Extragalactic Planetary Nebulae: tracers of the chemical evolution of
  nearby galaxies
  The study of the chemical composition of Planetary Nebulae in external
galaxies is of paramount importance in the fields of stellar evolution and of
the chemical enrichment history of galaxies. In the last years a number of
spectroscopic studies with 6-8m-class telescopes have been devoted to this
subject improving our knowledge of, among other, the time-evolution of the
radial metallicity gradient in disk galaxies, the chemical evolution of dwarf
galaxies, and the stellar evolution at low metallicity.
