In response to a sudden increase in light intensity, plants must cope with absorbed excess photon energy to protect photosystems from photodamage. Under fluctuating light, PSI is severely ...photodamaged in the Arabidopsis (
)
(
) mutant defective in the main pathway of PSI cyclic electron transport (CET). Here, we aimed to determine how PSI is protected by two proposed regulatory roles of CET via transthylakoid ΔpH formation: (1) reservation of electron sink capacity by adjusting the ATP/NADPH production ratio (acceptor-side regulation) and (2) down-regulation of the cytochrome
complex activity called photosynthetic control for slowing down the electron flow toward PSI (donor-side regulation). We artificially enhanced donor- and acceptor-side regulation in the wild-type and
backgrounds by introducing the
mutation conferring the hypersensitivity of the cytochrome
complex to luminal acidification and moss
flavodiiron protein genes, respectively. Enhanced photosynthetic control partially alleviated PSI photodamage in the
mutant background but restricted linear electron transport under constant high light, suggesting that the strength of photosynthetic control should be optimized. Flavodiiron protein-dependent oxygen photoreduction formed a large electron sink and alleviated PSI photoinhibition, accompanied by the induction of photosynthetic control. Thus, donor-side regulation is essential for PSI photoprotection but acceptor-side regulation also is important to rapidly induce donor-side regulation. In angiosperms, PGR5-dependent CET is required for both functions.
A recently identified chemical, 2-((4-Methylpentan-2-yl)amino)-5-(phenylamino)cyclohexa-2,5-diene-1,4-dione (6PPD-quinone; 6PPD-Q), is a transformation product of an additive used in the manufacture ...of tire rubber and causes acute lethality in coho salmon (Oncorhynchus kisutch) in urban watersheds. Despite its potential presence and ecotoxicity in receiving waters worldwide, information on the occurrence and fate of 6PPD-Q is limited. Here, we investigated the concentrations of 6PPD-Q and its parent chemical, 6PPD, in road dust collected from arterial and residential roads in Tokyo, Japan from May to October 2021. 6PPD-Q concentrations were highest from May to June, when atmospheric ozone concentrations are the highest in Japan; a correlation between 6PPD-Q and photochemical oxidants, as an alternative to ozone, corroborated this finding. We also found that 6PPD-Q concentrations at photochemical oxidant concentrations ranging from 35 to 47 ppbv were higher in dust collected from roads with high traffic volumes (i.e., arterial roads; median: 8.6 μg/g-OC) than in dust collected from roads with lower traffic volumes (i.e., residential roads; median: 6.3 μg/g-OC), indicating that 6PPD-Q is generated from traffic-related sources. We also found that 6PPD-Q was leached from dust particles within a few hours, with a log partitioning coefficient between organic carbon and water (KOC) of 3.2–3.5. The present results will help to understand the environmental occurrence, fate, and behavior of 6PPD-Q.
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•6PPD and 6PPD-Q were detected in road dust samples collected from May to October.•6PPD-Q concentrations were highest from May to June.•Higher concentrations of 6PPD-Q could be due to higher ozone concentrations.•6PPD-Q concentrations were higher for roads with higher traffic volumes.
Photosynthetic electron transport is coupled to proton translocation across the thylakoid membrane, re- sulting in the formation of a trans-thylakoid proton gradient （△pH） and membrane potential ...（△ψ）. Ion trans-porters and channels localized to the thylakoid membrane regulate the contribution of each component to the proton motive force （pmf）. Although both △pH and △ψ contribute to ATP synthesis as pmf, only ~pH downregulates photosynthetic electron transport via the acidification of the thylakoid lumen by inducing thermal dissipation of excessive absorbed light energy from photosystem II antennae and slowing down of the electron transport through the cytochrome bsf complex. To optimize the tradeoff between efficient light energy utilization and protection of both photosystems against photodamage, plants have to regulate the pmf amplitude and its components, △pH and △ψ. Cyclic electron transport around photosystem I （PSI） is a major regulator of the pmf amplitude by generating pmf independently of the net production of NADPH by linear electron transport. Chloroplast ATP synthase relaxes pmf for ATP synthesis, and its activity should be finely tuned for maintaining the size of the pmf during steady-state photosynthesis. Pseudo-cyclic electron transport mediated by flavodiiron protein （FIv） forms a large electron sink, which is essential for PSI photoprotection in fluctuating light in cyanobacteria. FIv is conserved from cyanobacteria to gymno- sperms but not in angiosperms. The Arabidopsis proton gradient regulation 50（pgr5） mutant is defective in the main pathway of PSI cyclic electron transport. By introducing Physcomitrella patens genes encoding Flvs, the function of PSI cyclic electron transport was substituted by that of FIv-dependent pseudo-cyclic electron transport. In transgenic plants, the size of the pmf was complemented to the wild-type level but the contribution of △pH to the total pmf was lower than that in the wild type. In the pgr5 mutant, the size of the pmf was drastically lowered by the absence of PSI cyclic electron transport. In the mutant, △pH occupied the majority ofpmf, suggesting the presence of a mechanism for the homeostasis of luminal pH in the light. To avoid damage to photosynthetic electron transport by periods of excess solar energy, plants employ an intricate regulatory network involving alternative electron transport pathways, ion transporters/channels, and pH-dependent mechanisms for downregulating photosynthetic electron transport.
Abstract
High gH+ of the pgr5 mutant is restored to the wild-type level by introduction of flavodiiron protein and strong downregulation of the cytochrome b6f complex, counteracting proton leakage ...from the thylakoid membrane.
Abstract
Despite generating an obvious mutant phenotype, whether the Arabidopsis (Arabidopsis thaliana) proton gradient regulation5 (pgr5) mutation influences cyclic electron transport (CET) around PSI is a topic of debate. Results of electrochromic shift analysis show that proton conductivity across the thylakoid membrane (gH+) in the pgr5 mutant is enhanced at high light intensity. Given this observation, PGR5 was proposed to regulate ATP synthase activity rather than mediating CET. The originally reported pgr5 phenotype reflects a smaller proton motive force (pmf) and could be explained by this H+ leakage model. In this study, we genetically reexamined the high-gH+ phenotype of the pgr5 mutant. Transgenic lines in which flavodiiron protein-dependent pseudo-CET replaced PGR5-dependent CET had wild-type levels of gH+, suggesting that the high-gH+ phenotype in pgr5 plants is caused secondarily by the low pmf. The pgr1 mutant shows a similar reduction in pmf because of enhanced sensitivity of its cytochrome b6f complex to lumenal acidification. In contrast to the pgr5 mutant, gH+ was lower in the pgr1 mutant than in the wild type. In the pgr1 pgr5 double mutants, gH+ was intermediate to gH+ values of the respective single mutants. It is unlikely that gH+ is upregulated simply in response to a low pmf. We did not observe uncoupling of the thylakoid membrane in the pgr5 mutant upon monitoring the quenching of 9-aminoacridine fluorescence. We conclude that the gH+ parameter may be influenced by other factors not related to the H+ leakage through ATP synthase. It is unlikely that the pgr5 mutant leaks protons from the thylakoid membrane.
The selective synthesis of nickel and copper complexes of 19‐benzoyl‐5,10,15‐triphenyl‐bilatrien‐1‐one (H2TPBT) is reported, a molecule which crystallizes as a molecular helix of one‐and‐a‐quarter ...which turns with a 5.7 Å radius and a 3.2 Å pitch, and all 26 participating atoms are sp2‐hybridized. UV/vis, ECD, ESR and cyclic voltammetry experiments reveal a strong interaction between metal and ligand and partial radical character when copper is coordinated instead of nickel. Strong ECD absorption in the 800 nm range is found which, using TD‐DFT calculations as well as literature spectra, is shown to be highly tunable both by metal coordination and variation of the aryl groups in the TPBT periphery. The radical character of the ligand in Cu(TPBT) enables rapid interconversion between (M)‐ and (P)‐enantiomers, possibly via intermittent breakage of a Cu−N bond. The 19‐benzoyl group kinetically stabilizes enantiopure (M/P)‐Ni(TPBT). The results are interpreted with regard to the application as circularly polarized light (CPL) detectors as well as to the chirality‐induced spin‐selectivity (CISS) effect which is currently lacking a concise theoretical model.
Helical metal complexes of tetraphenylbilatrienones (TPBT) have been selectively synthesized, and for the first time, their structure was revealed by XRD. Contrary to theoretical predictions, their 20‐phenyl group points alongside the tetrapyrrole backbone, yielding a well‐defined molecule with stable helicity, 800 nm ECD absorption and – if copper is coordinated – noninnocent properties.
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 20min 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 2h, 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.
•Two PSI cyclic pathways contribute to pmf to different extents.•In pgr5, a decrease in pmf was accompanied by enhanced proton conductivity (gH+).•Enhanced gH+ by high light in pgr5 was recovered to the low light level.•gH+ was higher in pgr5 than in WT even after long dark adaptation.•In WT, gH+ responded to high light like in pgr5, but with much lower amplitude.
A spin-polarized state is examined under charge current at room temperature without magnetic fields in chiral disilicide crystals NbSi2 and TaSi2. We found that a long-range spin transport occurs ...over ten micrometers in these inorganic crystals. A distribution of crystalline grains of different handedness is obtained via location-sensitive electrical transport measurements. The sum rule holds in the conversion coefficient in the current-voltage characteristics. A diamagnetic nature of the crystals supports that the spin polarization is not due to localized electron spins but due to itinerant electron spins. A large difference in the strength of antisymmetric spin-orbit interaction associated with 4d electrons in Nb and 5d ones in Ta is oppositely correlated with that of the spin polarization. A robust protection of the spin polarization occurs over long distances in chiral crystals.
Electric double layers (EDLs) of ionic liquids have been used in superconducting field-effect transistors as nanogap capacitors. Because of the freezing of the ionic motion below ∼200 kelvin, ...modulations of the carrier density have been limited to the high-temperature regime. Here we observe carrier-doping–induced superconductivity in an organic Mott insulator with a photoinduced EDL based on a photochromic spiropyran monolayer. Because the spiropyran can isomerize reversibly between nonionic and zwitterionic isomers through photochemical processes, two distinct built-in electric fields can modulate the carrier density even at cryogenic conditions.
Artificial molecular switches and machines that enable the directional movements of molecular components by external stimuli have undergone rapid advances over the past several decades. Particularly, ...overcrowded alkene-based artificial molecular motors are highly attractive from the viewpoint of chirality switching during rotational steps. However, the integration of these molecular switches into solid-state devices is still challenging. Herein, we present an example of a solid-state spin-filtering device that can switch the spin polarization direction by light irradiation or thermal treatment. This device utilizes the chirality inversion of molecular motors as a light-driven reconfigurable spin filter owing to the chiral-induced spin selectivity effect. Through this device, we found that the flexibility at the molecular scale is essential for the electrodes in solid-state devices using molecular machines. The present results are beneficial to the development of solid-state functionalities emerging from nanosized motions of molecular switches.
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