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

Abstract

Changes in the extent of P700 oxidation (P700 + ) were investigated after chilling of barley, rice, pumpkin, and cucumber leaf segments at 4°C for 1 h under light with various photon flux densities. At 50 µmol photons m −2 s −1 , the decrease in P700 + was observed only in cucumber, but at 150 µmol photons m −2 s −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.