Metabolic Response of Strawberry (Fragaria x ananassa) Leaves Exposed to the Angular Leaf Spot Bacterium (Xanthomonas fragariae).

Plants have evolved various defense mechanisms against biotic stress. The most common mechanism involves the production of metabolites that act as defense compounds. Bacterial angular leaf spot disease (Xanthomonas fragariae) of the strawberry (Fragaria x ananassa) has become increasingly destructive to strawberry leaves and plant production. In this study, we examined metabolic changes associated with the establishment of long-term bacterial disease stress using UPLC-QTOF mass spectrometry. Infected leaves showed decreased levels of gallic acid derivatives and ellagitannins, which are related to the plant defense system. The levels of phenylalanine, tryptophan, and salicylic acid as precursors of aromatic secondary metabolites were increased in inoculated leaves, whereas levels of coumaric acid, quinic acid, and flavonoids were decreased in infected plants, which are involved in the phenylpropanoid pathway. In addition, phenylalanine ammonia-lyase (PAL) activity, a key enzyme in the phenylpropanoid pathway, was decreased following infection. These results suggest that long-term bacterial disease stress may lead to down-regulation of select molecules of the phenylpropanoid metabolic pathway in strawberry leaves. This approach could be applied to explore the metabolic pathway associated with plant protection/breeding in strawberry leaves.

Kim MS ，Jin JS ，Kwak YS ，Hwang GS ... -  《-》

Non-targeted metabolite profiling highlights the potential of strawberry leaves as a resource for specific bioactive compounds.

The non-edible parts of horticultural crops, such as leaves, contain substantial amounts of valuable bioactive compounds which are currently only little exploited. For example, strawberry (Fragaria × ananassa) leaves may be a promising bioresource for diverse health-related applications. However, product standardization sets a real challenge, especially when the leaf material comes from varying cultivars. The first step towards better quality control of berry fruit leaf-based ingredients and supplements is to understand metabolites present and their stability in different plant cultivars, so this study surveyed the distribution of potentially bioactive strawberry leaf metabolites in six different strawberry cultivars. Non-targeted metabolite profiling analysis using LC/qTOF-ESI-MS with data processing via principal component analysis and k-means clustering analysis was utilized to examine differences and commonalities between the leaf metabolite profiles. Quercetin and kaempferol derivatives were the dominant flavonol groups in strawberry leaves. Previously described and novel caffeic and chlorogenic acid derivatives were among the major phenolic acids. In addition, ellagitannins were one of the distinguishing compound classes in strawberry leaves. In general, strawberry leaves also contained high levels of octadecatrienoic acid derivatives, precursors of valuable odour compounds. The specific bioactive compounds found in the leaves of different strawberry cultivars offer the potential for the selection of optimized leaf materials for added-value food and non-food applications. © 2016 Society of Chemical Industry.

Kårlund A ，Hanhineva K ，Lehtonen M ，McDougall GJ ，Stewart D ，Karjalainen RO ... -  《-》

NMR and UPLC-qTOF-MS/MS characterisation of novel phenylethanol derivatives of phenylpropanoid glucosides from the leaves of strawberry (Fragaria x ananassa cv. Jonsok).

Strawberry (Fragaria x ananassa) is rich in polyphenols, particularly anthocyanins, flavonols, condensed tannins and ellagic tannins. In addition to the fruits, the leaves of strawberry also contain a wide range of phenolic compound classes, but have not been investigated to the same extent as the fruit. To characterise a metabolite group present in the leaves of strawberry, that was not amenable for identification based on earlier information available in the literature. Methanolic extracts of strawberry leaves were analysed by UPLC-qTOF-MS/MS and iterative quantum mechanical NMR spectral analysis. The structures of phenylethanol derivatives of phenylpropanoid glucosides Eutigoside A ( F4) and its two isomeric forms 2-(4-hydroxyphenyl)ethyl-[6-O-(Z)-coumaroyl]-beta-D-glucopyranoside (F6) and 4-(2-hydroxyethyl)phenyl-[6-O-(E)-coumaroyl]-beta-D-glucopyranoside (F1) were resolved by NMR and UPLC-qTOF-MS/MS. In addition, two other derivatives of phenylpropanoid glucosides similar to Eutigoside A but possessing different phenolic acid moieties, namely Grayanoside A ( F5) and 2-(4-hydroxyphenyl)ethyl-[6-O-(E)-caffeoyl]-beta-D-glucopyranoside (F14), were similarly identified. Also, accurate characteristic coupling constants for the subunits are reported and their usefulness in structural analysis is highlighted. Chemical analysis of the leaves of strawberry (Fragaria x ananassa cv. Jonsok) resulted in the identification of a compound class, phenylethanol derivatives of phenylpropanoid glycosides, not previously found in strawberry.

Hanhineva K ，Soininen P ，Anttonen MJ ，Kokko H ，Rogachev I ，Aharoni A ，Laatikainen R ，Kärenlampi S ... -  《-》

A rapid and sensitive method for the detection of Xanthomonas fragariae, causal agent of angular leafspot disease in strawberry plants.

Angular leaf spot is a bacterial disease caused by Xanthomonas fragariae. It has become a serious disease in the USA and Europe in recent years. Several detection procedures are described for this plant pathogen. However, they are either too time-consuming, too insensitive or impractical when handling a large number of samples routinely. Here we describe a modified protocol of the REDExtract-N-Amp Plant PCR-Kit for the detection of X. fragariae in planta and demonstrate that it provides greater sensitivity, speed and high throughput potential than methods previously described.

Stöger A ，Ruppitsch W 《JOURNAL OF MICROBIOLOGICAL METHODS》

Pathogen-induced accumulation of an ellagitannin elicits plant defense response.

In an incompatible interaction between Colletotrichum fragariae and strawberry plants, the accumulation of phenolic compounds in plant leaves was observed. A particularly abundant penta-esterified ellagitannin that accumulated in response to pathogen attack was identified as 1-0-galloyl-2,3;4,6-bis-hexahydroxydiphenoyl-β-d-glucopyranose (HeT) by mass spectroscopy and nuclear magnetic resonance. Foliar application of purified HeT prior to inoculation with a virulent pathogen was shown to increase resistance toward C. acutatum in strawberry plants and to Xanthomonas citri subsp. citri in lemon plants. The induced resistance in strawberry was associated with a rapid oxidative burst, callose deposition, a transient increase of salicylic acid in phloem, and induction of gene expression responsive to salicylic acid. Results obtained suggested that HeT could be a common plant defense response molecule capable of inducing pathogen resistance in different plant species.

Mamaní A ，Filippone MP ，Grellet C ，Welin B ，Castagnaro AP ，Ricci JC ... -  《MOLECULAR PLANT-MICROBE INTERACTIONS》