Effects of low-dose γ-irradiation on the cell cycle duration of barley roots

Abstract

This study investigates the effects of 1.0 Gy or less of γ-irradiation on the duration of the cell cycle and its component phases in the root apical meristem of two-rowed barley seedlings. Germinating seeds were irradiated with 0.25, 0.5, 0.75 and 1.0 Gy of γ-rays, after which the mitotic index (MI) in the root apical meristem was subsequently observed and compared with corresponding non-irradiated samples (controls). The MI of the controls stayed at about 5–7% during germination from 74 to 100 hr, whereas after a 0.25- or 0.50-Gy exposure it was about 40% higher 4 hr later. Germinating seedlings were also pulse-labelled with 3H-thymidine soon after exposure, fixed at 2-hr intervals and observed by autoradiography. The durations of the cell cycle, S-phase and total duration of the G 2-phase, prophase and metaphase were then estimated. Relative to controls, the cell cycle duration was reduced by about 1.8 and 2.5 hr with 0.25 and 0.5 Gy, respectively, being primarily due to a reduction in the S-phase. When hydroxyurea-treated seedlings were irradiated with such low-doses and then immediately treated with 3H-thymidine, the average number of silver grains per interphase cell nucleus increased relative to that of the controls. The present results suggest that the increase in the quantity of division cells at 4 and 6 hr post-exposure with 0.25 or 0.5 Gy was probably caused by a reduction in the duration of the S-phase, G 2-phase, prophase and metaphase.