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Fig. 1. Ontogeny of the endosperm posterior pole. 3D reconstruction of the
endosperm posterior pole. Inset shows the location of the posterior pole in a
schematic whole seed. Nuclei in the cyst have been labelled in red and other
nuclei in yellow. The anteroposterior (AP) axis is indicated by the green
double arrow. (A) Embryo dermatogen stage, endosperm stage VII with approx. 50
nuclei. Two large nuclei in the cyst have undergone two cycles of
endoreduplication and are embedded in a pool of cytoplasm. Other nuclei in the
peripheral domain are surrounded by a small mass of cytoplasm that constitutes
a NCD. Scale bar: 25 µm. The 3D reconstruction was obtained from 85 optical
sections of 0.4 µm thickness. (B) Early globular stage embryo, endosperm
stage VIIIa with approx. 100 nuclei. Above the cyst that still contains only
two large nuclei, are two masses of cytoplasm that each contain two nuclei
(arrows). Other NCDs are still attached to the walls of the peripheral
endosperm. Scale bar: 25 µm. The 3D reconstruction was obtained from 46
optical sections of 0.65 µm thickness. (C) Early heart stage embryo,
endosperm stage IX with cellularisation initiated in the micropylar endosperm
at the anterior pole (not visible). The 3D reconstruction is represented as an
open book split in the middle, along a plane aligned with the anteroposterior
axis. The cyst contains multiple nuclei of similar size to those in NCDs.
Above the cyst, are observed seven nodules that contain from two up to ten
nuclei. In more anterior domains, free NCDs line the wall of the peripheral
endosperm. Scale bar: 50 µm. The 3D reconstruction was obtained from 96
optical sections of 0.4 µm thickness.
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