Fig. 5.

Stages of female gametophyte development in the wild type and flp-7 mutant. Ovule stages were determined from the development of the sporophyte using the nomenclature of Schneitz et al. (1995); see Supplementary Table S4 at JXB online. (A–O) DIC micrographs of ovules at different stages. (A, B, C, G, H, I) L. er. (D, E, F, J, K, L, M, N, O) flp-7. (A, D) Stage 2-III (pre-meiotic) with large MMCs near the tip of the nucellus (arrows). (B) Stage 2-V with tetrad of four megaspores (primary megaspore indicated by a dashed circle) in L. er. (C) At stage 3-I, the three non-functional megaspores begin to degenerate in L. er. (E) Varying numbers of cells are seen in flp-7 ovules. Here, three cells can be seen (two toward the apex, arrowheads; and a larger cell more basally, asterisk). (F) The abnormal cells formed in flp-7 ovules do not appear to be degenerating. (G) At stage 3-II, the first mitotic division of the megaspore to give rise to a two-nuclei (circled by dashed lines) female gametophyte in L. er. (J, M, N) No corresponding nuclear division can be seen in abnormal stage 3-II flp-7ovules; instead, a large cell remains with either zero (M), two (J), or three (N) other cells attached. (H) At stage 3-IV, a female gametophyte with four nuclei (dashed circles) is seen in L. er. In addition, the other cells of the nucellus have begun degenerating. (K) No such structures were seen in flp-7 ovules; instead the abnormal cells remain. (I) By stage 3-VI, the embryo sac has begun differentiating and cellularizing in L. er. (L, O) In flp-7 a single large cell is associated with a variable number of other cells (three in L, two in O). Asterisks indicate MMC-like/functional megaspore-like cells seen in flp-7 ovules. Arrowheads indicate megaspores in L. er and cells associated with the MMC-like/functional megaspore-like cell in flp-7