![]() Lumen acidification also regulates the oxidation of plastoquinol by the cytochrome b 6 f complex, slowing electron transfer from PSII and preventing the accumulation of electrons on PSI, which can otherwise lead to photodamage ( Nishio and Whitmarsh, 1993 Hope et al., 1994). Acidification of the thylakoid lumen activates the photoprotective energy-dependent exciton quenching (q E) process, which dissipates excess absorbed light energy in the photosynthetic antenna complexes by the activation of violaxanthin deepoxidase ( Demmig-Adams and Adams, 1992) and protonation of PsbS ( Li et al., 2004). In addition to its role in energy conservation, the pmf is also critical for feedback regulation of photosynthesis ( Cruz et al., 2005). The vectorial transfer of electrons across the membrane is tightly coupled with the generation of the pmf, composed of both electric field (Δ ψ) and pH (ΔpH) gradients. In oxygenic photosynthesis, light energy is captured by pigments in light-harvesting complexes and transferred to a subset of chlorophylls in photosystem I (PSI) and photosystem II (PSII), where it drives the extraction of electrons from water and their transfer through redox cofactors to ultimately reduce NADP +. The thylakoid proton motive force ( pmf), the transmembrane electrochemical gradient of protons generated during the light reactions of photosynthesis, is a fundamental entity of bioenergetics, coupling light-driven electron transfer reactions to the phosphorylation of ADP via the ATP synthase ( Avenson et al., 2004 Kramer and Evans, 2011). 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. Detailed analyses indicate this effect is related to an elevated electric field (Δ ψ) component of the pmf, rather than lumen acidification, which in vivo increased PSII charge recombination rates, producing singlet oxygen and subsequent photodamage. We observed the expected pmf-dependent alterations in photosynthetic regulation, but also strong effects on the rate of photosystem II (PSII) photodamage. 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. 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.
0 Comments
Leave a Reply. |