CHEMICAL SPECIES INDUCED BY X-RAYS IN CELLS 



99 



Therefore, the s])ecies produced iininediately in the spore are not the 

 only ones that are finally observed — migration of energy within the 

 spore after irradiation must take place. 



Also, theESR apparatus reports to us only two general kinds of rad- 

 icals, one an electron associated with two protons and the other associated 

 with a single proton. The simplicity of this result is quite unusual, and 

 probably indicates that in the well-ordered biological system, the 

 energy from the X-rays, although deposited at random, migrates and 

 becomes fixed in a limited number of ])laces. 



We have treated the irradiated spores by the methods that influence 



4xl0*r in He at-l95°C 

 Warmed in He at 25 C 



(00 gauss ^ 



Fig. 4. — Changes in the ESR spectrum (2nd derivative) with time after irradiation of 



dry spores at 77°K. The spores were returned to 77 "K for reading after each warming 



period. The arrow marks the position of g = 2-003. (From Ehret et al., 1960). 



radiation sensitivity as judged by biological criteria, and the results are 

 shown in Fig. 5 (Ehret et al, 196U; Powers et al, 1961). When the 

 irradiated spores are heated for 15 min at 80°, there is a loss in ampli- 

 tude with no qualitative change in the signal. The decrease appears to 

 be approximately 50 per cent, in agreement with the biological experi- 

 ments. When the spores are exposed to oxygen, we see the gradual 

 growth of a single oxyradical (peroxyradical) signal from the finely split 

 signals of the two other radicals. The radicals become oxygen com- 

 plexes; they seem to be irreversible, for removal of oxygen from the 

 system does not affect the signal. This is expected according to the bio- 

 logical result. Furthermore, the oxygen signal that develops from the 

 heated spores is small, in correspondence with the fewer number of 

 radicals available to form the complex. 



Now we discuss the question as to whether the radicals that cannot 

 be annealed by heat are responsible for damage when they are finally 



