The mechanism of exogenous gibberellin A3 protecting sorghum shoots from S-metolachlor Phytotoxicity

BACKGROUND S -metolachlor (MET) was used to prevent weed infestation in sorghum fields, but inappropriate application could result in phytotoxicity on sorghum. Exogenous gibberellin A 3 (GA 3 ) has been applied for alleviating the phytotoxicity of MET. However, its detoxification mechanism is still not well known. RESULTS Leaf deformity of sorghum caused by 200 mg/L MET was alleviated by treating sorghum shoots with 800 mg/L GA 3 , and the injury recovery rate of growth index was over 73%. More importantly, GA 3 could not accelerate the metabolic rate of MET in sorghum. The result of phytohormone metabolomics showed that endogenous GA 3 content in sorghum decreased by 78.10% with MET treatment, while abscisic acid (ABA) content increased by 120.2%, resulting in 10.3-fold increase of ABA/GA 3 ratio. Content of ABA and GA 3 increased by 11.9- and 21.1-fold with MET and GA 3 treatment, respectively, leading to ABA/GA 3 ratio restoration. Moreover, MET inhibited the expression of genes encoding key enzymes related to GA synthesis including CPS1 , KO2 , KAO , GA20ox1D and ABA8ox gene related to ABA metabolism. The transcription levels of GA metabolism-related genes CYP714D1 and GA2ox were up-regulated by 11.2- and 7.2-fold, while ABA synthesis-related genes NCED and ZEP were up-regulated by 8.0- and 3.0-fold, respectively, with MET and GA 3 treatment. Conclusion In this study, exogenous GA 3 protecting sorghum shoots from MET phytotoxicity was due to supplement the MET-induced GA 3 deficiency by absorbing exogenous GA 3 , and restore homeostasis of ABA and GA 3 by promoting ABA synthesis, which provides novel insights for mechanism of GA 3 alleviating MET phytotoxicity. © 2022 Society of Chemical Industry.