Fig. 5. Effect of low night temperature treatment and recovery on the effective PSI quantum yield [Y(I), A], non-photochemical quantum yield of PSI caused by donor side limitation [Y(ND), B], and non-photochemical quantum yield of PSI caused by acceptor side limitation [Y(NA), C]. Y(ND) (donor side limitation) represents the fraction of the overall P700 that is oxidized in a given state, which is enhanced by a trans-thylakoid proton gradient (photosynthetic control at the cytb/f complex as well as downregulation of PSII) and the photodamage to PSII. Y(NA) (acceptor side limitation) represents the fraction of the overall P700 that cannot be oxidized by a saturation pulse in a given state because of a lack of acceptors, and is enhanced by dark adaptation (deactivation of key enzymes of Calvin–Benson cycle) and damage at the site of CO2 fixation.