The Role of Trehalose in the Activation of Dormant Ascospores of Neurospora

Publisher Website
Google Scholar
Abstract
Dormant ascospores of Neurospora remain quiescent and metabolize at a slow rate unless activated by exposure to high temperatures or to chemicals, including certain furans, pyrroles, thiophenes, or organic solvents. As a result of this treatment, a stepwise series of changes is initiated, resulting in a greatly increased respiratory rate, a loss in thermal resistance, and a rise in the respiratory quotient. Up to 30 minutes after dormancy is broken, deactivation by incubation at 4[degree]C is possible, but after this time the process is irreversible. The locus of the metabolic activation has been shown not to reside in the cytochrome system and probably not in terminal oxidation. Moreover, pyruvate carboxylase, as well as the steps leading to oxygen, are probably not directly affected by the activation reaction, although there is evidence for an increase in the amount of cytochrome c available to the respiratory apparatus after activation. A study of the endogenous substrates of ascospores reveals that the carbohydrate fraction that is soluble in 80% ethanol is not utilized until immediately after heat-activation, and its gradual disappearance can be correlated with the respiratory changes which accompany the germination process. This fraction consists mainly of trehalose, which has been identified on the basis of an analysis of crystalline material obtained from dormant ascospores. A hypothesis is proposed suggesting that the activation process in Neurospora ascospores consists in the induction of an enzyme system through which trehalose is metabolized, whereas the dormant cell is restricted to a diet of endogenous lipids.