1. School of Biological Sciences Royal Holloway University of London Egham TW20 0EX UK
2. Department of Biology, Botany University of Osnabrück Barbarastraße 11 D‐49076 Osnabrück Germany
3. Laboratory of Growth Regulators Centre of the Region Haná for Biotechnological and Agricultural Research Institute of Experimental Botany Academy of Sciences of the Czech Republic Palacký University 78371 Olomouc Czech Republic