Starch is the major storage material in the cereal
endosperm, accounting for about 80% of the total dry
matter weight. Endosperm starch is a complex of the
two polymers, amylose and amylopectin, the former
comprising of the glucose moieties connected together
by α-1,4 glycosidic bonds, while in the latter the
glucose moieties are linked via α-1,6 glycosidic bonds.
Both amylose and amylopectin are synthesized in
amyloplast. Starch synthesis is a multi-step process,
beginning with glucose generated by photosynthesis,
and then glucose is converted into sucrose. Sucrose is
transported to grains through vascular bundles, which
is then converted into uridine diphosphate (UDP)
glucose and fructose by the hydrolysis of UDP-glucose
pyrophosphorylase (UGPase). The UDP-glucose then
is converted into 1-phosphate glucose, which is used
to synthesize adenosine diphosphate glucose (ADPG)