Cell Population Kinetics of Pisum Root Meristem Cells during and after a Mitotic-inhibitory Exposure to Protracted Gamma-irradiation

Summary

Primary root meristems of Pisum sativum with a mitotic cycle prolonged to ∼36 hours by lowering the temperature to 10°c, exhibited complete mitotic inhibition after 3 days of exposure to gamma-radiation at a rate of 0·83 R/min. ³H-thymidine autoradiography, ³H and ¹⁴C double-labelling autoradiography combined with Feulgen microspectrophotometry, and the colchicine-induced tetraploid technique were used to measure the cell population parameters. After mitotic inhibition occurred cells accumulated in G1 and G2 with some cells passing through S, and with time under irradiation cells moved at a reduced rate out of G1, through S and into G2, where they stopped cycle progression. After termination of irradiation, cells which were in G1 and S during irradiation were capable of division, whereas cells in G2 were not. Two extra days of exposure did not reduce the rate at which cells flowed from G1 → S after irradiation, but did produce a delay in the appearance of these cells in M. The first complete post-irradiation mitotic cycle was of slightly shorter duration than control and there was an indication that a compensatory proliferative reaction took place in order to repopulate cells lost from the meristem.