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Biochemical strategy of sequestration of pyrrolizidine alkaloids by adults and larvae of chrysomelid leaf beetles
Auteur(s)
Hartmann, Thomas
Theuring, Claudine
Jürgen Schmidt
Pasteels, Jacques M.
Maison d'édition
Elsevier
Date de parution
1999
In
Journal of Insect Physiology
Vol.
45
No
12
De la page
1085
A la page
1095
Résumé
Tracer feeding experiments with <sup>14</sup>C-labeled senecionine and senecionine N-oxide were carried out to identify the biochemical mechanisms of pyrrolizidine alkaloid sequestration in the alkaloid-adapted leaf beetle <i>Oreina cacaliae</i> (Chrysomelidae). The taxonomically closely related mint beetle (<i>Chrysolina coerulans</i>) which in its life history never faces pyrrolizidine alkaloids was chosen as a ‘biochemically naive’ control. In <i>C. coerulans</i> ingestion of the two tracers resulted in a transient occurrence of low levels of radioactivity in the hemolymph (1–5% of radioactivity fed). With both tracers, up to 90% of the radioactivity recovered from the hemolymph was senecionine. This indicates reduction of the alkaloid N-oxide in the gut. Adults and larvae of <i>O. cacaliae</i> sequester ingested senecionine N-oxide almost unchanged in their bodies (up to 95% of sequestered total radioactivity), whereas the tertiary alkaloid is converted into a polar metabolite (up to 90% of total sequestered radioactivity). This polar metabolite, which accumulates in the hemolymph and body, was identified by LC/MS analysis as an alkaloid glycoside, most likely senecionine <i>O</i>-glucoside. The following mechanism of alkaloid sequestration in <i>O. cacaliae</i> is suggested to have developed during the evolutionary adaptation of <i>O. cacaliae</i> to its alkaloid containing host plant: (i) suppression of the gut specific reduction of the alkaloid <i>N</i>-oxides, (ii) efficient uptake of the alkaloid <i>N</i>-oxides, and (iii) detoxification of the tertiary alkaloids by <i>O</i>-glucosylation. The biochemical mechanisms of sequestration of pyrrolizidine alkaloid <i>N</i>-oxides in Chysomelidae leaf beetles and Lepidoptera are compared with respect to toxicity, safe storage and defensive role of the alkaloids.
Identifiants
Type de publication
journal article
