A metabolic flux analysis to study the role of sucrose synthase in the regulation of the carbon partitioning in central metabolism in maize root tips.
In order to understand the role of sucrose synthase (SuSy) in carbon partitioning, metabolic fluxes were analyzed in maize root tips of a double mutant of SuSy genes, sh1 sus1 and the corresponding wild type, W22. [U-(14)C]-glucose pulse labeling experiments permitted the quantification of unidirectional fluxes into sucrose, starch and cell wall polysaccharides. Isotopic steady-state labeling with [1-(13)C]-, [2-(13)C]- or [U-(13)C]-glucose followed by the quantification by (1)H-NMR and (13)C-NMR of enrichments in carbohydrates and amino acids was also performed to determine 29 fluxes through central metabolism using computer-aided modeling. As a consequence of the suppression of SUS1 and SH1 isozymes, maize root tips diameter was significantly decreased and respiratory metabolism reduced by 30%. Our result clearly established that, in maize root tips, starch is produced from ADP-Glc synthesized in the plastid and not in the cytosol by sucrose synthase. Unexpectedly, the flux of cell wall synthesis was increased in the double mutant. This observation indicates that, in maize root tips, SH1 and SUS1 are not specific providers for cellulose biosynthesis.
Alonso
Ana Paula
AP
INRA, Université Bordeaux 1, Université Victor Segalen Bordeaux 2, UMR 619 Biologie du fruit, BP 81, 33883 Villenave d'Ornon cedex, France.
Raymond
Philippe
P
Hernould
Michel
M
Rondeau-Mouro
Corinne
C
de Graaf
Albert
A
Chourey
Prem
P
Lahaye
Marc
M
Shachar-Hill
Yair
Y
Rolin
Dominique
D
Dieuaide-Noubhani
Martine
M
D002247:Carbon Isotopes / Q000378:metabolism; D002451:Cell Compartmentation; D005947:Glucose / Q000378:metabolism; D051599:Glucose-1-Phosphate Adenylyltransferase / Q000096:biosynthesis; D005964:Glucosyltransferases / Q000235:genetics / Q000378:metabolism*; D007527:Isoenzymes / Q000378:metabolism; D007553:Isotope Labeling; D008954:Models, Biological; D009154:Mutation; D019906:Nuclear Magnetic Resonance, Biomolecular; D018517:Plant Roots / Q000166:cytology / Q000201:enzymology* / Q000378:metabolism*; D018087:Plastids / Q000378:metabolism; D013213:Starch / Q000096:biosynthesis; D003313:Zea mays / Q000033:anatomy & histology*
D002247:Carbon Isotopes; D007527:Isoenzymes; D013213:Starch; D005964:Glucosyltransferases; C022699:sucrose synthase; D051599:Glucose-1-Phosphate Adenylyltransferase; D005947:Glucose