Alonso Ana Paula, Raymond Philippe, Hernould Michel, Rondeau-Mouro Corinne, de Graaf Albert, Chourey Prem, Lahaye Marc, Shachar-Hill Yair, Rolin Dominique, Dieuaide-Noubhani Martine
INRA, Université Bordeaux 1, Université Victor Segalen Bordeaux 2, UMR 619 Biologie du fruit, BP 81, 33883 Villenave d'Ornon cedex, France.
Metab Eng. 2007 Sep-Nov;9(5-6):419-32. doi: 10.1016/j.ymben.2007.06.002. Epub 2007 Jul 10.
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.
为了了解蔗糖合酶（SuSy）在碳分配中的作用，对SuSy基因双突变体sh1 sus1的玉米根尖和相应的野生型W22的代谢通量进行了分析。[U-(14)C]-葡萄糖脉冲标记实验允许对进入蔗糖、淀粉和细胞壁多糖的单向通量进行定量。还进行了用[1-(13)C]-、[2-(13)C]-或[U-(13)C]-葡萄糖进行的同位素稳态标记，随后通过(1)H-NMR和(13)C-NMR对碳水化合物和氨基酸中的富集进行定量，以使用计算机辅助建模确定通过中心代谢的29种通量。由于SUS1和SH1同工酶的抑制，玉米根尖直径显著减小，呼吸代谢降低了30%。我们的结果清楚地表明，在玉米根尖中，淀粉是由质体中合成的ADP-葡萄糖产生的，而不是由蔗糖合酶在细胞质中产生的。出乎意料的是，双突变体中细胞壁合成的通量增加了。这一观察结果表明，在玉米根尖中，SH1和SUS1不是纤维素生物合成的特定提供者。
