1. Plant Research International, POB 16, 6700 AA Wageningen, the Netherlands;
2. Laboratory for Plant Physiology, Wageningen University, Arboretumlaan 4, 6703 BD Wageningen, the Netherlands;
3. Centre for BioSystems Genomics, POB 98, 6700 AB Wageningen, the Netherlands;
4. Department of Plant Genetics and Breeding, Institute of Plant Field and Garden Crops, The Volcani Center, PO Box 6, Bet Dagan, Israel 50250;
5. Laboratory of Biochemistry, Wageningen University, POB 9101, 6700 HB Wageningen, the Netherlands