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  • 1
    Electronic Resource
    Electronic Resource
    Regulation of glycolysis in heterotrophic cell suspension cultures of Chenopodium rubrum in response to proton fluxes at the plasmalemma (1991)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 81 (1991), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The present experiments were carried out to investigate the effect of increased fluxes of H+ across the plasmalemma on glycolysis in heterotrophic cell suspension cultures of Chenopodium rubrum L. (1) Increased H+ influx was produced by adding glucose, 6-deoxyglucose, 2-deoxyglucose, or sodium fluoride. The net influx decreased to zero after 3 min. This recovery was accompanied by an increase in the rate of O2 uptake, but not of dark CO2 fixation. When glucose or fluoride were added, the increase of O2 uptake occurred without a decrease in the ATP/ADP ratio, and was large enough to provide the ATP that would be needed for compensatory H+ extrusion via the plasmalemma H+-ATPase. When 2-deoxyglucose was added, the rise of respiration was restricted by sequestration of phosphate and depletion of phosphorylated metabolites, the ATP/ADP ratio declined, and a slow net H+ influx started again after 4 min. (2) Alkalinisation of the medium to induce an H+ efflux resulted in rapid activation of dark CO2 fixation, but not of O2-uptake. (3) A stimulation of respiration or dark CO2 fixation was always accompanied by a decrease of phosphoenolpyruvate. This shows that the primary sites for regulation of glycolysis are pyruvate kinase and phosphoenolpyruvate carboxylase, respectively. (4) There was no consistent relation between glycolytic flux and triose-phosphates or hexose-phosphates. This shows that the reactions involved in carbohydrate mobilisation and the conversion of hexose-phosphates to triose-phosphates only have a secondary role in stimulation of glycolysis. (5) Phosphofructokinase will be stimulated as a consequence of the decrease in phosphoenolpyruvate. (6) The increase in glycolytic flux occurred independently of (in the case of 2-deoxyglucose and fluoride), or before (in the case of glucose), any increase of fructose-2,6-bisphosphate. When fructose-2,6-bisphosphate did increase (after supplying glucose), this was accompanied by an increase of triose-phosphate and fructose-1,6-bisphosphate, which otherwise remained very low. It is argued that fructose-2,6-bisphosphate increases as a consequence of the decrease of glycerate-3-phosphate, a known inhibitor of the synthesis of this regulator metabolite. However, activation of pyrophosphate fructose-6-phosphate phosphotransferase by fructose-2,6-bisphosphate does not play an obligatory role in the stimulation of glycolysis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.1991.tb01720.x
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  • 2
    Electronic Resource
    Electronic Resource
    Metabolism of starch synthesis in developing grains of the shx shrunken mutant of barley (Hordeum vulgare) (1995)
    Copenhagen : Munksgaard International Publishers
    Physiologia plantarum 93 (1995), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The shx mutant of barley (Hordeum vulgare L. cv. Bomi) produces grains greatly decreased in starch content and containing smaller A-starch granules together with normal B-granules. Soluble starch synthase (SSS) and ADP-glucose pyrophosphorylase (AGP) are reduced to about 20% normal activity. To help determine the position of the block to starch synthesis in shx, we measured enzyme activities and metabolite levels in developing grains of normal and mutant genotypes in a cv. Bomi background. We demonstrate that sucrose, free hexose, hexose phosphates and, critically, ADP-Glc accumulate as a result of the mutation. In addition to AGP and SSS, several other enzyme activities are affected in the shx mutant, most of them showing activities 50-80% of normal. Northern blots showed that transcripts for the AGP small subunit are much less abundant, but of normal size, in shx. These and earlier results together indicate that the metabolic block is at the end of the starch synthetic pathway, with a primary effect on a type I, primer-independent soluble starch synthase.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1034/j.1399-3054.1995.930112.x
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  • 3
    Electronic Resource
    Electronic Resource
    Water stress, carbon dioxide, and light effects on sucrosephosphate synthase activity in Phaseolus vulgaris (1991)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 81 (1991), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The characteristics of sucrose-phosphate synthase (SPS; EC 2.4.1.14) activity in leaves of Phaseolus vulgaris L. cv. Linden was studied in plants subjected to water stress and various CO2 and light treatments. When water was withheld for 3 days causing mild water stress (–0.9 MPa), the activity of SPS measured in crude extracts was reduced ca 50%. The effect of water stress was most evident when the enzyme was assayed with saturating amounts of its substrates fructose 6-phosphate and UDP glucose. Placing a water-stressed plant in an atmosphere containing 1% CO2 reversed the effect of water stress on SPS activity over 5 h even though the water stress was not relieved. Holding unstressed leaves in low CO2 partial pressure reduced the extractable activity of SPS. After 1 h of low CO2 treatment the effect of low CO2 could be reversed by 20 min of 5% CO2. However, after 24 h of low CO2 treatment, less SPS activity was recovered by the 20 min treatment. The cytosolic protein synthesis inhibitor cycloheximide prevented the slow recovery of SPS activity, but did not affect the rapid recovery of SPS. We conclude that the effect of water stress on SPS activity was a consequence of the inhibition of photosynthesis caused by stomatal closure. Responses of Phaseolus vulgaris SPS to light were similar to the response to low CO2 in that the effects were most pronounced under Vmax assay conditions. This is the first report of this type of light response of SPS in a dicotyledonous species.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.1991.tb01709.x
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  • 4
    Electronic Resource
    Electronic Resource
    Photosynthetic carbon partitioning: its regulation and possibilities for manipulation (1989)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 77 (1989), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The regulation of photosynthetic sucrose synthesis and partitioning is reviewed with particular emphasis on the role of fructose-2,6-bisphosphate and sucrose phosphate synthase. It is concluded that a hierachy of regulatory mechanisms exist, which allows partitioning to be changed without this necessarily leading to a reduction in the rate of photosynthesis. Nevertheless, experimental conditions can be defined in which photosynthesis is limited by the rate of end-product synthesis. These systems can be used to screen for genetic mutants or specific inhibitors, and to investigate a shift in sink demand or environmental factors that specifically act on carbon partitioning and/or the rate of endproduct synthesis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.1989.tb05402.x
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  • 5
    Electronic Resource
    Electronic Resource
    Vanadate inhibits fructose-2,6-bisphosphatase and leads to an inhibition of sucrose synthesis in barley leaves (1990)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 78 (1990), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.1990.tb05243.x
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  • 6
    Electronic Resource
    Electronic Resource
    Phosphate sequestration by glycerol and its effects on photosynthetic carbon assimilation by leaves (1988)
    Springer
    Planta 176 (1988), S. 117-126 
    Details
    ISSN: 1432-2048
    Keywords: Glycerol ; Glycerol-3-phosphate ; Horderum (photosynthesis) ; Photosynthetic carbon metabolism (phosphate status) ; Spinacia (photosynthesis)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Glycerol induced a limitation on photosynthetic carbon assimilation by phosphate when supplied to leaves of barley (Hordeum vulgare L.) and spinach (Spinacia oleracea L.). This limitation by phosphate was evidenced by (i) reversibility of the inhibition of photosynthesis by glycerol by feeding orthophosphate (ii) a decrease in light-saturated rates of photosynthesis and saturation at a lower irradiance, (iii) the promotion of oscillations in photosynthetic CO2 assimilation and in chlorophyll fluorescence, (iv) decreases in the pools of hexose monophosphates and triose phosphates and increases in the ratio of glycerate-3-phosphate to triose phosphate, (v) decreased photochemical quenching of chlorophyll fluorescence, and increased non-photochemical quenching, specifically of the component which relaxed rapidly, indicating that thylakoid energisation had increased. In barley there was a massive accumulation of glycerol-3-phosphate and an increase in the period of the oscillations, but in spinach the accumulation of glycerol-3-phosphate was comparatively slight. The mechanism(s) by which glycerol feeding affects photosynthetic carbon assimilation are discussed in the light of these results.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00392487
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  • 7
    Electronic Resource
    Electronic Resource
    Carbohydrate metabolism during postharvest ripening in kiwifruit (1992)
    Springer
    Planta 188 (1992), S. 314-323 
    Details
    ISSN: 1432-2048
    Keywords: Actinidia ; Glycolysis ; Respiration ; Starch-sucrose interconversion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Mature fruit (kiwifruit) of Actinidia deliciosa var. deliciosa (A. Chev.), (C.F.) Liang and Ferguson cv. Haywood (Chinese gooseberry) were harvested and allowed to ripen in the dark at 20° C. Changes were recorded in metabolites, starch and sugars, adenine nucleotides, respiration, and sucrose and glycolytic enzymes during the initiation of starch degradation, net starch-to-sucrose conversion and the respiratory climacteric. The conversion of starch to sucrose was not accompanied by a consistent increase in hexose-phosphates, and UDP-glucose declined. The activity of sucrose phosphate synthase (SPS) measured with saturating substrate rose soon after harvesting and long before net sucrose synthesis commenced. The onset of sugar accumulation correlated with an increase in SPS activity measured with limiting substrates. Throughout ripening, until sucrose accumulation ceased, feeding [14C] glucose led to labelling of sucrose and fructose, providing evidence for a cycle of sucrose synthesis and degradation. It is suggested that activation of SPS, amplified by futile cycles, may regulate the conversion of starch to sugars. The respiratory climacteric was delayed, compared with net starchsugar interconversion, and was accompanied by a general decline of pyruvate and all the glycolytic intermediates except fructose-1,6-bisphosphate. The ATP/ ADP ratio was maintained or even increased. It is argued that the respiratory climacteric cannot be simply a consequence of increased availability of respiratory substrate during starch-sugar conversion, nor can it result from an increased demand for ATP during this process.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00192797
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  • 8
    Electronic Resource
    Electronic Resource
    “Sink” regulation of photosynthetic metabolism in transgenic tobacco plants expressing yeast invertase in their cell wall involves a decrease of the Calvin-cycle enzymes and an increase of glycolytic enzymes (1991)
    Springer
    Planta 183 (1991), S. 40-50 
    Details
    ISSN: 1432-2048
    Keywords: Cell-wall invertase ; Photosynthesis ; Sink regulation (photosynthetic metabolism) ; Transgenic plant (tobacco)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00197565
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  • 9
    Electronic Resource
    Electronic Resource
    Sucrose storage in cell suspension cultures of Saccharum sp. (sugarcane) is regulated by a cycle of synthesis and degradation (1991)
    Springer
    Planta 183 (1991), S. 31-39 
    Details
    ISSN: 1432-2048
    Keywords: Cell culture (sucrose storage) ; Invertase (metabolic levels) ; Nitrogen sucrose accumulation ; Saccharum ; Sucrose mobilisation ; Sucrose phosphate synthase ; Sucrose synthase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We have investigated the regulation of sucrose storage in cell-suspension cultures of sugarcane. When grown in batch culture, sucrose accumulation commences after about 5 d, when the nitrogen supply is exhausted. Sucrose storage is also induced by decreasing the nitrogen supply to cells growing in a chemostat. The measured activity of sucrose-phosphate synthase is high enough to account for the rate of sucrose accumulation, provided precautions are taken to avoid the hydrolysis of UDP during the assay. The cells contained high sucrose-synthase activity but pulsing experiments with [14C]glucose and unlabelled fructose indicated that this enzyme did not contribute substantially to the synthesis of sucrose, because the glucosyl and fructosyl moieties of sucrose were equally labelled. Several lines of evidence demonstrate the presence of a cycle in which sucrose is synthesized and degraded simultaneously; sucrosephosphate-synthase activity doubles during the phase when the cells are actively storing sucrose but activity is also high after storage has ceased, or when the sucrose is being remobilised; pulse experiments with [14C]fructose also showed that sucrose synthesis occurs not only during the storage phase, but also after storage has stopped and during the rapid mobilisation of sucrose; the cells contain high activities of sucrose synthase and alkaline invertase and these are both at a maximum when sucrose storage is occurring; even during the storage phase. [14C]fructose pulses lead to labelling of free glucose which is evidence for rapid synthesis and degradation of sucrose. It is proposed that the rate and extent of sucrose storage is regulated by this cycle of synthesis and degradation. Measurements of enzyme activities and metabolite levels are presented, and it is discussed which factors could contribute to the regulation of these two opposing fluxes and, hence, the rate of net sucrose storage and mobilisation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00197564
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  • 10
    Electronic Resource
    Electronic Resource
    Partial purification from potato tubers of three fructokinases and three hexokinases which show differing organ and developmental specificity (1993)
    Springer
    Planta 190 (1993), S. 156-165 
    Details
    ISSN: 1432-2048
    Keywords: Fructokinase ; Hexokinase ; Solanum ; Sucrose metabolism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A combination of chromatography on DE-52 cellulose, Cibacron Blue agarose, Mono Q anion exchanger and gel filtration was used to resolve different hexose-phosphorylating enzymes from growing “sink” potato tubers (Solanum tuberosum L.). Three enzymes (fructokinases: FK1, FK2 and FK3) are active with fructose and inactive with glucose, and three (hexokinases: HK1, HK2 and HK3) are active with glucose but not with fructose. Elution from DE-52 columns showed that the relative abundance of the six activities changes, depending on the organ and on the developmental stage. FK1 and FK2 were present at high activities in tubers but at very low activity in leaves; conversely FK3 was present at very low activity in tubers but at high activity in leaves. During storage of potato tuber, and also during sprouting, there was a decrease of FK1 and FK2. In contrast, glucose-phosphorylating activity was very low in growing tubers. During storage and sprouting the activity of the glucose-phosphorylating enzymes rose, until they exceeded FK1 and FK2. This was due particularly to an increase of HK1, whereas HK2 declined relative to HK1, and HK3 was always negligible. These changes in the pattern of hexose-phosphorylating enzyme forms are compared with the changing metabolic fluxes and pools of hexose sugars in potato tubers. It is concluded that organ- and development-specific changes in the abundance of the various enzyme forms contribute to the regulation of hexose metabolism in the potato.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00196607
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