Acetylcholine ameliorates the adverse effects of cadmium stress through mediating growth, photosynthetic activity and subcellular distribution of cadmium in tobacco (Nicotiana benthamiana)

Acetylcholine (ACh), a well-known major neurotransmitter, plays a potential role in response to abiotic stresses. However, the mechanism of ACh-mediated cadmium (Cd) toxicity in tobacco seedlings is largely uncharacterized. In this study, a hydroponics experiment was conducted under 100 mu M Cd stress in the presence or absence of ACh (50 mu M) to investigate the potential effects of ACh on Cd toxicity. The results revealed that ACh application effectively alleviated Cd-induced reductions in plant growth, photosynthetic pigments and gas exchange attributes and improved the photosystem II activity. Ultrastructural observation indicated that Cd exposure ruptured the internal structure of chloroplasts, and even caused the accumulation of osmiophilic granules in chloroplasts, whereas these phenomena were alleviated by the addition of ACh. Cd stress also caused a marked increase in oxidative stress, as evidenced by the accumulation of O-2(center dot-) and H2O2, which were efficiently minimized after ACh application by up-regulating antioxidant enzyme activities (superoxide dismutase, SOD; catalase, CAT; ascorbate peroxidase, APX; glutathione reductase, GR). Besides, Cd stress considerably increased the levels of glutathione (GSH), Non-protein thiols (NPTs) and phytochelatins (PCs), whereas ACh application to Cd-stressed seedlings further increased those contents, thereby enhancing the tolerance of Cd-stressed plants. Moreover, exogenously applied ACh declined the accumulation of Cd and minimized the damage from Cd toxicity by modulating the distribution of Cd in the vacuole and cell wall. Therefore, these results provide insights into the ameliorative effects of ACh on Cd-induced a series of physiological reactions.