Action potential in Chara cells intensifies spatial patterns of photosynthetic electron flow and non-photochemical quenching in parallel with inhibition of pH banding

Characean cells exposed to illumination arrange plasma-membrane H+ fluxes and photosynthesis in coordinated spatial patterns. The limited availability of CO2 in alkaline bands accounts for the lower effective quantum yield of photosystem II (Delta F/F-m') in chloroplasts of these bands compared to acidic zones. The effect of electrically triggered action potential on the spatial distribution of photosynthetic parameters (Delta F/F-m' and non-photochemical quenching, NPQ) and extracellular pH was studied with fluorescence imaging and pH microelectrodes. In the resting cell at a range of light intensities, the periodic profile of extracellular pH is parallel to the profile of NPQ and antiparallel to that of Delta F/F-m'. After triggering the action potential, the pH banding temporarily disappeared, but in contrast, the differences in effective quantum yield and NPQ patterns became more apparent. The transient changes in pH- banding, effective quantum yield and non- photochemical quenching are discussed in relation to alterations in intracellular Ca2+ and H+ concentrations during and after the action potential.