Insights from NMR metabolomics into plant responses to environmental stress

MSc. Anna Mascellani

Doctoral thesis

Abstract:

Nuclear magnetic resonance (NMR) spectroscopy is a valuable approach for quantifying plant metabolites and monitoring metabolic changes. Using this technique, significant plant metabolite changes emerge, with the advantages of a non-destructive, high-throughput and reproducible method that excels in structure elucidation. A curated set of 30–60 molecules with high physiological relevance can outperform datasets based on mass spectrometry, which often contain thousands of provisionally identified features, when it comes to classification and biological interpretation. This thesis is based on a comprehensive and original literature review and three original scientific papers with robust design and clear output for agricultural practice, where NMR has been used to tent metabolic changes associated with biotic and abiotic stress. In the last two decades, NMR metabolomics was limitedly chosen for assessing plant responses to biotic stress, although resistance mechanisms are detectable and clear. Our research has shown that polyketides in gerbera are biomarkers of resistance to powdery mildew. Gerberinside emerged as the key compound involved in resistance detection; when its level was low, higher levels of gerberin and parasorboside contributed to the resistance. Furthermore, a new compound probably involved in resistance, 5-hydroxyhexanoic acid 3-O-β-D-glucoside, was described. Maize overcomes the stress caused by the accumulation of carbamazepine with notable metabolic changes at the early phenological stage, including decreased photosynthesis and water potential, increased carotenoid levels, decreased carbohydrate levels (glucose and fructose) and γ-aminobutyric acid in roots, as well as increased maleic acid and phenylpropanoid (chlorogenic acid and its isomer, 5-O-caffeoylquinic acid) levels in aboveground biomass, whereas older plants adapt and only display minor effects. Salinity stress affects the expression of key sugar metabolism and transport genes, as well as the soluble carbohydrate content of ripe fig fruits. A general increase in the transcript levels of genes involved in the transport of soluble carbohydrates was observed. Alkaline-neutral and Acid Invertases transcripts, related to the synthesis of glucose and fructose, were up-regulated in ripe fruits of NaCl-stressed plants without a change in the content of glucose and fructose. The increases in sucrose and sorbitol contents were likely the result of the up-regulation of the transcription of sucrose synthase- and sorbitol dehydrogenase-encoding genes. The thesis concludes by pointing out the peculiarities of NMR-based metabolomics in plant science and presenting prospects for the technique.

Keywords

1H NMR, plant metabolomics, environmental stress

Language used: English

Date on which the thesis was submitted / produced: 8. 8. 2023

Thesis defence

• Supervisor: doc. Ing. Jaroslav Havlík, Ph.D.
• Reader: Lenka Burketová, externi, Otmar Urban, externi, Jan Sýkora, externi

Czech University of Life Sciences Prague

Faculty of Agrobiology, Food and Natural Resources

Doctoral programme:
Agricultural Chemistry