Starch, sucrose biosynthesis and partition of carbon in plants are regulated by orthophosphate and triose-phosphates

Inorganic phosphate is a potent inhibitor of the enzymes directly involved in the synthesis of sucrose and starch, while 3-phosphoglycerate is an activator of ADP-glucose synthetase, an enzyme involved in starch synthesis. Phosphate is also required for transport of triose phosphates from the chloroplasts to the cytosol and is an activator for the synthesis of fructose 2,6 bisphosphate, a metabolite that inhibits fructose-1,6-bisphasphatase and stimulates glycolysis in the cytosol. Coordination of these regulatory phenomena probably plays an important role in regulating both starch and sucrose synthesis and in partitioning carbon between the reserve polymer and disaccharide.