Journal Article

Distinct Roles of the Cytochrome Pathway and Alternative Oxidase in Leaf Photosynthesis

Keisuke Yoshida, Ichiro Terashima and Ko Noguchi

in Plant and Cell Physiology

Published on behalf of Japanese Society of Plant Physiologists

Volume 47, issue 1, pages 22-31
Published in print January 2006 | ISSN: 0032-0781
Published online January 2006 | e-ISSN: 1471-9053 | DOI: http://dx.doi.org/10.1093/pcp/pci219
Distinct Roles of the Cytochrome Pathway and Alternative Oxidase in Leaf Photosynthesis

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In illuminated leaves, mitochondria are thought to play roles in optimizing photosynthesis. However, the roles of the cytochrome pathway (CP) and alternative oxidase (AOX) in photosynthesis, in particular in the redox state of the photosynthetic electron transport chain, are not separately characterized. We examined the effects of specific inhibition of two respiratory pathways, CP and AOX, on photosynthetic oxygen evolution and the redox state of the photosynthetic electron transport chain in broad bean (Vicia faba L.) leaves under various light intensities. Under saturating photosynthetic photon flux density (PPFD; 700 µmol photon m–2 s–1), inhibition of either pathway caused a decrease in the steady-state levels of the photosynthetic O2 evolution rate and the PSII operating efficiency, ΦII. Because these inhibitors, at the concentrations applied to the leaves, had little effect on photosynthesis in the intact chloroplasts, two respiratory pathways are essential for maintenance of high photosynthetic rates at saturating PPFD. CP or AOX inhibition affected to Chl fluorescence parameters (e.g. photochemical quenching and non-photochemical quenching) differently, suggesting that CP and AOX contribute to photosynthesis in different ways. At low PPFD (100 µmol photon m–2 s–1), only the inhibition of AOX, not CP, lowered the photosynthetic rate and ΦII. AOX inhibition also decreased the ΦIII ratio even at low PPFD levels. These data suggest that AOX inhibition caused the over-reduction of the 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 for CP and AOX in the light.

Keywords: Alternative oxidase (AOX); Chloroplast–mitochondrion interaction; Chl fluorescence; Cytochrome pathway (CP); Improved oxygen electrode; Vicia faba L.; AL, actinic light; Ant A, antimycin A; AOX, alternative oxidase; CEF-PSI, cyclic electron flow around PSI; CP, cytochrome pathway; Fv/Fm, maximum quantum yield of PSII; ΦI or ΦII, operating efficiency of PSI or PSII; Mx, myxothiazol; nPG, n-propyl gallate; PPFD, photosynthetic photon flux density; PTOX, plastid terminal oxidase; qN (and NPQ), non-photochemical quenching; qP, photochemical quenching; ROS, reactive oxygen species; SHAM, salicylhydroxamic acid; SP, saturating pulse

Journal Article.  6624 words.  Illustrated.

Subjects: Biochemistry ; Molecular and Cell Biology ; Plant Sciences and Forestry

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