Initiation process of starch biosynthesis

Abstract

Plants have developed the metabolic system in which a great amount of starch can be synthesized and store them into granules with semicrystalline structure in the plastid. The fine structure of amylopectin, a major component of starch, is a highly organized distinct structure composed of a unit structure called cluster. Thus, it is highly possible that plants have a specific starch biosynthesis initiation different from that of the well-known glycogen biosynthesis initiation found in animals, fungi, and bacteria. Based on a working hypothesis that the starch biosynthesis initiation has two events, i.e., the initiation of amylopectin synthesis and that of starch granule formation, the possible roles of enzymes which are potentially involved in these events and mechanisms underlying the regulation of amylopectin synthesis from simple sugars and starch granule formation are discussed.