L ascorbic acid

Pepsin, trypsin, bile salt, Pyrogallol, L(+)-ascorbic acid, Ferrous sulfate, potassium ferricyanide and trichloroacetic acid were purchased from Solarbio Science & Technology Co., Ltd. (Beijing, China). DMEM medium and special modified DMEM medium were obtained from Dalian Meilun Biotech Co., Ltd. (Dalian, China). RNA Isolation Kit was purchased from Vazyme Biotech Co., Ltd. (Nanjing, China). Fluorescent quantitation and a Reverse Transcription kit were obtained from United States Biological (Shanghai, China). ELISA kit was purchased from Chenglin Biotechnology Co., Ltd. (Beijing, China). DPP-IV was purchased from Sigma Chemical (St. Louis, MO, USA). All other chemicals and reagents were purchased from Beyotime Biotechnology Co., Ltd. (Shanghai, China).

Plant’s physiological indicators were immediately measured after the leaves were collected. Malondialdehyde (MDA) was determined by thiobarbituric acid method, hydrogen peroxide (H₂O₂) was determined by titanium sulfate colorimetric method, Pro was determined by acid ninhydrin colorimetric method, soluble sugar was determined by anthrone colorimetric method, chlorophyll (Chl) content was determined by ethanol extraction colorimetric method, POD activity was measured by spectrophotometer at 470 nm, CAT activity was measured by UV-absorbance method at 240 nm, and APX activity was calculated by measuring the oxidation rate of L-ascorbic acid (Beijing Solarbio Science & Technology Co., Ltd.). UC-visible spectrophotometer (UV-5500, Shanghai Yuan Analysis, China) was used for measurement. Indophenol blue colorimetric method was applied to determine soil ammonium N (NH₄⁺-N), and ultraviolet spectrophotometry was used for the determination of soil nitrate N (NO₃⁻-N). This part is the same as our previous research (Liu, L. et al., 2022 (link)).