Pre-illumination of cucumber leaf discs at 4degreeC with low-irradiance white light (1) led to a marked decrease in the extent of photo-oxidation of P700 [the special chlorophyll pair in the photosystem I (PSI) reaction centre] in actinic light at room temperature and (2) hastened the post-illumination re-reduction of P700+. Quantifying the linear, cyclic and stroma-sourced electron fluxes to P700+ in two actinic-light regimes, we found that there was no increase in cyclic or linear electron fluxes to account for these changes. Rather, we observed a decrease in the maximum extent of P700 photo-oxidation assayed by a strong flash superimposed on continuous, background light of wavelength 723 nm, which we interpret to represent a loss of stable charge separation in PSI due to enhanced charge recombination as a result of the pre-illumination treatment. The funnelling of electrons towards fewer non-damaged PSI complexes could explain the hastened post-illumination re-reduction of P700+, aided by a slight increase in a stroma-sourced electron flux after prolonged pre-illumination at 4degreeC. Quantifying the separate fluxes to P700+ helps to elucidate the effects of chilling of cucumber leaf discs in the light and the reasons for the hastened post-illumination re-reduction of P700+.