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1.
Respiratory metabolism during cold storage of apple fruit. I. Sucrose metabolism and glycolysis 总被引:1,自引:0,他引:1
This study provides the first report on the occurrence of the respiratory climacteric during cold storage of apple fruit ( Malus domestica Borkh. cv. Reinette du Canada). The respiratory pattern at 4°C was very similar to that observed during postharvest ripening at room temperature, except that shelf life was considerably extended and the onset of the climacteric delayed. Increasing the calcium content of the apple fruit significantly reduced loss of firmness during cold storage, but showed no effect on respiration or on the other parameters determined. A gradual accumulation of soluble sugars occurred during the first 60 days after harvest and was effectively completed before the climacteric peak was reached. This increase in sugars correlated with an increase in the activity of sucrose-phosphate synthase (EC 2.4.1.14), and a marked change in the kinetic properties of the enzyme was observed after sucrose accumulation ceased. Changes in the hexose-phosphate pool and in glycolytic and gluconeogenic activities indicated an initial increase in the gluconeogenic flow at early stages of the climacteric, followed by activation of glycolysis, with the carbon flow being most likely regulated at the reversible phosphorylation of fructose-6-phosphate to fructose-1,6-bisphosphate (mostly via pyrophosphate:fructose-6-phosphate phosphotransferase, EC 2.7.1.90) and at the pyruvate kinase (EC 2.7.1.40) steps. The results presented indicate that the respiratory climacteric does not occur to accommodate extra ATP requirements during sucrose synthesis nor can it be a consequence of an increased supply of respiratory substrate. 相似文献
2.
(i) We have studied the influence of reduced phosphoglucose-isomerase (PGI) activity on photosynthetic carbon metabolism in mutants of Clarkia xantiana Gray (Onagraceae). The mutants had reduced plastid (75% or 50% of wildtype) or reduced cytosolic (64%, 36% or 18% of wildtype) PGI activity. (ii) Reduced plastid PGI had no significant effect on metabolism in low light. In high light, starch synthesis decreased by 50%. There was no corresponding increase of sucrose synthesis. Instead glycerate-3-phosphate, ribulose-1,5-bisphosphate, reduction of QA (the acceptor for photosystem II) and energy-dependent chlorophyll-fluorescence quenching increased, and O2 evolution was inhibited by 25%. (iii) Decreased cytosolic PGI led to lower rates of sucrose synthesis, increased fructose-2,6-bisphosphate, glycerate-3-phosphate and ribulose-1,5-bisphosphate, and a stimulation of starch synthesis, but without a significant inhibition of O2 evolution. Partitioning was most affected in low light, while the metabolite levels changed more at saturating irradiances. (iv) These results provide decisive evidence that fructose-2,6-bisphosphate can mediate a feedback inhibition of sucrose synthesis in response to accumulating hexose phosphates. They also provide evidence that the ensuing stimulation of starch synthesis is due to activation of ADP-glucose pyrophosphorylase by a rising glycerate-3-phosphate: inorganic phosphate ratio, and that this can occur without any loss of photosynthetic rate. However the effectiveness of these mechanisms varies, depending on the conditions. (v) These results are analysed using the approach of Kacser and Burns (1973, Trends Biochem. Sci. 7, 1149–1161) to provide estimates for the elasticities and flux-control coefficient of the cytosolic fructose-1,6-bisphosphatase, and to estimate the gain in the fructose-2,6-bisphosphate regulator cycle during feedback inhibition of sucrose synthesis.Abbreviations and symbols Chl
chlorophyll
- Fru6P
fructose-6-phosphate
- Frul,6bisP
fructose-1,6-bisphosphate
- Fru-1,6Pase
fructose-1,6-bisphosphatase
- Fru2,6bisP
fructose-2,6-bisphosphate
- Fru2,6Pase
fructose-2,6-bisphosphatase
- Glc6P
glucose-6-phosphate
- PGI
phosphoglucose isomerase
- Pi
inorganic phosphate
- QA
acceptor for photosystem II
- Ru1,5bisP
ributose-1,5-bisphosphate
- SPS
sucrose-phosphate synthase 相似文献
3.
It has been investigated whether diurnal rhythms of sucrose-phosphate synthase (SPS) are involved in controlling the rate of photosynthetic sucrose synthesis. Extracts were prepared from spinach (Spinacia oleracea L.) and barley (Hordeum vulgare L.) leaves and assayed for enzyme activity. The activity of SPS increased in parallel with a rising rate of photosynthesis, and was increased by feeding mannose and decreased by supplying inorganic phosphate. In leaf material where sucrose had accumulated during the photoperiod or when sucrose was supplied exogenously, SPS activity decreased. During a diurnal rhythm, SPS activity increased after illumination, declined gradually during the light period, decreased further after darkening and then recovered gradually during the night. These changes did not involve an alteration of the maximal activity, but were caused by changes in the kinetic properties, revealed as a change in sensitivity to inhibition by inorganic phosphate. In experiments which modelled the response of SPS to changing metabolite concentrations, it was shown that these alterations of kinetic properties would strongly modify the activity of SPS in vivo. It is proposed that SPS can exist in kinetically distinct forms in vivo, and that the distribution between these forms can be rapidly altered. As the rate of photosynthesis increases there is an activation of SPS, which may be directly or indirectly linked to changes in the availability of Pi. This activation can be modified by factors related to the accumulation of sucrose. Under normal conditions there is a balance between these factors, and the leaf contains a mixture of the different forms of SPS.Abbreviations Chl
chlorophyll
- Frul,6bisP
fructose-1,6-bisphosphate
- Fru2,6bisP
fructose-2,6-bisphosphate
- Fru6P
fructose-6-phosphate
- Fru1,6bisPase
fructose-1,6-bisphosphatase
- Fru6P 2kinase
fructose-6-phosphate, 2kinase
- Fru2,6bisPase
fructose-2,6-bisphosphatase
- Glc6P
glucose-6-phosphate
- Pj
inorganic phosphate
- SPS
sucrose-phosphate synthase
- UDPGLc
uridine 5-diphosphate glucose 相似文献
4.
Spinach leaf discs were floated on methyl-viologen solutions (5–200 nmol·l-1) and the effect on photosynthetic metabolism was then investigated under conditions of saturating CO2. Methyl viologen led to increased non-photochemical quenching, and the ATP/ADP ratio increased from <2 to >10. Comparison of the apparent quantum yield and non-photochemical quenching indicated that these concentrations of methyl viologen were only catalysing a marginal electron flux, and that the decrease in quantum yield was mainly the result of pH-triggered energy dissipation. Similar changes were also obtained after supplying tentoxin to inhibit the chloroplast ATP synthase and increase the energisation of the thylakoids. The photosystem-II acceptor, QA, was monitored by photochemical fluorescence quenching, and became more reduced. In contrast, the activation of NADP-malate dehydrogenase decreased, showing that the acceptor side of photosystem I becomes more oxidised. Similar changes were observed after supplying tentoxin. It is concluded that increased thylakoid energisation can lead to a substantial restriction of linear electron transport. Analysis of metabolite levels showed that glycerate-3-phosphate reduction was imporved, but that there was a large accumulation of triose phosphates and fructose-1,6-bisphosphate. This is the consequence of an inhibition of the regeneration of ribulose-1,5-bisphosphate, caused by inactivation of the stromal fructose-1,6-bisphosphatase and, to a lesser extent, phosphoribulokinase. Methyl viologen also led to inactivation of sucrose-phosphate synthase, and abolished the response of fructose-2,6-bisphosphate to rising rates of photosynthesis. This provides evidence for a primary role of glycerate-3-phosphate in controlling the activity of fructose-6-phosphate, 2-kinase and, thence, the fructose-2,6-bisphosphate concentration as the rate of photosynthesis increases. It is concluded that the very moderate ATP/ADP ratios found in chloroplasts are the results of constraints on the operation of ATP synthase. They can be increased if the thylakoid energisation is increased. However, the increased energisation acts directly or indirectly to disrupt many other aspects of photosynthetic metabolism including linear electron transport, activation of the Calvin cycle, and the control of sucrose and starch synthesis.Abbreviations and symbols Frul,6P2 (Fru1,6Pase)
fructose-1,6-bisphosphate(ase)
- Fru2,6P, (Fru2,6Pase)
fructose-2,6-bisphosphate(-ase)
- Fru6P
fructose-6-phosphate
- Glc6P
glucose-6-phosphate
- Pi
inorganic phosphate
- PSI and PSII
photosystems I and II
- qE
high energy' quenching of chlorophyll fluorescence
- PGA
glycerate-3-phosphate
- QA
primary stable acceptor of PSII
- Ru5P (Ru1,5P2)
ribulose-5-phosphate (-1,5-bisphosphate)
- SPS
sucrose-phosphate synthase
- triose P
dihydroxyacetone phosphate plus glyceraldehyde-3-phosphate
-
s
apparent quantum yield
Dedicated to Professor E. Latzko on the occasion of his 65th birthday 相似文献
5.
Leaves on transgenic tobacco plants expressing yeast-derived invertase in the apoplast develop clearly demarcated green and bleached sectors when they mature. The green areas contain low levels of soluble sugars and starch which are turned over on a daily basis, and have high rates of photosynthesis and low rates of respiration. The pale areas accumulate carbohydrate, photosynthesis is inhibited, and respiration increases. This provides a model system to investigate the sink regulation of photosynthetic metabolism by accumulating carbohydrate. The inhibition of photosynthesis is accompanied by a decrease of ribulose-1,5-bisphosphate and glycerate-3-phosphate, and an increase of triosephosphate and fructose-1,6-bisphosphate. The extracted activities of ribulose-1,5-bisphosphate carboxylase, fructose-1, 6-bisphosphatase and NADP-glyeraldehyde-3-phosphate dehydrogenase decreased. The activity of sucrose-phosphate synthase remained high or increased, an increased portion of the photosynthate was partitioned into soluble sugars rather than starch, and the pale areas showed few or no oscillations during transitions between darkness and saturating light in saturating CO2. The increased rate of respiration was accompanied by an increased level of hexose-phosphates, triose-phosphates and fructose-1,6-bisphosphate while glycerate-3-phosphate and phosphoenolpyruvate decreased and pyruvate increased. The activities of pyruvate kinase, phosphofructokinase and pyrophosphate: fructose-6-phosphate phosphotransferase increased two- to four-fold. We conclude that an increased level of carbohydrate leads to a decreased level of Calvin-cycle enzymes and, thence, to an inhibition of photosynthesis. It also leads to an increased level of glycolytic enzymes and, thence, to a stimulation of respiration. These changes of enzymes are more important in middle- or long-term adjustments to high carbohydrate levels in the leaf than fine regulation due to depletion of inorganic phosphate or high levels of phosphorylated metabolites.Abbreviations Fru 1,6bisP
fructose-1,6-bisphosphate
- Fru 1,6bisPase
fructose-1,6-bisphosphatase
- Fru6P
fructose-6-phosphate
- Glc 1P
glucose-1-phosphate
- Glc6P
glucose-6-phosphate
- NADP-GAPDH
NADP-dependent glyceraldehyde-3-phosphate dehydrogenase
- PFK
phosphofructokinase
- PEP
phosphoenolpyruvate
- PFP
pyrophosphate:fructose-6-phosphate phosphotransferase
- PGA
glycerate-3-phosphate
- PK
pyruvate kinase
- Pi
inorganic phosphate
- Ru1,5bisP
ribulose-1,5-bisphosphate
- Rubisco
ribulose-1,5-bisphosphate carboxylase-oxygenase
- SPS
sucrose-phosphate synthase
- triose-P
triose-phosphates 相似文献
6.
Banana ripening: implications of changes in glycolytic intermediate concentrations, glycolytic and gluconeogenic carbon flux, and fructose 2,6-bisphosphate concentration 下载免费PDF全文
In ripening banana (Musa sp. [AAA group, Cavendish subgroup] cv Valery) fruit, the concentration of glycolytic intermediates increased in response to the rapid conversion of starch to sugars and CO2. Glucose 6-phosphate (G-6-P), fructose 6-phosphate (Fru 6-P), and pyruvate (Pyr) levels changed in synchrony, increasing to a maximum one day past the peak in ethylene synthesis and declining rapidly thereafter. Fructose 1,6-bisphosphate (Fru 1,6-P2) and phosphoenolpyruvate (PEP) levels underwent changes dissimilar to those of G 6-P, Fru 6-P, and Pyr, indicating that carbon was regulated at the PEP/Pyr and Fru 6-P/Fru 1,6-P2 interconversion sites. During the climacteric respiratory rise, gluconeogenic carbon flux increased 50- to 100-fold while glycolytic carbon flux increased only 4- to 5-fold. After the climacteric peak in CO2 production, gluconeogenic carbon flux dropped dramatically while glycolytic carbon flux remained elevated. The steady-state fructose 2,6-bisphosphate (Fru 2,6-P2) concentration decreased to ½ that of preclimacteric fruit during the period coinciding with the rapid increase in gluconeogenesis. Fru 2,6-P2 concentration increased thereafter as glycolytic carbon flux increased relative to gluconeogenic carbon flux. It appears likely that the initial increase in respiration in ripening banana fruit is due to the rapid influx of carbon into the cytosol as starch is degraded. As starch reserves are depleted and the levels of intermediates decline, the continued enhancement of respiration may, in part, be maintained by an increased steady-state Fru 2,6-P2 concentration acting to promote glycolytic carbon flux at the step responsible for the interconversion of Fru 6-P and Fru 1,6-P2. 相似文献
7.
Xuemei Li Michael Pfiz Manfred Küppers Werner Einig Heinz Rennenberg Rüdiger Hampp 《Trees - Structure and Function》2003,17(3):221-227
Sucrose-phosphate synthase (SPS; E.C. 2.4.1.14) was studied in 1-year-old leaves of the xylem-parasitic mistletoe (Viscum album L.), growing on Abies alba. Glucose-6-phosphate served as an allosteric activator of mistletoe SPS, increasing the affinity for both substrates, fructose-6-phosphate and UDP-glucose. The activation state of SPS, i.e. the ratio of substrate limited versus non-limited activity, showed two clear peaks between February and July which coincided with increased rates of net photosynthesis of the parasite. Periods of decreased SPS activity were accompanied by a transient accumulation of sucrose and starch. In samples exhibiting a high activation state, activity was decreased by incubation of the extract with ATP; however, ATP did not affect SPS activity in samples exhibiting a low activation state of SPS. In parallel to the first increase of the activation state in March, pool sizes of the positive effector glucose-6-phosphate were high, whereas pool sizes of fructose-2,6-bisphosphate, an inhibitor of sucroneogenesis, were low. The decline in the activation state in April occurred in parallel with increased rates of transpiration of the parasite. This could have increased the availability of host-derived sugars, although the xylem sap of A. alba showed rather consistent concentrations of total soluble sugars throughout the vegetation period (1.1-3.9 mM). We thus speculate that sugar availability in the host xylem controls carbohydrate metabolism in the parasite. 相似文献
8.
Vanadate inhibits fructose-2,6-bisphosphatase and leads to an inhibition of sucrose synthesis in barley leaves 总被引:1,自引:0,他引:1
Vanadate (0.1–1 mM) was supplied to leaves of barley (Hordeum vulgare var. Roland) via the transpiration stream. It led to a selective inhibition of the rate of photosynthesis at high light without altering the initial slope of the light response curve, produced markedly biphasic photosynthesis induction kinetics, and selectively decreased sucrose synthesis compared to starch synthesis. There was a 3-fold increase of the steady state level of the signal metabolite fructose-2,6-bisphosphate in near saturating light. Fructose-2,6-bisphosphate is a potent inhibitor of cytosolic fruc-tose-l,6-bisphosphatase and, in agreement, the fructose-1,6-bisphosphatc level doubled. The increase of fructose-2,6-bisphosphate could not be accounted for by the known regulation of fructose-6-phosphate,2-kinase and fructose 2,6-bisphosphatase by 3-phosphoglycerate and fiuctose-6-phosphate, because these metabolites remained constant or even changed in the opposite direction to that required to generate an increase of fructose-2,6-bisphosphate. Instead, vanadate strongly inhibited the hydrolysis of fructose-2,6-bisphosphate in extracts, producing a half maximal inhibition at 2 \nM and 50 \iM in assays designed to preferentially measure the high-and low-affinity forms of fructose-2,6-bisphosphatase, respectively. Vanadale had no effect on fructosc-6-phosphate,2-kinase activity at these concentrations. Vanadate also led to a deactivation of sucrose phosphate synthase. The results are discussed in relation to the role of fructose-2,6-bisphosphate in regulating sucrose synthesis, and its interaction with the 'coarse' control of sucrose phosphate synthase. 相似文献
9.
The aim of this work was to identify which aspects of photosynthetic metabolism respond most sensitively to leaf water deficit. Spinach (Spinacia oleracea L.) leaf discs were floated on sorbitol concentrations of increasing molarity and changes of the protoplast volume were estimated using [14C]sorbitol and 3H2O penetration. Detached leaves were also wilted until 10% of their fresh weight was lost. Photosynthesis was studied at very high external CO2 concentrations, to eliminate the effect of closing stomata. There was no large inhibition of CO2 fixation after wilting leaves, or until the external water deficit was greater than-1.2 MPa. However, partitioning changed markedly at these moderate water deficits: more sucrose and less starch was made. When an inhibition of CO2-saturated photosynthesis did appear at a water deficit of-2.0 MPa and above, measurements of chlorophyll-fluorescence quenching and metabolite levels showed the thylakoid reactions were not especially susceptible to short-term water stress. The inhibition was accompanied by a small increase of the triose phosphate: ribulose-1,5-bisphosphate ratio, showing regeneration of ribulose-1,5-bisphosphate was affected. However, there was also a general increase of the estimated concentrations of most metabolites, indicating that there is no specific site for the inhibition of photosynthesis. Increasing water deficit led to a large increase of fructose-2,6-bisphosphate. This is explained in terms of a simultaneous increase of fructose-6-phosphate and inorganic phosphate as the cell shrinks. The high fructose-2,6-bisphosphate led to the accumulation of triose phosphates, and the potential significance of this for protection against photoinhibition is discussed. There was an increase in the extractable activity of sucrose-phosphate synthase. This was only detected when the enzyme was assayed in conditions which distinguish between different kinetic forms which have previously been identified in spinach leaves. It is proposed that activation of sucrose-phosphate synthase is one of the first sites at which spinach leaves respond to a rising water deficit. This could be of importance for osmoregulation.Abbreviations Chl
chlorophyll
- Fru1,6bisP
fructose-1,6-bisphosphate
- Fru2,6bisP
fructose-2,6-bisphosphate
- Fru6P
fructose-6-phosphate
- Glc6P
glucose-6-phosphate
- PGA
glycerate-3-phosphate
- Pi
inorgamic phosphate
- Ru1,5bisP
ribulose-1,5-bisphosphate
- SPS
sucrose-phosphate synthase
- triose-P
sum of glyceraldehyde-3-phosphate and dehydroxyacetone phosphate
- UDPGlc
uridine diphosphoglucose 相似文献
10.
Enzymes Catalyzing the Reversible Conversion of Fructose-6-Phosphate and Fructose-1,6-Bisphosphate in Maize (Zea mays L.) Kernels 总被引:1,自引:1,他引:0 下载免费PDF全文
The significance of the glycolytic and gluconeogenic conversion of fructose-6-phosphate and fructose-1,6-bisphosphate on sugar metabolism was investigated in maize (Zea mays L.) kernels. Maximum extractable activities of the pyrophosphate (PPi) dependent phosphofructokinase, fructose-1,6-bisphosphatase, and the ATP-dependent phosphofructokinase were measured in normal and four maize genotypes, which accumulate relatively more sugars and less starch, to determine how these enzymes are affected by the genetic lesions. Normal endosperm accumulated more dry matter than the high sugar/low starch genotypes, but protein contents did not differ greatly among the genotypes. Mutation of several starch biosynthetic enzymes had little impact on the activities of PPi-dependent phosphofructokinase, fructose-1,6-bisphosphatase, and ATP-dependent phosphofructokinase, despite the altered capacity of the cell to synthesize starch. The PPi-dependent phosphofructokinase appeared to be more active toward glycolysis in all genotypes studied. Activity of the PPi-dependent phosphofructokinase in shrunken (low sucrose synthase genotype) did not differ from the activity in other genotypes, suggesting that the gluconeogenic production of PPi may not be the primary role of the enzyme. As expected, shrunken kernels contained more sugars and less starch than normal kernels throughout kernel development except at the very early stages. Developmental profiles of normal kernels also showed marked changes in the PPi-dependent phosphofructokinase activity, whereas the level of ATP-dependent phosphofructokinase activity remained relatively steady during kernel development. In addition, the ATP-dependent phosphofructokinase, and not the PPi-dependent phosphofructokinase, appeared to correlate more closely with respiration rate. These findings suggest that glycolysis catalyzed by the ATP-dependent phosphofructokinase may serve primarily to support energy production, and glycolysis catalyzed by the PPi-dependent phosphofructokinase may contribute mainly to generation of biosynthetic intermediates. 相似文献
11.
The aim of this work was to determine the effects of hypoxia on the major fluxes of carbohydrate metabolism in climacteric fruit of banana (Musa cavendishii Lamb ex Paxton). Hands of bananas, untreated with ethylene, were allowed to ripen in air at 21°C in the dark. When the climacteric began, fruit were transferred to 15 or 10% oxygen and were analysed once the climacteric peak had been reached 8–12 h later. The rates of starch breakdown, sucrose, glucose and fructose accumulation, and CO2 production were determined, as were the contents of hexose monophosphates, adenylates and pyruvate. In addition, the detailed distribution of label was determined after supplying [U-14C]-, [1-14C]-, [3,4-14C]- and [6-14C]glucose, and [U-14C]glycerol to cores of tissue under hypoxia. The data were used to estimate the major fluxes of carbohydrate metabolism. There was a reduction in the rate of respiration. The ATP/ADP ratio was unaffected but there was a significant increase in the content of AMP. In 15% oxygen only minor changes in fluxes were observed. In 10% oxygen starch breakdown was reduced and starch synthesis was not detected. The rate of sucrose synthesis decreased, as did the rate of re-entry of hexose sugars into the hexose monophosphate pool. There was a large increase in both the glycolytic flux and in the flux from triose phosphates to hexose monophosphates. It is argued that the increase in these fluxes is due to activation of pyrophosphate: fructose-6-phosphate 1-phosphotransferase, and that this enzyme has an important role in hypoxia. The results are discussed in relation to our understanding of the control of carbohydrate metabolism in hypoxia.Abbreviations Glc6P
glucose-6-phosphate
- Glc1P
glucose-1-phosphate
- Fru6P
fructose-6-phosphate
- PPi
inorganic pyro-phosphate
We thank Geest Foods Group, Great Dunmow, Essex, UK for giving us the bananas. S.A.H. thanks the managers of the Brood bank Fund for a fellowship. 相似文献
12.
Carbon metabolism of chloroplasts in the dark: Oxidative pentose phosphate cycle versus glycolytic pathway 总被引:2,自引:0,他引:2
The conversion of U-labelled [14C]glucose-6-phosphate into other products by a soluble fraction of lysed spinach chloroplasts has been studied. It was found that both an oxidative pentose phosphate cycle and a glycolytic reaction sequence occur in this fraction. The formation of bisphosphates and of triose phosphates was ATP-dependent and occurred mainly via a glycolytic reaction sequence including a phosphofructokinase step. The conversion, of glucose-6-phosphate via the oxidative pentose phosphate cycle stopped with the formation of pentose monophosphates. This was found not to be because of a lack in transaldolase (or transketolase) activity, but because of the high concentration ratios of hexose monophosphate/pentose monophosphate used in our experiments for simulating the conditions in whole chloroplasts in the dark. Some regulatory properties of both the oxidative pentose phosphate cycle and of the glycolytic pathway were studied.Abbreviations DHAP
dihydroxyacetone phosphate
- GAP
3-phosphoglyceraldehyde
- PGA
3-phosphoglycerate
- HMP
hexose monophosphates
- including F6P
fructose-6-phosphate
- G6P
glucose-6-phosphate
- GIP
glucose-1-phosphate
- 6-PGL
phosphogluconate
- PMP
pentose monophosphates
- including R5P
ribose-5-phosphate
- Ru5P
ribulose-5-phosphate
- X5P
xylulose-5-phosphate
- E4P
erythrose-4-phosphate
- S7P
sedoheptulose-7-phosphate
- FBP
fructose-1,6-bisphosphate
- SBP
sedoheptulose-1,7-bisphosphate
- RuBP
ribulose-1,5-bisphosphate 相似文献
13.
Diurnal Changes in Maize Leaf Photosynthesis : II. Levels of Metabolic Intermediates of Sucrose Synthesis and the Regulatory Metabolite Fructose 2,6-Bisphosphate 总被引:4,自引:3,他引:1 下载免费PDF全文
Diurnal changes in the regulatory metabolite, fructose-2,6-bisphosphate (F26BP), and key metabolic intermediates of sucrose biosynthesis were studied in maize (Zea mays L. cv Pioneer 3184) during a day-night cycle. Whole leaf concentrations of dihydroxyacetonephosphate (DHAP) and fructose 1,6-bisphosphate changed markedly during the photoperiod. DHAP concentration was correlated positively with the rate of sucrose formation in vivo (assimilate export plus sucrose accumulation) and extractable activity of sucrose phosphate synthase (SPS). The changes closely followed net photosynthetic rate, which tracked irradiance. The other metabolic intermediates measured (glucose 6-phosphate, fructose 6-phosphate, and UDP-glucose) were either relatively constant over the 24 hour period or changed in a different pattern. Diurnal changes in leaf F26BP concentrations were pronounced, and fundamentally different than the pattern reported with other species. F26BP concentration decreased at the beginning of the day and remained low and constant; a 3- to 4-fold increase occurred with darkness, and slowly declined thereafter. In general, leaf F26BP concentration was negatively correlated with net photosynthetic rate, and also leaf DHAP concentration. Consequently, co-ordination of the regulation of cytosolic fructose 1,6-bisphosphatase and SPS was apparent. The results support the postulate that in maize leaves the activation state of SPS may be dependent on availability of DHAP and possibly other metabolites. 相似文献
14.
Ripening of avocado fruit is associated with a dramatic increase in respiration. In vivo31P nuclear magnetic resonance spectroscopy revealed large increases in ATP levels accompanying the increase in respiration. Both glycolytic enzymes, phosphofructokinase, and pyrophosphate: fructose-6-phosphate phosphotransferase were present in avocado fruit with the latter activity being highly stimulated by fructose 2,6-bisphosphate. Fructose 2,6-bisphosphate levels increased approximately 90% at the onset of ripening, suggesting that the respiratory increase in ripening avocado fruit may be regulated by the activation of pyrophosphate:fructose-6-phosphate phosphotransferase by an increase in fructose 2,6-bisphosphate. 相似文献
15.
Mohammad Hajirezaei Uwe Sonnewald Roberto Viola Sarah Carlisle David Dennis Mark Stitt 《Planta》1993,192(1):16-30
Potato (Solanum tuberosum L.) plants were transformed with antisense constructs to the genes encoding the -and -subunits of pyrophosphate: fructose-6-phosphate phosphotransferase (PEP), their expression being driven by the constitutive CaMV 35S promotor. (i) In several independent transformant lines, PFP expression was decreased by 70–90% in growing tubers and by 88–99% in stored tubers. (ii) The plants did not show any visual phenotype, reduction of growth or decrease in total tuber yield. However, the tubers contained 20–40% less starch than the wild type. Sucrose levels were slightly increased in growing tubers, but not at other stages. The rates of accumulation of sucrose and free hexoses when tubers were stored at 4° C and the final amount accumulated were the same in antisense and wild-type tubers. (iii) Metabolites were investigated at four different stages in tuber life history; growing (sink) tubers, mature tubers, cold-sweetening tubers and sprouting (source) tubers. At all stages, compared to the wild type, antisense tubers contained slightly more hexose-phosphates, two- to threefold less glycerate-3-phosphate and phosphoenolpyruvate and up to four-to fivefold more fructose-2,6-bisphosphate. (iv) There was no accumulation or depletion of inorganic pyrophosphate (PPi), or of UDP-glucose relative to the hexose-phosphates. (v) The pyruvate content was unaltered or only marginally decreased, and the ATP/ADP ratio did not change. (vi) Labelling experiments on intact tubers did not reveal any significant decrease in the unidirectional rate of metabolism of [U-14C]sucrose to starch, organic acids or amino acids. Stored tubers with an extreme (90%) reduction of PFP showed a 25% decrease in the metabolism of [U14-C] sucrose. (vii) Metabolism (cycling) of [U-14C]glucose to surcrose increased 15-fold in discs from growing antisense tubers, compared with growing wild-type tubers. Resynthesis of sucrose was increased by 10–20% when discs from antisense and wild-type tubers stored at 4° C (cold sweetening) were compared. The conversion of [U-14C]glucose to starch was decreased by about 30% and 50%, respectively. (viii) The randomisation of [1-13C]glucose in the glucosyl and fructosyl moieties of sucrose was decreased from 13.8 and 15.7% in the wild type to 3.6 and 3.9% in an antisense transformant. Simultaneously, randomisation in glucosyl residues isolated from starch was reduced from 14.4 to 4.1%. (ix) These results provide evidence that PFP catalyses a readily reversible reaction in tubers, which is responsible for the recycling of label from triose-phosphates to hexose-phosphates, but with the net reaction in the glycolytic direction. The results do not support the notion that PFP is involved in regulating the cytosolic PPi concentration. They also demonstrate that PFP does not control the rate of glycolysis, and that tubers contain exessive capacity to phosphorylate fructose-6-phosphate. The decreased concentration of phosphoenolpyruvate and glycerate-3-phosphate compensates for the decrease of PFP protein by stimulating ATP-dependent phosphofructokinase, and by stimulating fructose-6-phosphate,2-kinase to increase the fructose-2,6-bisphosphate concentration and activate the residual PFP. The decreased starch accumulation is explained as an indirect effect, caused by the increased rate of resynthesis (cycling) of sucrose in the antisense tubers.Abbreviations Fru1,6bisP
fructose-1,6-bisphosphate
- Fru2,6bisP
fructose-2,6-bisphosphate
- Fru6P
fructose-6-phosphate
- Glc1P
glucose-1-phosphate
- Glc6P
glucose-6-phosphate
- NMR
nuclear magnetic resonance
- 3PGA
glycerate-3-phosphate
- PEP
phosphoenolpyruvate
- PEP
pyrophosphate: fructose-6-phosphate phosphotransferase
- PFK
phosphofructokinase
- UDPGlc
UDP glucose
- WT
wild type
This research was supported by the Bundesministerium for Forschung and Technology (M.S., U.S.), the Canadian Research Council (S.C., D.D.), the Agricultural and Food Research Council (R.V.) and Sandoz Agro Ltd. (M.H., M.S.). 相似文献
16.
This work was carried out to investigate the relative roles of phosphofructokinase and pyrophosphate-fructose-6-phosphate 1-phosphotransferase during the increased glycolysis at the climacteric in ripening bananas (Musa cavendishii Lamb ex Paxton). Fruit were ripened in the dark in a continuous stream of air in the absence of ethylene. CO2 production, the contents of glucose 6-phosphate, fructose 6-phosphate, fructose 1,6-bisphosphate, phosphoenolpyruvate and PPi; and the maximum catalytic activities of pyrophosphate-fructose-6-phosphate 1-phosphotransferase, 6-phosphofructokinase, pyruvate kinase and phosphoenolpyruvate carboxylase were measured over a 12-day period that included the climacteric. Cytosolic fructose-1,6- bisphosphatase could not be detected in extracts of climacteric fruit. The peak of CO2 production was preceded by a threefold rise in phosphofructokinase, and accompanied by falls in fructose 6-phosphate and glucose 6-phosphate, and a rise in fructose 1,6-bisphosphate. No change in pyrophosphate-fructose-6-phosphate 1-phosphotransferase or pyrophosphate was found. It is argued that phosphofructokinase is primarily responsible for the increased entry of fructose 6-phosphate into glycolysis at the climacteric. 相似文献
17.
Till Jelitto Uwe Sonnewald Lothar Willmitzer Mohammad Hajirezeai Mark Stitt 《Planta》1992,188(2):238-244
Metabolite levels and carbohydrates were investigated in the leaves of tobacco (Nicotiana tabacum L.) and leaves and tubers of potato (Solanum tuberosum L.) plants which had been transformed with pyrophosphatase from Escherichia coli. In tobacco the leaves contained two- to threefold less pyrophosphate than controls and showed a large increase in UDP-glucose, relative to hexose phosphate. There was a large accumulation of sucrose, hexoses and starch, but the soluble sugars increased more than starch. Growth of the stem and roots was inhibited and starch, sucrose and hexoses accumulated. In potato, the leaves contained two- to threefold less pyrophosphate and an increased UDP-glucose/ hexose-phosphate ratio. Sucrose increased and starch decreased. The plants produced a larger number of smaller tubers which contained more sucrose and less starch. The tubers contained threefold higher UDP-glucose, threefold lower hexose-phosphates, glycerate-3-phosphate and phosphoenolpyruvate, and up to sixfold more fructose-2,6-bisphosphatase than the wild-type tubers. It is concluded that removal of pyrophosphate from the cytosol inhibits plant growth. It is discussed how these results provide evidence that sucrose mobilisation via sucrose synthase provides one key site at which pyrophosphate is needed for plant growth, but is certainly not the only site at which pyrophosphate plays a crucial role.Abbreviations Fru2,6bisP
fructose-2,6-bisphosphate
- Fru6P
fructose 6-phosphate
- FW
fresh weight
- Glc1P
glucose-1-phosphate
- Glc6P
glucose-6-phosphate
- PEP
phosphoenolpyruvate
- 3PGA
glycerate-3-phosphate
- PFK
phosphofructokinase
- PFP
pyrophosphate: fructose-6-phosphate phosphotransferase
- Pi
inorganic phosphate
- PPi
inorganic pyrophosphate
- UDPGlc
UDP-glucose
This research was supported by the Deutsche Forschungsgemein-Schaft (SFB 137) and Sandoz AG (T.J., M.H., M.S.) and by the Bundesminister für Forschung und Technologie (U.S., L.W.). 相似文献
18.
Gabriela Lorenc-Plucińska Anna Szadel Andrzej Pluciński Renata Matysiak 《Acta Physiologiae Plantarum》2002,24(2):123-129
Sulphite at concentrations from 0.5 to 5.0 mM was supplied to illuminated, detached poplar (Populus deltoides Bartr. ex Marsh) leaves via the transpiration stream. Chlorophyll a fluorescence parameters, the contents of fructose-2,6-bisphosphate (Fru2,6BP) and starch, and extractable specific activity
of sucrose-phosphate synthase (SPS), sucrose synthase (SuSy), acid invertase (AI), neutral invertase (NI), ATP-dependent fructose-6-phosphate
1-phosphotransferase (PFK) and pyrophosphate-dependent fructose-6-phosphate 1-phosphotransferase (PFP) were measured. Chlorophyll
fluorescence parameters appeared to be unaffected by sulphite. Application of ≥ 1.0 mM sulphite led to an increase in the
content of Fru2,6BP and starch. There was also a decline in the activity of SPS, NI and PFK. On the other hand, the influence
of sulphite on the activity of AI and PFP was negligible. Specific activity of SuSy was inhibited by 1.0 and 2.5 mM but activated
by 5.0 mM of sulphite. On the basis of the results obtained in the present study, we postulate that sulphite at concentrations
≥ 1.0 mM inhibits primarily sucrose synthesis, favours starch accumulation and has an indirect effect on the sucrolytic activities
in poplar leaves. 相似文献
19.
Light- and CO2-saturated photosynthesis of nonhardened rye (Secale cereale L. cv. Musketeer) was reduced from 18.10 to 7.17 mol O2·m–2·s–1 when leaves were transferred from 20 to 5°C for 30 min. Following cold-hardening at 5°C for ten weeks, photosynthesis recovered to 15.05 mol O2·m–2·s–1,comparable to the nonhardened rate at 20°C. Recovery of photosynthesis was associated with increases in the total activity and activation of enzymes of the photosynthetic carbon-reduction cycle and of sucrose synthesis. The total hexose-phosphate pool increase by 30% and 120% for nonhardened and cold-hardened leaves respectively when measured at 5°C. The large increase in esterified phosphate in coldhardened leaves occurred without a limitation in inorganic phosphate supply. In contrast, the much smaller increase in esterified phosphate in nonhardened leaves was associated with an inhibition of ribulose-1,5-bisphosphate carboxylase/oxygenase and sucrose-phosphate synthase activation. It is suggested that the large increases in hexose phosphates in cold-hardened leaves compensates for the higher substrate threshold concentrations needed for enzyme activation at low temperatures. High substrate concentrations could also compensate for the kinetic limitations imposed by product inhibition from the accumulation of sucrose at 5°C. Nonhardened leaves appear to be unable to compensate in this fashion due to an inadequate supply of inorganic phosphate.Abbreviations DHAP
dihydroxyacetone phosphate
- Fru6P
fructose-6-phosphate
- Fru 1,6BP
fructose-1,6-bisphosphate
- Fru1,6BPase
fructose-1,6-bisphosphatase
- Glc6P
glucose-6-phosphate
- PGA
3-phosphoglycerate
- PPFD
photosynthetic photon flux density
- CH
cold-hardened rye grown at 5°C
- NH
nonhardened rye grown at 24°C
- Rubisco
ribulose-1,5-bisphosphate carboxylase/oxygenase
- RuBP
ribulose-1,5-bisphosphate
- SPS
sucrose-phosphate synthase
- UDPGlc
uridine 5-diphosphoglucose
This work was supported by operating grants from the Swedish Natural Sciences Research Council to G.Ö. and P.G. 相似文献
20.
Photosystem II Excitation Pressure and Photosynthetic Carbon Metabolism in Chlorella vulgaris 下载免费PDF全文
Chlorella vulgaris grown at 5[deg]C/150 [mu]mol m-2 s-1 mimics cells grown under high irradiance (27[deg]C/2200 [mu]mol m-2 s-1). This has been rationalized through the suggestion that both populations of cells were exposed to comparable photosystem II (PSII) excitation pressures measured as the chlorophyll a fluorescence quenching parameter, 1 - qP (D.P. Maxwell, S. Falk, N.P.A. Huner [1995] Plant Physiol 107: 687-694). To assess the possible role(s) of feed-back mechanisms on PSII excitation pressure, stromal and cytosolic carbon metabolism were examined. Sucrose phosphate synthase and fructose-1,6-bisphosphatase activities as well as the ratios of fructose-1,6-bisphosphate/fructose-6-phosphate and sucrose/starch indicated that cells grown at 27[deg]C/2200 [mu]mol m-2 s-1 appeared to exhibit a restriction in starch metabolism. In contrast, cells grown at 5[deg]C/150 [mu]mol m-2 s-1 appeared to exhibit a restriction in the sucrose metabolism based on decreased cytosolic fructose-1,6- bisphosphatase and sucrose phosphate synthase activities as well as a low sucrose/starch ratio. These metabolic restrictions may feed-back on photosynthetic electron transport and, thus, contribute to the observed PSII excitation pressure. We conclude that, although PSII excitation pressure may reflect redox regulation of photosynthetic acclimation to light and temperature in C. vulgaris, it cannot be considered the primary redox signal. Alternative metabolic sensing/signaling mechanisms are discussed. 相似文献