  The recognition that the metallicity of Type Ia supernova (SNIa) progenitors
might bias their use for cosmological applications has led to an increasing
interest in its role on the shaping of SNIa light curves. We explore the
sensitivity of the synthesized mass of 56Ni, M(56Ni), to the progenitor
metallicity starting from Pre-Main Sequence models with masses M0 = 2 - 7 M_sun
and metallicities Z = 1e-5 - 0.10. The interplay between convective mixing and
carbon burning during the simmering phase eventually rises the neutron excess
and leads to a smaller 56Ni yield, but does not change substantially the
dependence of M(56Ni) on Z. Uncertain attributes of the WD, like the central
density, have a minor effect on M(56Ni). Our main results are: 1) a sizable
amount of 56 Ni is synthesized during incomplete Si-burning, which leads to a
stronger dependence of M(56Ni) on Z than obtained by assuming that 56Ni is
produced in material that burns fully to nuclear statistical equilibrium; 2) in
one-dimensional delayed detonation simulations a composition dependence of the
deflagration-to-detonation transition density gives a non-linear relationship
between M(56Ni) and Z, and predicts a luminosity larger than previously thought
at low metallicities (however, the progenitor metallicity alone cannot explain
the whole observational scatter of SNIa luminosities), and 3) an accurate
measurement of the slope of the Hubble residuals vs metallicity for a large
enough data set of SNIa might give clues to the physics of
deflagration-to-detonation transition in thermonuclear explosions.
