  The pseudospin symmetry is a relativistic dynamical symmetry connected with
the small component of the Dirac spinor. The origin of pseudospin symmetry in
single particle bound states in atomic nuclei has been revealed and studied
extensively. By examining the zeros of Jost functions corresponding to the
small components of Dirac wave functions and phase shifts of continuum states,
we show that the pseudospin symmetry in single particle resonant states in
nuclei is conserved when the attractive scalar and repulsive vector potentials
have the same magnitude but opposite sign. The exact conservation and the
breaking of pseudospin symmetry are illustrated for single particle resonances
in spherical square-well and Woods-Saxon potentials.
