CHEMICAL NATURE OF THE PHOTORECEPTOR 

 PIGMENT INDUCING FRUITING OF 

 PLASMODIA OF Physarum polycephalum 



FREDERICK T. WOLF 



Vanderbilt University, Nashville, Tennessee 



The Myxomycetes are organisms characterized by a vegetative stage 

 which is a plasmodium. Under proper conditions the plasmodium 

 fruits, and is transformed into a number of sporangia containing 

 spores. The conditions required for fruiting include nutritional factors 

 and a favorable temperature. The present work is concerned with 

 fruiting of plasmodia of Physarum polycephalum Schw., a species 

 which is rather easily grown in the laboratory on 1.0% water agar, 

 upon the surface of which are scattered sterile oat grains. 



Fruiting of P. polycephalum, which has yellow plasmodia, has previ- 

 ously been studied by Gray (1938, 1939, 1953). Except in a very few 

 cases, plasmodia grown from stock cultures maintained in the dark will 

 not form fruiting bodies in the complete absence of light. After ex- 

 posure to light, however, fruiting can then occur in darkness. The 

 length of the vegetative phase is conditioned by the total amount of 

 hght received; the more intense the light, the shorter is the time re- 

 quired for fruiting. 



Gray observed that the shorter wavelengths of the visible spectrum 

 (blue) were more effective in stimulating the fruiting response than 

 was yellow or red light. The blue line of the mercury arc (436 m/x) 

 was more effective than either the green line at 546 m^t or the yellow 

 at 578 m/i. The yellow pigment was extracted from the plasmodium 

 with acetone, and its spectrum showed an absorption maximum in the 

 blue. It was therefore concluded that the yellow pigment of the plas- 

 modia is a photoreceptor which interacts with light to bring about the 

 morphogenetic response of fruiting. 



In studying the influence of pH upon fruiting, by using Mcllvaine's 

 citric acid-NaH2P04 buffers of pH 3.0-8.0, Gray found that a higher 



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