Abstract: A widely targeted metabolomics approach based on ultra-high performance liquid chromatography-electrospray ionization-tandem mass spectrometry (UPLC-ESI-MS/MS) was used to analyze differences in metabolites between aromatic soft rice and ordinary rice cultivated in the saline-alkali soil in the Yellow River Delta. A total of 1 988 metabolites were detected. Principal component analysis (PCA) and cluster analysis (CA) revealed that both rice variety and growth stage significantly influenced rice metabolites, the difference being larger among varieties than among growth stages. Orthogonal partial least squares-discriminant analysis (OPLS-DA) showed that compared to ordinary rice, the differential metabolites were predominantly un-regulated. The most significant differences were observed at the filling stage (812 differential metabolites were identified, 670 of which were up-regulated) and there were smaller but significant differences at the maturity stage (569 differential metabolites were identified, including 433 up-regulated ones). The significantly differential metabolites were concentrated in terpenoids, flavonoids, and lipids. The up-regulation of terpenoids and lipids may be associated with the unique aroma of fragrant soft rice, while the up-regulation of flavonoids may be linked to its antioxidant capacity and various physiological activities. Totally 7 significant enrichment pathways were identified at the maturity stage (P < 0.05), including flavonoid biosynthesis, ascorbate and aldarate metabolism, biosynthesis of secondary metabolites, carotenoid biosynthesis, plant hormone signal transduction, pentose phosphate pathway and diterpenoid biosynthesis, while no significant enrichment pathways were identified at the filling stage. This study highlights the advantages of aromatic soft rice cultivated in saline-alkali soil in accumulating primary and secondary metabolites (especially terpenoids, flavonoids, and lipids), thereby providing a metabolomics basis for understanding its aroma formation and nutritional functionality.

Key words: aromatic soft rice; widely targeted metabolomics; differential metabolites; metabolic pathway