Section 5 — Mutagenesis 



In the first trials, the seeds were soaked in 

 cysteamine at 1, 2, 4 per cent during 24 hr at 

 20 C before irradiation. We observed a marked 

 protective action in the growth test, confirmed 

 by the percentage of plants attaining maturity. 



In 1957, we reduced the time of soaking to 1 hr 

 and used only cysteamine 1 per cent; the higher 

 number of surviving plants observed was 

 significant. 



In 1958 and 1961, the seeds were soaked during 

 1 hr in cysteamine 1 per cent, and then dessicated ; 

 the irradiation took place on seeds with normal 

 water content (13-14 per cent). The growth test 

 and the percentage of mature plants showed a 

 marked protective action from 20000 r and 

 above. The latest experiments proved that 

 presence of cysteamine is sufficient to account 

 for its action. 



It seems that the effect of cysteamine decreases 

 when the water content is low (4-5 per cent). 



In a number of experiments, ( 2 ) the cysteamine 

 applied before or after irradiation increased the 

 number of mutants but in other trials made in 

 1958 and 1959, the protection afforded by 

 cysteamine against the mutagenic effects of 

 X-rays is of the same order of magnitude as the 

 protection against lethality. 



1. Z. M. Bacq, et al.; Protection contre le 

 rayonnement X par la (3 mercaptoethylamine. 

 Arch. Internet. Physiol. 59, 442, 1951. 



2. A. Moes; L'action de la cysteamine chez 

 Forge. Bulletin de VInstitut Agronomique et des 

 Stations de Recherches de Gembloux. XXV, 

 98-107, 1957. 



3. A. Moes. Water content, wave-length and 

 sensitivity to X-rays in barley. Effects of 

 Ionizing Radiations on Seeds, I.A.E.A., 

 Vienna, 631-640., 1961. 



5.105. Some Factors Affecting the Action of Chemi- 

 cal Mutagens. C. F. Konzak, R. A. Nilan, 

 R. E. Heiner, and Edith E. Froese-Gertzen 

 (Pullman. U.S.A.). 



Diethyl sulfate and ethyl methanesulfonate 

 induce a remarkably high frequency of chloro- 

 phyll mutations and a negligible frequency of 

 gross chromosome aberrations in barley. This 

 high mutation frequency is induced at a high 

 rate of plant survival and low levels of seedling 

 injury. Recent studies provide a basis from 

 which an understanding of the relationship 

 between different kinds of biological damage can 

 be sought. It has become apparent that physical 

 and chemical factors play a determining role on 



the action of mutagens in biological systems. 

 Hydrolysis of diethyl sulfate in aqueous solution 

 is 26 times faster than that of ethyl methanesul- 

 fonate. The Qio for the in vitro hydrolysis of the 

 mutagen varies from 3.1 for the 0-1 0°C range 

 to 4.5 for the 30-40°C range, whereas the Qiu 

 for the in vivo seedling injury response is about 

 2.7. Our data indicate that the rate-controlling 

 factor in the in vivo system is duffusion. The 

 hydrolysis products tend to decrease seedling 

 growth and plant survival but do not induce 

 mutations. These injury effects are apparently 

 due to low pH. Highly concentrated mutagen 

 solutions reduce mutagenic effectiveness by 

 increasing undesirable side-effects through mass 

 action. The mass action is accentuated with 

 fast-reacting agents. Results from these studies 

 offer some likely explanations for differences 

 in the relative mutagenic efficiency of chemical 

 agents. 



Research supported in part by funds from the 

 U.S. Public Health Service GM 10838-05 and 

 from the U.S. Atomic Energy Commission 

 AT (45-l)-353 and conducted under Washington 

 State Experiment Stations Projects 1435 and 

 4068. 



5.106. The Effects of Some Combinations of Mu- 

 tagens on Mutation Frequency in Barley. 



T. J. Arnason, J. L. Minocha and Laila 

 Mohammed El-Sadek (Saskatoon, Canada). 



Two mutagens acting in sequence may produce 

 more than additive mutation frequencies if, for 

 example, one of these exposes previously 

 protected mutation sites to the second mutagen. 

 If two mutagens merely compete for the same 

 sites or if the effects are completely independent 

 the results should be additive or less than 

 additive. Combinations of mutagens that have 

 been tried on barley (Hordeutn vulgare L.), are 

 ethyl methanesulfonate (EMS) and ethylene 

 imine (EI); EMS and nucleotides and EI and 

 nucleotides. The frequencies of chlorophyll 

 mutations in Mi spikes and M2 seedlings were 

 recorded. 



The treatment with 0.5 per cent EMS solution 

 for 4 hr yielded 17 per cent Mi spike mutations. 

 A 4-hr treatment with 0.1 per cent EI solution 

 yielded 13.8 per cent of mutant spikes. When 

 grains were treated with both mutagens in 

 sequence the results were more than additive. 

 With EI applied first the mutation frequency was 

 43.8 per cent and when EMS was applied first 

 the mutation frequency was 36.7 per cent. On an 



93 



