Some Physiological Characteristics of Ascospore Activation in Neurospora crassa

The application of heat is used to break the dormant state in spores of several species of bacteria and fungi and ensure germination at a known time and in predictable numbers. Using the ascospores of Neurospora tetrasperma, Goddard (3) and Goddard and Smith (5) investigated this type of activation, paying particular attention to the critical temperature of the activation reaction and to the respiratory interrelations existing among dormant, activated, and germinating spores. A very large increase in the respiratory rate-from tento forty-fold-takes place when dormant spores are subjected to an activating temperature, and this rate doubles when germination occurs, approximately three hours after activation. The respiration of each stage differs qualitatively as well as quantitatively from the other stages as shown by the dissimilarities in inhibition in response to several respiratory poisons. Further, carboxylase activity could not be detected in dormant spores, but was found after heat treatment, suggesting that the activation of this enzyme may be the primary effect of heat which leads to the interruption of the dormant state. Acetaldehyde and ethanol, alone of many substrates tested, were able to induce a large increase in the Qo2 of dormant spores, but this increase was far short of the phenomenally large one accompanying activation; and in fact these substrates did not activate the spore, or at least, did not result in germination. Goddard (3, 4) also demonstrated that activated spores could be returned to the dormant condition by the inhibition of respiration after activation; that they could then be reactivated de novo, and that this sequence could be repeated at least several times. Later Emerson (1) found that furfural is as effective as heat in inducing activation of ascospores of N. crassa, and Mefford and Campbell (7) found that it is also successful in bringing about the germination of spores of a number of thermophilic and heat tolerant bacteria. The way the activation is effected is quite unknown, although Mefford and Campbell suggest that in bacterial spores it may be due to a detoxification of the medium. This would not explain activation in Neurospora where no medium other than distilled water need be involved. Recently Sussman (8) has tested a large number of analogues of furfural, and also many substances of known biological activity, for ability to activate dormant spores or to inhibit activation and growth. The results suggest that only unsaturated, 5-membered heterocyclic compounds are active (diethyl ether showed slight activity), and that many analogues of active substances (particularly those