Structure of clusters and building blocks in amylopectin from developing wheat endosperm.

Changes in internal structure of amylopectin (AP) during wheat endosperm development were studied by isolating clusters and building blocks of AP from both large A-type and small B-type starch granules at different maturity stages up to harvest time at 49 days after anthesis (DAA). Clusters isolated from B-type granules had a degree of branching (DB) of 16.5-16.8% and were more tightly branched than those isolated from A-type granules (DB 15.7-16.2%). The degree of polymerization (DP) of the clusters increased in both types of granules during the pre-physiological maturity stage up to 28 DAA. Clusters at maturity were smaller with less branches and building blocks than at the end of the pre-maturity stage. It is suggested that this was due to a continuous trimming of the cluster structure after the active period of starch synthesis. Differences were evident between A- and B-type granules with regards to glucan trimming and the type of new chains produced.