Plant defense against insect herbivores

Plants have been interacting with insects for several hundred million years, leading to complex defense approaches against various insect feeding strategies. Some defenses are constitutive while others are induced, although the insecticidal defense compound or protein classes are often similar. Insect herbivory induce several internal signals from the wounded tissues, including calcium ion fluxes, phosphorylation cascades and systemic- and jasmonate signaling. These are perceived in undamaged tissues, which thereafter reinforce their defense by producing different, mostly low molecular weight, defense compounds. These bioactive specialized plant defense compounds may repel or intoxicate insects, while defense proteins often interfere with their digestion. Volatiles are released upon herbivory to repel herbivores, attract predators or for communication between leaves or plants, and to induce defense responses. Plants also apply morphological features like waxes, trichomes and latices to make the feeding more difficult for the insects. Extrafloral nectar, food bodies and nesting or refuge sites are produced to accommodate and feed the predators of the herbivores. Meanwhile, herbivorous insects have adapted to resist plant defenses, and in some cases even sequester the compounds and reuse them in their own defense. Both plant defense and insect adaptation involve metabolic costs, so most plant-insect interactions reach a stand-off, where both host and herbivore survive although their development is suboptimal

No evidence of quantitative signal honesty across species of aposematic burnet moths (Lepidoptera: Zygaenidae)

This is the author accepted manuscript. The final version is available from Wiley via the DOI in this record.Many defended species use conspicuous visual warning signals to deter potential predators from attacking. Traditional theory holds that these signals should converge on similar forms, yet variation in visual traits and the levels of defensive chemicals is common, both within and between species. It is currently unclear how the strength of signals and potency of defences might be related: conflicting theories suggest that aposematic signals should be quantitatively honest, or, in contrast, that investment in one component should be prioritised over the other, while empirical tests have yielded contrasting results. Here, we advance this debate by examining the relationship between defensive chemicals and signal properties in a family of aposematic Lepidoptera, accounting for phylogenetic relationships and quantifying coloration from the perspective of relevant predators. We test for correlations between toxin levels and measures of wing colour across 14 species of day-flying burnet and forester moths (Lepidoptera: Zygaenidae), protected by highly aversive cyanogenic glucosides, and find no clear evidence of quantitative signal honesty. Significant relationships between toxin levels and coloration vary between sexes and sampling years, and several trends run contrary to expectations for signal honesty. Although toxin concentration is positively correlated with increasing luminance contrast in forewing pattern in one year, higher toxin levels are also associated with paler and less chromatically salient markings, at least in females, in another year. Our study also serves to highlight important factors, including sex-specific trends and seasonal variation, that should be accounted for in future work on signal honesty in aposematic species.The authors were funded by the BBSRC (SWBio DTP studentship, ref. 1355867) and Danish Council for Independent Research (DFF–1323-00088)

Cyanogenesis in Arthropods: From Chemical Warfare to Nuptial Gifts.

Chemical defences are key components in insect⁻plant interactions, as insects continuously learn to overcome plant defence systems by, e.g., detoxification, excretion or sequestration. Cyanogenic glucosides are natural products widespread in the plant kingdom, and also known to be present in arthropods. They are stabilised by a glucoside linkage, which is hydrolysed by the action of β-glucosidase enzymes, resulting in the release of toxic hydrogen cyanide and deterrent aldehydes or ketones. Such a binary system of components that are chemically inert when spatially separated provides an immediate defence against predators that cause tissue damage. Further roles in nitrogen metabolism and inter- and intraspecific communication has also been suggested for cyanogenic glucosides. In arthropods, cyanogenic glucosides are found in millipedes, centipedes, mites, beetles and bugs, and particularly within butterflies and moths. Cyanogenic glucosides may be even more widespread since many arthropod taxa have not yet been analysed for the presence of this class of natural products. In many instances, arthropods sequester cyanogenic glucosides or their precursors from food plants, thereby avoiding the demand for de novo biosynthesis and minimising the energy spent for defence. Nevertheless, several species of butterflies, moths and millipedes have been shown to biosynthesise cyanogenic glucosides de novo, and even more species have been hypothesised to do so. As for higher plant species, the specific steps in the pathway is catalysed by three enzymes, two cytochromes P450, a glycosyl transferase, and a general P450 oxidoreductase providing electrons to the P450s. The pathway for biosynthesis of cyanogenic glucosides in arthropods has most likely been assembled by recruitment of enzymes, which could most easily be adapted to acquire the required catalytic properties for manufacturing these compounds. The scattered phylogenetic distribution of cyanogenic glucosides in arthropods indicates that the ability to biosynthesise this class of natural products has evolved independently several times. This is corroborated by the characterised enzymes from the pathway in moths and millipedes. Since the biosynthetic pathway is hypothesised to have evolved convergently in plants as well, this would suggest that there is only one universal series of unique intermediates by which amino acids are efficiently converted into CNglcs in different Kingdoms of Life. For arthropods to handle ingestion of cyanogenic glucosides, an effective detoxification system is required. In butterflies and moths, hydrogen cyanide released from hydrolysis of cyanogenic glucosides is mainly detoxified by β-cyanoalanine synthase, while other arthropods use the enzyme rhodanese. The storage of cyanogenic glucosides and spatially separated hydrolytic enzymes (β-glucosidases and α-hydroxynitrile lyases) are important for an effective hydrogen cyanide release for defensive purposes. Accordingly, such hydrolytic enzymes are also present in many cyanogenic arthropods, and spatial separation has been shown in a few species. Although much knowledge regarding presence, biosynthesis, hydrolysis and detoxification of cyanogenic glucosides in arthropods has emerged in recent years, many exciting unanswered questions remain regarding the distribution, roles apart from defence, and convergent evolution of the metabolic pathways involved

The multiple strategies of an insect herbivore to overcome plant cyanogenic glucoside defence

Cyanogenic glucosides (CNglcs) are widespread plant defence compounds that release toxic hydrogen cyanide by plant β-glucosidase activity after tissue damage. Specialised insect herbivores have evolved counter strategies and some sequester CNglcs, but the underlying mechanisms to keep CNglcs intact during feeding and digestion are unknown. We show that CNglc-sequestering Zygaena filipendulae larvae combine behavioural, morphological, physiological and biochemical strategies at different time points during feeding and digestion to avoid toxic hydrolysis of the CNglcs present in their Lotus food plant, i.e. cyanogenesis. We found that a high feeding rate limits the time for plant β-glucosidases to hydrolyse CNglcs. Larvae performed leaf-snipping, a minimal disruptive feeding mode that prevents mixing of plant β-glucosidases and CNglcs. Saliva extracts did not inhibit plant cyanogenesis. However, a highly alkaline midgut lumen inhibited the activity of ingested plant β-glucosidases significantly. Moreover, insect β-glucosidases from the saliva and gut tissue did not hydrolyse the CNglcs present in Lotus. The strategies disclosed may also be used by other insect species to overcome CNglc-based plant defence and to sequester these compounds intact

454 pyrosequencing based transcriptome analysis of Zygaena filipendulae with focus on genes involved in biosynthesis of cyanogenic glucosides

<p>Abstract</p> <p>Background</p> <p>An essential driving component in the co-evolution of plants and insects is the ability to produce and handle bioactive compounds. Plants produce bioactive natural products for defense, but some insects detoxify and/or sequester the compounds, opening up for new niches with fewer competitors. To study the molecular mechanism behind the co-adaption in plant-insect interactions, we have investigated the interactions between <it>Lotus corniculatus </it>and <it>Zygaena filipendulae</it>. They both contain cyanogenic glucosides which liberate toxic hydrogen cyanide upon breakdown. Moths belonging to the <it>Zygaena </it>family are the only insects known, able to carry out both <it>de novo </it>biosynthesis and sequestration of the same cyanogenic glucosides as those from their feed plants. The biosynthetic pathway for cyanogenic glucoside biosynthesis in <it>Z. filipendulae </it>proceeds using the same intermediates as in the well known pathway from plants, but none of the enzymes responsible have been identified. A genomics strategy founded on 454 pyrosequencing of the <it>Z. filipendulae </it>transcriptome was undertaken to identify some of these enzymes in <it>Z. filipendulae</it>.</p> <p>Results</p> <p>Comparisons of the <it>Z. filipendulae </it>transcriptome with the sequenced genomes of <it>Bombyx mori</it>, <it>Drosophila melanogaster</it>, <it>Tribolium castaneum</it>, <it>Apis mellifera </it>and <it>Anopheles gambiae </it>indicate a high coverage of the <it>Z. filipendulae </it>transcriptome. 11% of the <it>Z. filipendulae </it>transcriptome sequences were assigned to Gene Ontology categories. Candidate genes for enzymes functioning in the biosynthesis of cyanogenic glucosides (cytochrome P450 and family 1 glycosyltransferases) were identified based on sequence length, number of copies and presence/absence of close homologs in <it>D. melanogaster</it>, <it>B. mori </it>and the cyanogenic butterfly <it>Heliconius</it>. Examination of biased codon usage, GC content and selection on gene candidates support the notion of cyanogenesis as an "old" trait within Ditrysia, as well as its origins being convergent between plants and insects.</p> <p>Conclusion</p> <p>Pyrosequencing is an attractive approach to gain access to genes in the biosynthesis of bio-active natural products from insects and other organisms, for which the genome sequence is not known. Based on analysis of the <it>Z. filipendulae </it>transcriptome, promising gene candidates for biosynthesis of cyanogenic glucosides was identified, and the suitability of <it>Z. filipendulae </it>as a model system for cyanogenesis in insects is evident.</p

Electrocardiography and echocardiography in athletic heart imagining

The aim of the study was evaluation of electrocardiographic and echocardiographic parameters in athletes. „Athletic heart” characteristics were compared with fit persons’ heart. 96 athletes participated in the study. Sportsmen were divided into: static (S), dynamic (D) and composite (SD) exercise groups and Polish (I), European (II), World (III) champions. 30 students from Sport Academy formed the control group (K). Electrocardiographic and echocardiographic examination were performed in everyone. As regards the type of exercise, the end-systolic left ventricular (LV) dimension was smaller in S in comparison with D and SD (28.9 vs 32.2 and 32.68 mm; P<0.05). LV mass was bigger in D in comparison with K (273.2 vs 218.6 g; P<0.05). Medium Pulmonary Artery Pressure (MPAP) in S and SD was lower in respect to D and K (11.75; 11.08 vs 15.52; 17.43 mm Hg; P<0.05). We observed lower heart rate in D, SD in comparison with K (58.64; 60.54 vs 68.8; P<0.05), bigger R wave amplitude in V5 (RV5) (21.65; 23.5 vs 15.03 mm; P<0.05) and V6 (RV6) (23.5 vs 15.3 mm; P<0.05) in group S in respect to K. LV mass was bigger in III than in K (261.3 vs 218.6 g; P<0.05). MPAP was lower in I and II in comparison with K (11.42; 13.13 vs 17.43 mmHg; P<0.05). HR was lower in categories I, II than in K (61.32; 60.13 vs 68.8; P<0.05), RV5 was bigger in I in comparison with K (19.5 vs 15.03 mm; P<0.05). The electrocardiography and echocardiography proves to find some significant differences between athletic and fit persons’ heart especially as concerns MPAP, RV5, RV6 values