Relationship to carbon partitioning

The results described above suggested that Fru-2,6-P2 could integrate the carbon metabolism of leaves by serving as a regulatory link between chloroplasts and cytosol. As such, it could function to control carbon partitioning — i.e., the conversion to and accumulation of newly fixed carbon as sucrose or starch. Hence, as more photosynthate is made available and the triose phosphate pools (especially 

In addition to this feed-forward mechanism, Fru-2,6-P2 functions in feedback control of sucrose synthesis. When sucrose accumulates in the leaf, the hexose phosphate concentration increases [51] (the reason for this is still unclear), leading to an activation of Fru-6-P,2K. The resultant increase of Fru-2,6-P2 then restricts the activity of cytosolic FBPase so that less sucrose, and more starch, is synthesized. In this way, when photosynthesis exceeds the rate at which sucrose can be exported, or stored in the leaf, an increasing proportion of the photosynthate is diverted into starch, which provides a store of carbohydrate that is especially important at night (see above). 

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