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BIOENERGETICS AND PHOTOSYNTHESIS

Photosystem II and Pigment Dynamics among Ecotypes of the Green Alga Ostreococcus¹

Biology Department, Mount Allison University, Sackville, New Brunswick, Canada E4L 1G7 (C.S., R.S., D.A.C.); and Institut des Sciences de la Mer, Université du Québec à Rimouski, Rimouski, Quebec, Canada G5L 3A1 (M.L., S.R.)

We investigated the photophysiological responses of three ecotypes of the picophytoplankter Ostreococcus and a larger prasinophyte Pyramimonas obovata to a sudden increase in light irradiance. The deepwater Ostreococcus sp. RCC809 showed very high susceptibility to primary photoinactivation, likely a consequence of high oxidative stress, which may relate to the recently noted plastid terminal oxidase activity in this strain. The three Ostreococcus ecotypes were all capable of deploying modulation of the photosystem II repair cycle in order to cope with the light increase, but the effective clearance of photoinactivated D1 protein appeared to be slower in the deepwater Ostreococcus sp. RCC809, suggesting that this step is rate limiting in the photosystem II repair cycle in this strain. Moreover, the deepwater Ostreococcus accumulated lutein and showed substantial use of the xanthophyll cycle under light stress, demonstrating its high sensitivity to light fluctuations. The sustained component of the nonphotochemical quenching of fluorescence correlated well with the xanthophyll deepoxidation activity. Comparisons with the larger prasinophyte P. obovata suggest that the photophysiology of Ostreococcus ecotypes requires high photosystem II repair rates to counter a high susceptibility to photoinactivation, consistent with low pigment package effects in their minute-sized cells.

² Present address: Marine Photosynthetic Prokaryotes Group, UMR 7144 Université Pierre et Marie Curie (Paris 6) and CNRS, Station Biologique de Roscoff, 29682 Roscoff, France.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Christophe Six (six{at}sb-roscoff.fr).

www.plantphysiol.org/cgi/doi/10.1104/pp.109.140566

^* Corresponding author; e-mail six{at}sb-roscoff.fr.

Received April 29, 2009; accepted July 5, 2009; published July 8, 2009.