Role of cyclic electron transport around photosystem I in regulating proton motive force

Abstract

In addition to ∆pH formed across the thylakoid membrane, membrane potential contributes to proton motive force (pmf) in chloroplasts. However, the regulation of photosynthetic electron transport is mediated solely by ∆pH. To assess the contribution of two cyclic electron transport pathways around photosystem I (one depending on PGR5/PGRL1 and one on NDH) to pmf formation, electrochromic shift (ECS) was analyzed in the Arabidopsis pgr5 mutant, NDH-defective mutants (ndhs and crr4-2), and their double mutants (ndhs pgr5 and crr4-2 pgr5). In pgr5, the size of the pmf, as represented by ECSt, was reduced by 30% to 47% compared with that in the wild type (WT). A gH+ parameter, which is considered to represent the activity of ATP synthase, was enhanced at high light intensities. However, gH+ recovered to its low-light levels after 20 min in the dark, implying that the elevation in gH+ is due to the disturbed regulation of ATP synthase rather than to photodamage. After long dark adaptation more than 2 h, gH+ was higher in pgr5 than in the WT. During induction of photosynthesis, gH+ was more rapidly elevated in pgr5 than that in the WT. Both results suggest that ATP synthase is not fully inactivated in the dark in pgr5. In the NDH-deficient mutants, ECSt was slightly but significantly lower than in the WT, whereas gH+ was not affected. In the double mutants, ECSt was even lower than in pgr5. These results suggest that both PGR5/PGRL1- and NDH-dependent pathways contribute to pmf formation, although to different extents. This article is part of a Special Issue entitled: Chloroplast Biogenesis.

Grana-Localized Proteins, RIQ1 and RIQ2, Affect the Organization of Light-Harvesting Complex II and Grana Stacking in Arabidopsis

“…The pmf was saturated at 249 mmol photons m -2 s -1 in the wild type. As reported previously (Wang et al, 2015), the pmf was significantly lower in pgr5 than in the wild type under AL of 249 and 1707 mmol photons m -2 s -1 . However, the size of the pmf was not affected in riq mutants (Supplemental Figure 5), suggesting that the NPQ phenotype is not due to a reduced ΔpH.…”

“…To measure NPQ induction under red AL, a DUAL-PAM-100 system (Walz) was used with supply of 635-nm red light. ECS signals were detected as an absorbance change at 515 nm using a DUAL-PAM-100 system equipped with a P515/ 535 emitter-detector module (Walz), as described previously (Wang et al, 2015). ECS ST was determined as 515-nm absorbance changes using a single turnover flash and used to standardize ECS t .…”

Thylakoid proteome modulation in pea plants grown at different irradiances: quantitative proteomic profiling in a non‐model organism aided by transcriptomic data integration

“…The NDH complex constitutes only about 0.2% of the total thylakoid proteins (Sazanov et al ., ), thus PSI–LHCI–NDH complexes should be a relatively small fraction of thylakoid proteins (Peng et al ., ). The NDH‐dependent CEF has been thought to make a minor contribution to electron transport (Wang et al ., ), exerted mainly by adjusting the redox level of electron carriers in LL (Shikanai, ). The NDH increase observed in ML versus LL and HL versus LL plants, however, is greater than that of PGR5/PGRL1 (Figure ), suggesting a major role for NDH‐dependent CEF in long‐term acclimation to increasing irradiance.…”

Photosynthesis Control: An underrated short-term regulatory mechanism essential for plant viability

“…9 That is obtained through the protonation of two glutamic acid residues in the lumenexposed loop of PsbS protein, [43][44][45] which is a component of PSII, and the activation of the Violaxanthin De-Epoxidase (VDE) that converts violaxanthin into zeaxanthin within the xanthophyll cycle. 13,14,46 Secondly, the pgr5 mutants of both Arabidopsis and rice have also been shown to exhibit an elevated proton conductance of the ATP-synthase, 37,47 as well as an increased amount of the ATP synthase b subunit. 48 It is unclear how the regulation of ATP-synthase activity is perturbed by the pgr5 defect, but activation of ATP-synthase may counteract, to some extent, the reduced supply of ATP for CO 2 fixation in Calvin-BensonBassham cycle.…”