  We discuss basic properties of the Baecklund transformations for the
classical string in AdS space in the context of the null-surface perturbation
theory. We explain the relation between the Baecklund transformations and the
energy shift of the dual field theory state. We show that the Baecklund
transformations can be represented as a finite-time evolution generated by a
special linear combination of the Pohlmeyer charges. This is a manifestation of
the general property of Baecklund transformations known as spectrality. We also
discuss the plane wave limit.
