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Fig. 4 | Botanical Studies

Fig. 4

From: Embryology of two mycoheterotrophic orchid species, Gastrodia elata and Gastrodia nantoensis: ovule and embryo development

Fig. 4

Light micrographs of megasporogenesis and megagametogenesis of G. elata. a Light micrograph showing the placental ridges with branches differentiated into nucellar filaments at the time of anthesis. The formation of archesporial cell (arrows) occurs at the terminus of the nucellar filament. Scale bar 50 μm. b The archesporial cell enlarges and differentiates into the megasporocyte. Scale bar 10 μm. c The megasporocyte undergoes the first meiotic division (arrow). Scale bar 10 μm. d After the first meiotic division, the functional dyad is located at the chalazal end of the ovule, and the non-functional dyad at the micropylar end degenerates gradually. Scale bar 10 μm. e After the second meiotic division, the smaller non-functional megaspore at the micropylar end degenerates soon. At the same time, the initiation of integument tissue has become visible (arrow). Scale bar 10 μm. f Light micrograph showing a functional megaspore with a few vacuoles and the non-functional megaspores have degenerated completely (arrow). Scale bar 10 μm. g The functional megaspore divides once resulting in the formation of a two-nucleate embryo sac, and the two-nucleate embryo sac expands further by vacuolation. Scale bar 10 μm. h At 4 DAP, a mature embryo sac showing one antipodal nucleus (arrow) and the egg apparatus, including the egg cell E and two synergids S. The integument tissue has not enclosed the embryo sac. Scale bar 10 μm

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