ARTICLE

5-AMINOURACIL TREATMENT : A Method for Estimating G₂

S. H. Socher ¹ and D. Davidson ¹

¹ From the Department of Biology, Case Western Reserve University, Cleveland, Ohio 44106, and the Department of Biology, McMaster University, Hamilton, Ontario, Canada.

Dr. Socher's present address is the Department of Obstetrics and Gynecology, Vanderbilt University, Nashville, Tennessee 37203

Treatment of Vicia faba lateral roots with a range of concentrations of 5-aminouracil (5-AU) indicate that cells are stopped at a particular point in interphase. The timing of the fall in mitotic index suggests that cells are held at the S - G₂ transition. When cells are held at this point, treatments with 5-AU can be used to estimate the duration of G₂ + mitosis/2 of proliferating cells. Treatment with 5-AU can also be used to demonstrate the presence of subpopulations of dividing cells that differ in their G₂ duration. Using this method, 5-AU-induced inhibition, we have confirmed that in V. faba lateral roots there are two populations of dividing cells: (a) a fast-dividing population, which makes up 85% of the proliferating cell population and has a G₂ + mitosis/2 duration of 3.3 hr, and (b) a slow-dividing population, which makes up 15% of dividing cells and has a G₂ duration in excess of 12 hr. These estimates are similar to those obtained from percentage labeled mitosis (PLM) curves after incorporation of thymidine-³H.

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