TY  - JOUR
A1  - Fettke, Jörg
A1  - Leifels, Lydia
A1  - Brust, Henrike
A1  - Herbst, Karoline
A1  - Steup, Martin
T1  - Two carbon fluxes to reserve starch in potato (Solanum tuberosum L.) tuber cells are closely interconnected but differently modulated by temperature
JF  - Journal of experimental botany
N2  - Parenchyma cells from tubers of Solanum tuberosum L. convert several externally supplied sugars to starch but the rates vary largely. Conversion of glucose 1-phosphate to starch is exceptionally efficient. In this communication, tuber slices were incubated with either of four solutions containing equimolar [U-C-14]glucose 1-phosphate, [U-C-14]sucrose, [U-C-14]glucose 1-phosphate plus unlabelled equimolar sucrose or [U-C-14]sucrose plus unlabelled equimolar glucose 1-phosphate. C-14-incorporation into starch was monitored. In slices from freshly harvested tubers each unlabelled compound strongly enhanced C-14 incorporation into starch indicating closely interacting paths of starch biosynthesis. However, enhancement disappeared when the tubers were stored. The two paths (and, consequently, the mutual enhancement effect) differ in temperature dependence. At lower temperatures, the glucose 1-phosphate-dependent path is functional, reaching maximal activity at approximately 20 degrees C but the flux of the sucrose-dependent route strongly increases above 20 degrees C. Results are confirmed by in vitro experiments using [U-C-14]glucose 1-phosphate or adenosine-[U-C-14]glucose and by quantitative zymograms of starch synthase or phosphorylase activity. In mutants almost completely lacking the plastidial phosphorylase isozyme(s), the glucose 1-phosphate-dependent path is largely impeded. Irrespective of the size of the granules, glucose 1-phosphate-dependent incorporation per granule surface area is essentially equal. Furthermore, within the granules no preference of distinct glucosyl acceptor sites was detectable. Thus, the path is integrated into the entire granule biosynthesis. In vitro C-14-incorporation into starch granules mediated by the recombinant plastidial phosphorylase isozyme clearly differed from the in situ results. Taken together, the data clearly demonstrate that two closely but flexibly interacting general paths of starch biosynthesis are functional in potato tuber cells.
KW  - glucose 1-phosphate
KW  - phosphorylase
KW  - potato tubers
KW  - starch
KW  - starch synthase
Y1  - 2012
U6  - https://doi.org/10.1093/jxb/ers014
SN  - 0022-0957
VL  - 63
IS  - 8
SP  - 3011
EP  - 3029
PB  - Oxford Univ. Press
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Malinova, Irina
A1  - Kunz, Hans-Henning
A1  - Alseekh, Saleh
A1  - Herbst, Karoline
A1  - Fernie, Alisdair R.
A1  - Gierth, Markus
A1  - Fettke, Jörg
T1  - Reduction of the cytosolic phosphoglucomutase in arabidopsis reveals impact on plant growth, seed and root development, and carbohydrate partitioning
JF  - PLoS one
N2  - Phosphoglucomutase (PGM) catalyses the interconversion of glucose 1-phosphate (G1P) and glucose 6-phosphate (G6P) and exists as plastidial (pPGM) and cytosolic (cPGM) isoforms. The plastidial isoform is essential for transitory starch synthesis in chloroplasts of leaves, whereas the cytosolic counterpart is essential for glucose phosphate partitioning and, therefore, for syntheses of sucrose and cell wall components. In Arabidopsis two cytosolic isoforms (PGM2 and PGM3) exist. Both PGM2 and PGM3 are redundant in function as single mutants reveal only small or no alterations compared to wild type with respect to plant primary metabolism. So far, there are no reports of Arabidopsis plants lacking the entire cPGM or total PGM activity, respectively. Therefore, amiRNA transgenic plants were generated and used for analyses of various parameters such as growth, development, and starch metabolism. The lack of the entire cPGM activity resulted in a strongly reduced growth revealed by decreased rosette fresh weight, shorter roots, and reduced seed production compared to wild type. By contrast content of starch, sucrose, maltose and cell wall components were significantly increased. The lack of both cPGM and pPGM activities in Arabidopsis resulted in dwarf growth, prematurely die off, and inability to develop a functional inflorescence. The combined results are discussed in comparison to potato, the only described mutant with lack of total PGM activity.
Y1  - 2014
U6  - https://doi.org/10.1371/journal.pone.0112468
SN  - 1932-6203
VL  - 9
IS  - 11
PB  - PLoS
CY  - San Fransisco
ER  -