Beneficial role of Acetylcholine in chlorophyll metabolism and photosynthesis gas exchange in Nicotiana benthamiana seedlings under salinity stress.

Acetylcholine (ACh) is believed to improve plant growth. However, regulation at biochemical and molecular levels is largely unknown. Present study investigated the impact of exogenously applied ACh (10 µM) on the growth and chlorophyll metabolism in hydroponically grown N. benthamiana under salt stress (150 mM NaCl). Salinity reduced root hydraulic conductivity while ACh treated seedlings exhibited significant increase resulting in increased relative water content. Salinity induced reduction in chlorophyll biosynthetic intermediates like protoporphyrin-IX, Mg-photoporphyrin-IX and protochlorophyllide was significantly ameliorated due to ACh. Such influence of ACh on chlorophyll synthesis was confirmed by up-regulation of HEMA1, CHLH, CAO and POR genes. Gas exchange parameters like stomatal conductance, internal CO₂ concentration and transpiration rate increased due to ACh thereby alleviating the salinity effects on photosynthesis. In addition, salinity induced enhancement in lipid peroxidation was declined due to ACh treatment via modulations in the activities of antioxidant enzymes assayed (superoxide dismutase and peroxidase). Importantly, ACh significantly reduced the uptake of Na and increased K resulting in declined Na/K ratio. Results of present study indicate that ACh can be affective in ameliorating NaCl induced osmotic stress, altered chlorophyll metabolism and photosynthesis by maintaining the ion homeostasis, hydraulic conductivity and water balance.