[(1->4)-alpha-D-glucosyl](n) + an NDP-alpha-D-glucose = [(1->4)-alpha-D-glucosyl](n+1) + a ribonucleoside 5'-diphosphate + H(+) Glycan biosynthesis; starch biosynthesis. Amyloplast or chloroplast, granule-bound. Belongs to the glycosyltransferase 1 family. Bacterial/plant glycogen synthase subfamily.