Tannins are believed to be particularly abundant in tropical tree foliage and are mainly associated with plant herbivore defense. Very little is known of the quantity, variation, and potential role of tannins in tropical leaf litter. Here we report on the interspecific variability of litter condensed tannin (CT) concentration among 16 co-occurring tropical rain forest tree species of French Guiana and explore the functional significance of variable litter CT concentration for litter decomposition. We compared some classical methods in the ecological literature to a method based on high-performance liquid chromatography (HPLC), coupled with CT degradation by phloroglucinolysis. The same litter was allowed to decompose in the field in the presence or absence of soil fauna. We found large interspecific differences in the average polymerization degree (2.7 to 21.3, for non-extractable CT) and concentration of litter CT (0-3.7% dry mass, for total CT) determined by HPLC, which did not correlate with Folin total phenolics but correlated reasonably well with acid butanol CT. The concentration and polymerization degree of HPLC-determined CT were the only variables of the multitude of measured initial litter quality parameters that explained a significant amount of variation in litter mass loss among species, irrespective of animal presence. However, animal presence increased mean litter mass loss by a factor of 1.5, and the fauna effect on decomposition was best explained by a negative correlation with total HPLC CT and by a positive correlation with hemicellulose. Our results suggest that the commonly used acid butanol assay yields a reliable estimate of interspecific variation in CT concentration. However, the chemical structure of CTs, such as the polymerization degree, adds important information for the understanding of the functional role of CTs in litter decomposition. We conclude that the wide variation in structure and concentration of leaf litter CTs among tropical tree species is an important driver of decomposition in this nutrient-poor Amazonian rain forest.

(C.V., E.M., V.C., A.A.)Anthocyanins are major pigments in colored grape (Vitis vinifera) berries, and most of them are monomethoxylated or dimethoxylated. We report here the functional characterization of an anthocyanin O-methyltransferase (AOMT) from grapevine. The expression pattern in two cultivars with different anthocyanin methylation profiles (Syrah and Nebbiolo) showed a peak at start ripening (véraison), when the concentrations of all methylated anthocyanins begin to increase. The purified recombinant AOMT protein was active on both anthocyanins and flavonols in vitro, with K m in the micromolar range, and was dependent on divalent cations for activity. AOMT showed a preference for 3#,5# methylation when a 3#,4#,5# hydroxylated anthocyanin substrate was tested. In order to assess its in planta activity, we performed transient expression of AOMT in tobacco (Nicotiana benthamiana) leaves expressing the Production of Anthocyanin Pigment1 (PAP1) transcription factor from Arabidopsis (Arabidopsis thaliana). PAP1 expression in leaves induced the accumulation of the nonmethylated anthocyanin delphinidin 3-rutinoside. The coexpression of PAP1 and AOMT resulted in an accumulation of malvidin 3-rutinoside. We also showed that AOMT localized exclusively in the cytoplasm of tobacco leaf cells. These results demonstrate the ability of this enzyme to methylate anthocyanins both in vitro and in vivo, indicating that AOMT plays a major role in anthocyanin biosynthesis in grape berries.

The results indicate that date seeds are a very rich source of bioactive compounds, thus constituting strong candidates for functional food additives and nutraceuticals.

No abstract

The reaction between procyanidin dimer Ec-EcG (B2 3'-O-gallate) and malvidin 3-O-glucoside (Mv3glc) was studied in a model solution system at two different pH values, 2.0 and 3.8. Disappearance of both species was much faster at pH 3.8 than at pH 2.0. That of Mv3glc was increased in the presence of Ec-EcG, whereas that of Ec-EcG was the same in the presence or absence of the anthocyanin. Values of absorbance at 520 nm measured at pH 2.0 were correlated with the amount of residual Mv3glc. Those measured at pH 3.8 hardly changed during the incubation, but absorbance values at 420 and 620 nm as well as resistance to sulfite bleaching were much increased, confirming that Mv3glc was converted to other pigments. Anthocyanin-flavanol adducts were observed at both pH values, but their structures were different. At pH 2.0, cleavage of the procyanidin linkage followed by nucleophilic addition of flavanol or anthocyanin moieties led to (Ec)(n)-EcG and (Ec)(n)-Mv3glc, respectively. At pH 3.8, nucleophilic addition of Ec-EcG onto the anthocyanin yielded Mv3glc-(Ec-EcG).

No abstract

HighlightFunctional analysis of the four grapevine shikimate dehydrogenases (VvSDH1–4) reveals that two of them are involved in gallic acid biosynthesis.

A rapid, sensitive and selective analysis method using Ultra High Performance Liquid Chromatography coupled to triple-quadrupole Mass Spectrometry (UHPLC-QqQ-MS) has been developed for the quantification of polyphenols in rosé wines. The compound detection being based on specific MS transitions in Multiple Reaction Monitoring (MRM) mode, the present method allows the selective quantification of up to 152 phenolic and two additional non-phenolic wine compounds in 30 min without sample purification or pre-concentration, even at low concentration levels. This method was repeatably applied to a set of 12 rosé wines and thus proved to be suitable for high-throughput and large-scale metabolomics studies.