Environmental and genetic control of differentiation in Neurospora 



protoperithecia, perithecia and ascospores contain a black pigment, and that strains 

 growing under conditions where no protoperithecia develop never turn brown or 

 black, it was assumed that these pigments were melanins and that a causal relation- 

 ship exists between melanin metabolism and protoperithecium formation. The black 

 pigments associated with protoperithecium formation were identified as melanins 

 by various chemical reactions, by studying their absorption spectra, and by the pre- 

 sence of a tyrosinase. No melanins could be demonstrated in mycelia on which proto- 

 perithecia were not found. 



This observation of course made it important to study tyrosinase activity in greater 

 detail in strains growing under different conditions, favouring or suppressing proto- 

 perithecium formation, as it is well known that tyrosinase converts tyrosine or other 



Table II 



Tyrosinase activity of ground suspensions of Neurospora crassa. Strain W 2/49 A grown 

 for 7 days on flter-paper on: (1) P-minimal medium at 25 C; (2) P-minimal medium plus 

 3,000 mg. ofamino-N (hydrol. casein A) per litre at 25 C. ; (3) P-minimal medium at 35 C. 

 The figures given are net increases {zero time readings deducted) in optical density, multiplied 



by 100. 



substrates into melanins via dopa, dopachrome and a number of other intermediates 

 (see Lerner, 1953). 



Hirsch showed that no tyrosinase activity could be demonstrated in strains grown 

 at 35 C, whereas tyrosinase activity was present in mycelia grown at 25 C. 

 (Table II). As shown in Figure 3, tyrosinase activity on P-minimal medium at 25 C. 

 started on the third day, reached its maximum on the fourth day, and then went down 

 again. It will be noticed from the figure that the highest tyrosinase activity was found 

 in the period when protoperithecium formation was most intense. 



Table II also includes an experiment in which Neurospora was grown on P-minimal 

 supplemented with 3,000 mg./litre amino-N (the AA-mycelium) . Very little tyrosinase 

 activity was found in mycelium grown on this substrate in 7-day old cultures, and 

 the red pigment did not turn black (melanic), as did the pigment in culture grown 



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