Section 5 — Mutagenesis 



0.5 x lO- 3 m NaN 3 and (iv) 98 per cent CO. Cyto- 

 logical analysis took place after 24, 36, 48 hr of 

 recovery. It was found that NaN3, by itself in- 

 active, brought about a 4-fold increase in both 

 the percentage of aberrant anaphases and the 

 number of breaks per cell induced by lasiocar- 

 pine alone; with monocrotaline, a still stronger 

 effect of NaN3 was observed (6-fold increase over 

 the control). Also CO influenced the radiomimetic 

 effect of monocrotaline by doubling the per- 

 centage of induced aberrant anaphases. 



Parallel experiments with 2,4-DNP 30' pre- 

 treatment with 10~ 4 2,4-DNP followed by a 8 hr 

 treatment with 5 x 10~ 3 m lasiocarpine and subse- 

 quent recovery in water indicated that this in- 

 hibitor only slightly enhanced the chromosome 

 breaking effect of lasiocarpine. 



These results seem to indicate that the radio- 

 mimetic effect of monocrotaline and lasiocarpine 

 is not positively correlated with either respiration 

 or phosphorilation. 



1. Avanzi, Caryologia, 15, 351-356, 1962. 



5.92. Interaction of Chemically Induced Chromatid 

 Lesions in Vicia faba. Rigomar Rieger, (Ber- 

 lin, Germany). 



After treatment of primary roots with ethyl- 

 methane-sulfonate, myleran and ethylalcohol in 

 all possible combinations of the agents two by 

 two and the second treatment following the first 

 one immediately, the number of isolocus breaks 

 was found to be approximately additive, whereas 

 the number of chromatid translocations was in 

 accordance with the values theoretically ex- 

 pected for full interaction of the breaks induced 

 by each of the agents. Thus it might be concluded 

 that all agents tested are breaking the same kinds 

 of chemical bonds in the chromosomes. 



Two treatments with triethylenemelamine or 

 with triethylenmelamine and nitrogen mustard 

 one following the other immediately or seperated 

 by intervals in water up to 8 hr showed that even 

 after the longest interval used in both cases the 

 number of exchanges fitted the expectation for 

 full interaction of the breaks induced by the first 

 with those induced by the second treatment. On 

 the basis of the breakage-reunion-hypothesis and 

 on the supposition that the fractination effect is 

 really an expression of the time of rejoining, this 

 result might be interpreted as meaning that 

 breaks induced by the first treatment are staying 

 open at least for 8 hr, suggesting the bonds 

 broken to be of the covalent type. Full interaction 



was found to be confined to recovery times giving 

 the aberration peak. 



Because of the complexity of events leading to 

 aberration production, a lot of which are un- 

 known, interpretations of this type should be 

 accepted with due reserve and cannot be more 

 than working hypotheses for further experimental 

 tests. 



5.93. Chromosome Breakage by Triethylenmelamine 

 in Vicia faba in Relation to the Mitotic Cycle. 



M. Buiatti and Vittoria Nuti Ronchi (Pisa, 

 Italy). 



Experiments were carried out on the induction 

 of chromosomal aberrations by triethylenmela- 

 mine (TEM) in relation to the mitotic cycle. 

 Seedlings of Vicia faba with lateral roots 5-10mm 

 in length, were treated for one hour with 0.5 x 

 10~ 4 TEM at 19 C, after which they were trans- 

 ferred either into water or into 0.5 per cent 

 colchicine. 



Anaphase and metaphase scores at 2 hr inter- 

 vals after TEM treatment showed an increase in 

 aberration frequency from the 6th to the 45th 

 hour of recovery with a slight drop at 16-18 hr. 



As revealed by the relative proportions of 

 diploid and tetraploid cells in TEM-treated and 

 control roots subjected to continuous colchicine 

 action, a mitotic delay by TEM of 8 to 10 hr was 

 calculated. This might indicate that cells carrying 

 aberrations at the first recovery hours were under 

 treatment at the end of G2, possibly suggesting 

 some mechanism of aberration induction, in 

 absence of DNA synthesis. 



A strong decrease in mitotic index from the 4th 

 to the 26th hour of recovery (mitotis index: 5,61 

 and 3,47 respectively) was observed; at 30 hr, 

 no significant difference was found between 

 treated and control root tips (mitotic index: 10, 

 63 and 9,98 respectively). 



Roots treated with colchicine for 40 hr sfter 

 TEM treatment were scored for diploid(Xi)and 

 tetraploid (X 2 ) cells showing aberrations: apart 

 from the twofold increase in aberrations fre- 

 quency per cell in tetraploids, no differences in 

 aberration types between Xi and X2 were noticed. 



Achromatic lesions, so called '"gaps", showed 

 a continuous increase, both at anaphase and 

 metaphase, up to 45 hr recovery, a time when 

 most cells were in the second division. This 

 could support the idea of "gaps" being partial 

 breaks. Scoring of gaps at anaphase gave, in all 

 cases, higher values than metaphase scoring; 

 this might result from the stronger contraction of 

 metaphase chromosomes, leading to under- 

 estimation of "gaps". 



88 



