Pyrrolizidine alkaloids between plants and insects: A new chapter of an old story |
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Authors: | Hartmann Thomas |
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Institution: | (1) Institut für Pharmazeutische Biologie, Technische Universität, D-38106 Braunschweig, Germany |
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Abstract: | Summary Among alkaloids the pyrrolizidine alkaloids (PAs) play a unique role in the interactions between plants and adapted insects. InSenecio spp. (Asteraceae) PAs are synthesized in the roots as alkaloidN-oxides which are specifically translocated into shootsvia the phloem-path and channeled to the preferred sites of storage (e.g. inflorescences) where they are stored in the cell vacuoles. In differentSenecio spp. senecionineN-oxide is produced as the common product of biosynthesis, which subsequentlyvia a number of simple but specific reactions is transformed into typical speciesspecific PA-patterns. Insects from diverse taxa sequester PAs for their own defense. Lepidopterans (e.g. arctiids such asTyria jacobaeae andCreatonotos transiens) may hydrolyze plant acquired ester-PAs and convert the resulting necine base into insect-specific PAs by esterification with an acid of their own metabolism. Adapted arctiids and the grasshopperZonocerus take up PAs in the state of the tertiary amine.N-Oxides are reduced in the guts prior to uptake. In the bodies the tertiary PAs are rapidlyN-oxidized by a specific mixed-function oxigenase and are maintained in theN-oxide state. The importance of the reversible interconversion of the nontoxicN-oxide (pro-toxine) into the toxic tertiary alkaloid is discussed as the specific feature of PAs in plant-insect interactions. |
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Keywords: | biochemistry of plants sequestration by insects transformation by insects pyrrolizidine alkaloids alkaloidN-oxides Asteraceae Senecio Lepidoptera Arctiidae Tyria Creatonotos |
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