Abstract
Prasinophyceae are primitive eukaryotic green algae. These ubiquitous marine picophytoplankton contribute considerably to global carbon-fixation. Prasinophytes contain unique antenna proteins, dubbed Lhcp, which predate modern light-harvesting complex (LHC). Ostreococcus tauri, the first prasinophyte to be completely sequenced, is an ideal species for primitive algal studies. Characterization of photosynthetic systems in this species will clarify early stages in eukaryotic photosynthetic evolution. In this study we isolated O. tauri LHC, photosystem I, and photosystem II complexes using sucrose density gradient centrifugation. This reveals novel PSI complexes formed by strong association with both Lhca (PSI-specific LHC) and Lhcp. Both this complex and purified PSI-core are devoid of the far-red chlorophyll fluorescence (>700 nm) typical of PSI in other oxygenic phototrophs. Here we discuss the implication of this PSI-Lhcp association and the full characterization of O. tauri photosynthetic components using a variety of biochemical techniques, including HPLC, spectroscopy, and proteomic identification by mass spectrometry.
