1. Department of Plant Physiology, Faculty of Science, Charles University, Viničná 5, 128 44, Prague 2, Czech Republic;
2. Institute of Experimental Botany, Academy of Sciences of the Czech Republic, Na Karlovce 1, 160 00, Prague 6, Czech Republic;
3. School of Biosciences, Cardiff University, PO Box 915, Cardiff CF10 3TL, UK