  We study X-ray to K-band luminosity ratios (L_X/L_K) of late-type galaxies in
the 0.3-0.7 keV energy range. From the Chandra archive, we selected nine spiral
and three irregular galaxies with point source detection sensitivity better
than 5 x 10^36 erg/s in order to minimize the contribution of unresolved X-ray
binaries. In late-type galaxies cold gas and dust may cause significant
interstellar absorption, therefore we also demanded the existence of publicly
available HI maps. The obtained L_X/L_K ratios vary between (5.4-68) x 10^27
erg/s/L_K,sun exceeding by factor of 2-20 the values obtained for gas-poor
early-type galaxies. Based on these results we constrain the role of supersoft
X-ray sources as progenitors of type Ia supernovae (SNe Ia). For majority of
galaxies the upper limits range from ~3% to ~15% of the SN Ia frequency
inferred from K-band luminosity, but for a few of them no meaningful
constraints can be placed. On a more detailed level, we study individual
structural components of spiral galaxies: bulge and disk, and, for grand design
spiral galaxies, arm and interarm regions.
