CYTOLOGICAL EFFECT OF CHRONIC GAMMA IRRADIATION 



amount of fragments ( Table I) . By the use of the film badge method, it was 

 indicated that the plants received a total dose of 50 r in all experiments. 

 The number of both acentric fragments and bridges per 100 cells at anaphase 

 was determined. Conclusions regarding the eflfects of chemical treatments, 

 however, were based upon the fragment data only, since bridges occurred 

 in such low frequencies that it was difficult to evaluate the data {Cf. Table I). 

 Glutathione— In the presence of glutathione a marked and significant 

 reduction in fragment frequency was obtained. The experiments included 

 concentrations of glutathione ranging from lO^^M to 1 -5 X 10 =^M. None 

 of these concentrations seemed to cause any serious disturbances to the 

 roots not subjected to radiation. The protective property increased with 

 increasins' concentrations and the maximum effect is obtained at 1 • 5 X 

 10-^M, where the fragment frequency was reduced 53 per cent. At a 

 higher concentration (3 X 10~^M) the roots became soft and were obviously 

 injured. They were unsuitable for study. 



Cvsteine— Cysteine was applied as cysteine-HCl in two different series of 

 experiments. The presence of cysteine-HCl, lowered the pH-value of the 

 nutrient solution, particularly with the two strongest concentrations. One 

 series of experiments was performed with these acid solutions. Thus, the 

 plants were grown and exposed to cysteine under quite different pH-values. 

 Judging by mitotic activity, the different pH-values did not seriously disturb 

 the roots since equal numbers of dividing cells were present in all series. 



The maximum effect of cysteine in acid solutions was 60 per cent reduc- 

 tion in fragment frequency at 3xlO-*M. A concentration of 3xl0-3M 

 could not be tolerated and proved to be toxic to the roots. 



In another series of experiments with cysteine-HCl, the solutions were 

 neutralized with potassium hydroxide (KOH), so all cysteine and the control 

 series had the same pH {^'6) during the radiation exposure. Compared 

 with the previous series, less reduction in fragment frequency was obtained. 

 The maximum effect was a reduction of 35 per cent at lO-^M. 



In both series of experiments the protective effect of cysteine increased 

 with increasing concentrations. 



Thiourea— The chemical formula of thiourea is usually presented as 

 NHg— S— NHg. In oxidation processes, however, it reacts ^^ as a sulphydryl 

 compound NHg— SH=NH. Its effectiveness increased with concentrations 

 and the maximum effect was 48 per cent reduction in fragment frequency 

 at 10-3M. 



Sodium hyposulphite (Na2S204)— Sodium hyposulphite, a strong reducing 

 agent, showed a remarkable and optimal effect already at a concentration 

 of 10 "^M, where the reduction in fragments amounted to 45 per cent. At 

 10-^M no increase could be detected and lO^M proved to be toxic to the 

 roots. 



Sodiu?n cyanide (NaCN)— With sodium cyanide a smaller but significant 

 reduction of 25 per cent in fragment frequency was obtained at 10"^M. 



Conclusive evidence is presented of the modifying or protective property 

 of glutathione, cysteine, thiourea, sodium hyposulphite, and sodium cyanide 

 against chromosome fragmentation induced by gamma radiation. The 

 mechanism by which these chemicals exert their protection is not clear. First, 

 do these chemicals prevent chromosome breakage or do they heal broken 



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