Regulation of reactive oxygen species metabolism and oxidative stress signaling by abscisic acid pretreatment in rice (Oryza sativa L.) seedlings through sub1A QTL under salinity

In this experiment, we investigated salinity-induced oxidative stress in rice with the involvement of sub1A quantitative trait loci for reactive oxygen species metabolism. We pretreated 15-day-old seedlings of cv. Swarna sub1 (a salt-susceptible variety) and Gosaba 5 (a salt-tolerant variety) using either 10 µM abscisic acid (ABA) or absence. The seedlings were then transferred to hydroponic cultures with either 0 or 100 mM NaCl to induce stress. Oxidative stress in the rice plants was investigated through both in vitro and in vivo detection of superoxide, hydrogen peroxide, and biosynthetic enzymes, including NADP oxidase activity under salinity. cv. Swarna sub1 exhibited enhanced retention of relative water content, elevated K+/Na+ ratio, and membrane stabilization with ABA. ABA also mitigated cell viability loss, though to varying extents among the cultivars, as observed through fluorescence imaging and Evans blue staining. Additionally, ABA treatment reduced cell wall peroxidation, resulting in expanded endodermal lumens and a decrease in malondialdehyde content. Pigment fluorescence and NADP-malic enzyme activity supported oxidative tolerance. A higher ratio of oxidized to reduced states of glutathione and ascorbate indicated improved tolerance when treated with ABA. The biogenesis of ABA was found to correlate with cultivar-specific tolerance, particularly when exogenous ABA was applied. ABA treatment appeared to heighten the sensitivity of enzymatic antioxidant cascades and showed variations in gene polymorphism. The detoxification of methylglyoxal, regulated by ABA, accentuated glyoxalase activities as potential biomarkers for oxidative stress. The study further discusses the roles of ABA metabolism in managing salinity-induced oxidative stress in both sensitive and tolerant rice cultivars.