Section 5 — Mutagenesis 



strated by use of the tritiated analogues with 

 autoradiography. Replacement in DNA was 

 shown utilizing I 131 labeled IUdR and by CeCl 

 density gradient centrifugation. Phasing of DNA 

 synthesis in Vicia faba cells was accomplished by 

 treatment with 5-aminouracil (5AU). Studies on 

 the rate of entering and leaving DNA synthesis 

 during 5AU treatment were made with double 

 labeling techniques involving H 3 and C 14 labeled 

 thymidine. Uptake of H 3 deoxycytidine ap- 

 parently forms a pool which is used slowly in 

 DNA synthesis, thus providing a means for 

 autoradiographic studies of various other 

 subsequent treatments affecting rate of DNA 

 synthesis. Incorporation of H 3 labeled arginine 

 into chromosomes of Vicia faba has been success- 

 ful and is of significance in investigations on 

 nuclear proteins. 



In Arabidopsis thaliana the normal distribution 

 of DNA synthesizing cells in the shoot meristem, 

 as well as the morphogenetic effects of incor- 

 porated IUdR, have been traced with tritiated 

 thymidine. The inco poration of IUdR into 

 gametophytic tissue, .: prerequisite to mutagenic 

 studies, is being investigated with an I 125 labeled 

 form of this nucleoside analogue. 



Kinetin (6-furfurylaminopurine) in combi- 

 nation with indolacetic acid initiates tumor 

 formation when applied to the apical meristem of 

 genetically tumor conditioned seedlings of 

 Nicotiana suaveolens-langsdorffii. Tritiated kine- 

 tin is being used to investigate the fate of this 

 aminopurine in cells of the meristematic region. 



Research carried out at Brookhaven National 

 Laboratory under the auspices of the U.S. 

 Atomic Energy Commission. 



5.87. Effect of Metabolic Inhibitors on X-induced 

 Chromosome Breakage in the Ehrlich Ascites 

 Tumour. Carmen Bertucci de Lozzio and 

 Juan I. Valencia (Buenos Aires, Argentina). 



Increased sensitivity to X-irradiation has been 

 found with pretreatments with chloramphenicol, 

 5-fluordeoxiuridine, sodium azide or oxygen, in 

 the Ehrlich ascites tumor ELD. 



Irradiation with 2000 r at 500r/min, 240 kV, 

 15 mA, 1 mm Al, do not inhibit tumor growth. 

 When the same 2000 r were delivered after one 

 hour treatment with either chloramohenicol 

 500 Hg/ml to 2 mg/ml, 5-fluordeoxiuridine 

 (5-fluoruracil deoxiriboside, FUDR) 4xlO -5 M, 

 sodium azide 0.005 m or oxygen at 30-60 mm 

 Hg (over the normal atmospheric tension), the 

 result was a permanent inhibition of the tumor 



growth. The same pre-treatments before irra- 

 diation with 500r did not inhibit tumor growth. 



The cytological analysis showed a high 

 frequency of chromosome aberrations in the 

 first post-irradiation division. All pretreatments 

 increased the number of breaks per cell compared 

 to that observed when the same dose of radiation 

 was given alone. The qualitative and quan- 

 titative yield varied in each case. For example. 

 FUDR produced a segmental shattering of the 

 chromosomes while oxygen or chloramphenicol 

 induced a high frequency of chromosome 

 fragments and few chromosome and chromatid 

 exchanges; sodium azide increased the frequency 

 of all types of aberrations, including chromatid 

 exchanges, but no chromosome shattering. 



It is apparent that pretreatment with FUDR 

 induces a very typical kind of aberration by 

 interfering with DNA synthesis and perhaps 

 some other processes, which seems to be related 

 to the normal integration of the chromosome. 

 On the other hand oxygen, sodium azide and 

 chloramphenicol seems to act on the rejoining 

 mechanism by preventing synthetic processes of 

 restitution. 



This research was supported by a grant of the 

 Argentine National Research Council. 



5.88. The Influence of Nucleic Acid Base Analogues 

 on the Scales of Ephestia kiihniella. Ernest W. 

 Caspari and F. W. Muth (Rochester, U.S.A.). 



Larvae of Ephestia kiihniella strain NCR were 

 injected with varying amounts of 5-bromodeoxy- 

 uridine(5 BDU), lug60ug per animal. The animals 

 developed normally, and no reduced viability 

 compared to the controls was observed. The 

 hind wings were studied for the occurrence of 

 aberrant scales. Abnormal scales occurred with 

 high frequency. In the lower range of concen- 

 trations, 1-10 ug, the number of aberrant scales 

 rises with increasing dosage, but between 10-30 ug 

 the number of aberrant scales remains stable. 

 At still higher dosages a further increase appears 

 probable. The production of aberrant scales is 

 strongly reduced or completely inhibited by 

 equimolar amounts of thymidine. 5-bromouracil 

 and 2-aminopurine produce few if any aberrant 

 scales. The types of aberrant scales appear differ- 

 ent from those induced by radiation. A charac- 

 teristic type called 1 ("leaf") is predominant at 

 low concentrations of BDU, but does not 

 increase at medium levels while it decreases at 

 higher concentration. It has not been found on 

 irradiated wings. Other characteristic types of 



86 



