Amitosis, including nucleolar behaviour during fragmentation, in both axial and cortical cells of Chara contraria (Charales, Charophyta).

VOUILLOUD AMELIA; CÁCERES EDUARDO; LEONARDI PATRICIA

PHYCOLOGIA

International Phycological Society

Lugar: Lawrence; Año: 2007 vol. 46 p. 178 - 186

0031-8884

The results from the present paper indicate that in Chara contraria the morphology of resting nuclei and amitosis depend essentially on the cell type as well to on same extent on the age and development of the cells. Young axial cells of principal axes and branches exhibited C-shaped resting nuclei. During amitosis nuclei initially stretched out and became helical-shaped, and they then divided themselves into two similar C-shaped nuclei that remained close to each other. The nucleolar material gradually merged together to eventually form a central nucleolus, which adopted the curving of the nucleus. Spindle-shaped resting nuclei with numerous and irregularly distributed ovoid nucleolar structures were also observed. They duplicated their length during amitosis, underwent a constriction in the middle portion, and finally broke obliquely giving rise to two daughter nuclei, both with similar size. Young corticating cells exhibited initially ovoid nuclei. Then, gradually stretched out concomitantly with the extension of the cell, giving rise to worm-shaped nuclei that bend irregularly and eventually divided themselves by constriction in portions of different sizes. The ultrastructure of amitotic nuclei in corticating cells was studied. The nuclear envelope remained intact in dividing nuclei. In section, resting nuclei exhibited numerous, small nuclear profiles.  All nuclei show electron dense nucleolar material. Resting nuclei exhibit numerous, small nucleolar profiles homogeneously distributed. In dividing nuclei, in contrast, few, large nucleolar profiles occupied the middle portion of the nucleus.  Bundles of 3-66 tubular elements c.20 nm in diameter run approximately parallel to the long axis of the nucleus.Tubules were made of circular subunits c. 2 nm diameter in cross section, and frequently they contacted nucleolar profiles and the inner membrane of the nuclear envelope.