Ultrastructure and Differentiation in Chara Sp. II. Mitosis

Abstract

The ultrastructure of some dividing cells of Chara are described. No centrioles have ever been detected in vegetative cells. Asymmetric cell division, forming a predetermined pattern of cells, was apparently not preceded by any characteristic grouping of cell organelles. The nucleoli became dispersed during pre-prophase, and most of the nucleolar material appeared intimately associated with the chromosomes throughout division, although some seemed excluded from the nucleus at late telophase. Polar zones of endoplasmic reticulum were formed in early prophase, and attachment of microtubules to daughter chromosomes slightly preceded the formation of a very precisely aligned metaphase plate. The chromosome arms were also apparently all aligned in the plane of this plate.