Control and Measurement of Photosynthetic Electron Transport in Vivo

Kramer, David; Crofts, Antony R.

doi:10.1007/0-306-48135-9_2

Cited by 31 publications

(24 citation statements)

References 203 publications

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“…The results were not significantly altered by forcing the linear fits through the origin. Although these small differences could be the result of small systematic errors, e.g., in LEF measurements (37), they are also consistent with results from Munekage et al (31,32) that PGR5 is important for steady-state CEF1, and we thus adopt this view as our working model. This model is supported in separate estimates of proton flux and pmf.…”

Section: Effects Of Lowering Co2 Levels and Loss Of Pgr5 On Contributsupporting

confidence: 91%

Regulating the proton budget of higher plant photosynthesis

Avenson

Cruz

Kanazawa

et al. 2005

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

274

246

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In higher plant chloroplasts, transthylakoid proton motive force serves both to drive the synthesis of ATP and to regulate light capture by the photosynthetic antenna to prevent photodamage. In vivo probes of the proton circuit in wild-type and a mutant strain of Arabidopsis thaliana show that regulation of light capture is modulated primarily by altering the resistance of proton efflux from the thylakoid lumen, whereas modulation of proton influx through cyclic electron flow around photosystem I is suggested to play a role in regulating the ATP͞NADPH output ratio of the light reactions.ATP synthase proton conductivity ͉ cyclic electron flow ͉ linear electron flow ͉ energy-dependent nonphotochemical quenching ͉ protein motive force P hotosynthesis converts light energy into chemical energy, ultimately powering the vast majority of our ecosystem (1). Higher plant photosynthesis is initiated through absorption of light by antennae complexes that funnel the energy to photosystem (PS) II and I. The photosystems operate in sequence with the plastoquinone pool, the cytochrome b 6 f complex, and plastocyanin to oxidize H 2 O and reduce NADP ϩ to NADPH in what is termed linear electron flow (LEF). LEF is coupled to proton translocation, establishing a transthylakoid electrochemical gradient of protons, termed the proton motive force (pmf ) (2), comprised of electric field (⌬ ) and pH (⌬pH) gradients (3). Dual Role of the pmfThe pmf plays two central roles in higher plant photosynthesis (4). First, pmf drives the normally endergonic synthesis of ATP through the CF 1 -CF 0 ATP synthase (ATP synthase) (5). Both the ⌬pH and ⌬ components of pmf contribute to ATP synthesis in a thermodynamically, and probably kinetically, equivalent fashion (6). Second, pmf is a key signal for initiating photoprotection of the photosynthetic reaction centers through energydependent nonphotochemical quenching (q E ), a process that harmlessly dissipates excessively absorbed light energy as heat (7-10). Only the ⌬pH component of pmf, through acidification of the lumen, is effective in initiating q E by activating violaxanthin de-epoxidase, a lumen-localized enzyme that converts violaxanthin to antheraxanthin and zeaxanthin, and by protonating lumen-exposed residues of PsbS, a pigment-binding protein of the PS II antenna complex (11). A Need for Flexibility in the Light ReactionsA major open question concerns how the light reactions achieve the flexibility required to meet regulatory needs and match downstream biochemical demands (12). In LEF to NADP ϩ , the synthesis of ATP and the production of NADPH are coupled, producing a fixed ATP͞NADPH output ratio. LEF alone is probably unable to satisfy the variable ATP͞NADPH output ratios required to power the sum of the Calvin-Benson cycle (13,14) and other metabolic processes (alternate electron and ATP sinks) that are variably engaged under different physiological conditions (12,15,16). Failure to match ATP͞NADPH output with demand will lead to buildup of products and depletion of substrates for the...

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Section: Effects Of Lowering Co2 Levels and Loss Of Pgr5 On Contributsupporting

confidence: 91%

Regulating the proton budget of higher plant photosynthesis

Avenson

Cruz

Kanazawa

et al. 2005

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

274

246

View full text Add to dashboard Cite

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“…3 and 4). This lack of change implies that cyclic electron transfer is negligible or is a constant fraction of linear electron transfer, as previously suggested (48). The demands for ATP and NADPH may change under adverse environmental conditions or under altered metabolite demands (e.g., in young leaves, where nitrite reduction is expected to be large).…”

Section: A Technique For Estimating Steady-state Proton Fluxes In Vivomentioning

confidence: 80%

“…[46][47][48]. It has been argued that, in some cases, these deviations may be due to secondary effects of high-intensity light pulses on other properties of the system (49)(50)(51)(52)(53)(54) or from the operation of alternative electron acceptors or cycles around one or the other photosystem (e.g., 2, 22, 26, 47, 55-62).…”

Section: Saturation Pulse Fluorescence Assays Of Psii Electron Transfmentioning

confidence: 99%

The proton to electron stoichiometry of steady-state photosynthesis in living plants: A proton-pumping Q cycle is continuously engaged

Sacksteder

Kanazawa

Jacoby

et al. 2000

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

178

122

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A noninvasive technique is introduced with which relative proton to electron stoichiometries (H ؉ ͞e ؊ ratios) for photosynthetic electron transfer can be obtained from leaves of living plants under steady-state illumination. Both electron and proton transfer fluxes were estimated by a modification of our previously reported dark-interval relaxation kinetics (DIRK) analysis, in which processes that occur upon rapid shuttering of the actinic light are analyzed. Rates of turnover of linear electron transfer through the cytochrome (cyt) b 6f complex were estimated by measuring the DIRK signals associated with reduction of cyt f and P700. The rates of proton pumping through the electron transfer chain and the CF O-CF1 ATP synthase (ATPase) were estimated by measuring the DIRK signals associated with the electrochromic shifting of pigments in the light-harvesting complexes. Electron transfer fluxes were also estimated by analysis of saturation pulse-induced changes in chlorophyll a fluorescence yield. It was shown that the H ؉ ͞e ؊ ratio, with respect to both cyt b6f complex and photosystem (PS) II turnover, was constant under low to saturating illumination in intact tobacco leaves. Because a H ؉ ͞e ؊ ratio of 3 at a low light is generally accepted, we infer that this ratio is maintained under conditions of normal (unstressed) photosynthesis, implying a continuously engaged, proton-pumping Q cycle at the cyt b 6f complex.steady-state electron and proton transfer ͉ chemiosmotic coupling ͉ cyclic electron transfer ͉ energy budget T he energy budget of a plant depends upon the ratio of protons pumped across the thylakoid membrane to electrons passed through photosynthetic electron transfer complexes (the H ϩ ͞e Ϫ ratio), which sets the stoichiometries of ATP and NADPH production for use in the Calvin-Benson cycle and other biochemical pathways (reviewed in refs. 1 and 2). There has been a long-standing debate about the magnitude of H ϩ ͞e Ϫ for green plant photosynthesis, particularly regarding the proton pumping reactions of the cytochrome (cyt) b 6 f complex. It is generally accepted (see review in ref.3) that for each electron transferred through the linear pathway, one proton is released into the lumen at the level of water splitting; another is transported across the thylakoid membrane by the reduction and reoxidation of plastoquinone (PQ) at the photosystem II (PSII) Q B site and the cyt b 6 f complex Q o site, respectively; and a third proton is pumped, at least under some conditions, by the turnover of a Q cycle associated with the oxidation of plastoquinol at the cyt b 6 f complex (see refs. 4-7 for reviews). However, in vitro measurements of H ϩ ͞e Ϫ ratios for linear electron transport in isolated thylakoids range from 2 (e.g., refs. 8-10) to 3 (e.g., refs. 11 and 12), and several groups have suggested that it changes from 3 to 2 with increasing light intensity (1,11,(13)(14)(15)(16)(17). Such indications of variable coupling ratios have led several groups to suggest that the Q cycle or its proton pumping rea...

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“…Although such measurements need to be interpreted with caution, the most likely explanation for the decrease in the signal would be a loss of total PSI centres occurring per unit area of leaf. The use of a dualwavelength pulse-modulation system makes measurements quite specific to P700, reducing contributions from light scattering and also from plastocyanin or ferredoxin (Klughammer and Schreiber 1991;Kramer and Crofts 1996). The total concentration of P700 oxidised under steady-state conditions ($DS) remained largely constant during most of the treatment (Fig.…”

Section: Photosynthetic Acclimation During Mg Deficiencymentioning

confidence: 99%

Physiological characterisation of magnesium deficiency in sugar beet: acclimation to low magnesium differentially affects photosystems�I and II

Hermans

Johnson

Strasser

et al. 2004

Planta

209

187

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Magnesium deficiency in plants is a widespread problem, affecting productivity and quality in agriculture, yet at a physiological level it has been poorly studied in crop plants. Here, a physiological characterization of Mg deficiency in Beta vulgaris L., an important crop model, is presented. The impact of Mg deficiency on plant growth, mineral profile and photosynthetic activity was studied. The aerial biomass of plants decreased after 24 days of hydroponic culture in Mg-free nutrient solution, whereas the root biomass was unaffected. Analysis of mineral profiles revealed that Mg decreased more rapidly in roots than in shoots and that shoot Mg content could fall to 3 mg g À1 DW without chlorosis development and with no effect on photosynthetic parameters. Sucrose accumulated in most recently expanded leaves before any loss in photosynthetic activity. During the development of Mg deficiency, the two photosystems showed sharply contrasting responses. Data were consistent with a downregulation of PSII through a loss of antenna, and of PSI primarily through a loss of reaction centres. In each case, the net result was a decrease in the overall rate of linear electron transport, preventing an excess of reductant being produced during conditions under which sucrose export away from mature leaf was restricted.

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Control and Measurement of Photosynthetic Electron Transport in Vivo

Cited by 31 publications

References 203 publications

Regulating the proton budget of higher plant photosynthesis

Regulating the proton budget of higher plant photosynthesis

The proton to electron stoichiometry of steady-state photosynthesis in living plants: A proton-pumping Q cycle is continuously engaged

Physiological characterisation of magnesium deficiency in sugar beet: acclimation to low magnesium differentially affects photosystems�I and II

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