Determination of glutathione and ascorbate contents
For measuring the reduced glutathione (GSH) and oxidized glutathione (GSSG) content in soybean leaves, we used a GSH and GSSG assay kit (Comin Biotechnology, Suzhou, China) following the manufacturer’s instructions. GSH and GSSG content were measured at OD412. The ascorbic acid (ASA) and dehydroascorbate (DHA) content determination of the soybean leaves were measured the manufacturer’s protocols for the ASA and DHA kits (Comin Biotechnology, Suzhou, China). ASA and DHA content were measured at OD402 and OD265. The activities of monodehydro reductase (MDHAR), dehydroascorbate reductase (DHAR), and glutathione reductase (GR) were measured using enzymatic activity assay kits (Comin Biotechnology, Suzhou, China) according to the manufacturer’s instructions. MDHAR, DHAR, and GR activities were determined at OD340, OD265 and OD340, respectively.