The breaking of the dormancy of Neurospora ascospores results in a 20-to 30-fold increase in their respiratory rate (5, 6). Germination can be induced by means of a heat-shock at 600 C for 10 to 30 minutes as (lescribed by Shear and Dodge (17) and Goddard (5). In addition, treatment with very low concentrations of furfural (2) and related heterocyclics (22) have also proven to be effective, as have high concentrations of aliphatic alcohols, esters and ketones (26).Two general types of explanation of the activation process have been offered, including those relating the effect to changes in permeability and those which propose a metabolic explanation. A change in permeability is probably not directly responsible for acconmplishing the activation of these ascospores because they (1o not require exogenous nutrients (23) nor (1o they respond to increased concentrations of oxygen (6). Furthermore, unpublished experiments in this laboratory have suggested that permeability to water is not a factor so that our attention has been concentrate(l upon an explanation based upoln a metabolic control mechanism.As a preliminary to an investigatioln of the enzynmatic changes which ensue upon activation, a study of the substrates which are usedlduring this time was un(lertaken. Previous work has shown that substrates provi(led exogenously are not utilized by dormant and newly activated ascospores (23,25)
The anthrone-positive material extractable in 80 percent alcohol, whose disappearance is correlated with the breaking of dormancy, has been found to be a non-reducing sugar which yields only glucose upon hydrolysis. On the basis of its crystal structure, infrared spectrum, melting point, specific rotation, and chromatographic properties, this material has been identified as trehalose.
The extent to which trehalose is accumulated in the vegetative mycelium of strains of Neurospora crassa is significantly affected by conidiation. In heavily conidiating strains a rapid decrease in mycelial trehalose occurs following the initiation of conidiation. Meanwhile, trehalase activity in the vegetative mycelium of heavily conidiating strains increases rapidly following the initiation of conidiation, although apparently it is not directly caused by the sporulation process. High levels of both trehalase and trehalose appear concomitantly in the newly formed conidia.
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