The extraordinary longevity of kleptoplasts derived from the Ross Sea haptophyte Phaeocystis antarctica within dinoflagellate host cells relates to the diminished role of the oxygen-evolving Photosystem II and to supplementary light harvesting by mycosporine-like amino acid/s

• Published in: Biochimica et Biophysica Acta (BBA) - Bioenergetics
• Main Authors: Stamatakis, K., Vayenos, D., Kotakis, Christos, Gast, R. J., Papageorgiou, G. C.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Elsevier 2017
• Subjects: QH3011 Biochemistry / biokémia; QH3020 Biophysics / biofizika; Ross Sea; Antarc*; Antarctica
• Online Access: http://real.mtak.hu/73345/; http://real.mtak.hu/73345/1/StamatakisBBABioenergmanu.pdf; https://doi.org/10.1016/j.bbabio.2016.12.002

The haptophyte Phaeocystis antarctica and the novel Ross Sea dinoflagellate that hosts kleptoplasts derived from P. antarctica (RSD; R.J. Gast et al., 2006, J.Phycol. 42233-242) were compared for photosynthetic light harvesting and for oxygen evolution activity. Both chloroplasts and kleptoplasts emit chlorophyll a (Chl a) fluorescence peaking at 683 nm (F683) at 277 K and at 689 (F689) at 77 K. Second derivative analysis of the F689 band at 77 K revealed two individual contributions centered at 683 nm (Fi-683) and at 689 (Fi-689). Using the p-nitrothiophenol (p-NTP) treatment of Kobayashi et al. (Biochim. Biophys. Acta 423 (1976) 80-90) to differentiate between Photosystem (PS) II and I fluorescence emissions, we could identify PS II as the origin of Fi-683 and PS I as the origin of Fi-689. Both emissions could be excited not only by Chl a-selective light (436 nm) but also by mycosporine-like amino acids (MAAs)-selective light (345 nm). This suggests that a fraction of MAAs must be proximal to Chls a and, therefore, located within the plastids. On the basis of second derivative fluorescence spectra at 77 K, of p-NTP resolved fluorescence spectra, as well as of PSII-driven oxygen evolution activities, PS II appears substantially less active (-1/5) in dinoflagellate kleptoplasts than in P. antarctica chloroplasts. We suggest that a diminished role of PS II, a known source of reactive oxygen species, and a diminished dependence on nucleus-encoded light-harvesting proteins, due to supplementary light-harvesting by MAAs, may account for the extraordinary longevity of RSD kleptoplasts. (C) 2016 Elsevier B.V. All rights reserved.