Foliar application of procyanidins enhanced the biosynthesis of 2-acetyl-1-pyrroline in aromatic rice (Oryza sativa L.)

BACKGROUND: Procyanidins is a polyphenolic compound with multiple properties. However, the application of exogenous procyanidins in crops has not been reported. Aromatic rice is a high-quality rice with a special aroma and popular with consumers. The 2-acetyl-1-pyrroline (2-AP) is a key compound of aromatic rice aroma. In the current study, aromatic rice plants were sprayed with procyanidins solutions at 0.25 (Pr0.25), 0.50 (Pr0.50), 1.00 (Pr1.00), 2.00 (Pr2.00) g L(−1), respectively and treatment sprayed with distilled water was taken as control (CK). The effects of exogenous procyanidins on growth and 2-AP biosynthesis of aromatic rice plants were explored. RESULTS: Compared with CK, Pr1.00 and Pr2.00 treatments significantly increased 2-AP content by 16.67% and 37.68%, respectively. Higher proline, 1-pyrroline-5-carboxylic acid (P5C), 1-pyrroline, methylglyoxal contents, and lower γ- aminobutyric acid (GABA) content were recorded in Pr1.00 and Pr2.00 treatments than CK. Compared with CK, Pr1.00 and Pr2.00 treatments significantly improved the activities of P5CS and OAT and diminished the activity of BADH. Furthermore, compared with CK, Pr1.00 and Pr2.00 treatments significantly up-regulated the transcript levels of P5CS2, P5CR, OAT, DAO4 and down-regulated the transcript levels of BADH2. Exogenous procyanidins had no substantial effects on plant height, stem diameter, fresh weight, and dry weight of aromatic rice plants. CONCLUSIONS: In conclusion, our findings reported the increment of 2-AP content in aromatic rice under exogenous procyanidins. Our results indicated that the application of exogenous procyanidins enhanced 2-AP biosynthesis by improving proline biosynthesis and inhibiting GABA formation.