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1

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Regulation of sedoheptulose-1,7-bisphosphatase by sedoheptulose-7-phosphate and glycerate, and of fructose-1,6-bisphosphatase by glycerate in spinach chloroplasts (1990)

Schimkat, Dieter ; Heineke, Dieter ; Heldt, Hans W.

Springer

Planta 181 (1990), S. 97-103

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ISSN: 1432-2048

Keywords: Carbon dioxide fixation ; Fructose-1,6-bisphosphatase ; Glycerate ; Photosynthesis (enzyme regulation) ; Sedoheptulose-1,7-bisphosphatase ; Sedoheptulose-7-phosphate ; Spinacia (chloroplasts)

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract Using partially purified sedoheptulose-1,7-bisphosphatase from spinach (Spinacia oleracea L.) chloroplasts the effects of metabolites on the dithiothreitoland Mg2+-activated enzyme were investigated. A screening of most of the intermediates of the Calvin cycle and the photorespiratory pathway showed that physiological concentrations of sedoheptulose-7-phosphate and glycerate specifically inhibited the enzyme by decreasing its maximal velocity. An inhibition by ribulose-1,5-bisphosphate was also found. The inhibitory effect of sedoheptulose-7-phosphate on the enzyme is discussed in terms of allowing a control of sedoheptulose-1,7-bisphosphate hydrolysis by the demand of the product of this reaction. Subsequent studies with partially purified fructose-1,6-bisphosphatase from spinach chloroplasts showed that glycerate also inhibited this enzyme. With isolated chloroplasts, glycerate was found to inhibit CO2 fixation by blocking the stromal fructose-1,6-bisphosphatase. It is therefore possible that the inhibition of the two phosphatases by glycerate is an important regulatory factor for adjusting the activity of the Calvin cycle to the ATP supply by the light reaction.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00202330

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2

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Effect of antisense repression of the chloroplast triose-phosphate translocator on photosynthetic metabolism in transgenic potato plants (1994)

Heineke, Dieter ; Kruse, Anne ; Flügge, Ulf-Ingo ; [et al.]

Springer

Planta 193 (1994), S. 174-180

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ISSN: 1432-2048

Keywords: Antisense repression ; Photosynthesis ; Solanum ; Starch synthesis ; Triose phosphate translocator

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract The introduction of an antisense DNA into transgenic potato (Solanum tuberosum L.) plants decreased the expression of the chloroplast triose-phosphate translocator and lowered its activity by 20–30%. With plants propagated from tubers, the effect of the transformation on photosynthetic metabolism was analysed by measuring photosynthesis, the formation of leaf starch, and the total and subcellular metabolite contents in leaves. Although the transformants, in contrast to those propagated from cell cultures, did not differ from the wild-type plants in respect to rates of photosynthesis, plant appearance, growth and tuber production, their photosynthetic metabolism was found to be severely affected. The results show that the decrease in activity of the triose-phosphate translocator in the transformants caused a fourfold increase in the level of 3-phosphoglycerate and a corresponding decrease in inorganic phosphate in the stromal compartment, resulting in a large increase in the synthesis of starch. Whereas during a 12-h day period wild-type plants deposited 43% of their CO2 assimilate into starch, this value rose to 61–89% in the transformants. In contrast to the wild-type plants, where the rate of assimilate export from the leaves during the night period was about 75% of that during the day, the export rate from leaves of transformants appeared to be much higher during the night than during the day. As the mobilisation of starch occurs in part hydrolytically, resulting in the formation of glucose, the triose-phosphate translocator loses its exclusive function in the export of carbohydrates from the chloroplasts when the photoassimilates are temporarily deposited as starch. It appears that by directing the CO2 assimilates mainly into starch, the transformants compensate for the deficiency in triose-phosphate translocator activity in such a way that the productivity of the plants is not affected by the transformation.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00192527

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3

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Solute accumulation and decreased photosynthesis in leaves of potato plants expressing yeast-derived invertase either in the apoplast, vacuole or cytosol (1997)

Büssis, Dirk ; Heineke, Dieter ; Sonnewald, Uwe ; [et al.]

Springer

Planta 202 (1997), S. 126-136

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ISSN: 1432-2048

Keywords: Key words: Invertase overexpression ; Photosynthesis ; Solanum (invertase overexpression) ; Transgenic plant (potato) ; Water stress

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract. Potato (Solanum tuberosum cv. Désirée) plants expressing yeast invertase directed either to the apoplast, vacuole or cytosol were biochemically and physiologically characterised. All lines of transgenic plants showed similarities to plants growing under water stress. Transformants were retarded in growth, and accumulated hexoses and amino acids, especially proline, to levels up to 40-fold higher than those of the wild types. In all transformants rates of CO2 assimilation and leaf conductance were reduced. From the unchanged intercellular partial pressure of CO2 and apoplastic cis-abscisic acid (ABA) content of transformed leaves it was concluded that the reduced rate of CO2 assimilation was not caused by a limitation in the availability of CO2 for␣the ribulose-1,5-bisphosphate carboxylase-oxygenase (Rubisco). In the transformants the amount of Rubisco protein was not reduced, but both activation state and carboxylation efficiency of photosynthesis were lowered. In vacuolar and cytosolic transformants this inhibition of Rubisco might be caused by a changed ratio of organic bound and inorganic phosphate, as indicated by a doubling of phosphorylated intermediates. But in apoplastic transformants the pattern of phosphorylated intermediates resembled that of leaves of water-stressed potato plants, although the cause of inhibition of photosynthesis was not identical. Whereas in water-stressed plants increased contents of the phytohormone ABA are supposed to mediate the adaptation to water stress, no contribution of ABA to reduction of photosynthesis could be detected in invertase transformants.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/s004250050111

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4

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Sucrose is metabolised by sucrose synthase and glycolysis within the phloem complex of Ricinus communis L. seedlings (1993)

Geigenberger, Peter ; Langenberger, Silke ; Wilke, Ingo ; [et al.]

Springer

Planta 190 (1993), S. 446-453

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ISSN: 1432-2048

Keywords: Glycolysis ; Phloem ; Pyrophosphate ; Ricinus ; Sucrose synthase ; Transport

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract Metabolites and enzyme activities were measured in the phloem sap exuding from a cut hypocotyl of germinating castor-bean (Ricinus communis L.) seedlings. The sap contained considerable quantities of adenine nucleotides, uridine nucleotides, uridine diphosphoglucose (UDPGlc), all the major phosphorylated metabolites required for glycolysis, fructose-2,6-bisphosphate and pyrophosphate. Supplying 200 mM glucose instead of sucrose to the cotyledons resulted in high concentrations of glucose in the sap, but did not modify the metabolite levels. In contrast, when 200 mM fructose was supplied we found only a low level of fructose but a raised sucrose concentration in the sap, which was accompanied by a three-to fourfold decrease of UDPGlc, and an increase of pyrophosphate, UDP and UTP. The measured levels of metabolites are used to estimate the molar mass action ratios and in-vivo free-energy change associated with the various reactions of sucrose breakdown and glycolysis in the phloem. It is concluded that the reactions catalysed by ATP-dependent phosphofructokinase and pyruvate kinase are removed from equilibrium in the phloem, whereas the reactions catalysed by sucrose synthase, UDPGlc-pyrophosphorylase, phosphoglucose mutase, phosphoglucose isomerase, aldolase, triose-phosphate isomerase, phosphoglycerate mutase and enolase are close to equilibrium within the conducting elements of the phloem. Since the exuded sap contained negligible or undetectable activities of the enzymes, it is concluded, that the responsible proteins are bound, or sequesterd behind plasmodesmata, possibly in the companion cells. It is argued that sucrose mobilisation via a reversible reaction catalysed by sucrose synthase is particularily well suited to allow the rate of sucrose breakdown in the phloem to respond to changes in the metabolic requirement for ATP, and for UDPGlc during callose production. It is also calculated that the transport of nucleotides in the phloem sap implies that there must be a very considerable uptake or de-novo biosynthesis of these cofactors in the phloem.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00224782

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5

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Accumulation of hexoses in leaf vacuoles: Studies with transgenic tobacco plants expressing yeast-derived invertase in the cytosol, vacuole or apoplasm (1994)

Heineke, Dieter ; Wildenberger, Kathrin ; Sonnewald, Uwe ; [et al.]

Springer

Planta 194 (1994), S. 29-33

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ISSN: 1432-2048

Keywords: Amino acid ; Hexose uptake ; Nicotiana ; Photosynthesis ; Sucrose

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract The subcellular distribution of hexoses, sucrose and amino acids among the stromal, cytosolic and vacuolar compartments was analysed by a nonaqueous fractionation technique in leaves of tobacco (Nicotiana tabaccum L.) wild-type and transgenic plants expressing a yeast-derived invertase in the cytosolic, vacuolar or apoplasmic compartment. In the wild-type plants the amino acids were found to be located in the stroma and in the cytosol, sucrose mainly in the cytosol and up to 98% of the hexoses in the vacuole. In the leaves of the various transformants, where the contents of hexoses were greater than in wild-type plants, again 97–98% of these hexoses were found in the vacuoles. It is concluded that leaf vacuoles contain transporters for the active uptake of glucose and fructose against a high concentration gradient. A comparison of estimated metabolite concentrations in the subcellular compartments of wild-type and transformant plants indicated that the decreased photosynthetic capacity of the transformants is not due to an osmotic effect on photosynthesis, as was shown earlier to be the case in transformed potato leaves, but is the result of a long-term dedifferentiation of tobacco leaf cells to heterotrophic cells.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00201031

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6

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On the role of chloroplastic phosphoglucomutase in the regulation of starch turnover (1999)

Hattenbach, Andrea ; Heineke, Dieter

Springer

Planta 207 (1999), S. 527-532

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ISSN: 1432-2048

Keywords: Key words: Plastidic phosphoglucomutase ; Spinacia Starch turnover

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract. When spinach (Spinacia oleracea L.) leaf disks were incubated in 10% polyethylene glycol to induce water stress, the ratio of glucose-1-phosphate to glucose-6-phosphate increased. This increase indicated an imbalance in the phosphoglucomutase (EC 2.7.5.1) reaction, which was earlier observed to be close to equilibrium, and was accompanied by higher fructose-1,6-bisphosphate and ribulose-1,5-bisphosphate concentrations. Because starch degradation was assumed to be the source of the glucose-1-phosphate accumulation, the kinetic properties of plastidic phosphoglucomutase were analysed. It was found that physiological concentrations of both sugar bisphosphates inhibited phosphoglucomutase by about 50%. From this observation it was concluded that under conditions in which fructose-1,6-bisphosphate and ribulose-1,5-bisphosphate accumulated, an inhibition of phosphoglucomutase activity restricted the carbon exchange between the Calvin cycle and starch turnover.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/s004250050513

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7

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Antisense inhibition of cytosolic NADP-dependent isocitrate dehydrogenase in transgenic potato plants (1998)

Kruse, Anne ; Fieuw, Sabine ; Heineke, Dieter ; [et al.]

Springer

Planta 205 (1998), S. 82-91

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ISSN: 1432-2048

Keywords: Key words: Amino acid ; Antisense inhibition ; Isocitrate dehydrogenase ; Solanum (transgenic) ; Transgenic plant (potato)

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract. Cytosolic NADP-dependent isocitrate dehydrogenase (cyt-NADP-ICDH; EC 1.1.1.42) has been suggested to play a major role in the production of 2-oxoglutarate, an important precursor for amino acid synthesis. Using an antisense RNA approach under the control of the cauliflower mosaic virus 35S promoter, transgenic potato plants were created in which NADP-ICDH activity was reduced to 8% of the wild-type level in leaves. Residual activity was almost completely due to mitochondrial and chloroplastic NADP-ICDH isoforms. Activity staining after non-denaturing polyacrylamide gel electrophoresis revealed the complete absence of a major activity band in leaves of antisense plants. No differences in growth or development, including flower formation and tuber yield, were observed between transgenic and wild-type plants. Photosynthesis and respiration were also unchanged. Levels of amino acids were the same in wild-type and cyt-NADP-ICDH antisense plants, even when accumulation of amino acids was induced by incubation of detached leaves in tap water in the dark (`induced senescence'). Consistent with a reduction in NADP-ICDH activity, however, were slight increases in the levels of isocitrate (up to 2.5-fold) and citrate (up to 2-fold). 2-Oxoglutarate was not reduced. Our data indicate that potato plants can cope with a severe reduction in cyt-NADP-ICDH activity without major shifts in growth and metabolism.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/s004250050299

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