the CO 2 concentration in the leaves and was independent of the solubility ratio of oxygen and CO 2 in the leaf cell. At photosynthesis-limiting concentrations of CO 2, the ratio of PR/TPS significantly increased from 18 to 30°C and the rate of PR increased from 4.3 mg CO 2 dm -2 h -1 at 18°C to 8.6 mg CO 2 dm -2 h -1 at 30°C. The specific activity of photorespired CO 2 was CO 2-dependent but temperature-independent, and the carbon traversing the glycolate pathway appeared to be derived both from recently fixed assimilate and from older reserve materials. It is concluded that PR as a percentage of TPS is affected by the concentrations of O 2 and CO 2 around the photosynthesizing cells, but the rate of PR may also be controlled by other factors.Abbreviations APS
apparent photosynthesis (net CO 2 uptake)
- PR
photorespiration (CO 2 evolution in light)
- RuBP
ribulose-1,5-bisphosphate
- TPS
true photosynthesis (true CO 2 uptake) 相似文献
17.
The depressions of photosynthetic CO 2 uptake following O 3 exposures of 200 and 400 nmol mol -1 for between 4 and 16 h were compared between Pisum sativum, Quercus robur and Triticum aestivum, and the potential causes of change identified in vivo. Photosynthetic change was examined by analysis of CO 2, O 2, O 3 and water vapour exchanges together with chlorophyll fluorescence in controlled environments. Under identical fumigation conditions, each species showed very similar rates of O 3 consumption. The light-saturated rate of CO 2 uptake showed a statistically significant decrease in each species with increasing O 3 dose. Although stomatal conductance declined in parallel with CO 2 uptake this did not account for the observed decrease in photosynthesis. The decrease in mesophyll conductance resulted primarily from a decrease in the apparent carboxylation capacity, implying in decreased activity of ribulose 1,5-bisphosphate carboxylase/oxygenase. The maximum capacity of carboxylation was consequently reduced by over 30% and 50% after 16 h fumigation with 200 and 400 nmol mol -1 O 3 respectively. Additionally, in Q. robur, a statistically significant inhibition of the CO 2 saturated rate of photosynthesis occurred after 16 h with 400 nmol mol -1 O 3, suggesting that the ability to regenerate ribulose 1,5-bisphosphate was also impaired. None of the species showed any significant decrease in the efficiency of light-limited photosynthesis following fumigation at 200 nmol mol -1 O 3, but effects were apparent at 400 nmol mol -1 O 3. The common feature in all three species was a decline in carboxylation capacity which preceded any other change in the photosynthetic apparatus.Abbreviations A sat
net CO 2 uptake rate per unit leaf area at light saturation
- A
net CO 2 uptake rate per unit leaf area
- A max
net CO 2 uptake rate per unit leaf area at CO 2 and light saturation
- c i
mole fraction of CO 2 in the intercellular air space
- g s
stomatal conductance to CO 2
- F m
maximum chlorophyll fluorescence
- F v
variable chlorophyll fluorescence
- c
quantum yield of CO 2 uptake for absorbed light
- 0
quantum yield of oxygen evolution for incident light
- PPFD
photosynthetically active radiation
- Rubisco
ribulose 1,5-bisphosphate carboxylase/oxygenase
- RuBP
ribulose 1,5-bisphosphate
- Vc max
maximum rate of carboxylation 相似文献
18.
Concurrent O 2 evolution, O 2 uptake, and CO 2 uptake by illuminated maize ( Zea mays) leaves were measured using 13CO 2 and 18O 2. Considerable O 2 uptake occurred during active photosynthesis. At CO 2 compensation, O 2 uptake increased. Associated with this increase was a decrease in O 2 release such that a stoichiometric exchange of O 2 occurred. The rate of O 2 exchange at CO 2 compensation was directly related to O 2 concentration in the atmosphere at least up to 8% (v/v). 相似文献
19.
Membrane inlet mass spectrometry indicated massive light-dependent cycling of inorganic carbon between the medium and the
cells of various phytoplankton species representing the main groups of aquatic primary producers. These included diatoms,
symbiotic and free living dinoflagellates, a coccolithophorid, a green alga and filamentous and single cell cyanobacteria.
These organisms could maintain an ambient CO 2 concentration substantially above or below that expected at chemical equilibrium with HCO 3
−. The coccolithophorid Emiliania huxleyishifted from net CO 2 uptake to net CO 2 efflux with rising light intensity. Differing responses of CO 2 uptake and CO 2 fixation to changing light intensity supported the notion that these two processes are not compulsorily linked. Simultaneous
measurements of CO 2 and O 2 exchange and of the fluorescence parameters in Synechococcus sp. strain PCC 7942, showed that CO 2 uptake can serve as a sensitive probe of the energy status of the photosynthetic reaction centers. However, during transitions
in light intensity, changes in CO 2 uptake did not accord with those expected from fluorescence change. Quantification of the net fluxes of CO 2, HCO 3
− and of photosynthesis at steady-state revealed that substantial HCO 3
− efflux accompanied CO 2 uptake and fixation in the case of `CO 2 users'. On the other hand, `HCO 3
− users' were characterized by a rate of net CO 2 uptake below that of CO 2 fixation. The results support the notion that entities associated with the CCM function not only in raising the CO 2 concentration at the site of Rubisco; they may also serve as a means of diminishing photodynamic damage by dissipating excess
light energy.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
20.
The hypothesis that net photosynthesis is diminished in many plant species because of a high rate of CO 2 evolution in the light has been tested further. High rates of CO 2 output in CO 2-free air in comparison with dark respiration were found in Chlamydomonas reinhardi, wheat leaves, tomato leaves, and to a lesser extent in Chlorella pyrenoidosa by means of the 14C-photorespiration assay. In tobacco leaves high photorespiration was characteristic of a standard variety, Havana Seed, and a possibly still higher rate was found in a yellow heterozygous mutant, JWB Mutant. However, the dark homozygous sibling of the latter, JWB Wild, had a low photorespiration for the tobacco species. The relative rates of photorespiration were in the same sequence when measured by the 14CO 2 released in normal air from leaf disks supplied with glycolate-1- 14C in the light. As would be predicted by the hypothesis, the maximal net rate of photosynthesis at 300 ppm of CO2 in the air in JWB Wild leaves was greater (24%) than in Havana Seed, while JWB Mutant had less CO2 uptake than the standard variety (21%). At 550 ppm of CO2 the differences in net photosynthesis were not as great between the 2 siblings as at 200 ppm. The relative leaf expansion rates of seedlings of the 3 tobacco varieties in a greenhouse had the same relationship as their rates of CO2 assimilation. Thus within the tobacco species, as in a comparison between tobacco and maize, low photorespiratory CO2 evolution was correlated with higher photosynthetic efficiency. Therefore it seems that increased CO2 uptake should be achieved by genetic interference with the process of photorespiration. 相似文献
|