# Metabolic Profiling of Sugarloaf Chicory Roots: Structural Assignment of Sesquiterpene Lactone Conjugates and Response to Reduced Irrigation

## TL;DR

This study uses NMR to analyze how sugarloaf chicory roots adapt metabolically to water stress, identifying changes in compounds like sugars and sesquiterpene lactones.

## Contribution

A novel solid-phase extraction protocol and NMR-based identification of STL conjugates in chicory roots under water stress.

## Key findings

- Root STLs (lactucin, 8-deoxylactucin, lactucopicrin) are 15-oxalate conjugates with increased water solubility.
- Water deficit caused significant decreases in STL conjugates and inositol compounds, while increasing sucrose and amino acids.
- NMR metabolomics proved effective for studying stress adaptation and identifying bioactive compounds in chicory roots.

## Abstract

Sugarloaf chicory (Cichorium intybus var. porphyreum) represents a valuable crop for investigating metabolic responses to environmental stress. This study applied quantitative 1H-NMR-based metabolomics to characterize the water-soluble metabolome and evaluate root metabolic adaptations under water-deficit (WD) conditions compared to well-watered (WW) conditions. A total of 44 compounds were identified across roots and leaves, with inulin being root-specific. To address the lack of aqueous NMR data for chicory sesquiterpene lactones (STLs), a solid-phase extraction and fractionation protocol was implemented. Comparison of 1H-NMR and 13C chemical shifts with data from the literature, 2D NMR experiments (HSQC, HMBC), and spiking with standards confirmed that the major root STLs (lactucin, 8-deoxylactucin, and lactucopicrin) are 15-oxalate conjugates with enhanced water solubility. Under water deficit, root profiles revealed significant stress-induced alterations: sucrose, alanine, threonine and phospho-choline increased, whereas asparagine, glutamic acid, chiro-inositol, myo-inositol, and all three STL conjugates decreased markedly (−39% to −50%). These shifts reflect adaptive osmotic adjustments and carbon reallocation strategies under stress. As roots represent a remarkable source of bioactive STLs, these findings support their potential valorization as functional ingredients. This study establishes quantitative NMR metabolomics as a robust tool for assessing physiological responses to water deficit, providing insights into stress adaptation mechanisms and identifying roots as promising targets for alternative applications.