Mitochondrial membrane potential and ageing in Podospora anserina

Some filamentous fungi exhibit a limited vegetative growth with modificatio ns in the mitochondria, suggesting the involvement of mitochondria in the p rocess of ageing. Nevertheless, the relationship between the ability to gro w or the fate of these cells relative to their mitochondrial membrane poten tial (Psi (mt)) level has not been investigated. Using flow cytometric anal ysis, we have assessed Psi (mt) in young and senescent cultures of wild typ e strains and mitochondrial or nuclear mutant strains of Podospora anserina that present very long or brief life span. When we compared two distinct p opulations of cells obtained from the same strain. we can show a correlatio n not only between Psi (mt) and ageing, but also between Psi (mt) and the f requency of regeneration and/or the life span. However, this relationship i s not observed when we compared the cells obtained from different physiolog ical states or mutants strains. These results allow us to suggest that the Psi (mt) modifications juring senescence could be only one of the possible consequences of the process and are not the factor driving towards death. W e also show that the driving force of Psi (mt) is principally maintained by the alternative pathway during ageing, suggesting a role of the alternativ e oxidase pathway. (C) 2001 Elsevier Science Ireland Ltd. All rights: reser ved.