A Volatile Lactone of Hymenoscyphus pseudoalbidus,Pathogen of European Ash Dieback,Inhibits Host Germination

The largely unknown secondary metabolism of the plant pathogenic fungus Hymenoscyphus pseudoalbidus was investigated by use of the CLSA method. A set of volatile lactones was identified by GC/MS. The lactones were synthesized and used in bioassays in which one of the compounds was found to be a strong germination inhibitor for ash seeds, causing necroses in the plant tissue.     

A secoiridoid dilactone fromFraxinus ornus bark

Summary The isolation and structure elucidation of the secoiridoid hydroxyornoside is described. The behaviour of secoiridoid dilactones on acid methanolysis is discussed.

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Ein Secoiridoiddilacton aus der Rinde vonFraxinus ornus

Zusammenfassung Die Isolierung und Strukturaufklärung des Secoiridoids Hydroxyornosid wird beschrieben. Das Verhalten von Secoiridoiddilactonen bezüglich saurer Methanolyse wird diskutiert.

     

The Influence of Ammonium on Nitrate Uptake and Assimilation in 2-Year-Old Ash and Oak Trees - A Tracer-Study with 15N

Abstract

Interactions between ammonium and nitrate as competitive N sources depend on various biotic and abiotic factors. The preference for one of these N sources and the influence of ammonium on nitrate uptake and nitrate reductase activity was investigated in a ¹⁵N labelling experiment using 2-year-old potted plants of ash (Fraxinus excelsior L.) and oak (Quercus robur L.) under greenhouse conditions.

Seedlings of both tree species use ammonium and nitrate in equal amounts when both N forms are supplied in a 1:1 ratio (1.5 mM NH₄ ⁺ + 1.5 mM NO₃ ^?), although there is a slight tendency that ammonium is preferred. In both species total N uptake is higher if ammonium and nitrate are supplied simultaneously when compared with uptake of nitrate alone (3 mM nitrate). If nitrate is the sole N source N uptake is only half as high as if ammonium and nitrate are supplied in a ratio of 1:1.

The distribution of nitrate reductase between shoot and roots is not influenced by the N-form: nitrate reductase activity is always highest in the roots of both species under the conditions of this experiment.

Xylem sap analyses showed that both species transport higher concentrations of amino acids than of nitrate from the roots to the shoot. The amino acid composition is independent of the type of N source. Furthermore, ash trees contain more nitrate in the xylem sap than oak trees, reflecting the higher N uptake and the higher nitrate reductase activity in the leaves of this species.     

LC‐DAD/ESI‐MS/MS study of phenolic compounds in ash (Fraxinus excelsior L. and F. americana L.) heartwood. Effect of toasting intensity at cooperage

The phenolic composition of heartwood extracts from Fraxinus excelsior L. and F. americana L., both before and after toasting in cooperage, was studied using LC‐DAD/ESI‐MS/MS. Low‐molecular weight (LMW) phenolic compounds, secoiridoids, phenylethanoid glycosides, dilignols and oligolignols compounds were detected, and 48 were identified, or tentatively characterized, on the basis of their retention time, UV/Vis and MS spectra, and MS fragmentation patterns. Some LMW phenolic compounds like protocatechuic acid and aldehyde, hydroxytyrosol and tyrosol, were unlike to those for oak wood, while ellagic and gallic acid were not found. The toasting of wood resulted in a progressive increase in lignin degradation products with regard to toasting intensity. The levels of some of these compounds in medium‐toasted ash woods were much higher than those normally detected in toasted oak, highlighting vanillin levels, thus a more pronounced vanilla character can be expected when using toasted ash wood in the aging wines. Moreover, in seasoned wood, we found a great variety of phenolic compounds which had not been found in oak wood, especially oleuropein, ligstroside and olivil, along with verbascoside and isoverbascoside in F. excelsior, and oleoside in F. americana. Toasting mainly provoked their degradation, thus in medium‐toasted wood, only four of them were detected. This resulted in a minor differentiation between toasted ash and oak woods. The absence of tannins in ash wood, which are very important in oak wood, is another peculiar characteristic that should be taken into account when considering its use in cooperage. Copyright © 2012 John Wiley & Sons, Ltd.     

Secoiridoid Glucosides and Anti-Inflammatory Constituents from the Stem Bark of Fraxinus chinensis

Qin Pi (Fraxinus chinensis Roxb.) is commercially used in healthcare products for the improvement of intestinal function and gouty arthritis in many countries. Three new secoiridoid glucosides, (8E)-4′′-O-methylligstroside (1), (8E)-4′′-O-methyldemethylligstroside (2), and 3′′,4′′-di-O-methyl-demethyloleuropein (3), have been isolated from the stem bark of Fraxinus chinensis, together with 23 known compounds (4–26). The structures of the new compounds were established by spectroscopic analyses (1D, 2D NMR, IR, UV, and HRESIMS). Among the isolated compounds, (8E)-4′′-O-methylligstroside (1), (8E)-4′′-O-methyldemethylligstroside (2), 3′′,4′′-di-O-methyldemethyloleuropein (3), oleuropein (6), aesculetin (9), isoscopoletin (11), aesculetin dimethyl ester (12), fraxetin (14), tyrosol (21), 4-hydroxyphenethyl acetate (22), and (+)-pinoresinol (24) exhibited inhibition (IC₅₀ ≤ 7.65 μg/mL) of superoxide anion generation by human neutrophils in response to formyl-L-methionyl-L-leuckyl-L-phenylalanine/cytochalasin B (fMLP/CB). Compounds 1, 9, 11, 14, 21, and 22 inhibited fMLP/CB-induced elastase release with IC₅₀ ≤ 3.23 μg/mL. In addition, compounds 2, 9, 11, 14, and 21 showed potent inhibition with IC₅₀ values ≤ 27.11 μM, against lipopolysaccharide (LPS)-induced nitric oxide (NO) generation. The well-known proinflammatory cytokines, tumor necrosis factor-alpha (TNF-α) and interleukin 6 (IL-6), were also inhibited by compounds 1, 9, and 14. Compounds 1, 9, and 14 displayed an anti-inflammatory effect against NO, TNF-α, and IL-6 through the inhibition of activation of MAPKs and IκBα in LPS-activated macrophages. In addition, compounds 1, 9, and 14 stimulated anti-inflammatory M2 phenotype by elevating the expression of arginase 1 and Krüppel-like factor 4 (KLF4). The above results suggested that compounds 1, 9, and 14 could be considered as potential compounds for further development of NO production-targeted anti-inflammatory agents.     

Phenylethanoid glycosides from the bark of <Emphasis Type="Italic">Fraxinus mandschurica</Emphasis>

The new phenylethanoid glycoside calceolarioside A-2′-α-L-rhamnopyranoside and calceolarioside A and calceolarioside B were isolated from the bark of Fraxinus mandschurica Rupr. for the first time by column chromatography. Published in Khimiya Prirodnykh Soedinenii, No. 3, pp. 283–284, May–June, 2009.     

Isofraxisecoside,a new coumarin-secoiridoid from the stem bark of Fraxinus xanthoxyloides

A new coumarin-secoiridoid diglucoside, named Isofraxisecoside, was isolated from the stem bark of Fraxinus xanthoxyloides (G. Don) Wall. ex A. DC. along with nine known compounds. The structure of new compound has been determined on the basis of ¹H, ¹³C, 2D NMR and HRMS methods.     

Emissions of biogenic volatile organic compounds from Fraxinus excelsior and Quercus robur under ambient conditions in Flanders (Belgium)

A dynamic branch enclosure system was used to measure emission rates of biogenic volatile organic compounds (BVOCs) from two common European tree species: Fraxinus excelsior and Quercus robur under ambient conditions in Flanders (Belgium). Both tree species were studied for seasonal variability of BVOC emission rates under natural biotic stress (infestations). Emissions were normalized at standard conditions of temperature and photosynthetic active radiation (PAR) (30°C and 1000?µmol?m^?2?s^?1, respectively). Emission rates from Fraxinus excelsior were highest in May (9.56?µg?g_DW ^?1?h^?1) and lowest in October (1.17?µg?g_DW ^?1?h^?1). This tree species emitted (Z)-β-ocimene, (E)-β-ocimene and α-farnesene during the entire measurement period and additionally isoprene only in May. Quercus robur showed isoprene emission variations according to the seasonal cycle with rates of 30, 106 and 29?µg?g_DW ^?1?h^?1 in May, August and October, respectively. Apart from isoprene, (E)-β-ocimene and β-caryophyllene were emitted through the entire experimental period.