Figure 2. Biosynthesis of storage starch in cereal crops.

During the grain filling period, sucrose localized in vegetative organs (i.e., leaves) is intensively unloaded from the phloem and transported into the reproductive organs (i.e., grains). Multiple starch biosynthetic enzymes co-operate to produce starch granules both in transient and storage starch biosynthesis. Grain-filling is associated with the normal development of amyloplasts, delivery of carbon precursors and energy from leaves to endosperm by sucrose transporters (SUTs), and enzymes of endosperm starch biosynthesis during grain-filling periods, which are greatly susceptible to fluctuated environments.