Endosperm development in Arabidopsis thaliana (L.) Heynh.

According to many reports, the endosperm of arabidopsis thaliana. (L.) Heyn h. follows Nuclear-type development whereby the primary endosperm nucleus d ivides without cytokinesis, ultimately to produce a peripheral, multinuclea r endosperm tissue. However, some features of endosperm development in seed s collected from populations in central South Carolina reveal striking diff erences from the Nuclear type of other Brassicaceae. Nuclei produced by the first division of the central or slightly chalazal primary endosperm nucle us quickly migrate to opposite poles on the longitudinal axis, where the ch alazal nucleus immediately becomes enshrouded with dense cytoplasm. Divisio ns from that point onward are free-nuclear and frequent in the micropylar p ortion, which enlarges markedly as it becomes multinucleate. The chalazal e ndosperm is sometimes positioned in a different focal plane as a result of curvature of the immature seed toward amphitropous form. It does not enlarg e appreciably and accumulates only 2-8 nuclei before it gradually degenerat es, persisting until digested during maturation of the developing embryo. T hus, the functional endosperm is produced primarily by the micropylar chamb er.