1. Isotope Laboratory, Institute of Experimental Botany, Academy of Sciences of the Czech Republic (AS CR), Vídeňská 1083, 142 20 Prague 4, Czech Republic
2. Laboratory of Growth Regulators, Centre of the Region Haná for Biotechnological and Medicinal Research, Institute of Experimental Botany AS CR & Palacky University, Slechtitelu 11, Olomouc 783 71, Czech Republic