Electron‐dependent competition between plastoquinone and inhibitors for binding to photosystem II

Velthuys, B.R.

doi:10.1016/0014-5793(81)80260-8

Cited by 258 publications

(106 citation statements)

References 22 publications

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“…2 A. Note that these data reflect changes caused only by radiationless energy dissipation because PSII photochemistry was arrested with an electron-transport inhibiting herbicide (6,20). At the start of the recovery period, a high proportion of the PSII fluorescence lifetimes was distributed below 1 ns.…”

Section: Resultsmentioning

confidence: 91%

Protection and storage of chlorophyll in overwintering evergreens

Gilmore

Ball

2000

Proc. Natl. Acad. Sci. U.S.A.

163

126

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How evergreen species store and protect chlorophyll during exposure to high light in winter remains unexplained. This study reveals that the evergreen snow gum (Eucalyptus pauciflora Sieb. ex Spreng.) stores and protects its chlorophylls by forming special complexes that are unique to the winter-acclimated state. Our in vivo spectral and kinetic characterizations reveal a prominent component of the chlorophyll fluorescence spectrum around 715 nm at 77 K. This band coincides structurally with a loss of chlorophyll and an increase in energy-dissipating carotenoids. Functionally, the band coincides with an increased capacity to dissipate excess light energy, absorbed by the chlorophylls, as heat without intrathylakoid acidification. The increased heat dissipation helps protect the chlorophylls from photo-oxidative bleaching and thereby facilitates rapid recovery of photosynthesis in spring.U nder favorable light and temperatures, most plants operate with a high quantum efficiency (better than 80%) to use absorbed photons to catalyze photosynthetic electron transport, ATP synthesis, and carbon fixation. However, photosynthetic efficiency in leaves of evergreens such as holly (1), pines (2, 3), and snow gum (4, 5), naturally declines to very low levels during winter and remains inhibited until conditions become favorable for growth in spring. These evergreen species maintain significant levels of chlorophyll (Chl), which exists in a state that has not been characterized previously with respect to the Chl electronic-excited state or fluorescence lifetimes, or the Chl excitation vs. emission spectra of photosystems I and II (PSI and PSII). This characterization is essential for understanding mechanisms of Chl protection and storage in overwintering evergreens.We report that winter acclimation of the photosynthetic apparatus in the snow gum Eucalyptus pauciflora Sieb. ex Spreng results in a large loss of Chl in the leaf and profound changes in the Chl a fluorescence emission spectrum at 77 K in the form of a broad emission maximum featured in the 715-nm region. Concomitantly there is a significant increase in the amplitudes of room temperature PSII Chl a fluorescence emission components with subnanosecond fluorescence lifetimes. The subnanosecond lifetime components indicate a more rapid rate of thermal excitation dissipation compared to the main 2.5-ns components (6) that typify the deacclimated state. Although the spectral and kinetic changes during winter acclimation are induced by excess light and chloroplast intrathylakoid acidification (6, 7), the slowly reversing changes during deacclimation are sustained largely independently of intrathylakoid acidification. The enhanced thermal dissipation during winter acclimation correlates with a massive build-up of the same xanthophyll cycle pigments (8) that are most widely known to correlate with PSII thermal dissipation when there is intrathylakoid acidification (6,7,(9)(10)(11)(12). The primary steps of winter deacclimation correlate with a slow, stoichiometric conversi...

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Section: Resultsmentioning

confidence: 91%

Protection and storage of chlorophyll in overwintering evergreens

Gilmore

Ball

2000

Proc. Natl. Acad. Sci. U.S.A.

163

126

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“…PSII herbicides are known to displace Q B from its binding niche and to inhibit the electron transfer from Q A to Q B (Velthuys, 1981 ;Wraight, 1981 ). In our modeling, we used DCMU, one of the most commonly used phenylurea type of herbicides and modeled its position in the Q B site.…”

Section: Herbicide Dcmu Bindingmentioning

confidence: 99%

Modeling of the D1/D2 proteins and cofactors of the photosystem II reaction center: Implications for herbicide and bicarbonate binding

1996

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A three-dimensional model of the photosystem I1 (PSII) reaction center from the cyanobacterium Synechocystis sp. PCC 6803 was generated based on homology with the anoxygenic purple bacterial photosynthetic reaction centers of Rhodobacter sphaeroides and Rhodopseudomonas viridis, for which the X-ray crystallographic structures are available. The model was constructed with an alignment of Dl and D2 sequences with the L and M subunits of the bacterial reaction center, respectively, and by using as a scaffold the structurally conserved regions (SCRs) from bacterial templates. The structurally variant regions were built using a novel sequence-specific approach of searching for the best-matched protein segments in the Protein Data Bank with the "basic local alignment search tool" (Altschul SF, Gish W, Miller W, Myers EW, Lipman DJ, 1990, J Mol Biol 215:403-410). and imposing the matching conformational preference on the corresponding D l and D2 regions. The structure thus obtained was refined by energy minimization. The modeled D l and D2 proteins contain five transmembrane a-helices each, with cofactors (4 chlorophylls, 2 pheophytins, 2 plastoquinones, and a non-heme iron) essential for PSII primary photochemistry embedded in them. A p-carotene, considered important for PSII photoprotection, was also included in the model. Four different possible conformations of the primary electron donor P680 chlorophylls were proposed, one based on the homology with the bacterial template and the other three on existing experimental suggestions in literature. The P680 conformation based on homology was preferred because it has the lowest energy.Redox active tyrosine residues important for P680' reduction as well as residues important for PSI1 cofactor binding were analyzed. Residues involved in interprotein interactions in the model were also identified. Herbicide 3-(3,4-dichlorophenyI)-I , 1 -dimethylurea (DCMU) was also modeled in the plastoquinone QB binding niche using the structural information available from a DCMU-binding bacterial reaction center.A bicarbonate anion, known to play a role in PSII, but not in anoxygenic photosynthetic bacteria, was modeled in the non-heme iron site, providing a bidentate ligand to the iron. By modifying the previous hypothesis of Blubaugh and Govindjee (1988, Photosyn Res 1 9 3 -1 2 8 ) , we modeled a second bicarbonate and a water molecule in the Qe site and we proposed a hypothesis to explain the mechanism of QB protonation mediated by bicarbonate and water. The bicarbonate, stabilized by DLR257, donates a proton to Qi-through the intermediate of DLH252; and a water molecule donates another proton to Qi-. Based on the discovery of a "water transport channel" in the bacterial reaction center, an analogous channel for transporting water and bicarbonate is proposed in our PSII model. The putative channel appears to be primarily positively charged near QB and the non-heme iron, in contrast to the polarity distribution in the bacterial water transport channel. The constructed model has ...

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“…Herbicides acting at the Qs site bind less tightly when HCO 3 is removed, supporting the conclusion that the site of HCO Z action is at the quinone level [10][11][12]. It is now generally accepted that Qs is a bound PQ which, when fully reduced, exchanges for an oxidized PQ from the PQ pool [13,14]. Competitive binding between herbicides and quinones supports this view [15][16][17][18].…”

mentioning

confidence: 64%

Bicarbonate, not CO2, is the species required for the stimulation of Photosystem II electron transport

Blubaugh

Govindjee

1986

Biochimica et Biophysica Acta (BBA) - Bioenergetics

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Evidence is presented that the bicarbonate ion (HCOf), not CO 2, H2CO 3 or CO~-, is the species that stimulates electron transport in Photosystem II from spinach (Spinacia oleracea). Advantage was taken of the pH dependence of the ratio of HCO 3-to CO 2 at equilibrium in order to vary effectively the concentration of one species while holding the other constant. The Hill reaction was stimulated in direct proportion with the equilibrium HCO 3-concentration, but it was independent of the equilibrium CO 2 concentration. The other two carbonic species, H2CO 3 and CO 2-, are also shown to have no direct involvement. It is suggested that HCO 3-is the species which binds to the effector site.Bicarbonate appears to be an allosteric activator of the photosynthetic reduction of plastoquinone (PQ) in plant thylakoids. Warburg and Krippahl [1] demonstrated that the Hill reaction is impaired when CO 2 is removed from thylakoid membranes. It was later shown that this impairment is on the reducing side of Photosystem II (PS II; for a review, see Ref. 2). A number of anions, particularly formate and acetate, have been shown to interact with the binding of bicarbonate (HCO 3) suggesting a more general anion binding site (see e.g., Refs. 3 and 4). However, only HCO 3 has been shown to exert a stimulatory effect on PS II. Although a partial inhibition of the quinone reactions has been observed in CO2-depleted thylakoids * To whom correspondence and reprint requests should be addressed. Abbreviations: Chl, chlorophyll; [CO2], the CO 2 concentration; DCIP, 2,6-dichlorophenolindophenol; [HCO3], the HCO 3 concentration; PQ, plastoquinone; PS II, Photosystem II; QA and QB, first and second quinone acceptors of PS II, respectively. in the absence of other anions [5], the full inhibitory effect seems to require their presence.In the presence of formate, electron transfer from the secondary quinone Q s to the PQ pool is blocked by HCO 3 depletion [6][7][8], and electron transfer from the primary quinone QA tO QB is slowed down [7,9]. Herbicides acting at the Qs site bind less tightly when HCO 3 is removed, supporting the conclusion that the site of HCO Z action is at the quinone level [10][11][12]. It is now generally accepted that Qs is a bound PQ which, when fully reduced, exchanges for an oxidized PQ from the PQ pool [13,14]. Competitive binding between herbicides and quinones supports this view [15][16][17][18]. Our current hypothesis for the HCO 3 requirement, as noted earlier, is that HCO 3 acts as an allosteric activator for the reduction of bound PQ, and induces a conformational change which permits the efficient exchange between the bound PQH 2 and an oxidized PQ. Bicarbonate may also be involved in the protonation of PQH 2 [19,20]. The exact mechanism of action, however, is unknown. Before a reasonable mechanistic model 0005-2728/86/$03.50

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Electron‐dependent competition between plastoquinone and inhibitors for binding to photosystem II

Cited by 258 publications

References 22 publications

Protection and storage of chlorophyll in overwintering evergreens

Protection and storage of chlorophyll in overwintering evergreens

Modeling of the D1/D2 proteins and cofactors of the photosystem II reaction center: Implications for herbicide and bicarbonate binding

Bicarbonate, not CO2, is the species required for the stimulation of Photosystem II electron transport

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