title: Modulation of fructokinase activity of potato (Solanum tuberosum) results in substantial shifts in tuber metabolism.
abstract: Potato plants (Solanum tuberosum L. cvs Desiree and Record) transformed with sense and antisense constructs of a cDNA encoding the potato fructokinase StFK1 exhibited altered transcription of this gene, altered amount of protein and altered enzyme activities. Measurement of the maximal catalytic activity of fructokinase revealed a 2-fold variation in leaf (from 90 to 180% of wild type activity) and either a 10- or 30-fold variation in tuber (from 10 or 30% to 300% in Record and Desiree, respectively) activity. The comparative effect of the antisense construct in leaf and tuber tissue suggests that this isoform is only a minor contributor to the total fructokinase activity in the leaf but the predominant isoform in the tuber. Antisense inhibition of the fructokinase resulted in a reduced tuber yield; however, its overexpression had no impact on this parameter. The modulation of fructokinase activity had few, consistent effects on carbohydrate levels, with the exception of a general increase in glucose content in the antisense lines, suggesting that this enzyme is not important for the control of starch synthesis. However, when metabolic fluxes were estimated, it became apparent that the transgenic lines display a marked shift in metabolism, with the rate of redistribution of radiolabel to sucrose markedly affected by the activity of fructokinase. These data suggest an important role for fructokinase, acting in concert with sucrose synthase, in maintaining a balance between sucrose synthesis and degradation by a mechanism independent of that controlled by the hexose phosphate-mediated activation of sucrose phosphate synthase.
authors.affiliation: Quality, Health and Nutrition Programme, Scottish Crop Research Institute, Dundee DD2 5DA, UK.
authors.forename: Howard V
authors.initials: HV
authors.lastname: Davies
authors.forename: Louise V T
authors.initials: LV
authors.lastname: Shepherd
authors.forename: Michael M
authors.initials: MM
authors.lastname: Burrell
authors.forename: Fernando
authors.initials: F
authors.lastname: Carrari
authors.forename: Ewa
authors.initials: E
authors.lastname: Urbanczyk-Wochniak
authors.forename: Andrea
authors.initials: A
authors.lastname: Leisse
authors.forename: Robert D
authors.initials: RD
authors.lastname: Hancock
authors.forename: Mark
authors.initials: M
authors.lastname: Taylor
authors.forename: Roberto
authors.initials: R
authors.lastname: Viola
authors.forename: Heather
authors.initials: H
authors.lastname: Ross
authors.forename: Diane
authors.initials: D
authors.lastname: McRae
authors.forename: Lothar
authors.initials: L
authors.lastname: Willmitzer
authors.forename: Alisdair R
authors.initials: AR
authors.lastname: Fernie
mesh_terms: D050260:Carbohydrate Metabolism; D005631:Fructokinases / Q000235:genetics / Q000378:metabolism*; D010641:Phenotype; D018515:Plant Leaves / Q000378:metabolism; D035281:Plant Tubers / Q000201:enzymology / Q000378:metabolism*; D030821:Plants, Genetically Modified; D011198:Solanum tuberosum / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic
chemical_list: D005631:Fructokinases; C046173:fructokinase