In vivo regulation of thylakoid proton motive force in immature leaves
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In chloroplast, proton motive force (pmf) is critical for ATP synthesis and photoprotection. To prevent photoinhibition of photosynthetic apparatus, proton gradient (ΔpH) across the thylakoid membranes needs to be built up to minimize the production of reactive oxygen species (ROS) in thylakoid membranes. However, the regulation of thylakoid pmf in immature leaves is little known. In this study, we compared photosynthetic electron sinks, P700 redox state, non-photochemical quenching (NPQ), and electrochromic shift (ECS) signal in immature and mature leaves of a cultivar of Camellia. The immature leaves displayed lower linear electron flow and cyclic electron flow, but higher levels of NPQ and P700 oxidation ratio under high light. Meanwhile, we found that pmf and ΔpH were higher in the immature leaves. Furthermore, the immature leaves showed significantly lower thylakoid proton conductivity than mature leaves. These results strongly indicated that immature leaves can build up enough ΔpH by modulating proton efflux from the lumenal side to the stromal side of thylakoid membranes, which is essential to prevent photoinhibition via thermal energy dissipation and photosynthetic control of electron transfer. This study highlights that the activity of chloroplast ATP synthase is a key safety valve for photoprotection in immature leaves.
KeywordsChloroplast ATP synthase Electron transfer Immature leaves Lumenal acidification P700 redox state Photoprotection
Cyclic electron flow around photosystem I;
Proton gradient across the thylakoid membranes
Thylakoid proton conductivity
Linear electron flow
Proton motive force
The fraction of open PSII reaction centers based on the “lake model” of PSII antenna pigment organization
Quantum yield of PSI photochemical quenching
Effective quantum yield of PSII photochemistry
The quantum yield of PSI non-photochemical energy dissipation due to the acceptor-side limitation
The quantum yield of PSI non-photochemical energy dissipation due to the donor-side limitation
This work is supported by National Natural Science Foundation of China (Grant No. 31670343) and Youth Innovation Promotion Association of the Chinese Academy of Sciences (Grant No. 2016347).
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
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