  The elastic backward proton-deuteron scattering is analyzed within a
covariant approach based on the Bethe-Salpeter equation with realistic
meson-exchange interaction. Contributions of the one-nucleon and one-pion
exchange mechanisms to the cross section and polarization observables are
investigated in explicit form. Results of numerical calculations for the cross
section, tensor analyzing power and spin transfers are presented. The one-pion
exchange contribution is essential for describing the spin averaged cross
section, while in polarization observables it is found to be less important.
