1. Laboratory for Plant Genetics; Free University of Brussels; Paardenstraat 65 B1640 Sint-Genesius-Rode Belgium
2. Laboratoire de Biologie Cellulaire; Université de Bordeaux II; Avenue des Facultés 33405 Talence France
3. Kansas State University; Throckmorton Hall Manhattan Kansas 66506 USA
4. Department of Botany; University of Nottingham; Nottingham NG7 2RD UK
5. Academy of Sciences of Ukrainian SSR; Institute of Botany; Repina 2 252601, Kiev-GSP-1 USSR