A bittersweet family of plants

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  • Published: Apr 14, 2016
  • Author: Ryan De Vooght-Johnson
  • Channels: Laboratory Informatics / Chemometrics & Informatics
thumbnail image: A bittersweet family of plants

Plants of the Gentian family

Plants provide most of the world’s oxygen, as well as food in the form of grains, fruits and vegetables and many essential medicines. Overall, there are thought to be over 300,000 species of plants.

Plants provide most of the world’s oxygen, as well as food in the form of grains, fruits and vegetables and many essential medicines. Overall, there are thought to be over 300,000 species of plants. Over 1000 of these are within the Gentian family, which are found worldwide but especially in northern temperate areas such as Europe and North America. They have distinctive bell-shaped blossoms and are extremely bitter.

These bitter elements, while unpleasant to the tongue, have useful properties. They stimulate the body to produce digestive fluids, helping to prevent indigestion. The bitter-tasting elements are called secondary metabolites, chemicals that are produced by all plants.

Secondary metabolites are essential to protect plants from external threats, but can also have medicinal purposes and be used for quality assessment. What’s more, they can be used to understand the relationships between plants and classify them into families and species. This – the biological classification of organisms based on the structure of compounds – is called chemotaxonomy.

In a study newly published in Phytochemical Analysis, researchers applied this principle to Gentian plants by studying their metabolic profiles. Some Gentian species cannot currently be classified due to their very similar chemical profiles, and there is debate as to the structure of this family. Some scientists suggest certain Gentian plants should be attributed to a new genus (the taxonomic category above species but below family).

A range of chemicals have been isolated from these plants, and iridoids, flavonoids and xanthones have been put forward as promising chemotaxonomic markers, but a comprehensive profile of these compounds has been lacking.

Metabolite mayhem

Analysing the plethora of metabolites commonly found in biological samples is not an easy task. Separation techniques such as liquid chromatography (LC) and gas chromatography (GC) can sensitively detect metabolites in combination with mass spectrometry (MS). However, sample preparation can be time consuming and complex, metabolites with different polarities often cannot be analysed simultaneously, and results may be made invalid due to the interference of other compounds. Fourier transform infrared (FT-IR) spectroscopy is another established tool for metabolite profiling, but this also has problems – mainly a lack of specificity and sensitivity.

This study, led by Yunnan Academy of Agricultural Sciences in China, used both. By combining FT-IR spectroscopy with LC-MS, the researchers could overcome their respective limitations to monitor changes to specific metabolites in plant samples. They also used chemometrics techniques to analyse the chemical data and visualise the differences between species.

The researchers analysed nine different Gentianaceae species collected from the west of China, including six from the Gentiana genus and three from Swertia. The samples were first analysed by FT-IR spectroscopy and the spectral data were subjected to two chemometrics techniques (hierarchical and principal component analyses). This separated the Gentiana and Swertia groups, showing clear differences in their metabolic profiles. However, relationships among species could not be clearly visualised due to overlapping chemical information in the spectrum.

Chemical classification

The researchers next applied a more targeted technique (LC-MS/MS) to clarify the spectroscopy results. Metabolic profiling showed clear differences between the nine species. Data was again subjected to principal component analysis, which this time differentiated the genera and individual species.

Chemometrics also separated the samples based on their where they were grown, which suggests that geographical origin as well as genetics is important for the metabolic profile and classification of plants. In fact, the results suggest that origin may be even more important than genetics for classification, but other factors such as harvest time and temperature may be at play and further work is needed to clarify the relationship.

Overall, the analyses showed clear and significant differences between species, especially between those in different genera. By matching mass data and fragmentation patterns with known compounds, the researchers were also able to identify seven characteristic metabolites which could be used as chemotaxonomic markers. This may help plant scientists to better understand this large family of plants, and close some of the debate surrounding their origins and relationships.

Related Links

Phytochem. Anal., 2016, Early View paper. Pan . Chemotaxonomic Studies of Nine Gentianaceae Species from Western China Based on Liquid Chromatography Tandem Mass Spectrometry and Fourier Transform Infrared Spectroscopy.

Gentianaceae: Plants of the Gentian Family

Gentianaceae plant family

Article by Ryan De Vooght-Johnson

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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