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1.
Respiratory O 2 consumption was investigated in dark-adapted barley ( Hordeum vulgare L. cv. Gunilla) protoplasts and after illumination for 10 min at high and very low CO 2 in the presence of respiratory and photorespiratory inhibitors. In dark-adapted protoplasts no difference was observed between inhibitor treatments in high and very low CO 2. The respiratory rate increased somewhat after illumination and a difference in responce to inhibitors was in some cases observed between high and very low CO 2. Thus, the operation of the mitochondrial electron transport chain is affected following a period of active photosynthesis. In all situations tested, oligomycin inhibited respiratiory O 2 uptake indicating that respiration of mitochondria in protoplasts is not strictly ADP limited. Antimycin A inhibited respiration more in dark-adapted protoplasts than after illumination whereas SHAM gave the opposite response. Rotenone inhibited respiration both in dark-adapted protoplasts (about 30%) and after illumination where the inhibition was much greater in very low CO 2 (50%) than in high CO 2 (10%). After illumination in very low CO 2. SHAM + rotenone inhibited respiration almost completely (70%). Photorespiratory inhibitors had very small effect on O 2 consumption in darkness. After illumination the effect of aminoacetonitrile (AAN) was also very low whereas α-hydroxypyridine-2-methane sulphonate (HPMS) in photorespiratory conditions inhibited O 2 uptake much stronger (35%). The addition of glyoxylate enhanced respiration in the presence of HPMS up to the control level suggesting that alternative pathways of glyoxylate conversion might be operating. The differences in inhibitor responses may reflect fine mechanisms for the regulation of energetic balance in the plant cell which consists of switching from electron transport coupled to ATP production to non-coupled transport. Photorespiratory flux is also very flexible, and the suppression of glycine decarboxylation can induce bypass reactions of glyoxylate metabolism. 相似文献
2.
This study aims to elucidate the molecular mechanism for the transient increase in the O 2‐uptake rate in tobacco ( Nicotiana tabacum cv Xanthi) leaves after turning off actinic lights (ALs). The photosynthetic O 2 evolution rate reaches a maximum shortly after the onset of illumination with ALs and then decreases to zero in atmospheric CO 2/O 2 conditions. After turning off the ALs, tobacco leaves show a transient increase in the O 2‐uptake rate, the post‐illumination transient O 2‐uptake, and thereafter, the O 2‐uptake rate decreases to the level of the dark‐respiration rate. Photosynthetic linear electron flow, evaluated as the quantum yield of photosystem II [Y(II)], maintained a steady‐state value distinct from the photosynthetic O 2‐evolution rate. In high‐[CO 2] conditions, the photosynthetic O 2‐evolution rate and Y(II) showed a parallel behavior, and the post‐illumination transient O 2‐uptake was suppressed. On the other hand, in maize leaves (a C4 plant), even in atmospheric CO 2/O 2 conditions, Y(II) paralleled the photosynthetic O 2‐evolution rate and the post‐illumination transient O 2‐uptake was suppressed. Hypothesizing that the post‐illumination transient O 2‐uptake is driven by C3 plant photorespiration in tobacco leaves, we calculated both the ribulose 1,5‐bisphosphate carboxylase‐ and oxygenase‐rates (Vc and Vo) from photosynthetic O 2‐evolution and the post‐illumination transient O 2‐uptake rates. These values corresponded to those estimated from simultaneous chlorophyll fluorescence/O 2‐exchange analysis. Furthermore, the H +‐consumption rate for ATP synthesis in both photosynthesis and photorespiration, calculated from both Vc and Vo that were estimated from chlorophyll fluorescence/CO 2‐exchange analysis, showed a positive linear relationship with the dissipation rate of the electrochromic shift signal. Thus, these findings support our hypothesis. 相似文献
3.
The dye H 2DCF-DA, which forms the fluorescent molecule DCF in the reaction with hydrogen peroxide, H 2O 2, was used to study light-induced H 2O 2 production in isolated intact chloroplasts and in protoplasts of mesophyll cells of Arabidopsis, pea, and maize. A technique to follow the kinetics of light-induced H 2O 2 production in the photosynthesizing cells using this dye has been developed. Distribution of DCF fluorescence in these cells
in the light has been investigated. It was found that for the first minutes of illumination the intensity of DCF fluorescence
increases linearly after a small lag both in isolated chloroplasts and in chloroplasts inside protoplast. In protoplasts of
Arabidopsis mutant vtc2-2 with disturbed biosynthesis of ascorbate, the rate of increase in DCF fluorescence intensity in chloroplasts was considerably
higher than in protoplasts of the wild type plant. Illumination of protoplasts also led to an increase in DCF fluorescence
intensity in mitochondria. Intensity of DCF fluorescence in chloroplasts increased much more rapidly than in cytoplasm. The
cessation of cytoplasmic movement under illumination lowered the rate of DCF fluorescence intensity increase in chloroplasts
and sharply accelerated it in the cytoplasm. It was revealed that in response to switching off the light, the intensity of
fluorescence of both DCF and fluorescent dye FDA increases in the cytoplasm in the vicinity of chloroplasts, while it decreases
in the chloroplasts; the opposite changes occur in response to switching on the light again. It was established that these
phenomena are connected with proton transport from chloroplasts in the light. In the presence of nigericin, which prevents
the establishment of transmembrane proton gradients, the level of DCF fluorescence in cytoplasm was higher and increased more
rapidly than in the chloroplasts from the very beginning of illumination. These results imply the presence of H 2O 2 export from chloroplasts to cytoplasm in photosynthesizing cells in the light; the increase in this export falls in the same
time interval as does the cessation of cytoplasmic movement. 相似文献
4.
DCMU-sensitive synthesis of ATP can be shown to continue in KCN-treated chloroplasts after cessation of O 2 evolution. The catalyst for this reaction, -phenylenediamine, also stimulates synthesis of ATP in NH 2OH-treated chloroplasts, but at much higher rates. This ATP synthesis can be observed in the presence of the quinone antagonist dibromothymoquinone, and under the appropriate conditions it is completely sensitive to DCMU. Since neither uptake nor evolution of O 2 can be observed during illumination, these results are interpreted as evidence for catalysis of cyclic photophosphorylation by photosystem II. 相似文献
5.
Summary The effect of anaerobic (N 2+CO 2) pre-incubation in the dark on photosynthetic reactions (O 2 evolution, measured manometrically and with the oxygraph; fluorescence; and photoproduction of H 2, measured with the mass spectrometer) was studied in algae with hydrogenase (strains of Chlorella fusca, C. kessleri, C. vulgaris f. tertia, and Ankistrodesmus braunii) and in algae without hydrogenase (strains of Chlorella vulgaris, C. saccharophila, and C. minutissima).The inhibition by anaerobic incubation of photosynthetic O 2 evolution is much stronger in algae without hydrogenase than it is in algae with hydrogenase. The effect of anaerobiosis is most pronounced at rather low light intensity (about 1000 lux), in acid medium (pH 4), and after prolonged anaerobic incubation in the dark (about 20 h). These results indicate that the presence of hydrogenase might be ecologically advantageous for algae under certain conditions.Chlorophyll fluorescence showed the fastest response to anaerobic incubation, and the most pronounced difference between algae with and without hydrogenase. After only 30 min under N 2+CO 2, fluorescence in algae with hydrogenase starts with a peak and decreases within 10 to 20 sec to a rather low steady-state level which is only slightly higher than that found under aerobic conditions. In algae without hydrogenase, fluorescence is rather low during the first 1 to 2 sec and then rises to a higher steady-state level which is much higher than that of the aerobic controls. This indicates an inhibition due to anaerobiosis of photosystem II in algae without hydrogenase.Algae with hydrogenase can react in different ways during the first minutes of illumination. In some cases there is an immediate photoproduction of H 2, which is followed after a few minutes by photosynthetic O 2 evolution; in other algae there is a simultaneous production of H 2 and O 2 from the very beginning; in a few experiments there was no photoproduction of H 2 at all, and in this case there was no photosynthetic O 2 evolution either. Thus, photoproduction of H 2 seems to be the process which normally enables algae with hydrogenase to oxidise and thereby activate their photosynthetic electron transport system after anaerobic incubation.A mass spectrometric search for nitrogen fixation (using N 2 and acetylene) in eucaryotic green algae gave negative results, even with species containing hydrogenase and under anaerobic conditions. 相似文献
6.
ATP production has been shown to take place on illumination of Rhodobacter sphaeroides chromatophores by a single light flash, i.e., in the absence of a proton gradient (which would form as a result of electron transport should a second flash occur). ATP synthesis was accompanied by H 2O 2 formation. Simultaneous formation of ATP and H 2O 2 is indicative of oxidative activation of phosphate during ATP synthesis, as in model systems with isolated chlorophyll. These data provide a theoretical background for selecting illumination parameters in laboratory and industrial photobioreactors used for cultivation of photosynthetic bacteria in biotechnological processes. 相似文献
7.
An increase of medium NaCl concentration induces Dunaliella cells to evolve O 2 photosynthetically even in the absence of CO 2. This NaCl-induced O 2 evolution may reflect the induced conversion of reserve carbohydrate to glycerol. The quantum yield for the NaCl-induced O 2 evolution, in the absence of CO 2, is 1.5-fold higher than that obtained for CO 2 fixation. Since the synthesis of glycerol from reserve carbohydrate in the absence of CO 2 requires only 0.5 ATP/NADPH, whereas photosynthesis requires at least 1.3 ATP/NADPH, it is concluded that the ATP/2e − ratio coupled to NADP reduction in Dunaliella is lower than required for CO 2 fixation. 相似文献
8.
With microsensors, we measured the steady‐state microprofiles of O 2, pH and Ca 2+ on the topside of young segments of Halimeda discoidea, as well as the surface dynamics upon light–dark shifts. The effect of several inhibitors was studied. The steady‐state measurements showed that under high light intensity, calcium and protons were taken up, while O 2 was produced. In the dark, O 2 was consumed, the pH decreased to below seawater level and Ca 2+ uptake was reduced to 50%. At low light intensity (12 mmol photons m ‐2 s ‐1), Ca 2+ efflux was observed. Upon light–dark shifts, a complicated pattern of both the pH and calcium surface dynamics was observed. Illumination caused an initial pH decrease, followed by a gradual pH increase: this indicated that the surface pH of H. discoidea is determined by more than one light‐induced process. When photosynthesis was inhibited by dichlorophenyl dimethyl urea (DCMU), a strong acidification was observed upon illumination. The nature and physiological function of this putative pump is not known. The calcium dynamics followed all pH dynamics closely, both in the presence and absence of DCMU. The Ca‐channel blockers verapamil and nifedipine had no effect on the Ca 2+ dynamics and steady‐state profiles. Thus, in H. discoidea, calcification is not regulated by the alga, but is a consequence of pH increase during photosynthesis. Acetazolamide had no effect on photosynthesis, whereas ethoxyzolamide inhibited photosynthesis at higher light intensities. Therefore, all carbonic anhydrase activity is intracellular. Carbonic anhydrase is required to alleviate the CO 2 limitation. Calcification cannot supply sufficient protons and CO 2 to sustain photosynthesis. 相似文献
9.
Light-dependent O 2 reduction concomitant with O 2 evolution, ATP formation, and NADP reduction were determined in isolated spinach ( Spinacia oleracea L. var. America) chloroplast lamellae fortified with NADP and ferredoxin. These reactions were investigated in the presence or absence of catalase, providing a tool to estimate the reduction of O 2 to H 2O 2 (Mehler reaction) concomitant with NADP reduction. In the presence of 250 micromolar O 2, O 2 photoreduction, simultaneous with NADP photoreduction, was dependent upon light intensity, ferredoxin, Mn 2+, NADP, and the extent of coupling of phosphorylation to electron flow. In the presence of an uncoupling concentration of NH4+, saturating light intensity (>500 watts/square meter), saturating ferredoxin (10 micromolarity) rate-limiting to saturating NADP (0.2-0.9 millimolarity), and Mn2+ (50-1000 micromolarity), the maxium rates of O2 reduction were 13-25 micromoles/milligram chlorophyll per hour, while concomitant rates of O2 evolution and NADP reduction were 69 to 96 and 134 to 192 micromoles/milligram chlorophyll per hour, respectively. Catalase did not affect the rate of NADPH or ATP formation but decreased the NADPH:O2 ratios from 2.3-2.8 to 1.9-2.1 in the presence of rate-limiting as well as saturating concentrations of NADP. Photosynthetic electron flow at a rate of 31 micromoles O2 evolved/milligram chlorophyll per hour was coupled to the synthesis of 91 micromoles ATP/milligram chlorophyll per hour, while the concomitant rate of O2 reduction was 0.6 micromoles/milligram chlorophyll per hour and was calculated to be associated with an apparent ATP formation of only 2 micromoles/milligram chlorophyll per hour. Thus, electron flow from H2O to O2 did not result in ATP formation significantly above that produced during NADP reduction. 相似文献
10.
Abstract Effect of light on the uptake, utilization and transport of sugars. — The effect of light on the uptake of saccharides, their incorporation into insoluble fractions and their transport by green tissues has been studied under conditions of complete inhibition of the photosynthetic assimilation of CO2. Such conditions were obtained by means of either an inhibitor of O2 evolution (CMU), or by running the experiment in CO2-free atmosphere. When Wolffia arryza plants are incubated with glucose-C14, light stimulates the incorporation of C14 into all fractions examined, and especially into the polysaccharides, like cellulose,' which are synthesized outside the chloroplasts. Experiments with Elodea canadensis have shown that light stimulates the transport of glucose-C14 from the leaves to the stems, independently of the presence or absence of CO2 assimilation. These experiments support the hypothesis that ATP synthesyzed in the light by chloroplasts can be utilized by green cells as an energy source for biosyntheses outside the plastids, as well as for other types of biological work, such as active uptake and transport. 相似文献
11.
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
12.
Regulation of light harvesting in response to changes in light intensity, CO 2 and O 2 concentration was studied in C 4 species representing three different metabolic subtypes: Sorghum bicolor (NADP-malic enzyme), Amaranthus edulis (NAD-malic enzyme), and Panicum texanum (PEP-carboxykinase). Several photosynthetic parameters were measured on the intact leaf level including CO 2 assimilation rates, O 2 evolution, photosystem II activities, thylakoid proton circuit and dissipation of excitation energy. Gross rates of O 2 evolution (
J\textO2 J_{{{\text{O}}_{2} }} , measured by analysis of chlorophyll fluorescence), net rates of O 2 evolution and CO 2 assimilation responded in parallel to changes in light and CO 2 levels. The C 4 subtypes had similar energy requirements for photosynthesis since there were no significant differences in maximal quantum
efficiencies for gross rates of O 2 evolution (average value = 0.072 O 2/quanta absorbed, ~14 quanta per O 2 evolved). At saturating actinic light intensities, when photosynthesis was suppressed by decreasing CO 2, ATP synthase proton conductivity ( g
H
+) responded strongly to changes in electron flow, decreasing linearly with
J\textO2 J_{{{\text{O}}_{2} }} , which was previously observed in C 3 plants. It is proposed that g
H
+ is controlled at the substrate level by inorganic phosphate availability. The results suggest development of nonphotochemical
quenching in C 4 plants is controlled by a decrease in g
H
+, which causes an increase in proton motive force by restricting proton efflux from the lumen, rather than by cyclic or pseudocyclic
electron flow. 相似文献
13.
Summary Manometric measurements show that oxygen evolution proceeds in synchronised cells of Ankistrodesmus braunii even in an atmosphere of pure nitrogen. In this case the slow oxygen evolution is dependent on the presence of nitrate (Table 1). Light saturation is found at a low light intensity at pH 5.6, at a higher light intensity at pH 8.0 (Fig. 1). The light saturation curves are in good agreement with those of 32P-labelling in Ankistrodesmus under the same conditions (Fig. 2).DCMU inhibition in N 2 of both O 2-evolution and 32P-labelling begins only at a DCMU concentration of 5×10 -7M or more. Complete inhibition of O 2-evolution is reached only at 10 -5M (Fig.3). In 32P-labelling a variable percentage is still left uninhibited at 10 -5 M DCMU (Fig. 4, Table 2), which is at least partly due to cyclic photophsphorylation. Nitrate starvation for several hours causes a considerable decrease in O 2-evolution and also in the sensitivity to those high concentrations of DCMU (Fig. 5), but it leads to a sensitivity to antimycin A not observed under normal conditions (Table 3). The effects of nitrate starvation thus become comparable to those of far-red light, under which noncyclic electron transport is slow or completely prevented.The inhibition by DCMU of electron transport in photosystem II is also estimated by measuring the increase in fluorescence at 684 nm in air containing additional CO 2. This fluorescence is saturated only at 10 -5M DCMU and shows that a certain percentage of photosystem II remains uninhibited at 5×10 -7M (Fig. 6), a concentration found to be almost ineffective in inhibiting O 2-evolution and 32P-labelling in an N 2-atmosphere.The results indicate that in synchronised cells of Ankistrodesmus noncyclic electron flow and noncyclic photophosphorylation can proceed in an atmosphere of pure nitrogen if nitrate is available as the electron acceptor. In this case noncyclic photophosphorylation, inspite of its low rates, still dominates over cyclic photphosphorylation. At low pH, when nitrate reduction is slow, cyclic photophosphorylation accounts for a greater part of the total phosphorylation than at high pH. Thus in the absence of CO 2 and O 2 cyclic photophosphorylation can be regarded as the main process of ATP formation only after nitrate starvation, in far-red light or in the presence of high concentrations of DCMU.Inhibition by DCMU, though very efficient under conditions of high photosynthetic activity, becomes rate-limiting only if the electron transport is so far reduced by DCMU that the remaining rate is of the same order as the low rate of the control or less. Therefore high concentrations of DCMU are required for the inhibition of low rates of noncyclic photophosphorylation. 相似文献
14.
In isolated intact chloroplasts, maximal rates of photosynthetic O 2 evolution (in saturating HCO ?3) are associated with a critical transthylakoid proton gradient as a result of the stoichiometric consumption of 2 mol NADPH and 3 mol ATP/mol CO 2 fixed. Studies with the fluorescent probe 9-aminoacridine reveal that in the illuminated steady state the critical ΔpH is 3.9.CO 2-dependent O 2 evolution is inhibited by increases of 0.1–0.2 in ΔpH that occur when catalase is omitted from the medium, NO ?2 is included as an electron acceptor, or when chloroplasts are illuminated under low partial pressures of O 2. Low concentrations of antimycin (0.33 μM) or NH 4Cl (0.33 mM) decrease ΔpH and relieve this inhibition of electron flow. The energy transfer inhibitor quercetin lowers the high ATP/ADP ratio associated with these conditions, but does not lower ΔpH or relieve the inhibition.A decrease of ΔpH below 3.9 by weaker illumination, millimolar levels of NH 4Cl or micromolar levels of antimycin, results in lower rates of photosynthesis owing to limitation by the phosphorylation rate.These findings show that in absence of rate limitation by the carbon cycle, the extent of thylakoid energization is related to the ratio of ATP to NADPH production and in turn, the rate of CO 2 assimilation. 相似文献
15.
A Haxo-Blinks rate-measuring oxygen electrode together with a modulated light source gave an average current signal (change in net O 2 exchange) and a modulated current signal (photosynthetic O 2 evolution). Using this apparatus, net O 2 exchange and photosynthetic O 2 evolution at low intensities have been studied in the green alga, Chlamydomonas reinhardi. At both 645 nm and 695 nm, the curves of net O 2 exchange as a function of light intensity were steeper at lowest intensities than about compensation, indicative of the Kok effect. The effect was greater at 695 nm than at 645 nm. The corresponding curves of photosynthetic O 2 evolution, on the other hand, showed no Kok effect; here, the slope was lowest at lowest intensity. The absence of the Kok effect in O 2 evolution, together with its sensitivity to monofluoroacetic acid, show that it is due to an interaction of photosynthesis and respiration. The effect was exaggerated by 3-(3,4-dichlorophenyl)-1,1-dimethylurea. In the presence of concentrations of this inhibitor sufficient to inhibit O 2 evolution completely, a light-induced change in net O 2 exchange remained. This was interpreted as a system I dependent depression of respiratory O 2 uptake. The Kok effect remained undiminished in concentrations of carbonyl cyanide m-chlorophenylhydrazone and 2,4-dinitrophenol which partially uncoupled either oxidative phosphorylation alone or both oxidative and photosynthetic phosphorylations. The above results can be explained within a model of the Kok effect in which O 2 uptake is depressed by diversion of reductant away from respiratory electron transport and into photosystem I. The same photodepression of O 2 uptake also appears to account for a transient in net O 2 exchange seen in several algae upon turning off the light. 相似文献
16.
Application of NaHSO 3 solution at low concentrations (20–200 μM) to the culture medium enhanced photosynthetic oxygen evolution in cyanobacterium
Synechocystis PCC6803 by more than 10%. The slow phase of ms-DLE was strengthened, showing that the transmembrane proton motive force related
to photophosphorylation was enhanced. It was also observed that dry weight as well as ATP content under illuminated conditions
were both increased after the treatment, indicating that low concentrations of NaHSO 3 could enhance the supply of ATP and thus increase biomass accumulation. In accord with the promotion in the photosynthetic
oxygen evolution and ATP content, the transient increase in chlorophyll fluorescence after the termination of actinic light
was increased; and meanwhile, the half-time of re-reduction of P700 + in the presence of DCMU after a pulse light under background far-red light was shortened by approximately 30%, indicating
that cyclic electron flow around PS I was accelerated by the treatment. Based on these results it is suggested that the increase
in photosynthesis in Synechocystis PCC6803 caused by low concentrations of NaHSO 3 solution might be due to the stimulation of the cyclic electron flow around PS I and thus the increase in photophosphorylation.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
17.
Intact Lemna gibba plants were photoinhibited under anaerobic conditions on illumination with monochromatic light which selectively excited the photosystems. Photoinhibition was less when PS 1 was excited and greatest when mainly PS 2 was excited, which suggests that PS 2 was most damaged by photoinhibition induced in complete absence of O 2 and CO 2.The illumination of plants with monochromatic light exciting PS 1, at different O 2 concentrations (in CO 2 deficient conditions), showed that PS 1 photoinhibition was increased at the low O 2 concentrations. The damage to PS 1 was more evident at 2% O 2 than at the higher O 2 concentrations.CO 2 as well as O 2 at atmospheric concentration, (air), was necessary for complete protection of the plant from photoinhibition when both photosystems were excited either separately or together.Abbreviations I
irradiance, photon fluence rate
- PCO
photosynthetic carbon oxidation cycle
- PCR
photosynthetic carbon reduction cycle
- PS 1
photosystem 1
- PS 2
photosystem 2 相似文献
18.
Changes in chlorophyll fluorescence yield were studied during a dark period in pre-illuminated leaves of various C3 and C4 plants. The oxygen content in the gaseous atmosphere was either normal (21 kPa) or low (1.5 or 0.36 kPa). C3 and C4 plants of the NAD malic enzyme subgroup showed an initial rise in fluorescence at the onset of the dark period with an amplitude depending on the O 2 level in the gas. In C4 plants belonging to the other two subgroups, the slow rise was absent or of very low size. At high [O 2], the fluorescence level decreased in some minutes to the initial F 0 level (determined in dark-adapted leaves). Conversely at low [O 2], the fluorescence yield remained higher than F 0 in all the C4 plants studied, whereas it decreased slowly to the F 0 level in the different C3 plants. At low [O 2], the fluorescence level decreased rapidly to F 0 when introducing for 30 s, a high O 2 level or when giving a 15-s far-red illumination. At the end of these treatments, the fluorescence level re-increased. These results demonstrate the presence at low [O 2] of highly fluorescent ‘closed' photosystem II centres containing Q-A in equilibrium with reduced plastoquinone molecules of the chloroplastic pool. Reoxidation of the plastoquinone pool would be dependent on the functioning of an oxidase probably dependent on a chlororespiration process fully active at O 2 levels higher than 2 kPa. The source of reducing equivalents for the plastoquinone pool is discussed. 相似文献
19.
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
20.
Soybean ( Glycine max cv Hodgson) nitrogenase activity (C 2H 2 reduction) in the presence or absence of nitrate was studied at various external O 2 tensions. Nitrogenase activity increased with oxygen partial pressure up to 30 kilopascals, which appeared to be the optimum. A parallel increase in ATP/ADP ratios indicated a limitation of respiration rate by low O 2 tensions in the nodule, and the values found for adenine nucleotide ratios suggested that the nitrogenase activity was limited by the rate of ATP regeneration. In the presence of nitrate, the nitrogenase activity was low and less stimulated by increased pO 2, although the nitrite content per gram of nodules decreased from 0.05 to 0.02 micromole when pO 2 increased from 10 to 30 kilopascals. Therefore, the accumulation of nitrite inside the nodule was probably not the major cause of the inhibition. Instead, inhibition by nitrate could be due to competition for reducing power between nitrate reduction and bacteroid or mitochondrial respiration inside the nodule. This is supported by the observation of decrease in ATP/ADP ratios from 1.65, in absence of nitrate, to 0.93 in the presence of this anion at 30 kilopascals O 2. Furthermore, the inhibition was suppressed by the addition, to the plant nutrient solution, of 15 millimolar l-malate, a carbon substrate that is considered to be the major source of reductant for the bacteroids in the symbiosis. 相似文献
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