Photosystem I acceptor side limitation is a prerequisite for the reversible decrease in the maximum extent of P700 oxidation after short-term chilling in the light in four plant species with different chilling sensitivities

Changes in the extent of P700 oxidation (P700⁺) were investigated after chilling of barley, rice, pumpkin, and cucumber leaf segments at 4°C for 1h under light with various photon flux densities. At 50 μmol photons m^-2s^-1, the decrease in P700⁺ was observed only in cucumber, but at 150 μmol photons m^-2s ^-1, it was found in all plants except barley, revealing their expected chilling sensitivities. However, the decrease in P700⁺ by this short-term chilling was reversible in the presence of 3-(3′,4′- dichlorophenyl)-1,1-dimethylurea or methyl viologen, and it did not show any causal relationship with the decrease in the electron transfer rate nor with the down-regulation of photosystem II through the accumulation of zeaxanthin and the development of non-photochemical quenching. These results led to the suggestion that photosystem I (PSI) acceptor side limitation is a prerequisite for the decrease of P700⁺. Furthermore, PSI acceptor side limitation could be mainly due to limitation of electron-sink pathways such as CO ₂ assimilation and ascorbate-glutathione cycle, because treatment with glycolaldehyde which inhibits the former pathway, and with KCN which inhibits both pathways, decreased P700⁺ by 20-30% in barley leaves after chilling in the light.