TY - JOUR T1 - Long-Term Acclimation of the Cyanobacterium <em>Synechocystis</em> sp. PCC 6803 to High Light Is Accompanied by an Enhanced Production of Chlorophyll That Is Preferentially Channeled to Trimeric Photosystem I JF - Plant Physiology JO - Plant Physiol. SP - 2239 LP - 2250 DO - 10.1104/pp.112.207274 VL - 160 IS - 4 AU - Kopečná, Jana AU - Komenda, Josef AU - Bučinská, Lenka AU - Sobotka, Roman Y1 - 2012/12/01 UR - http://www.plantphysiol.org/content/160/4/2239.abstract N2 - Cyanobacteria acclimate to high-light conditions by adjusting photosystem stoichiometry through a decrease of photosystem I (PSI) abundance in thylakoid membranes. As PSI complexes bind the majority of chlorophyll (Chl) in cyanobacterial cells, it is accepted that the mechanism controlling PSI level/synthesis is tightly associated with the Chl biosynthetic pathway. However, how Chl is distributed to photosystems under different light conditions remains unknown. Using radioactive labeling by 35S and by 14C combined with native/two-dimensional electrophoresis, we assessed the synthesis and accumulation of photosynthetic complexes in parallel with the synthesis of Chl in Synechocystis sp. PCC 6803 cells acclimated to different light intensities. Although cells acclimated to higher irradiances (150 and 300 μE m−2s−1) exhibited markedly reduced PSI content when compared with cells grown at lower irradiances (10 and 40 μE m−2 s−1), they grew much faster and synthesized significantly more Chl, as well as both photosystems. Interestingly, even under high irradiance, almost all labeled de novo Chl was localized in the trimeric PSI, whereas only a weak Chl labeling in photosystem II (PSII) was accompanied by the intensive 35S protein labeling, which was much stronger than in PSI. These results suggest that PSII subunits are mostly synthesized using recycled Chl molecules previously released during PSII repair-driven protein degradation. In contrast, most of the fresh Chl is utilized for synthesis of PSI complexes likely to maintain a constant level of PSI during cell proliferation.GlossaryHLhigh lightChlchlorophyllALAaminolevulinic acidMLmoderate lightLLlow lightOD750optical density at 750 nmCO2carbon dioxideFv/Fmratio of variable to maximal fluorescenceCNclear-nativeTLCthin-layer chromatographyHLIPto be defined ER -