Extracellular ATP Exert Systemic Effects On Photosystem ? Photochemistry Of Kidney Bean (Phaseolus Vulgaris) Leaf And Affects The Photosynthesis Activity Of Kidney Bean Leaves Under Water Stress

Although adenosine 5?-triphosphate?ATP? is usually considered to be localized in intracellular spaces, plant cells can secrete ATP from the cytosol into the extracellular matrix. This extracellular ATP?eATP? which can activate the intracellular second messenger(Ca²⁺ and ROS etc.) is an important signal molecule.Ca²⁺ and ROS have unraveled systemic signaling pathways. Extracellular ATP adjusts plant photosynthesis systemic reactions. Using bean?Phaseolus vulgaris L? leaves as experiment material, we studied the systemic effects of eATP on photochemical characterization and high light of systemic effects of plant and its physiological role under drought environmental changes was explored. The main findings are described as below:?1? Extracellular ATP exerts systemic effects on photosystem ? photochemistry of Kidney Bean?Phaseolus vulgaris? Leaf.Treatment of a half of a bean leaf with exogenous ATP had no significant effect on the maximal photochemical efficiency of photosystem ??F_v/F_m? and the quantum yield of non-regulated energy dissipation?Y?NO?? of the treated half and the untreated,opposite half of the same leaf. However, this treatment significantly increased the values of photochemical efficiency?Y????, the rate of photosynthetic electron transport?ETR?, and photochemical quenching?qP?, while the values of the non-photochemical quenching?qN? and the quantum yield of regulated energy dissipation?Y?NPQ?? were significantly decreased by exogenous 1 mM ATP. These observations indicate that eATP can function in systematically enhancing the PS ? photochemistry of kidney bean leaves.In order to explore the possible signaling pathway of eATP in systemically regulating photosystem ? photochemistry of plant, Ca²⁺, LaCl₃(an inhibitor of Ca²⁺channels), H₂O₂?hydrogen peroxide?, and DMTU?dimethylthiourea, a scavenger of H₂O₂? were used. Similar to the effects of exogenous ATP, treatment with exogenous Ca²⁺ or H₂O₂ also led to a significant increase in Y???, qP and ETR and a significant decrease in qN and Y?NPQ? of the treated half and the untreated, opposite half of the same leaf. And, LaCl₃ and DMTU weakened the systemic effects of exogenous ATPon the photosystem ? photochemistry of leaves. These observations indicate that an increase in eATP concentration of partial region of bean leaf can enhance the PS? photochemistry of the adjacent tissues, and such function of eATP could be dependent of Ca²⁺ and H₂O₂.?2? Extracellular ATP participated in the systemic effects on photosystem ? photochemistry of Kidney Bean by high lights.Treatment of the first of pinnate compound leaves of bean with high light?HL?significantly decreased F_m?the maximal fluorescence yield?, F_v/F_m, Y???, ETR, NPQ?non-photochemical quenching? and Y?NPQ?, while the values of F0?the original fluorescence yield?, qP and Y?NO? were significantly increased by HL. However,Untreatment of the systemic leaves of the same plant with HL significantly increased F_v/F_m, Y???, ETR, qP and Y?NO?, while the values of F_m, Y?NPQ? and NPQ were significantly decreased. These observations indicate that treatment of leaves with HL produce stress and untreatment of the systemic leaves of the same plant on photosystem ? photochemistry were inproved. In order to further explore the systemic influence, we tested the extracellular ATP of systemic leaves petioles tissue, result was significantly increased. AMP-PCP and ATP phosphohydrolase abolished the increases of the Y???, ETR, qP and the decreases of NPQ and Y?NPQ? induced by HL influncen on the systemic leaves of the same plant. In conclusion that the change of eATP can affect the PS? photochemistry of the systemic leaves of the same plant under HL.?3? Extracellular ATP can regulate the photosystem ? of kidney bean?Phaseolus vulgaris? leaves under the condition of water stress induced by PEG.Treatment of a bean leaf with PEG had no significant effect on F_v'/F_m' of the leaf.However, this treatment significantly decreased the values of F_v/F_m, Y???, ETR, qP,and NPQ, indicating that water stress induced by PEG decrease the PS?photochemistry activity. This treatment also caused a significant decrease in the eATP of bean leaves. 0.2 mM exogenous ATP almost completely abolished the decreases of the Y???, ETR, qP and NPQ induced by PEG stress, and the application of this concentration of exogenous ATP also alleviated the decrease of eATP that wasinduced by PEG. These results suggest that eATP can function in regulating the photosystem ? photochemistry activity under water stress.In conclusion, as an important extracellular signaling molecule, eATP can systemically promote the PS ? photochemistry of plants, and the mechanism for such role of eATP could be related to a Ca²⁺ or H₂O₂ systemic signaling pathway.Furthermore, eATP regulate the systemic effects of the PS ? photochemistry of plant by high light. We research expanded the effect of eATP on photosynthesis of bean leaf under the condition of water stress. It also laid a theoretical basis for researching the systemic effect of eATP on plant by drought.