title: Obstacles in the quantification of the cyclic electron flux around Photosystem I in leaves of C3 plants.
abstract: Sixty years ago Arnon and co-workers discovered photophosphorylation driven by a cyclic electron flux (CEF) around Photosystem I. Since then understanding the physiological roles and the regulation of CEF has progressed, mainly via genetic approaches. One basic problem remains, however: quantifying CEF in the absence of a net product. Quantification of CEF under physiological conditions is a crucial prerequisite for investigating the physiological roles of CEF. Here we summarize current progress in methods of CEF quantification in leaves and, in some cases, in isolated thylakoids, of C3 plants. Evidently, all present methods have their own shortcomings. We conclude that to quantify CEF in vivo, the best way currently is to measure the electron flux through PS I (ETR1) and that through PS II and PS I in series (ETR2) for the whole leaf tissue under identical conditions. The difference between ETR1 and ETR2 is an upper estimate of CEF, mainly consisting, in C3 plants, of a major PGR5-PGRL1-dependent CEF component and a minor chloroplast NDH-dependent component, where PGR5 stands for Proton Gradient Regulation 5 protein, PGRL1 for PGR5-like photosynthesis phenotype 1, and NDH for Chloroplast NADH dehydrogenase-like complex. These two CEF components can be separated by the use of antimycin A to inhibit the former (major) component. Membrane inlet mass spectrometry utilizing stable oxygen isotopes provides a reliable estimation of ETR2, whilst ETR1 can be estimated from a method based on the photochemical yield of PS I, Y(I). However, some issues for the recommended method remain unresolved.
authors: State Key Laboratory of Vegetation and Environmental Change, Institute of Botany, The Chinese Academy of Sciences, Beijing, 100093, China.|Division of Plant Sciences, Research School of Biology, The Australian National University, 46 Sullivans Creek Road, Acton, ACT, 2601, Australia.
authors: Da-Yong
authors: DY
authors: Fan
authors: Division of Plant Sciences, Research School of Biology, The Australian National University, 46 Sullivans Creek Road, Acton, ACT, 2601, Australia.
authors: Duncan
authors: D
authors: Fitzpatrick
authors: Graduate School of Life Sciences, Tohoku University, Sendai, Miyagi, 980-8578, Japan.|Division of Plant Sciences, Research School of Biology, The Australian National University, 46 Sullivans Creek Road, Acton, ACT, 2601, Australia.
authors: Riichi
authors: R
authors: Oguchi
authors: College of Life & Environment Sciences, Shanghai Normal University, Guilin Road 100, Shanghai, 200234, China.|Division of Plant Sciences, Research School of Biology, The Australian National University, 46 Sullivans Creek Road, Acton, ACT, 2601, Australia.
authors: Weimin
authors: W
authors: Ma
authors: College of Animal Science and Technology, Northwest A&F University, Yangling, 712100, China.|Division of Plant Sciences, Research School of Biology, The Australian National University, 46 Sullivans Creek Road, Acton, ACT, 2601, Australia.
authors: Jiancun
authors: J
authors: Kou
authors: Division of Plant Sciences, Research School of Biology, The Australian National University, 46 Sullivans Creek Road, Acton, ACT, 2601, Australia. Fred.Chow@anu.edu.au.
authors: Wah Soon
authors: WS
authors: Chow
mesh_terms: D000968:Antimycin A / Q000494:pharmacology*; D002736:Chloroplasts / Q000378:metabolism; D004579:Electron Transport / Q000187:drug effects; D004583:Electrons; D010788:Photosynthesis / Q000187:drug effects; D045331:Photosystem I Protein Complex / Q000187:drug effects / Q000378:metabolism*; D045332:Photosystem II Protein Complex / Q000378:metabolism; D018515:Plant Leaves / Q000187:drug effects / Q000378:metabolism; D010944:Plants / Q000187:drug effects / Q000378:metabolism*; D020524:Thylakoids / Q000378:metabolism
chemical_list: D045331:Photosystem I Protein Complex; D045332:Photosystem II Protein Complex; D000968:Antimycin A
keywords: Cyclic electron flux; Linear electron flux; Membrane inlet mass spectrometry; P700; Photosystem I; Photosystem II