Integrating the proton circuit into photosynthesis: progress and challenges

Abstract

The formation of trans -thylakoid proton motive force ( pmf ) is coupled to light-driven electron transfer and both powers the synthesis of ATP and acts as a signal for initiating antenna regulation. This key intermediate has been difficult to study because of its ephemeral and variable qualities. This review covers recent efforts to probe pmf in vivo as well as efforts to address one of the key questions in photosynthesis: How does the photosynthetic machinery achieve sufficient flexibility to meet the energetic and regulatory needs of the plant in a varying environment? It is concluded that pmf plays a central role in these flexibility mechanisms.Key-words : CF 1 -CF 0 ATP synthase proton conductivity; cyclic electron flow around photosystem I; proton motive force.Abbreviations : CEF1, cyclic electron flow around photosystem I; cyt, cytochrome; CF 1 -CF O , chloroplast ATP synthase; D pH, pH component of pmf ; D y , electric field component of pmf ; D G ATP , the free energy of ATP formation; DIRK, dark interval relaxation kinetics; ECS, electrochromic shift; ECS t , total magnitude of ECS decay during a light-dark transition; ECS ss , steady-state ECS; ECS inv , ECS change from inverted D y ; Fd, ferredoxin; g H + , CF 1 -CF O ATP synthase proton conductivity; LEF, linear electron flow; LHCs, light harvesting complexes; n , number protons required for formation of one ATP; P 700 , primary electron donor of photosystem I; P 700 + , oxidized primary donor of photosystem I; pmf , transthylakoid proton motive force; pmf LEF , pmf generated solely by LEF; PQ, plastoquinone; PQH 2 , plastoquinol; PS, photosystem; f I , photochemical yield of photosystem I; f II , photochemical yield of photosystem II; q E , energy-dependent quenching of antenna excitons; t ECS , time constant for ECS decay in response to a brief dark interruption of steady state; v CEF1 , steady-state rate of CEF1; v H + , steady-state rate of proton flux; v LEF , steady-state rate of electron flux through LEF.

Analysis of light-induced transmembrane ion gradients and membrane potential in Photosystem I proteoliposomes

“…Numerous aspects of cyclic operation of PSI have been recently investigated, both on isolated photosynthetic membranes and in vivo [10][11][12][13]. However, the parameters controlling the extent and kinetics of ΔpH and Δψ when PSI is reconstituted in liposomes were not thoroughly investigated yet.…”

Photosynthetic electron turnover in the tropical and subtropical Atlantic Ocean

“…Under ambient light, modifications of s PSII , (Fig. 6C) are dependent upon the capacity with which ETR can build the transthylakoid H+ gradient (Allen, 2002;Kramer et al, 2004;Avenson et al, 2005) and on the maximum capacity for the antenna bed to quench excitation energy via processes such as xanthophyll cycling (Kramer et al, 2004).…”

Regulating the proton budget of higher plant photosynthesis

“…Recently, a series of in vivo probes of the pmf have been introduced (2,3,16,(25)(26)(27)(28), allowing contributions from Types I and II flexibility mechanisms to be directly assessed. These Abbreviations: CEF1, cyclic electron flow associated with PSI; ECS, electrochromic shift; LC, low CO2 (50 ppm CO2, 21% O2); LEF, linear electron flow; PS, photosystem; pmf, proton motive force; pmfLEF, pmf generated by LEF; qE, energy-dependent nonphotochemical quenching.…”

“…Recently, a series of in vivo probes of the pmf have been introduced (2,3,16,(25)(26)(27)(28), allowing contributions from Types I and II flexibility mechanisms to be directly assessed. These techniques are based on kinetic analyses of the ECS (26) of photosynthetic pigments, which yields absorbance changes proportional to changes in transthylakoid ⌬ (29).…”