Cationic penetrating antioxidants switch off Mn cluster of photosystem II in situ.

Mitochondria-targeted antioxidants (also known as 'Skulachev Ions' electrophoretically accumulated by mitochondria) exert anti-ageing and ROS-protecting effects well documented in animal and human cells. However, their effects on chloroplast in photosynthetic cells and corresponding mechanisms are scarcely known. For the first time, we describe a dramatic quenching effect of (10-(6-plastoquinonyl)decyl triphenylphosphonium (SkQ1) on chlorophyll fluorescence, apparently mediated by redox interaction of SkQ1 with Mn cluster in Photosystem II (PSII) of chlorophyte microalga Chlorella vulgaris and disabling the oxygen-evolving complex (OEC). Microalgal cells displayed a vigorous uptake of SkQ1 which internal concentration built up to a very high level. Using optical and EPR spectroscopy, as well as electron donors and in silico molecular simulation techniques, we found that SkQ1 molecule can interact with Mn atoms of the OEC in PSII. This stops water splitting giving rise to potent quencher(s), e.g. oxidized reaction centre of PSII. Other components of the photosynthetic apparatus proved to be mostly intact. This effect of the Skulachev ions might help to develop in vivo models of photosynthetic cells with impaired OEC function but essentially intact otherwise. The observed phenomenon suggests that SkQ1 can be applied to study stress-induced damages to OEC in photosynthetic organisms.

Similarity and diversity of the Desmodesmus spp. microalgae isolated from associations with White Sea invertebrates.

Similarity and diversity of the phenotype and nucleotide sequences of certain genome loci among the single-celled microalgae isolated from White Sea benthic invertebrates were studied to extend the knowledge of oxygenic photoautotrophs forming microbial communities associated with animals. We compared four Desmodesmus isolates (1Hp86E-2, 1Pm66B, 3Dp86E-1, 2Cl66E) from the sponge Halichondria panicea, trochophore larvae of the polychaete Phyllodoce maculata, and the hydroids Dynamena pumila and Coryne lovenii, respectively. The microalgae appeared to be very similar featuring the phenotypic and genetic traits characteristics of unicellular representatives of the genus Desmodesmus. At the same time, isolates from different animal species displayed certain differences in (i) the epistructure morphology; (ii) type and number of the inclusions such as interthylakoid starch grains and cytoplasmic oil bodies and (iii) fatty acid composition; in Desmodesmus sp. 1Hp86E-2, these differences were most pronounced. Phylogenetic analysis based on ITS1-5.8S rRNA-ITS2 and rbcL sequences showed that all isolates studied differ from known classified representatives of Desmodesmus combining a deletion in the conservative 5.8S rRNA gene and long AC-microsatellite repeats in the ITS1 whereas 1Hp86E-2 represented a distinct branch within this group.