ULTRAVIOLET RADIATION 



429 



4. ULTRAVIOLET RADIATION 



The lethality and mutagenicity of ultraviolet radiation are prob- 

 lems of general biological interest; studies on fungi have made sig- 

 nificant contributions toward their solution. The early, and now 

 largely obsolete, literature is reviewed by Smith (127), more recent 

 work by Pomper and Atwood (116). Techniques for the irradiation 

 of spores and isolation of radiation-induced mutants are well developed 

 (7, 120, 138, 152). 



Virtually all studies of the action spectrum of killing and of muta- 

 genesis in fungi, as in other organisms, agree that the most effective 

 wavelength is in the region 260-265 m^. The action spectrum of 

 lethality to Trichophyton mentagrophytes is shown in Figure 3; similar 

 spectra prevail in Neurospora crassa (67, 109), Penicillium notatum 

 (69), Ustilago zeae (85), and Aspergillus oryzae (102). The primary 

 peak is generally accepted to be consequent upon the specific absorption 

 of this wavelength by nucleoproteins. 



McAulay and associates (92, 93, 94) have reported that biological 

 activity for Chaetomium globosum is greatest at 280 m^, in the region 

 of absorption by proteins. These observations cannot be reconciled 

 with any other data and merit re-examination. 



Aspergillus terreus conidia mutate after exposure to higher wave- 

 lengths (297 and 313 m /j( ,) or to sunlight (65). Efficiency, however, is 



Figure 3. The action spectrum 

 of killing of spores of Tricho- 

 phyton ynentagropliytes. Re- 

 drawn from original of Figure 

 4, A. Hollaender and C. W. 

 Emmons, Journal of Cellular 

 and Comparative Physiology, 

 Vol. 13, p. 391-402 (1938), by 

 permission of the Wistar In- 

 stitute of Anatomy and Biol- 

 ogy- 



240 260 280 



Wavelength, mju 



