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1.
The rate and extent of light activation of PEPC may be used as another criterion to distinguish C 3 and C 4 plants. Light stimulated phospho enolypyruvate carboxylase (PEPC) in leaf discs of C 4 plants, the activity being three times greater than that in the dark but stimulation of PEPC was limited about 30% over the dark-control in C 3 species. The light activation of PEPC in leaves of C 3 plants was complete within 10 min, while maximum activation in C 4 plants required illumination for more than 20 min, indicating that the relative pace of PEPC activation was slower in C 4 plants than in C 3 plants. Similarly, the dark-deactivation of the enzyme was also slower in leaves of C 4 than in C 3 species. The extent of PEPC stimulation in the alkaline pH range indicated that the dark-adapted form of the C 4 enzyme is very sensitive to changes in pH. The pH of cytosol-enriched cell sap extracted from illuminated leaves of C 4 plants was more alkaline than that of dark-adapted leaves. The extent of such light-dependent alkalization of cell sap was three times higher in C 4 leaves than in C 3 plants. The course of light-induced alkalization and dark-acidification of cytosol-enriched cell sap was markedly similar to the pattern of light activation and dark-deactivation of PEPC in Alternanthera pungens, a C 4 plant. Our report provides preliminary evidence that the photoactivation of PEPC in C 4 plants may be mediated at least partially by the modulation of cytosolic pH.Abbreviations CAM
Crassulacean acid metabolism
- G-6-P
glucose-6-phosphate
- PMSF
phenylmethylsulfonyl fluoride
- PEPC
phospho enolpyruvate carboxylase
- PEPC-PK
phospho enolpyruvate ca carboxylase-protein kinase 相似文献
2.
Feeding K + or Na + nitrate salts in vivo enhanced the activity of phospho enolpyruvate carboxylase (PEPC) in the leaf extracts of Alternanthera pungens (C 4 plant) and A. sessilis (C 3 species). The increase was more pronounced in A. pungens than in A. sessilis. Chloride salts increased the PEPC activity only marginally. However, the sulfate salts were either not effective or inhibitory. Feeding nitrate modulated the regulatory properties of PEPC in A. pungens, resulting in increased K I (malate) and decreased K A (glucose-6-P). The sensitivity of PEPC to malate, which gives a measure of phosphorylation status of the enzyme, indicated that feeding leaves with NO 3
– enhanced the phosphorylation status of the enzyme. The reduction in PEPC activity due to cycloheximide treatment suggested that increased synthesis of PEPC protein kinase may be one of the reasons for the enhancement in PEPC activity, after the nitrate feeding. We suggest that nitrate salts could be used as a tool to modulate and analyze the properties of PEPC in C 3 and C 4 plants. 相似文献
3.
Aiming at understanding the odd case of CAM expression by a C 4 plant, some properties of phospho enolpyruvate carboxylase (PEPC, EC 4.1.1.31, orthophosphate: oxaloacetate carboxylyase, phosphorylating) were comparatively studied
in leaves of CAM-expressing and non-expressing Portulaca oleracea L. plants. CAM expression was induced by growing plants under an 8-h photoperiod and under water-stress. CAM induction in
leaves of these plants (designated as CAM) is indicated by the nocturnal acidification and by the clear diurnal oscillation
pattern and amplitude of acidity, malic acid, and PEPC activity characteristic of CAM plants. Treatment of the other plant
group (designated as C 4) by growth under a 16-h photoperiod and well-watered conditions did not induce expression of the tested criteria of CAM in
plants. In these C 4 plants, the mentioned CAM criteria were undetectable. PEPC from CAM and C 4
Portulaca responded differently to any of the studied assay conditions or effectors. For example, extent and timing of sensitivity
of PEPC to pH change, inhibition by malate, activation by glucose-6-phosphate or inorganic phosphate, and the enzyme affinity
to the substrate PEP were reversed with induction of CAM from the C 4- P. oleracea. These contrasting responses indicate distinct kinetic and regulatory properties of PEPC of the two modes. Thus by shifting
to CAM in the C 4
Portulaca a new PEPC isoform may be synthesised to meet CAM requirements. Simultaneous occurrence of both C 4 and CAM is suggested in P. oleracea when challenged with growth under stress.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
4.
Kinetic characteristics of phospho enolpyruvate carboxylase (PEPC) from the epiphytic C 3 or C 4: CAM intermediate plant, Peperomia camptotricha, were investigated. Few day versus night differences in Vmax, Km(PEP)), or malate inhibition were observed, even in extracts from water-stressed plants which characteristically perform CAM, regardless of efforts to stabilize day/night forms. The PEPC extracted from plants during the light period remained stable, without much of an increase or decrease in activity for at least 22 hours at 0 to 4°C. Extracts from mature, fully developed leaves had slightly greater PEPC activity than from very young, developing leaves. Generally, however, the kinetic properties of PEPC extracted from mature leaves of plants grown under short day (SD), long day (LD), or 1-week water-stress conditions, as well as from young, developing leaves, were similar. The PEPC inhibitor, l-malate, decreased the Vmax and increased the Km(PEP) for all treatments. Under specific conditions, malate did not inhibit PEPC rates in the dark extracts as much as the light. The PEPC activator, glucose-6-phosphate (G-6-P), lowered the Km(PEP) for all treatments. At saturating PEP concentrations, PEPC activity was independent of pH in the range of 7.5 to 9.0. At subsaturating PEP concentrations, the pH optimum was 7.8. The rates of PEPC activity were lower in the light period extracts than the dark, at pH 7.1, but day/night PEPC was equally active at pH 7.8. At pH 7.5 and a subsaturating PEP concentration, G-6-P significantly activated PEPC. At pH 8, however, only slight activation by G-6-P was observed. The lower pH of 7.5 combined with l-malate addition, greatly inhibited PEPC, particularly in extracts from young, developing leaves which were completely inhibited at an l-malate concentration of 1 millimolar. However, malate did not further inhibit PEPC activity in mature leaves when assayed at pH 7.1. The fairly constant day/night kinetic and regulatory properties of PEPC from P. camptotricha are unlike those of PEPC from CAM or C 4 species studied, and are consistent with the photosynthetic metabolism of this plant. 相似文献
5.
The effects of phosphate and several phosphate-containing compounds on the activity of purified phosphoenolpyruvate carboxylase (PEPC) from the crassulacean acid metabolism plant, Crassula argentea, were investigated. When assayed at subsaturating phosphoenolpyruvate (PEP) concentrations, low concentrations of most of the compounds tested were found to stimulate PEPC activity. This activation, variable in extent, was found in all cases to be competitive with glucose 6-phosphate (Glc-6-P) stimulation, suggesting that these effectors bind to the Glc-6-P site. At higher concentrations, depending upon the effector molecule studied, deactivation, inhibition, or no response was observed. More detailed studies were performed with Glc-6-P, AMP, phosphoglycolate, and phosphate. AMP had previously been shown to be a specific ligand for the Glc-6-P site. The main effect of Glc-6-P and AMP on the kinetic parameters was to decrease the apparent Km and increase Vmax/Km. AMP also caused a decrease in the Vmax of the reaction. In contrast, phosphoglycolate acted essentially as a competitive inhibitor increasing the apparent Km for PEP and decreasing Vmax/Km. Inorganic phosphate had a biphasic effect on the kinetic parameters, resulting in a transient decrease in Km followed by an increase of the apparent Km for PEP with increasing concentration of phosphate. The Vmax also was decreased with increasing phosphate concentrations. Further, the enzyme appeared to respond to the complex of phosphate with magnesium. In the presence of a saturating concentration of AMP, no activation but rather inhibition was observed with increasing phosphate concentration. This is consistent with the binding of phosphate to two separate sites--the Glc-6-P activation site and an inhibitory site, a phenomenon that may be occurring with other phosphate containing compounds. High concentrations of phosphate with magnesium were found to protect enzyme activity when PEPC, previously shown to contain an essential arginine at the active site, was incubated with the specific arginyl reagent 2,3-butanedione, consistent with the binding of phosphate at the active site. Data were successfully fitted to a rapid equilibrium model allowing for binding of the phosphate-magnesium complex to both the activation site and the active site which accounts for the activation/deactivation observed at low substrate concentrations. Effects on the Vmax of the reaction are also addressed. Factors controlling the differential affinity of various effectors to the active site or activation site appear to include charge distribution, size, and other steric factors. 相似文献
6.
C4-like plants represent the penultimate stage of evolution from C3 to C4 plants. Although Coleataenia prionitis (formerly Panicum prionitis) has been described as a C4 plant, its leaf anatomy and gas exchange traits suggest that it may be a C4-like plant. Here, we reexamined the leaf structure and biochemical and physiological traits of photosynthesis in this grass. The large vascular bundles were surrounded by two layers of bundle sheath (BS): a colorless outer BS and a chloroplast-rich inner BS. Small vascular bundles, which generally had a single BS layer with various vascular structures, also occurred throughout the mesophyll together with BS cells not associated with vascular tissue. The mesophyll cells did not show a radial arrangement typical of Kranz anatomy. These features suggest that the leaf anatomy of C. prionitis is on the evolutionary pathway to a complete C4 Kranz type. Phosphoenolpyruvate carboxylase (PEPC) and pyruvate, Pi dikinase occurred in the mesophyll and outer BS. Glycine decarboxylase was confined to the inner BS. Ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) accumulated in the mesophyll and both BSs. C. prionitis had biochemical traits of NADP-malic enzyme type, whereas its gas exchange traits were close to those of C4-like intermediate plants rather than C4 plants. A gas exchange study with a PEPC inhibitor suggested that Rubisco in the mesophyll could fix atmospheric CO2. These data demonstrate that C. prionitis is not a true C4 plant but should be considered as a C4-like plant. 相似文献
7.
Pyruvate kinase (EC2.7.1.40) from Rhodopseudomonas sphaeroides was purified 40-fold by precipitation with protamine sulfate and ammonium sulfate followed by gelfiltration. The preparations obtained from cells grown with different carbon sources or cultural conditions differ with respect to specific activity but not with respect to molecular weight (250000 dalton) or regulatory properties. The phosphoenolpyruvate (PEP)-saturation curve of the enzyme is sigmoidal with Hill coefficients varying from n H =1.8 (pH 9.2) to 2.7 (pH 6.0). The enzyme is activated by adenosinemonophosphate (AMP) and the sugarmonophosphates ribose-5-phosphate (R-5-P), glucose-6-phosphate (G-6-P), and-to a lesser extent-fructose-6-phosphate (F-6-P). Fructose-1.6-bisphosphate (FDP) has no measurable effect. Inhibitors of the enzyme are adenosintriphosphate (ATP), inorganic phosphate ( P i ) and the dicarboxylic acids succinate and fumarate. Kinetic analysis reveals that the sugar-phosphates and the dicarboxylic acids act as true allosteric ligands, wheras the effects of AMP, ATP, and P i cannot be interpreted solely in terms of allosteric interactions. Cold-treatment of the enzyme leads to a rapid loss of activity, but does not change the regulatory properties of the enzyme. Analysis of the kinetics of cold-inactivation and its reversal at 30°C, together with studies on the gelfiltration behaviour of the native and the cold-treated enzyme make it likely that the cold-induced loss of activity is due to a dissociation of the enzyme. 相似文献
8.
C 4 plants can more efficiently fix carbon in drought, high temperatures, and limitations of nitrogen or CO 2. Primary carboxylation is mediated by phosphoenolpyruvate carboxylase (PEPC, 4.1.1.31) in mesophyll cytosol of C 4 plants. Studies on hormonal regulation of C 4 PEPC have been quite limited. We have examined the activity/regulation of PEPC by abscisic acid (ABA), a plant hormone, in the leaves of Amaranthus hypochondriacus. PEPC activity was enhanced upon 1-h incubation with 20 μM ABA by about 30% in dark and more than 2-fold in light. Glucose-6-phosphate activation of PEPC was enhanced, and sensitivity to l-malate was decreased after ABA treatment. Butyric acid (a weak acid) decreased PEPC activity and restricted the stimulation by ABA. In contrast, methylamine (an alkalinizing agent) increased the PEPC activity and enhanced the effect of ABA. ABA increased the levels of PEPC protein as well as its mRNA. Butyric acid/methylamine modulated the changes induced by ABA of PEPC protein and mRNA levels, indicating that acidification/alkalinization of leaf disks was very important. Our results emphasize the marked modulation of PEPC in C 4 plants, by ABA. Such modulation by ABA could be significant when C 4 plants are under water stress, when ABA is known to accumulate. When present, cycloheximide decreased the PEPC protein levels and restricted the extent of activation by ABA. We conclude that the enhancement by ABA of PEPC activity depends on cellular alkalinization as well as elevated PEPC protein levels. 相似文献
9.
Phosphoenolpyruvate carboxylase (PEPC) from several C 3 plants was compared to maize PEPC by immunoblotting using an antibody against maize PEPC and by peptide mapping. In C 3 gramineous plants, PEPCs of slightly different monomeric sizes were detected as two bands for wheat and barley leaves, as three bands for etiolated maize leaves and as four bands for rice leaves by SDS-polyacrylamide gel electrophoresis and immunoblotting, whereas only one PEPC band was detected for maize leaves, a C 4 plant, or tobacco leaves, a dicotyledonous C 3 plant. The peptide fragment patterns of the lower molecular weight PEPC (major band in immunoblotting) in wheat leaves was similar to that of maize PEPC in peptide mapping by protein staining or by immunological detection, but the upper one (minor band) had a different pattern from the lower one in peptide mapping by immunological detection and few peptide fragments from this were recognized by the anti-(maize) PEPC antibody. These results suggest that there are multiple forms of PEPC subunits in the gramineous plants tested, and the major PEPC has a primary structure similar to that of maize PEPC. To obtain information about the expression of PEPCs in C 3 plants, changes in the amount of PEPC protein were investigated during the greening of rice and wheat seedlings. Judging from the regulation by light, there were two types of PEPCs in greening rice seedlings, one induced by light and the other reduced by it. Greening wheat seedlings also show a PEPC band induced by light. These findings indicate that some PEPCs in C 3 gramineous plants not only have structures similar to that of maize PEPC, but also are regulated by light in a similar manner. 相似文献
10.
Phospho enolpyruvate carboxylase (PEPC) was purified from leaves of four species of Alternanthera differing in their photosynthetic carbon metabolism: Alternanthera sessilis (C 3), A. pungens (C 4), A. ficoides and A. tenella (C 3-C 4 intermediates or C 3-C 4). The activity and properties of PEPC were examined at limiting (0.05 mM) or saturating (10 mM) bicarbonate concentrations.
The V max as well as K m values (for Mg 2+ or PEP) of PEPC from A. ficoides and A. tenella (C 3-C 4 intermediates) were in between those of C 3 ( A. sessilis) and C 4 species ( A. pungens). Similarly, the sensitivity of PEPC to malate (an inhibitor) or G-6-P (an activator) of A. ficoides and A. tenella (C 3-C 4) was also of intermediate status between those of C 3 and C 4 species of A. sessilis and A. pungens, respectively. In all the four species, the maximal activity (V max), affinity for PEP (K m), and the sensitivity to malate (K I) or G-6-P (K A) of PEPC were higher at 10 mM bicarbonate than at 0.05 mM bicarbonate. Again, the sensitivity to bicarbonate of PEPC from
C 3-C 4 intermediates was in between those of C 3- and C 4-species. Thus the characteristics of PEPC of C 3-C 4 intermediate species of Alternanthera are intermediate between C 3- and C 4-type, in both their kinetic and regulatory properties. Bicarbonate could be an important modulator of PEPC, particularly
in C 4 plants.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
11.
When Tris–SO 4was used as an extraction buffer for phosphoenolpyruvate carboxylase (PEPC) from leaves of the C 4plant Cynodon dactylon(L.) Pers., a higher extractable activity was obtained as compared to Tris–HCl, especially at low phosphoenolpyruvate concentrations and an assay pH of 7.2. The Tris–SO 4-extracted PEPC activity was stable under dilution and remained unchanged for at least 24 h at 22°C. This enzyme was less sensitive to both activation by glucose-6-phosphate and inhibition by L-malate. The effects of Tris–SO 4could be attributed to its preferential exclusion from the enzymic protein domain and, therefore, to a shifting of this oligomeric enzyme to a more aggregable form that is more stable and active. 相似文献
12.
To compare the differences in physiology and metabolism between phosphoenolpyruvate carboxylase (PEPC) transgenic rice and its control, untransformed wild rice, dry matter accumulation, soluble sugar, starch and protein contents and enzyme activities were determined in different plant parts during flowering. Results revealed that PEPC transgenic rice had higher dry weights for leaf, stem and sheath as well as panicle than the untransformed wild rice did, with the largest increase in the panicle. Soluble sugar and protein content in the grains of PEPC transgenic rice were significantly enhanced while starch content changed less. PEPC transgenic rice exhibited high levels of PEPC activity, manifesting in high net photosynthetic rates during flowering. Moreover, transgenic rice with high PEPC expression levels also had elevated levels of the enzymes such as sucrose- p-synthase and sucrose synthase, which may confer a higher capacity to assimilate CO 2 into sucrose. Little increase in grain starch content was observed in transgenic plants due to the stable activities of starch synthase and Q enzyme. However, the PEPC transgenic rice plant induced the activities of nitrate reductase, glutamate oxaloacetate transaminase, glutamate pyruvate transaminase, glutamine synthetase, and asparagine synthase to high levels, as compared with the untransformed rice plant. PEPC activity was correlated with protein content in grains and the enzymes of nitrogen metabolism, suggesting that high PEPC activity in transgenic rice might be able to redirect carbon and nitrogen flow by regulating some enzymes related to carbon or nitrogen metabolisms. These results may help to understand how the C 3 plants possessing a C 4-like photosynthesis pathway worked by expression of PEPC. 相似文献
13.
A Zea mays callus culture containing chlorophyll was established and grown photomixotrophically. Cell chloroplast structure, and pigment and soluble protein contents were examined. Expression of some key enzymes of C 4 carbon metabolism was compared with that of etiolated (heterotrophic) and green photoautotrophic leaves. Chlorophyll content of the callus was 15–20% that of green leaves. Soluble protein content of callus was half that of leaf cells. Electron microscopic observations showed that green callus cells contained only typical granal chloroplasts. Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco, EC 4.1.1.38) activities in green callus were ca 30% those of green leaves but 2–3 times higher than in etiolated leaves. Quantitative enzyme protein determination, using antibodies specific to maize leaf Rubisco showed that the chloroplastic carboxylase represented about 7% of total soluble protein in green callus, in parallel to its low chlorophyll content. The specific activity of Rubisco in callus and leaves was unchanged. Phosphoenolpyruvate carboxylase (PEPC, EC 4.1.1.31) activity in green callus was about 20% that of green leaves and similar to that measured in etiolated leaves. Apparent K m (PEP) values (0.08 m M) for PEPC isolated from green callus and etiolated leaves were very different from values (0.5 m M) obtained with PEPC from green leaves. These kinetic characteristics together with the absence of inhibition by malate and activation by glucose-6-phosphate suggest that the properties of PEPC isolated from green callus and etiolated maize leaves are very similar to those of PEPPC from C 3 plants. Using PEPC antibodies specific to green maize leaf enzyme, immunotitration of PEPC preparations containing identical enzyme units allowed complete precipitation of the green leaf enzyme with increasing antibody volumes. In contrast, 60–70% of the activity of PEPC from etiolated and green callus was inhibited, suggesting low affinity for the maize green leaf PEPC antiserum (typical C 4 form). Ouchterlony double diffusion tests revealed only partial recognition of PEPC in green callus and etiolated leaves. NAD-malate dehydrogenase (NAD-MDH, EC 1.1.1.37) activity in callus was 2 and 3 times higher, respectively, than in etiolated and green leaves. NADP-malic enzyme (NADP-ME, EC 1.1.1.40) activity in callus cultures was much lower than in green leaves. All our data support the hypothesis that cultures of fully dedifferentiated chlorophyllous tissues of Zea mays possess a C 3-like metabolism. 相似文献
14.
The induction of a Crassulacean acid like metabolism (CAM) was evidenced after 21–23 days of drought stress in the C 4 succulent plant Portulaca oleracea L. by changes in the CO 2 exchange pattern, in malic acid content and in titratable acidity during the day–night cycle. Light microscopy studies also
revealed differences in the leaf structure after the drought treatment. Following the induction of the CAM-like metabolism,
the regulatory properties of phosphoenolpyruvate carboxylase (PEPC, EC 4.1.1.31), the enzyme responsible for the diurnal fixation
of CO 2 in C 4 plants but nocturnal in CAM plants, were studied. The enzyme from stressed plants showed different kinetic properties with
respect to controls, notably its lack of cooperativity, higher sensitivity to L-malate inhibition, higher PEP affinity and
lower enzyme content on a protein basis. In both conditions, PEPC's subunit mass was 110 kDa, although changes in the isoelectric
point and electrophoretic mobility of the native enzyme were observed. In vivo phosphorylation and native isoelectrofocusing studies indicated variations in the phosphorylation status of the enzyme of
samples collected during the night and day, which was clearly different for the control and stressed groups of plants. The
results presented suggest that PEPC activity and regulation are modified upon drought stress treatment in a way that allows
P. oleracea to perform a CAM-like metabolism.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
15.
Phospho enolpyruvate carboxylase (PEPC) genes from Corynebacterium glutamicum (cppc), Escherichia coli (eppc) or Flaveria trinervia (fppc) were transferred to Solanum tuberosum. Plant regenerants producing foreign PEPC were identified by Western blot analysis. Maximum PEPC activities measured in eppc and fppc plants grown in the greenhouse were doubled compared to control plants. For cppc a transgenic plant line could be selected which exhibited a fourfold increase in PEPC activity. In the presence of acetyl-CoA, a known activator of the procaryotic PEPC, a sixfold higher activity level was observed. In cppc plants grown in axenic culture PEPC activities were even higher. There was a 6-fold or 12-fold increase in the PEPC activities compared to the controls measured in the absence or presence of acetyl-CoA, respectively. Comparable results were obtained by transient expression in Nicotiana tabacum protoplasts. PEPC of C. glutamicum (PEPC C.g.) in S. tuberosum leaf extracts displays its characteristic K
m(PEP) value. Plant growth was examined with plants showing high expression of PEPC and, moreover, with a plant cell line expressing and antisense S. tuberosum (anti-sppc) gene. In axenic culture the growth rate of a cppc plant cell line was appreciably diminished, whereas growth rates of an anti-sppc line were similar or slightly higher than in controls. Malate levels were increased in cppc plants and decreased in antisense plants. There were no significant differences in photosynthetic electron transport or steady state CO 2 assimilation between control plants and transformants overexpressing PEPC C.g. or anti-sppc plants. However, a prolonged dark treatment resulted in a delayed induction of photosynthetic electron transport in plants with less PEPC. Rates of CO 2 release in the dark determined after a 45 min illumination period at a high proton flux density were considerably enhanced in cppc plants and slightly diminished in anti-sppc plants. When CO 2 assimilation rates were corrected for estimated rates of mitochondrial respiration in the light, the electron requirement for CO 2 assimilation determined in low CO 2 was slightly lower in transformants with higher PEPC, whereas transformants with decreased PEPC exhibited an appreciably elevated electron requirement. The CO 2 compensation point remained unchanged in plants (cppc) with high PEPC activity, but might be increased in an antisense plant cell line. Stomatal opening was delayed in antisense plants, but was accelerated in plants overexpressing PEPC C.g. compared to the controls.Abbreviations
CO 2 compensation point
- CO 2
quantum efficiency of CO 2 assimilation
- PSII
quantum efficiency of photosystem II electron transport
- A
CO 2 assimilation rate
- C i
intercellular CO 2 concentration; e, electron
- PFD
photon flux density
- Q A
primary quinone electron acceptor of photosystem II
- Q N
non-photochemical chlorophyll a fluorescence quenching
- q P
photochemical chlorophyll a fluorescence quenching 相似文献
16.
Antiserum was prepared in rabbits against purified alfalfa ( Medicago sativa L.) nodule phosphoenolpyruvate carboxylase (PEPC). Immunotitration assays revealed that the antiserum recognized the enzyme from alfalfa nodules, uninoculated alfalfa roots, and from soybean nodules. Tandem-crossed immunoelectrophoresis showed that the PEPC protein from alfalfa roots and nodules was immunologically indistinguishable. The 101 kilodalton polypeptide subunit of alfalfa nodule PEPC was identified on Western blots. The PEPC polypeptide was detected in low quantities in young alfalfa roots and nodules but was present at increased levels in mature nodules. Senescent nodules appeared to contain a reduced amount of the PEPC polypeptide. PEPC was also detected by western blot in some plant- and bacterially-conditioned ineffective alfalfa nodules but was not detected in bacteroids isolated from effective nodules. Alfalfa nodule PEPC is constitutively expressed in low levels in roots. In nodules, expression of PEPC polypeptide increases several-fold, resulting in increased PEPC activity. Antiserum prepared against the C 4 PEPC from maize leaves recognized the PEPC enzyme in all legume nodules and roots tested, while the antiserum prepared against alfalfa nodule PEPC also recognized the leaf PEPC of several C 4 plant species. Neither antiserum reacted strongly with any C 3 leaf proteins. The molecular weight of the PEPC polypeptide from C 4 leaves and legume nodules appears to be similar. 相似文献
17.
This review attempts to summarize the large body of information on the structure, regulation and biosynthesis of the enzyme phosphoenolpyruvate carboxylase in C 4 plants which has accumulated particularly since the appearance of the last review in 1987. Among the major discoveries are the involvement of protein phosphorylation-dephosphorylation cascade in the light activation of the enzyme, extraction and characteristics of PEPC-protein serine kinase, dynamic changes in oligomeric state of the enzyme in response to pH or temperature, isolation of multiple cDNAs encoding different forms of PEPC and cloning and expression of maize/sorghum PEPC in transgenic tobacco or transformed E. coli cells. Further experiments using advanced techniques of biochemistry and molecular biology would help in understanding the molecular mechanism of reaction, regulation of enzyme activity, gene expression and evolutionary pattern of C 4 PEPC. 相似文献
18.
Measurements of net CO 2 exchange, malate accumulation, properties and capacity of phosphoenolpyruvate carboxylase (PEPC, EC 4.1.1.31) in leaves of different ages of two short-day dependent Crassulacean acid metabolism (CAM) plants ( Kalanchoe blossfeldiana v. Poelln. Tom thumb and K. velutina Welw.) show that, in both species: a) young leaves from plants grown under long days display a CO 2 exchange pattern typical of C 3 plants; b) leaf aging promotes CAM under long-day conditions; c) short-day treatment induces CAM in young leaves to a higher degree than aging under long days; d) at least in K. blossfeldiana, the PEPC form developed with leaf aging under long days and the enzyme form synthetized de novo in young leaves grown under short days were shown to have similar properties. Short days also promote CAM in older leaves though at a lesser extent than in young leaves: The result is that this photoperiodic treatment increases the general level of CAM performance by the whole plant. The physiological meaning of the control of PEPC capacity by photoperiodism could be to afford a precisely timed seasonal increase in CAM potentiality, enabling the plant to immediately optimize its response to the onset of drought periods.Abbreviations CAM
Crassulacean acid metabolism
- PEP
phosphoenolpyruvate
- PEPC
phosphoenolpyruvate carboxylase (EC 4.1.1.31)
- LD
long day
- SD
short day 相似文献
20.
A comparison of the activity and properties of the enzyme phosphoenolpyruvatecarboxylase (PEPC) was made for plants of Sedum telephium L.grown under low (70 µmol m 2 s 1) or high(500µmol m 2 s 1) PPFD and subjected to varyingdegrees of water stress. Under well-watered conditions onlyplants grown under high PPFD accumulated titratable acidityovernight and the extractable activity of PEPC was almost 2-foldhigher in these plants than in plants grown under low PPFD.Increasing drought stress resulted in a substantial increasein the activity of PEPC extracted both during the light anddark periods and a decrease in the sensitivity to inhibitionby malic acid. The magnitude of these changes was determinedby the severity and duration of drought and by light intensity.A comparison of the kinetic properties of PEPC from severelydroughted plants revealed that plants droughted under high PPFDhad a lower Km for PEP than plants under low PPFD. Additionof 2·0 mol m 3 malate resulted in an increase inthe K m for PEP, with plants draughted under low PPFD havinga significantly higher Km in the presence of malic acid comparedto those under high PPFD. Response to the activator glc-6-P,which lowered the Km for PEP, also varied between plants grownunder the two light regimes. Under well-watered conditions PEPCextracted from plants under high PPFD was more sensitive toactivation by glc-6-P than those under low PPFD. After the severedrought treatment, however, the Km for PEP in the presence ofglc-6-P was similar for enzyme extracted from plants grown underboth light regimes. Soluble sugars and starch were depletedovernight and were both possible sources of substrate for PEPC.With increasing drought, however, the depletion of starch relativeto soluble sugars increased under both light regimes. The propertiesof PEPC and the characteristics of carbohydrate accumulation/depletionare discussed in relation to the regulation of CAM in S. telephiumgrown under different light and watering regimes. Key words: PEP carboxylase, CAM, carbohydrates, Sedum telephium 相似文献
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