The handle http://hdl.handle.net/1887/119363 holds various files of this Leiden University dissertation.
Author: Salome Abarca, L.F.
Title: Metabolomic characterization of plant exudates and their correlation with plant defense systems
General introduction
Salomé Abarca Luis FranciscoNatural Products Laboratory, Institute of Biology, Leiden, Leiden University, Leiden, The Netherlands.
Plant exudates appeared long time ago in the history line of life since the early Devonian (Lambert et al. 2005). They are saps produced by diverse type of specialized cells that can be naturally excreted outside the plant or as result of mechanical damage or pathogen infections (Konno 2011). Since they were discovered by the mankind, diverse cultures recognized them as valuable sources of bioactive and commercial substances (Lambert et al. 2005). The most distinctive and widespread groups of plant exudates are categorized as gums, mucilage, essential oils, oleoresins, resins, phloem like saps, and latexes (Coppen 1995; Gaupels and Ghirardo 2013; Choudhar and Pawar 2014; Dhifi et al. 2016). These groups can be distinguished not only by their physical characteristics but also by their chemical compositions. In fact, the solid state 13C NMR analysis of some groups of exudates was able to discriminate distinctive chemical signatures among them when the spectral data was approached by multivariate data analysis (Lambert et al. 2010). These chemical differences might represent the reflection of specific plant-environmental adaptation processes involving specialized herbivores or microorganisms that interact with the plant exudate bearing species.
interactions have focused on inducible defenses (Biere et al. 2004; Vos et al. 2013; de Vries et al. 2017), however, there has been a re-emerging interest in constitutive defenses against herbivores and microorganisms (Biere et al. 2004; Boots and Best 2018).
In the case of plant exudates, even if they are mainly consider of constitutive character, after plant infection or infestation they can also act as inducible defenses (Lombardero et al. 2000; Konno et al. 2004, 2006, 2011; Moreira et al. 2012). In this context, plant exudates are not just a valuable source of commercial resins, but can be considered as promissory sources of bioactive metabolites, potential compound formulations and also key models to unravel plant chemical selection and variation. Furthermore, these features are of great interest for bioactive metabolites discovering, especially in an era of new resistant pathogens and insect pests that wild plants have handled to survive and coexist in challenging ecosystems.
However, even if these exudates may possess the chemical mechanisms to successfully fight against pathogens and herbivores, one of the biggest challenges in plant sciences is to unravel the meaning of the plant chemical language, behavior, and how they reach their chemical diversity. In this regard, metabolomics represents a powerful approach to accomplish this aim (Kim et al. 2010). The ultimate goal of metabolomics is to provide a complete image of the metabolome of diverse organisms living under specific conditions. However, because of the extreme complexity of the metabolome, a single analytical platform standing alone cannot resolve it completely. Instead, a multi-analytical platform approach is more appropriated (Gromski et al. 2015).
this technique as a real metabolomics tool. On the other hand, MS-based methods possess an unbeatable sensitivity and resolution by hyphenation with chromatographic methods such as LC and GC. Depicting its sensitivity, ion suppression and reproducibility still drawbacks of this approach. Thus, the use of other complementary tools is unavoidable. Because of this, in this research different metabolomics approaches were used to unravel the effect of environmental factors over the metabolic composition and variation in plant exudates and the outcome of these changes in plant-organisms interactions.
Aims of the thesis
As previously exposed, the use of exudate bearing plant species is worldwide spread by diverse cultures. Their empirical use and their effectiveness against a broad range of illnesses have attracted the attention of the scientific scrutiny as potential sources of new bioactive compounds. It is been around one century since there was maybe one of the first scientific reports on a latex bearing Euphorbia species and since that moment till nowadays there are thousands of studies on different plant exudates that resulted in the discovery of diverse bioactive natural products. Even, they have been recognized as valuable biological models for the understanding of ecological interactions. However, plant exudates still have much more to offer for the understanding of plant natural chemical selection. In this regard, understanding the chemical language of plants is one of the most challenging scenarios in plant sciences. Thanks to the recent development of metabolomics analytical tools the gap between chemical diversity and ecological functions starts to be closed. Nonetheless, there is still a big way to the final understanding of the plant chemical behavior. In order to contribute to the understading of plant chemical selection for their exudate constitutions, the following objectives were stablished in this thesis.
1 Employ a metabolomics multi-analytical platform approach to unravel the chemical distribution and differentiation in plant exudates.
3 Determine geographical and species metabolic differentiations at tissue level in latex bearing Euphorbia species.
4 Perform a multi-species metabolic comparison between latex and leaves, and determine whether there is an effect on their anti-herbivore activity and the general role of metabolite families generally found on latexes.
5 Isolate endophytic fungi from latex bearing plants and test their metabolic capability and its possible contribution to the chemical diversity and fitness of their host-plants.
Outline of the thesis
NMR-based metabolomics and GC-MS as complementary tool. The comparison was done on latex and leaves. Also, a comparison between their anti-herbivore activity and the general role of some organic acids and triterpenes were tested and further discussed. In chapter 7, fungal endophytes were isolated from Alstonia scholaris and Euphorbia myrsinites and classified based on their chemical complexity by means of HPTLC-based metabolomics. Furthermore, some fungal strains were selected to test their role as a defense line in co-culture bioassays and their capability to increase their chemical diversity when exposed to their host-plant specialized metabolites. The general conclusions, future perspectives and summary from this thesis are described in chapter 8.
References
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