Some Kinetic Aspects of Recovery of G 1 and G 2 Cells in Stationary-Phase Excised Pea Roots

Abstract

Recovery after 300 R of γ-rays by G1 and G2 stationary-phase meristematic cells of excised pea root tips was measured as a function of the duration of an induced postirradiation stationary phase. The recovery indices measured were the initiation of DNA synthesis by G1 cells (3 H-thymidine incorporation) and the entrance of G2 cells into mitosis. Results showed that cells in each phase required 24 to 26 hours for full recovery. Recovery rate of G1 cells was relatively constant throughout the 24-hour period, while that of G2 cells varied, being higher in the first half and lower during the last half of the recovery period. Recovery of G1 and G2 cells exposed to a total of 300 R at a rate of 300 R/min or 0.19 R/min was the same, provided the stationary phase was not continued after γ-ray exposure.