1. Institute of Molecular Biology and Biotechnology; Adam Mickiewicz University; Fre Dry 10 Poznañ 61-701 Poland
2. Botanisches Institut; Universität Bonn; Venusbergweg 23 Bonn D-53115 Germany
3. Department of Plant Cell Biology, Institute of Botany; Rheinische-Friedrich-Wilhelms-University of Bonn; Kirschallee 1 Bonn D-53115 Germany