Planetary nebulae and H ii regions in the spiral galaxy NGC 300 - Clues on the evolution of abundance gradients and on AGB nucleosynthesisG. Stasińska, M. Peña, F. Bresolin and Y. G. TsamisA&A, 552 (2013) A12DOI: https://doi.org/10.1051/0004-6361/201220345