234 A. M. KUZIN 



the correct mechanism for the protective action of such polyphenols as 

 for example oxytyramine or propylgallate (Gorodetsky et al., 1960). 



REFERENCES 



Alexandrov, S. N. (1957). C.B. Acad. Sci. U.R.S.S. 113, No. 2. 311. 



Bak, C. (1955). In "Radiobiology" 



BoYARKiN, A. N. (1951). Biodioiiistry, LenuKjr. 16, 353. 



Gorodetsky, A. A., Baroboy, V. A., and Chernecky, V. P. (1960). In "Proceedings, 



Scientific Conference in Biojjhysics and Mechanism of Action of Ionizing Radiation", 



Kiev. 

 Grayevsky, E. Y., and Shapiro, X. V. (1958). Adv. Mod. Biol.. Moscow, 47, 185, 

 Gray, L. H. (1956). //( "Ionizing Radiations and Cell Metabolism". London. 

 KruKova, L. M., and Kuzin, A. M. (1960). Fhi/.siol. Plant. 7, 220. 

 Rode, G. (1950). Strahlenthercqne, 81, 103. 

 Shabadash, a. L. (1960). C.R. Acad. Sci. U.R.S.S. 135. 

 Shapiro, N. (1958). Biophysics (Rjiss.) 3, 466. 

 Shmidt, I. N. (1948). C.R.\4cad. Sci. U.R.S.S. 59, 747. 

 Strelin, G. S. (1950). C.R. Acad. Sci. U.R.S.S. 73, 1283. 



DISCUSSION 



ALEXANDER: What exiDeriments did you perform with quinones and with DNA? 

 It occui's to me that the effects of quinones on mitosis miglit be due to cell re- 

 activity. We have never obtained any data indicating that quinones are effective 

 in vitro. 



KUZIN : Discussing the possible role of the oxidation half-products of the tyrosine 

 in these phenomena I want once again to refer to two groups of facts. On the one 

 hand artificially obtaiiied products of the enzymatic oxidation of tyrosine greatly 

 inhibit mitosis and decrease the root's mitotic index : on the other hand they have 

 a protective effect on highly polymerized DNA. 



shekhtman : The data you have presented are very interesting, but this question 

 arises from them. If these products inhibiting mitosis are formed in the cytoplasm, 

 then how do you explain data pointing to an extremely high radiosensitivity for 

 the niicleus and the great difference in radiosensitivity existing between nucleus 

 and cytoplasm, as demonstrated by Rodgers, Uh'ich, Astaurov and other investi- 

 gators? Maybe it holds trvie for plants, whereas in embryonic cells is it not true? 



KUZIN : In our experiments plant material was used. I think however that we are 

 justified in believing that the general mechanisms of radiation effects have much 

 in common ; only, in the animal body neurohmnoral influences are obscuring the 

 picture somewhat. 



BACQ: I believe that your choice of plants for the preliminary study is quite 

 correct. I worked for many years with quinones and know that adrenochrome is 

 one of the very strong mitotic poisons. Lettre used it, too, with tissue cultures. It is 

 of interest to note also, that cysteamine is an excellent oxidase inhibitor. Your 

 data are in good agreement with Dr. Gray's ideas, since it is the tyrosinase 

 which requires molecular oxygen. But the trouble is that in mammalian cells 

 there is no tyi'osinase and polyphenol oxidase, although the mitoses there are 

 inhibited just the same. 



KUZIN: I quite agree with you. I cannot say from my own experiments how 

 matters stand for animal cells. But in the literature, for example in Dr. 



