Figure 9.

Model Depicting the Mechanisms of Accumulation and Transport of Zeins in Starchy Endosperm and Aleurone Cells.

In starchy endosperm cells (left), zeins are synthesized and stored in the ER as protein bodies (asterisk). In aleurone cells (right), zeins first accumulate in the ER as protein aggregates (asterisk) and then are sequestered into complex prevacuolar compartments (PVC) that fuse with the PSV. The presence of internal membranes and ribosomes inside the prevacuolar compartments suggest that these compartments are originating, at least partially, by autophagy. The glycoproteins found in the PSV matrix traffic through a typical ER-Golgi-MVB pathway, although it is possible that the MVBs carrying these glycoproteins fuse with the autophagic PVCs before reaching the PSV.