EFFECTS OF BOSCALID EXPOSURE ON PHOTOSYNTHETIC AND ANTIOXIDANT RESPONSES OF RICE SEEDLINGS

The widespread application of succinate dehydrogenase inhibitor fungicides (SDHIs) poses risks for ecosystems. This study investigated the impacts of boscalid (0-10 mg/L) exposure on photosynthesis and antioxidant systems in rice seedlings. The results showed that 1.5-2.5 mg/L boscalid increased chlorophyll (Chl) contents, photosynthetic rate (Pn) and Rubisco activities along with upregulating the genes psbA and psaB, leading to the improvement of photosynthesis. However, 10 mg/L boscalid triggered the generation of O-2.(-), enhancing the activities of NADPH oxidase, superoxide dismutase (SOD), ascorbate peroxidase (APX) isozymes as well as glutathione S-transferases (GSTs), suggesting reactive oxygen species (ROS) overproduction and a defensive response in the seedlings. Meanwhile, 10 mg/L boscalid decreased Chl contents, Pn and Rubisco activities accompanied by downregulation of the genes atpB, psbA and psaB, as well as Lhcb1 protein, resulting in the impairment of photosynthesis via inhibition of ATP synthesis and photosynthetic electron transfer. Additionally, SOD and APX isozymes together with GSTs and reduced glutathione (GSH) alleviated boscalid-induced toxicity suggesting their role in the defense and detoxification in rice seedlings.