BIOCHEanCAL MECHANISM OF CELL DIVISION DISTURBANCE 225 



Table I. DNA from irradiated organs (1,000) and unirradiated rats. 



DNA concentration for the viscosity measurement was 0-004 per cent (average 



data from 3 to 5 experiments). 



viscosity of DNA, isolated by the phenol method, are presented in Table 

 I, and its polymerization spectrum, obtained after chromatography on 

 Ecteola-celliilose, is given in Fig. 1. These data illustrate very well the 

 relative stability of the DNA molecule immediately after irradiation. 



The change of viscosity of DNA observed in thymus cells four hours 

 after irradiation appears to be the consequence of the activation of the 

 DNase in the cytoplasm of the exposed cells. 



The disturbance of metabolic processes plays a special part in stop- 

 pmg cell division after irradiation. This is due to the distant effect of 

 radiation on cell mitosis. 



Many papers in which the distant effect of radiation on the mitotic 

 index has been shown for animal organisms have been published, for in- 

 stance by Shmidt (1948); Strelin (1950); Rode (1950); Grayevsky and 

 Shapiro (1958); Alexandrov (1957) and Shapiro (1958). 



The complexity of the neurohumoral regulatory system, of mitotic 

 activity in the animal organism, however, makes the biochemical 

 analysis of the phenomenon difficult. We thought it might be interesting, 

 therefore, to trace the existence of the distant effect of radiation on 

 mitosis for plants and to try to investigate the biochemical mechanisms, 

 on which it is based. 



Krukova and Kuzin (1960) showed that if a fully -grown leaf of Vicia 

 faba was irradiated, (the rest of the plant being well screened), then, 

 one or two days after irradiation, it is possible to observe a sharp de- 

 crease in the mitotic index. This was observed both in the apical point 

 of growth and in the meristem of the root tip, as the results given in 

 Fig. 2, show. 



Plants placed in the same lead chamber as the experimental ones 

 (with the leaf outside the chamber) were used for control; thus we 



