Beam-averaged column densities (N_X in cm⁻², left), and SO and SiO abundances (right) versus the source internal luminosity (L_int in L_⊙). Molecular abundances are with respect to H₂ on the left axis (assuming [CO]/[H₂] = 10⁻⁴) and with respect to CO on the right axis. The values are inferred for the 12 Class 0 protostars driving an SiO jet detected at > 10σ in the integrated maps (see Table 3) at the position of the closest blue- and red-shifted SiO knots, B and R (filled and empty small diamonds, respectively; see Tables 4 and 5). Black, red, and blue symbols are for CO, SO, and SiO, respectively. Lower and upper limits are indicated by upward and downward arrows. The jet knots where no CO is detected (the “CO-poor” jets) are indicated by larger empty diamonds. For these knots we derive upper limits on N_CO, and lower limits on X_SiO.