1. School of Biological Sciences, Stopford Building, University of Manchester, Manchester M13 9PT, UK1
2. Centre for Phytotechnology, Institute for Molecular Plant Sciences, Clusius Laboratory, Wassenaarseweg 64, 2333 Al Leiden, The Netherlands2
3. Department of Genetics and Microbiology, Institute of Food Research, Norwich Laboratory, Norwich Research Park, Colney, Norwich NR4 7UA, UK3
4. Department of Cell Biology, John Innes Centre, Colney Lane, Norwich NR4 7UH, UK5
5. TNO Nutrition and Food Research Institute, Department of Molecular Genetics and Gene Technology, Utrechtseweg 48, PO Box 360, 3700 AJ Zeist, The Netherlands4