Atsushi Tatara

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 3 H-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 3 H-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.

Accessibility of γ-ray induced primer toward DNA polymerase I of Escherichia coli during soaking of barley seed☆

Abstract After dry barley seeds were irradiated with γ-rays and soaked for various times, the squashed preparations were made of the first leaf meristems and incubated with E. coli DNA polymerase I with appropriate substrates. The incorporation of nucleotides with DNA polymerase occurred in the cells fixed at late G 1 after 15 kR and at middle and late G 1 after 30 kR, respectively. There was an interrelation between the incorporation of nucleotides by DNA polymerase and the chromatin diffusion throughout a nucleus. The observations were interpreted in terms of the accessibility of 3′-OH groups of DNA breaks which accompanies the change of the conformation of chromatin fibres.

Induction of single-strand DNA breaks with synchrotron radiation in dry Barley nucleus

Abstract Nuclei isolated from the embryos of dry seeds were exposed to synchrotron radiation (SR) from an electron storage ring (0.3 GeV). Dried nuclei were also gamma-irradiated for comparison. SR of broad wavelength above 115 nm increased the number of 3′-OH termini, which were produced from single-strand DNA breaks in the nucleus. The observed DNA damage is causally-related to the vacuum-u.v. component of SR.