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1.
Wheat ( Triticum aestivum L. cv Albis) was grown in open-top chambers in the field and fumigated daily with charcoal-filtered air (0.015 microliters per liter O 3), nonfiltered air (0.03 microliters per liter O 3), and air enriched with either 0.07 or 0.10 microliters per liter ozone (seasonal 8 hour/day [9 am-5 pm] mean ozone concentration from June 1 until July 10, 1987). Photosynthetic 14CO 2 uptake was measured in situ. Net photosynthesis, dark respiration, and CO 2 compensation concentration at 2 and 21% O 2 were measured in the laboratory. Leaf segments were freeze-clamped in situ for the determination of the steady state levels of ribulose 1,5-bisphosphate, 3-phosphoglycerate, triose-phosphate, ATP, ADP, AMP, and activity of ribulose, 1,5-bisphosphate carboxylase/oxygenase. Photosynthesis of flag leaves was highest in filtered air and decreased in response to increasing mean ozone concentration. CO 2 compensation concentration and the ratio of dark respiration to net photosynthesis increased with ozone concentration. The decrease in photosynthesis was associated with a decrease in chlorophyll, soluble protein, ribulose bisphosphate carboxylase/oxygenase activity, ribulose bisphosphate, and adenylates. No decrease was found for triose-phosphate and 3-phosphoglycerate. The ratio of ATP to ADP and of triosephosphate to 3-phosphoglycerate were increased suggesting that photosynthesis was limited by pentose phosphate reductive cycle activity. No limitation occurred due to decreased access of CO 2 to photosynthetic cells since the decrease in stomatal conductance with increasing ozone concentration did not account for the decrease in photosynthesis. Ozonestressed leaves showed an increased degree of activation of ribulose bisphosphate carboxylase/oxygenase and a decreased ratio of ribulose bisphosphate to initial activity of ribulose bisphosphate carboxylase/oxygenase. Nevertheless, it is suggested that photosynthesis in ozone stressed leaves is limited by ribulose bisphosphate carboxylation possibly due to an effect of ozone on the catalysis by ribulose bisphosphate carboxylase/oxygenase. 相似文献
2.
A simple approach to determine CO 2/O 2 specificity factor () of ribulose 1,5-bisphosphate carboxylase/oxygenase is described. The assay measures the amount of CO 2 fixation at varying [CO 2]/[O 2] ratios after complete consumption of ribulose 1,5-bisphosphate (RuBP). Carbon dioxide fixation catalyzed by the carboxylase was monitored by directly measuring the moles of 14CO 2 incorporated into 3-phosphoglycerate (PGA). This measurement at different [CO 2]/[O 2] ratios is used to determine graphically by several different linear plots the total RuBP consumed by the two activities and the CO 2/O 2 specificity factor. The assay can be used to measure the amounts of products of the carboxylase and oxygenase reactions and to determine the concentration of the substrate RuBP converted to an endpoint amount of PGA and phosphoglycolate. The assay was found to be suitable for all [CO 2]/[O 2] ratios examined, ranging from 14 to 215 micromolar CO 2 (provided as 1–16 mM NaHCO 3) and 614 micromolar O 2 provided as 50% O 2. The procedure described is extremely rapid and sensitive. Specificity factors for enzymes of highly divergent values are in good agreement with previously published data.Abbreviations HEPPS
N-(2-hydroxyethyl)piperazine-N-(3-propanesulfonic acid)
- L
large subunit of rubisco
- PGA
3-phosphoglyceric acid
- rubisco
ribulose 1,5-bisphosphate carboxylase/oxygenase
- RuBP
d-ribulose 1,5-bisphosphate
- S
small subunit of rubisco
- XuBP
d-xylulose 1,5-bisphosphate 相似文献
3.
An assay was developed for simultaneous kinetic analysis of the activities of the bifunctional plant enzyme ribulose 1,5-bisphosphate carboxylase/oxygenase [EC 4.1.1.39]. [1- 14C,5- 3H]Ribulose 1,5-bisphosphate (RuBP) was used as the labeled substrate. Tritium enrichment of the doubly labeled 3-phosphoglycerate (3-PGA) product, common to both enzyme activities, may be used to calculate V c/V o ratios from the expression A/(B-A) where A and B represent the 3H/ 14C isotope ratios of doubly labeled RuBP and 3-PGA, and V c and V o represent the activities of carboxylase and oxygenase, respectively. Doubly labeled substrate was synthesized from [2- 14C]glucose and [6- 3H]glucose using the enzymes of the pentose phosphate pathway coupled with phosphoribulokinase. 相似文献
4.
Nitrogen effects on the regulation of photosynthesis in wheat ( Triticum aestivum L., cv Remia) seedlings were examined. Ribulose 1,5-bisphosphate carboxylase/oxygenase was rapidly extracted and tested for initial activity and for activity after incubation in presence of CO 2 and Mg 2+. Freeze clamped leaf segments were extracted for determinations of foliar steady state levels of ribulose 1,5-bisphosphate, triose phosphate, 3-phosphoglycerate, ATP, and ADP. Nitrogen deficient leaves showed increased ATP/ADP and triose phosphate/3-phosphoglycerate ratios suggesting increased assimilatory power. Ribulose 1,5-bisphosphate levels were decreased due to reduced pentose phosphate reductive cycle activity. Nevertheless, photosynthesis appeared to be limited by ribulose 1,5-bisphosphate carboxylase/oxygenase, independent of nitrogen nutrition. Its degree of activation was increased in nitrogen deficient plants and provided for maximum photosynthesis at decreased enzyme protein levels. It is suggested that ribulose 1,5-bisphosphate carboxylase/oxygenase activity is regulated according to the amount of assimilatory power. 相似文献
5.
A new method is presented for measurement of the CO 2/O 2 specificity factor of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco). The [ 14C]3-phosphoglycerate (PGA) from the Rubisco carboxylase reaction and its dilution by the Rubisco oxygenase reaction was monitored by directly measuring the specific radioactivity of PGA. 14CO 2 fixation with Rubisco occurred under two reaction conditions: carboxylase with oxygenase with 40 micromolar CO 2 in O 2-saturated water and carboxylase only with 160 micromolar CO 2 under N 2. Detection of the specific radioactivity used the amount of PGA as obtained from the peak area, which was determined by pulsed amperometry following separation by high-performance anion exchange chromatography and the radioactive counts of the [ 14C]PGA in the same peak. The specificity factor of Rubisco from spinach ( Spinacia oleracea L.) (93 ± 4), from the green alga Chlamydomonas reinhardtii (66 ± 1), and from the photosynthetic bacterium Rhodospirillum rubrum (13) were comparable with the published values measured by different methods. 相似文献
6.
Two dual label methods were used to investigate kinetic variability of ribulose 1,5-bisphosphate (RuBP) carboxylase/oxygenase (EC 4.1.1.39). In addition to using [1- 14C,5- 3H]RuBP (method 1), we describe here the detailed assay with 14CO 2 and [5- 3H]RuBP (method 2), which generates [ 3H, 14C]3-phosphoglyceric acid and unlabeled (noncontaminating) phosphoglycolate; the carboxylase/oxygenase activity ratio ( vc/vo) is calculated from 3H/ 14C ratios of substrates and products. vc/vo was found to be a linear function of [CO 2]/[O 2], constant over a 4-minute assay interval, and invariant of the degree of enzyme activity. Accurately measurable vc/vo ratios range from approximately 0.3 to 6. The Km and Vmax of both enzymes may be determined as a composite constant, VcKo/VoKc. By method 2, the directly compared, relative values at 40 micromolar CO 2 and 1240 micromolar O 2 were: Spinacia oleracea (74), Chlorella pyrenoidosa (31), Plectonema boryanum (32), and Rhodospirillum rubrum (8). With method 1, the values for S. oleracea and R. rubrum were 75, and 9, respectively. Under tight experimental controls, the absolute value for S. oleracea was 69 ± 3. 相似文献
7.
The level of 2-carboxyarabinitol 1-phosphate (CA1P) in leaves of 12 species was determined by an isotope dilution assay. 14C-labeled standard was synthesized from [2- 14C]carboxyarabinitol 1,5-bisphosphate using acid phosphatase, and was added at the initial point of leaf extraction. Leaf CA1P was purified and its specific activity determined. CA1P was found in dark-treated leaves of all species examined, including spinach ( Spinacea oleracea), wheat ( Triticum aestivum), Arabidopsis thaliana, and maize ( Zea mays). The highest amounts were found in bean ( Phaseolus vulgaris) and petunia ( Petunia hybrida), which had 1.5 to 1.8 moles CA1P per mole ribulose 1,5-bisphosphate carboxylase catalytic sites. Most species had intermediate amounts of CA1P (0.2 to 0.8 mole CA1P per mole catalytic sites). Such intermediate to high levels of CA1P support the hypothesis that CA1P functions in many species as a light-dependent regulator of ribulose 1,5-bisphosphate carboxylase activity and whole leaf photosynthetic CO 2 assimilation. However, CA1P levels in spinach, wheat, and A. thaliana were particularly low (less than 0.09 mole CA1P per mole catalytic sites). In such species, CA1P does not likely have a significant role in regulating ribulose 1,5-bisphosphate carboxylase activity, but could have a different physiological role. 相似文献
8.
A sensitive assay procedure is described for the simultaneous determination of ribulose-1,5-bisphosphate (RuBP) carboxylase and oxygenase activities. In this assay, [1- 3H]RuBP is incubated with 14CO 2 and O 2. Carboxylation rate is determined from 14CO 2 incorporation and oxygenation rate is determined from [2- 3H]glycolate-phosphate production. The assay was found to be suitable at all CO 2 and O 2 concentrations examined, which ranged from 0 to 300 micromolar CO 2 (20 millimolar NaHCO 3) and 0 to 1.15 millimolar (100%) O 2. In combination with a polarographic assay, the stoichiometry of the RuBP oxygenase reaction was found to be RuBP-O 2-glycolate phosphate-glycerate phosphate (1:1:1:1). 相似文献
9.
Ribulose bisphosphate carboxylase (rubisco) is the first enzyme in photosynthetic CO 2 assimilation. It is also the single largest sink for nitrogen in plants. Several parameters of rubisco activity are often measured including initial activity upon extraction, degree of carbamylation, catalytic constant of the enzyme (k cat), and the total amount of enzyme present in a leaf. We report here improvements of the photometric assay of rubisco in which rubisco activity is coupled to NADH oxidation which is continuously monitored in a photometer. The initial lag usually found in this assay was eliminated by assaying rubisco activity at pH 8.0 instead of 8.2, using a large amount of phosphoglycerate kinase, and adding monovalent cations to the assay buffer. We found that when using the photometric assay, the ratio of activity found initially upon extraction divided by the activity after incubating with CO 2 and Mg 2+ reflects the degree of carbamylation as determined by 14carboxyarabinitol bisphosphate/ 12carboxyarabinitol bisphosphate competition. We developed methods for measuring the catalytic constant of rubisco as well as the total amount of enzyme present using the photometric assay and carboxyarabinitol 1,5-bisphosphate. We believe that the photometric assay for activity will prove more useful than the 14CO 2 assay in many studies.Abbreviations CA1P
2-carboxyarabinitol 1-phosphate
- GAP
glyceraldehyde 3-phosphate
- OD
optical density
- PGA
3-phosphoglycerate
- rubisco
ribulose-1,5-bisphosphate carboxylase/oxygenase
- RuBP
ribulose 1,5-bisphosphate 相似文献
10.
Ribulose-1,5-bisphosphate carboxylase activity was found in endosperm of germinating castor bean seed Ricinus communis and was localized in proplastids. The endosperm carboxylase has been extensively purified and is composed of two different subunits. The molecular weights of the native carboxylase and its subunits were 560,000, 55,000, and 15,000 daltons, respectively. The Michaelis-Menten constants, Km, for the endosperm carboxylase with respect to ribulose 1,5-bisphosphate, bicarbonate, CO 2, and magnesium in millimolar are 0.54, 13.60, 0.92, and 0.57, respectively. The endosperm carboxylase was activated by Mg 2+ and HCO 3−. The preincubation of the carboxylase with 1 millimolar HCO 3− and 5 millimolar MgCl 2 resulted in activation by low and inhibition by high concentrations of 6-phosphogluconate. In studies of dark 14CO2 fixation by endosperm slices, [14C]malate and [14C]citrate were the predominantly labeled products after 30 seconds of exposure of the tissue to H14CO3−. In pulse-chase experiments, 87% of the label is malate, and citrate was transferred to sugars after a 60-minute chase with a small amount of the label appearing in the incubation medium as 14CO2. The minimal incorporation of the label from 14CO2 into phosphoglyceric acid indicated a lack of the endosperm ribulose-1,5-bisphosphate carboxylase participation in the endosperm's CO2 fixation system. The activities of key Calvin cycle enzymes were examined in the endosperms and cotyledons of dark-grown castor bean seedlings. Many of these autotrophic enzymes develop in the dark in these tissues. The synthesis of ribulose-1,5-bisphosphate carboxylase in the nonphotosynthetic endosperms is not repressed in the dark, and high levels of enzymic activity appear with germination. All of the Calvin cycle enzymes are present in the castor bean endosperm except NADP-linked glyceraldehyde 3-P dehydrogenase, and the absence of this dehydrogenase probably prevents the functioning of these series of reactions in dark CO2 fixation. 相似文献
11.
At bicarbonate concentrations equivalent to air levels of CO 2, activation of ribulosebisphosphate carboxylase/oxygenase (rubisco) was inhibited by micromolar concentrations of glyoxylate in intact, lysed, and reconstituted chloroplasts and in stromal extracts. The concentration of glyoxylate required for 50% inhibition of light activation in intact chloroplasts was estimated to be 35 micromolar. No direct inhibition by glyoxylate was observed with purified rubisco or rubisco activase at micromolar concentrations. Levels of ribulose 1,5-bisphosphate and ATP increased in intact chloroplasts following glyoxylate treatment. Results from experiments with well-buffered lysed and reconstituted chloroplast systems ruled out lowering of pH as the cause of inhibition. With intact chloroplasts, micromolar glyoxylate did not prevent activation of rubisco at high (10 mM) concentrations of bicarbonate, indicating that rubisco could be spontaneously activated in the presence of glyoxylate. These results suggest the existence of a component of the in vivo rubisco activation system that is not yet identified and which is inhibited by glyoxylate.Abbreviations PEP
phosphoenolpyruvate
- PGA
3-phosphoglycerate
- rubisco
ribulosebisphosphate carboxylase/oxygenase
- RuBP
ribulose 1,5-bisphosphate 相似文献
12.
Xylulose 1,5-bisphosphate (XuBP) is synthesized from ribulose 1,5-bisphosphate (RuBP) at carbamylated catalytic sites on ribulose 1,5-bisphosphate carboxylase (Rubisco) with significant amounts of XuBP being formed at pH less than 8.0. XuBP has been separated by high performance liquid chromatography and identified by pulsed amperometry from compounds bound to Rubisco during catalysis with the purified enzyme and from celery ( Apium graveolens var Utah) leaf extracts. XuBP does not bind tightly to carbamylated sites, but does bind tightly to decarbamylated sites. Upon incubation of fully activated Rubisco with 5 micromolar XuBP, loss of activator CO 2 occurred before XuBP bound to the enzyme catalytic sites, even in the presence of excess CO 2 and Mg 2+. Binding of XuBP to decarbamylated Rubisco sites was highly pH dependent. At pH 7.0 and 7.5 with 10 millimolar MgCl 2 and 10 millimolar KHCO 3, the apparent dissociation constant for XuBP, Kd, was 0.03 micromolar, whereas at pH 8.0 and 8.5, the apparent Kd was 0.35 and 2.0 micromolar, respectively. This increase in Kd with pH was a result of a decrease in the association rate constant and an increase in the dissociation rate constant of XuBP bound to decarbamylated sites on Rubisco. The Kd of 2-carboxyarabinitol 1-phosphate binding to carbamylated sites was only slightly pH dependent. 相似文献
13.
Crystalline ribulose 1,5-bisphosphate carboxylase-oxygenase (EC 4.1.1.39) was isolated from tobacco ( Nicotiana tabacum L.) leaf homogenates and the two competing reactions were examined for differential regulation in vitro by temperature pretreatment and chloroplast metabolites. Both the carboxylase and oxygenase activities were inactivated 50% by storing the dissolved protein at 0 °C and fully reactivated by heating the solution at 50 °C in the absence of Mg 2+ and a sulfhydryl reagent. When the heat-activated enzyme was preincubated with physiological levels of various chloroplast metabolites and CO 2 and the two reactions were assayed simultaneously in the same reaction vessel upon initiation with ribulose 1,5-bisphosphate, three classes of effectors were observed: (a) those which stimulated both activities (NADPH, 6-phosphogluco-bisphosphate gluconate, fructose 1,6-bisphosphate, 3-phosphoglycerate glycerate), (b) those which essentially had no effect (fructose 6-phosphate, glucose 6-phosphate), and (c) one, ribose 5-phosphate, which inhibited the two reactions. However, within the limits of experimental error, none of the metabolites examined produced a differential regulation of the ribulose 1,5-bisphosphate carboxylase-oxygenase activities. The similar response of the two competing activities to temperature pretreatment and various chloroplast metabolites is consistent with the notion that both reactions are associated with the same or adjacent catalytic sites on this bifunctional enzyme. 相似文献
14.
Ribulose 1,5-bisphosphate in the chloroplast has been suggested to regulate the activity of the ribulose bisphosphate carboxylase/oxygenase. To generate high levels of ribulose bisphosphate, isolated and intact spinach chloroplasts were illuminated in the absence of CO 2. Under these conditions, chloroplasts generate internally up to 300 nanomoles ribulose 1,5-bisphosphate per milligram chlorophyll if O 2 is also absent. This is equivalent to 12 millimolar ribulose bisphosphate, while the enzyme, ribulose bisphosphate carboxylase, offers up to 3.0 millimolar binding sites for the bisphosphate in the chloroplast stroma. During illumination, the ribulose bisphosphate carboxylase is deactivated, due mostly to the absence of CO 2 required for activation. The rate of deactivation of the ribulose bisphosphate carboxylase was not affected by the chloroplast ribulose bisphosphate levels. Upon addition of CO 2, the carboxylase in the chloroplast was completely reactivated. Of interest, addition of 3-phosphoglycerate stopped deactivation of the carboxylase in the chloroplast while ribulose bisphosphate accumulated. With intact chloroplasts in light, no correlation between deactivation of the carboxylase and ribulose bisphosphate levels could be shown. 相似文献
15.
Isolated mesophyll protoplasts from Valerianella locusta L. were subjected to freeze-thaw cycles. Subsequently, steady-state pool sizes of 14C-labeled intermediates of the photosynthetic carbon reduction cycle were determined by high performance liquid chromatography. Protoplasts in which CO 2 fixation was inhibited by preceding freezing stress, showed a strong increase in the proportion of fructose-1,6-bisphosphate, sedoheptulose-1,7-bisphosphate and triose phosphates. These results indicate an inhibition of the activities of stromal fructose-1,6-bisphosphatase and sedoheptulose-1,7-bisphosphatase. Furthermore, freezing stress caused a slight increase in the proportion of labeled ribulose-1,5-bisphosphate, which may be based on an inhibition or ribulose bisphosphate carboxylase activity. It was shown earlier (Rumich-Bayer and Krause 1986) that freezing-thawing readily affects photosynthetic CO 2 assimilation independently of thylakoid inactivation. The present results are interpreted in terms of an inhibition of the light-activation system of the photosynthetic carbon reduction cycle, caused by freezing stress.Abbreviations FBP
Fructose-1,6-bisphosphate
- HMP
Hexose Monophosphates
- PGA
3-phosphoglycerate
- PMP
Pentose Monophosphates
- RBP
Ribulose-1,5-bisphosphate
- SBP
Sedoheptulose-1,7-bisphosphate
- TP
Triose Phosphates 相似文献
16.
A rapid method to determine the CO 2/O 2 specificity factor of ribulose 1,5-bisphosphate carboxylase/oxygenase is presented. The assay measures the amount of CO 2 and O 2 fixation at varying CO 2/O 2 ratios to determine the relative rates of each reaction. CO 2 fixation is measured by the incorporation of the moles of 14CO 2 into 3-phosphoglycerate, while O 2 fixation is determined by subtraction of the moles of CO 2 fixed from the moles of RuBP consumed in each reaction. By analyzing the inorganic phosphate specifically hydrolyzed from RuBP under alkaline conditions, the amount of RuBP present before and after catalysis by rubisco can be determined. 相似文献
17.
Barley, Panicum milioides and Panicum maximum were exposed to 14CO 2 near their photosynthetic CO 2 compensation points and their respective 14C-products were determined. In short exposure times Panicum maximum had 100% of its 14C in malate and aspartate whereas Panicum milioides and barley had 16 and 3% of their respective 14C in C 4 organic acids. Near the respective CO 2 compensation points a linear relationship occurs in plotting the ratio of glycine, serine, and glycerate to C 4 organic acids. The ratio of ribulose 1,5-bisphosphate oxygenase to phosphoenolpyruvate carboxylase is linear with their CO 2 compensation points. The photosynthetic CO 2 compensation point apparently is controlled by the activity of enzymes producing photorespiration metabolites and the activity of phospheonolpyruvate carboxylase. 相似文献
18.
Complete stoichiometry of the reaction catalyzed by ribulose 1,5-bisphosphate (RuBP) oxygenase from spinach and Rhodospirillum rubrum has been determined. Before initiation and after termination, RuBP has been measured either by release of equimolar orthophosphate at 25°C in the presence of 1 n NaOH or by complete carboxylation using 14CO 2 and RuBP carboxylase. The RuBP-dependent oxygen consumption has been measured continuously with an oxygen electrode. After termination of catalysis, 3-phosphoglycerate production has been determined spectrophotometrically using phosphoglycerokinase, glyceraldehyde-3-phosphate dehydrogenase, triose phosphate isomerase, α-glycerophosphate dehydrogenase, ATP, and NADH. To measure phosphoglycolate, this product was first hydrolyzed with alkaline phosphatase and the resultant glycolate oxidized by glycolate oxidase. Attendant H 2O 2 formation catalyzed by peroxidase has then been measured colorimetrically. Interference by ribulose in the measurement of glycolate can be easily corrected. Procedures are rapid and do not require separation of reactants and products. Results are in excellent accord with the expected stoichiometry for catalysis by RuBP oxygenase and also enable an estimate of competing catalysis by RuBP carboxylase. 相似文献
19.
When envelope-free spinach chloroplasts are incubated with stromal protein, catalytic NADP, catalytic ADP, radioactive bicarbonate and fructose 1,6-bisphosphate, 14CO 2 fixation starts immediately upon illumination but oxygen evolution is delayed. The delay is increased by the addition of fructose 6-phosphate and by a variety of factors known (or believed) to increase fructose bisphosphatase activity (such as dithiothreitol, more alkaline pH, higher [Mg] and antimycin A). Conversely, the lag can be decreased or eliminated by the addition of an ATP-generating system. Bearing in mind the known inhibition, by ADP, of sn-phospho-3-glycerate (3-phosphoglycerate) reduction it is concluded that the lag in O 2 evolution results from the production of ribulose 5-phosphate from fructose bisphosphate and that this in turn inhibits the reoxidation of NADPH by adversely affecting the ADP/ATP ratio. The results are discussed in their relation to the mode of action of antimycin A and to regulation of the reductive pentose phosphate pathway. 相似文献
20.
Bundle sheath strands capable of assimilating up to 68 μmoles CO 2 per mg chlorophyll per hr in the dark have been isolated from fully expanded leaves of Zea mays L. This dark CO 2-fixing system is dependent on exogenous ribose-5-phosphate, ADP or ATP, and Mg 2+ for maximum activity. The principal product of dark fixation in this system is 3-phosphoglycerate, indicating that the CO 2-fixing reaction is mediated by ribulose-1,5-bisphosphate carboxylase (EC 4.1.1.39). The rate of dark CO 2 uptake in the strands in the presence of saturating levels of ribose-5-phosphate plus ADP is inhibited by oxygen. The inhibitory effect of oxygen is rapidly and completely reversible, and is relieved by increased levels of CO 2. Glycolate is synthesized in this dark system in the presence of [U- 14C]ribose-5-phosphate, ADP, oxygen, and an inhibitor of glycolate oxidase (EC 1.1.3.1). Glycolate formation is completely abolished by heating the strands, and the rate of glycolate synthesis is markedly reduced by either lowering the oxygen tension or increasing the level of CO 2.These results, obtained with intact cells in the absence of light, indicate that the direct inhibitory effect of oxygen on photosynthesis is associated with photosynthetic carbon metabolism, probably at the level of ribulose-1,5-bisphosphate carboxylase, and not with photophosphorylation or photosynthetic electron transport. Furthermore, the findings indicate that the synthesis of glycolate from exogenous substrate can readily occur in the absence of photosynthetic electron transport, an observation consistent with the ribulose-1, 5-bisphosphate “oxygenase” scheme for glycolate formation during photosynthesis. 相似文献
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