Section 5 — Mutagenesis 



log. phase culture, grown at 25 c in glucose-tryp- 

 tophan-salts medium, was centrifuged and the 

 cells resuspended in salts medium (l-2xl0 8 /ml) 

 and incubated for 48 hr at 25° with aeration. 

 This resulted in a population of largely uninu- 

 cleate cells. 



Upon addition of glucose and tryptophan, 

 DNA synthesis began and the amount in the 

 cells had doubled by about 150 min. At this time 

 the nuclei were seen to divide with a reasonably 

 high degree of synchrony. No cell division oc- 

 curred during this time. Aliquots of the suspen- 

 sion were irradiated (2000 rad 250 kV X-rays) 

 at intervals during the period of 150 min and 

 estimates of the number of induced mutants 

 (revertants to prototrophy) were made immedia- 

 tely after irradiation. 



If the genes for tryptophan requirement re- 

 plicate in synchrony, a rapid change in the num- 

 ber and type of induced mutants might be ex- 

 pected to result. It is hoped to present results 

 obtained using this technique with WP2 and 

 other strains of E. coli. 



5.121. (D.) Somatic Mutations in Ephestia kiihniella: 

 Their Dose-relationships in the Low and High 

 Dose-range of X-irradiation and the Influence 

 of Pretreatment on the Mutational Spectrum. 



Ilse Muller (Koln-Lindenthal, Germany). 



After irradiation of young pupae different 

 types of mutant scales are to be observed on the 

 hind wings of adult moths, their absolute and 

 their relative number depending on the dose of 

 X-rays. From 20 r up to 1000 r the frequencies of 

 the mutants are proportional to the square of 

 the dose, approximately. The spontaneous and 

 the 10 r-frequencies are lower than expected from 

 the curve in the higher dose-range. 



If pupae are kept at different temperatures for 

 some hours prior to irradiation, the mutational 

 spectrum at certain doses differs significantly 

 between the groups which were subjected to low 

 resp. high temperature treatment. This difference 

 is brought about by a change in the exponents 

 of the dose-effect curves, which is alike for all 

 mutant types, and a change in the sensitivity to 

 irradiation, the amount of which is larger in the 



types with a relative low frequency than in the 

 more frequent ones. 



Graphs and formulas, showing the quantita- 

 tive relationships, will be presented. The different 

 mutant scales will be demonstrated under the 

 microscope. 



5.122. Contribution to the Determination of the Rules 

 of Radioresistance of Agiarian Plants. E. San- 



duleac (Bucharest, Rumania). 



The Rumanian research works from 1959- 

 1962, with wet and dry irradiation of the seeds, 

 in order to determine the critical dose for the 

 main agrarian plants irradiated with u, x and (3 

 emitents, have shown that the most radioresistant 

 plants are the following: Linum ussitatissimum, 

 Brassica rapa, Sinapis sp., Lallemantia iberica, 

 which have the critical dose = 100,000 r; after 

 that Ricinus communis, Sesanum indicum and 

 Camelina sativa have more than 50,000 r. A few 

 textile plants like Abut Hon avicenaew ith 1 00,000 r 

 and Cannabis sativa with 30,000 r are also radio- 

 resistant. Nicotiana sp. has the critical dose over 

 50,000 r too. From Gramineae the following are 

 radioresistant: Oriza sativa > 80,000 r, Sorgum 

 sp. > 30,000 r, Panicum miliaceum > 25,000 r, 

 Avena sativa 25,000 r, Hordeum sp. 20,000 r; 

 relatively resistant are Triticum sp. 15,000 r and 

 Secale cereale 15,000 r. Radiosensitive are Zea 

 mays < 10,000 r, and from other families, Helian- 

 thus annuus < 8000 r, Vicia faba > 5000 r, 

 Solatium tuberosum > 5000 r, Beta vulgaris 5000 

 r. The annual Leguminosae have in a majority 

 the critical dose 15,000 r, Trifolium pratensa 

 20,000 r, Medicago sativa 25,000 r, Melilotus 

 albus 15,000 r, Pisum sp. 10,000 r. 



We have established the following: (a) the 

 amplitude of the doses is narrow for cereals about 

 the dose 15,000 r, but the Leguminosae have a 

 variable radioresistance ;(b) the oily plants have 

 the bigest radioresistance; (c) the plant roots are 

 radiosensitive; (d) the polyploid sorts are more 

 radioresistant than those with 2 n. The elabo- 

 ration of a precise method for using the radiations 

 as action factors which condition the change of 

 plant heredity must have as a scientific base the 

 rules of the radioresistance. 



99 



