Transgenic Arabidopsis plants with decreased activity of fructose-6-phosphate,2-kinase/fructose-2,6-bisphosphatase have altered carbon partitioning.
The role of fructose-2,6-bisphosphate (Fru-2,6-P(2)) as a regulatory metabolite in photosynthetic carbohydrate metabolism was studied in transgenic Arabidopsis plants with reduced activity of Fru-6-phosphate,2-kinase/Fru-2,6-bisphosphatase. A positive correlation was observed between the Fru-6-phosphate,2-kinase activity and the level of Fru-2,6-P(2) in the leaves. The partitioning of carbon was studied by (14)CO(2) labeling of photosynthetic products. Plant lines with Fru-2,6-P(2) levels down to 5% of the levels observed in wild-type (WT) plants had significantly altered partitioning of carbon between sucrose (Suc) versus starch. The ratio of (14)C incorporated into Suc and starch increased 2- to 3-fold in the plants with low levels of Fru-2,6-P(2) compared with WT. Transgenic plant lines with intermediate levels of Fru-2,6-P(2) compared with WT had a Suc-to-starch labeling ratio similar to the WT. Levels of sugars, starch, and phosphorylated intermediates in leaves were followed during the diurnal cycle. Plants with low levels of Fru-2,6-P(2) in leaves had high levels of Suc, glucose, and Fru and low levels of triose phosphates and glucose-1-P during the light period compared with WT. During the dark period these differences were eliminated. Our data provide direct evidence that Fru-2,6-P(2) affects photosynthetic carbon partitioning in Arabidopsis. Opposed to this, Fru-2,6-P(2) does not contribute significantly to regulation of metabolite levels in darkness.
Draborg
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Plant Biochemistry Laboratory, Department of Plant Biology, The Royal Veterinary and Agricultural University, 40 Thorvaldsensvej, DK-1871 Frederiksberg C, Copenhagen, Denmark.
Villadsen
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Nielsen
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D017360:Arabidopsis / Q000201:enzymology*; D001483:Base Sequence; D050260:Carbohydrate Metabolism; D002244:Carbon / Q000378:metabolism*; D002245:Carbon Dioxide / Q000378:metabolism; D017931:DNA Primers; D006597:Fructose-Bisphosphatase / Q000378:metabolism*; D009097:Multienzyme Complexes / Q000378:metabolism*; D010732:Phosphofructokinase-1 / Q000378:metabolism*; D025481:Phosphofructokinase-2; D010766:Phosphorylation; D010788:Photosynthesis; D030821:Plants, Genetically Modified / Q000201:enzymology
D017931:DNA Primers; D009097:Multienzyme Complexes; D002245:Carbon Dioxide; D002244:Carbon; D025481:Phosphofructokinase-2; D010732:Phosphofructokinase-1; D006597:Fructose-Bisphosphatase