Chlororespiration and cyclic electron flow around PSI during photosynthesis and plant stress response. Plant Cell Environ
Laboratoire d'Ecophysiologie Moléculaire des Plantes, CEA Cadarache, DSV, IBEB, SBVME, UMR 6191 CNRS/CEA/Université Aix-Marseilles, Saint Paul lez Durance F-13108, France. Plant Cell and Environment
(Impact Factor: 6.96).
10/2007; 30(9):1041-51. DOI: 10.1111/j.1365-3040.2007.01675.x
Besides major photosynthetic complexes of oxygenic photosynthesis, new electron carriers have been identified in thylakoid membranes of higher plant chloroplasts. These minor components, located in the stroma lamellae, include a plastidial NAD(P)H dehydrogenase (NDH) complex and a plastid terminal plastoquinone oxidase (PTOX). The NDH complex, by reducing plastoquinones (PQs), participates in one of the two electron transfer pathways operating around photosystem I (PSI), the other likely involving a still uncharacterized ferredoxin-plastoquinone reductase (FQR) and the newly discovered PGR5. The existence of a complex network of mechanisms regulating expression and activity of the NDH complex, and the presence of higher amounts of NDH complex and PTOX in response to environmental stress conditions the phenotype of mutants, indicate that these components likely play a role in the acclimation of photosynthesis to changing environmental conditions. Based on recently published data, we propose that the NDH-dependent cyclic pathway around PSI participates to the ATP supply in conditions of high ATP demand (such as high temperature or water limitation) and together with PTOX regulates cyclic electron transfer activity by tuning the redox state of intersystem electron carriers. In response to severe stress conditions, PTOX associated to the NDH and/or the PGR5 pathway may also limit electron pressure on PSI acceptor and prevent PSI photoinhibition.
- "The change of NDH-H expression corresponds to the rise in the transient increase in Chl fluorescence after turning off actinic light and the dark re-reduction of P700 + in both varieties, implying that NDH-H may play an important role in regulation of CEF under salt stress. Many studies have demonstrated that NDH-B is essential for stabilizing other subunits (Hashimoto et al., 2003; Munshi et al., 2005) and that NDH-H is unstable without other subunits (Hashimoto et al., 2003; Kotera et al., 2005; Rumeau et al., 2007). Additionally, Takabayashi et al. (2009) reported that in ndf (NDH-dependent CEF) mutants, the amount of NDH-H subunit was greatly decreased and the loss of NDH activity was caused by a defect in accumulation of NDH complex. "
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ABSTRACT: In land plants, the NAD(P)H dehydrogenase (NDH) complex reduces plastoquinones and drives cyclic electron flow (CEF) around PSI. It also produces extra ATP for photosynthesis and improves plant fitness under conditions of abiotic environmental stress. To elucidate the role of CEF in salt tolerance of the photosynthetic apparatus, Na(+) concentration, chlorophyll fluorescence, and expression of NDH B and H subunits, as well as of genes related to cellular and vacuolar Na(+) transport, were monitored. The salt-tolerant Glycine max (soybean) variety S111-9 exhibited much higher CEF activity and ATP accumulation in light than did the salt-sensitive variety Melrose, but similar leaf Na(+) concentrations under salt stress. In S111-9 plants, ndhB and ndhH were highly up-regulated under salt stress and their corresponding proteins were maintained at high levels or increased significantly. Under salt stress, S111-9 plants accumulated Na(+) in the vacuole, but Melrose plants accumulated Na(+) in the chloroplast. Compared with Melrose, S111-9 plants also showed higher expression of some genes associated with Na(+) transport into the vacuole and/or cell, such as genes encoding components of the CBL10 (calcineurin B-like protein 10)-CIPK24 (CBL-interacting protein kinase 24)-NHX (Na(+)/H(+) antiporter) and CBL4 (calcineurin B-like protein 4)-CIPK24-SOS1 (salt overly sensitive 1) complexes. Based on the findings, it is proposed that enhanced NDH-dependent CEF supplies extra ATP used to sequester Na(+) in the vacuole. This reveals an important mechanism for salt tolerance in soybean and provides new insights into plant resistance to salt stress.
© The Author 2015. Published by Oxford University Press on behalf of the Society for Experimental Biology.
Available from: Nick Fisher
- "LEF in its unmodified form should provide a fixed stoichiometry of reducing equivalents (i.e., reduced Fd, NADPH) and ATP, therefore any changes in the metabolic demands of the chloroplast must be met by rapid changes in alternative electron flow to prevent formation of reactive intermediates   . Multiple alternative electron pathways have been identified or proposed including the water–water cycle  , the malate shunt , the plastid terminal oxidase   , and cyclic electron flow around photosystem I (CEF) . CEF can alleviate an ATP deficit by passing electrons from the acceptor side of PS I back to PQ, driving the translocation of protons into the lumen without net reduction of NADP + . "
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ABSTRACT: The chloroplast must regulate supply of reducing equivalents and ATP to meet rapid changes in downstream metabolic demands. Cyclic electron flow around photosystem I (CEF) is proposed to balance the ATP/NADPH budget by using reducing equivalents to drive plastoquinone reduction, leading to the generation of proton motive force and subsequent ATP synthesis. While high rates of CEF have been observed in vivo, isolated thylakoids show only very slow rates, suggesting that the activity of a key complex is lost or down-regulated upon isolation We show that isolation of thylakoids while in the continuous presence of reduced thiol reductant dithiothreitol (DTT), but not oxidized DTT, maintains high CEF activity through an antimycin A sensitive ferredoxin:quinone reductase (FQR). Maintaining low concentrations (~2mM) of reduced DTT while modulating the concentration of oxidized DTT leads to reversible activation/inactivation of CEF with an apparent midpoint potential of -306mV (+/- 10mV) and n=2, consistent with redox modulation of a thiol/disulphide couple and thioredoxin-mediated regulation of the plastoquinone reductase involved in the antimycin A-sensitive pathway, possibly at the level of the PGRL1 protein. Based on proposed differences in regulatory modes, we propose that the FQR and NADPH:plastoquinone oxidoreductase (NDH) pathways for CEF are activated under different conditions and fulfill different roles in chloroplast energy balance.
Copyright © 2015. Published by Elsevier B.V.
Available from: Joaquim Azcon-Bieto
- "performed by the thylakoidal NAD(P)H dehydrogenase complex ( Ndh ; Burrows et al., 1998 ; Endo et al., 1998 ; Sazanov et al., 1998 ) or a type II NAD ( P ) H dehydrogenase ( Desplats et al . , 2009 ) . Chloroplast respiration has been extensively studied and reviewed ( Peltier and Cournac , 2002 ; Rumeau et al . , 2007 ; McDonald et al. , 2011 ; Foudree et al . , 2012 ; Nawrocki et al . , 2015 ) , but there is no consensus about its biological role . The most accepted hypothesis is that chlororespiration acts as a safety valve to prevent the over - reduction of the photosynthetic machinery in stress conditions ( Laureau et al . , 2013 ; Paredes and Qu"
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ABSTRACT: Chlororespiration is a respiratory process located in chloroplast thylakoids which consists in an electron transport chain from NAD(P)H to oxygen. This respiratory chain involves the NAD(P)H dehydrogenase complex, the plastoquinone pool and the plastid terminal oxidase (PTOX), and it probably acts as a safety valve to prevent the over-reduction of the photosynthetic machinery in stress conditions. The existence of a similar respiratory activity in non-photosynthetic plastids has been less studied. Recently, it has been reported that tomato fruit chromoplasts present an oxygen consumption activity linked to ATP synthesis. Etioplasts and amyloplasts contain several electron carriers and some subunits of the ATP synthase, so they could harbor a similar respiratory process. This review provides an update on the study about respiratory processes in chromoplasts, identifying the major gaps that need to be addressed in future research. It also reviews the proteomic data of etioplasts and amyloplasts, which suggest the presence of a respiratory electron transport chain in these plastids.
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