Methyl jasmonate elicits distinctive hydrolyzable tannin, flavonoid, and phyto-oxylipin responses in pomegranate (Punica granatum L.) leaves

Main conclusion Transcriptome and biochemical analyses suggested that, while suppression of multiple flavonoids and anthocyanins occurs at least partially at the transcriptional level, increased biosynthesis of non-jasmonate phyto-oxylipins is likely controlled non-transcriptionally. Abstract Methyl jasmonate (MeJA) produced in plants can mediate their response to environmental stresses. Exogenous application of MeJA has also shown to activate signaling pathways and induce phytoalexin accumulation in many plant species. To understand how pomegranate plants respond biochemically to environmental stresses, metabolite analysis was conducted in pomegranate leaves subjected to MeJA application and revealed unique changes in hydrolyzable tannins, flavonoids, and phyto-oxylipins. Additionally, transcriptome and real-time qPCR analyses of mock- and MeJA-treated pomegranate leaves identified differentially expressed metabolic genes and transcription factors that are potentially involved in the control of hydrolyzable tannin, flavonoid, and phyto-oxylipin pathways. Molecular, biochemical, and bioinformatic characterization of the only lipoxygenase with sustained, MeJA-induced expression showed that it is capable of oxidizing polyunsaturated fatty acids, though not located in the subcellular compartment where non-jasmonate (non-JA) phyto-oxylipins were produced. These results collectively suggested that while the broad suppression of flavonoids and anthocyanins is at least partially controlled at the transcriptional level, the induced biosynthesis of non-JA phyto-oxylipins is likely not regulated transcriptionally. Overall, a better understanding of how pomegranate leaves respond to environmental stresses will not only promote plant health and productivity, but also have an impact on human health as fruits produced by pomegranate plants are a rich source of nutritional compounds.

Effects of hydrolyzable tannin extract obtained from sweet chestnut wood (Castanea sativa Mill.) against bacteria causing subclinical mastitis in Thai Friesian dairy cows

Background and Aim: Hydrolyzable tannins are an important group of secondary plant metabolites, which are known for antimicrobial activity. This study aimed to assess the efficiency with which a hydrolyzable tannin extract from sweet chestnut wood (Castanea sativa Mill.) could inhibit mastitis-causing bacteria in vitro. Materials and Methods: The negative control used was sterile water, and the positive controls were penicillin and gentamicin. The treatments included five concentrations of hydrolyzable tannins (63, 190, 313, 630, and 940 mg/mL). In cows with subclinical mastitis, the bacteria causing the disease were isolated and identified. Then, the antibacterial activity of the hydrolyzable tannin extract was assessed by the disk diffusion method, by determining the minimum inhibitory concentration (MIC) and by determining the minimum bactericidal concentration (MBC). Results: Penicillin inhibited (p<0.01) the growth of Staphylococcus aureus, Streptococcus uberis, and Pseudomonas aeruginosa but could not inhibit (p>0.05) the growth of Streptococcus agalactiae, Escherichia coli, and Klebsiella pneumoniae. However, gentamicin and hydrolyzable tannins could inhibit (p<0.01) all isolated bacteria. Increasing the concentration of hydrolyzable tannin extract resulted in a quadratic increase in the inhibition zone diameter of S. aureus and S. agalactiae and a linear increase in the inhibition zone diameter of E. coli, K. pneumoniae, and P. aeruginosa. In addition, 630 and 940 mg/mL of hydrolyzable tannin extract showed the highest antibacterial activity against S. agalactiae and E. coli (p<0.01), while 940 mg/mL concentration had the highest antibacterial activity against K. pneumoniae (p<0.01). The MIC and MBC of the extract were 27.3-190 mg/mL and 58.8-235 mg/mL, respectively, with the MBC: MIC ratio being 2:1. Conclusion: The antimicrobial activity of the hydrolyzable tannin extract against subclinical mastitis bacteria was comparable to the antibiotics (positive controls) at concentrations over 630 mg/mL. Although these in vitro findings are promising, further research is needed to determine whether hydrolyzable tannins could be used to control or prevent subclinical mastitis in dairy cows.

Correction: Yang et al. Chebulagic Acid, a Hydrolyzable Tannin, Exhibited Antiviral Activity in Vitro and in Vivo against Human Enterovirus 71. Int. J. Mol. Sci. 2013, 14, 9618

The authors wish to make the following corrections to this paper [...]

Ellagitannins and Oligomeric Proanthocyanidins of Three Polygonaceous Plants

The aim of this study was to characterize hydrolyzable tannins in Polygonaceous plants, as only a few plants have previously been reported to contain ellagitannins. From Persicaria chinensis, a new hydrolyzable tannin called persicarianin was isolated and characterized to be 3-O-galloyl-4,6-(S)-dehydrohexahydroxydiphenoyl-d-glucose. Interestingly, acid hydrolysis of this compound afforded ellagic acid, despite the absence of a hexahydroxydiphenoyl group. From the rhizome of Polygonum runcinatum var. sinense, a large amount of granatin A, along with minor ellagitannins, helioscpoinin A, davicratinic acids B and C, and a new ellagitannin called polygonanin A, were isolated. Based on 2D nuclear magnetic resonance (NMR) spectroscopic examination, the structure of polygonanin A was determined to be 1,6-(S)-hexahydroxydiphenoyl-2,4-hydroxychebuloyl-β-d-glucopyranose. These are the second and third hydrolyzable tannins isolated from Polygonaceous plants. In addition, oligomeric proanthocyanidins of Persicaria capitatum and P. chinensis were characterized by thiol degradation. These results suggested that some Polygonaceous plants are the source of hydrolyzable tannins not only proanthocyanidins.

Dehydroquinate dehydratase/shikimate dehydrogenases involved in gallate biosynthesis of the aluminum-tolerant tree species Eucalyptus camaldulensis

Main conclusion Eucalyptus camaldulensis EcDQD/SDH2 and 3 combine gallate formation, dehydroquinate dehydratase, and shikimate dehydrogenase activities. They are candidates for providing the essential gallate for the biosynthesis of the aluminum-detoxifying metabolite oenothein B. Abstract The tree species Eucalyptus camaldulensis shows exceptionally high tolerance against aluminum, a widespread toxic metal in acidic soils. In the roots of E. camaldulensis, aluminum is detoxified via the complexation with oenothein B, a hydrolyzable tannin. In our approach to elucidate the biosynthesis of oenothein B, we here report on the identification of E. camaldulensis enzymes that catalyze the formation of gallate, which is the phenolic constituent of hydrolyzable tannins. By systematical screening of E. camaldulensis dehydroquinate dehydratase/shikimate dehydrogenases (EcDQD/SDHs), we found two enzymes, EcDQD/SDH2 and 3, catalyzing the NADP+-dependent oxidation of 3-dehydroshikimate to produce gallate. Based on extensive in vitro assays using recombinant EcDQD/SDH2 and 3 enzymes, we present for the first time a detailed characterization of the enzymatic gallate formation activity, including the cofactor preferences, pH optima, and kinetic constants. Sequence analyses and structure modeling suggest the gallate formation activity of EcDQD/SDHs is based on the reorientation of 3-dehydroshikimate in the catalytic center, which facilitates the proton abstraction from the C5 position. Additionally, EcDQD/SDH2 and 3 maintain DQD and SDH activities, resulting in a 3-dehydroshikimate supply for gallate formation. In E. camaldulensis, EcDQD/SDH2 and 3 are co-expressed with UGT84A25a/b and UGT84A26a/b involved in hydrolyzable tannin biosynthesis. We further identified EcDQD/SDH1 as a “classical” bifunctional plant shikimate pathway enzyme and EcDQD/SDH4a/b as functional quinate dehydrogenases of the NAD+/NADH-dependent clade. Our data indicate that in E. camaldulensis the enzymes EcDQD/SDH2 and 3 provide the essential gallate for the biosynthesis of the aluminum-detoxifying metabolite oenothein B.

Phytochemical Analysis of Ampelopteris Prolifera (Retzius) Copeland

The fronds of Ampelopteris prolifera are used in stomach ache as well as vegetable. Dried and powdered fronds of A. prolifera was extracted successively with hexane, chloroform, ethyl acetate, methanol and 50% aqueous methanol. The results of phytochemical screening revealed that alkaloids were absent in all extracts. Hexane extract showed the absence of all the tested phytochemicals while chloroform extract showed the presence of only terpenoids and quinones. Ethylacetate extract showed the presence of all tested phytochemicals except quinones and saponins.Methanol and 50% aqueous methanol extracts showed the presence of phenolics, flavonoids, terpenoids, glycosides, tannins, quinones and saponins. The total content of phenolics, flavonoids, tannins and sugars as well as antioxidant activity were determined in ethyl acetate, methanol and 50% aqueous methanol extracts. Total phenolic content was measured spectrophotometrically by using Folin-Ciocalteu, total flavonoid content by using aluminium chloride, total hydrolyzable tannin content by using Folin-Ciocalteu, total condensed tannin content using vanillin-HCl and total sugar content by using anthrone reagent. Gallic acid was used as the standard for the calibration of phenolics, catechin for flavonoids and condensed tannins, tannic acid for hydrolyzable tannins and glucose for carbohydrates. The highest amount of phenolic was detected in 50% methanol extract (114.27±10.37 mg GAE/g). The highest amount of flavonoid was detected in ethylacetate extract (151.47±3.57 mg CE/g extract). The highest amount of hydrolyzable tannin was detected in 50% methanol extract (31.21±2.14 mg TAE/g extract). The highest amount of condensed tannin was detected in ethylacetate extract (337.50±5.00 mg CE/g extract), and the highest amount of sugar was detected in methanol extract (809.74±7.86 mg GE/g). The antioxidant activity was determined by using DPPH free radical and IC50 value was determined. All the tested extracts showed only weak antioxidant activity. Among the tested extracts, 50% aqueous methanol extract showed better activity with an IC50 value of 185.03μg/mL. The HPLC-ESI-MS analysis of methanol extract allowed the tentative identification of peganine, 1-methyltryptophan and rutin. The study thus demonstrates the potential value of A. proliferain the medicinal application.

Two New Phenolic Constituents from the Stems of Euphorbia griffithii

Phytochemical studies on MeOH extract of stems of Euphorbia griffithii led to the isolation of one new hydrolyzable tannin dimer, corilagiffithiin (1) and one new galloyl-glucoside (2), alongside six known ones (3–8). Their structures and absolute configurations were determined by in depth spectroscopic analyses and comparison of their 1D NMR and MS data with literature reported values. Configurations of sugar moieties were determined by acidic hydrolysis and subsequent GC analysis of their corresponding trimethylsilylated l-cysteine adduct. At a concentration of 50 μM, compounds 1–3 showed no anti-inflammatory activities. Graphic Abstract

Oak or chestnut tannin dose responses on silage pH, proteolysis and in vitro digestibility in laboratory-scale silos

Description of the subject. This short note documents the use of hydrolyzable tannins as silage additives to reduce proteolysis thanks to a laboratory-scale ensiling method. Objectives. To study oak (OTE) and chestnut tannin extract (CTE) dose responses on chemical composition, pH and ammoniacal nitrogen (N-NH3) content of silage. Method. A mixture of cocksfoot, white and red clovers was ensiled in vacuum packs, with OTE or CTE at doses of 0, 10, 30, 50 and 70 g·kg-1 DM. Results. Hydrolyzable tannin extracts decreased N-NH3 content of silage up to 18% (p < 0.05). For the investigated range of doses, OTE induced a linear decrease of N-NH3 content (R² = 0.76) whereas CTE resulted in a quadratic decrease (R² = 0.68). High doses of tannin extracts reduced in vitro organic matter digestibility (OMD) by 3% (p < 0.05). Conclusions. Both tannins reduced proteolysis in silos but highest doses induced a decrease in OMD.