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1.
Summary
14CO 2-fixation rates in green carrot callus cultres (about 35 g chlorophyll/g fresh wt) were determined in gaseous and liquid media using a range of light intensities and CO 2 concentrations. Main products of light-dependent CO 2-fixation were sucrose, alanine, glutamine, serine/glycine and malic acid. In darkness, glutamine and malic acid were formed.Light CO 2-fixation rates were about ten times higher than dark fixation rates and reached 50–90 mol/mg chlorophyll/h in 10000 lux, 1% CO 2 in air. Net O 2-evolution by the tissue was demonstrated polarographically under these conditions. Light CO 2-fixation rates were linearly related to chlorophyll levels while dark fixation was independent of chlorophyll content. Lowered O 2 partial pressures in gaseous conditions increased 14CO 2-fixation rates. Ribulose diphosphate carboxylase and phosphoenol pyruvate carboxylase activities and their distribution in subcellular fractions were examined.When carrot tissue cultures were grown for two or four weeks on agar media lacking a carbohydrate source, in 10000 lux and 1% CO 2 in either air or N 2, dry weight increases were obtained although chlorophyll levels eventually declined. 相似文献
2.
To evaluate the relative significance of CO 2-fixing enzymes in the metabolism of rat brain, the subcellular distribution of pyruvate carboxylase, phosphoenolpyruvate carboxykinase, NADP-isocitrate dehydrogenase and NADP-malate dehydrogenase, as well as the fixation of H 14CO 3? by the cytosol and the mitochondria was investigated. Pyruvate carboxylase and phosphoenol-pyruvate carboxykinase are mainly localized in the mitochondria whereas NADP-isocitrate dehydrogenase and NADP-malate dehydrogenase are present in both the cytosol and the mitochondria. In the presence of pyruvate rat brain mitochondria fixed H 14CO 3? at a rate of about 170 nmol/g of tissue/min whereas these organelles fixed negligible amounts of H 14CO 3? in the presence of α-ketoglutarate or phosphoenolpyruvate. Rat brain cortex slices fixed H 14CO 3? at a rate of about 7 nmol/g of tissue/min and it was increased by two-fold when pyruvate was added to the incubation medium. The carboxylation of α-ketoglutarate and pyruvate by the reversal of the cytosolic NADP-isocitrate dehydrogenase and NADP-malate dehydrogenase respectively was very low as compared to that by pyruvate carboxylase. The rate of carboxylation reaction of both NADP-isocitrate dehydrogenase and NADP-malate dehydrogenase was only about 1/10th of that of decarboxylation reaction of the same enzyme. It is suggested that under physiological conditions these two enzymes do not play a significant role in CO 2-fixation in the brain. In rat brain cytosol, citrate is largely metabolized to α-ketoglutarate by a sequential action of aconitate hydratase and NADP-isocitrate dehydrogenase. The operation of the citrate-cleavage pathway in rat brain cytosol is demonstrated. The data show that among four CO 2-fixing enzymes, pyruvate carboxylase, an anaplerotic enzyme, plays the major role in CO 2-fixation in the brain. 相似文献
3.
Euglena gracilis strain (Z) cells were synchronized under photoautotrophic conditions using a 14 hour light:10 hour dark regimen. The cells grew during the light period (growth phase) and divided during the following 10 hour period either in the dark or in the light (division phase). Changes in morphology of the pyrenoid and in the distribution of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) within the chloroplasts were followed by immunoelectron microscopy during the growth and division phases of Euglena cells. Epon-embedded sections were labeled with an antibody to the holoenzyme followed by protein A-gold. The immunoreactive proteins were concentrated in the pyrenoid, and less densely distributed in the stroma during the growth phase. During the division phase, the pyrenoid could not be detected and the gold particles were dispersed throughout the stroma. Toward the end of the division phase, the pyrenoid began to form in the center of a chloroplast, and the immunoreactive proteins started to concentrate over that rudimentary pyrenoid. During the growth phase, small areas rich in gold particles, called `satellite pyrenoid,' were observed, in addition to the main pyrenoid. From a comparison of photosynthetic CO 2-fixation with the total carboxylase activity of Rubisco extracted from Euglena cells in the growth phase, it is suggested that the carboxylase in the pyrenoid functions in CO 2-fixation in photosynthesis. 相似文献
4.
Photosynthetic CO 2-fixation in isolated pea ( Pisum sativum L., cv Little Marvel) chloroplasts during induction is markedly inhibited by 0.4 millimolar sulfite. Sulfate at the same concentration has almost no effect. The 14CO 2-fixation pattern indicates that the primary effect of sulfite is inhibition of the reaction catalyzed by ribulose bisphosphate carboxylase and a stimulation of export of intermediates out of the chloroplasts. Inhibition of light modulation of stromal enzyme activity does not appear to account for the toxicity of SO 2 in this Pisum variety. Arsenite at 0.2 millimolar concentrations inhibits light activation and inhibits photosynthetic CO 2 fixation. The 14CO 2-fixation pattern indicates that the primary effect of arsenite is inhibition of light activation of reductive pentose phosphate pathway enzyme activity. 相似文献
5.
Mature leaves of a variegated cultivar of Coleus blumei Benth. with a green border and central albino region constitute a source-sink system suitable for studies on assimilate partitioning. Leaves treated with 14CO 2 on a small part of the intact green border export assimilate via the shortest path into the stem. Leaves with all but a small lobe of the green border removed show different partitioning of labeled assimilates when the leaf is exposed to 14CO 2 (Fisher and Eschrich, 1985): The whole albino region of the leaf is supplied but no tracer is exported into the stem. When the green border is completely removed, 14CO 2-treatment of the albino region leads to the fixation of CO 2, obviously by PEP carboxylase, as indicated by the occurrence of labeled malate. Results show that the albino region of the variegated leaf constitutes a potential sink when deprived of its green border. In addition, CO 2-fixation by PEP carboxylase in albino tissue seems to indicate a common capacity of leaves which is normally masked by photosynthesis. The difference of assimilate partitioning between leaves with intact and leaves with partly removed green borders demonstrates that the unlabeled assimilates control the movement of labeled assimilates. 相似文献
6.
The concentration effect of aqueous CO 2 on the reaction velocity of spinach leaf ribulose-1,5-diphosphate carboxylase has been reevaluated. The homotropic effect of CO 2 in the enzyme reaction supports the previously reported allosteric nature of the enzyme in the CO 2-fixation process in chloroplasts. The concentration of CO 2 giving the half maximal reaction velocity, S 0.5, has been calculated to be 1.47 × 10 −5M. 相似文献
7.
An enzymatic method for the quantitative determination of biotin has been developed. The method involves the enzymatic binding of biotin in situ to the pyruvate carboxylase apoprotein of biotin-deficient bakers' yeast and the subsequent estimation of the pyruvate carboxylase activity by a 14CO 2-fixation method. The method is specific for biotin. Several biotin analogs and precursors were tested, and only biocytin was found to interfere, Biotin amounts of less than 5 pg can be estimated. 相似文献
8.
The in vitro activities of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) and phosphoenolpyruvate carboxylase (PEPC) were measured
in cell-free extracts of Platycerium coronarium callus cultured for up to 42 days under photoautotrophic conditions with CO 2 enrichment. With an increase in CO 2 in the culture environment to 10% (v/v) at low light, the apparent photoautotrophic fixation of CO 2 by Rubisco declined, whereas the non-photoautotrophic CO 2 fixation by PEPC activity was enhanced. Hence, photosynthesis appears to play a lesser role in providing carbon skeletons
and energy with prolonged culture in a CO 2-enriched environment. Instead, the anaplerotic supply of C-skeletons by PEPC may be important under such a situation. Short-term
H 14CO 3-fixation experiments indicated that photoautotrophic callus cultured for 3 weeks with 10% CO 2 enrichment assimilated less 14CO 2 than the control (0.03% CO 2). Analyses of 14C-metabolites indicated that about 50% of the total soluble 14CO 2 fixed was in the organic acid fraction and 35% in the amino acid fraction. Despite the changes in the in vitro Rubisco/PEPC activity-ratio, no significant change in the 14C distribution pattern was apparent in response to increasing sucrose or CO 2 concentrations. The suppression of Rubisco activity and total chlorophyll content in high sucrose or elevated CO 2 concentrations suggests an inhibition of the capacity for photoautotrophic callus growth under these conditions.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
9.
Various stages of the life cycle of the marine brown alga Laminaria saccharina (L.) Lamour. (Laminariales, Phaeophyta) including male and female gametophytes, female gametes, zygotes and young sporophytes of different age were investigated for their potentials of carbon dioxide ( 14CO 2) fixation. Rates of photosynthesis attain the same order of magnitude in all stages. Photosynthetic 14CO 2-fixation is accompanied by a substantial light independent carbon assimilation. This is confirmed by rate determinations of the equivalent carboxylating enzymes present in the plants, ribulose-1,5-bisphosphate carboxylase (EC 4.1.1.39) and phosphoenolpyruvate carboxokinase (EC 4.1.1.32) as well as by chromatographic analyses of the appropriate [ 14C]-assimilate patterns.Abbreviations RuBP-C
ribulose-1,5-bisphosphate carboxylase
- PEP-CK
phosphoenolpyruvate carboxykinase
- PEP
phosphoenolpyruvate
- PS
photosynthesis
- DF
dark fixation 相似文献
10.
In continuous cultures of Chlorella fusca under steady state conditions, the CO 2-fixation rate, the ATP-level, the apparent rate of photophosphorylation as calculated from the changes in the ATP-level during light to dark or dark to light transients and the energy charge were measured at various environmental conditions. During growth the energy charge was around 0.64. CO 2-assimilation and the apparent ATP-synthesis were strongly dependant on light intensity, however the ATP-level was independant on it. Since the rates of apparent ATP-synthesis and of the CO 2-fixation do not seem to be strictly correlated in a logic way when environmental factors are changed and furthermore the stoichiometry of 3 ATP necessary per CO 2 fixed was never achieved, the described method frequently used for procaryotes to determine the in vivo rate of phosphorylation does not give valid results in highly compartimented eukaryotic cells. 相似文献
11.
A photoautotrophic soybean suspension culture (SB-P) was used to study CO 2 assimilation while exposed to elevated or ambient CO 2 levels. These studies showed that under elevated CO 2 (5% v/v) malate is the dominant fixation product, strongly suggesting that phosphoenolpyruvate carboxylase (PEPCase) is the primary enzyme involved in carbon fixation in these cells under their normal growth conditions. Citrate and [aspartate + glutamate] were also significant fixation products during fifteen minutes of exposure to 14CO 2. During the ten minute unlabeled CO 2 chase however, 14C-malate continued to increase while citrate and [aspartate + glutamate] declined. Fixation of 14CO 2 under ambient CO 2 levels (0.037%) showed a very different product pattern as 3-phosphoglycerate was very high in the first one to two minutes followed by increases in [serine + glycine] and [aspartate + glutamate]. Hexose phosphates were also quite high initially but then declined relatively rapidly. Thus, the carbon fixation pattern at ambient CO 2 levels resembles somewhat that seen in C3 leaf cells while that seen at elevated CO 2 levels more closely resembles that of a C 4 plant. The initial fixation product of C 3 plants, 3-PGA, was never detectable under high CO 2 conditions. These data suggest that an in vitro photoautotrophic system would be suitable for studying carbon fixation physiology during photosynthetic and non-photosynthetic growth.Abbreviations SB-P
photoautotrophic soybean cells
- PEPCase
phosphoenol-pyruvate carboxylase
- RuBPCase
ribulose bisphosphate carboxylase/oxygenase
- 3-PGA
3-phosphoglycerate 相似文献
12.
Experiments were designed to determine the significance of dark CO 2 fixation in excised maize roots, carrot slices and excised tomato roots grown in tissue culture. Bicarbonate- 14C was used to determine the pathway and amounts of CO 2 fixation, while leucine- 14C was used to estimate protein synthesis in tissues aerated with various levels of CO 2. Organic acids were labeled from bicarbonate-14C, with malate being the major labeled acid. Only glutamate and aspartate were labeled in the amino acid fraction and these 2 amino acids comprised over 90% of the 14C label in the ethanol-water insoluble residue. Studies with leucine-14C as an indicator of protein synthesis in carrot slices and tomato roots showed that those tissues aerated with air incorporated 33% more leucine-14C into protein than those aerated with CO2-free air. Growth of excised tomato roots aerated with air was 50% more than growth of tissue aerated with CO2-free air. These studies are consistent with the suggestion that dark fixation of CO2 is involved in the growth of plant tissues. 相似文献
13.
Light-dependent CO-evolution by the green leaves of C 3 and C 4 plants depends on the CO 2/O 2 ratio in the ambient atmosphere. This and other physiological responses suggest that CO-evolution is a byproduct of photorespiration. At CO 2/O 2 ratios up to 10 -3, the ratio of CO evolved: CO 2 fixed in photosynthesis is significantly higher in C 3 than in C 4 plants. This discrepancy disappears when a correction is made for the CO 2-concentrating mechanism in C 4 photosynthesis, by which CO 2-concentration at the site of ribulose-bis-phosphate carboxylase/oxygenase in the bundle sheaths is raised significantly as compared to the ambient atmosphere. Since the oxygenase function of this enzyme is responsible for glycolate synthesis, i.e., the substrate of photorespiration, this result seems to support the conclusion that CO-evolution is a consequence of photorespiration. CO-evolution may turn out to be a useful and rather straightforward indicator for photorespiration in ecophysiological studies.Abbreviations CAM
crassulacean acid metabolism
- CO
net CO-evolution
- CO 2
net CO 2-fixation
- PEP-C
phosphoenolpyruvate carboxylase
- RubP-C
ribulose-bisphosphate carboxylase/oxygenase
Dedicated to Professor André Pirson on the occasion of his 70th birthday 相似文献
14.
Photosynthetic CO 2-fixation of mesophyll protoplasts of lambs lettuce [ Valerianella locusta (L.) Betcke] was inhibited by short time exposure to Cd +. Inhibition was due to uptake of the metal ion into the protoplasts and increased with increasing Cd 2+ concentrations and the time of preincubation. A 10 min pretreatment at 2 m M Cd 2+ reduced CO 2-fixation by 40–60%. Inhibition of photosynthesis was independent of the light intensity to which the protoplasts were exposed. Measurement of the lightinduced electrochromic pigment absorption change at 518nm and chlorophyll fluorescence studies revealed that primary photochemical reactions associated with the thylakoid membranes were not affected by the metal ion. Also, light activation of the ribulose-1,5-bisphosphate carboxylase (EC 4.1.1.39) was not inhibited by Cd 2+. Under rate-limiting CO 2 concentrations, inhibition of CO 2-fixation was smaller than at V max of CO 2 reduction indicating that the carboxylation reaction of the Calvin cycle is not susceptible to Cd 2+. Cd 2+ treatment of protoplasts significantly extended the lagphase of CO 2-supported O 2-evolution and partly inhibited light activation of the glyceraldehyde-3-phosphate dehydrogenase (EC 1.2.1.13) and the ribulose-5-phosphate kinase (EC 2.7.1.19). Measurement of relative concentrations of [ 14C]-labeled Calvin cycle intermediates showed that Cd 2+ caused a decrease in the 3-phosphoglycerate/triose phosphate ratio and an increase in the triose phosphate/ribulose-1,5-bisphosphate ratio. It is concluded that in protoplasts Cd 2+ affects photosynthesis mainly at the level of dark reactions and that the site of inhibition may be localized in the regenerative phase of the Calvin cycle. 相似文献
15.
Seven day old wheat and maize seedlings were exposed to 1300 or 2000 microeinsteins per square meter per second photosynthetically active radiation in CO 2-free air for 3 hours with either 1% O 2 in N 2 or N 2-only and then returned to normal air of 340 microliters per liter CO 2, 21% O 2 in N 2. Activity of the ribulose bisphosphate carboxylase and amount of the substrate, ribulose 1,5-bisphosphate, were measured during and following the CO 2-free treatments as was photosynthetic CO 2 fixation. Photoinhibition of photosynthesis was observed only with wheat seedlings following the N 2 only treatment. During the CO 2-free treatments, the levels of RuBP rose during all experiments except when wheat was photoinhibited. The activity of the ribulose bisphophate carboxylase, measured directly upon grinding the leaves, declined during the CO 2-free conditions. The carboxylase total activity increased in minutes in the leaf during and following the CO 2-free treatments. The specific activities of the wheat carboxylase went from 0.16 to 1.06 micromoles CO 2 fixed per milligram protein per minute while the maize carboxylase varied from 0.05 to 0.36 micromole CO 2 fixed per millogram protein per minute. This suggests that in these seedlings considerable inactive carboxylase must be stored in a form not activatable in extracts by CO 2 and Mg 2+. Possible mechanisms of regulation of photosynthesis by the ribulose bisphosphate carboxylase must consider not only the amount of active enzyme, but the amount of enzyme which the plant can make activatable upon demand. 相似文献
16.
Cadmium (100, 400 and 1000 μM CdCl 2) treatments resulted in the inhibition of root dry biomass, root elongation and increased Cd accumulation in wheat ( Triticum aestivum L.) roots. Further, these treatments decreased relative water content, chlorophyll content, 14CO 2-fixation, activities of phosphoenolpyruvate carboxylase and ribulose-1,5-bisphosphate carboxylase and abscisic acid content
while increased malondialdehyde, hydrogen peroxide and free proline contents. Chloroplast and root ultrastructure was also
changed. Pretreatment of seeds with SA (500 μM) for 20 h resulted in amelioration of these effects. 相似文献
17.
Perennial legume such as alfalfa have the capacity to sustain shoot regrowth and some nodule N 2-fixation after removal (cutting) of shoots which contain practically all of the plant's photosynthetic capacity. The role of the roots in supporting these processes has not been fully described. Measurements were made of the nodules' responses to removal of shoots from 8-week-old seedlings in terms of N 2-fixation, as nitrogenase activity (NA) measured as acetylene reduction, dark CO 2 fixation, measured as in vitro phosphoenolpyruvate carboxylase (PEPC) activity, and total non-structural carbohydrate (NSC) content. These properties decreased and recovered in that sequence, which suggests that nodule NSC supported the substrate requirements of NA and PEPC immediately after cutting. The utilization and redistribution or root carbon and nitrogen, prelabeled with 14C and 15N, were also followed after cutting 8-week-old alfalfa seedlings. In the first 2 weeks of regrowth 12% of root C and 25% of root N were transferred for incorporation into new shoots. Up to 40% of the root C was used for plant respiration to support 28 days of shoot regrowth and N 2-fixation. The decline of N 2-fixation was slower after cutting and its minimum activity rose up 45% of pre-cut activity as root reserves were built up with plant age. Therefore, the stored reserves of nodulated roots play an important role in support of N 2-fixation after cutting.Contribution No. 1265 from Plant Research Center.Contribution No. 1265 from Plant Research Center. 相似文献
18.
Photosynthesis and light O 2-uptake of the aerial portion of the CAM plant Ananas comosus (L.) merr. were studied by CO 2 and O 2 gas exchange measurements. The amount of CO 2 which was fixed during a complete day-night cycle was equal to the amount of total net O 2 evolved. This finding justifies the assumption that in each time interval of the light period, the difference between the rates of net O 2-evolution and of net light atmospheric CO 2-uptake give the rates of malate-decarboxylation-dependent CO 2 assimilation. Based upon this hypothesis, the following photosynthetic characteristics were observed: (a) From the onset of the light to midphase IV of CAM, the photosynthetic quotient (net O 2 evolved/net CO 2 fixed) was higher than 1. This indicates that malate-decarboxylation supplied CO 2 for the photosynthetic carbon reduction cycle during this period. (b) In phase III and early phase IV, the rate of CO 2 assimilation deduced from net O 2-evolution was 3 times higher than the maximum rate of atmospheric CO 2-fixation during phase IV. A conceivable explanation for this stimulation of photosynthesis is that the intracellular CO 2-concentration was high because of malate decarboxylation. (c) During the final hours of the light period, the photosynthetic quotient decreased below 1. This may be the result of CO 2-fixation by phosphoenolpyruvate-carboxylase activity and malate accumulation. Based upon this hypothesis, the gas exchange data indicates that at least 50% of the CO 2 fixed during the last hour of the light period was stored as malate. Light O 2-uptake determined with 18O 2 showed two remarkable characteristics: from the onset of the light until midphase IV the rate of O 2-uptake increased progressively; during the following part of the light period, the rate of O 2-uptake was 3.5 times higher than the maximum rate of CO 2-uptake. When malate decarboxylation was reduced or suppressed after a night in a CO 2-free atmosphere or in continuous illumination, the rate of O 2-uptake was higher than in the control. This supports the hypothesis that the low rate of O 2-uptake in the first part of the light period is due to the inhibition of photorespiration by increased intracellular CO 2 concentration because of malate decarboxylation. In view of the law of gas diffusion and the kinetic properties of the ribulose-1,5-bisphosphate carboxylase/oxygenase, O 2 and CO 2 gas exchange suggest that at the end of the light period the intracellular CO 2 concentration was very low. We propose that the high ratio of O 2-uptake/CO 2-fixation is principally caused by the stimulation of photorespiration during this period. 相似文献
19.
Recycling of carbon dioxide (CO 2) into fuels and chemicals is a potential approach to reduce CO 2 emission and fossil-fuel consumption. Autotrophic microbes can utilize energy from light, hydrogen, or sulfur to assimilate atmospheric CO 2 into organic compounds at ambient temperature and pressure. This provides a feasible way for biological production of fuels and chemicals from CO 2 under normal conditions. Recently great progress has been made in this research area, and dozens of CO 2-derived fuels and chemicals have been reported to be synthesized by autotrophic microbes. This is accompanied by investigations into natural CO 2-fixation pathways and the rapid development of new technologies in synthetic biology. This review first summarizes the six natural CO 2-fixation pathways reported to date, followed by an overview of recent progress in the design and engineering of CO 2-fixation pathways as well as energy supply patterns using the concept and tools of synthetic biology. Finally, we will discuss future prospects in biological fixation of CO 2. 相似文献
20.
When photosynthesis of the blue-green alga Anacystis nidulans was measured as 14CO 2-fixation, the inhibitory effect of DCMU at low concentrations was greatest when mainly Photosystem 1 (PS 1) (excitation at 446 or 687 nm) was operative. At concentrations above 10- 6M the inhibition on 14CO 2-fixation was greatest when mainly Photosystem 2 (PS 2) was operative (excitation at 619). During excitation of PS 1, the excretion of glycolate was stimulated at low concentrations of DCMU (5 × 10 -8M and lower), while higher concentrations inhibited excretion. All concentrations of DCMU inhibited glycolate excretion when mainly PS 2 was excited. The curves showing the relative effect of DCMU on the two photosystems, measured as PS 1/PS 2, had opposite shapes for 14CO 2-fixation and glycolate excretion. An increase in 14CO 2-fixation coincided with a decrease in glycolate excretion and vice versa. It appears that the increased rate of photosynthesis when mainly PS 1 was operative relative to that when mainly PS 2 was excited, increases the consumption of glycolate in an oxidation process associated with the excitation of PS 1, resulting in less excretion of glycolate to the medium. The influence of DCMU inhibition on labelled amino acid pools connected to the glycolate pathway (glycine-serine) is quite similar to that for 14CO 2-fixation. At concentrations below 10 -6M DCMU, inhibition of 14CO 2- incorporation into the amino acids was greatest when PS 1 was excited, while at the higher concentrations tested, inhibition was greater when PS 2 was excited. We conclude that the metabolism of glycine and serine is closely connected to the rate of photosynthesis. 相似文献
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