Stress Priming Enhances Tolerance Mechanisms in Rice Species (Oryza sativa and O. glaberrima) under Flooding.

African rice faces flooding, leading to hypoxia, which triggers the accumulation of reactive oxygen species and oxidative stress. Stress priming involves subjecting a plant to mild stress to enhance its tolerance to abiotic stress. This study examined the physiological, biochemical, and anatomical responses of two rice species, Oryza glaberrima (CG 14) and Oryza sativa (FARO 44), under various flooding conditions. The treatments included plants exposed to flooding stress once (FS1) and plants subjected to flood-priming (FP) treatments. Phenotypically, CG 14 and FARO 44 respond to flooding through stem elongation and reduced root formation. Flood priming induced superoxide dismutase, peroxidase, glutathione, and flavonoids in both rice species. FARO 44 differentially increased phenylalanine ammonia-lyase activity, which activates the production of secondary metabolites. Carbohydrate-active enzymes (CAZymes), with primed FARO 44 displaying increased glycoside hydrolase and polysaccharide lyase activities, support cell wall loosening and membrane remodeling, facilitating the formation of wider aerenchyma. Thickened root endodermis and exodermis observed in primed FARO 44 suggest barrier formation, whereas CG 14 showed accumulation of reduced ascorbate with limited anatomical adaptation. Adenosine triphosphatase (ATPase) activity decreased in CG 14 and increased in FARO 44, suggesting superior energy management in FARO 44 to support enzymatic and structural adjustments. Together, enhanced antioxidant defenses, CAZyme-mediated cell wall remodeling, PAL-ATPase integration, and anatomical plasticity underpin the superior flooding tolerance of FARO 44 and demonstrate the metabolic reprogramming benefits of flood priming in rice.