1. IACR-Long Ashton Research Station, Department of Agricultural Sciences, University of Bristol, Long Ashton, Bristol BS41 9AF, UK.
2. Present address: Department of Biochemistry and Nutrition, Seltofts Plads, Technical University of Denmark, Building 224, 2800 Lyngby, Denmark.
3. Corresponding author. Phone: +44 (0)1275 392181. E-mail: peter.shewry@bbsrc.ac.uk