Antioxidant Enzyme Activities and MDA Levels

The activities of antioxidant enzymes, i.e., superoxide dismutase (SOD) and peroxidase (POD), and contents of the organic compound malondialdehyde (MDA) were determined in L0 and L12 under non-fumigated and S-fumigated treatments, respectively. The activities of SOD and POD were determined using a superoxide dismutase assay kit (Solarbio, Beijing, China) and a peroxidase assay kit (Solarbio, Beijing, China), respectively. The malondialdehyde assay kit (Solarbio, Beijing, China) measured the MDA contents. In brief, collected leaves were ground using liquid nitrogen, and SOD, POD, and MDA were extracted using the extraction buffer. The extracts were centrifuged at 12,000 × g for 10 min, and the supernatants were then measured for SOD, POD activities, and MDA contents using the multimode microplate reader (Tecan, Switzerland) (Yin et al., 2018 (link)). Each indicator had three replicate measurements.