Effects of extracellular ATP on the characteristics of photochemical reaction in bean (Phaseolus vulgaris) leaves under different light intensities

Aims Although adenosine 5′-triphosphate (ATP) is usually considered to be localized in intracellular spaces, plant and animal cells can secrete ATP from the cytosol into the extracellular matrix. This extracellular ATP (eATP) is an important signal molecule for many physiological responses in plants. However, whether eATP could also have effects on photosynthesis in plants has not been extensively studied.
Methods With bean (Phaseolus vulgaris) leaves as experiment material, the effects of eATP on the chlorophyll fluorescence characteristics and photosynthetic O₂ evolution rate were studied under different light intensities.
Important findings The maximal photosystem II (PSII) quantum yield in light adaptation (F_v′/F_m′), effective photochemical quantum yield of PSII (Y(II)), and photochemical quenching coefficient (q_P) gradually decreased, and the electron transport rate (ETR), non-photochemical quenching coefficient (q_N), and the quantum yield of regulated energy dissipation (Y(NPQ)) increased, with increases in light intensity. Treatment of leaves with eATP significantly increased the values of the potential maximal photochemical efficiency of PSII (F_v/F_m), F_v′/F_m′, Y(II), q_P, ETR, and photosynthetic O₂ evolution rate, but did not affect the values of q_N and Y(NPQ). In contrast, treatment of leaves with β,γ-methyleneadenosine triphosphate (AMP-PCP, an inhibitor of eATP receptors) significantly reduced the values of F_v/F_m, F_v′/F_m′, Y(II), ETR, and photosynthetic O₂ evolution rate, but increased the values of q_N and Y(NPQ). These results show that the levels of eATP exert important influences on the photochemical reaction in photosynthesis.