In higher plants, the PsbS subunit of photosystem II (PSII) plays a crucial role in pH-and xanthophyll-dependent nonphotochemical quenching of excess absorbed light energy, thus contributing to the defense mechanism against photoinhibition. We determined the amino acid sequence of Zea mays PsbS and produced an antibody that recognizes with high specificity a region of the protein located in the stroma-exposed loop between the second and third putative helices. By means of this antiserum, the thylakoid membranes of various higher plant species revealed the presence of a 42-kDa protein band, indicating the formation of a dimer of the 21-kDa PsbS protein. Crosslinking experiments and immunoblotting with other antisera seem to exclude the formation of a heterodimer with other PSII protein components. The PsbS monomer͞dimer ratio in isolated thylakoid membranes was found to vary with luminal pH in a reversible manner, the monomer being the prevalent form at acidic and the dimer at alkaline pH. In intact chloroplasts and whole plants, dimer-to-monomer conversion is reversibly induced by light, known to cause luminal acidification. Sucrose-gradient centrifugation revealed a prevalent association of the PsbS monomer and dimer with light-harvesting complex and PSII core complexes, respectively. The finding of the existence of a light-induced change in the quaternary structure of the PsbS subunit may contribute to understanding the mechanism of PsbS action during nonphotochemical quenching.

A novel Zn(II)-phthalocyanine (1). peripherally substituted with four bis(N,N,N-trimethyl)amino-2-propyloxy groups prepared by chemical synthesis is shown to be an efficient photodynamic sensitizer with a quantum yield of 0.6 for singlet oxygen generation in neat water, which is reduced to about 0.3 in phosphate-buffered saline. The physicochemical properties of 1 in both the ground and the electronically excited states strongly depend on the nature of the medium; in particular, aggregation of 1 was favoured by polar media of high ionic strength. Compound 1 exhibited an appreciable affinity for a typical Gram-positive bacterium (Staphylococcus aureus) and a typical Gram-negative bacterium (Escherichia coli). Both bacterial strains were extensively inactivated upon 5 min-irradiation with 675 nm light in the presence of 1 microM photosensitizer, even though the binding of 1 to the two bacterial cells appears to occur according to different pathways. In particular, E. coli cells underwent initial photodamage at the level of specific proteins in the outer wall, thus promoting the penetration of the photosensitizer to the cytoplasmic membrane where some enzymes critical for cell survival were inactivated.

BackgroundThe productivity of an algal culture depends on how efficiently it converts sunlight into biomass and lipids. Wild-type algae in their natural environment evolved to compete for light energy and maximize individual cell growth; however, in a photobioreactor, global productivity should be maximized. Improving light use efficiency is one of the primary aims of algae biotechnological research, and genetic engineering can play a major role in attaining this goal.ResultsIn this work, we generated a collection of Nannochloropsis gaditana mutant strains and screened them for alterations in the photosynthetic apparatus. The selected mutant strains exhibited diverse phenotypes, some of which are potentially beneficial under the specific artificial conditions of a photobioreactor. Particular attention was given to strains showing reduced cellular pigment contents, and further characterization revealed that some of the selected strains exhibited improved photosynthetic activity; in at least one case, this trait corresponded to improved biomass productivity in lab-scale cultures.ConclusionsThis work demonstrates that genetic modification of N. gaditana has the potential to generate strains with improved biomass productivity when cultivated under the artificial conditions of a photobioreactor.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-015-0337-5) contains supplementary material, which is available to authorized users.

The epidermis of different scales in the lizard Anolis carolinensis expresses specific keratin‐associated beta‐proteins (beta‐keratins). In order to localize the sites of accumulation of different beta‐proteins, we have utilized antibodies directed against representative members of the main families of beta‐proteins, the glycine‐rich (HgG5), glycine–cysteine rich (HgGC3), glycine–cysteine medium‐rich (HgGC10), and cysteine‐rich (HgC1) beta‐proteins. Immunoblotting and immunocytochemical controls confirm the specificity of the antibodies made against these proteins. Light and ultrastructural immunocytochemistry shows that the glycine‐rich protein HgG5 is present in beta‐layers of different body scales but is scarce in the oberhautchen and claws, and is absent in alpha‐layers and adhesive setae. The cysteine–glycine‐rich protein HgGC3 is low to absent in the oberhautchen, beta‐layer, and mesos‐layer but increases in alpha‐layers. This beta‐protein is low in claws where it is likely associated with the hard alpha‐keratins previously studied in this lizard. The glycine–cysteine medium‐rich HgGC10 protein is low in the beta‐layer, higher in alpha‐layers, and in the oberhautchen. This protein forms a major component of setal proteins including those of the adhesive spatula that allow this lizard to stick on vertical surfaces. HgC1 is poorly localized in most epidermis analyzed including adhesive setae and claws and appears as a minor component of the alpha‐layers. In conclusion, the present study suggests that beta‐ and alpha‐layers of lizard epidermis represent regions with different accumulation of glycine‐rich proteins (mainly for mechanical resistance and hydrophobicity in the beta‐layer) or cysteine–glycine‐rich proteins (for both resistance and elasticity in both alpha‐ and beta‐layers). J. Exp. Zool. (Mol. Dev. Evol.) 318B:388‐403, 2012. © 2012 Wiley Periodicals, Inc.

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A potassium channel (SynK) of the cyanobacterium Synechocystis sp. PCC 6803, a photoheterotrophic model organism for the study of photosynthesis, has been recently identified and demonstrated to function as a potassium selective channel when expressed in a heterologous system and to be located predominantly to the thylakoid membrane in cyanobacteria. To study its physiological role, a SynK-less knockout mutant was generated and characterized. Fluorimetric experiments indicated that SynK-less cyanobacteria cannot build up a proton gradient as efficiently as WT organisms, suggesting that SynK might be involved in the regulation of the electric component of the proton motive force. Accordingly, measurements of flash-induced cytochrome b 6 f turnover and respiration pointed to a reduced generation of ΔpH and to an altered linear electron transport in mutant cells. The lack of the channel did not cause an altered membrane organization, but decreased growth and modified the photosystem II/photosystem I ratio at high light intensities because of enhanced photosensitivity. These data shed light on the function of a prokaryotic potassium channel and reports evidence, by means of a genetic approach, on the requirement of a thylakoid ion channel for optimal photosynthesis.bioenergetics | ion flux | membrane potential T he unicellular photoheterotrophic transformable cyanobacterium Synechocystis sp. PCC 6803 is the first photosynthetic organism for which the complete genome sequence was known. This prokaryote is characterized by an intracellular membrane system with thylakoids, where both photosynthesis and respiration take place. Cyanobacteria provide suitable model systems for studies on photosynthesis because these prokaryotes perform oxygenic photosynthesis using an apparatus similar to that found in chloroplasts of higher plants and algae. Moreover, cyanobacterial cultures can easily be exposed directly to defined stress conditions, and they are able to acclimate to a wide range of environments. Cyanobacteria are considered to represent the progenitors of chloroplasts, and Synechocystis has been widely used for genetic and biochemical studies of photosynthesis and various related metabolic processes (1).In a recent study, we identified in the genome of Synechocystis sp. PCC 6803 SynK (slr0498), displaying the amino acid sequence (TMTTVGYGD) that is typical of all known K + channels (2). This sequence forms a structural element known as a selectivity filter, which prevents the passage of Na + ions but allows K + ions to pass across the membrane at rates approaching the diffusion limit. SynK was found to function as potassiumselective channel when expressed in mammalian cells. Furthermore, SynK complemented K + uptake in a K + -transporter-deficient Escherichia coli strain, and its localization within cyanobacteria was determined. SynK represents a thylakoid-located ion channel identified in cyanobacteria and is conserved in various photosynthetic cyanobacteria species (2).During photosynthesis, in cyanobacteria a light-...

Bioinformatic approaches have allowed the identification in Arabidopsis thaliana of twenty genes encoding for homologues of animal ionotropic glutamate receptors (iGLRs). Some of these putative receptor proteins, grouped into three subfamilies, have been located to the plasmamembrane, but their possible location in organelles has not been investigated so far. In the present work we provide multiple evidence for the plastid localization of a glutamate receptor, AtGLR3.4, in Arabidopsis and tobacco. Biochemical analysis was performed using an antibody shown to specifically recognize both the native protein in Arabidopsis and the recombinant AtGLR3.4 fused to YFP expressed in tobacco. Western blots indicate the presence of AtGLR3.4 in both the plasmamembrane and in chloroplasts. In agreement, in transformed Arabidopsis cultured cells as well as in agroinfiltrated tobacco leaves, AtGLR3.4::YFP is detected both at the plasmamembrane and at the plastid level by confocal microscopy. The photosynthetic phenotype of mutant plants lacking AtGLR3.4 was also investigated. These results identify for the first time a dual localization of a glutamate receptor, revealing its presence in plastids and chloroplasts and opening the way to functional studies.

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