Abstract
The RBE of 0·43-MeV monoenergetic neutrons and 250-kVp X-rays for somatic cell aberrations or mutations in the heterozygous Tradescantia subacaulis Bush (clone 4405) was determined and compared with known RBE values for similar end points in Tradescantia clone 02. Young inflorescences were irradiated with 0·04–15 rad of 0·43-MeV neutrons and with 6·25–150 rad of 250-kVp X-rays. Stamen hairs were scored daily over the peak response period from day 11–15 postirradiation. Data were recorded for cell color changes from normal blue to pink, plum and colorless and for changes in cell size from normal to dwarf and giant. Dose-response curves based on 5-day mean numbers of aberrant events were plotted for the various end points and their natural slopes computed. The slopes of the dose-response curves for each aberrant cell type resulting from X irradiation were higher than +1 but in 5 out of 6 cases significantly less than +1 for neutron irradiation. RBE values increased with decreasing doses, at least over the dose range investigated. Maximum RBE values for plum, dwarf, colorless, pink and giant were 124, 110, 99, 93 and 57 respectively. The RBE values were higher for color changes but lower for cell size aberrations in T. subacaulis than in clone 02. The reasons for these differences in RBE are not known. The possible dependence of RBE on interphase chromosome volume (ICV) is discussed.
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