43-t 



RADIATION BIOLOGY 



Yeajst cells irradiated with ultraviolet of wave leufitlus 2800-3800 A (at 

 somewhat higher do.ses than used l)y Xadson and Philippov, 1928a) did 

 not begin to hud as early as the controls — in some cases they never 

 budtled, whereas in others they finally grew like the controls (Lacassagne, 

 1930). Other investigators, working with somewhat shorter wave 

 lengths, also ft)und delayed budding phenomena and killing in various 

 species of Saccharomyces (Wyckoff and Luyet, 1931; Oster, 1934a, b, c). 

 The spores of Rhizopiis suiniis show a similar behavior in that, after irradi- 

 ation at 2050 A, they exhibit delayed germination or complete lack 



thereof, as well as a somewhat retarded 

 growth rate of the germinated spores 

 (I)imond and Duggar, 1940a, b). Usti- 

 lago zeae has- been reported to behave 

 in this way (Landen, 1939) , as has 

 Aspcryillus niger (Zahl et at., 1939). 



Effects on respiration have been ob- 

 served by various w-orkers (Oster, 1934a; 

 Giese, 1942; Giese and Swanson, 1947). 

 There appears to be an increase in en- 

 dogenous respiration with a decrease in 

 exogenous respiration of various sub- 

 strates by S. cerevisiae (experimental 

 conditions used by Giese, 1942, and 

 Giese and Swanson, 1947: 2 X 10^^ 

 cells/ml in a quartz Warburg vessel, 

 Sterilamp as source of ultraviolet radia- 

 tion, 10- to lo-min exposures, approxi- 

 mate dose of 70 ergs/mm^/sec). A de- 

 creased fermentation rate was also ob- 

 served (Giese and Swanson, 1947). 



Wave-length Dependence in the Ultra- 

 violet. For yeast, maximum killing effici- 

 ency was found to lie between 2600 and 

 2700 A, and Fig. 11-1 (Oster, 1934c) is 

 representative of the action spectra. 

 The suggestion was made that "the 

 effects of ultraviolet irradiation may result from the absorption of 

 energy by . . . nucleoproteins" (Oster, 1934c), because of the corre- 

 spondence between the killing action spectiiun and the absorption spec- 

 trum of nucleoproteins (see Loofbourow, 1948; Giese, 1950, for discussions 

 of the significance of action spectra). Similar results for killing and 

 mutation have been obtained in various fungi as shown in Table 1 1-3. In 

 a series of papers dealing with Chaetominm glohosum a sectorial colonial 

 change, designated as "K/' has been found to be selectively produced at 



0.22 



0,30 



24 26 28 



WAVE LENGTH,^ 



Fig. 11-1. Comparison of the de- 

 structive efficioncy of ultraviolet 

 energy on yeast at different wave 

 lengths. Ordinate, reciprocals of 

 the energies required to "iciH" 

 50 per cent of the yeast cells. 

 {Oster, 1934c.) 



