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1.
Fifteen species of freshwater macrophytes, mainly from cool,temperate waters, were assayed for ribulose bisphosphate carboxylase-oxygenase(RuBPCase) and phosphoenolpyruvate carboxylase (PEPCase) activities.In extracts from all the species RuBPCase was the most activecarboxylation enzyme, and the RuBPCase/PEPCase ratio was atleast 2·0, even for the submersed species Isoetes lacustrisL. and Littorella unifiora (L.) Aschers. which have been reportedto show Crassulacean Acid Metabolism (CAM) activity. The PEPCaseactivity in I.lacustris was lower than that found in some non-CAM-likespecies. In this respect, I.lacustris and L unifiora differfrom most terrestrial CAM plants. However, these two species,along with Potamogeton praelongus Wulf. and Juncus bulbosusvar. fluitans L., had the lowest RuBPCASE/PEPCase ratios, lowerthan found in terrestrial C 3 species; suggesting that the potentialfor substantial photosynthetic metabolism of C 4 acids existsin some temperate, submersed plants. In the three amphibiousspecies ( Potamogeton polygonifolius Pourr., Mentha aquaticaL., and Hippuris vulgaris L.) examined, the aerial leaves exhibitedhigher RuBPCase activities than the submersed leaves. Key words: Ribulose bisphosphate carboxylase-oxygenase, phosphoenolpruvate carboxylase, freshwater macrophytes 相似文献
2.
In vivo CO 2 fixation activity and in vitro phosphoenolpyruvate carboxylase activity were demonstrated in effective and ineffective nodules of alfalfa ( Medicago sativa L.) and in the nodules of four other legume species. Phosphoenolpyruvate carboxylase activity was greatly reduced in nodules from both host and bacterially conditioned ineffective alfalfa nodules as compared to effective alfalfa nodules. Forage harvest and nitrate application reduced both in vivo and in vitro CO2 fixation activity. By day 11, forage harvest resulted in a 42% decline in in vitro nodule phosphoenolpyruvate carboxylase activity while treatment with either 40 or 80 kilograms nitrogen per hectare reduced activity by 65%. In vitro specific activity of phosphoenolpyruvate carboxylase and glutamate synthase were positively correlated with each other and both were positively correlated with acetylene reduction activity. The distribution of radioactivity in the nodules of control plants (unharvested, 0 kilograms nitrogen per hectare) averaged 73% into the organic acid and 27% into the amino acid fraction. In nodules from harvested plants treated with nitrate, near equal distribution of radioactivity was observed in the organic acid (52%) and amino acid (48%) fractions by day 8. Recovery to control distribution occurred only in those nodules whose in vitro phosphoenolpyruvate carboxylase activity recovered. The results demonstrate that CO2 fixation is correlated with nitrogen fixation in alfalfa nodules. The maximum rate of CO2 fixation for attached and detached alfalfa nodules at low CO2 concentrations (0.13-0.38% CO2) were 18.3 and 4.9 nanomoles per hour per milligram dry weight, respectively. Nodule CO2 fixation was estimated to provide 25% of the carbon required for assimilation of symbiotically fixed nitrogen in alfalfa. 相似文献
3.
Two-dimensional electrophoresis was performed on proteins of bundle sheath and mesophyll cells isolated from the C 4 grass Digitaria sanguinalis (L.) Scop. Two-dimensional maps of these proteins were constructed and ribulose-1,5-biphosphate carboxylase and phosphoenolpyruvate carboxylase were identified. Of the total number of proteins found in both cell types, 36% were found only in bundle sheath cells, 17% only in mesophyll cells, and 47% in both cell types. By comparison, the distributions of 48 enzymes assayed in these cell types were 35%, 21%, and 44%, respectively. Protein patterns were also compared with C4 plants exhibiting different decarboxylation pathways and, in both bundle sheath and mesophyll cells, proteins were found which were unique to each species. Bundle sheath proteins of one C4 species were found to be more like bundle sheath proteins of another C4 species than like mesophyll proteins of the same species. 相似文献
4.
Plants with the C 3, C 4, and crassulacean acid metabolism (CAM) photosynthetic pathways show characteristically different discriminations against 13C during photosynthesis. For each photosynthetic type, no more than slight variations are observed within or among species. CAM plants show large variations in isotope fractionation with temperature, but other plants do not. Different plant organs, subcellular fractions and metabolises can show widely varying isotopic compositions. The isotopic composition of respired carbon is often different from that of plant carbon, but it is not currently possible to describe this effect in detail. The principal components which will affect the overall isotope discrimination during photosynthesis are diffusion of CO 2, interconversion of CO 2 and HCO ?3, incorporation of CO 2 by phosphoenolpyruvate carboxylase or ribulose bisphosphate carboxylase, and respiration. Theisotope fractionations associated with these processes are summarized. Mathematical models are presented which permit prediction of the overall isotope discrimination in terms of these components. These models also permit a correlation of isotope fractionations with internal CO 2 concentrations. Analysis of existing data in terms of these models reveals that CO 2 incorporation in C 3 plants is limited principally by ribulose bisphosphate carboxylase, but CO 2 diffusion also contributes. In C 4 plants, carbon fixation is principally limited by the rate of CO 2 diffusion into the leaf. There is probably a small fractionation in C 4 plants due to ribulose bisphosphate carboxylase. 相似文献
5.
The activities of the carboxylating enzymes ribulose-1,5-biphosphate (RuBP) carboxylase and phosphoenolpyruvate (PEP) carboxylase in leaves of three-week old Zea mays plants grown under phytotron conditions were found to vary according to leaf position. In the lower leaves the activity of PEP carboxylase was lower than that of RuBP carboxylase, while the upper leaves exhibited high levels of PEP carboxylase. Carbon dioxide compensation points and net photosynthetic rates also differed in the lower and upper leaves. Differences in the fine structure of the lowermost and uppermost leaves are shown. The existence of both the C 3 and C 4 photosynthetic pathways in the same plant, in this and other species, is discussed.Abbreviations PEP
phosphoenolpyruvate
- RuBP
ribulose-1,5-biphosphate 相似文献
6.
Incubation of the submersed aquatic macrophyte, Hydrilla verticillata Royle, for up to 4 weeks in growth chambers under winter-like or summer-like conditions produced high (130 to 150 μl CO 2/1) and low (6 to 8 μl CO 2/l) CO 2 compensation points (Γ), respectively. The activities of both ribulose bisphosphate (RuBP) and phosphoenolpyruvate (PEP) carboxylases increased upon incubation but the major increase was in the activity of PEP carboxylase under the summer-like conditions. This reduced the ratio of RuBP/PEP carboxylases from 2.6 in high Γ plants to 0.2 in low Γ plants. These ratios resemble the values in terrestrial C 3 and C 4 species, respectively. Kinetic measurements of the PEP carboxylase activity in high and low Γ plants indicated the Vmax was up to 3-fold greater in the low Γ plants. The Km (HCO 3 ?) values were 0.33 and 0.22 mM for the high and low Γ plants, respectively. The Km (PEP) values for the high and low Γ plants were 0.23 and 0.40 mM, respectively; and PEP exhibited cooperative effects. Estimated Km (Mg 2+) values were 0.10 and 0.22 mM for the high and low Γ plants, respectively. Malate inhibited both PEP carboxylase types similarly. The enzyme from low Γ plants was protected by malate from heat inactivation to a greater extent than the enzyme from high Γ plants. The results indicated that C 4 acid inhibition and protection were not reliable methods to distinguish C 3 and C 4 PEP carboxylases. The PEP carboxylase from low Γ plants was inhibited more by NaCl than that from hight Γ plants. These analyses indicated that Hydrilla PEP carboxylases had intermediate characteristics between those of terrestrial C 3 and C 4 species with the low Γ enzyme being different from the high Γ enzyme, and closer to a C 4 type. 相似文献
7.
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
8.
A detailed comparison of green leaf phosphoenolpyruvate carboxylases from the C 4-species Atriplex spongiosa and the C 3-species Atriplex hastata revealed significant physical and kinetic differences. The two alloenzymes can be separated by anion exchange chromatography but have comparable molecular weights (350,000). Maximal velocity estimates were 38.0 and 1.48 micromoles per minute per milligram of chlorophyll for the carboxylases of A. spongiosa and A. hastata, respectively. K m phosphoenolpyruvate estimates were 0.49 and 0.08 m m for the C 4A. spongiosa and C 3A. hastata and the K m Mg estimates were 0.33 m m for the C 4 species and 0.017 m m for the C 3 species. The activity of the phosphoenolpyruvate carboxylase of A. spongiosa is more sensitive to chloride and phosphate than the phosphoenolpyruvate carboxylase of A. hastata, but both are equally sensitive to Mg chelating substances such as ATP, ADP, and citrate if assayed at their respective K m Mg values. A survey of the phosphoenolpyruvate carboxylases from 18 C 4 and C 3 species resulted in mean maximal velocity estimates of 29.0 ± 13.2 and 1.50 ± 0.57 micromoles per minute per milligram of chlorophyll for the C 4 species and C 3 species, respectively. K m phosphoenolpyruvate estimates were 0.59 ± 0.35 m m and 0.14 ± 0.07 m m for the C 4 and C 3, and K m Mg estimates were 0.50 ± 0.30 and 0.097 ± 0.057 m m for C 4 and C 3. All differences between means were significant at the 0.01 confidence level, supporting our hypothesis that the phosphoenolpyruvate carboxylase alloenzymes of C 4 and C 3 plants are functionally different and are associated with different photosynthetic roles. Both function in the photosynthetic production of C 4 acids, the phosphoenolpyruvate carboxylase of C 4 species largely producing malate or aspartate (or both) as a photosynthetic intermediate and the phosphoenolpyruvate carboxylase of C 3 species producing malate or aspartate (or both) as a photosynthetic product. 相似文献
9.
Incubation of the submersed aquatic macrophyte, Hydrilla vertieillata Royle, for up to 4 weeks in growth chambers under winter-like or summer-like conditions produced high (130 to 150 μl CO 2/l) and low (6 to 8 μl CO 2/l) CO 2 compensation points (Γ), respectively. The activities of both ribulose bisphosphate (RuBP) and phosphoenolpyruvate (PEP) carboxylases increased upon incubation but the major increase was in the activity of PEP carboxylase under the summer-like conditions. This reduced the ratio of RuBP/PEP carboxylases from 2.6 in high Γ plants to 0.2 in low Γ plants. These ratios resemble the values in terrestrial C 3 and C 4 species, respectively. Kinetic measurements of the PEP carboxylase activity in high and low Γ plants indicated the Vmax was up to 3-fold greater in the low Γ plants. The Km (HCO 3 -) values were 0.33 and 0.22 mM for the high and low Γ plants, respectively. The Km (PEP) values for the high and low Γ plants were 0.23 and 0.40 mM, respectively; and PEP exhibited cooperative effects. Estimated Km (Mg 2+) values were 0.10 and 0.22 mM for the high and low Γ plants, respectively. Malate inhibited both PEP carboxylase types similarly. The enzyme from low Γ plants was protected by malate from heat inactivation to a greater extent than the enzyme from high Γ plants. The results indicated that C 4 acid inhibition and protection were not reliable methods to distinguish C 3 and C 4 PEP carboxylases. The PEP carboxylase from low Γ plants was inhibited more by NaCl than that from high Γ plants. These analyses indicated that Hydrilla PEP carboxylases had intermediate characteristics between those of terrestrial C 3 and C 4 species with the low Γ enzyme being different from the high Γ enzyme, and closer to a C 4 type. 相似文献
11.
Photosynthesis was examined in leaves of Flaveria brownii A. M. Powell, grown under either 14% or 100% full sunlight. In leaves of high light grown plants, the CO 2 compensation point and the inhibition of photosynthesis by 21% O 2 were significantly lower, while activities of ribulose 1,5-bisphosphate carboxylase/oxygenase and various C 4 cycle enzymes were considerably higher than those in leaves grown in low light. Both the CO 2 compensation point and the degree of O 2 inhibition of apparent photosynthesis were relatively insensitive to the light intensity used during measurements with plants from either growth conditions. Partitioning of atmospheric CO 2 between Rubisco of the C 3 pathway and phosphoenolpyruvate carboxylase of the C 4 cycle was determined by exposing leaves to 14CO 2 for 3 to 16 seconds, and extrapolating the labeling curves of initial products to zero time. Results indicated that ~94% of the CO 2 was fixed by the C 4 cycle in high light grown plants, versus ~78% in low light grown plants. Thus, growth of F. brownii in high light increased the expressed level of C 4 photosynthesis. Consistent with the carbon partitioning patterns, photosynthetic enzyme activities (on a chlorophyll basis) in protoplasts from leaves of high light grown plants showed a more C 4-like pattern of compartmentation. Pyruvate, Pi dikinase and phosphoenolpyruvate carboxylase were more enriched in the mesophyll cells, while NADP-malic enzyme and ribulose 1,5-bisphosphate carboxylase/oxygenase were relatively more abundant in the bundle sheath cells of high light than of low light grown plants. Thus, these results indicate that F. brownii has plasticity in its utilization of different pathways of carbon assimilation, depending on the light conditions during growth. 相似文献
13.
The physiological and photosynthetic responses of Littorella uniflora (L.) Ascherson, an amphibious macrophyte of isoetid life form, to rapid and prolonged emersion onto dry land, was studied at a reservoir. Water relations were little affected in the short term, but declining water potential and turgor pressure indicated water stress after flowering. High leaf lacunal CO 2 concentrations suggested continued CO 2 uptake from sediments. In contrast, a switch from Crassulacean acid metabolism (CAM) to C 3 photosynthesis was indicated by much lower levels of ΔH + (down minus dusk titratable acidity) and phosphoenolpyruvate carboxylase (PEPC) activity in new terrestrial leaves, 7–8‐fold higher activity of ribulose bisphosphate carboxylase oxygenase (Rubisco), and increased chlorophyll and soluble protein contents. Accumulated nitrate and amino acid pools were depleted, whereas storage of carbohydrates as soluble sugars, fructan and starch increased. Plant carbon and nitrogen isotope ratios (δ 13C and δ 15N) declined, perhaps reflecting changes in C fixation processes, N metabolism, and source C and N. In leaves of plants grown half‐emersed for an extended period, contrasting activities of PEPC and Rubisco were found in submersed and emersed portions. Overall, L. uniflora showed considerable phenotypic plasticity, yet seemed to remain poised for re‐submersion; these characteristics could be adaptive in the unpredictable water margin habitat. 相似文献
14.
In response to water stress, Portulacaria afra (L.) Jacq. (Portulacaceae) shifts its photosynthetic carbon metabolism from the Calvin-Benson cycle for CO 2 fixation (C 3) photosynthesis or Crassulacean acid metabolism (CAM)-cycling, during which organic acids fluctuate with a C 3-type of gas exchange, to CAM. During the CAM induction, various attributes of CAM appear, such as stomatal closure during the day, increase in diurnal fluctuation of organic acids, and an increase in phosphoenolpyruvate carboxylase activity. It was hypothesized that stomatal closure due to water stress may induce changes in internal CO 2 concentration and that these changes in CO 2 could be a factor in CAM induction. Experiments were conducted to test this hypothesis. Well-watered plants and plants from which water was withheld starting at the beginning of the experiment were subjected to low (40 ppm), normal ( ca. 330 ppm), and high (950 ppm) CO 2 during the day with normal concentrations of CO 2 during the night for 16 days. In water-stressed and in well-watered plants, CAM induction as ascertained by fluctuation of total titratable acidity, fluctuation of malic acid, stomatal conductance, CO 2 uptake, and phosphoenolpyruvate carboxylase activity, remained unaffected by low, normal, or high CO 2 treatments. In well-watered plants, however, both low and high ambient concentrations of CO 2 tended to reduce organic acid concentrations, low concentrations of CO 2 reducing the organic acids more than high CO 2. It was concluded that exposing the plants to the CO 2 concentrations mentioned had no effect on inducing or reducing the induction of CAM and that the effect of water stress on CAM induction is probably mediated by its effects on biochemical components of leaf metabolism. 相似文献
15.
Panicum milioides represents the first well-documented example of a higher plant species with reduced photorespiration and O 2 inhibition of photosynthesis. We have investigated the biochemical mechanism(s) involved in reducing O 2 sensitivity of photosynthesis in this species by parallel enzyme inhibitor experiments with thin leaf slices of P. milioides and C 3 and C 4Panicum species. The reduced O 2 sensitivity of net photosynthesis in P. milioides gradually increased with increasing concentrations of the phosphoenolpyruvate carboxylase (EC 4.1.1.31) inhibitors, maleate and malonate. At saturating levels of inhibitor, photosynthesis in 2% O 2 was decreased by about 18%, and the inhibitory effects of both 21% O 2 and 49% O 2 were identical to those observed with a C 3Panicum species in the absence or presence of inhibitor. A significant potential for C 4 photosynthesis in P. milioides, compared to its complete absence in a C 3Panicum species, was demonstrated on the basis of: (a) a coupling of leaf slice CO 2 fixation by phosphoenolpyruvate carboxylase with the C 3 cycle; (b) NAD-malic enzyme (EC 1.1.1.39)-dependent aspartate and malate decarboxylation in leaf slices; (c) a full complement of C 4 cycle enzymes in leaf extracts, including pyruvate, P i dikinase (EC 2.7.9.1) and NAD-malic enzyme; and (d) Kranz-like leaf anatomy with numerous plasmodesmata traversing the mesophyll-bundle sheath interfacial cell wall. These data indicate that the reduced photorespiration and O 2 inhibition of photosynthesis in P. milioides is due to phosphoenolpyruvate carboxylase participation, possibly by creating a limited C 4-like CO 2 pump, rather than an altered ribulose 1,5-bisphosphate carboxylase-oxygenase (EC 4.1.1.39). 相似文献
16.
Photosynthetic characteristics were studied in several F 1 hybrids between C 4 and C 3-C 4 species of Flaveria. Stable carbon isotope ratios, O 2 inhibition of apparent photosynthesis, and phosphoenolpyruvate carboxylase activities in the hybrids were similar to the means for the parents. Values of CO 2 compensation concentrations were nearer to those of the C 4 parent and apparent photosynthesis was below that of both parents, being only 60 and 74% of that of the lowest (C 3-C 4) parent in two experiments. Reductions of CO 2 compensation concentration and O 2 inhibition of apparent photosynthesis as well as increases in carbon isotope ratios and phosphoenolpyruvate carboxylase activities compared to values in C 3-C 4 species suggest transfer of a limited degree of C 4 photosynthesis to the F 1 hybrids. However, the lower apparent photosynthesis of the hybrids suggests that transfer of C 4 characteristics to non-C 4 species is detrimental unless characteristics associated with C 4 photosynthesis are fully developed. There was a highly significant negative correlation ( r = −0.90) between CO 2 compensation concentration and the logarithm of phosphoenolpyruvate carboxylase activity in the parents and hybrids, suggesting involvement of this enzyme in controlling the CO 2 compensation concentration. Although bundle-sheath cells were more developed in leaves of hybrids than in C 3-C 4 parents, they appeared to contain lower quantities of organelles than those of the C 4 parent. Reduced quantities of organelles in bundle-sheath cells could indicate incomplete compartmentation of partial pathways of the C 4 cycle in the hybrids. This may mean that the reduction of CO 2 compensation and O 2 inhibition of apparent photosynthesis relative to the C 3-C 4 parents is less dependent on fully developed Kranz anatomy than is increased apparent photosynthesis. 相似文献
17.
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
18.
Fucus serratus L., Fucus spiralis L., and Fucus vesiculosus L. (Fucales, Phaeophyceae) as well as Laminaria digitata (Huds.) Lamour., Laminaria hyperborea (Gunn.) Fosl., and Laminaria saccharina (L.) Lamour. (Laminariales, Phaeophyceae) have been investigated for the distribution of enzymic CO 2 fixation capacities via phosphoenolpyruvate carboxykinase (EC 4.1.1.32) (PEP-CK) and via ribulose-1,5-bisphosphate carboxylase (EC 4.1.1.39) (RubP-C) in different regions of the thalli. The maximum of PEP-CK activity is found to be confined to the growing regions of the algae, while the activity of RubP-C achieves its highest values in the entirely differentiated parts of the fronds. These findings are confirmed by the results of photosynthetic and light-independent (dark) carbon assimilation as determined by in vivo 14CO 2 fixation. The physiological significance of these differential patterns of carboxylation patterns is discussed with respect to the ontogenetic stage and the chemical constitution of the different thallus parts. 相似文献
19.
Ribulose bisphosphate carboxylase/oxygenase (RuBPCase) from several plants had substantially greater activity in extracts from lightexposed leaves than dark leaves, even when the extracts were incubated in vitro with saturating HCO 3− and Mg 2+ concentrations. This occurred in Glycine max, Lycopersicon esculentum, Nicotiana tabacum, Panicum bisulcatum, and P. hylaeicum (C 3); P. maximum (C 4 phosphoenolpyruvate carboxykinase); P. milioides (C 3/C 4); and Bromelia pinguin and Ananas comosus (Crassulacean acid metabolism). Little or no difference between light and dark leaf extracts of RuBPCase was observed in Triticum aestivum (C 3); P. miliaceum (C 4 NAD malic enzyme); Zea mays and Sorghum bicolor (C 4 NADP malic enzyme); Moricandia arvensis (C 3/C 4); and Hydrilla verticillata (submersed aquatic macrophyte). It is concluded that, in many plants, especially Crassulacean acid metabolism and C 3 species, a large fraction of ribulose-1,5-bisphosphate carboxylase/oxygenase in the dark is in an inactivatable state that cannot respond to CO 2 and Mg 2+ activation, but which can be converted to an activatable state upon exposure of the leaf to light. 相似文献
20.
The role of phosphoenolpyruvate carboxylase in photosynthesis in the C 3 plant Nicotiana tabacum has been probed by measurement of the 13C content of various materials. Whole leaf and purified ribulose bisphosphate carboxylase are within the range expected for C 3 plants. Aspartic acid purified following acid hydrolysis of this ribulose bisphosphate carboxylase is enriched in 13C compared to whole protein. Carbons 1-3 of this aspartic acid are in the normal C 3 range, but carbon-4 (obtained by treatment of the aspartic acid with aspartate β-decarboxylase) has an isotopic composition in the range expected for products of C 4 photosynthesis (−5‰), and it appears that more than half of the aspartic acid is synthesized by phosphoenolpyruvate carboxylase using atmospheric CO 2/HCO 3−. Thus, a primary role of phosphoenolpyruvate carboxylase in C 3 plants appears to be the anapleurotic synthesis of four-carbon acids. 相似文献
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