  Polarization phenomena are essential for the understanding of elementary
processes, and are typically large in the threshold region. The selection rules
with respect to P-parity, angular momentum, isotopic spin and the Pauli
principle allow to parametrize in a model independent way, the spin structure
of the matrix elements for the near-threshold heavy meson production in
NN-collisions in terms of a small number of partial amplitudes. Such
parametrization is very powerful for the analysis of polarization phenomena and
possible $t-$exchange mechanisms.
