Characterization of the difference of starch branching enzyme activities in normal and low-amylopectin maize during kernel development

In order to determine the reasons for the differences in structure between starch from a normal and a low-amylopectin maize variety the activities of all the enzymes in the committed pathway of starch synthesis were studied throughout kernel development. Levels of ADP glucose pyrophosphorylase and starch synthase activity were found to he broadly similar between the two varieties but the low-amylopectin starch (LAPS) maize variety showed dramatically reduced starch branching enzyme activity, with an almost total absence of the branching enzyme II isoform. Scanning electron microscopy showed a significant alteration in the morphology of the starch granules of the low-amylopectin maize. The results suggest that the increased amylose and the reduction of high molecular weight amylopectin in the LAPS starch results from the absence of the branching enzyme II isoform. This evidence supports the theory that the different branching enzyme isoforms contribute separately to the synthesis and final structure of amylopectin. (C) 1998 Academic Press Limited.