Effects Of Exogenous Acetylcholine On Some Physiological Parameters And Photosynthetic Characteristics Of Nicotiana Benthamiana Under Drought Stress

Acetylcholine,similar to phytohormone,plays regulatory roles in plant growth under both normal and abiotic stress conditions.There are abundant studies of acetylcholine in plant physiology such as stomatal movement,seed germination,photosynthesis and so on.However,little research has been done in drought resistance.The present study was conducted to investigate the effects of acetylcholine?0.01 mM and 0.1 mM?root application on some physiological parameters and photosynthetic characteristics of tobacco?Nicotiana Benthamiana?under drought stress,which was simulated by 10%polyethylene glycol?PEG-6000?.The main conclusions are as following:1.Exogenous acetylcholine could improve the water retaining capacity of tobacco leaves.The relative water content?RWC%?,the content of soluble sugars,proline and soluble proteins were enhanced by acetylcholine?0.01 mM?root application.Compared with the treatment of10%PEG,RWC%was increased by 4.71%at 36 h.2.Exogenous acetylcholine could alleviate oxidative damage of tobacco leaves.Acetylcholine?0.01 mM?root application remarkably increased the activities of superoxide dismutase?SOD?,peroxidase?POD?,catalase?CAT?and ascorbate peroxidase?APX?and the content of ascorbic acid?AsA?and glutathione?GSH?,decreased the content of H₂O₂,O₂^-and MDA under drought stress in tobacco.SOD and APX activities were increased by 19.73%and11.17%than drought stress alone at 36 h respectively.3.Exogenous acetylcholine could be beneficial to maintain high cell viability of leaves and root activity in tobacco.The cell viability of leaves were significantly improved by 0.01mM acetylcholine under drought stress,and it was 1.69 times of 10%PEG treatment at 36 h.Due to the drought stress,the roots became fracture and deeper color,0.01 mM acetylcholine could alleviate this phenomenon and significantly increase the root activity of tobacco.4.Exogenous acetylcholine could affect the photosynthetic characteristics of tobacco by regulating stomatal limiting factors.0.01 mM acetylcholine significantly increased the P_N of tobacco,while the trend of stomatal conductance?g_s?and intercellular carbon dioxide concentration?C_i?was first decreased and then at a relatively stable level under drought stress;Besides,the circumference,area,stomatal opening and opening rate of the stomata could be improved by 0.01 mM acetylcholine.5.Exogenous acetylcholine could improve the photosynthetic characteristics of tobacco by regulating non-stomatal limiting factor.Acetylcholine?0.01 mM?could protect photosynthesis organs,enhance photochemical reactivity and carbon assimilation potential by regulating the absorption,distribution and transformation of light of tobacco leaves under drought stress.Compared with the treatment of 10%PEG,the photosynthetic pigments?chlorophyll a,chlorophyll b and carotenoid?content,photochemical quenching?qP?as well as non-photochemical quenching?NPQ?was increased and the fixed fluorescence?Fo?was decreased by 0.01 mM acetylcholine under drought stress;Fv/Fm,QY-Lss,Fv/Fo and Rfd-Lss were improved by 0.01 mM acetylcholine in different degrees under drought stress;The M peak of chlorophyll fluorescence kinetics curve was lower than that treated with 10%PEG,which indicated that photophosphorylation was promoted;ATP content and rubisco activities was 2.40 and 1.40 times than that under 10%PEG treatment respectively,which reflected the carbon assimilation ability was improved.6.Based on the methods of principal factors analysis and regression analysis,the main factors of influencing Net photosynthetic rate include Mg²⁺-ATPase?chlorophyll a?qP?ATP?Rfd-Lss?Fv/Fm?C_i?Rubisco?QY-Lss?Fv/Fo?Fo and POD,which shows the decline of net photosynthetic rate mainly caused by non-stomatal limiting factor.The effect of exogenous acetylcholine on drought resistance of tobacco was related to the concentration,and the effect of 0.01 mM was better than 0.1 mM.This current study showed that exogenous acetylcholine?0.01mM?had a significant effect on the drought tolerance of tobacco by up-regulating the content of osmoregulation substance,antioxidant ability and photosynthetic characteristics.What's more,the photosynthetic rate of tobacco leaves could be improved by exogenous acetylcholine through increasing the stomatal opening,decreasing the decomposition rate of photosynthetic pigment,protecting the photosynthetic organs,and improving the electron transfer activity,photosynthetic phosphorylation and carbon assimilation.