Olli Martiskainen

Feeding on poplar leaves by caterpillars potentiates foliar peroxidase action in their guts and increases plant resistance

Peroxidases (PODs) are believed to act as induced and constitutive defenses in plants against leaf-feeding insects. However, little work has examined the mode of action of PODs against insects. Putative mechanisms include the production of potentially antinutritive and/or toxic semiquinone free radicals and quinones (from the oxidation of phenolics), as well as increased leaf toughness. In this study, transgenic hybrid poplar saplings (Populustremula × Populus alba) overexpressing horseradish peroxidase (HRP) were produced to examine the impact of elevated HRP levels on the performance and gut biochemistry of Lymantria dispar caterpillars. HRP-overexpressing poplars were more resistant to L. dispar than wild-type (WT) poplars when the level of a phenolic substrate of HRP (chlorogenic acid) was increased, but only when leaves had prior feeding damage. Damaged (induced) leaves produced increased amounts of hydrogen peroxide, which was used by HRP to increase the production of semiquinone radicals in the midguts of larvae. The decreased growth rates of larvae that fed on induced HRP-overexpressing poplars resulted from post-ingestive mechanisms, consistent with the action of HRP in their midguts. The toughness of HRP-overexpressing leaves was not significantly greater than that of WT leaves, whether or not they were induced. When leaves were coated with ellagitannins, induced HRP leaves also produced elevated levels of semiquinone radicals in the midgut. Decreased larval performance on induced HRP leaves in this case was due to post-ingestive mechanisms as well as decreased consumption. The results of this study provide the first demonstration that a POD is able to oxidize phenolics within an insect herbivore’s gut, and further clarifies the chemical conditions that must be present for PODs to function as antiherbivore defenses.

Hepatoprotective and Antioxidant Effect of Bauhinia hookeri Extract against Carbon Tetrachloride-Induced Hepatotoxicity in Mice and Characterization of Its Bioactive Compounds by HPLC-PDA-ESI-MS/MS

The hepatoprotective and antioxidant activity of Bauhinia hookeri ethanol extract (BHE) against CCl4-induced liver injury was investigated in mice. BHE was administered (500 and 1000 mg/kg/day) along with CCl4 for 6 weeks. The hepatic marker enzymes: alanine aminotransferase (ALT), aspartate aminotransferase (AST), and alkaline phosphatase (ALP) were determined in the serum. The antioxidant parameters: glutathione (GSH), superoxide dismutase (SOD), glutathione peroxidase (GPx), glutathione reductase (GR), glutathione transferase (GST), and malondialdehyde (MDA) were estimated in the liver homogenate. BHE treatment significantly inhibited the CCl4-induced increase in ALT (44 and 64%), AST (36 and 46%), ALP (28 and 42%), and MDA (39 and 51%) levels at the tested doses, respectively. Moreover, BHE treatment markedly increased the activity of antioxidant parameters GSH, GPx, GR, GST, and SOD. Histological observations confirmed the strong hepatoprotective activity. These results suggest that a dietary supplement of BHE could exert a beneficial effect against oxidative stress and various liver diseases by enhancing the antioxidant defense status, reducing lipid peroxidation, and protecting against the pathological changes of the liver. The hepatoprotective activity of BHE is mediated, at least in part, by the antioxidant effect of its constituents. The active constituents of BHE were identified by HPLC-PDA-ESI/MS/MS.

Electron ionization mass spectra and tautomerism of substituted 2-phenacylquinolines.

Tautomerism has been studied conventionally in solutions or in the solid state. However, the importance of mass spectrometry in the gas phase was realized relatively late. 2-Phenacylquinolines are known to undergo ketimine-enaminone tautomerism. The ratio of tautomers is dependent on the nature of the phenyl ring substituent and the Hammett substituent constants sigma. Theoretical calculations indicate the presence of ketimine and enaminone tautomers in the gas phase. The electron ionization mass spectra of eight 2-phenacylquinolines (ketimine form) were recorded at 70 eV in order to determine the fragmentation routes and to screen for the presence of their enaminone tautomers, (Z)-2-benzoylmethylene-1,2-dihydroquinolines, in the gas phase. The relative abundances or total ion currents of some ions correlated with the Hammett substituent constants and Hammett-Brown constants. The product ions [M-CO](+.) and [M-HCO](+) were observed. A reaction mechanism is suggested for the formation of these ions, requiring skeletal rearrangements. The results furnish information relating to tautomerism in the gas phase.

Electron ionization mass spectra and tautomerism of 2-phenacylpyridines.

The electron ionization mass spectra of 2-phenacylpyridine (ketimine form) and its 13 derivatives substituted in the benzene ring (1a–n: a R = H, b 3-Me, c 4-Me, d 4-NH2, e 3-F, f 4-F, g 4-OMe, h 4-Cl, i 4-N(CH3)2, j 4-NO2, k 4-CF3, l 4-N(CH2)4, m 4-Br, n 3-Br) were recorded at 70 eV to determine the fragmentation routes and to screen the presence of their enolimine tautomers, (Z-)-2-(2-hydroxy-2-phenylvinyl)pyridines in the gas phase. The total ion currents (TIC) of the ions [M – H]+, [M – HCO]+, 2-PyCH2O+, and RC6H4CO+ (= ArCO+) showed a fair or good correlation with the Hammett σ constants (R = 0.859, 0.876, 0.912, and −0.926, respectively). The relative abundances (RA) of both the [M – CO]+• and the [M – HCO]+ ion increased with the decreasing electron donating ability of the substituents and also correlated relatively well with the Hammett constants (R = 0.834 and 0.907, respectively). These observations, in comparison to the NMR results, show that the relative contribution of the ketimine tautomer also increases in the gas phase with the increasing electron donating ability of the phenyl substituent, i.e. the TIC of the ArCO+ ion decreases whereas that of [M – H]+ ion increases.

Profiling of Coumarins in Peucedanum palustre (L.) Moench Populations Growing in Finland

The coumarin composition of Peucedanum palustre (L.) Moench populations growing in Finland was investigated. A total of 132 flowering P. palustre specimens from 43 locations in southern and central Finland were collected, divided into root, stem, leaf, and umbel samples, and analyzed by HPLC. HPLC coupled to high‐resolution mass spectrometry was used to aid the identification of coumarins. A total of 13 coumarin‐structured compounds were quantitatively analyzed from the samples. The coumarin profile of root samples was found to differ from the aerial plant parts. The main coumarins in roots were oxypeucedanin and columbianadin. In aerial parts, peulustrin isomers were the most abundant coumarin components. Umbels and leaves also contained a considerable amount of umbelliprenin, which was only found in traces in roots. Based on hierarchical cluster analysis of the coumarin profiles, some populations shared common characteristics. The most distinct property connecting certain populations was their high peulustrin content. Another notable common property between some populations was the high umbelliprenin content in aerial plant parts. Some populations were clustered together due to their low overall coumarin content.