Restriction theorems for homogeneous bundles

We prove that for an irreducible representation $tau:GL(n)to GL(W)$, the associated homogeneous ${bf P}_k^n$-vector bundle $W_{tau}$ is strongly semistable when restricted to any smooth quadric or to any smooth cubic in ${bf P}_k^n$, where $k$ is an algebraically closed field of characteristic $ eq 2,3$ respectively. In particular $W_{tau}$ is semistable when restricted to general hypersurfaces of degree $geq 2$ and is strongly semistable when restricted to the $k$-generic hypersurface of degree $geq 2$.