The present invention relates to polypeptides, and polynucleotides encoding therefor, which influence seed dormancy in cereals such as wheat and barley. In particular, the present invention relates to polypeptides with ABA 8'-hydroxylase activity, and polynucleotides encoding these proteins. Also provided are cereal plants which produce seeds that have altered rates of germination, and/or levels of dormancy, when compared to seeds from wild-type plants, as well as methods of producing such plants.