Cyclic Electron Flow around Photosystem I in C3Plants. In Vivo Control by the Redox State of Chloroplasts and Involvement of the NADH-Dehydrogenase Complex

Abstract The mutualistic relationship existing between scleractinian corals and their photosynthetic endosymbionts involves a complex integration of the metabolic pathways within the holobiont. Respiration and photosynthesis are the most important of these processes and although they have been extensively studied, our understanding of their interactions and regulatory mechanisms is still limited. In this work we performed chlorophyll-a fluorescence, oxygen exchange and time-resolved absorption spectroscopy measurements on small and thin fragments (0.3 cm2) of the coral Stylophora pistillata. We showed that the capacity of mitochondrial alternative oxidase accounted for ca. 25% of total coral respiration, and that the high-light dependent oxygen uptake, commonly present in isolated Symbiodiniaceae, was negligible. The ratio between photosystem I (PSI) and photosystem II (PSII) active centers as well as their respective electron transport rates, indicated that PSI cyclic electron flow occurred in high light in S. pistillata and in some branching and lamellar coral species freshly collected in the field. Altogether, these results show the potential of applying advanced biophysical and spectroscopic methods on small coral fragments to understand the complex mechanisms of coral photosynthesis and respiration and their responses to environmental changes.

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Inhibition of Photosynthetic Electron Transport by Halogenated 4-Hydroxy-pyridines

Zeitschrift für Naturforschung C ◽

10.1515/znc-1985-5-618 ◽

1985 ◽

Vol 40 (5-6) ◽

pp. 391-399 ◽

Cited By ~ 17

Author(s):

A. Trebst ◽

B. Depka ◽

S. M. Ridley ◽

A. F. Hawkins

Keyword(s):

Electron Transport ◽

Photosystem Ii ◽

Photosystem I ◽

Electron Flow ◽

Essential Element ◽

Photosynthetic Electron Transport ◽

Cyclic Electron Flow ◽

Acceptor Side

Abstract Herbicidal halogen substituted 4-hydroxypyridines are inhibitors of photosynthetic electron flow in isolated thylakoid membranes by interfering with the acceptor side of photosystem II. Tetrabromo-4-hydroxypyridine, the most active compound found, has a pI50-value of 7.6 in the inhibition of oxygen evolution in both the reduction of an acceptor of photosystem I and an acceptor of photosystem II. The new inhibitors displace both metribuzin and ioxynil from the membrane. The 4-hydroxypyridines, like ioxynil, have unimpaired inhibitor potency in Tristreated chloroplasts, whereas the DCMU-type family of herbicides does not. It is suggested that 4-hydroxypyridines are complementary to phenol-type inhibitors, and a common essential element is proposed. The 4-hydroxypyridines do not inhibit photosystem I or non-cyclic electron flow through the cytochrome b/f complex. But they do have a second inhibition site in photosynthetic electron transport since they inhibit ferredoxin-catalyzed cyclic electron flow, indicating an antimycin-like property. A comparison of the in vitro potency of the compounds with the in vivo potency shows no correlation. A major herbicidal mode of action of the group is related to the inhibition of carotenoid synthesis, and access to the chloroplast lamellae in vivo for inhibition of electron transport may be restricted.

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Photosystem I cyclic electron flow via chloroplast NADH dehydrogenase-like complex performs a physiological role for photosynthesis at low light

Scientific Reports ◽

10.1038/srep13908 ◽

2015 ◽

Vol 5 (1) ◽

Cited By ~ 53

Author(s):

Wataru Yamori ◽

Toshiharu Shikanai ◽

Amane Makino

Keyword(s):

Electron Transport ◽

Light Intensity ◽

Photosystem I ◽

Nadh Dehydrogenase ◽

Physiological Function ◽

Electron Flow ◽

Cyclic Electron Flow ◽

Cyclic Electron Transport ◽

Low Light ◽

Ps I

Abstract Cyclic electron transport around photosystem I (PS I) was discovered more than a half-century ago and two pathways have been identified in angiosperms. Although substantial progress has been made in understanding the structure of the chloroplast NADH dehydrogenase-like (NDH) complex, which mediates one route of the cyclic electron transport pathways, its physiological function is not well understood. Most studies focused on the role of the NDH-dependent PS I cyclic electron transport in alleviation of oxidative damage in strong light. In contrast, here it is shown that impairment of NDH-dependent cyclic electron flow in rice specifically causes a reduction in the electron transport rate through PS I (ETR I) at low light intensity with a concomitant reduction in CO2 assimilation rate, plant biomass and importantly, grain production. There was no effect on PS II function at low or high light intensity. We propose a significant physiological function for the chloroplast NDH at low light intensities commonly experienced during the reproductive and ripening stages of rice cultivation that have adverse effects crop yield.

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