  We calculate the scalar, axial, and pseudoscalar charges of the quark in the
Schwinger-Dyson formalism of Landau gauge QCD. It is found that the dressed
quark scalar density of the valence quark is significantly enhanced against the
bare quark contribution, and the result explains qualitatively the
phenomenologically known value of the pion-nucleon sigma term and also that
given by lattice QCD. Moreover, we show that the Richardson's interquark
potential suppresses the quark scalar density in the Higashjima-Miransky
approximation. This fact suggests that the quark scalar density is an
observable that is sensitive to quark confinement. For the quark axial charge,
we find that it is suppressed due to the gluon dynamics. The result of the
quenched analysis agrees qualitatively with the experimental data of the
isovector axial coupling constant $g_A$. We show that the suppression of the
quenched axial charge is due to a mechanism similar to that of the quark tensor
charge. In the Schwinger-Dyson equation with the leading unquenching quark-loop
contribution the quark axial charge is more suppressed, due to the anomaly
effect. The quark pseudoscalar density is found to be large, and is divergent
as the bare quark becomes massless. This result is in agreement with the
phenomenological current algebraic analysis, and explains well the dominance of
the pion-pole contribution.
