1. Institute of Pharmaceutical Biology, University of Bonn, Nussallee 6, D-53115 Bonn, Germany; Federal Centre for Breeding Research on Cultivated Plants, Institute of Plant Analysis, Neuer Weg 22/23, D-06484 Quedlinburg, Germany; and Institute for Pharmaceutical Chemistry, University of Marburg, Marbacher Weg 6, D-35032 Marburg, Germany