[(1->4)-alpha-D-glucosyl](n) + ADP-alpha-D-glucose = [(1->4)-alpha-D-glucosyl](n+1) + ADP + H(+) Glycan biosynthesis; starch biosynthesis. Amyloplast or chloroplast, granule-bound. In leaves, flowers and fruits. Observed in all floral whorls at early developmental stages, but restricted to carpel before anthesis. Expressed with a circadian rhythm with peak expression at the end of the day. Belongs to the glycosyltransferase 1 family. Bacterial/plant glycogen synthase subfamily.