Photoinhibition of photosystem I under fluctuating light is linked to the insufficient ΔpH upon a sudden transition from low to high light

•We examine the PSI redox state and ΔpH after transition from low to high light.•PSI is over-reduced upon a sudden transition from low to high light in angiosperms.•The insufficient ΔpH induced over-reduction of PSI in fluctuating light.•PSI photoinhibition in fluctuating light is caused by the insufficient ΔpH.