Distribution of the abundance slopes as a function of the morphological type of the galaxies (left panel), depending on the presence or absence of bars (middle panel) and as a function of the g-band absolute magnitude of the galaxies (right panel). We also show the histograms for each distribution, where N is the number of galaxies and colours indicate the different classification types: (i) early spirals, Sa-Sab (red); intermediate spirals, Sb-Sbc (green); late spirals, Sc-Sm (blue) for the left panel. (ii) Clearly unbarred galaxies (red); clearly barred (blue); an intermediate stage (green) for the middle panel. (iii) Luminous galaxies, M_g−SDSS< −21.25 mag (red); intermediate galaxies, −21.25 <M_g−SDSS< −20.5 mag (green); faint galaxies, M_g−SDSS> −20.5 mag (blue) for the right panel. Black diamonds represent the median values for the distributions, together with the standard deviation shown as error bars.