Estimation of the steady-state cyclic electron flux around PSI in spinach leaf discs in white light, CO2-enriched air and other varied conditions
Jiancun Kou A B , Shunichi Takahashi B , Riichi Oguchi B , Da-Yong Fan B C , Murray R. Badger B and Wah Soon Chow B DA College of Animal Science and Technology, Northwest A & F University, Yangling, Shaanxi 712 100, China.
B Division of Plant Science, Research School of Biology, College of Medicine, Biology and Environment, The Australian National University, Canberra, ACT 0200, Australia.
C State Key Laboratory of Vegetation and Environmental Change, Institute of Botany, The Chinese Academy of Sciences, 100 093 Beijing, China.
D Corresponding author. Email: fred.chow@anu.edu.au
Functional Plant Biology 40(10) 1018-1028 https://doi.org/10.1071/FP13010
Submitted: 10 January 2013 Accepted: 30 April 2013 Published: 29 May 2013
Abstract
Cyclic electron flux (CEF) around PSI is essential for efficient photosynthesis and aids photoprotection, especially in stressful conditions, but the difficulty in quantifying CEF is non-trivial. The total electron flux through PSI (ETR1) and the linear electron flux (LEFO2) through both photosystems in spinach leaf discs were estimated from the photochemical yield of PSI and the gross oxygen evolution rate, respectively, in CO2-enriched air. ΔFlux = ETR1 – LEFO2 is an upper estimate of CEF. Infiltration of leaf discs with 150 μM antimycin A did not affect LEFO2, but decreased ΔFlux 10-fold. ΔFlux was practically negligible below 350 μmol photons m−2 s−1, but increased linearly above it. The following results were obtained at 980 μmol photons m−2 s−1. ΔFlux increased 3-fold as the temperature increased from 5°C to 40°C. It did not decline at high temperature, even when LEFO2 decreased. ΔFlux increased by 80% as the relative water content of leaf discs decreased from 100 to 40%, when LEFO2 decreased 2-fold. The method of using ΔFlux as a non-intrusive upper estimate of steady-state CEF in leaf tissue appears reasonable when photorespiration is suppressed.
Additional keywords: antimycin A, cyclic electron flow, linear electron flow, P700, photosystem I.
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