CHROMOSOME BREAKAGE BY DIEPOXIDE 



AND BY X-RAYS 



G. Roy Lane 



Botany Department, Uni\ersity of Southampton 



The effects of X-rays and other ionizing radiations on the meristematic 

 cells of the root of Vicia faba have been studied by a number of workers, 

 e.g. Darlington and La Cour\ Ford"^, Thoday^-*, Gray and Scholes^, 

 and Revell^' ^. The latter author has made a special study of the effects 

 of di(2 : 3-epoxypropyl) ether and some other radiomimetic substances on 

 Vicia root cells whilst McLeish^ has studied the effects of maleic hydrazide 

 on the same material. 



This paper deals with experiments now being carried out with X-rays 

 and radiomimetic substances on the root cells of Tradescantia. This material 

 was chosen for the following reasons : 



(7) The effects of radiation on the haploid pollen cells of this plant have 

 been extensively studied by many workers and of certain radiomimetic 

 substances by Darlington and Roller'' and recently by Smith and Lofty^". 

 Until now, no study has been made of the effects on the diploid root meristem 

 cells of this plant, although it forms adventitious roots freely and the roots 

 can be grown readily in culture under controlled conditions. 



(2) The chromosome breaks induced by diepoxide in the root cells of 

 Vicia occur largely in the demonstrable heterochromatin (Revell^'^). So 

 also do those induced by maleic hydrazide (McLeish^). The effects on 

 Tradescantia chromosomes, which possess no demonstrable heterochromatin 

 should make an interesting comparison. 



{3) Chromosome reunion (R") to form polycentrics and rings is relatively 

 rare in Vicia following radiation treatment. This has been related to the 

 presence of heterochromatin by Darlington^^. Chromosome reunion (R") 

 probably does not occur at all in the first mitosis after treatment with 

 diepoxide or maleic hydrazide, reunion being entirely between chromatids, 

 i.e. of the SR and R' types. In Tradescantia pollen cells, chromosome 

 reunion is extremely common and predominates if treatment is carried out 

 during the first part of the resting phase. Here again the effects of diepoxide 

 and maleic hydrazide on the root cells of Tradescantia should make an inter- 

 esting comparison. 



{4) Revell^^' ^^ has postulated a new interpretation of the mode of origin 

 of X-ray and radiomimetic chromosome structural changes, based on his 

 work on Vicia. Results from Tradescantia in which the chromosomes differ 

 in their chromatic make up and in their properties of reunion may be expected 

 to assist in assessing the alternative interpretations. 



EXPERIMENTAL 



Details of the culture and technique vised in this work will be published 

 elsewhere. The plants used are of a single clone of Tradescantia paludosa. 



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