Acetylcholine mechanism of action to enhance tolerance to salt stress in Nicotiana benthamiana

Acetylcholine (ACh) is one of the important neurotransmitters, involved in signal transduction function in human and animal brain. However, the influence of ACh treatment on salt-stress tolerance in plants is yet unknown. Salt stress caused a reduction in gas-exchange parameters, chlorophyll content, antioxidant enzyme activities, and leaf relative water content of Nicotiana benthamiana plants. However, the above inhibitions could be significantly alleviated by application of leaf spray or root application of ACh. Exogenous ACh reduced the accumulation of malondialdehyde by enhancing activities of antioxidant enzymes such as peroxidase and superoxide dismutase. In addition, enhanced accumulation of organic osmolytes including soluble sugars and proline possibly regulated the signal mechanisms related to stress. Application of ACh could also improve gas-exchange parameters and photosynthetic pigment accumulation in leaves of salt-stressed plants. These effects of ACh were beneficial for maintaining better water status in plants, the concentration of 10 µM ACh applied both in the form of leaf spray or root application was the most effective. Therefore, our findings provided a stronger evidence for a physiological role of ACh and its potential use at optimal concentration by leaf or root application to alleviate damage caused by salt-stress in plants.