After the issuance of the bonds authorized by former Act No. 76 of the Public Acts of 1968 or this part, or any series of the bonds, the legislature shall each year make appropriations fully sufficient to pay promptly when due the principal of and interest on all outstanding bonds authorized by former Act No. 76 of the Public Acts of 1968 or this part and all costs incidental to the payment of that principal and interest.
MCL 324.4510