According to many reports, the endosperm of Arabidopsis thaliana (L.) Heynh. follows Nuclear-type development whereby the primary endosperm nucleus divides without cytokinesis, ultimately to produce a peripheral, multinuclear endosperm tissue. However, some features of endosperm development in seeds collected from populations in central South Carolina reveal striking differences from the Nuclear type of other Brassicaceae. Nuclei produced by the first division of the central or slightly chalazal primary endosperm nucleus quickly migrate to opposite poles on the longitudinal axis, where the chalazal nucleus immediately becomes enshrouded with dense cytoplasm. Divisions from that point onward are free-nuclear and frequent in the micropylar portion, which enlarges markedly as it becomes multinucleate. The chalazal endosperm is sometimes positioned in a different focal plane as a result of curvature of the immature seed toward amphitropous form. It does not enlarge appreciably and accumulates only 2-8 nuclei before it gradually degenerates, persisting until digested during maturation of the developing embryo. Thus, the functional endosperm is produced primarily by the micropylar chamber.
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