The Possible Relationship of Starch and Phytoglycogen in Sweet Corn. II. The Role of Branching Enzyme I

Abstract Developing maize kernels contain three starch branching enzymes. Homogeneous branching enzyme I has now been shown to be capable of branching amylose as well as amylopectin but not glycogens. The formation of glycogen‐like molecules by the further branching of amylopectin suggests that branching enzyme I plays a role in phytoglycogen formation. Its presence in nonmutant kernels which do not accumulate phytoglycogen, however, indicates that amylopectin per se is not accessible to branching enzyme I for phytoglycogen formation. Treatment of sugary (su) starch granules with enzyme I resulted in soluble phytoglycogen‐like glucan. No glucan was released by treatment of nonmutant starch granules. In addition, nonsolublized amylopectin and amylose fractions of the su starch were branched during the incubations. These observations are consistent with plastid changes which show a conversion of starch granules to phytoglycogen in sugary endosperm cells.