  We study anomalous Wess-Zumino couplings of D-branes and O-planes in a
general background and derive them from a direct string computation by
factorizing in the RR channel various one-loop amplitudes. In particular, we
find that Op-planes present gravitational anomalous couplings involving the
Hirzebruch polynomial L, similarly to the roof genus A encoding Dp-brane
anomalous couplings. We determine, in each case, the precise dependence of
these couplings on the curvature of the tangent and normal bundles.
