Light-adaptive state transitions in the Ross Sea haptophyte Phaeocystis antarctica and in dinoflagellate cells hosting kleptoplasts derived from it |
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Authors: | Kostas Stamatakis Panayiotis-Ilias Broussos Angeliki Panagiotopoulou Rebecca J Gast Maria Pelecanou George C Papageorgiou |
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Institution: | 1. Institute of Biosciences and Applications, NCSR “Demokritos”, 15310, Aghia Paraskevi Attikis, Greece;2. Biology Department, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA |
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Abstract: | Light state transitions (STs) is a reversible physiological process that oxygenic photosynthetic organisms use in order to minimize imbalances in the electronic excitation delivery to the reaction centers of Photosystems I and II, and thus to optimize photosynthesis. STs have been studied extensively in plants, green algae, red algae and cyanobacteria, but sparsely in algae with secondary red algal plastids, such as diatoms and haptophytes, despite their immense ecological significance. In the present work, we examine whether the haptophyte alga Phaeocystis antarctica, and dinoflagellate cells that host kleptoplasts derived from P. antarctica, both endemic in the Ross Sea, Antarctica, are capable of light adaptive STs. In these organisms, Chl a fluorescence can be excited either by direct light absorption, or indirectly by electronic excitation (EE) transfer from ultraviolet light absorbing mycosporine-like amino acids (MAAs) to Chl a (Stamatakis et al., Biochim. Biophys. Acta 1858 2017] 189–195). Here we show that, on adaptation to PS II-selective light, dark-adapted P. antarctica cells shift from light state 1 (ST1; more EE ending up in PS II) to light state 2 (ST2; more EE ending up in PS I), as revealed by the spectral distribution of directly-excited Chl a fluorescence and by changes in the macro-organization of pigment-protein complexes evidenced by circular dichroism (CD) spectroscopy. In contrast, no STs are clearly detected in the case of the kleptoplast-hosting dinoflagellate cells, and in the case of indirectly excited Chls a, via MAAs, in P. antarctica cells. |
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Keywords: | Chl chlorophyll Dd diadinoxanthin Dt diatoxanthin EE electronic excitation EEE excess electronic excitation MAAs mycosporine-like amino-acids PS I Photosystem I PS II Photosystem II qE high energy non-photochemical quenching STs state transitions ST1 state 1 ST2 state 2 VAZ violaxanthin - antheraxanthin - zeaxanthin XC xanthophyll cycle Δλ bandwidth at half-maximum Kleptoplasts Ross Sea dinoflagellates Secondary plastids Light state transitions |
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