Spatio-Temporal Dynamics of Lettuce Metabolome: A Framework for Targeted Nutritional Quality Improvement

Lettuce (Lactuca sativa L.) is a popular leafy vegetable valued for its dietary fiber, antioxidants, and beneficial vitamins. This study presents a comprehensive spatio-temporal analysis of the lettuce metabolome, revealing complex dynamics in metabolite accumulation influenced by plant age, leaf position, proximodistal distribution within a leaf, and head closure. Samples were collected from plants at five maturity stages (ranging from baby leaf to full commercial maturity and eventually to bolting) and from five leaf positions (from the apex to the base of each plant). A widely targeted metabolomics approach identified 1905 compounds, with flavonoids, phenolic acids, and lipids as the largest classes. Younger plants exhibited higher levels of flavonoids, while older plants accumulated more saccharides and amino acids. Metabolites showed distinct proximodistal distributions, with flavonoids and vitamins concentrated at leaf tips and terpenoids declining from base to tip. Head closure significantly reduced levels of flavonoids, retinol (vitamin A1), and riboflavin (vitamin B2), while it was associated with increased content of other beneficial vitamins, such as thiamine (B1), pantothenate (B5), and pyridoxine (B6). Broad-sense heritability (H²) estimates for metabolites yielded mean H² values of 0.648 and 0.743 for plants at baby-leaf and commercial maturity stages, respectively. The overall highest heritability was observed in tannins (H² = 0.909) in younger plants and chalcones (H² = 0.894) in older plants, suggesting strong genetic control over specific metabolite classes and subclasses. These findings offer a robust framework for optimizing lettuce's nutritional profile by linking metabolite distributions to developmental processes, plant architecture, and genetic regulation. By leveraging these insights, breeders and producers can develop targeted strategies to enhance metabolite content through optimized breeding and harvesting strategies.