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1.
Abstract. The supply of oxygen to respiring shoot tissue was investigated for three submerged macrophytes (Potamogeton crispus L., Egeria densa Planch, and Myriophyllum triphyllum Orchard). For all species, the response of oxygen uptake rates to the external O2 concentration was a rectangular hyperbola over the range 0–5.0 × 10?3m3 m?3. However, the response pattern for material with water-infiltrated lacunar airspaces was non-hyperbolic over this range. The change in response was interpreted as an increased substrate (O2) limitation, resulting from lower radial diffusion rates within the infiltrated material. Neither the uninfiltrated nor the infiltrated responses obeyed the linear and logarithmic formulae of the type observed for submerged macrophytes by earlier authors. These results suggest that the responses observed are affected by factors such as water velocity, internal restrictions to diffusion and the range of oxygen tensions investigated. Therefore, it is unlikely that one response formula can adequately account for the effects of oxygen concentration on submerged macrophyte oxygen uptake. The lacunar airspaces also represent a possible oxygen source for dark respiration. The consumption of oxygen from the airspaces was investigated by displacing the gas from the lacunae and measuring the subsequent increase in the rate of oxygen assimilation from the external liquid. Approximately 30% of the oxygen consumed by E. densa and P. crispus, and more than 40% of that consumed by M. triphyllum, was derived from the lacunar system. This O2 supply is a consequence of the higher oxygen concentration in the lacunae than in the external medium, due to the low solubility of oxygen in water. Storage of photosynthetically-produced oxygen in the lacunae could not be identified during a light/dark transient, due to rate changes caused by the effects of light on the respiratory metabolism. However, O2 partial pressure gradients artificially set up between the lacunae and water equilibrated within an hour, suggesting that excess oxygen would be lost to the water within this time. 相似文献
2.
B. J. Finlay U.-G. Berninger L. J. Stewart R. M. Hindle W. Davison 《The Journal of eukaryotic microbiology》1987,34(4):349-356
The vertical distributions of two pond-dwelling zoochlorellae-bearing ciliates (Euplotes daidaleos Diller & Kounaris, 1966 and Frontonia vernalis Ehrenberg, 1838) were monitored over a 24-h period. Both species maintained peak abundance at a low O2 level (usually < 1 mg/liter). They did not migrate in response to the changing light level. Experiments with laboratory cultures indicated that the characteristic distribution in an O2 gradient in the dark was largely controlled by the oxygen tension. The increased motility in anoxia and high pO2 was independent of large changes in pCO2 and pH. Ciliates living in anoxia or a very low pO2 would migrate out of the dark and into the dimly lit (10 μE m-2 sec-1) part of a glass cell because there they could photosynthesize, produce O2, and create a suitable oxygenated microenvironment; a further increase in the light level caused a slow migration out of the light. Similar migrations were observed when the light level remained low but the pO2 was artificially raised. Ciliates suspended in 1 μM DCMU (an inhibitor of photosynthetic O2 evolution) took longer to migrate into the light and they did not avoid high light levels (> 100, μE m-2 sec-1)- Frontonia suspended in water with a pO2 of 1% aggregated at a low light level (1 μE m-2 sec-1); peak daytime abundance in the pond occurred at about this light level. Frontonia vernalis tends to swim vertically upwards (anterior end up) when suspended in anoxic water. This apparent negative geotaxis compensates for the high sedimentation velocity (0.36 mm sec-1) of this large ciliate and facilitates its aggregation at the metalimnion. The O2 tension appears to be the principal factor controlling the vertical distributions of both species. Occasional, enhanced convection within the metalimnion has a secondary influence. Light influences the vertical profile only if it promotes photosynthesis and increases the intracellular pO2. 相似文献
3.
LAURE MICHELET THOMAS ROACH BEAT B. FISCHER MARIETTE BEDHOMME STÉPHANE D. LEMAIRE ANJA KRIEGER‐LISZKAY 《Plant, cell & environment》2013,36(6):1204-1213
In photosynthetic organisms, excess light is a stress that induces production of reactive oxygen species inside the chloroplasts. As a response, the capacity of antioxidative defence mechanisms increases. However, when cells of Chlamydomonas reinhardtii were shifted from dark to high light, a reversible partial inactivation of catalase activity was observed, which correlated with a transient increase in the level of H2O2 in the 10 μm range. This concentration range seems to be necessary to activate H2O2‐dependent signalling pathways stimulating the expression of H2O2 responsive genes, such as the heat shock protein HSP22C. Catalase knock‐down mutants had lost the transient accumulation of H2O2, suggesting that a decrease in catalase activity was the key element for establishing a transient H2O2 burst. Catalase was inactivated by a one‐electron event consistent with the reduction of a single cysteine. We propose that under high light intensity, the redox state of the photosynthetic electron transport chain is sensed and transmitted to the cytosol to regulate the catalase activity. This allows a transient accumulation of H2O2, inducing a signalling event that is transmitted to the nucleus to modulate the expression of chloroplast‐directed protection enzymes. 相似文献
4.
5.
A biochemical model of C
3photosynthesis has been developed by G.D. Farquhar et al. (1980, Planta 149, 78–90) based on Michaelis-Menten kinetics of ribulose-1,5-bisphosphate (RuBP) carboxylase-oxygenase, with a potential RuBP limitation imposed via the Calvin cycle and rates of electron transport. The model presented here is slightly modified so that parameters may be estimated from whole-leaf gas-exchange measurements. Carbon-dioxide response curves of net photosynthesis obtained using soybean plants (Glycine max (L.) Merr.) at four partial pressures of oxygen and five leaf temperatures are presented, and a method for estimating the kinetic parameters of RuBP carboxylase-oxygenase, as manifested in vivo, is discussed. The kinetic parameters so obtained compare well with kinetic parameters obtained in vitro, and the model fits to the measured data give r
2values ranging from 0.87 to 0.98. In addition, equations developed by J.D. Tenhunen et al. (1976, Oecologia 26, 89–100, 101–109) to describe the light and temperature responses of measured CO2-saturated photosynthetic rates are applied to data collected on soybean. Combining these equations with those describing the kinetics of RuBP carboxylase-oxygenase allows one to model successfully the interactive effects of incident irradiance, leaf temperature, CO2 and O2 on whole-leaf photosynthesis. This analytical model may become a useful tool for plant ecologists interested in comparing photosynthetic responses of different C3 plants or of a single species grown in contrasting environments.Abbreviations PCO
photorespiratory carbon oxidation
- PCR
photosynthetic carbon reduction
- PPFD
photosynthetic photon-flux density
- RuBP
ribulose bisphosphate 相似文献
6.
A mass spectrometric 16O2/18O2-isotope technique was used to analyse the rates of gross O2 evolution, net O2 evolution and gross O2 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 O2 evolution and net O2 evolution increased with increasing salinity as well as with photon fluence rate. Light compensation was also enhanced with increased salinities. Light saturation of net O2 evolution was reached at about 1000 mol m-2s-1 for all salt concentrations tested. Gross O2 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 O2 uptake at 1000 mol photons m-2s-1, dark respiration before illumination and immediately after darkening of each experiment showed that gross O2 uptake in the light paralleled but was lower than mitochondrial O2 consumption in the dark.From these results it is suggested that O2 uptake by Dunaliella tertiolecta in the light is mainly influenced by mitochondrial O2 uptake. Therefore, it appears that the light dependent inhibition of gross O2 uptake is caused by a reduction in mitochondrial O2 consumption by light.Abbreviations DCMU
3-(3, 4-dichlorophenyl)-1, 1-dimethylurea
- DHAP
dihydroxy-acetonephosphate
- DIC
dissolved inorganic carbon
- DRa
rate of dark respiration immediately after illumination
- DRb
rate of dark respiration before illumination
- E0
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
- U0
rate of gross oxygen uptake in the light 相似文献
7.
SILKE LAUTNER MICHAELA STUMMER RAINER MATYSSEK JÖRG FROMM THORSTEN E. E. GRAMS 《Plant, cell & environment》2014,37(1):254-260
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 CO2 or lowered O2 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 CO2 release simultaneously with stomatal opening, hence reflecting direct involvement of respiratory stimulation in the drop of the net CO2 uptake rate. However, persistence of the transient decline in net CO2 uptake rate under illumination and elevated CO2 or 1% O2 makes it unlikely that photorespiration is the metabolic origin of the respiratory CO2 release. In conclusion, the transient knockout of net CO2 uptake is at least partially attributed to an increased CO2 release through mitochondrial respiration as stimulated by electrical signals. Putative CO2 limitation of Rubisco due to decreased activity of carbonic anhydrase was ruled out as the photosynthesis effect was not prevented by elevated CO2. 相似文献
8.
Andrej Meglič Gregor Zupančič 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》2011,197(3):301-310
Time courses of mitochondrial responses to illumination-induced physiological loads and to hypoxia, were recorded optically
from eyes of blowflies Calliphora vicina chalky. We isolated changes in redox states of haems a3, a, c, and b. Two types of responses to light stimulation were observed. Haems b and a3 responded with transient oxidation and haems a and c with reduction. The same two groups emerged in response to anoxic exposure.
The onset of reduction of haems a and c had virtually no latency, while haems a3 and b exhibited a transient oxidation followed by reduction only after 10–20 s. The dependence of the steady-state reduction
level on
P\textO2 P_{{{\text{O}}_{2} }} produced the same groups. Haems a and c were significantly reduced at
P\textO2 P_{{{\text{O}}_{2} }} levels around 10 kPa while with haems b and a3 load-induced oxidation was only replaced by reduction below 2 kPa. We propose haems respond to physiological loads in accordance
with their steady-state reduction, which in turn depends largely on barriers for electron transport imposed by the mitochondrial
membrane potential. We also propose it may be possible to assess the values of tissue
P\textO2 P_{{{\text{O}}_{2} }} and O2 consumption by monitoring haems that are highly oxidized at rest such as haem a. 相似文献
9.
10.
S. Aota D. J. Randall 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1993,163(2):138-146
Ventilation frequency, opercular pressure amplitude, heart rate, dorsal aortic pressure, arterial pH, arterial O2 tension, and plasma catecholamine levels were recorded in rainbow trout, Oncorhynchus mykiss, during normoxia (19.7 kPa, 148 mmHg) or hyperoxia (51.2 kPa, 384 mmHg) after injection of various concentrations of catecholamines. In normoxic fish, adrenaline injection resulted in a depression of arterial O2 tension, hypoventilation due to a drop in ventilation frequency, and a drop in heart rate, while dorsal aortic pressure increased. Noradrenaline depressed ventilation frequency, but opercular pressure amplitude increased to a far greater extent, and dorsal aortic pressure increased. During hyperoxia, adrenaline injection lowered ventilation frequency, opercular amplitude and heart rate, but dorsal aortic pressure increased. The stimulatory effects of noradrenaline on ventilation were abolished during hyperoxia, but the cardiac responses were similar to those seen during normoxia. These results indicate that catecholamines can modify the ventilatory output from the respiratory centre, and modification of ventilation frequency can occur independently of opercular pressure amplitude.Abbreviations
f
g
ventilation frequency
- HPLC
high performance liquid chromatography
-
P
op
opercular pressure amplitude
-
f
h
heart rate
-
P
DA
dorsal aortic pressure
- pHa
arterial pH
-
P
aO2
arterial oxygen tension
-
PO2
oxygen tension 相似文献
11.
Sbong S Dzialowski EM 《Comparative biochemistry and physiology. Part A, Molecular & integrative physiology》2007,148(4):761-768
During the first day of hatching, the developing chicken embryo internally pips the air cell and relies on both the lungs and chorioallantoic membrane (CAM) for gas exchange. Our objective in this study was to examine respiratory and cardiovascular responses to acute changes in oxygen at the air cell or the rest of the egg during internal pipping. We measured lung (V·O2lung) and CAM (V·O2CAM) oxygen consumption independently before and after 60 min exposure to combinations of hypoxia, hyperoxia, and normoxia to the air cell and the remaining egg. Significant changes in V·O2total were only observed with combined egg and air cell hypoxia (decreased V·O2total) or egg hyperoxia and air cell hypoxia (increased V·O2total). In response to the different O2 treatments, a change in V·O2lung was compensated by an inverse change in V·O2CAM of similar magnitude. To test for the underlying mechanism, we focused on ventilation and cardiovascular responses during hypoxic and hyperoxic air cell exposure. Ventilation frequency and minute ventilation (VE) were unaffected by changes in air cell O2, but tidal volume (VT) increased during hypoxia. Both VT and VE decreased significantly in response to decreased PCO2. The right-to-left shunt of blood away from the lungs increased significantly during hypoxic air cell exposure and decreased significantly during hyperoxic exposure. These results demonstrate the internally pipped embryo's ability to control the site of gas exchange by means of altering blood flow between the lungs and CAM. 相似文献
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13.
Jacek Kamczyc Maciej Skorupski Marcin K. Dyderski Anna Gazda Mariusz Hachułka Paweł Horodecki Izabela Kałucka Marek Malicki Remigiusz Pielech Michał Smoczyk Sylwia Wierzcholska Andrzej M. Jagodziński 《Experimental & applied acarology》2018,75(3):269-280
Hydrogen peroxide (H2O2) and hydroxyl radicals (HO·) are generated through partial reduction of oxygen. The HO· are the most reactive and have a shorter half-life than H2O2, they are produced from comparatively stable H2O2 through Fenton reaction. Although controlling HO· is important and biologically advantageous for organisms, it may be difficult. Ticks are obligate hematophagous arthropods that need blood feeding for development. Ticks feed on vertebrate blood containing high levels of iron. Ticks also concentrate iron-containing host blood, leading to high levels of iron in ticks. Host-derived iron may react with oxygen in the tick body, resulting in high concentrations of H2O2. On the other hand, ticks have antioxidant enzymes, such as peroxiredoxins (Prxs), to scavenge H2O2. Gene silencing of Prxs in ticks affects their blood feeding, oviposition, and H2O2 concentration. Therefore, Prxs could play important roles in ticks’ blood feeding and oviposition through the regulation of the H2O2 concentration. This review discusses the current knowledge of Prxs in hard ticks. Tick Prxs are also multifunctional molecules related to antioxidants and immunity like other organisms. In addition, tick Prxs play a role in regulating the host immune response for ticks’ survival in the host body. Tick Prx also can induce Th2 immune response in the host. Thus, this review would contribute to the further understanding of the tick’s antioxidant responses during blood feeding and the search for a candidate target for tick control. 相似文献
14.
Ventilatory response of the diamondback water snake,Natrix rhombifera to hypoxia, hypercapnia and increased oxygen demand 总被引:3,自引:3,他引:0
Ronald K. Gratz 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1979,129(2):105-110
Summary Simultaneous measurements of ventilatory frequency, tidal volume, O2 uptake, CO2 output and cardiac frequency were made in the diamondback water snake,Natrix rhombifera while breathing hypoxic (15% to 5% O2 in N2) or hypercarbic (2% to 10% CO2 and 21% O2 in N2) gases. The snakes responded to hypoxia by increasing tidal volume and decreasing ventilatory frequency resulting in little change in ventilation (50% increase at 5% inspired O2), or O2 uptake and only a light increase in CO2 output. Hypercarbia to 4.2% inspired CO2 resulted in a slight hyperventilation but ventilation was depressed at 6.3% inspired CO2 and became erratic at higher concentrations. The resting rate of O2 uptake was maintained throughout hypercapnia. Heart rate increased during hypoxia and decreased during hypercapnia. Cutaneous O2 uptake increased during extreme hypoxia (5% inspired O2) and cutaneous CO2 output increased during hypercapnia, probably due to changes in the body-to-ambient gas gradients (Crawford and Schultetus, 1970). Both pulmonary oxygen uptake and ventilation were dramatically increased immediately following 10–15 min experimental dives. The increased ventilation was achieved primarily through an increased tidal volume. 相似文献
15.
Tom Fenchel Bland Finlay 《Biological reviews of the Cambridge Philosophical Society》2008,83(4):553-569
Oxygen has two faces. On one side it is the terminal electron acceptor of aerobic respiration – the most efficient engine of energy metabolism. On the other hand, oxygen is toxic because the reduction of molecular O2 creates reactive oxygen species such as the superoxide anion, peroxide, and the hydroxyl radical. Probably most prokaryotes, and virtually all eukaryotes, depend on oxygen respiration, and we show that the ambiguous relation to oxygen is both an evolutionary force and a dominating factor driving functional interactions and the spatial structure of microbial communities.We focus on microbial communities that are specialised for life in concentration gradients of oxygen, where they acquire the full panoply of specific requirements from limited ranges of PO2 , which also support the spatial organisation of microbial communities. Marine and lake sediments provide examples of steep O2 gradients, which arise because consumption or production of oxygen exceeds transport rates of molecular diffusion. Deep lakes undergo thermal stratification in warm waters, resulting in seasonal anaerobiosis below the thermocline, and lakes with a permanent pycnocline often have permanent anoxic deep water. The oxycline is here biologically similar to sediments, and it harbours similar microbial biota, the main difference being the spatial scale. In sediments, transport is dominated by molecular diffusion, and in the water column, turbulent mixing dominates vertical transport.Cell size determines the minimum requirement of aerobic organisms. For bacteria (and mitochondria), the half‐saturation constant for oxygen uptake ranges within 0.05 – 0.1% atmospheric saturation; for the amoeba Acanthamoeba castellanii it is 0.2%, and for two ciliate species measuring around 150 μm, it is 1‐2 % atmospheric saturation. Protection against O2 toxicity has an energetic cost that increases with increasing ambient O2 tension. Oxygen sensing seems universal in aquatic organisms. Many aspects of oxygen sensing are incompletely understood, but the mechanisms seem to be evolutionarily conserved. A simple method of studying oxygen preference in microbes is to identify the preferred oxygen tension accumulating in O2 gradients. Microorganisms cannot sense the direction of a chemical gradient directly, so they use other devices to orient themselves. Different mechanisms in different prokaryotic and eukaryotic microbes are described. In O2 gradients, many bacteria and protozoa are vertically distributed according to oxygen tension and they show a very limited range of preferred PO2. In some pigmented protists the required PO2 is contingent on light due to photochemically generated reactive oxygen species. In protists that harbour endosymbiotic phototrophs, orientation towards light is mediated through the oxygen production of their photosynthetic symbionts. Oxygen plays a similar role for the distribution of small metazoans (meiofauna) in sediments, but there is little experimental evidence for this. Thus the oxygenated sediments surrounding ventilated animal burrows provide a special habitat for metazoan meiofauna as well as unicellular organisms. 相似文献
16.
W. R. Dawson G. C. Whittow 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1994,164(4):292-298
Eggs with pip-holes of the black-footed (Diomedea nigripes) and Laysan (Diomedea immutabilis) albatrosses were exposed to various air temperatures in the range 20–35°C in order to detect signs of incipient endothermy in late embryos. No evidence of endothermy was found. In contrast, the O2 consumption of most hatchlings increased in response to cooling, the O2 consumption at an air temperature of 25° C exceeding that between 34 and 35°C by 40%. In a minority of hatchlings this response was not seen. It was suggested that endothermy may develop at some time during the 24 h after hatching.Abbreviations bm
body mass
-
C
total
total thermal conductance of tissues and plumage
-
f
respiratory frequency
-
FEO
2
fractional concentration of oxygen in air leaving chamber
-
FIO
2
fractional concentration of oxygen in air entering chamber
-
T
a
an temperature
-
T
b
deep-body temperature
-
V
air-flow rate
-
VO2
oxygen consumption 相似文献
17.
Our knowledge on the nature and quantity of reactive O2forms generated in phagocytes, particularly in neutrophil leucocytes, and their role in nonspecific immunity is reviewed. In thermodynamical terms, oxygen is a very reactive molecule and, hence, can react with most chemical elements and many organic molecules. In kinetic terms, O2is rather inert. Its reactivity can be increased either by reduction or excitation. After accepting four electrons, O2is finally reduced to H2O. Partial reduction resulting in highly reactive intermediates, namely, superoxide anion (O2
·–), hydrogen peroxide (H2O2), and hydroxyl radical (·OH), is possible. Singlet oxygen (1O2) is the product of O2excitation. Phagocytes acting like agents of nonspecific immunity generate such reactive forms of O2. 相似文献
18.
Absence of Cu–Zn superoxide dismutase BCSOD1 reduces Botrytis cinerea virulence in Arabidopsis and tomato plants,revealing interplay among reactive oxygen species,callose and signalling pathways
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Jaime López‐Cruz Crespo‐Salvador Óscar Fernández‐Crespo Emma García‐Agustín Pilar González‐Bosch Carmen 《Molecular Plant Pathology》2017,18(1):16-31
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The influence of oxygen concentration in the range 0–21% on photosynthesis in intact leaves of a number of higher plants has been investigated. Photosynthetic Co2 fixation of higher plants is markedly inhibited by oxygen in concentrations down to less than 2%. The inhibition increases with oxygen concentration and is about 30% in an atmosphere of 21% O2 and 0.03% Co.2. Undoubtedly, therefore, oxygen in normal air exerts a strong inhibitory effect on photosynthetic Co2 fixation of land plants under natural conditions. The inhibitory effect of oxygen is rapidly produced and fully reversible. The degree of inhibition is independent of light intensity. The quantum yield for Co2 fixation, i.e. the slope of the linear part of the curve for Co2 uptake versus absorbed quanta, is inhibited to the same degree as the light saturated rate at all oxygen concentrations studied. Diverse species of higher plants, varying greatly in photosynthetic response to light intensity and Co2 concentration, and with light saturated roles of Co2 fixation differing by a factor of more than 10 times, show a remarkable similarity in their response to oxygen concentration. By contrast, when studied under the same conditions as the higher plants, the green algae Chlorella and Ulva did not show-any measurable inhibition of photosynthetic Co2 fixation. Similarity, the increase in fluorescence intensity with increasing oxygen concentrations found in higher plants also was not seen in Chlorella. The present results, together with previous data on the photosynthetic response of algae to oxygen concentration, indicate that the photosynthetic apparatus of higher plants differs considerably from that of algae in its sensitivity to oxygen. The inhibitory effect of oxygen on photosynthetic Co2 fixation in higher plants is somewhat higher at wavelengths which excite preferentially photosystem I. Also, the Emerson enhancement of Co2 fixation measured when a far red beam of low intensity is imposed on a background of red light is greater under low oxygen concontrution than under air. Measurements of reversible light-induced absorbance changes reveal that the change at 591 nm, probably caused by pla.stocyanin, is affected by oxygen concentration only if photosystem II is excited. the reducing effect on plastocyanin, caused by excitation of this system, decreases with increasing oxygen concentration. From these results it is suggested that a possible site of the inhibition by oxygen is in the electron carrier chain between the two photosystems. Oxygen might act as an electron acceptor at this site, causing reducing power to react back with molecular oxygen. However, this hypothesis does not account for equal inhibitions of the quantum yield and the light saturated rate of photosynthetic CO2 uptake. Through the photosynthetic process plants take up carbon dioxide and evolve oxygen. The present high concentration of molecular oxygen in the atmosphere is generally considered to have arisen from the activity of photo-synthetic organisms. The effect of oxygen concentration would seem, therefore, to he a problem of great interest, not only in the field of the biophysics and biochemistry of photosynthesis, but in ecology and other branches of biology as well. It was discovered by Warburg (1920) that high concentrations of oxygen inhibit the rate of photosynthetic oxygen evolution in the unicellular alga Chlorella. Since then, it has been confirmed by various authors that oxygen cconcentrations in the range 21–100 per cent have a marked inhibitory effect on photosynthesis, particularly at saturating light intensities. There is some evidence that under conditions when carbon dioxide concentration limits photosynthesis, the inhibition may become obvious even in 21 per cent oxygen. The inhibition has not been considered to operate at low light intensities. A review on the subject has been given by Turner and Brittain (1962). Various hypotheses have been put forward to explain the inhibitory effect of oxygen, commonly referred to as the Warhurg effect. Some authors favor the idea of enzyme inhibition; Turner et al. (1958) that one or more enzymes of the carbon reduction cycle are inactivated by oxygen: lirianlals (1962) that enzymes of the oxygen-evolving complex are inhihited. Other hypotheses concern back-reactions in which molecular oxygen is taken up, thus reversing the photosynthetic process. These reactions include photo-oxidation, photorespiration, and the Mehler reaction (Tamiya et al., 1957). At present, there is no generally accepted hypothesis explaining the effect. The often conflicting results on which these hypotheses were based have been obtained mostly on algae. The first observation of an inhibitory effect on photosynthesis in a higher plant was made hy McAlister and Myers (1940) in wheat leaves. They found that the photosyntlietic CO2 uptake was markedly lower in air than in an atmosphere of about 0.5 per cent oxygen. At the CO2 concentration used (0.03%) the inhibition was present both at high and moderate light intensities. No data were obtained at low light intensities. Although the study of the effect of oxygen concentration on photosynthesis in higher plants would seem to be of great interest, particularily since the natural environment of most land plants is an atmosphere with an oxygen content of 21 per cent, it has attracted very little attention. To the author's knowledge no thorough investigation on the subject has been published. The present investigalion is directed toward elucidatirng the photosynthetic response of higher plants to oxygen concentrations up to that of normal air. Data are presented showing that the photosynthetic CO2 fixation in intact leaves of higher plants, regardless of light intensity, is strongly inhibited by oxygen in normal air, and that the pholosynthetic response to oxygen differs considerably from that of green algae. The present investigalion is directed toward elucidatirng the photosynthetic response of higher plants to oxygen concentrations up to that of normal air. Data are presented showing that the photosynthetic CO2 fixation in intact leaves of higher plants, regardless of light intensity, is strongly inhibited by oxygen in normal air, and that the pholosynthetic response to oxygen differs considerably from that of green algae. 相似文献