pH sensitivity of chlorophyll fluorescence quenching is determined by the detergent/protein ratio and the state of LHCII aggregation

AbstractHere we show how the protein environment in terms of detergent concentration/protein aggregation state, affects the sensitivity to pH of isolated, native LHCII, in terms of chlorophyll fluorescence quenching. Three detergent concentrations (200, 20 and 6μM n-dodecyl β-d-maltoside) have been tested. It was found that at the detergent concentration of 6μM, low pH quenching of LHCII is close to the physiological response to lumen acidification possessing pK of 5.5. The analysis has been conducted both using arbitrary PAM fluorimetry measurements and chlorophyll fluorescence lifetime component analysis. The second led to the conclusion that the 3.5ns component lifetime corresponds to an unnatural state of LHCII, induced by the detergent used for solubilising the protein, whilst the 2ns component is rather the most representative lifetime component of the conformational state of LHCII in the natural thylakoid membrane environment when the non-photochemical quenching (NPQ) was absent. The 2ns component is related to a pre-aggregated LHCII that makes it more sensitive to pH than the trimeric LHCII with the dominating 3.5ns lifetime component. The pre-aggregated LHCII displayed both a faster response to protons and a shift in the pK for quenching to higher values, from 4.2 to 4.9. We concluded that environmental factors like lipids, zeaxanthin and PsbS protein that modulate NPQ in vivo could control the state of LHCII aggregation in the dark that makes it more or less sensitive to the lumen acidification. This article is part of a Special Issue entitled: Photosynthesis Research for Sustainability: Keys to Produce Clean Energy

The Lhcb protein and xanthophyll composition of the light harvesting antenna controls the ΔpH-dependency of non-photochemical quenching in Arabidopsis thaliana

AbstractNonphotochemical quenching (NPQ) is the photoprotective dissipation of energy in photosynthetic membranes. The hypothesis that the ΔpH-dependent component of NPQ (qE) component of non-photochemical quenching is controlled allosterically by the xanthophyll cycle has been tested using Arabidopsis mutants with different xanthophyll content and composition of Lhcb proteins. The titration curves of qE against ΔpH were different in chloroplasts containing zeaxanthin or violaxanthin, proving their roles as allosteric activator and inhibitor, respectively. The curves differed in mutants deficient in lutein and specific Lhcb proteins. The results show that qE is determined by xanthophyll occupancy and the structural interactions within the antenna that govern allostericity

Absence of photosynthetic state transitions in alien chloroplasts

MAIN CONCLUSION:The absence of state transitions in a Nt(Hn) cybrid is due to a cleavage of the threonine residue from the misprocessed N-terminus of the LHCII polypeptides. The cooperation between the nucleus and chloroplast genomes is essential for plant photosynthetic fitness. The rapid and specific interactions between nucleus-encoded and chloroplast-encoded proteins are under intense investigation with potential for applications in agriculture and renewable energy technology. Here, we present a novel model for photosynthesis research in which alien henbane (Hyoscyamus niger) chloroplasts function on the nuclear background of a tobacco (Nicotiana tabacum). The result of this coupling is a cytoplasmic hybrid (cybrid) with inhibited state transitions-a mechanism responsible for balancing energy absorption between photosystems. Protein analysis showed differences in the LHCII composition of the cybrid plants. SDS-PAGE analysis revealed a novel banding pattern in the cybrids with at least one additional 'LHCII' band compared to the wild-type parental species. Proteomic work suggested that the N-terminus of at least some of the cybrid Lhcb proteins was missing. These findings provide a mechanistic explanation for the lack of state transitions-the N-terminal truncation of the Lhcb proteins in the cybrid included the threonine residue that is phosphorylated/dephosphorylated in order to trigger state transitions and therefore crucial energy balancing mechanism in plants

Photoprotective energy dissipation is greater in the lower, not the upper, regions of a rice canopy: a 3D analysis.

High light intensities raise photosynthetic and plant growth rates but can cause damage to the photosynthetic machinery. The likelihood and severity of deleterious effects are minimised by a set of photoprotective mechanisms, one key process being the controlled dissipation of energy from chlorophyll within PSII known as non-photochemical quenching (NPQ). Although ubiquitous, the role of NPQ in plant productivity is important because it momentarily reduces the quantum efficiency of photosynthesis. Rice plants overexpressing and deficient in the gene encoding a central regulator of NPQ, the protein PsbS, were used to assess the effect of protective effectiveness of NPQ (pNPQ) at the canopy scale. Using a combination of three-dimensional reconstruction, modelling, chlorophyll fluorescence, and gas exchange, the influence of altered NPQ capacity on the distribution of pNPQ was explored. A higher phototolerance in the lower layers of a canopy was found, regardless of genotype, suggesting a mechanism for increased protection for leaves that experience relatively low light intensities interspersed with brief periods of high light. Relative to wild-type plants, psbS overexpressors have a reduced risk of photoinactivation and early growth advantage, demonstrating that manipulating photoprotective mechanisms can impact both subcellular mechanisms and whole-canopy function

Reactions of iminophosphanes with chlorotris(triphenylphosphine)rhodium(I): generation and NMR identification of the first iminophosphanerhodium(I) and iminophosphanerhodium(III) complexes

Iminophosphanes [RO-P=NAr] (R = Me, 2-MeC6H4; Ar = 2,4,6-Bu'3C6H2) 1a,b react with RhClL3 (L = Ph3P) via ligand exchange to give KP-iminophosphane complexes of rhodium(i) [RhCl(MeOP=NAr)2L] 2 and [PhCl(2-MeC6H4OP=NAr)L2] 3. Under analogous conditions, P-halogenoiminophosphanes [X-P=NAr] (X = Cl, Br, I) 3a–c undergo a facile oxidative addition of the P-X bond, forming five-coordinate iminophosphanerhodium(III) complexes of composition [L2Cl(X)Rh(σ-P=BAr)] 5

Disentangling the low-energy states of the major light-harvesting complex of plants and their role in photoprotection

The ability to dissipate large fractions of their absorbed light energy as heat is a vital photoprotective function of the peripheral light-harvesting pigment–protein complexes in photosystemII of plants. The major component of this process, known as qE, is characterised by the appearance of low-energy (red-shifted) absorption and fluorescence bands. Although the appearance of these red states has been established, the molecular mechanism, their site and particularly their involvement in qE are strongly debated. Here, room-temperature single-molecule fluorescence spectroscopy was used to study the red emission states of the major plant light-harvesting complex (LHCII) in different environments, in particular conditions mimicking qE. It was found that most states correspond to peak emission at around 700 nm and are unrelated to energy dissipative states, though their frequency of occurrence increased under conditions that mimicked qE. Longer-wavelength emission appeared to be directly related to energy dissipative states, in particular emission beyond 770nm. The ensemble average of the red emission bands shares many properties with those obtained from previous bulk in vitro and in vivo studies. We propose the existence of at least three excitation energy dissipating mechanisms in LHCII, each of which is associated with a different spectral signature and whose contribution to qE is determined by environmental control of protein conformational disorder. Emission at 700 nmis attributed to a conformational change in the Lut 2 domain,which is facilitated by the conformational change associated with the primary quenching mechanism involving Lut 1.This work was supported by the EU FP7Marie Curie Reintegration Grant (ERG 224796) (C.I.); the CEA-Eurotalents Program(PCOFUNDGA- 2008-228664) (C.I.); research and equipment grants from UK BBSRC and EPSRC (M.P.J. and A.V.R.); Grants from the Netherlands Organization for Scientific Research (700.58.305 and 700.56.014 from the Foundation of Chemical Sciences) (T.P.J.K., C.I., and R.v.G.),and the Advanced Investigator Grant (267333, PHOTPROT) from the European Research Council (ERC) (C.I., T.P.J.K., and R.v.G.).http://www.elsevier.com/locate/bbabiohb2014ai201

Viewing oxidative stress through the lens of oxidative signalling rather than damage

Concepts of the roles of reactive oxygen species (ROS) in plants and animals have shifted in recent years from focusing on oxidative damage effects to the current view of ROS as universal signalling metabolites. Rather than having two opposing activities, i.e. damage and signalling, the emerging concept is that all types of oxidative modification/damage are involved in signalling, not least in the induction of repair processes. Examining the multifaceted roles of ROS as crucial cellular signals, we highlight as an example the loss of PSII function called photoinhibition, where photo-protection has classically been conflated with oxidative damage

The role of photoprotection in defence of two wheat genotypes against Zymoseptoria tritici

This study provides new insights into the role of photoprotection in preformed and induced defence of two wheat genotypes with contrasting phenotypes to infection by Zymoseptoria tritici. We investigated the mechanisms of the photoprotective response during early infection, including nonphotochemical quenching (NPQ), β-carotene-derived xanthophylls, reactive oxygen species, and the phytohormones abscisic acid (ABA), jasmonic acid (JA), and salicylic acid (SA). Furthermore, we quantified the effects of pathogenesis on photosynthesis, stomatal control, and expression of plant defence molecular markers. The photoprotective mechanism of successful defence involved the qI component of NPQ leading to rapid down-regulation of photosystem II quantum yield and chlorophyll a:b, increased biosynthesis of the xanthophyll neoxanthin and ABA, and the expression of chloroplast-specific enzymes to engage in scavenging of O2●−. Elevated ABA in the resistant genotype correlated with preformed leaf defence traits including low stomatal density, increased expression of wax biosynthesis, and lignification. Z. tritici exhibited reduced germination and branching on the resistant host genotype and hijacked stomatal control in both genotypes by enhancing stomatal sensitivity to light. Increased biosynthesis of JA and anthocyanins, in contrast to SA, were quantified in the incompatible interaction. Our results indicate that ABA and JA in antagonistic action to SA were associated with defence in the resistant genotype, Cougar, against Z. tritici