1. Limnological Institute, University of Konstanz, 78457 Konstanz, Germany, Novartis Pharma AG, Preclinical Research, CH-4002 Basel, Switzerland, Institute of Organic Chemistry, University of Konstanz, 78457 Konstanz, Germany, and Limnological Station, Institute of Plant Biology, University of Zürich, Seestrasse 187, 8802 Kilchberg, Switzerland