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SUMMARY : Eleven 5-membered heterocyclic compounds, in addition to furfural and furfuryl alcohol, were effective in overcoming the dormancy of ascospores of Neurospora tetrasperma. The substitution of a nitro group in the 5-position imparted fungistatic properties to otherwise innocuous furans and pyrroles ; carboxylic acid derivatives of these heterocyclic compounds likewise were toxic. From data on the time-course of furfural activation, it is shown that the Qlo for this process is 4-1 over the temperature range from 20 to 30°. The work of Shear & Dodge (1927) and of Goddard (1935,1939) and Goddard & Smith (1938) established that ascospores of Neurospora spp. can be activated by heat treatment. No chemical means of inducing germination was known until Emerson (1948) showed that furfural and furfuryl alcohol are effective activa- tors of such ascospores at concentrations as low as 1 part per million. That this effect is probably not an isolated one is suggested by the recent demonstra- tion that furfural will also activate the spores of certain thermophilic bacteria (Mefferd & Campbell, 1951). In order to extend the spectrum of chemical activators of ascospores of Neurospora spp., and to explore the mechanism of their action, analogues of furfural, other heterocyclic compounds, and some miscellaneous compounds having physiological activity were tested for their effect on germination. MATERIALS AND METHODS Ascospores were obtained by crossing strains 374 and 377 of N. tetrasperma which were grown as outlined by Goddard (1935). Spores were used im- mediately after harvesting, since Emerson (personal communication) has shown that they gradually lose their sensitivity to furfural until, after 3 months, they become almost unresponsive to such treatment; this has since been confirmed by the present author. Tests for activators were carried out by a modification of the method described by Davies, Duckworth & Harris (1948). After suspending the spores in 0.05 % (w/v) Nacconal (Allied Chemical and Dye Corp., New York, N.Y.) for a few minutes, they were rinsed 4 times by centrifugation in distilled water. Then the spores were collected on a sintered glass filter or in the bottom of centrifuge tubes and were placed in 25 ml. Erlenmeyer flasks to which had been added 5 ml. of the solutions to be tested. The flasks were shaken for 6-7 hr. at a rate of 80 oscillations/min. with a throw of 10 em. at a temperature of 25". At the end of this period of time it was usually found that germination had progressed to a point where the germ tubes were about 30p. long, whereupon formaldehyde was added to the flasks in order to kill GMVIII2 14

The Effect of Heterocyclic and other Compounds upon the Germination of Ascospores of Neurospora tetrasperma