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Fig. 4 in Cytotoxic cardenolides from Calotropis gigantea

Fig. 4. (A, C) A172 cells were exposed to 0, 50 or 100 nM of 8 or 10 for 24 h. PI staining was used to distinguish the cell cycle distribution of different treatment groups. Flow cytometry was used to analyse the respective cell cycle distribution after staining. (B, D) Statistical analysis representation of the percentage of the three cell cycles (G0/G1, S, and G2/M) analysed by flow cytometry. Error bars were calculated from three independent experiments. *P <0.05; **P <0.01; ***P <0.001 vs. Control.

Fig. 2. 1H 1H in Cytotoxic cardenolides from Calotropis gigantea

Fig. 2. 1H 1H COSY (blue bold), key HMBC (red arrows) and NOESY (black double arrow) correlations of compounds 1–5. (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)

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Data from: Relative selectivity of plant cardenolides for Na+/K+-ATPases from the monarch butterfly and non-resistant insects

A major prediction of coevolutionary theory is that plants may target particular herbivores with secondary compounds that are selectively defensive. The highly specialized monarch butterfly (Danaus plexippus) copes well with cardiac glycosides (inhibitors of animal Na+/K+-ATPases) from its milkweed host plants, but selective inhibition of its Na+/K+-ATPase by different compounds has not been previously tested. We applied 17 cardiac glycosides to the D. plexippus-Na+/K+-ATPase and to the more susceptible Na+/K+-ATPases of two non-adapted insects (Euploea core and Schistocerca gregaria). Structural features (e.g., sugar residues) predicted in vitro inhibitory activity and comparison of insect Na+/K+-ATPases revealed that the monarch has evolved a highly resistant enzyme overall. Nonetheless, we found evidence for relative selectivity of individual cardiac glycosides reaching from 4- to 94-fold differences of inhibition between non-adapted Na+/K+-ATPase and D. plexippus-Na+/K+-ATPase. This toxin receptor specificity suggests a mechanism how plants could target herbivores selectively and thus provides a strong basis for pairwise coevolutionary interactions between plants and herbivorous insects.

Fig. 3 in 21-Hydroxypregnane 21-O-malonylation, a crucial step in cardenolide biosynthesis, can be achieved by substrate-promiscuous BAHD-type phenolic glucoside malonyltransferases from Arabidopsis thaliana and homolog proteins from Digitalis lanata

Fig. 3. Size exclusion chromatography (SEC) and indication of relative 21MaT activity investigation pools III (A) and IV (B) of the ammonium sulfate precipitation.

Fig. 4 in 21-Hydroxypregnane 21-O-malonylation, a crucial step in cardenolide biosynthesis, can be achieved by substrate-promiscuous BAHD-type phenolic glucoside malonyltransferases from Arabidopsis thaliana and homolog proteins from Digitalis lanata

Fig. 4. Docking of modeled AtPMaT1 (ribbon diagram) with an overlay of the potential pregnane substrates (Sub) (shown in grey). The catalytic histidine (His) and the cosubstrate (CoS) are also shown.

Fig. 1 in 21-Hydroxypregnane 21-O-malonylation, a crucial step in cardenolide biosynthesis, can be achieved by substrate-promiscuous BAHD-type phenolic glucoside malonyltransferases from Arabidopsis thaliana and homolog proteins from Digitalis lanata

Fig. 1. Postulated biosynthetic pathway of cardenolide formation in Digitalis. The malonylation step [8] is marked by a rectangle. 1 Putative side chain cleaving enzyme (SCCE), 2 NAD:3β-hydroxysteroid dehydrogenase (3βHSD), 3 Δ4,5-3-ketosteroid-isomerase (3KSI), 4 progesterone-5β-reductase (P5βR), 5 NAD:3β-hydroxysteroid dehydrogenase (3βHSD), 6 putative pregnane 14β-hydroxylase, 7 putative pregnane 21β-hydroxylase, 8 malonyl coenzyme A:21- hydroxypregnane 21-O-malonyltransferase (21MaT).

Fig. 6 in 21-Hydroxypregnane 21-O-malonylation, a crucial step in cardenolide biosynthesis, can be achieved by substrate-promiscuous BAHD-type phenolic glucoside malonyltransferases from Arabidopsis thaliana and homolog proteins from Digitalis lanata

Fig. 6. Docking of homology modeled malonyltransferases with 3-O-acetylketol (displayed in grey) showing the distances between the catalytic histidine (His), the hydroxy group to be malonylated (Sub) and the malonyl residue presented by the co-substrate (CoA). A AtPMaT1 B AtPMaT2 C DlMaT1.

Fig. 5 in 21-Hydroxypregnane 21-O-malonylation, a crucial step in cardenolide biosynthesis, can be achieved by substrate-promiscuous BAHD-type phenolic glucoside malonyltransferases from Arabidopsis thaliana and homolog proteins from Digitalis lanata

Fig. 5. Expression of Dlmat1, Dlmat2, Dlmat3, and Dlmat4 in different plant tissues measured by real-time quantitative PCR (qPCR). Expression rates are standardized to the values of the actin transcript in each tissue and were displayed in relation to the expression in young leaves (set to equal 1) for each Dlmat gene.

Fig. 8 in Acropetal and basipetal cardenolide transport in Erysimum cheiranthoides (wormseed wallflower)

Fig. 8. Intermediate cardenolide profiles in inflorescence-grafted plants. Plants were grafted at the inflorescence stage, with the graft junction above the leaves of the stock and below the developing inflorescence of the scion. Cardenolide content was measured in (A) flowers, (B) green siliques, and (C) dry seeds of the grafted plants. The principal component analysis (PCA) is of eight detected cardenolides. Ellipses signify 95% confidence intervals. Bar graphs of the data are in Supplemental Fig. S4.

Fig. 7 in Acropetal and basipetal cardenolide transport in Erysimum cheiranthoides (wormseed wallflower)

Fig. 7. Cardenolides transport in aboveground tissue. The stalks of three to four-week-old wildtype and 454 cardenolide mutant plants were grafted. Two weeks later, cardenolides were measured in (A) leaves above the graft junction, (B) leaves below the graft junction, (C) stems immediately above the graft junction, and (D) stems immediately below the graft junction. The principal component analysis (PCA) is of eight detected cardenolides. Bar graphs of the data are in Supplemental Fig. S3. Ellipses signify 95% confidence intervals.

Fig. 5 in Acropetal and basipetal cardenolide transport in Erysimum cheiranthoides (wormseed wallflower)

Fig. 5. Cotyledons retain the maternal plant cardenolide phenotype until true leaf emergence. Cardenolides were measured in F2 progeny of wt x 454 F1 plants. (A) Cardenolide content of single F2 seeds, (B) cardenolide content of F2 cotyledons from individual plants before true leaf emergence, (C) principal component analysis (PCA) of cardenolide content of true leaves of F2 plants, and (D) cardenolide content of F2 true leaves. Different letters indicate P <0.05 differences for each cardenolide, ANOVA followed by Tukey's HSD test. Bars are mean ± s.d. of N = 4–6 homozygotes and 20–24 F2s. wt = wildtype E. cheiranthoides var. Elbtalaue, 454 = 454 cardenolide mutant line. Ellipses in the PCA plot represent 95% confidence intervals. Peak areas were normalized to an ouabain internal standard.

Fig. 6 in Acropetal and basipetal cardenolide transport in Erysimum cheiranthoides (wormseed wallflower)

Fig. 6. Grafting experiments show that shoot genotype determines root cardenolide phenotype. Seedlings were grafted at the cotyledon stage and cardenolides were measured in leaves and roots after three weeks. (A) Scion (leaf) cardenolides in grafted plants. (B) Stock (root) cardenolides in grafted plants. Different letters indicate P <0.05 differences for each cardenolide, ANOVA followed by Tukey's HSD test. Bars are mean ±s.d. of N =5–13 for shoot samples and 4–10 for root samples. wt = wildtype E. cheiranthoides var Elbtalaue; 454 = 454 cardenolide mutant line. Peak areas were normalized to an ouabain internal standard.

Fig. 3 in Acropetal and basipetal cardenolide transport in Erysimum cheiranthoides (wormseed wallflower)

Fig. 3. Maternal genotype determines seed cardenolide phenotype. Seed cardenolide content was measured in seeds from naturally self-pollinated and manually crossed plants. Different letters indicate P <0.05 differences for each cardenolide, ANOVA followed by Tukey's HSD test. Bars are mean ± s.d. of N = 4–5. wt = wildtype E. cheiranthoides var. Elbtalaue, 454 = 454 cardenolide mutant line. Peak areas were normalized to an ouabain internal standard.

Fig. 4 in Acropetal and basipetal cardenolide transport in Erysimum cheiranthoides (wormseed wallflower)

Fig. 4. Cotyledons retain the maternal plant cardenolide phenotype until true leaf emergence. (A) Cardenolide content of cotyledons before true leaf emergence, (B) cardenolide content of cotyledons after true leaf emergence, (C) cardenolide content of true leaves. Different letters indicate P <0.05 differences for each cardenolide, ANOVA followed by Tukey's HSD test. Bars are mean ± s.d. of N = 6–10. wt = wildtype E. cheiranthoides var. Elbtalaue, 454 = 454 cardenolide mutant line. Peak areas were normalized to an ouabain internal standard.

Fig. 1 in Acropetal and basipetal cardenolide transport in Erysimum cheiranthoides (wormseed wallflower)

Fig. 1. As described by Züst et al. (2020), abundant cardenolides in E. cheiranthoides have digitoxigenin, cannogenol, cannogenin, or strophanthidin as the steroid core. Sugar side chains added to these steroid cores provide additional structural variation. The side chains of Dig-10, Dig-19, Dig-20, and Can-32 have not been fully characterized but are predicted based on MS fragmentation.

Fig. 2 in Acropetal and basipetal cardenolide transport in Erysimum cheiranthoides (wormseed wallflower)

Fig. 2. Principal component analysis (PCA) biplot of genin abundance as a percentage of total cardenolide abundance. Variable loadings for the first two principal components are displayed as vectors.

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Data from: Relative selectivity of plant cardenolides for Na+/K+-ATPases from the monarch butterfly and non-resistant insects

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Fig. 3 in Cytotoxic cardenolides from Calotropis gigantea

Fig. 3. The ECD spectra of compounds 1–5.

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Fig. 1 in Cytotoxic cardenolides from Calotropis gigantea

Fig. 1. Structures of compounds 1 16.