| Abstrakt: |
The relation of environment to the differentiation of protoperithecia and two closely allied phenomena, tyrosinase and melanin formation, has been studied in Neurospora crassa. A temperature of 25° C is optimal as regards the formation of protoperithecia while a temperature of 35° inhibits both the formation of protoperithecia and fruitbodies. Increasing amounts of nitrogen, both organic and inorganic, depress and eventually suppress protoperithecia formation specifically; protoperithecia formed at intermediate concentrations of nitrogen appear unpigmented and are largely or wholly nonfunctional, the latter depending in a secondary way on the carbon/nitrogen ratio of the medium on which growth has taken place. The pigment present in the protoperithecia has been found to be melanic in nature: it is produced to a considerable extent only under conditions permitting the formation of functional protoperithecia. Mycelia grown under conditions permitting optimal protoperithecia formation show strong tyrosinase activity which makes its appearance concomitant with or slightly precedes protoperithecial formation; the greatest increase in rate of protoperithecia production coincides with maximal tyrosinase activity of the mycelium. Tyrosinase and melanin are low or absent in mycelia growth at 35°. Mycelia in which protoperithecia formation bas been completely suppressed through the addition of organic nitrogen show very little tyrosinase activity after 7 days' growth and tyrosine is oxidized only to a red pigment; after 14 days a strong tyrosinase can be demonstrated which rapidly oxidizes tyrosine to melanin, but during actual growth only a very small amount of melanin deposition takes place. This inhibition is not due lo the presence of sulfur-containing substances. The possible significance of these findings is discussed. By appropriate changes in the relative and absolute amounts of carbon and nitrogen different stages in the sexual cycle of the organism can be affected, but any condition which prevents the exhaustion of nitrate (and possibly nitrogen in general) always affects in a deleterious manner both the number and normal functioning of the protoperithecia formed. The processes of fertilization and fruit formation, on the other hand, are not greatly affected by the presence of nitrate. Use of tyrosinase inhibitors suppresses the formation of protoperithecia and melanin more or less completely; some other enzyme inhibitors used do not show the same effect and apparently have another site of action. The question of whether tyrosine metabolism has a causal relation to the differentiation and normal functioning of protoperithecia, or whether tyrosinase and melanin are invariable, though accidental, concomitants of protoperithecial formation is discussed. [ABSTRACT FROM AUTHOR] |
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