The conversion of carbon and nitrogen into starch and storage proteins in developing storage organs: an overview

Abstract

In this article we provide an overview on recent developments in starch and storage protein biosynthesis, two seemingly distinct biochemical processes, which have been shown to be inter-dependent based on results from genetic and transgenic studies. The pathway of carbon to starch in cereal seeds has been found to be substantially different from other plants in having ADPglucose, the precursor of starch biosynthesis, formed mainly in the cyto-plasm in addition to the normal site of synthesis, the plastid. Analysis of starch mutants and the use of antisense technology have shed considerable light on the possible roles of individual starch synthase and branching enzyme isoforms as well as those of enzyme activities normally associated with a degradative function in starch formation. Analysis of storage protein in the model system rice indicates that sites of protein synthesis and compartmentation of macromolecules are stratified within specific intracellular regions. The possible implications of this intracellular partitioning of carbon (starch) and nitrogen (storage protein) utilization are discussed.