Chromosome Duplication in Root Tip Cells of the Female Plant of Humulus lupulus

Abstract

Using autoradiographic technique with ³H-TdR as a marker for DNA synthesis, the chromosome duplication (DNA synthesis) in root tip cells of the female plant of Humulus lupulus, was investigated.
The average duration of the each phase of mitotic cycle was found to be as follows: G₁ (pre DNA synthesis stage) 2 hours, S (DNA synthesis stage) 3 hours, G₂ (post DNA synthesis stage) 4.3 hours and M (mitosis) 0.7 hours.
It was also shown that an asynchronous replication of DNA occurred in chromosomes, and that heterochromatin synthesized the DNA at a different time from euchromatin.
It was discussed that the late replication might be something characteristic of the DNA in positive heteropycnotic regions, whether they are in autosomes or in sex chromosomes.