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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 leaf disks of the ndh mutant to irradiance in the presence of antimycin A. Values are means ± SE. (n = 3 leaf disks). Other conditions are as in Figure 1.
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Figure 6: Response of steady-state ETR1, LEFO2 and ΔFlux (A), and Y(ND) and Y(NA) (B) in leaf disks of the ndh mutant to irradiance in the presence of antimycin A. Values are means ± SE. (n = 3 leaf disks). Other conditions are as in Figure 1.

Mentions: In the presence of antimycin A, the ndh mutant showed a large acceptor side limitation, Y(NA) being 0.7–0.75 throughout the irradiance range. In particular, even when the irradiance was 135 μmol photons m-2 s-1, Y(NA) reached 0.76 (Figure 6B). By comparison, Y(NA) was only 0.37 in the pgr5 mutant in the presence of antimycin A and at the same irradiance (Figure 4B). An obvious difference between (a) the ndh mutant in the presence of antimycin A and (b) the pgr5 mutant in the presence of antimycin A is that the latter has NDH activity. It appears that when NDH-mediated CEF is permitted, over-reduction of the acceptor side is prevented. Thus, NDH may act as a safety valve when the stroma or, indeed, the acceptor side of PS I, is highly reduced; that is, NDH may contribute to redox homeostasis in chloroplasts at low irradiance (Shikanai, 2014).


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 leaf disks of the ndh mutant to irradiance in the presence of antimycin A. Values are means ± SE. (n = 3 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 6: Response of steady-state ETR1, LEFO2 and ΔFlux (A), and Y(ND) and Y(NA) (B) in leaf disks of the ndh mutant to irradiance in the presence of antimycin A. Values are means ± SE. (n = 3 leaf disks). Other conditions are as in Figure 1.
Mentions: In the presence of antimycin A, the ndh mutant showed a large acceptor side limitation, Y(NA) being 0.7–0.75 throughout the irradiance range. In particular, even when the irradiance was 135 μmol photons m-2 s-1, Y(NA) reached 0.76 (Figure 6B). By comparison, Y(NA) was only 0.37 in the pgr5 mutant in the presence of antimycin A and at the same irradiance (Figure 4B). An obvious difference between (a) the ndh mutant in the presence of antimycin A and (b) the pgr5 mutant in the presence of antimycin A is that the latter has NDH activity. It appears that when NDH-mediated CEF is permitted, over-reduction of the acceptor side is prevented. Thus, NDH may act as a safety valve when the stroma or, indeed, the acceptor side of PS I, is highly reduced; that is, NDH may contribute to redox homeostasis in chloroplasts at low irradiance (Shikanai, 2014).

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.