Spermidine and brassinosteroid regulate root anatomical structure, photosynthetic traits and antioxidant defense systems to alleviate waterlogging stress in maize seedlings

Frequent flooding and waterlogging adversely impair maize production in China mainly; maize seedlings are extremely sensitive to waterlogging stress at early growth stages. Therefore, improving the resistance of maize seedlings under waterlogging stress is essential for maize production. This study investigated the effects of exogenous spermidine (Spd) and brassinolide (BRs) application on maize seedling adaptation to severe waterlogging. Maize cultivar Xingken-6 (XK-6) was used and treated with Spd (1.5 mg L-1) and BRs (1.0 mmol L-1) under 14-days waterlogging treatments at three-leaf (V3) and fifth-leaf (V5) stages. We found that waterlogging stress decreased overall maize seedling growth by increasing oxidative damage due to reactive oxygen species (ROS) accumulation, decreased photosynthetic capacity, chlorophyll concentration, and significantly damaged chloroplast structure and root anatomy. Spd and BRs treatments effectively relieved impairment of waterlogging by increasing root dry matter (DM), shoot DM, root length, root volume, number of living cortical cells in seminal roots, and net photosynthetic rate. On the other hand, Spd and BRs decreased root aerenchyma area and ROS production across growth stages. Our results demonstrated that Spd and BRs enhanced maize seedling tolerance to waterlogging stress by simultaneously regulating root anatomical structures, photosynthetic machinery, and antioxidant defense systems. (C) 2021 Published by Elsevier B.V. on behalf of SAAB.