Using a metabolomic approach, this study aims to identify metabolites present in the argan tree and to detect biomarkers associated with water stress in two ecotypes adapted to contrasting environmental conditions. Understanding which metabolites and metabolic pathways are mobilized in response to drought provides an essential scientific basis for targeting truly effective adaptation mechanisms.
The seeds used originated from two distinct sites: Aoulouz, located to the west at the bottom of the Souss plain at the foothills of the High Atlas Mountains (altitude: 700–850 m; average annual rainfall of approximately 232 mm; mean minimum and maximum temperatures of 5.6 °C and 35.7 °C, respectively), and Lakhssas, situated to the south in the Guelmim region (altitude: 916–988 m; annual rainfall of approximately 189 mm; mean minimum and maximum temperatures of 7.3 °C and 31.2 °C, respectively).
The experiment involved twelve one-year-old plants grown in 15 × 15 cm pots containing a substrate composed of a 4:1 mixture of forest soil and peat, and evenly distributed between the two ecotypes and the two experimental conditions (water stress and control). Metabolite identification was carried out using an analytical technique combining gas chromatography and mass spectrometry (GC–MS).
Under water stress conditions, statistical analysis (t-test, p < 0.05) identified 44 metabolites significantly affected in the Lakhssas ecotype and 56 in the Aoulouz ecotype.
A volcano plot was then used to distinguish overexpressed and underexpressed metabolites under water stress. In this graph, the log₂ fold change (log₂FC), representing the relative variation in metabolite abundance between water-stressed and control conditions, is plotted on the x-axis, while the y-axis (−log₁₀(p)) indicates statistical significance. Metabolites located on the right side of the graph (positive log₂FC) correspond to overexpressed metabolites (significantly higher concentration under water stress compared to the control), whereas those on the left (negative log₂FC) are underexpressed (significantly decreased concentration under water stress compared to the control). Accordingly, 34 metabolites were overexpressed and 10 underexpressed in Lakhssas, while in Aoulouz, 25 metabolites were overexpressed and 31 were underexpressed.
The relative importance of each metabolite was assessed using Variable Importance in Projection (VIP) analysis, which allows identification, within a multivariate model, of compounds contributing most to the discrimination between the two ecotypes. Based on this analysis, twenty metabolites with a VIP score ≥ 1, indicating a significant contribution, were selected.
Principal component analysis (PCA) and orthogonal partial least squares discriminant analysis (OPLS-DA) revealed a clear separation between control samples and those subjected to water stress. Based on the importance of variables in projection scores as well as receiver operating characteristic (ROC) curve analyses, ten potential biomarkers of drought tolerance were identified.
In the Aoulouz ecotype, two overexpressed metabolites, M65 (lupeol) and M102 (octadecane), as well as three underexpressed metabolites, M108 (octacosane), M123 (5-octadecene, E), and M200 (diethyl ester of 4-nitrobenzylidenemalonic acid), were found to be determinant. In contrast, the Lakhssas ecotype exhibited five overexpressed biomarkers: M6 (methyl hexadecanoate), M54 (1,3,6,10-cyclotetradecatetraene, 3,7,11-trimethyl-14-(1-methylethyl)), M88, M91, and M142.
Metabolites M65 and M102 in Aoulouz likely contribute to strengthening cuticular integrity and mitigating oxidative stress responses. Conversely, the overexpression of M6 and M54 in Lakhssas suggests an adaptation strategy relying more heavily on lipid signaling and energy metabolism. However, this ecotype may prove less resilient to prolonged drought due to a greater capacity for metabolic reallocation.
In conclusion, the study demonstrates that the two ecotypes adopt distinct strategies: the Aoulouz ecotype develops durable tolerance through reinforcement of the cuticle and improved management of oxidative stress, while the Lakhssas ecotype relies on transient metabolic adjustments. These findings are valuable as they link measurable metabolic signatures to effective physiological strategies, paving the way for practical applications in plant breeding and sustainable agriculture under water stress conditions.
Réf. Rabeh K., Farid Rachidi F., Sbabou L. et al.,2025 - Potential metabolite biomarkers of drought tolerance in contrasting Sideroxylon spinosum L. ecotypes using a metabolomic approach. J. Sci. Food Agric. (wileyonlinelibrary.com) DOI 10.1002/jsfa.70365
Posted by Jean-Paul Peltier.