1 Institute for Molecular Biosciences, Molecular Cell Biology of Plants, Goethe University Frankfurt, Frankfurt, Germany. fragkost@bio.uni-frankfurt.de.
2 Volcani Center, Plant Sciences Institute, Agricultural Research Organization, Rishon LeZion, Israel.
3 Laboratory of Pollen Biology, Institute of Experimental Botany of the Czech Academy of Sciences, Prague, Czech Republic.
4 Department of Experimental Plant Biology, Faculty of Science, Charles University, Prague, Czech Republic.