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Purification of structurally intact grana from plant thylakoids membranes
No full textThylakoid membranes in higher plant chloroplasts are composed by two distinct domains: stacked grana and stroma lamellae. We developed a procedure for biochemical isolation of grana membranes using mild detergent to maintain membrane structure. Pigment and polypeptide analyses of membrane preparation showed the preparations were indeed enriched in grana membranes. The method was shown to be effective in four different plant species, although with small changes in detergent concentration. Electron microscopy analyses also showed that the preparation consisted of large membrane patches with roughly round shape and diameter comparable with grana membranes in vivo. Furthermore, protein complexes distribution was shown to be maintained with respect to freeze fracture studies, demonstrating that the protocol was successful in isolating membranes close to their in vivo state
Distribution of Specific Keratin-Associated Beta-Proteins (Beta-Keratins) in the Epidermis of the Lizard Anolis carolinensis Helps to Clarify the Process of Cornification in Lepidosaurians
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The chloroplast NADH dehydrogenase-like complex influences the photosynthetic activity of the moss Physcomitrella patens
Full text linkAlternative electron pathways contribute to regulation of photosynthetic light reactions to adjust to metabolic demands in dynamic environments. The chloroplast NADH dehydrogenase-like (NDH) complex mediates the cyclic electron transport pathway around photosystem I (PSI) in different cyanobacteria, algae and plant species, but it is not fully conserved in all photosynthetic organisms. In order to assess how this complex's physiological role changed during plant evolution, we isolated Physcomitrella patens lines knocked out of the NDHM gene that encodes for a subunit fundamental for the activity of the complex. ndhm knock-out (KO) mosses indicated high PSI acceptor side limitation upon abrupt changes in illumination. In P. patens, pseudo-cyclic electron transport mediated by Flavodiiron proteins (FLVs) was also shown to prevent PSI overreduction in plants exposed to light fluctuations. flva ndhm double KO mosses had altered photosynthetic performance and growth defects under fluctuating light compared to wild-type and single KO mutants. The results evidenced that while NDH contribution to electron transport is minor compared to FLV, NDH still participates in modulating photosynthetic activity, and it is critical to avoid PSI photoinhibition, especially when FLVs are inactive. The functional overlap between NDH- and FLV-dependent electron transport supports PSI activity and prevents its photoinhibition under light variations
Involvement of potassium transport systems in the response of synechocystis PCC 6803 cyanobacteria to external pH change, high-intensity light stress and heavy metal stress
Full text linkThe unicellular photosynthetic cyanobacterium, able to sur- vive in varying environments, is the only prokaryote that directly converts solar energy and CO2 into organic material and is thus relevant for primary production in many ecosys- tems. To maintain the intracellular and intrathylakoid ion homeostasis upon different environmental challenges, the concentration of potassium as a major intracellular cation has to be optimized by various K+ uptake-mediated trans- port systems. We reveal here the specific and concerted physiological function of three K+ transporters of the plasma and thylakoid membranes, namely of SynK (K+ chan- nel), KtrB (Ktr/Trk/HKT) and KdpA (Kdp) in Synechocystis sp. strain PCC 6803, under specific stress conditions. The behavior of the wild type, single, double and triple mutants was compared, revealing that only Synk contributes to heavy metal-induced stress, while only Ktr/Kdp is involved in os- motic and salt stress adaptation. With regards to pH shifts in the external medium, the Kdp/Ktr uptake systems play an important role in the adaptation to acidic pH. Ktr, by affect- ing the CO2 concentration mechanism via its action on the bicarbonate transporter SbtA, might also be responsible for the observed effects concerning high-light stress and calcification. In the case of illumination with high-intensity light, a synergistic action of Kdr/Ktp and SynK is required in order to avoid oxidative stress and ensure cell viability. In summary, this study dissects, using growth tests, measurement of photosynthetic activity and analysis of ultrastructure, the physiological role of three K+ transporters in adaptation of the cyanobacteria to various environmental changes
Isolation and characterization of photosystem II subcomplexes from cyanobacteria lacking photosystem I
No full textA photosystem. II (PSII) core complex lacking the internal antenna CP43 protein was isolated from the photosystem II of Synechocystis PCC6803, which lacks photosystem I (PSI). CP47-RC and reaction centre (RCII) complexes were also obtained in a single procedure by direct solubilization of whole thylakoid membranes. The CP47-RC subcore complex was characterized by SDS/PAGE, immunoblotting, MALDI MS, visible and fluorescence spectroscopy, and absorption detected magnetic resonance. The purity and functionality of RCII was also assayed. These preparations may be useful for mutational analysis of PSII RC and CP47-RC in studying primary reactions of oxygenic photosynthesi
Heat dissipation in the moss Physcomitrella patens: lessons on evolution of protection mechanisms upon land colonization
No full textInvited Lecture at Western Photosynthesis Conference, Asilomar, CA, US
Characterization of the photosynthetic apparatus of the Eustigmatophycean Nannochloropsis gaditana: evidence of convergent evolution in the supramolecular organization of photosystem I.
No full textAbstractNannochloropsis gaditana belongs to Eustigmatophyceae, a class of eukaryotic algae resulting from a secondary endosymbiotic event. Species of this class have been poorly characterized thus far but are now raising increasing interest in the scientific community because of their possible application in biofuel production. Nannochloropsis species have a peculiar photosynthetic apparatus characterized by the presence of only chlorophyll a, with violaxanthin and vaucheriaxanthin esters as the most abundant carotenoids. In this study, the photosynthetic apparatus of this species was analyzed by purifying the thylakoids and isolating the different pigment-binding complexes upon mild solubilization. The results from the biochemical and spectroscopic characterization showed that the photosystem II antenna is loosely bound to the reaction center, whereas the association is stronger in photosystem I, with the antenna-reaction center super-complexes surviving purification. Such a supramolecular organization was found to be conserved in photosystem I from several other photosynthetic eukaryotes, even though these taxa are evolutionarily distant. A hypothesis on the possible selective advantage of different associations of the antenna complexes of photosystems I and II is discussed
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