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
Plant exudates are liquids excreted constitutively, continuously or after herbivore damage or pathogenic infections. Thus, they are strongly associated to plant defense, especially against herbivores. Some are used on large scale for industrial purposes like rubber. Other exudates are considered to be valuable substances with mystic and medicinal properties. They represent an alternative source of bioactive molecules resulting from long-term coevolutionary plant-environmental interactions. Their role in the plant defense makes the exudates good models to study the effect of a mixture of compounds on herbivores and microorganisms. However, to reach this goal, the factors that govern the chemistry of plant exudates needs to be established, including the changes due to different external conditions and the biological variation (Chapter 2).
indicate that in these species during these periods the main forces driving metabolic differentiation were species factors. In this way, we can also state that mono- and sesquiterpenes were more related to genetic (species) background and diterpenes to environmental (time of collection) effects (Chapter 3).
In order to minimize species effects and observe the influence of environmental factors from geographical origin on diterpenoids, ten ecotypes of Cistus monspeliensis L. were collected in different regions of the island of Sardegnia (Italy). Following the same approach as in the previous chapter, the samples were first profiled by 1H NMR. Most ecotypes could be distinguished based on their terpenoids and phenolic compounds. According to 1H NMR spectra, the total amount of labdane like compounds varied depending on geographical region. According to an OPLS model, the chemical variation of the Cistus ecotypes is correlated to their differences in antifungal activity against Fusarium oxysporum. HPTLC-based profiling was able to extend the NMR results. The PCA and SIMCA score plots of these data, showed that ecotypes not discriminated by NMR, formed well separated clusters. The antifungal activity showed a correlation to the HPTLC data set. The Rf values matched to those of isolated diterpenes and methoxylated flavonoids also detected and identified by NMR spectroscopy. Moreover, the bioautographic test of the chromatographed extracts showed that the compounds correlated to the antifungal activity, were the ones showing antifungal activity on the HPTLC plate. Furthermore, there were diterpenes with low MEC values, and others with higher MEC values but longer lasting effect against F. oxysporum. Finally, one methoxylated flavonoid was found to provide additive effects to one diterpenoid. The interaction of the plant with microorganisms seems to be determined by the balance between the plant defense and virulence factors from microorganisms. However, these results show that environmental factors shape the chemical background of the ecotypes and this is decisive for the potential outcome of plant-fungal interactions (Chapter 4).
latexes, leaves and roots from three Euphorbia species were collected at different regions of Serbia. All of the samples were profiled by 1H NMR and the results were analyzed by MVDA. Interestingly, the PCA score plot showed a more compact cluster for the latexes as compared to those of the leaves and roots. Mainly species effects drove the cluster separation of the latexes. On the other hand, especially in leaves samples, the clusters were well separated by geographical origin. Moreover, the interpretation of the SIMCA and PLS-DA models indicated that geographical effects chemically less affect latexes than the other two tissues. The strength of the species effects on the metabolic variation is stronger for roots than for latexes and leaves. The metabolic constraints of latexes provide more stable metabolomes which also results in a more stable protection against herbivores and pathogens (Chapter 5).
