For the purposes of this Part, the term “lessor” shall refer to and include the Register of the State Land Office, the commissioner of conservation, and any and all other branches, departments or agencies of the state, or any school district, levee district, drainage district, municipal or parochial subdivision of this state, or any penal or charitable institution, or state university or college, or other unit or institution, deriving its authority and powers from the sovereignty of the state.