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Two carbon fluxes to reserve starch in potato (Solanum tuberosum L.) tuber cells are closely interconnected but differently modulated by temperature
- Source :
- Journal of Experimental Botany
- Publication Year :
- 2012
- Publisher :
- Oxford University Press (OUP), 2012.
-
Abstract
- 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.
- Subjects :
- Sucrose
Physiology
Starch
phosphorylase
Plant Science
Complex Mixtures
Isozyme
Carbon Cycle
starch synthase
chemistry.chemical_compound
Glycogen phosphorylase
Biosynthesis
Polysaccharides
Plastids
Glucans
Institut für Biochemie und Biologie
Solanum tuberosum
Carbon Isotopes
biology
starch
Granule (cell biology)
Glucosephosphates
Temperature
food and beverages
Starch Phosphorylase
Plants, Genetically Modified
Research Papers
Isoenzymes
Plant Tubers
Solubility
glucose 1-phosphate
chemistry
Biochemistry
biology.protein
Starch synthase
potato tubers
Subjects
Details
- ISSN :
- 14602431 and 00220957
- Volume :
- 63
- Database :
- OpenAIRE
- Journal :
- Journal of Experimental Botany
- Accession number :
- edsair.doi.dedup.....268102fbd7b5bb72ad6d9200d4589d5f