Minimum gamma-radiation exposure and oxygen concentration to produce post-irradiation oxygen-enhancement of damage in Barley seeds

Abstract

Himalaya (C.I. 620) barley seeds were adjusted to water contents ranging from 2 to 10% by storage in vacuum desiccators over calcium oxide or mixtures of glycerin and water. The seeds were irradiated with 60Co gamma rays in vacuo. After irradiation, the seeds were soaked at ±0.5°C in water bubbled with oxygen, nitrogen or mixtures of oxygen and nitrogen. Biological effects of the treatment were recorded as M 1 seedling height and percentage of shoot tip cells showing chromosomal aberrations. Oxygen concentrations in the gas phase of the soaking medium (OCHG) of less than 1.60% oxygen caused a slight increase in the seedling heights (compared to controls with 0.05% OCHG) when seeds were given 50 krad. With 12.5% OCHG, oxygen enhanced seedling injury with 20 and 30 krad in all cases and with 15 and 20 krad on seeds of 6% water content and with 10 krad and above on seeds of 2 and 4% water content. At 6.25% OCHG, oxygen enhanced seedling injury with 30 krad on seeds of 6, 8 and 10% water content, at 20 krad on seeds of 2–10% water content. Oxygen enhanced the production of chromosome aberrations, with a 6.25% OCHG for seeds of 2.2 and 3.8% water content, when exposed to 5 and 10 krad. Chromosomal damage was a more sensitive test than seedling injury. Oxygen enhancement was obtained for all radiation exposures above 200 krad on seeds of 2 and 4% water content. The magnitude of oxygen enhancement increased with radiation exposure. Regression analysis of seedling height data showed a radiation-induced oxygen enhancement above 830 rad for seeds containing 2% water. Oxygen enhancement was significant at all radiation exposures above 2125 rad.