Abscisic acid primes rice seedlings for enhanced tolerance to alkaline stress by upregulating antioxidant defense and stress tolerance-related genes

Abscisic acid (ABA) has been shown to prime rice seedlings for enhanced tolerance to alkaline stress under both greenhouse and field conditions. This study aimed to understand the mechanism of the ABA priming effect. Rice seedlings were grown hydroponically and pretreated with ABA (10 μM) for 24 h, and then subjected to alkaline stress simulated by 15 mM Na2CO3 solution (pH 10.87). Paraquat (2.5–25 μM) was used as an intracellular generator of reactive oxygen species (ROS). Compared to the control treatment, pretreatment with ABA significantly mitigated root damage and improved the survival rate of rice seedlings under alkaline conditions. Furthermore, ABA pretreatment increased the antioxidant enzyme activities of superoxide dismutase, catalase, peroxidase and ascorbate peroxidase, and reduced the alkalinity- and paraquat-induced ROS accumulation (O2·- and H2O2) and seedling injury and mortality. In addition, the expression of the ABA-responsive genes SalT and OsWsi18, as well as the stress tolerance-related genes OsJRL, OsPEX11, OsNAC9, OsAKT1 and OsHKT1, was superinduced by ABA pretreatment under alkaline conditions. ABA priming enhances tolerance to alkaline stress by upregulating the antioxidant defense system and stress tolerance-related genes in the roots of rice seedlings.