*Article* **Physiological and Biochemical Regulation Mechanism of Exogenous Hydrogen Peroxide in Alleviating NaCl Stress Toxicity in Tartary Buckwheat (***Fagopyrum tataricum* **(L.) Gaertn)**

**Xin Yao <sup>1</sup> , Meiliang Zhou <sup>2</sup> , Jingjun Ruan 1,\* , Yan Peng <sup>1</sup> , Chao Ma <sup>1</sup> , Weijiao Wu <sup>1</sup> , Anjing Gao <sup>1</sup> , Wenfeng Weng <sup>1</sup> and Jianping Cheng 1,\***


**Abstract:** We aimed to elucidate the physiological and biochemical mechanism by which exogenous hydrogen peroxide (H2O<sup>2</sup> ) alleviates salt stress toxicity in Tartary buckwheat (*Fagopyrum tataricum* (L.) Gaertn). Tartary buckwheat "Chuanqiao-2" under 150 mmol·L −1 salt (NaCl) stress was treated with 5 or 10 mmol·L <sup>−</sup><sup>1</sup> H2O<sup>2</sup> , and seedling growth, physiology and biochemistry, and related gene expression were studied. Treatment with 5 mmol·L <sup>−</sup><sup>1</sup> H2O<sup>2</sup> significantly increased plant height (PH), fresh and dry weights of shoots (SFWs/SDWs) and roots (RFWs/RDWs), leaf length (LL) and area (LA), and relative water content (LRWC); increased chlorophyll a (Chl a) and b (Chl b) contents; improved fluorescence parameters; enhanced antioxidant enzyme activity and content; and reduced malondialdehyde (MDA) content. Expressions of all stress-related and enzyme-related genes were up-regulated. The *F3*0*H* gene (flavonoid synthesis pathway) exhibited similar up-regulation under 10 mmol·L <sup>−</sup><sup>1</sup> H2O<sup>2</sup> treatment. Correlation and principal component analyses showed that 5 mmol·L <sup>−</sup><sup>1</sup> H2O<sup>2</sup> could significantly alleviate the toxic effect of salt stress on Tartary buckwheat. Our results show that exogenous 5 mmol·L <sup>−</sup><sup>1</sup> H2O<sup>2</sup> can alleviate the inhibitory or toxic effects of 150 mmol·L <sup>−</sup><sup>1</sup> NaCl stress on Tartary buckwheat by promoting growth, enhancing photosynthesis, improving enzymatic reactions, reducing membrane lipid peroxidation, and inducing the expression of related genes.

**Keywords:** Tartary buckwheat; H2O<sup>2</sup> ; NaCl; physiology and biochemistry
