title: Photosystem II and pigment dynamics among ecotypes of the green alga Ostreococcus.
abstract: 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.
authors: Biology Department, Mount Allison University, Sackville, New Brunswick, Canada E4L 1G7. six@sb-roscoff.fr
authors: Christophe
authors: C
authors: Six
authors: Ryan
authors: R
authors: Sherrard
authors: Marie
authors: M
authors: Lionard
authors: Suzanne
authors: S
authors: Roy
authors: Douglas A
authors: DA
authors: Campbell
mesh_terms: D000460:Chlorophyta / Q000145:classification* / Q000502:physiology*; D017753:Ecosystem; D008027:Light; D045332:Photosystem II Protein Complex / Q000502:physiology*; D010827:Physiology; D010860:Pigments, Biological / Q000502:physiology*; D010940:Plant Proteins
chemical_list: D045332:Photosystem II Protein Complex; D010860:Pigments, Biological; D010940:Plant Proteins