Gibberellic acid (GA) alleviates Al toxicity in rice (Oryza sativa) through a nitric oxide (NO) dependent pathway

Over 50% of global arable soils are acidic; acidic soil-induced aluminum (Al) phytotoxicity primarily inhibits root elongation, thereby reducing the plant's absorption of water and nutrients, which suppresses crop yield. Gibberellic acid (GA), a class of critical plant hormones, acts as a core regulator of plant development and growth mechanisms and contributes to the physiological adaptation of plants under stress conditions. In this study, we selected the rice variety Nipponbare (Nip) to investigate whether GA exerts an effect on alleviating Al toxicity and to explore the underlying mechanisms in rice. This study shows that Al stress quickly elevated the endogenous GA content in rice root tissues, consequently alleviating Al-induced suppression of root development. Exogenous GA application increased the expression of the Oryza sativa Cysteine-rich Peptide (Peptide with Cysteine-rich TDIF motif) 3 (OsCDT3) and Oryza sativa Ferric Reductase Defective Like 4 (OsFRDL4) genes, which reduce the toxicity of Al to plants and conversely decreased the expression of the Oryza sativa Natural Resistance-Associated Macrophage Protein 1 for Aluminum Transport (OsNRAT1) gene, which transports Al ions from the extracellular environment to the intracellular space. Furthermore, exogenous GA treatment modified the hemicellulose and pectin levels, therefore decreasing the absorption of Al. Further research shows that GA reduced the endogenous nitric oxide (NO) levels; nevertheless, the application of an exogenous nitric oxide donor sodium nitroprusside (SNP) offset the alleviatory role of GA. In conclusion, GA accelerated the cell wall Al exclusion mechanism, probably improving rice tolerance to Al toxicity via regulating the accumulation of NO.