Brassinolide alleviated drought stress faced by bulbil formation of Pinellia ternata by reducing ROS metabolism and enhancing AsA-GSH cycle

Drought occurs frequently because of global climate change. The involvement of brassinolide (BR) in regulating plant tolerance to stress is one of its research hotspots. Bulbil formation and development of Pinellia ternata is the key to its yield formation. However, drought in spring and waterlogging in summer often occur in the bulbil development process, which seriously affects the yield and quality of P. ternata. The study investigated the effects of BR and BR biosynthesis inhibitors (propiconazole, PCZ) on formation and growth of P. ternata bulbil under spring drought and rehydration condition. The results showed that BR treatment improved the biomass of P. ternata by increasing the bulbils formation, tillers numbers, and fresh weight of bulbils, tuber, steam and leaf when compared with control or PCZ groups both in drought and rehydration condition. Compared with the control or PCZ groups, BR application significantly elevated the photosynthetic pigment contents, PSⅡ photoprotective capacity, osmosis-regulating substance levels, and active ingredients contents in P. ternata both in drought and rehydration conditions, which promoted the growth of P. ternata. In addition, BR application enhanced antioxidant contents (AsA, GSH, AsA/DHA ratio, GSH/GSSG ratio) and enzymes activities (SOD, APX, DHAR, MDHAR), but reduced the levels of membrane lipid peroxidation and reactive oxygen in P. ternata both in drought and rehydration conditions. This study revealed that BR application could help P. ternata to cope with the drought stress during bulbil formation periods by improving AsA-GSH cycle and diminishing ROS damage.