Pyrrolizidine alkaloids and pentacyclic triterpene saponins in the defensive secretions of Platyphora leaf beetles |
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Authors: | Jacques M Pasteels Arnaud Termonia Donald M Windsor Ludger Witte Claudine Theuring Thomas Hartmann |
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Institution: | Laboratory of Animal and Cellular Biology, P.O. Box 160/12, University of Brussels, 50 Av. F.D. Roosevelt, 1050 Brussels, Belgium, e-mail: jmpastee@ulb.ac.be, BE Smithsonian Tropical Research Institute, Apartado 2072, Balboa-Ancon, Panama, PA Institut für Pharmazeutische Biologie der Technischen Universit?t Braunschweig, Mendelssohnstrasse 1, 38106 Braunschweig, Germany, e-mail: t.hartmann@tu-bs.de, DE
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Abstract: | Summary. Field collected exocrine defensive secretions of nine neotropical Platyphora species were analyzed for the presence of plant acquired pyrrolizidine alkaloids (PAs) and pentacyclic triterpene saponins.
All species secrete saponins. In addition, five species feeding on Tournefortia (Boraginaceae), Koanophyllon (Asteraceae, tribe Eupatorieae) and Prestonia (Apocynaceae) were shown to sequester PAs of the lycopsamine type, which are characteristic for species of the three plant
families. The PA sequestering species commonly store intermedine, lycopsamine and their O3′-acetyl or propionyl esters as well as O7- and O9-hydroxyisovaleryl esters of retronecine. The latter as well as the O3′-acyl esters were not found in the beetles’ host plants, suggesting the ability of the beetles to esterify plant derived retronecine
and intermedine or its stereoisomers. Despite the conformity of the beetles’ PA patterns, considerable inconsistencies exist
regarding the PA patterns of the respective host plants. One host plant was devoid of PAs, while another contained only simple
necines. Since the previous history of the field collected beetles was unknown this discrepancy remains obscure. In contrast
to the Palearctic chrysomeline leaf beetles, e.g. some Oreina species which ingest and store PAs as their non-toxic N-oxides, Platyphora leaf beetles absorb and store PAs as the toxic free base (tertiary PA), but apparently avoid to accumulate PAs in the haemolymph.
This suggests that Chrysolina and Platyphora leaf beetles developed different lines of adaptations in their parallel evolution of PA mediated chemical defense.
Received 30 November 2000; accepted 5 February 2001 |
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Keywords: | , Alkaloid sequestration –, chemical defense –, Platyphora leaf beetles –, pyrrolizidine alkaloids –, triterpene saponins |
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