Protein Bodies: Storage Vacuoles in Seeds

Abstract

Publisher Summary This chapter discusses protein storage vacuoles (PSV) in seeds. Seeds of many plant species store reserve proteins in protein storage vacuoles. The questions of the ontogeny of seed PSVs parallel the questions on the origin of the central vacuole in meristematic cells. The primary purpose of PSV formation is to sequester nitrogen in the form of storage proteins for utilization during germination. Seed storage cells consist of two functional types; cells that survive into germination, including both the developing embryo and some endosperm or aleurone cells of dicotyledonous seeds and the aleurone cells of cereals; and cells that do not continue into germination, such as starchy endosperm cells of cereal grains. The current models for PSV formation in dicotyledonous plants are based on the concept that protein deposition occurs as the consequence a Golgi-mediated secretory process that delivers precursor or pro–storage proteins to the incipient PSV. The storage proteins are first deposited as inclusions in the small vacuoles. The small vacuoles appear to fuse and concurrently the storage protein aggregates inside them also fuse to form large protein inclusions. The major globulin storage proteins fall into three major classes collectively called legumins, vicilins and lectins. All vacuolar proteins, including the storage proteins, cotranslationally enter into the rough endoplasmic reticulum (ER).