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Rahier, Martine

Nom
Rahier, Martine
Affiliation principale
Fonction
Professeure ordinaire
Email
Martine.Rahier@unine.ch
Identifiants
https://libra.unine.ch/handle/123456789/99

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  • Publication
    Accès libre
    Biochemical strategy of sequestration of pyrrolizidine alkaloids by adults and larvae of chrysomelid leaf beetles
    (Elsevier, 1999)
    Hartmann, Thomas
    ;
    Theuring, Claudine
    ;
    Jürgen Schmidt
    ;
    Rahier, Martine 
    ;
    Pasteels, Jacques M.
    Tracer feeding experiments with 14C-labeled senecionine and senecionine N-oxide were carried out to identify the biochemical mechanisms of pyrrolizidine alkaloid sequestration in the alkaloid-adapted leaf beetle Oreina cacaliae (Chrysomelidae). The taxonomically closely related mint beetle (Chrysolina coerulans) which in its life history never faces pyrrolizidine alkaloids was chosen as a ‘biochemically naive’ control. In C. coerulans 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 O. cacaliae 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 O-glucoside. The following mechanism of alkaloid sequestration in O. cacaliae is suggested to have developed during the evolutionary adaptation of O. cacaliae to its alkaloid containing host plant: (i) suppression of the gut specific reduction of the alkaloid N-oxides, (ii) efficient uptake of the alkaloid N-oxides, and (iii) detoxification of the tertiary alkaloids by O-glucosylation. The biochemical mechanisms of sequestration of pyrrolizidine alkaloid N-oxides in Chysomelidae leaf beetles and Lepidoptera are compared with respect to toxicity, safe storage and defensive role of the alkaloids.
  • Publication
    Accès libre
    Sequestration, Maintenance, and Tissue Distribution of Pyrrolizidine Alkaloid N-Oxides in Larvae of Two Oreina Species
    (1999)
    Ehmke, Adelheid
    ;
    Rahier, Martine 
    ;
    Pasteels, Jacques M.
    ;
    Theuring, Claudine
    ;
    Hartmann, Thomas
    Oreina cacaliae and O. speciosissima are leaf beetles that, as larvae and adults, sequester pyrrolizidine alkaloid N-oxides (PAs) as defensive compounds from their host plants Adenostyles alliariae and Senecio nemorensis. As in most Oreina species, O. speciosissima is also defended by autogenously produced cardenolides (mixed defensive strategy), whereas O. cacaliae does not synthesize cardenolides and is exclusively dependent on host-plant-acquired PAs (host-derived defense). Adults of the two Oreina species were found to have the same PA storage capacity. The larvae, however, differ; larvae of O. speciosissima possess a significantly lower capability to store PAs than O. cacaliae. The ability of Oreina larvae to sequester PAs was studied by using tracer techniques with 14C-labeled senecionine N-oxide. Larvae of the two species efficiently take up [14C]senecionine N-oxide from their food plants and store the alkaloid as N-oxide. In O. cacaliae, there is a slow but continuous loss of labeled senecionine N-oxide. This effect may reflect the equilibrium between continuous PA uptake and excretion, resulting in a time-dependent tracer dilution. No noticeable loss of labeled alkaloid is associated with molting. Senecionine N-oxide is detectable in all tissues. The hemolymph is, with ca. 50–60% of total PAs, the major storage compartment, followed by the integument, with ca 30%. The alkaloid concentration in the hemolymph is approximately sixfold higher than in the solid tissues. The selectivity of PA sequestration in larvae is comparable to PA sequestration in the bodies of adult beetles.
  • Publication
    Accès libre
    Selective sequestration and metabolism of plant derived pyrrolizidine alkaloids by chrysomelid leaf beetles
    (1997)
    Hartmann, Thomas
    ;
    Witte, Ludger
    ;
    Ehmke, Adelheid
    ;
    Theuring, Claudine
    ;
    Rahier, Martine 
    ;
    Pasteels, Jacques M.
    Pyrrolizidine alkaloids (PAs) are assumed to function as plant defence compounds against herbivory. A number of adapted insects are known to sequester plant derived PAs for their own benefit. Here we summarize the chemical interactions between leaf beetles of the genus Oreina (Coleoptera, Chrysomelidae) and their host plants Adenostyles spp., Senecio nemorensis, and S. fuchsii (Asteraceae, tribe Senecioneae). Seneciphylline N-oxide and senecionine N-oxide, the main PAs of Adenostyles, are sequestered in the bodies and exocrine defensive glands of the leaf beetles. The comparison with the PA patterns of the Senecio host plant indicates a selective PA uptake. The uptake into the body (hemolymph) is less specific, whereas the translocation into the defensive glands is highly specific. Only the N-oxides of macrocyclic retronecine esters of the senecionine type are found in significant amounts in the defensive secretions. Many other PAs such as monoesters and open-chain diesters as well as PAs of other structural types (e.g. monocrotaline N-oxide and senkirkine) are not transferred into the defensive glands. Leaf beetles sequester PAs exclusively as N-oxides. A novel PA not found in the food plants was detected in the defensive secretions of Oreina elongata; it was identified as 13,19-expoxisenecionine N-oxide (oreine), the epoxidation product of seneciphylline N-oxide. Besides this transformation, leaf beetles are able to catalyse further transformations such as the O-dealkylation of heliotrine N-oxide to rinderine N-oxide and the O-deacetylation of acetylseneciphylline N-oxide to seneciphylline N-oxide. The plant-beetle interactions are discussed in the functional context of PAs as powerful plant defensive chemicals.
  • Publication
    Accès libre
    Distribution of autogenous and host-derived chemical defenses in Oreina leaf beetles (Coleoptera: Chrysomelidae)
    (1995)
    Pasteels, Jacques M.
    ;
    Dobler, Susanne
    ;
    Rahier, Martine 
    ;
    Ehmke, Adelheid
    ;
    Hartmann, Thomas
    ;
    Pasteels, Jacques M.
    ;
    Dobler, Susanne
    ;
    Ehmke, Adelheid
    ;
    Hartmann, Thomas
    The pronotal and elytral defensive secretions of 10 Oreina species were analyzed. Species feeding on Apiaceae, i.e., O. frigida and O. viridis, or on Cardueae (Asteraceae), i.e., O. bidentata, O. coerulea, and O. virgulata, produce species-specific complex mixtures of autogenous cardenolides. O. melanocephala, which feeds on Doronicum clusii (Senecioneae, Asteraceae), devoid of pyrrolizidine alkaloids (PAs) in its leaves, secretes, at best, traces of cardenolides. Sequestration of host-plant PAs was observed in all the other species when feeding on Senecioneae containing these alkaloids in their leaves. O. cacaliae is the only species that secretes host-derived PA N-oxides and no autogenous cardenolides. Differences were observed in the secretions of specimens collected in various localities, because of local differences in the vegetation. The other species, such as O. elongata, O. intricata, and O. speciosissima, have a mixed defensive strategy and are able both to synthesize de novo cardenolides and to sequester plant PA N-oxides. This allows a great flexibility in defense, especially in O. elongata and O. speciosissima, which feed on both PA and non-PA plants. Populations of these species were found exclusively producing cardenolides, or exclusively sequestering PA N-oxides, or still doing both, depending on the local availability of food-plants. Differences were observed between species in their ability to sequester different plant PA N-oxides and to transform them. Therefore sympatric species demonstrate differences in the composition of their host-derived secretions, also resulting from differences in host-plant preference. Finally, within-population individual differences were observed because of local plant heterogeneity in PAs. To some extent these intrapopulation variations in chemical defense are tempered by mixing diet and by the long-term storage of PA N-oxides in the insect body that are used to refill the defensive glands.
  • Publication
    Accès libre
    Sequestration of plant pyrrolizidine alkaloids by chrysomelid beetles and selective transfer into the defensive secretions
    (1991)
    Rahier, Martine 
    ;
    Witte, Ludger
    ;
    Ehmke, Adelheid
    ;
    Hartmann, Thomas
    ;
    Pasteels, Jacques M.
    Oreina cacaliae and O. speciosissima (Coleoptera, Chrysomelidae) sequester in their elytral and pronotal defensive secretions pyrrolizidine alkaloids (PAs) as Noxides (PA N-oxides). The PA N-oxide patterns found in the beetles and their host plants were evaluated qualitatively and quantitatively by capillary gas chromatography/mass spectrometry (GC-MS). Of the three host plants Adenostyles alliariae (Asteraceae) is the exclusive source for PA N-oxide sequestration in the defensive secretions of the beetles. With the exception of O-acetylseneciphylline the N-oxides of all PAs of A. alliariae, i.e. senecionine, seneciphylline, spartioidine, integerrimine, platyphylline and neoplatyphylline were identified in the secretion. PA N-oxides typical of Senecio fuchsii (Asteraceae) were detected in the bodies of the beetles but not in their secretion. No PAs were found in the leaves of the third host plant, Petasites paradoxus (Asteraceae). The results suggest the existence of two distinctive storage compartments for PA N-oxides in the beetle: (1) the defensive secretion, containing specifically PA N-oxides acquired from A. alliariae; (2) the body of the beetle, sequestering additionally but less selectively PA N-oxides from other sources, e.g. S. fuchsii or monocrotaline N-oxide fed in the laboratory. The concentration of PA N-oxides in the defensive secretion is in the range of 0.1 to 0.3 mol/1, which is more than 2.5 orders of magnitude higher than that found in the body of the beetle. No significant differences exist in the ability of the two species of beetles to sequester PA N-oxides from A. alliariae, although O. speciosissima, but not O. cacaliae, produces autogenous cardenolides. A negative correlation seems to exist between the concentrations of plant-derived PA N-oxides andde novo synthesized cardenolides in the defensive secretion of O. speciosissima.
  • Publication
    Accès libre
    Sequestration of ingested [14C]senecionine N-oxide in the exocrine defensive secretions of chrysomelid beetles
    (1991)
    Ehmke, Adelheid
    ;
    Rahier, Martine 
    ;
    Pasteels, Jacques M.
    ;
    Hartmann, Thomas
    Oreina cacaliae (Chrysomelidae) sequesters in its elytral and pronotal defensive secretion the N-oxides of pyrrolizidine alkaloids (PA N-oxides) from its food plant Adenostyles alliariae (Asteraceae). [14C]Senecionine N-oxide was applied for detailed studies of PA N-oxide sequestration. An average of 11.4% of total radioactivity is taken up by individual beetles which had received [14C]senecionine N-oxide with their food leaves 8 days before. An average of 28.9% of the ingested radioactivity could be recovered from the defensive secretions collected twice, i.e., 5 and 8 days after tracer feeding. The tracer transfer into the secretion seems to be a slow but progressive process as indicated by the high percentage of tracer still recovered from the secretion sampled after 8 days. Chromatographic analysis revealed that [14C]senecionine N-oxide is the only labeled compound in the defensive secretion. Beetles that fed on tertiary [14C]senecionine sequestered only trace amounts of radioactivity (exclusively present as labeled IV-oxide) in their secretions. O. speciosissima, a species also adapted to PA containing food plants, was shown to sequester [14C]senecionine N-oxide with the same efficiency as O. cacaliae. O. bifrons, a specialist feeding on Chaerophyllum hirsutum (Apiaceae), rejected PA treated leaf samples already at very low PA concentrations (10 nmol/leaf piece). In both O. cacaliae and O. speciosissima, [14C]senecionine N-oxide applied by injection into the hemolymph is rapidly transferred into the glands. O. bifrons, not adapted to pyrrolizidine alkaloid containing plants was unable to sequester [14C]-senecionineN- oxide in the secretion but rapidly eliminated the tracer with the frass. Again, only traces of labeled [14C]senecionine N-oxide were found in the defensive secretions of the two PA adapted species if labeled senecionine was injected. It is suggested that the beetles are adapted to the N-oxide form of PAs, similarly as their food plants, and that they lack the ability to efficiently N-oxidize tertiary PAs. No indication forde novo PA synthesis by the beetles was found in tracer feeding experiments with the biogenetic PA precursor putrescine.