Accessory Cells in <i>lis-1</i> Gametophytes Morphologically Resemble Gametic Cells

<div><p>(A–D) Schematic representation of wild-type female gametophyte development. Sporophytic structures are shown in grey; gametophytic structures are colored. (A) After meiosis, the haploid functional megaspore is formed. (B) A series of three mitotic divisions results in the formation of an eight-nucleate syncytium. (C) After nuclear migration and cellularization, a seven-celled gametophyte is formed containing two synergids at the micropylar end (dark green), one egg cell (red), one central cell (orange) with two polar nuclei, and three antipodal cells at the chalazal pole (light green). (D) Prior to fertilization, the two polar nuclei fuse to form one large central cell nucleus, and the antipodal cells degenerate.</p> <p>(E) Wild-type silique showing full seed set.</p> <p>(F) Silique of <i>lis-1/LIS</i> plants containing aborted ovules (arrowheads).</p> <p>(G–I) Mature wild-type gametophyte. (G) At the micropylar end, the two small synergid nuclei are detected (stars). The larger egg cell nucleus (arrowhead) is oriented towards the adjacent central cell. (H) A large central cell nucleus (arrowhead) resulting from the fusion of the two polar nuclei can be detected. (I) The antipodal cells at the chalazal end degenerate (star).</p> <p>(J–N) <i>lis-1</i> gametophytes. (J) The synergid nuclei are enlarged and mis-polarized (star). As a consequence, synergid and egg cell become indistinguishable when lying in a similar position (arrowheads). (K) Polar nuclei are unfused (arrowheads) and occasionally ectopically cellularized (arrowheads in M). (L and M) Antipodal cells do not degenerate, but enlarge and protrude towards the center (stars). (N) Disintegration of antipodal cells and fused antipodal nuclei (star).</p>