Biomedical subjects

Anke Steppuhn

Publications and source records attributed to Anke Steppuhn.

3 recordsLinked to original sources

PubMed2004

Nicotine's defensive function in nature.

Plants produce metabolites that directly decrease herbivore performance, and as a consequence, herbivores are selected for resistance to these metabolites. To determine whether these metabolites actually function as defenses requires measuring the performance of plants that are altered only in the production of a certain metabolite. To date, the defensive value of most plant resistance traits has not been demonstrated in nature. We transformed native tobacco(Nicotiana attenuata) with a consensus fragment of its two putrescine N-methyl transferase (pmt) genes in either antisense or inverted-repeat (IRpmt) orientations. Only the latter reduced (by greater than 95%) constitutive and inducible nicotine. With D(4)-nicotinic acid (NA), we demonstrate that silencing pmt inhibits nicotine production, while the excess NA dimerizes to form anatabine. Larvae of the nicotine-adapted herbivore Manduca sexta (tobacco hornworm) grew faster and, like the beetle Diabrotica undecimpunctata, preferred IRpmt plants in choice tests. When planted in their native habitat, IRpmt plants were attacked more frequently and, compared to wild-type plants, lost 3-fold more leaf area from a variety of native herbivores, of which the beet armyworm, Spodoptera exigua, and Trimerotropis spp. grasshoppers caused the most damage. These results provide strong evidence that nicotine functions as an efficient defense in nature and highlights the value of transgenic techniques for ecological research.

Animals↗

PubMed2004

Individual variability in herbivore-specific elicitors from the plant's perspective.

Lepidopteran larvae oral secretions and regurgitant (R), which contain a plethora of potential elicitors, are known to dramatically change a plant's wound response. We demonstrate, with a detailed microarray and secondary metabolite analysis, that the two most abundant fatty acid-amino acid conjugates (FACs) in the R of the specialist herbivore Manduca sexta (Lepidoptera, Sphingidae) can account for all measured direct (trypsin proteinase inhibitor: TPI) and indirect (cis-alpha-bergamotene) defences, the endogenous jasmonic acid burst that elicits them, and 86% of the induced transcriptional changes (89% up and 83% down) in its native host Nicotiana attenuata and hence are necessary and sufficient for the Manduca-specific modulation of the wound response. FACs were not found in eggs, but detected in larvae of all instars after their first meal. FACs were found in all regions of the alimentary canal and in the frass, but did not occur in salivary or mandibular glands, extracts of which were not active in any assay. Individual larvae differed substantially in their FAC composition and two FAC chemotypes were discernible: N-linolenoyl-L-glutamine biased R and N-linolenoyl-L-glutamate biased R. We created synthetic blends of FACs to mimic these chemical phenotypes and determined whether plants respond differently to the different R chemotypes. Micorarray and TPI analysis revealed that plants do not differentiate. N. attenuata plants use FACs from feeding caterpillars to tailor their wound responses but do not use the variability in FAC ratios to recognize attack from an individual caterpillar.

Animals↗

PubMed2003

Specific foraging kairomones used by a generalist parasitoid.

In general, it is assumed that generalist natural enemies do not innately use specific cues for the location of their host or prey species. This hypothesis was tested using naïve females of the generalist parasitoid Lariophagus distinguendus Förster and two of its hosts, larvae of the lesser grain borer Rhyzopertha dominica (F.) and of the granary weevil Sitophilus granarius L., feeding in wheat grains. In a four-chamber olfactometer, female parasitoids were attracted to volatiles emanating from the feces of both host species. Chemical analysis of the volatiles from the feces of R. dominica revealed the presence of dominicalure 1 and 2, the species specific aggregation pheromones of R. dominica. The main compounds in the volatiles from feces of S. granarius were identified as chemicals related to mites that are associated with hosts of L. distinguendus. Because these mites are not specific for S. granarius but also co-occur with other hosts, the mite chemicals have to be considered as general cues. In bioassays, synthetic dominicalure was attractive to naïve L. distinguendus, explaining the attraction of feces volatiles from R. dominica. Synthetic mite chemicals and sitophilate, the aggregation pheromone of S. granarius, had no effect on naïve parasitoids. It remains to be determined which innate chemical cues from feces of S. granarius are used by L. distinguendus. In contrast to our initial hypothesis, the generalist L. distinguendus is innately using specific cues for foraging. Two ideas are provided to explain this result.

Animals↗