The structure of clusters isolated from AP changes as a function of the maturity stage of wheat endosperm development. Through out development, there are only small differences between clustersin A- and B-type starch granules; however, the clusters in B-type granules are more tightly branched than in A-type granules. Clusters initially increase in size in both types of granules. Markedchanges in cluster characteristics occur between the end of the pre-physiological maturity stage (28 DAA) and the maturity stage(49 DAA): cluster sizes become smaller, and the number of chains and building blocks are lower in clusters at 49 DAA. The reductionin the number of building blocks at post-physiological maturity isdue mainly to the lower number of building blocks that containtwo chains (group 2). A trimming activity is a possible cause of the modifications after the pre-physiological maturity period.AcknowledgementAuthors are grateful to the efforts of Mr. Mark Etienne at DowAgroSciences, who assisted with sampling wheat in the field.