Environmental and genetic control of differentiation in Neurospora 



m 



Plate i (d) 



Plate I. (a) protoperithecia in normal Neurospora grown on P-minimal ; (b) sterile mutant grown on 



the same substrate, no protoperithecia are formed; (c) mutant with abnormal protoperithecia, associated 



with excessive melanin production; (d) ^-day-old culture of a sterile mutant to which tyrosine -+- 



tyrosinase has been added. (Photos by A. 0ye, linear magnification X 20.) 



Discussion 

 Chairman: H. V. Bmndsted 



E. N. Willmer. What do you consider to be the relationship between the formation 

 of melanin and that of carotenoids? In the chromatophores of vertebrates, which are 

 derived from neural crest tissue and are thus among the earliest cells to begin differ- 

 entiation in the body, the formation either of melanin or of carotenoids is of frequent 

 occurrence. Occasionally both products occur together. The other tissues in the body 

 where carotenoids abound are of course those in the reproductive system and in the 

 adrenal cortex. In the latter case it is interesting to consider whether there may be 

 some connexion between the carotenoid pigmentation of the cortex and the tyrosine- 

 adrenaline metabolism of the medulla. It is well known that adrenal cortical disease 

 often leads to abnormalities of melanin formation. 



M, Westergaard. Wild type Neurospora has both carotenoids and melanins. We may 

 consider the conidia, which have the carotenoids, as part of the male sex system; 

 just as the protoperithecia, which have the melanins, represent the female sex 

 system. Mutation in one system does not affect the other, i.e. strains with no conidia 

 may have perfectly normal protoperithecia and vice versa. Unfortunately the male 

 sex in Neurospora is rather degenerate, because fragments of mycelia can also fertilize 

 the protoperithecia. Probably the biochemistry of the male sex should be studied 

 on a species where it is better differentiated. 



n 183 



