The nucleolus in the induced amitosis

Nucleolar cycles were related to mitotic and amitotic phases in meristematic cells of Allium cepa L. roots growing in control conditions and in others where amitosis was induced by a 6-h treatment with ethidium bromide.The induced amitosis in these cells was followed by an unbalanced distribution of chromosomal material between the two independent daughter cells resulting from it.The first discrepancy between mitosis and amitosis was found at the level of prophase nucleolar disorganization, which was greatly modified. The nucleolar cycle was permanently stopped in amitosis even when recovery from treatment was allowed. The kinetics of amitosis appearance in the meristem suggest a decision point located round about mid-prophase. This decision point seems to involve nucleolar function in prophase. These observations confirm the fact that prophase is one of the decisive stages in the differentiation of a cell.