Fig. 5

Light micrographs of embryo development of A. roxburghii at the late stages. a The cell at the terminus divides vertically and increases in size in preparation for further divisions. The suspensor (S) continues to elongate and a few starch grains (arrow) accumulate around the nucleus. At this stage, the inner seed coat has degenerated (arrowhead) and has been resorbed by the developing embryo. Scale bar = 30 µm. b The suspensor has elongated further, but it never extends beyond the lumen enclosed by the outer seed coat. Scale bar = 30 µm. c Additional periclinal and anticlinal divisions within the embryo proper that result in the formation of the inner tier of cells and the protoderm (arrows). Scale bar = 30 µm. d Light micrograph showing an early globular embryo with a discernible protoderm. Numerous starch grains (arrow) accumulate within the cells of embryo proper. Scale bar = 30 µm. e As the globular embryo approaches maturity, more starch grains (arrow) accumulate within the embryo proper and the suspensor (S) is going to degenerate. Within the embryo proper, the smaller cell toward the chalazal end is marked by the dashed line and the larger cell toward the micropylar end is marked by the solid line. Scale bar = 30 µm. f A longitudinal section through a mature seed. Within the embryo proper, the smaller cell toward the chalazal end is marked by the dashed line and the larger cell toward the micropylar end is marked by the solid line. The suspensor cell (double arrowhead) became dehydrated and finally collapsed. At this stage, the starch grains (arrow) have most disappeared, and numerous small protein bodies (arrowhead) can be seen within the embryo proper. Although the lipid cannot be preserved in this historesin, the spaces between the protein bodies could be the storage lipid bodies (double arrow). Scale bar = 30 µm. g Nile red staining fluorescence micrograph of an early globular embryo at the same stage as that seen in c. The surface wall (arrow) of the embryo proper reacts positively to the stain, and the fluorescence is absent in the suspensor wall. Scale bar = 30 µm. h Nile red staining fluorescence micrograph of a globular embryo at the same stage as that seen in e. The surface wall (arrow) of the embryo proper reacts positively to the stain, and seed coat (arrowhead) only reacts weakly. Scale bar = 30 µm