et al., 1989). GA-deficient mutants of tomato (gibl) and Ara-
bidopsis (gal-3) require an exogenous supply of GA to
complete germination (Koornneef and Van der Veen, 1980;
Groot and Karssen, 1987). Embryos of GA-deficient tomato
will germinate if removed from their surrounding structures.
Thus, the role of GA in these seeds is probably restricted to
the induction of endosperm-weakening enzymes (see below).