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- Title
Metabolite pools and carbon flow during C<sub>4</sub> photosynthesis in maize: <sup>13</sup>CO<sub>2</sub> labeling kinetics and cell type fractionation.
- Authors
Arrivault, Stéphanie; Obata, Toshihiro; Szecówk, Marek; Mengin, Virginie; Guenther, Manuela; Hoehne, Melanie; Fernie, Alisdair R.; Stitt, Mark
- Abstract
Worldwide efforts to engineer C4 photosynthesis into C3 crops require a deep understanding of how this complex pathway operates. CO2 is incorporated into four-carbon metabolites in the mesophyll, which move to the bundle sheath where they are decarboxylated to concentrate CO2 around RuBisCO. We performed dynamic 13CO2 labeling in maize to analyze C flow in C4 photosynthesis. The overall labeling kinetics reflected the topology of C4 photosynthesis. Analyses of cell-specific labeling patterns after fractionation to enrich bundle sheath and mesophyll cells revealed concentration gradients to drive intercellular diffusion of malate, but not pyruvate, in the major CO2-concentrating shuttle. They also revealed intercellular concentration gradients of aspartate, alanine, and phosphenolpyruvate to drive a second phosphoenolpyruvate carboxykinase (PEPCK)-type shuttle, which carries 10-14% of the carbon into the bundle sheath. Gradients also exist to drive intercellular exchange of 3-phosphoglycerate and triose-phosphate. There is rapid carbon exchange between the Calvin-Benson cycle and the CO2-concentrating shuttle, equivalent to ~10% of carbon gain. In contrast, very little C leaks from the large pools of metabolites in the C concentration shuttle into respiratory metabolism. We postulate that the presence of multiple shuttles, alongside carbon transfer between them and the Calvin-Benson cycle, confers great flexibility in C4 photosynthesis.
- Subjects
PHOTOSYNTHESIS; METABOLITES; DECARBOXYLATION; CELL fractionation; MESOPHYLL tissue; TRIOSE-phosphate isomerase
- Publication
Journal of Experimental Botany, 2017, Vol 68, Issue 2, p283
- ISSN
0022-0957
- Publication type
Article
- DOI
10.1093/jxb/erw414