Depletion of extracellular ATP affects the photosystem II photochemistry and the role of salicylic acid in this process

In the present work, treatment with AMP-PCP (β,γ-methyleneadenosine-5'-triphosphate - a competitive inhibitor of the extracellular ATP pool) or apyrase (an ATP-degrading enzyme) decreased the PSII operating efficiency (ΦPSII), photochemical quenching (qp), and maximum quantum efficiency of PSII photochemistry (Fv/Fm) of Arabidopsis leaves illuminated with high light intensity. Mutation of extracellular ATP receptor, DORN1, also caused decreases of ΦPSII, qp, and Fv/Fm when the leaves were exposed to high light. Either the treatment with AMP-PCP and apyrase or the mutation in DORN1 increased the salicylic acid content in the illuminated leaves. Salicylic acid deficiency in NahG transgenic mutant made the PSII photochemistry more sensitive to AMP-PCP or apyrase. These results indicate that extracellular ATP depletion can affect the PSII photochemistry, whereas salicylic acid can relieve this effect.