Stereology of Allium cepa root meristem cells was done to evaluate changes in the nuclear envelope during cell cycle. A naturally synchronous population was labelled as binucleate by caffeine inhibition of cytokinesis. Growth of the nuclear envelope preferentially occurs from mid G2 to the next mid G1, most probably in relation to the reforming sister nuclei after mitosis. On the other hand, the number of nuclear pores doubles from mid G1 to mid G2, their growth rate being higher in the first half of interphase (from mid G1 to mid S). Hence, the new nuclear envelope probably lacks nuclear pores, which appear later.

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