Quench correction of incorporation carbon-14 in Aspergillus nidulans counted on filter discs

Abstract

We have developed a convenient method for 14C quench correction for Aspergillus nidulans counted in liquid scintillator using disc technique. By comparing intact and solubilized samples labelled to constant specific activity, a quench correction factor (QCF) was obtained for a range sample sizes. Large differences, in quenching, including sample self-absorption, were found amongst ungerminated conidiospores and mycelia of different ages and also amongst strains of different genotypes. The sample channels ratio (SCR) method of quench correction was shown to be inadequate (even for extremely low weights of conidiospores and mycelia). The correlation between sample dry weight and sample channels ratio of standards, once established, can adapted to form a convenient means of determining sample size, and hence specific activity, by counting alone. As a cautionary example, a study of d-glucose uptake by conidiospores and mycelia of wild-type and certain carbon catabolite derepressed mutants is presented. Whereas the uncorrected data suggest an uptake defect in the mutants, no such deficiency is apparent after applying QCF. This method should be suitable for other fungi and for other low energy β-emitting nuclides.