1. Botanical Institute and Cluster of Excellence on Plant Sciences (CEPLAS), Cologne Biocenter, University of Cologne, D-50674 Cologne, Germany
2. Plant Physiology, Technical University of Kaiserslautern, D-67653 Kaiserslautern, Germany
3. Max Planck Institute for Plant Breeding Research, D-50829 Cologne, Germany
4. Plant Physiology and Biotechnology, University of Hohenheim, D-70593 Stuttgart, Germany