  Assuming helicity independence for q-qbar scattering in the color-dipole
picture, or, equivalently proportionality of sea quark and gluon distributions,
we find R(W^2,Q^2) = 0.5 (approximately) at large Q^2, where R(W^2,Q^2) denotes
the ratio of the longitudinal and transverse photoabsorption cross sections.
The forthcoming direct measurements of R(W^2,Q^2) allow one to test the
underlying hypotheses.
