Smith, H. H. and Rossi, H. H. and Kellerer, Albrecht M.
Relation between mutation yield and cell lethality over a wide range of X-ray and fission neutron doses in maize.
UNSPECIFIED, 22.-26. Oktober 1973, Neuherberg (Munich).
Dry maize seeds, of a genetic stock heterozygous for the yellow-green locus (Yg^ Λ ^ ) ι were irradiated
with fission neutron doses up to 2700 rads and with 250 kVp X-rays to 40 000 rads. The frequency of
yellow-green (yg) sectors in seedling leaves 4 and 5 is largely a measure of the frequency of breakage (or
incomplete exchange) and loss of the part of the short arm of chromosome I X carrying Yj>. Plots of dose
versus yj* sector frequency per leaf show a linear increase with neutrons which reaches a maximum
(leaf 4 = S. 5, leaf 5 = 2. 5) followed by a rapid decline; and a curvilinear increase with X-rays reaching
a higher maximum (leaf 4 = 8. 5, leaf 5 = 3.6) followed by a decrease. The observed rise and subsequent
fall of numbers of yg_ mutations can be accounted for by a model in which the decline of the curves is
due to cell killing which may also be due to chromosome breakage and deletion. The interpretation is
based on the principles of the dual action theory, which explains radiobiological action in terms of microdosimetry.
One of the observations accounted for is the higher maximum mutation rate for X-rays as
compared to neutrons.