Limnological Institute, University of Konstanz, D-78457 Konstanz, Germany.
Submersed growing freshwater angiosperms may produce bioactive secondary metabolites with multiple functions to obstruct tissue loss due to herbivory and prevent shading by algae and cyanobacteria. Studies by Wium-Andersen et al. had shown that cyclic sulfur compounds in another freshwater macrophyte (Chara sp.) exhibit both algicidal and insecticidal activity. Myriophyllum spicatum L. (Haloragaceae) is a highly competitive freshwater angiosperm growing at a water depth of 1-5 m in meso- to eutrophic lakes. This macrophyte contains about 6-10% (w/w) hydrolyzable polyphenols (HPPs) which are also released into the water. The major HPP is Tellimagrandin II (T-II), present at 0.2-1.5% (w/w). The production of HPPs in M. spicatum is influenced by light and nitrogen availability. T-II exerts strong algicidal activity against cyanobacteria and algae, exhibiting little specificity for one single group of organisms. Interference with alkaline phosphatase, an important algal exoenzyme, is a predominant mode of action of this inhibitor. Since hydrolyzable polyphenols may deter herbivores and exert antimicrobial activity, we are currently investigating the effect of M. spicatum derived HPP on aquatic insect herbivores, e.g., Acentria ephemerella (Lepidoptera) and its gut microorganisms.