Fig. 5

Light micrographs of megasporogenesis and megagametogenesis of G. nantoensis. a Light micrograph showing the placental ridges with several branches differentiated into nucellar filaments at the time of anthesis. The archesporial cell (arrow) can be observed at the terminus of the nucellar filament. Scale bar 50 μm. b The archesporial cell has differentiated into the megasporocyte. Before the first meiotic division, the chromatin (arrow) is going to condense. Scale bar 20 μm. c Soon, the megasporocyte undergoes the first meiotic division (arrow). Scale bar 20 μm. d After the first meiotic division, the functional dyad at the chalazal end of the ovule successively undergoes the second meiotic division (arrow), and the non-functional dyad at the micropylar end has degenerated (arrowhead). Scale bar 20 μm. e The second meiotic division results in the formation two megaspores of unequal size. The smaller non-functional megaspore (arrow) at the micropylar end will degenerate. Scale bar 20 μm. f Light micrograph showing a functional megaspore with several small vacuoles and the non-functional megaspores have degenerated completely (arrow). Scale bar 20 μm. g Light micrograph showing the two-nucleate embryo sac with a prominent vacuole (V) located at the center of cell. Scale bar 20 μm. h At 6 DAP, a longitudinal section through a mature embryo sac showing the egg apparatus, including the egg cell (arrow) and two synergids (S) at the micropylar end and two antipodal nuclei at the chalazal end (arrowheads). At this stage, the integument has completely enclosed the embryo sac. Several starch grains (double arrowheads) start to accumulate in the integument tissue. Scale bar 20 μm