Radiation genetics in wheat, VIII. The RBE of heavy particles from B 10 ( n, α) L i7 reaction for cytogenetic effects in Einkorn wheat

Abstract

The relative biological effectiveness (RBE) of α plus Li 7 recoil particles relative to gamma-rays has been studied for seedling height depression, chromosome aberrations and chlorophyll mutations in Einkorn wheat. Irradiation with these heavy particles was administered by using the reaction of B 10 (n, α) Li 7; wheat seeds, which had been previously soaked in aqueous solution at different borax concentrations (0 to 1.0 per cent), were exposed to thermal neutrons in a reactor. Subtracting the radiobiological effects of thermal neutrons for seeds soaked in pure water from those found for seeds soaked in borax solution, the net effects of the heavy particles were estimated and compared with the gamma-ray effects for seeds under the same soaking conditions as for neutron treatments. The RBE values obtained for chromosome aberrations in pollen mother cells and for chlorophyll mutations were 23 ±10 and 29 ± 10, respectively. These figures are of the same order as those for fast neutrons previously reported for wheat and barley. Most of the present results are explicable on the assumption that chromosome breakage in wheat requires many ionizations to occur within a chromosome and that the majority of radiation-induced chlorophyll mutations result not from point mutations but from chromosome breakage events.