Enzymic Mechanism of Starch Breakdown in Germinating Rice Seeds

The formation of multiple forms of amylases in germinating rice (Oryza sativa L. cv Kimmaze) grains was examined by means of isoelectric focusing, cross-immunoelectrophoresis, and rocket-line immunoelectrophoresis followed by a reaction of enzymic characterization by using beta-limit dextrin or starch as substrate. The constituents detected by isoelectric focusing were identified as three electrophoretically heterogeneous antigens. The major alpha-amylase bands A and B corresponded to a same antigen, the main portion of which was produced within 2 days' germination. The bulk of alpha-amylase D appeared between 2 and 4 days' germination. Component E, a debranching enzyme according to its action on the beta-limit dextrin, already exists in the ungerminated seeds; its amount decreases within the first 2 days of germination and increases again thereafter.Evidence showing that beta-amylase (band C) is produced by the scutellum at an early stage of germination was provided. The enzyme appeared in a suspension of the scutellum after a prolonged incubation.