1. Laboratory of Plant Biochemistry and Physiology, Department of Biology, University of Antwerp (UA), B−2610 Antwerp, Belgium;
2. Department of Plant Systems Biology, University of Ghent (RUG), B−9000 Ghent, Belgium;
3. Present address: Crop Design, Technologiepark 3, B−9052 Zwijnaarde, Belgium;
4. Laboratory of Horticulture and Plant Biotechnology, Department of Plant Production, University of Ghent (RUG), B−9000 Ghent, Belgium;
5. Present address: Laboratory of Plant Genetics, Department of Experimental Botany, University of Nijmegen (KUN), Toernooiveld 1, NL−6525 ED Nijmegen, The Netherlands