Effects of Abscisic Acid on Rice Seed Dormancy: Antioxidant Response and Accumulations of Melatonin, Phenolics and Momilactones

Abscisic acid (ABA) is a well-known phytohormone that initiates seed dormancy. This is the first study elucidating the variability and relationship in the accumulation of phenolics, melatonin, and momilactones A (MA) and B (MB) during a rice (Oryza sativa L. var. Koshihikari, Akisakari, and Akiroman) seed dormancy process treated by ABA with concentrations of 0 (control), 10, 50, and 100 µM over 8 days. Accordingly, increased concentrations of ABA resulted in an extended dormancy period of rice seeds, along with reducing fresh weight while maintaining stable dry weight in all varieties. ABA treatment elevated total phenolic (TPC) and flavonoid (TFC) contents. Particularly, quantities of ferulic and cinnamic acids were enhanced, in line with the promoted antioxidant capacities of ABA-treated rice seeds. Momilactone contents were increased (3.8% to 32.6% for MA and 16.3% to 31.3% for MB) during the extension of rice seed dormancy regulated by ABA. Notably, the accumulation tendency of MA and MB under ABA effects was consistent with that of melatonin, a phytohormone associated with seed dormancy prolongation. The finding implies that MA and MB may play a role alongside melatonin in signaling the extended dormancy of rice seeds through the ABA pathway. Future research should delve into the molecular mechanisms underlying these observations.