Exogenous acetylcholine alleviates cadmium-induced phytotoxicity by modulating photosynthetic metabolism and antioxidant potential in tobacco (Nicotiana benthamiana)

Abstract

Acetylcholine (ACh) plays a potential role in mediating various physiological processes in plants. However, the involvement of acetylcholine in cadmium (Cd) stress tolerance is unknown. Cd stress caused a decline in biomass, pigment, and photosynthetic capacity in Nicotiana benthamiana plants. A significant oxidative stress was evident through enhancing the accumulation of reactive oxygen species and lipid peroxidation. However, pretreatment with acetylcholine (50 and 100 µM) effectively decreased oxidative damage, especially by 50 µM ACh, which reduced H2O2 and O2*- contents by 50.4 and 45.3%, respectively, in plants treated with Cd. Our results indicated that the protection of photosynthesis by ACh was attributed to the improved photochemical activity of PSII and inhibited stomatal closure. Additionally, ACh-induced Cd toxicity tolerance was closely associated with improved activities of antioxidant enzymes and ascorbate and glutathione pools. Thus, our results suggest that acetylcholine may act as a positive regulator against Cd toxicity in tobacco.

Keywords

• antioxidant system
• chlorophyll fluorescence
• gas exchange
• photoinhibition