The Effect of Oxygen Concentration on the Dose-Action Survival Curves Obtained for Habrobracon Eggs Irradiated during Meiotic Prophase and Metaphase

Abstract

A comparison of the effect of oxygen in modifying lethality induced by X-rays in meiotic metaphase and in meiotic prophase Habrobracon eggs has been made. Since restitution of damaged chromosomes is considered to be rare in meiotic metaphase eggs and frequent in meiotic prophase eggs, the data obtained are of interest in deciding whether oxygen has a role in initial damage to chromosomes or in preventing restitution of damage. Studies of total embryo lethals induced in 4,570 eggs X-rayed in nitrogen, air, and oxygen during meiotic metaphase with doses ranging from 396r to 2,450r were made. The nitrogen series differed very significantly from the air and oxygen series with a maximum difference of 48.5 per cent at one dose. Similar studies were made of 4,846 prophase eggs X-rayed in nitrogen, air, and oxygen with doses ranging from 2,100r to 44,100r. Again the nitrogen series differed significantly from the air and oxygen series with the maximum differences reaching 52.0 per cent at one dose. The oxygen effect appears to be of the same magnitude in metaphase and prophase eggs despite a considerable difference in the X-ray dose necessary to induce lethality in each of these two stages. This similarity is believed by the author to support the initial damage hypothesis of oxygen action proposed by Giles and Riley (1950) and to be contrary to the expectations of the differential restitution hypothesis proposed by Schwartz (1952).