Cell Death and 'Unbalanced Growth' in Neurospora

Abstract

Mutant spores of Neurospora crassa incubated on minimal medium showed two main types of behaviour. One mutant type survived incubation for a week on minimal medium and then responded to the addition of growth substance. The second mutant type died after incubation for one or two days. Strains which died were characterized by an ability to germinate in minimal medium and to begin immediately synthetic processes such as the synthesis of protein and nucleic acid. Addition of ethionine to minimal medium prolonged the survival of strains which committed ‘suicide’. Non-germinated Neurospora conidia withstood freezing and storage at -10° for extended periods, whereas conidia which had been incubated in growth medium died, indicating a difference between dormant and synthetically active spores in their response to the environment. The suicide phenomenon is reminiscent of the cell death due to ‘unbalanced growth’ reported for the thymine-requiring mutant of Escherichia coli. In this case, however, cells requiring substances other than nucleic acid constituents display the effect.