Rinya Kawashima1, Ryoichi Sato1,2, Kyohei Harada1, Shinji Masuda3,4. 1. Graduate School of Bioscience and Biotechnology, Tokyo Institute of Technology, Yokohama, Japan. 2. Division of Environmental Photobiology, National Institute for Basic Biology, Okazaki, 444-8585, Japan. 3. Center for Biological Resources and Informatics, Tokyo Institute of Technology, Yokohama, Japan. shmasuda@bio.titech.ac.jp. 4. Earth-life Science Institute, Tokyo Institute of Technology, Tokyo, Japan. shmasuda@bio.titech.ac.jp.
Abstract
MAIN CONCLUSION: Respective contributions of PGR5- and NDH-dependent cyclic electron flows around photosystem I for generating the proton gradient across the thylakoid membrane are ~30 and ~5%. The proton concentration gradient across the thylakoid membrane (ΔpH) produced by photosynthetic electron transport is the driving force of ATP synthesis and non-photochemical quenching. Two types of electron transfer contribute to ΔpH formation: linear electron flow (LEF) and cyclic electron flow (CEF, divided into PGR5- and NDH-dependent pathways). However, the respective contributions of LEF and CEF to ΔpH formation are largely unknown. We employed fluorescence quenching analysis with the pH indicator 9-aminoacridine to directly monitor ΔpH formation in isolated chloroplasts of Arabidopsis mutants lacking PGR5- and/or NDH-dependent CEF. The results indicate that ΔpH formation is mostly due to LEF, with the contributions of PGR5- and NDH-dependent CEF estimated as only ~30 and ~5%, respectively.
MAIN CONCLUSION: Respective contributions of PGR5- and NDH-dependent cyclic electron flows around photosystem I for generating the proton gradient across the thylakoid membrane are ~30 and ~5%. The proton concentration gradient across the thylakoid membrane (ΔpH) produced by photosynthetic electron transport is the driving force of ATP synthesis and non-photochemical quenching. Two types of electron transfer contribute to ΔpH formation: linear electron flow (LEF) and cyclic electron flow (CEF, divided into PGR5- and NDH-dependent pathways). However, the respective contributions of LEF and CEF to ΔpH formation are largely unknown. We employed fluorescence quenching analysis with the pH indicator 9-aminoacridine to directly monitor ΔpH formation in isolated chloroplasts of Arabidopsis mutants lacking PGR5- and/or NDH-dependent CEF. The results indicate that ΔpH formation is mostly due to LEF, with the contributions of PGR5- and NDH-dependent CEF estimated as only ~30 and ~5%, respectively.
Entities:
Keywords:
Arabidopsis; Cyclic electron transfer; Non-photochemical quenching; PGR5; Photosynthesis; ΔpH
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