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Partially dissecting the steady-state electron fluxes in Photosystem I in wild-type and pgr5 and ndh mutants of Arabidopsis.

Kou J, Takahashi S, Fan DY, Badger MR, Chow WS - Front Plant Sci (2015)

Bottom Line: We obtained the linear electron flux (LEFO2) through both photosystems and the total electron flux through PS I (ETR1) in Arabidopsis in CO2-enriched air.ΔFlux = ETR1 - LEFO2 is an upper estimate of CEF, which consists of two components, an antimycin A-sensitive, PGR5 (proton gradient regulation 5 protein)-dependent component and an insensitive component facilitated by a chloroplastic nicotinamide adenine dinucleotide dehydrogenase-like complex (NDH).Using wild type as well as pgr5 and ndh mutants, we observed that (1) 40% of the absorbed light was partitioned to PS I; (2) at high irradiance a substantial antimycin A-sensitive CEF occurred in the wild type and the ndh mutant; (3) at low irradiance a sizable antimycin A-sensitive CEF occurred in the wild type but not in the ndh mutant, suggesting an enhancing effect of NDH in low light; and (4) in the pgr5 mutant, and the wild type and ndh mutant treated with antimycin A, a residual ΔFlux existed at high irradiance, attributable to charge recombination and/or pseudo-cyclic electron flow.

View Article: PubMed Central - PubMed

Affiliation: College of Animal Science and Technology, Northwest A&F University Yangling, China ; Division of Plant Sciences, Research School of Biology, The Australian National University Canberra, ACT, Australia.

ABSTRACT
Cyclic electron flux (CEF) around Photosystem I (PS I) is difficult to quantify. We obtained the linear electron flux (LEFO2) through both photosystems and the total electron flux through PS I (ETR1) in Arabidopsis in CO2-enriched air. ΔFlux = ETR1 - LEFO2 is an upper estimate of CEF, which consists of two components, an antimycin A-sensitive, PGR5 (proton gradient regulation 5 protein)-dependent component and an insensitive component facilitated by a chloroplastic nicotinamide adenine dinucleotide dehydrogenase-like complex (NDH). Using wild type as well as pgr5 and ndh mutants, we observed that (1) 40% of the absorbed light was partitioned to PS I; (2) at high irradiance a substantial antimycin A-sensitive CEF occurred in the wild type and the ndh mutant; (3) at low irradiance a sizable antimycin A-sensitive CEF occurred in the wild type but not in the ndh mutant, suggesting an enhancing effect of NDH in low light; and (4) in the pgr5 mutant, and the wild type and ndh mutant treated with antimycin A, a residual ΔFlux existed at high irradiance, attributable to charge recombination and/or pseudo-cyclic electron flow. Therefore, in low-light-acclimated plants exposed to high light, ΔFlux has contributions from various paths of electron flow through PS I.

No MeSH data available.


Response of steady-state ETR1, LEFO2 and ΔFlux (A), and Y(ND) and Y(NA) (B) in wild-type leaf disks to irradiance in the presence of antimycin A. Values are means ± SE. (n = leaf disks). Other conditions are as in Figure 1.
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Figure 2: Response of steady-state ETR1, LEFO2 and ΔFlux (A), and Y(ND) and Y(NA) (B) in wild-type leaf disks to irradiance in the presence of antimycin A. Values are means ± SE. (n = leaf disks). Other conditions are as in Figure 1.

Mentions: In the presence of antimycin A, the antimycin A-sensitive component of CEF should have been largely inhibited. Below 265 μmol photons m-2 s-1, ETR1 and LEFO2 were similar in magnitude (Figure 2A). Presumably below this irradiance, there was little or no pseudo-cyclic electron flux or charge recombination. Above this irradiance, however, ΔFlux increased steadily. Given that the acceptor side limitation was quite high at high irradiance, Y(NA) being ∼0.55, it is likely there was enhanced charge recombination and/or pseudo-cyclic electron flow due to a more reduced state of electron carriers on the acceptor side of PS I. Increased charge recombination might have been the more important of the two components of the electron flux in this situation: P700 was kept more reduced [lower Y(ND), Figure 2B] compared with the absence of antimycin A (Figure 1B), presumably by charge recombination, whereas pseudocyclic electron flow should have kept P700 more oxidized. Thus, it appears that inhibition of CEF by antimycin A resulted in a more reduced acceptor side, which in turn enhanced charge recombination and, potentially, also pseudo-cyclic electron flow at high irradiance.


Partially dissecting the steady-state electron fluxes in Photosystem I in wild-type and pgr5 and ndh mutants of Arabidopsis.

Kou J, Takahashi S, Fan DY, Badger MR, Chow WS - Front Plant Sci (2015)

Response of steady-state ETR1, LEFO2 and ΔFlux (A), and Y(ND) and Y(NA) (B) in wild-type leaf disks to irradiance in the presence of antimycin A. Values are means ± SE. (n = leaf disks). Other conditions are as in Figure 1.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4584955&req=5

Figure 2: Response of steady-state ETR1, LEFO2 and ΔFlux (A), and Y(ND) and Y(NA) (B) in wild-type leaf disks to irradiance in the presence of antimycin A. Values are means ± SE. (n = leaf disks). Other conditions are as in Figure 1.
Mentions: In the presence of antimycin A, the antimycin A-sensitive component of CEF should have been largely inhibited. Below 265 μmol photons m-2 s-1, ETR1 and LEFO2 were similar in magnitude (Figure 2A). Presumably below this irradiance, there was little or no pseudo-cyclic electron flux or charge recombination. Above this irradiance, however, ΔFlux increased steadily. Given that the acceptor side limitation was quite high at high irradiance, Y(NA) being ∼0.55, it is likely there was enhanced charge recombination and/or pseudo-cyclic electron flow due to a more reduced state of electron carriers on the acceptor side of PS I. Increased charge recombination might have been the more important of the two components of the electron flux in this situation: P700 was kept more reduced [lower Y(ND), Figure 2B] compared with the absence of antimycin A (Figure 1B), presumably by charge recombination, whereas pseudocyclic electron flow should have kept P700 more oxidized. Thus, it appears that inhibition of CEF by antimycin A resulted in a more reduced acceptor side, which in turn enhanced charge recombination and, potentially, also pseudo-cyclic electron flow at high irradiance.

Bottom Line: We obtained the linear electron flux (LEFO2) through both photosystems and the total electron flux through PS I (ETR1) in Arabidopsis in CO2-enriched air.ΔFlux = ETR1 - LEFO2 is an upper estimate of CEF, which consists of two components, an antimycin A-sensitive, PGR5 (proton gradient regulation 5 protein)-dependent component and an insensitive component facilitated by a chloroplastic nicotinamide adenine dinucleotide dehydrogenase-like complex (NDH).Using wild type as well as pgr5 and ndh mutants, we observed that (1) 40% of the absorbed light was partitioned to PS I; (2) at high irradiance a substantial antimycin A-sensitive CEF occurred in the wild type and the ndh mutant; (3) at low irradiance a sizable antimycin A-sensitive CEF occurred in the wild type but not in the ndh mutant, suggesting an enhancing effect of NDH in low light; and (4) in the pgr5 mutant, and the wild type and ndh mutant treated with antimycin A, a residual ΔFlux existed at high irradiance, attributable to charge recombination and/or pseudo-cyclic electron flow.

View Article: PubMed Central - PubMed

Affiliation: College of Animal Science and Technology, Northwest A&F University Yangling, China ; Division of Plant Sciences, Research School of Biology, The Australian National University Canberra, ACT, Australia.

ABSTRACT
Cyclic electron flux (CEF) around Photosystem I (PS I) is difficult to quantify. We obtained the linear electron flux (LEFO2) through both photosystems and the total electron flux through PS I (ETR1) in Arabidopsis in CO2-enriched air. ΔFlux = ETR1 - LEFO2 is an upper estimate of CEF, which consists of two components, an antimycin A-sensitive, PGR5 (proton gradient regulation 5 protein)-dependent component and an insensitive component facilitated by a chloroplastic nicotinamide adenine dinucleotide dehydrogenase-like complex (NDH). Using wild type as well as pgr5 and ndh mutants, we observed that (1) 40% of the absorbed light was partitioned to PS I; (2) at high irradiance a substantial antimycin A-sensitive CEF occurred in the wild type and the ndh mutant; (3) at low irradiance a sizable antimycin A-sensitive CEF occurred in the wild type but not in the ndh mutant, suggesting an enhancing effect of NDH in low light; and (4) in the pgr5 mutant, and the wild type and ndh mutant treated with antimycin A, a residual ΔFlux existed at high irradiance, attributable to charge recombination and/or pseudo-cyclic electron flow. Therefore, in low-light-acclimated plants exposed to high light, ΔFlux has contributions from various paths of electron flow through PS I.

No MeSH data available.