The influence of cytosolic phosphoglucomutase on photosynthetic carbohydrate metabolism

Abstract

The aim of this work was to examine the role of cytosolic phosphoglucomutase (cPGM; EC 5.4.2.2) in photosynthetic carbon partitioning. We have previously described the generation and characterisation of the tuber metabolism of transgenic potato ( Solanum tuberosum cv. Desiree) lines expressing the StcPGM gene in the antisense orientation under the control of the 35S promoter. Here we extend the characterisation of leaf metabolism within these lines, examining properties of gas exchange, carbon partitioning, and the effect of the genetic manipulation on a wide range of metabolites including metabolites of the sucrose-starch transition, glycolysis, the Krebs cycle and amino acid metabolism. The data acquired in the present study surprisingly reveal that the photosynthetic sucrose synthetic capacity of the leaves is largely unaltered but that these plants display a reduced rate of photosynthesis, a dramatic reduction in nucleotide levels, and a general decline of biosynthesis. We conclude that these lines exhibit only moderate changes in sucrose synthesis but more complex changes on a range of diverse metabolic pathways.

Metabolic Profiling of Transgenic Tomato Plants Overexpressing Hexokinase Reveals That the Influence of Hexose Phosphorylation Diminishes during Fruit Development

“…The initial characterization of the hexokinase transformants revealed an inhibition of photosynthesis in these lines, which could explain why the drop in adenylates and in the ATP to ADP ratio was more severe in the leaf tissue. However, it should be noted that although reduced photosynthesis can correlate with reduction in the adenylate pool size (for example, see Lytovchenko et al, 2002b), this is not always the case (for example, see Lytovchenko et al, 2002a). In contrast, the less dramatic changes observed in the adenylate pool sizes of the fruit most probably result merely from the increased demand for ATP imposed by the expression of the transgene.…”

“…Hexokinase activity was measured as described by Dai et al (1999), enolase activity according to Fernie et al (2001a), fructokinase and phosphoGlc isomerase activities as described by Fernie et al (2001b), whereas ADP-Glc pyrophosphorylase, aldolase, phosphoglucomutase, pyruvate kinase, phosphofructokinase, glyceraldehyde-3-phosphate dehydrogenase, and triose-phosphate isomerase activities were determined according to Lytovchenko et al (2002b).…”

Antisense Inhibition of the Iron-Sulphur Subunit of Succinate Dehydrogenase Enhances Photosynthesis and Growth in Tomato via an Organic Acid–Mediated Effect on Stomatal Aperture

“…The 14 C-labeling pattern of sucrose, starch, and other cellular constituents was performed by illuminating leaf discs (10-mm diameter) in a leafdisc oxygen electrode (Hansatech) in saturating 14 CO 2 at a PFD of 700 mmol m 22 s 21 at 258C for 30 min, and subsequent fractionation was performed exactly as detailed by Lytovchenko et al (2002). Fluorescence emission was measured in vivo using a PAM fluorometer (Walz) on plants maintained at fixed irradiance (100 and 700 mmol photons m 22 s 21 ) for 30 min prior to measurement of chlorophyll a fluorescence yield and relative ETR, which were calculated using the WinControl software package (Walz).…”

Amperometric determination of phosphoglucomutase activity with a bienzyme screen-printed biosensor

“…PGM catalyzes the interconversion of glucose-1-phosphate and glucose-6-phosphate. In this process, the enzyme links various catabolic pathways to yield energy ATP or reducing power NAD(P)H, and several anabolic pathways, such as to lead to the synthesis of polysaccharides [1][2][3][4].Due to its importance, measurements for the enzymatic activity of PGM have been widely performed, by the use of optical methods with coupled enzyme system [3][4][5][6][7][8][9][10][11], or the use of a combination of ion/molecule reactions and FT-ICR mass spectrometry [12]. However, these measurements either result in a long detection time, a large amount of enzyme consumption, or complex procedures which need to be performed by skilled personnel.…”

“…PGM catalyzes the interconversion of glucose-1-phosphate and glucose-6-phosphate. In this process, the enzyme links various catabolic pathways to yield energy ATP or reducing power NAD(P)H, and several anabolic pathways, such as to lead to the synthesis of polysaccharides [1][2][3][4].…”