The Main Structural and Functional Characteristics of Photosystem-II-Enriched Membranes Isolated from Wild Type and cia3 Mutant Chlamydomonas reinhardtii

Abstract

Photosystem II (PSII)-enriched membranes retain the original PSII architecture in contrast to PSII cores or PSII supercomplexes, which are usually isolated from Chlamydomonas reinhardtii. Here, we present data that fully characterize the structural and functional properties of PSII complexes in isolated PSII-enriched membranes from C. reinhardtii. The preparations were isolated from wild-type (WT) and CAH3-deficient mutant cia3 as the influence of CAH3 on the PSII function was previously proposed. Based on the equal chlorophyll content, the PSII-enriched membranes from WT and cia3 have the same amount of reaction centers (RCs), cytochrome b559, subunits of the water-oxidizing complex, Mn ions, and carotenes. They differ in the ratio of other carotenoids, the parts of low/intermediate redox forms of cytochrome b559, and the composition of outer light-harvesting complexes. The preparations had 40% more chlorophyll molecules per RC compared to higher plants. Functionally, PSII-enriched membranes from WT and cia3 show the same photosynthetic activity at optimal pH 6.5. However, the preparations from cia3 contained more closed RCs even at pH 6.5 and showed more pronounced suppression of PSII photosynthetic activity at shift pH up to 7.0, established in the lumen of dark-adapted cells. Nevertheless, the PSII photosynthetic capacities remained the same.

Structure of photosystem I-LHCI-LHCII from the green alga Chlamydomonas reinhardtii in State 2

“…The HPLC measurements also show the presence of a small amount of a pigment involved in the xanthophyll cycle, antheraxanthin (Ant), in both the PSI-LHCI and PSI-LHCI-LHCII supercomplexes isolated from the state 2 cells. Since this pigment was not found in PSI-LHCI isolated from state 1 cells of C. reinhardtii 12 , this indicates that the xanthophyll cycle may occur during the state transition of C. reinhardtii 37 .…”

Assembly and Repair of Photosystem II in Chlamydomonas reinhardtii

“…PSII in Chlamydomonas is undergoing frequent damage and repair. When PSII is isolated from Chlamydomonas cultures grown under optimal conditions, the observed manganese content is lower than expected suggesting that up to 20% of centers are in damaged or assembly states [ 140 , 141 ]. The PSII D1 subunit is most prone to oxidative damage and is rapidly turned over.…”

Action of 2,6-Dichloro-1,4-benzoquinone on the O2-Evolving Activity of Photosystem II in Chlamydomonas reinhardtii Cells with and without Cell Wall: Inhibitory Effect of Its Oxidized Form

“…The two strains of C. reinhardtii studied in the present work were the cell wall-less mutant CC-503 cw92 mt+, taken as the standard wild type (WT) in the series of previous work [ 3 , 22 , 30 , 31 , 32 ], and the basic 137c (CC-125 mt+) WT. Cultures were grown photoautotrophically in parallel in the minimal medium at 25 °C under aeration with air enriched with 5% CO 2 .…”