Plant and Cell Physiology Advance Access first published online on October 20, 2005
This version published online on October 25, 2005
Plant and Cell Physiology, doi:10.1093/pcp/pci219
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1 Department of Biology, Graduate School of Science, Osaka University, 1-1 Machikaneyama-cho, Toyonaka, Osaka 560-0043, Japan
* To whom correspondence should be addressed. In illuminated leaves, mitochondria are thought to play roles in optimizing photosynthesis. However, roles of the cytochrome pathway (CP) and alternative oxidase (AOX) on photosynthesis, in particular, on the redox state of the photosynthetic electron transport chain, are not separately characterized. We examined the effects of specific inhibitions of two respiratory pathways, CP and AOX, on the photosynthetic oxygen evolution and redox state of photosynthetic electron transport chain in broad bean (Vicia faba L.) leaves under various light intensities. Under the saturating PPFD (700 µmol photon m-2 s-1), inhibition of either pathway caused the decrease in the steady-state levels of the photosynthetic O2 evolution rate and the PSII operating efficiency,
Received July 9, 2005
Accepted October 17, 2005
Regular Paper
Distinct Roles of the Cytochrome Pathway and Alternative Oxidase in Leaf Photosynthesis
Keisuke Yoshida, E-mail: kyoshi80{at}bio.sci.osaka-u.ac.jp
Abstract 
II. Because these inhibitors, at the concentrations applied to the leaves, had little effects on photosynthesis in the intact chloroplasts, two respiratory pathways are essential for maintenance of high photosynthetic rates at the saturating PPFD. CP or AOX inhibition differently affected to Chl fluorescence parameters (e.g. qP, qN), suggesting that CP and AOX contribute to photosynthesis in different ways. At the low PPFD (100 µmol photon m-2 s-1), only the inhibition of AOX, not CP, lowered the photosynthetic rate and II. AOX inhibition also decreased the II/I even at low PPFD levels. These data suggests that AOX inhibition caused the overreduction of photosynthetic electron transport chain and induced the cyclic electron flow around PSI (CEF-PSI) even at the low PPFD. Based on these results, we discuss possible roles of CP and AOX in the light.
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