On the behaviour of root elements in modular representations of symplectic groups

For the algebraic groups of type $C_n$, $n\ge 2$, in characteristic $p>2$ the Jordan block structure of images of long root elements in irreducible $p$-restricted representations with highest weights $m_1\omega_1+\ldots+m_n\omega_n$ and $m_{n-1}<p-1$ is described.