Polyamine toxicity in Neurospora crassa: protective role of the vacuole.

We used mutant strains of Neurospora crassa to define the discretionary capacity of this species for excess putrescine. The spe-3 mutant, which accumulates putrescine internally, and the puu-1 mutant, which accumulates toxic levels of putrescine from the medium, both sequestered large excesses of putrescine in vacuoles. Concomitantly in puu-1, inorganic polyphosphate increased modestly and some of the monovalent cation of the vacuole was discharged. These two factors contribute to the increased capacity for polyamines in this fungus. Putrescine, however, can exceed the capacity of vacuoles such that they no longer protect the cytosol from toxic levels of the amine. The puu-1 mutant illustrates the importance of the sequestration of intracellular polyamines, as well as the control of polyamine uptake through the cell membrane.