EFFECT OF THE FLOURY-2 LOCUS ON PROTEIN BODY FORMATION DURING MAIZE ENDOSPERM DEVELOPMENT

The seed storage proteins of maize (Zea mays L.) are synthesized during endosperm development on membrane-bound polyribosomes. These proteins, collectively called zeins, are translocated into the lumen of the rough endoplasmic reticulum, where they assemble into protein bodies. Protein body formation in normal genotypes occurs via an ordered deposition of the various types of zeins, and leads to the formation of spherical structures with a diameter of about 1 mum. These structures consist of a central core that contains predominantly alpha-zein; this central region is surrounded by a peripheral layer of beta- and gamma-zeins, and the entire structure is bounded by rough endoplasmic reticulum. In the endosperm mutant floury-2 the levels of all classes of zeins are reduced; these kernels exhibit an opaque phenotype instead of the vitreous phenotype observed in normal genotypes. In contrast to the discrete, spherical protein bodies which are formed in normal maize endosperm, the protein bodies within floury-2 endosperm are irregular and the zeins are disorganized; patches of beta- and gamma-zeins occur within irregularly lobed clusters of alpha-zein within the lumen of the rough endoplasmic reticulum. The implications of this aberrant distribution are discussed, both with respect to protein body development and kernel characteristics.