Role of SS bridges in mitotic condensation of chromatin.

The effects of beta-mercaptoethanol on the mitotic index, phase index, condensation of chromatin in late G2 phase and in metaphase chromosomes, and on the content of protein -SH groups in successive developmental stages of antheridial filaments of Chara vulgaris L. were investigated. It has been shown earlier that as the development of antheridial filaments proceeds, the content of condensed chromatin in the late G2 phase increases, prophase duration shortens and metaphase chromosomes become more condensed. As cytophotometric measurements have shown, the concentration of the protein -SH groups is similar in all developmental stages, their total content, however, decreases in parallel with the shortening of cell length in successive generations. The more advanced developmental stage of antheridial filaments, the higher increase in the concentration of the protein -SH groups is induced by 2 h incubation with beta-mercaptoethanol. After 2 h incubation with beta-mercaptoethanol, the surface area of condensed chromatin decreases in late G2 phase, but the number of chromocenters remains unchanged, beta-mercaptoethanol does not modify the mitotic index but, beginning from the 4-celled stage, it increases the prophase index. In 1-,2-,4- and 8-celled antheridial filaments after 2 h incubation with beta-mercaptoethanol the chromosomes show a lower degree of condensation in about 30% of metaphases.