Stages of female gametophyte development relative to ovule stages in the Atmnd1 mutant and wild type. A total of 759 and 637 ovules were scored for the Atmnd1 mutant and wild-type respectively. Megagametogenesis defects are evident from stage 3-1 in case of the mutant, which leads to embryo sac arrest and eventually its degeneration. Ovule stages are according to : 3-1, 3-2, and 3-4 are postmeiotic stages of the sporophyte with respect to elongation of the integuments where the wild type gametophyte would normally reach the 1n, 2n, and 4n stages; 3-6 corresponds to a mature ovule prior to fertilization. MES, Mature embryo sac; Degen, Degenerated embryo sac; M, mutant; +, wild type; ND, Not detected.