Mutants arrested late in seed development. (a) Shown is a scheme of seed development in Arabidopsis. A globular embryo (EM) develops into heart stage (1). Note that the peripheral endosperm nuclei surrounding the globular embryo are organized into three distinct domains: micropylar endosperm (ME), chalazal endosperm (CE), and free nuclear endosperm (FNE). Following rapid cellularization of endosperm, a torpedo stage embryo and then an upturned-U stage embryo is formed (2). (b-e) Morphology of wild-type seed development corresponding to representative events described above. (f) In oma-1 the embryo arrested at the mid-globular stage. The size of cells in embryo and endosperm were larger than that in (g) the wild type. (h,i) In fey-1 the embryo arrested at around the late globular stage. Note that the cells of the embryo and suspensor were large, and the suspensor displays a bend due to the irregularly bulged cells (panel i, arrow). (j) The majority of the ila-1 embryos arrested when they were at upturned U stage. (k) A small fraction of late-heart ila-1 embryos could also be observed. Scale bars: 10 μm for panels b, f, h, j, and k; and 20 μm for panels c, d, e, g, and i.