Carnitine modulates antioxidative defense in ABI2 mutant under salt stress

Carnitine, a ubiquitous compound in living organisms, fulfills diverse roles in energy metabolism, stress resilience, and detoxification. Its antioxidant and osmolyte traits offer relief to stressed plants. Antagonizing abscisic acid (ABA), carnitine influences ABA-responsive genes. Our study, using Arabidopsis thaliana wild-type Ler. (Landsberg erecta) and ABA-insensitive abi2-1 mutants, explored carnitine’s impact on antioxidative responses and ABI2’s role in salt-induced carnitine metabolism. The application of 5 µM carnitine has alleviated the decrease in RWC, shoot weight, and rosette diameter WT plants caused by 80 mM salt stress for 4 days. Carnitine reduced cell membrane damage and salinity effects, evidenced by decreased lipid peroxidation and H₂O₂. In contrast, the impaired ABI2 of abi2-1, due to deficient phosphatase activity, further exacerbated the inhibitory effect of carnitine on the enzymes of the ascorbate-glutathione cycle, consequently reducing stress mitigation. While abi2-1 mutants exhibited unchanged superoxide dismutase (SOD) activity, they demonstrated increased catalase and peroxidase activity following carnitine treatment under salt stress compared to WT plants. Conversely, wild-type WT plants treated with carnitine exhibited elevated total glutathione content under salt stress, a response not observed in abi2-1 mutants under carnitine treatment. These results underscore the crucial role of ABI2-dependent ABA signaling in regulating plant carnitine metabolism.