GENEKAL DISCUSSION 361 



lysis of water (transition H— ^HO-i) has such an overall significance for 

 any living cell that the oxygen effect from our point of view must be 

 regarded as a universal factor in radiobiology. 



BUDNITASKAYA : When discussing the question of the universality of 

 the "oxygen effect", one should emphasize that many destructions of 

 normal biochemical reactions under radiation action on the living 

 organism are characterized by intensive oxidation. In connection with 

 this the biochemical changes connected with the formation in the 

 irradiated organism of lipid peroxides with the particij)ation of lip- 

 oxidase are of great interest. 



The enzymatic oxidation which is carried out by means of the per- 

 oxidase proceeds only with the formation of primary peroxides. Under 

 these conditions, the action of the oxygen on the double bonds, through 

 the mutual influence of the atoms of the intermediate free radicals and 

 the formation of hydroperoxides, is strengthened under the influence 

 of the radiation. 



We have suceeded in showing that when the leaves of plants of 

 various kinds are irradiated with doses of 1 to 20 kr their lipid content 

 is altered very sharply. The chromatographic division of the fraction 

 of free lipids from the irradiated and non-irradiated leaves, allowed 

 us to establish the disappearance of certain unsaturated acids from the 

 extract of free lipids of irradiated plants even within 15 min after irra- 

 diation. At the same time, we observed sharp changes in the content 

 of lipid p»eroxides. In comparison with the non-irradiated leaves, the 

 amount of peroxides in the fraction of free lipids in the irradiated 

 plants increases even within 10 min of irradiation by approximately 

 2 to 6 times. But the irradiation of the leaves in which the enzyme, 

 lipoxidase was inactivated by steam did not lead to an increase of 

 the content of peroxides. 



Consequently, the biological action of ionizing radiation on the plant 

 is manifested in the activation of the enzyme system of the lipoxidase 

 (by 30 to 50 per cent) during the first 24 hr after irradiation which 

 oxidizes by means of molecular oxygen the unsaturated fatty acids, 

 thus strengthening the "oxygen effect" in vivo. 



bacq: VII, Concerning the mechanism of action of protective sub- 

 stances. 



The chemical protective substances have various mechanisms of 

 operation which can be simultaneous or synergetic. Each protective 

 system must be examined separately. 



