Section 5 — Mutagenesis 



cronuclei, release of droplets of DNA in the cyto- 

 plasm, and disturbance or inhibition of the reg- 

 ular mitotic distribution (stathmokinesis, mero- 

 kinesis, non-congression). The maximal effect 

 was obtained with both substances at a concen- 

 tration between 1 and 2 per cent, which allows 

 normal growth of the roots. However the number 

 of cells showing cytogenetic effects often varied 

 considerably between the different roots of the 

 same bulb. 



A dose of 60-80 r of roentgen rays gives about 

 the same number of structural effects as 1.5 per 

 cent of I, but nearly no abnormalities of mitotic 

 distribution. No clearcut results as to a synergis- 

 tic or antagonistic action of simultaneous chemi- 

 cal and radiation treatment were obtained be- 

 cause of the high numerical variability of all the 

 cytogenetic effects mentioned above. 



As the substance I is administered also in sal- 

 pingography (in concentrations from 30-70 per 

 cent) one has to take in account dysgenic effects 

 in ovaries and follicles. 



The results will be published in full in the 

 journal Strahlentherapie. 



5.100. Cytogenetic Analysis of the Sensitivity of 

 Plants to Different Kinds of Radiation. V. V. 



Khvostova and S. A. Valeva (Moscow, 

 U.S.S.R.). 



1. After irradiation of seeds of resistant varie- 

 ties of plants, belonging to the same species, with 

 the same dose of ionizing radiations a lower per 

 cent of ana- and telophases with chromosome 

 rearrangements are produced in first mitoses of 

 seedling roots, than in radiosensitive forms. 



2. A comparison of the action on seeds of 

 related varieties of sparcely and densely ionizing 

 radiations has revealed the existence of two kinds 

 of chromosome protection against radiations: 

 (a) two varieties of peas, markedly different as to 

 sensitivity to gamma-rays, showed equal sensi- 

 tivity to fast neutrons; (b) whereas one of two 

 varieties of maize manifested a parallel resistance 

 to both gamma-rays and fast neutrons. These 

 sensitivity differences were manifested at various 

 stages of the development of the plant: after irra- 

 diation of dry seeds and seedlings as well. 



3. Experiments on the storage of pea seeds 

 during 6 months after irradiation with gamma- 

 rays showed, that the sensitive variety exhibits 

 after storage twice as many per cent of anaphases 

 with chromosome rearrangements. The suppo- 

 sition is made that potential chromosome dam- 

 ages occurring under the action of gamma-rays, 

 transforms into real breaks under the influence of 

 the biochemical peculiarties of the cellular me- 



dium of the sensitive variety during storage. 



4. Studies on the action of 2-4, dinitriphenol 

 on germinating seeds of two varieties of maize 

 clearly showed that 2-4, dinitriphenol has no 

 effect on the number of rearrangements after 

 neutron irradiation; after irradiation with gam- 

 ma-rays, dinitriphenol increases the number of 

 rearrangements, especially in the radiation-sen- 

 sitive variety. These experiments show that the 

 damage of chromosomes by the action of neu- 

 trons is not subject to modifications by the energy 

 processes in the cell after irradiation; (2) and 

 that, apparently, the potential damages, occur- 

 ring under the action of gamma-rays, are not 

 transformed into real ones under the conditions 

 of the high energetic level of the cell, and are 

 transformed only when the energetic level of the 

 cell becomes lowered. 



5.101. Selection for Radioresistance and Resistance 

 to Chemical Mutagenes in Diploid and Tetra- 

 ploid Forms of Buckwheat (Fagopyrum esculen- 

 tum). R. N. Platonova and V. V. Sacharov 

 (Moscow, U.S.S.R.). 



1. Experiments on A-irradiation of four seed 

 progenies and on the selection of the most 

 radioresistant plants, grown from these seeds, 

 produced resistant forms of diploid and tetra- 

 ploid buckweat populations. 



In the usual (2 x =16) buckhweat form one 

 first selection resulted in an increase of survival 

 of the irradiated plants. In the autotetraploids 

 (4 =32) an increase in survival after irradiation 

 was produced only after two or more selections. 



2. Our 2 x and 4 x lines, resistant to A-rays, 

 were checked for two years following for resist- 

 ance to densely ionizing radiations (fast neu- 

 trons). The results obtained were positive for all 

 characters (survival, power of development and 

 seed bearing). This was proven by comparative 

 cytological investigations. In the gamma-resistant 

 forms there were less chromosome damages, 

 caused by fast neutrons, than in the usual 

 populational seeds, receiving the same radiation 

 dose. 



3. Selection for radioresistance caused the 

 occurrence of forms resistant also to the chemical 

 mutagene — diethylsulphate. 



4. In order to make clear the character of 

 inheritance in the radioresistant diploid plants, 

 resistant (selected) plants were crossed with 

 plants from usual, non-irradiated populations. 

 The same kind of experiment was carried out on 

 tetraploid plants. The hybrid plants show a 

 dominant inheritance, and radioresistance in 

 2 x hybrids appeared even to be higher, than in 



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