Section 5 — Mutagenesis 



additive basis the expected frequency was 

 30.8 per cent. 



Solutions of nucleotides induced very few 

 mutations. The highest rate (0.54 per cent) was 

 produced by adenosine-5-monophosphate. When 

 adenosine-5-monophosphate was applied before 

 treatment with 2000 r of Co 60 A-radiation a 

 slightly more than additive result was obtained. 

 Experiments with EI and nucleotides are not yet 

 completed. Three combinations of nucleotides 

 and EMS resulted in notable increases in the 

 mutation rate. Here, it is possible that guanine in 

 DNA degraded by EMS was sometimes replaced 

 by the supplied base. 



5.107. Mutations Induced by the Action of Metal 

 Ions in Pisum. Gosta von Rosen (Landskrona, 

 Sweden). 



Radiomimetic effects and gene mutations are 

 induced by a deficiency or surplus of for a vital 

 organism important micro elements. The 

 frequency of mutations induced by the action 

 of metal ions is lower than the frequency induced 

 by ionizing radiation or some intense active 

 chemical substances. The mutation-spectrum in 

 chlorophyll mechanism induced by treatment 

 with surplus doses does not differ from the 

 spectrum at hard ionizing radiations. Treatment 

 with a simultaneous combination of several 

 micro metals is more effective than treatment 

 with single metal ions. Individual metal ions do 

 not show any trend to specific chlorophyllmuta- 

 tions spectra at present, but they induce some 

 other specific types of mutations indeed. 



By adding treatments with metal ions and 

 X-ray the mitoses and cell disturbances are 

 arrested, and the mutagene activity of the 

 ionizing particles is somewhat reduced. The 

 activity of the metal ions seems to be additative 

 to the effect of the X-rays. 



The micro metal elements in a living cell have 

 functions in specific and very important pro- 

 cesses, usually in complex protein structures. 

 Their concentrations and activities in the cell 

 are regulated by chelating with protein radicals 

 in co-valent and semi-polar bonds in the protein 

 molecule, a balance which is very sensitive and 

 limited. It is that force of the metal ions to form 

 complexes with protein radicals that causes 

 their radiomimetic and mutagenic activity. By 

 oscillating of the dissociation balance destruc- 

 tions in the cell metabolism occur, which may 

 induce chromosomal disturbances and gene 

 mutations. It is suggested that the complex 

 forming metal ions in the evolution of the plant 

 and animal kingdom have played a limited role, 



partly through their own activities, partly 

 through an indirect effect on the active radicals 

 from the natural radiation. 



5.108. The Magnitude of the Oxygen Effect in 

 Irradiated Barley Seeds. R. A. Nilan, 

 C. F. Konzak, J. R. Harle, and R. R. Le- 

 gault (Pullman, U.S.A.). 



The extent to which radiation-induced damage 

 in barley seeds can be amplified by oxygen 

 posttreatment depends on the radiation energy 

 (LET), the tissue moisture content, and the 

 temperature and time of storage from the 

 initiation of irradiation to the initiation of 

 germination. In very dry seeds ( ^ 2 per cent 

 moisture) oxygen-effect factors as high as 10 were 

 demonstrated for high intensity Co 60 gamma- 

 rays, and as high as 7 for 300 kVp X-rays. These 

 dose-increase factors were obtained for radia- 

 tion-induced damage measured as Mi seedling 

 injury, chromosome aberrations in mitotic 

 cells of Mi seeds, and chlorophyll-deficient 

 mutations in M2 seedlings. With seeds differing 

 in moisture from 2.5 to 13 per cent, the oxygen- 

 effect factors measured by seedling injury 

 ranged from 9 to 1, respectively. Very dry 

 irradiated seeds stored at room temperature 

 appeared to maintain indefinitely their high 

 sensitivity response to oxygen. Seeds stored at 

 higher temperatures exhibited a reduced oxygen 

 sensitivity but developed greater radiation-indu- 

 ced seedling injury. These results are consistent 

 with established evidence from electron spin reso- 

 nance analyses of the influence of temperature, 

 moisture, and LET on the interaction of oxygen 

 and radiation products in seed embryos. 



Research supported by U.S. A. E.G. Contract 

 AT (45-l)-353, U.S.P.H.S. Grant GM 10838-05 

 and funds provided for Medical and Biological 

 Research by State of Washington Initiative 

 Measure 171. 



5.109. Electron Spin Resonance Studies on Plant 

 Seeds of Differential Radiosensitivity. S. Bhas- 



karan (Karlsruhe, Germany). 



Electron spin resonance studies on plant seeds 

 of differential radiosensitivity were conducted 

 with a view to evaluate the relationship between 

 the production and decay of radicals and the 

 observed differences in the radiation sensitivity. 

 Dry seeds (moisture content 5 and 2 per cent 



94 



