A NOVEL TUBULAR ARRAY ASSOCIATED WITH PROTEIN BODIES IN THE ROUGH ENDOPLASMIC-RETICULUM OF OPAQUE-2 MAIZE

The seed storage proteins of maize (Zea mays L.) are synthesized durin g endosperm development on membrane-bound polyribosomes. Protein body formation in normal genotypes occurs via a sequential deposition of th e various types of zeins, and leads to the formation of spherical stru ctures with a diameter of about 1 mu m. In the endosperm mutant opaque -2 the level of one zein class is reduced; these kernels exhibit an op aque phenotype instead of the vitreous phenotype displayed in normal g enotypes, presumably due to the decrease in total zein protein at the time of desiccation. Previous microscopic examination of opaque-2 prot ein bodies at 22 DAP (days after pollination) showed that the protein bodies were morphologically similar to those of normal genotypes. Howe ver, the endosperm of opaque-2 maize at 14 DAP contains tubular arrays within the rough endoplasmic reticulum. These tubular arrays are tigh tly associated with the developing protein bodies. Long strands of tub ules, sometimes 10 mu m in length, are observed in the endosperm, and partially formed protein bodies often seem to be forming directly from these tubular arrays. No immunostaining is associated with this tubul ar material when any of the anti-zein antibodies are used.