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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.


Related in: MedlinePlus

(A) Response of steady-state electron fluxes to irradiance of white light in the absence of antimycin A. ΔFlux = ETR1 - LEFO2. Each leaf disk was exposed to an irradiance that increased to the maximum using white halogen light filtered through neutral density filters. The leaf disk was maintained under each irradiance for about 10 min to reach steady-state photosynthesis. Oxygen evolution was first measured. Immediately afterward P700 kinetics were measured while maintaining steady-state photosynthesis. The temperature was 25°C. (B) The non-photochemical yield of PS I due to limitation on the donor side [Y(ND)] and the acceptor side [Y(NA)], measured simultaneously as ETR1 in (A). Values are means ± SE. (n = 8 leaf disks).
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Figure 1: (A) Response of steady-state electron fluxes to irradiance of white light in the absence of antimycin A. ΔFlux = ETR1 - LEFO2. Each leaf disk was exposed to an irradiance that increased to the maximum using white halogen light filtered through neutral density filters. The leaf disk was maintained under each irradiance for about 10 min to reach steady-state photosynthesis. Oxygen evolution was first measured. Immediately afterward P700 kinetics were measured while maintaining steady-state photosynthesis. The temperature was 25°C. (B) The non-photochemical yield of PS I due to limitation on the donor side [Y(ND)] and the acceptor side [Y(NA)], measured simultaneously as ETR1 in (A). Values are means ± SE. (n = 8 leaf disks).

Mentions: In the absence of antimycin A, ETR1 (the total electron flux through PS I), calculated by assuming fI = 0.4, did not show saturation even at the highest irradiance of white light used (Figure 1A). By contrast, LEFO2, assayed as the gross rate of O2 evolution multiplied by 4, almost peaked at about 250 μmol photons m-2 s-1, showing a slight increase at higher irradiances. The maximum LEFO2 reached about 50 μmol electrons m-2 s-1 (gross O2 evolution rate, about 12 μmol m-2 s-1). The difference between ETR1 and LEFO2 (=ΔFlux) increased approximately linearly with irradiance, even at low irradiance (Figure 1A). At the highest irradiance, ΔFlux exceeded LEFO2.


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)

(A) Response of steady-state electron fluxes to irradiance of white light in the absence of antimycin A. ΔFlux = ETR1 - LEFO2. Each leaf disk was exposed to an irradiance that increased to the maximum using white halogen light filtered through neutral density filters. The leaf disk was maintained under each irradiance for about 10 min to reach steady-state photosynthesis. Oxygen evolution was first measured. Immediately afterward P700 kinetics were measured while maintaining steady-state photosynthesis. The temperature was 25°C. (B) The non-photochemical yield of PS I due to limitation on the donor side [Y(ND)] and the acceptor side [Y(NA)], measured simultaneously as ETR1 in (A). Values are means ± SE. (n = 8 leaf disks).
© Copyright Policy
Related In: Results  -  Collection

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

Figure 1: (A) Response of steady-state electron fluxes to irradiance of white light in the absence of antimycin A. ΔFlux = ETR1 - LEFO2. Each leaf disk was exposed to an irradiance that increased to the maximum using white halogen light filtered through neutral density filters. The leaf disk was maintained under each irradiance for about 10 min to reach steady-state photosynthesis. Oxygen evolution was first measured. Immediately afterward P700 kinetics were measured while maintaining steady-state photosynthesis. The temperature was 25°C. (B) The non-photochemical yield of PS I due to limitation on the donor side [Y(ND)] and the acceptor side [Y(NA)], measured simultaneously as ETR1 in (A). Values are means ± SE. (n = 8 leaf disks).
Mentions: In the absence of antimycin A, ETR1 (the total electron flux through PS I), calculated by assuming fI = 0.4, did not show saturation even at the highest irradiance of white light used (Figure 1A). By contrast, LEFO2, assayed as the gross rate of O2 evolution multiplied by 4, almost peaked at about 250 μmol photons m-2 s-1, showing a slight increase at higher irradiances. The maximum LEFO2 reached about 50 μmol electrons m-2 s-1 (gross O2 evolution rate, about 12 μmol m-2 s-1). The difference between ETR1 and LEFO2 (=ΔFlux) increased approximately linearly with irradiance, even at low irradiance (Figure 1A). At the highest irradiance, ΔFlux exceeded LEFO2.

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.


Related in: MedlinePlus