L. EHRENBERG 



In the case of X-irradiation of dormant seeds, especially those irradiated 

 at high humidities, the development of the lesion can be interfered with. 

 The effects of germination temperature and storage are additive. The 

 relative protection obtained at the higher germination temperature, and 

 which can be measured as a lower frequency of chromosomal rearrangements* 

 as well as a reduced growth inhibition, cannot be explained only as a repair 

 of chromosome breaks. Earlier results^ had already indicated cytoplasmic 

 damage by X-rays, as a cause of growth inhibition. The protective effect 

 of an increase in water content seems to be related to the increased 

 respiration rate. 



When germinating seeds are irradiated, the damage seems to be caused 

 by quite a different mechanism, and the observed effect cannot be influenced 

 by post-irradiation factors. Compared to the dormant seeds, with a 

 relatively low water content (10-20 per cent) and a low metabolic rate, 

 the germinating seeds contain more water (about 40 per cent) and show a 

 much higher metabolic rate, different enzyme systems being activated. 



The difference in the action of neutrons and X-rays is well illustrated by 

 barley seedlings ; these show a higher dry-weight after their growth has been 

 inhibited by neutrons than by X-rays^. One cause for this difference might 

 be that neutron damage is primarily located in the roots of the seedling and 

 interferes with water uptake, while the X-rays cause a relatively greater 

 inhibition of the shoot part of the plant. 



REFERENCES 



^ GusTAFSsoN, A. This Symposium. 



2 Ehrenberg, L. and Nybom, N. Acta Agr. Scand. 1954, 4 396. 



^ Ehrenberg, L. and Andersson, G. Nature, Lond. 1954, 173 1086. 



* Gelin, O. Agri. Hort. Genet. 1953, 11 66. 



^ Unpubl. investigation in co-operation with D. v. Wettstein. 



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