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Plant and Cell Physiology Advance Access originally published online on April 20, 2008
Plant and Cell Physiology 2008 49(6):901-911; doi:10.1093/pcp/pcn064
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© The Author 2008. Published by Oxford University Press on behalf of Japanese Society of Plant Physiologists. All rights reserved. For permissions, please email: journals.permissions@oxfordjournals.org

Separation of Light-induced Linear, Cyclic and Stroma-sourced Electron Fluxes to P700+ in Cucumber Leaf Discs after Pre-Illumination at a Chilling Temperature

Da-Yong Fan1,3, Alexander B. Hope2, Husen Jia3 and Wah Soon Chow3,*

1State Key Laboratory of Vegetation and Environmental Change, Institute of Botany, The Chinese Academy of Sciences, Beijing 100093, PR China
2School of Biological Sciences, Flinders University, GPO Box 2100, Adelaide, SA 5001, Australia
3Photobioenergetics Group, Research School of Biological Sciences, Australian National University, Canberra, ACT 0200, Australia

*Corresponding author: E-mail, chow{at}rsbs.anu.edu.au; Fax, +61-2-6125-8056.


  Abstract

Pre-illumination of cucumber leaf discs at 4°C with low-irradiance white light (i) led to a marked decrease in the extent of photo-oxidation of P700 (the special chlorophyll pair in the PSI reaction center) in actinic light at room temperature and (ii) hastened the post-illumination re-reduction of P700+. Quantifying the linear, cyclic and stroma-sourced electron fluxes to P700+ in two actinic light regimes, we found that there was no increase in cyclic or linear electron fluxes to account for these changes. Rather, we observed a decrease in the maximum extent of P700 photo-oxidation assayed by a strong flash superimposed on continuous, background light of wavelength 723 nm, which we interpret to represent a loss of stable charge separation in PSI due to enhanced charge recombination as a result of the pre-illumination treatment. The funneling of electrons towards fewer non-damaged PSI complexes could explain the hastened post-illumination re-reduction of P700+, aided by a slight increase in a stroma-sourced electron flux after prolonged pre-illumination at 4°C. Quantifying the separate fluxes to P700+ helps to elucidate the effects of chilling of cucumber leaf discs in the light and the reasons for the hastened post-illumination re-reduction of P700+.

Keywords: Cucumis sativus - Cyclic electron flow - P700 - Photoinactivation - Photoinhibition - PSI

Abbreviations: FA, FB, FX, cubane iron–sulfur center bound to subunits of PsaC, PsaC and PsaA/PsaB, respectively; Fd, ferredoxin; Fo, Fm, minimum and maximum Chl fluorescence yield of a dark-adapted leaf, corresponding to open and closed PSII reaction center traps, respectively; FNR, ferredoxin-NADP reductase; FQR, ferredoxin-quinone reductase; LED, light-emitting diode; MV, methyl viologen; P700, special Chl pair in the PSI reaction center; ROS, reactive oxygen species; Rubisco, ribulose 1,5-bisphosphate carboxylase/oxygenase.

(Received January 7, 2008; Accepted April 15, 2008)
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