Ala. Code § 22-3A-13

The bonds and the income therefrom shall be exempt from all taxation in the state. Any of the bonds may be used by the holder thereof as security for the deposit of any funds belonging to the state or to any instrumentality or agency of the state in any instance where security for such deposits may be required. Unless otherwise directed by the court having jurisdiction thereof, or by the document that is the source of authority, a trustee, executor, administrator, guardian, or one acting in any other fiduciary capacity may, in addition to any other investment powers conferred and with the exercise of reasonable business prudence, invest trust funds in any of the bonds.