THE INFLUENCE OF POST-RADIATION FACTORS ON EFFECTS PRODUCED IN BARLEY 



When the irradiation conditions are changed {e.g. temperature, oxygen 

 tension, presence of protectors), it is often difficult to prove if there is an 

 influence at the moment of energy absorption or if the treatment affects 

 the secondary reactions. To a certain extent the absence of an effect of 

 such a change, when applied immediately after the irradiation, can prove 

 that the factor has an influence on the primary act. The post-irradiation 

 influences provide information about the secondary processes, which may be 

 chemical, biochemical or biological and are referred to here as post-irradiation 

 effects, or after-effects. 



The water content of the seeds at the moment of irradiation influences the 

 radio-sensitivity markedly. For all observed effects^- ^ of sparsely ionizing 

 radiations (e.g. X-rays) the damage (or change) is greater when the water 

 content of the seeds is reduced, and smaller when the water content is 

 increased. In the case of such a densely ionizing radiation as fast neutrons 



Figure 2. Mutation frequencies in per 

 cent per spike progeny. Dormant seeds 

 equilibrated with air oJO, 30 and 100 per 

 cent relative humidity irradiated with 

 different X-ray doses. Water content of 

 the seeds 8-6, 10-5 and 18 ■ 1 per cent, 

 respectively. 



(around 8 MeV), the water content of the seeds has no effect on the radiation 

 sensitivity. The growth of seeds equilibrated with dry air is four times more 

 sensitive to X-rays than for seeds equilibrated with air of 100 per cent 

 relative humidity. Figure 2 illustrates the influence of the water content 

 on the frequencies of chlorophyll-deficient mutations obtained after irradia- 

 tion with X-rays (180 kV, unfiltered). At low doses the mutation fre- 

 quencies are linear functions of dose, the greatest deviation being obtained 

 for the lowest water content. For the production of mutations an increased 

 water content protects. At higher doses the curves bend, because of the 

 elimination of genetically changed cells which shows a different dependence 

 on the water content of the seeds than does the mutation frequency. The 

 influence of the water content on the radiation sensitivity of the seeds seems 

 to be restricted to the primary reaction, since changes of the water content, 

 immediately after the irradiation but still before the starting of the germina- 

 tion, have no influence on the observed effect (measurements of seedling 

 growth). 



Effect of germination temperature — Figure 3 shows the relative growth of 

 seedlings, after irradiation of seeds of two different water contents with 



286 



