AtFIS2:GUS Expression during Early Ovule Development in Hieracium AtFIS2:GUS Expression during Early Ovule Development in Hieracium.Ovules from sexual Hieracium P4 ([A] to [D]), apomictic Hieracium D3 ([E] to [H]), and apomictic Hieracium A3.4 ([I] to [L]) were stained with GUS and viewed whole mount using dark-field micr... AtFIS2:GUS Expression during Early Ovule Development in Hieracium.Ovules from sexual Hieracium P4 ([A] to [D]), apomictic Hieracium D3 ([E] to [H]), and apomictic Hieracium A3.4 ([I] to [L]) were stained with GUS and viewed whole mount using dark-field microscopy ([A], [E], and [I]) or Nomarski differential interference contrast microscopy. The numbers at the top right indicate the ovary stage (Koltunow et al., 1998). Bars = 50 μM in (A), (E), (I), and (L), and bars = 25 μM in (B) to (D), (F) to (H), (J), and (K).(A) P4 ovule in the chalazal (ch) to micropylar (mp) orientation showing GUS stain in pink.(B) Enlarging selected spore (ss) and blue GUS-stained degenerating megaspores (dms) surrounded by the nucellar epidermis. Indicated structures are outlined with a black line.(C) Enlarging functional megaspore (fm) with a large nucleus (n) chalazal to degenerated megaspores. Indicated structures are outlined with a black line.(D) Ovule containing an early embryo sac (es) containing dividing embryo sac nuclei (esn) and surrounded by the endothelium (et).(E) D3 ovule showing the corresponding stage of apomictic development to (A).(F) Enlarging aposporous initial (ai) at the corresponding stage of apomictic development to (B). The aposporous initial, outlined with a broken line, is forming in a slightly different plane to the other structures, which are outlined with an unbroken line.(G) Enlarging aposporous initial cell above two smaller initials.(H) D3 ovule containing a dividing aposporous embryo sac (aes) with embryo sac nuclei (esn) at the corresponding stage of apomictic development to (D).(I) A3.4 ovule showing the corresponding stage of apomictic development to (A) and (E).(J) Enlarging aposporous initials at the corresponding stage of apomictic development to (B) and (F). Multiple aposporous initial cells are indicated with broken lines, and some form in slightly different planes compared with the sexual structures; these are outlined with an unbroken line.(K) Enlarging aposporous initial cells.(L) Aposporous embryo sac structures at the corresponding stage of apomictic development to (D) and (H).Figure reprinted from Tucker et al. (2003) with permission. Ross A. Bicknell, and Anna M. Koltunow Plant Cell 2004;16:S228-S245 ©2004 by American Society of Plant Biologists