1. Institute of Experimental Botany, the Academy of Sciences of the Czech Republic, 165 02 Prague 6, Czech Republic.
2. Department of Plant Physiology, Faculty of Science, Charles University, 128 44 Prague 2, Czech Republic.
3. Center for Plant Molecular Biology (ZMBP), University Tübingen, D-72076 Tübingen, Germany.
4. Zurich-Basel Plant Science Center, University of Zurich, Institute of Plant Biology, CH 8007 Zurich, Switzerland.
5. Department of Horticulture, Purdue University, West Lafayette, IN 47907, USA.