1. Centre of Environmental Sciences, Environmental Biology Group, Limburgs Universitair Centrum, Universitaire Campus, B‐3590 Diepenbeek, Belgium;
2. Brookhaven National Laboratory, Biology Department, Building 463, Upton, New York 11973‐5000, USA;
3. Laboratory of Developmental Biology, Institute of Botany and Microbiology, Katholieke Universiteit Leuven, Kasteelpark Arenberg 31, B‐3001 Heverlee, Belgium