TRANSIENT EXPRESSION OF STORAGE-PROTEIN GENES DURING EARLY EMBRYOGENESIS OF VICIA-FABA - SYNTHESIS AND METABOLIZATION OF VICILIN AND LEGUMIN IN THE EMBRYO, SUSPENSOR AND ENDOSPERM

Seed storage proteins are thought to be accumulated exclusively in the cell-expansion phase of embryogenesis and metabolized during germinat ion and seedling growth. Here we show by a sensitive immunohistologica l technique that the two Vicia faba L. storage proteins vicilin and le gumin are accumulated in substantial amounts in the suspensor and coen ocytic endosperm and to a lesser extent in the mid-globular embryo. Bo th proteins appear and disappear at precise stages specific for each t issue. In the endosperm the accumulation starts around 12 d after poll ination (DAP). After a maximum attained at 14-15 DAP, storage proteins are degraded within about 4 d. Accumulation is restricted to that par t of the endosperm which covers the embryo and displays the highest le vels of endoploidy (maximum 96n). In all other parts of the endosperm, storage proteins do not appear to accumulate, although storage-protei n-specific mRNA synthesis takes place. In the suspensor, storage prote ins are already observed at 6 DAP and disappear very quickly at approx imately 10 DAP. Low amounts of legumin and vicilin are also detectable in the mid-globular embryo, but disappear completely as the embryo en ters the heart stage. We conclude that storage proteins of Vicia faba accumulated transiently during early seed development are used as nutr itive reserves for the growing embryo.