Starch is formed in the plastid by the sequential activities of ADP-Glc pyrophosphorylase, converting Glc-1-P to ADP-Glc, and starch synthases and starch branching enzymes, which catalyze the formation of α-1,4- and α-1,6-glycosidic bonds, respectively, to generate amylose and amylopectin (Smith, 1999).