Fig. 2

Light micrographs of developing seeds of C. subtropicum. A The zygote (arrow) after fertilization at 45 DAP. At the micropylar end, one synergid has degenerated (DS). Inner seed coat (IS), outer seed coat (OS). Scale bar = 30 µm. B The first cell division of the zygote results in the formation of a smaller terminal cell (T) and a larger basal cell (B). Inner seed coat (IS), outer seed coat (OS). Scale bar = 30 µm. C A three-cell embryo. Primary endosperm nuclei (arrows) are observed within the cavity, but the endosperm fails to develop and eventually degenerates. Inner seed coat (IS), outer seed coat (OS). Scale bar = 30 µm. D The terminal cell of a three-cell embryo divides vertically, resulting in the formation of a T-shaped, four-cell embryo. Inner seed coat (IS), outer seed coat (OS). Scale bar = 30 µm. E The embryo proper continues to develop by cell division to form an early globular embryo. The suspensor (S) of this species consists of a single cell and does not further enlarge. At this stage, the cytoplasm in cells of the embryo proper appears dense, and a few tiny starch grains can be observed within the cytoplasm, indicating the accumulation of storage products. Inner seed coat (IS), outer seed coat (OS). Scale bar = 30 µm. F Longitudinal section of a globular embryo. At this stage, the suspensor is degenerating (arrow), and the cells of the inner seed coat (IS) and outer seed coat (OS) are beginning to degenerate and dehydrate. Several protein bodies (arrow) are present in the cells of the embryo proper. Scale bar = 30 μm. G Longitudinal section of a mature seed. At maturity, the embryo is enveloped by the shriveled inner seed coat (IS) and the outer seed coat (OS). Starch grains are apparent, and a few tiny protein bodies (arrow) can be observed within the embryo proper. Although lipids cannot be preserved in historesin, the abundant translucent vesicles within the cytoplasm of the embryo proper indicate the deposition of lipid bodies. Scale bar = 30 μm. H Fluorescent outline of a mature seed at the same stage shown in Fig. 2G after Nile red staining. The surface wall (SW) of the embryo proper reacts positively, while the compressed inner seed coat (IS) and outer seed coat (OS) react weakly. Scale bar = 30 μm