Exogenous application of abscisic acid enhanced 2-acetyl-1-pyrroline biosynthesis, accumulation, and antioxidant activities in aromatic rice.

Background: Abscisic acid (ABA) is a crucial endogenous hormone in plants, regulating a myriad of processes integral to plant growth and development. However, there has been no reported impact on the production of aromatic rice following the application of exogenous ABA. Aromatic rice not only possesses intense aroma but also boasts higher nutritional value. 2-Acetyl-1-pyrroline (2-AP) is the primary compound responsible for the distinctive aroma of aromatic rice. A two-year field experiment was conducted to explore the impact of exogenous ABA application on the biosynthesis and accumulation of 2-AP, as well as the physiological characteristics, yield, and quality of aromatic rice varieties.

Results: The two aromatic rice varieties, Meixiangzhan-2 (MXZ2) and Nanjingxiangzhan (NJXZ), underwent five applications of 20 mg/L abscisic acid (ABA) from the breakthrough stage, whereas the control group (CK) received deionized water sprays.The results indicated that the application of exogenous ABA significantly boosted the 2-AP content by 20.7%, primarily by enhancing the levels of its precursors and the activities of enzymes involved in 2-AP biosynthesis. Exogenous ABA also upregulated the transcription levels of ProDH, P5CS2, OAT, and DAO4 while downregulating BADH2 transcription. Furthermore, exogenous ABA strengthened the antioxidant activites (superoxide dismutase, peroxidase, and catalase) of aromatic rice, although it led to increased malondialdehyde content and slight decreases in yield and quality. Notably, compared with superior grains, exogenous ABA application had a more pronounced effect on enhancing the aroma of inferior grains in aromatic rice with fewer negative effects.

Conclusions: The exogenous application of ABA from the breakthrough stage notably elevated the biosynthesis and accumulation of 2-AP in aromatic rice production. This was achieved by augmenting the content of its precursors and the activities of related synthetic enzymes, along with an enhancement in antioxidant activities. However, the impact on the yield and quality of aromatic rice remained relatively modest.