Chilling cucumber leaf discs in light causes faster re-reduction of a key chlorophyll pair in photosystem I. This is mainly due to charge recombination and partly from previous electron flow. Inhibiting forward electron flow enhances charge recombination in photosystem I. Photosystem II is also affected, but to a lesser extent. Controlled charge recombination and cyclic electron flow during chilling may protect both photosystems from damage.