Effect of N2 on the mutagenic and lethal activities of ICR-170 in Neurospora crassa.

The nature of the N2 effect for ICR-170, i.e., the greater mutagenic and lethal activities of this agent in the presence of N2 than O2, has been studied at the ad-3 region of Neurospora crassa. The characteristics of the N2 effect for ICR-170 were that (1) the N2 effect with ICR-170 was displayed in conidia when N2 was administered during, but not before or after, ICR-170 treatment, (2) the highly increased mutagenic and lethal activities of ICR-170 in the presence of N2 were due to an anoxic condition rather than to the presence of N2 per se, (3) the high killing activity of ICR-170 under N2 was due largely to increased cytoplasmic inactivation, (4) the N2 effect was a general phenomenon at the ad-3 region of N. crassa, and (5) the highly ICR-170-induced mutation in conidia under N2 was attributable to an actual enhancement in the mutagenic activity of ICR-170 rather than to selective killing. With regard to the mechanisms of the N2 effect with ICR-170, results indicate that this effect (1) was not due to more extracellular oxidative degradation of ICR-170 molecules in the presence of O2, or to a greater uptake of ICR-170 by conidia under N2, but (2) was due to the inhibition of conidial respiration under an anoxic environment.