The contribution of plastidial phosphoglucomutase to the control of starch synthesis within the potato tuber

Abstract

The aim of this work was to evaluate the extent to which plastidial phosphoglucomutase (PGM) activity controls starch synthesis within potato (Solanum tuberosum L. cv. Desirée) tubers. The reduction in the activity of plastidial PGM led to both a correlative reduction in starch accumulation and an increased sucrose accumulation. The control coefficient of plastidial PGM on the accumulation of starch was estimated to approximate 0.24. The fluxes of carbohydrate metabolism were measured by investigating the metabolism of [U-14C]glucose in tuber discs from wild-type and transgenic plants. In tuber discs the control coefficient of plastidial PGM over starch synthesis was estimated as 0.36, indicating that this enzyme exerts considerable control over starch synthesis within the potato tuber.

Mitochondrial uncoupling protein is required for efficient photosynthesis

“…Metabolites were quantified in rosette leaves harvested at the midpoint of the photoperiod as described: amino acids (47), nucleotides (48), hexose phosphates and 3-phosphoglyceric acid (49), and organic acids, sugars, and other metabolites (50).…”

Alteration of Photosynthate Partitioning by High-Level Expression of Phosphoglucomutase in Tobacco Chloroplasts

“…16) Likewise, estimated control coefficients of 0.01 and 0.21 under low and high light conditions respectively in Arabidopsis thaliana leaves 17) have been reported. In addition to flux analysis, osmotic stress dramatically increases the ratio of Glc1P to Glc6P in the leaf disc of spinach, 3) suggesting that PGM activity can be regulated by stress-responsive metabolites.…”

“…15) Measuring fluxes of the carbohydrate metabolism of transgenic potato tuber discs exhibiting reduced plastidial PGM activity indicated an estimated control coefficient of 0.36 on starch synthesis in tubers. 16) Likewise, estimated control coefficients of 0.01 and 0.21 under low and high light conditions respectively in Arabidopsis thaliana leaves 17) have been reported. In addition to flux analysis, osmotic stress dramatically increases the ratio of Glc1P to Glc6P in the leaf disc of spinach, 3) suggesting that PGM activity can be regulated by stress-responsive metabolites.…”

Decreasing the Mitochondrial Synthesis of Malate in Potato Tubers Does Not Affect Plastidial Starch Synthesis, Suggesting That the Physiological Regulation of ADPglucose Pyrophosphorylase Is Context Dependent

“…The levels of starch, Suc, Fru, and Glc in the potato tuber tissue were determined exactly as described previously (Fernie et al, 2001b). Malate and fumarate were determined exactly as detailed by Nunes-Nesi et al (2007).…”

“…Fru-6-P is freely converted to Glc-6-P, in which form it normally enters the amyloplast (Kammerer et al, 1998;Tauberger et al, 2000;Zhang et al, 2008), and once in the plastid, it is converted to starch via the concerted action of plastidial phosphoglucomutase, ADP-Glc pyrophosphorylase (AGPase), and the various isoforms of starch synthase (Martin and Smith, 1995;Geigenberger, 2011). Of these reactions, although some of the control of starch synthesis resides in the plastidial phosphoglucomutase reaction (Fernie et al, 2001b), the AGPase reaction harbors the highest proportion of control within the linear pathway (Sweetlove et al, 1999;Geigenberger et al, 1999Geigenberger et al, , 2004. In addition, considerable control resides in both the Glc-6-P phosphate antiporter (Zhang et al, 2008) and the amyloplastidial adenylate transporter (Tjaden et al, 1998;Zhang et al, 2008) as well as in reactions external to the pathways, such as the amyloplastidial adenylate kinase (Regierer et al, 2002), cytosolic UMP synthase (Geigenberger et al, 2005), and mitochondrial NAD-malic enzyme (Jenner et al, 2001).…”