Figure 7

Detailed characteristics of embryos 5 min to 10 min after the initiation of inversion (early inversion stage). SEM images of isolated intact or fragmented embryos and LM images of physical midsagittal cross-sections (see Figures 3C and 4C for an overview). (A) SEM view of the bend region; the anterior hemisphere is in the upper part of the image; arrow with asterisk: the viewing direction of the cells from the posterior hemisphere shown in the inset in the lower left corner; arrow with circle: the area shown in the inset in the upper right corner; arrowheads: CBs; rectangle: detail shown in (B). (B) SEM view of cells in the bend region; arrowheads: CBs. (C) SEM side view of cells of the posterior hemisphere (fragmented embryo); arrowheads: outgrowing flagella; rectangle: detail shown in the inset; arrowheads in the inset: CBs. (D) Slanted SEM side view of cells of the bend region (fragmented embryo); arrowheads: outgrowing flagella; rectangle: detail shown in (E). (E) Slanted SEM side view of the chloroplast ends of the cells shown in (D); arrowheads: CBs. (F) SEM view of the anterior pole of the embryo; arrowheads: ring of broken CBs that connected the embryo with the somatic cells of its parent spheroid. (G) Slanted SEM top view of cells of the anterior hemisphere (fragmented embryo); arrowheads: outgrowing flagella. (H, I) LM images of a physical midsagittal cross-section of the bend region and the posterior hemisphere, respectively. Arrow in (H): the viewing direction of the cells shown in (A); however, the stage in (H) is somewhat earlier than the stage in (A). (C, G and I) The inside and outside of the embryo are indicated. Scale bars: (A, C, D, G and insets in A) 3 μm; (B, E and inset in C) 1 μm; (F) 10 μm; (H, I) 5 μm. CB: cytoplasmic bridge; LM: light microscopy; SEM: scanning electron microscopy.