skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Chloroplast ATP Synthase Modulation of the Thylakoid Proton Motive Force: Implications for Photosystem I and Photosystem II Photoprotection

Abstract

In wild type plants, decreasing CO 2 lowers the activity of the chloroplast ATP synthase, slowing proton efflux from the thylakoid lumen resulting in buildup of thylakoid proton motive force (pmf). The resulting acidification of the lumen regulates both light harvesting, via the qE mechanism, and photosynthetic electron transfer through the cytochrome b 6f complex. Here in this paper, we show that the cfq mutant of Arabidopsis, harboring single point mutation in its γ-subunit of the chloroplast ATP synthase, increases the specific activity of the ATP synthase and disables its down-regulation under low CO 2. The increased thylakoid proton conductivity (g H +) in cfq results in decreased pmf and lumen acidification, preventing full activation of qE and more rapid electron transfer through the b6f complex, particularly under low CO 2 and fluctuating light. These conditions favor the accumulation of electrons on the acceptor side of PSI, and result in severe loss of PSI activity. Comparing the current results with previous work on the pgr5 mutant suggests a general mechanism where increased PSI photodamage in both mutants is caused by loss of pmf, rather than inhibition of CEF per se. Overall, our results support a critical role for ATP synthasemore » regulation in maintaining photosynthetic control of electron transfer to prevent photodamage.« less

Authors:
 [1];  [2];  [2];  [3];  [2];  [2];  [2];  [4];  [2];  [4];  [4]
  1. Michigan State Univ., East Lansing, MI (United States). MSU-DOE Plant Research Lab.; Michigan State Univ., East Lansing, MI (United States). Dept. of Chemistry
  2. Michigan State Univ., East Lansing, MI (United States). MSU-DOE Plant Research Lab.
  3. Michigan State Univ., East Lansing, MI (United States). MSU-DOE Plant Research Lab.; Michigan State Univ., East Lansing, MI (United States). Dept. of Cell and Molecular Biology
  4. Michigan State Univ., East Lansing, MI (United States). MSU-DOE Plant Research Lab.; Michigan State Univ., East Lansing, MI (United States). Dept. Biochemistry and Molecular Biology
Publication Date:
Research Org.:
Michigan State Univ., East Lansing, MI (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1368188
Grant/Contract Number:
FG02-91ER20021
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Frontiers in Plant Science
Additional Journal Information:
Journal Volume: 8; Journal ID: ISSN 1664-462X
Publisher:
Frontiers Research Foundation
Country of Publication:
United States
Language:
English
Subject:
59 BASIC BIOLOGICAL SCIENCES; ATP synthase; proton motive force; pmf, photoprotection; PSI; PSII

Citation Formats

Kanazawa, Atsuko, Ostendorf, Elisabeth, Kohzuma, Kaori, Hoh, Donghee, Strand, Deserah D., Sato-Cruz, Mio, Savage, Linda, Cruz, Jeffrey A., Fisher, Nicholas, Froehlich, John E., and Kramer, David M. Chloroplast ATP Synthase Modulation of the Thylakoid Proton Motive Force: Implications for Photosystem I and Photosystem II Photoprotection. United States: N. p., 2017. Web. doi:10.3389/fpls.2017.00719.
Kanazawa, Atsuko, Ostendorf, Elisabeth, Kohzuma, Kaori, Hoh, Donghee, Strand, Deserah D., Sato-Cruz, Mio, Savage, Linda, Cruz, Jeffrey A., Fisher, Nicholas, Froehlich, John E., & Kramer, David M. Chloroplast ATP Synthase Modulation of the Thylakoid Proton Motive Force: Implications for Photosystem I and Photosystem II Photoprotection. United States. doi:10.3389/fpls.2017.00719.
Kanazawa, Atsuko, Ostendorf, Elisabeth, Kohzuma, Kaori, Hoh, Donghee, Strand, Deserah D., Sato-Cruz, Mio, Savage, Linda, Cruz, Jeffrey A., Fisher, Nicholas, Froehlich, John E., and Kramer, David M. 2017. "Chloroplast ATP Synthase Modulation of the Thylakoid Proton Motive Force: Implications for Photosystem I and Photosystem II Photoprotection". United States. doi:10.3389/fpls.2017.00719. https://www.osti.gov/servlets/purl/1368188.
@article{osti_1368188,
title = {Chloroplast ATP Synthase Modulation of the Thylakoid Proton Motive Force: Implications for Photosystem I and Photosystem II Photoprotection},
author = {Kanazawa, Atsuko and Ostendorf, Elisabeth and Kohzuma, Kaori and Hoh, Donghee and Strand, Deserah D. and Sato-Cruz, Mio and Savage, Linda and Cruz, Jeffrey A. and Fisher, Nicholas and Froehlich, John E. and Kramer, David M.},
abstractNote = {In wild type plants, decreasing CO2 lowers the activity of the chloroplast ATP synthase, slowing proton efflux from the thylakoid lumen resulting in buildup of thylakoid proton motive force (pmf). The resulting acidification of the lumen regulates both light harvesting, via the qE mechanism, and photosynthetic electron transfer through the cytochrome b6f complex. Here in this paper, we show that the cfq mutant of Arabidopsis, harboring single point mutation in its γ-subunit of the chloroplast ATP synthase, increases the specific activity of the ATP synthase and disables its down-regulation under low CO2. The increased thylakoid proton conductivity (gH+) in cfq results in decreased pmf and lumen acidification, preventing full activation of qE and more rapid electron transfer through the b6f complex, particularly under low CO2 and fluctuating light. These conditions favor the accumulation of electrons on the acceptor side of PSI, and result in severe loss of PSI activity. Comparing the current results with previous work on the pgr5 mutant suggests a general mechanism where increased PSI photodamage in both mutants is caused by loss of pmf, rather than inhibition of CEF per se. Overall, our results support a critical role for ATP synthase regulation in maintaining photosynthetic control of electron transfer to prevent photodamage.},
doi = {10.3389/fpls.2017.00719},
journal = {Frontiers in Plant Science},
number = ,
volume = 8,
place = {United States},
year = 2017,
month = 5
}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record

Save / Share:
  • The thylakoid proton motive force ( pmf ) generated during photosynthesis is the essential driving force for ATP production; it is also a central regulator of light capture and electron transfer. We investigated the effects of elevated pmf on photosynthesis in a library of Arabidopsis thaliana mutants with altered rates of thylakoid lumen proton efflux, leading to a range of steady-state pmf extents. We observed the expected pmf- dependent alterations in photosynthetic regulation, but also strong effects on the rate of photosystem II (PSII) photodamage. Detailed analyses indicate this effect is related to an elevated electric field (Δ ψ )more » component of the pmf , rather than lumen acidification, which in vivo increased PSII charge recombination rates, producing singlet oxygen and subsequent photodamage. The effects are seen even in wild type plants, especially under fluctuating illumination, suggesting that Δ ψ -induced photodamage represents a previously unrecognized limiting factor for plant productivity under dynamic environmental conditions seen in the field.« less
  • The thylakoid proton motive force ( pmf ) generated during photosynthesis is the essential driving force for ATP production; it is also a central regulator of light capture and electron transfer. We investigated the effects of elevated pmf on photosynthesis in a library of Arabidopsis thaliana mutants with altered rates of thylakoid lumen proton efflux, leading to a range of steady-state pmf extents. We observed the expected pmf- dependent alterations in photosynthetic regulation, but also strong effects on the rate of photosystem II (PSII) photodamage. Detailed analyses indicate this effect is related to an elevated electric field (Δ ψ )more » component of the pmf , rather than lumen acidification, which in vivo increased PSII charge recombination rates, producing singlet oxygen and subsequent photodamage. The effects are seen even in wild type plants, especially under fluctuating illumination, suggesting that Δ ψ -induced photodamage represents a previously unrecognized limiting factor for plant productivity under dynamic environmental conditions seen in the field.« less
  • According to the chemiosmotic theory, proton pumps and ATP synthases are coupled by lateral proton flow through aqueous phases. Three long-standing challenges to this concept were examined in the light of experiments carried out with thylakoids: (1) Nearest neighbor interaction between pumps and ATP synthases. Considering the large distances between photosystem II and CFoCF1, in stacked thylakoids this is a priori absent. (2) Enhanced proton diffusion along the surface of the membrane. This could not be substantiated for the outer side of the thylakoid membrane. Even for the interface between pure lipid and water, two laboratories have reported the absencemore » of enhanced diffusion. (3) Localized proton ducts in the membrane. Intramembrane domains that can transiently trap protons do exist in thylakoid membranes, but because of their limited storage capacity for protons, they probably do not matter for photophosphorylation under continuous light. Seemingly in favor of localized proton ducts is the failure of a supposedly permeant buffer to enhance the onset lag of photophosphorylation. However, it was found that failure of some buffers and the ability of others in this respect were correlated with their failure/ability to quench pH transients in the thylakoid lumen, as predicted by the chemiosmotic theory. It was shown that the chemiosmotic concept is a fair approximation, even for narrow aqueous phases, as in stacked thylakoids. These are approximately isopotential, and protons are taken in by the ATP synthase straight from the lumen. The molecular mechanism by which F0F1 ATPases couple proton flow to ATP synthesis is still unknown. The threefold structural symmetry of the headpiece that, probably, finds a corollary in the channel portion of these enzymes appeals to the common wisdom that structural symmetry causes functional symmetry.« less
  • Thylakoid membrane proteins are organized so as to shield 30-50 nmol H+ (mg Chl)-1 from freely equilibrating with either the external or the lumen aqueous phases. Amine groups provide binding sites for this metastable buffering array and can be quantitatively measured by acetylation using (3H)acetic anhydride. The principle of the assay is that a metastable acidic domain will have relatively less of the reactive neutral form of the amine compared to the amount present after addition of an uncoupler. The extent of the acetylation reaction is strongly influenced by whether the lumen pH comes to complete equilibrium with the externalmore » pH prior to adding the acetic anhydride. Determination of the lumen pH by (14C)methylamine distribution after the standard 3 or 5 min equilibration in pH 8.6 buffer indicated that the lumen may have been 0.2 to 0.3 pH more acidic than the external phase. This effect was taken into account by determining the pH dependence, in the pH 8.2-8.6 range, of acetylation of the membrane proteins studied, and the labeling data were conservatively corrected for this possible contribution. Experiments were carried out to identify the thylakoid proteins that contribute such metastable domain amine groups, using the above conservative correction. Surprisingly, plastocyanin contributes buried amine groups, but cytochrome f did not give evidence for such a contribution, if the conservative correction in the labeling was applied. If the correction was too conservative, cytochrome f may contribute amines to the sequestered domains. The new methodology verified earlier results suggesting that three Tris-releasable photosystem II-associated proteins also contribute significantly to the sequestered amine-buffering array.« less