Section 5 — Mutagenesis 



aberrations nave similar characteristics dose 

 curves. Frequently, two aberrant scales are 

 found very close together, so that they may be 

 regarded as the derivatives of one affected cell. 

 The two aberrant scales may be either of the 

 same type, or may be different from each other. 

 The former case occurs most frequently in 

 irradiated wings, the latter type of doublets is 

 more frequent in BDU-induced aberrations. 

 Since BDU is an analogue of thymidine, and 

 thymidine suppresses the described effects of 

 BDU, it is suggested that the effects are due to 

 incorporation of BDU into the DNA of the 

 developing cells and represent mutational 

 changes in the genetic material. 



This investigation was supported by grant AT 

 (30-l)-2902 from the U.S. Atomic Energy 

 Commission. 



5.89. Interactions between Cations and Chromosome 

 Damage induced with Mesyloxy Compounds. 

 J. Moutschen and M. Moutschen-Dahmen 

 (Liege, Belgium). 



Chromosome aberrations induced with several 

 mono- and difunctional mesyloxy compounds 

 were modified by some cations in broad bean 

 and barley. Cu ++ and Zn ++ considerably 

 enhanced the rate of chromosome aberrations 

 induced with EMS (ethyl methane sulfonate) 

 and to a lesser degree MES (Methyl ethane 

 sulfonate) and MMS (Methyl methane sulfo- 

 nate). The optimal conditions for this interaction 

 were investigated. The effects of these ions were 

 observed to be lesser for difunctional compounds 

 Myleran and dimethyl myleran. Some cations 

 like Ca ++ and Mg ++ were inefficient with 

 monofunctional compounds but reduced th^ 

 rate of aberrations with difunctional. The 

 modifications of the types of aberrations were 

 considered. One cation: A1+++ not only modified 

 the efficiency of Myleran but also the distribution 

 of aberrations. Some interpretations are given. 



5.90.EfFects of Substances Blocking Heavy Metals on 

 Interphase Nuclei and Mitosis. Dolores An- 

 gulo and F. Silio (Madrid, Spain). 



In our previous publication we called attention 

 to the action provoked on interphase nuclei by 

 EDTA. The abnormalities induced by this agent 

 encouraged us to realize another work on biolo- 

 gic activity of substances blocking heavy metals, 



using also CNK to verify its effect on plant 

 species with the test of Allium cepa. 



In these experiments we have used CNK, that 

 does not present any chelating action on Ca and 

 Mg, in order to compare its effects with those 

 produced by EDTA in relation to the belief that 

 this agent owes its action to the chelation of 

 divalent cations Ca ++ and Mg ++ . 



The effects obtained with either agent show 

 similar effects in many aspects such as a remark- 

 able swelling of the interphase nuclei that dis- 

 covers fine reticulate or filamentous structures 

 and furthermore heteropicnotic areas which may 

 correspond to chromocentres, observing at the 

 same time in mitosis the helicoidal structure 

 owing to the disturbance of the chromosomic 

 proteins. Likewise the great neatness observed in 

 the material under treatment is remarkable, sup- 

 plying favourable conditions for the study of 

 chromosomic structures. 



On the other hand, the EDTA produces a 

 beginning of c-mitotic action, which effect we 

 have observed, though very seldom, in material 

 treated with CNK. However with this agent there 

 appear the corresponding radiomimetic effects, 

 which are not observed in material treated with 

 EDTA. 



Therefore the biologic action of EDTA, che- 

 lating heavy metals, may be identified in some 

 aspects with that of CNK, which is not a 

 chelating substance of Ca and Mg. 



5.91. The Influence of Respiratory Inhibitors on Chro- 

 mosome Breakage by Lasiocarpine and Mono- 

 crotaline. S. Avanzi (Rome, Italy). 



In a previous publication ( x ) data on the radio- 

 mimetic effect of monocrotaline and lasiocarpine 

 in Vicia faba were reported. To test whether the 

 radiomimetic effect of the two alkaloids is re- 

 lated to respiration, lateral root tips of Vicia faba 

 seedlings were subjected to the following treat- 

 ments : 



(1) simultaneous treatment with 5xl0~ 3 m 

 lasiocarpine and 0.5 xlO" 3 m NaN 3 for 

 8 hr at 15°C, followed by recovery in water. 



(2) simultaneous treatment with 5<10 -3 m 

 monocrotaline and 0.5 x 10 -3 m NaN 3 for 

 8 hr at 15°C, followed by recovery in 

 water; 



(3) simultaneous treatment with 5 x 10 -3 m 

 monocrotaline and 98 per cent CO for 8 hr, 

 followed by recovery in water. 



As control material served lateral root tips 

 recovering in water after an 8 hr treatment with : 

 (i) 5xl0- 3 m lasiocarpine at 15°C; (ii) with 

 5xl0- 3 m monocrotaline at 15° or 21°C; (hi) 



87 



