Starch-debranching enzyme that plays a role in the degradation of transitory starch during the night in leaf blades, facilitates the formation of spherical amyloplasts containing compound granules in the endosperm, and affects morphological characteristics of plastids. Hydrolysis of (1->6)-alpha-D-glucosidic branch linkages in glycogen, amylopectin and their beta-limit dextrins. Localizes in amyloplast stroma of seed endosperm. Expressed in leaves. Expressed at low levels in developing endosperm. Belongs to the glycosyl hydrolase 13 family.