PHOTORECEPTOR PIGMENT OF Physarum polycepholum 325 



were examined in tlie infrared region, with a Perkin-Elmer model 21 

 spectrophotometer. Component 1 showed a large peak at 3400 cm~^ 

 attributed to an — OH group, a small peak at 1600 attributed to an 

 — NH2 group, a large peak at 1440 attributed to an ^OH group, a 

 small peak at 1120 attributed to an — NH2 group, and a small peak 

 at 880 cm~^ possibly due to meta-disubstituted or trisubstituted ring 

 structure. The infrared spectrum of component 2 was somewhat more 

 complex. There was a large peak at 3300 cm^^ attributed to an — OH 

 group, a large peak at 2900, small peaks at 2300 and 1750, a large 

 peak at 1560 attributed to an — NH2 group, a large peak at 1420 

 attributed to an — OH group, a small peak at 1 240, a large peak at 

 1050 attributed to an — NHi> group, and small peaks at 920 and 830 

 cm~^ Thus the infrared spectra, demonstrating the presence of — OH 

 and — NH2 groups, support the conclusion that both pigments are 

 pteridines. 



Component 2 cannot possibly be the photoreceptor of blue light 

 which activates fruiting in P. polycephaliim, since its longest wave- 

 length absorption maxima lie fairly deep in the ultraviolet. Compo- 

 nent 1, however, appears to have the characteristics expected for the 

 photoreceptor. In acid solution, it has a prominent peak at 420 ni/^, 

 and a large amount of absorption in the lower limits of the visible 

 spectrum. In neutral (or alkaline) solution, the peak shifts to 380 

 m/x, so that the amount of absorption in the visible is greatly reduced. 

 These absorption characteristics, and their shift with pH would seem 

 to offer a reasonable explanation of both the influence of blue light 

 in the photoinduction of the fruiting response and the superiority of 

 acid conditions for fruiting. 



The preceding results were obtained with pigments extracted from 

 Plasmodia grown under the normal conditions of alternate light and 

 darkness in the laboratory. It became of interest to determine whether 

 both pigments would be produced in plasmodia grown in constant 

 darkness. In such plasmodia, both components are present, and no 

 indication was obtained that their quantities are grossly different 

 from those which characterize light-grown cultures. This result is 

 consistent with the hypothesis that it is not component 1 per se which 

 triggers the fruiting response, but rather the interaction of this com- 



