5G8 RADIATION BIOLOGY 



To determine whether temperature during X irradiation in the tolerated 

 range above freezing (0.6°-40°C) exerts its effect on aberration production 

 in Tradescantia microspores solely through its influence in decreasing the 

 amount of dissolved oxygen at higher temperatures, Giles, Beatty, and 

 Riley (1951) tested the effect of changing the temperature while holding 

 the outside partial pressure of oxygen constant {\'2Q and atm, respec- 

 tively) and of changing the outside oxygen pressure while holding the 

 temperature constant (27°C). The results indicated that only a part of 

 the effect of temperature in this range is caused by its influence on oxygen 

 concentration; for when there is outside oxygen present and it is held 

 constant, there is some additional mechanism which also acts to cause 

 the production of fewer aberrations (and, presumably, fewer primary 

 breaks) at higher temperatures. It is not clear, however, just what varia- 

 tions occur in the intracellular oxygen under these conditions. More- 

 over, paradoxically, when all outside oxygen is absent, higher tempera- 

 tures in this "normal" range have the reverse effect, that of promoting 

 aberrations. 



The complexity of temperature influence shown in the results of 

 Faberge, of Lewis, of Haas et al., and of Giles, Beatty, and Riley is perhaps 

 not too surprising once it is realized that breakage and mutation (and 

 joining also) depend on a chain of chemical events, readily influenced by 

 varied reactions occurring in the protoplasm. In view of this it is also 

 understandable that these temperature effects will not be identical in all 

 biological objects or on all types of genetic changes. This is evidenced, 

 for example, by the finding of Baker and vSgourakis (1949, 1950) that, in 

 Drosophila spermatozoa in the absence of oxygen, no temperature effect on 

 lethal production is to be found and by the findings of Kaplan (1951) that 

 in dry dormant barley seeds (unlike the Tradescantia pollen in Faberge's 

 experiments) the frequencies of both chromosome aberrations and visible 

 mutations are unaffected, regardless of whether the X irradiation is con- 

 ducted at 17° or — 65°C or followed by a posttreatment at — 65°C. The 

 same consideration may also help to reconcile the contradictory results 

 obtained in some of the other experiments on the temperature effect in 

 Drosophila. 



In all work on the effect of temperature on the production of chromo- 

 some changes, its possible influence on the process of union is also to be 

 taken nito account. Thus, in some other work of Faberge (1947) on 

 Tradescantia microspores, it was found that mere changes in temperature 

 in either direction favored the production of aberrations, presumably by 

 creating convection currents which moved the chromosome pieces about. 



Still other modes of action of temperature seem to be involved in the 

 influence of high-temperature shocks. Caldecott and Smith (1951), 

 working with dry dormant barley seeds, found that either a pretreatment 

 or a posttreatment with a temperature of about 80°C for >^ hour (a 



