Responses of amino acid and aroma metabolism of fragrant pumpkin leaves to foliar feeding: insights from metabolomic and transcriptomic technologies

Pumpkin leaf is an emerging and popular vegetable with high nutritional value. However, amino acids and aromatic compounds, as critical flavour components, vary greatly across different cultivars or conditions, making flavour regulation challenging. Although considerable attention has been paid to the properties of pumpkin leaves, few studies have comprehensively profiled these flavor components in pumpkin leaves, and the biosynthetic pathways underlying the formation of its characteristic flavour remain to be discovered. Here, foodomics was employed to examine the flavour constituents in fragrant pumpkin leaves, evaluate effects of a combined foliar formulation on vegetable quality and illustrate the underlying formation mechanisms of key substances. A total of 1003 of metabolites were identified in leaves of Cucurbita moschata , among which 40 were volatiles. The top six classes—phenolic acids (150), amino acids and derivatives (93), organic acids (83), free fatty acids (77), saccharides and alcohols (77), and flavonols (70), accounted for over 54% of the total discovered substances. Many of these components, for instance, phenolic acids and flavonols, are well-recognised bioactive constituents with potential health-promoting properties, suggesting the value of pumpkin leaves as a health-functional vegetable. After foliar treatment, a total of 28 amino acids and derivatives were significantly regulated, among which 23 components were substantially accumulated. Notably, glutamic acid, the essential constitute of proteins and key contributor of the umami taste, rose by 50% and became the most abundant metabolite. In addition, the key taro-like aroma contributor 2-acetyl-1-pyrroline (2-AP) increased by 189%, while (Z)-3-hexen-1-ol with fresh-cut grass smell reduced by 65.5%, which prominently improved the aroma characteristics of pumpkin leaves as vegetables. Further integrated transcriptome and metabolome analysis revealed an alternative 2-AP biosynthetic route involving the key precursor putrescine and gene CmoADC encoding arginine decarboxylase. Both putrescine and CmoADC were significantly up-regulated (2.48- and 8.33-fold, respectively). Additionally, a large portion of hormone-responsive transcription factors were differentially regulated. Phytohormone analysis found 42 out of 66 identified components were impacted, including 18 cytokinin- and 11 auxin-associated compounds. These changes in phytohormones and transcription factors could play important role in the metabolite regulation and aroma formation. The study provide important insights into pumpkin leaf rich profile of bioactive constituents and nutrition. The combined foliar formulation improved amino acid nutrition and umami, and enhanced the taro-like aroma through the putrescine-involved 2-AP biosynthetic pathway, providing a metabolically defined strategy for vegetable quality improvement through agricultural management.