Integrable hierarchies of nonlinear difference-difference equations and symmetries

We construct the hierarchy of nonlinear difference-difference equations associated with the discrete Schrodinger spectral problem. As examples of equations contained in this hierarchy we obtain the discrete-time Toda and Volterra lattice equations. In the case of the time-discrete Toda lattice, we construct its Lie point and generalized symmetries. Finally, we present its Backlund transformations and relate it to the already constructed symmetries.