Seed storage proteins are thought to be accumulated exclusively in the cell-expansion phase of embryogenesis and metabolized during germination and seedling growth. Here we show by a sensitive immunohistological technique that the two Vicia faba L. storage proteins vicilin and legumin are accumulated in substantial amounts in the suspensor and coenocytic endosperm and to a lesser extent in the mid-globular embryo. Both proteins appear and disappear at precise stages specific for each tissue. In the endosperm the accumulation starts around 12 d after pollination (DAP). After a maximum attained at 14-15 DAP, storage proteins are degraded within about 4 d. Accumulation is restricted to that part of the endosperm which covers the embryo and displays the highest levels of endoploidy (maximum 96n). In all other parts of the endosperm, storage proteins do not appear to accumulate, although storage-protein-specific mRNA synthesis takes place. In the suspensor, storage proteins are already observed at 6 DAP and disappear very quickly at approximately 10 DAP. Low amounts of legumin and vicilin are also detectable in the mid-globular embryo, but disappear completely as the embryo enters the heart stage. We conclude that storage proteins of Vicia faba accumulated transiently during early seed development are used as nutritive reserves for the growing embryo.
