  We point out that the pseudo-spin symmetry (PSS) of nuclei significantly
depends on the proton ($Z$) and neutron numbers ($N$), sometimes giving rise to
the characteristic structures. By using the non-relativistic spherical
Hartree-Fock calculation with a realistic tensor force, we show that the tensor
force may be deeply relevant to the $Z$- and $N$-dependence of the PSS. While
the PSS has often been discussed in the context of the relativistic symmetry,
the tensor-force effects on the PSS sometimes look analogous to the $Z$-and
$N$-dependence of the PSS in the relativistic mean-field (RMF) calculations
without explicit tensor force. The observed variation of the
$p0d_{3/2}$-$p1s_{1/2}$ levels from $^{40}$Ca to $^{34}$Si is consistent with
the tensor-force-driven $Z$-dependence of the PSS, but not necessarily with the
RMF result. Even though it is too early to be conclusive, this result
elucidates the significance of the tensor force when discussing the PSS.
