Overexpression of S-adenosylmethionine synthetase 1 enhances tomato callus tolerance to alkali stress through polyamine and hydrogen peroxide cross-linked networks

S-adenosylmethionine synthetase is a member of the stress-induced family genes. Our previous research indicated that overexpression of SlSAMS1 confers alkali stress tolerance to tomato seedlings. However, information regarding the alkali stress tolerance mechanism of SlSAMS1 and the cross-linked network between SlSAMS1 and downstream signal has been limited. To study how SlSAMS1 improves alkali stress tolerance, we manipulated the SlSAMS1 transgenic calluses through a pharmacological approach and found that overexpression of SlSAMS1 was positively correlated with polyamine (PA) and hydrogen peroxide (H₂O₂) accumulation leading to improve alkali stress tolerance. Additionally, the accumulation of H₂O₂ in SlSAMS1 overexpression calluses depended on polyamine oxidase activity. The activities of antioxidant system, accumulation of organic acid, Na⁺ detoxification as well as alkali stress tolerance of the SlSAMS1 transgenic calluses were reversed by PA biosynthesis inhibitors, but not significantly influenced by ethylene biosynthesis inhibitors. These results suggest that overexpression of SlSAMS1 enhances alkali stress tolerance through PA and H₂O₂ cross-linked networks, which provide new insight into how SlSAMS1 functions as a stress mediatory element in regulating plants tolerance to alkali stress.