title: Long-term acclimation of the cyanobacterium Synechocystis sp. PCC 6803 to high light is accompanied by an enhanced production of chlorophyll that is preferentially channeled to trimeric photosystem I.
abstract: 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 (35)S and by (14)C 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(-2)s(-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 (35)S 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.
authors.affiliation: Institute of Microbiology, Department of Phototrophic Microorganisms, Academy of Sciences, 37981 Trebon, Czech Republic.
authors.forename: Jana
authors.initials: J
authors.lastname: Kopecná
authors.forename: Josef
authors.initials: J
authors.lastname: Komenda
authors.forename: Lenka
authors.initials: L
authors.lastname: Bucinská
authors.forename: Roman
authors.initials: R
authors.lastname: Sobotka
mesh_terms: D000064:Acclimatization / Q000528:radiation effects*; D001426:Bacterial Proteins / Q000378:metabolism; D053898:Biosynthetic Pathways / Q000528:radiation effects; D002247:Carbon Isotopes; D002734:Chlorophyll / Q000096:biosynthesis*; D008027:Light; D045331:Photosystem I Protein Complex / Q000378:metabolism*; D045332:Photosystem II Protein Complex / Q000378:metabolism; D013057:Spectrum Analysis; D046939:Synechocystis / Q000166:cytology / Q000502:physiology* / Q000528:radiation effects* / Q000648:ultrastructure; D013997:Time Factors; D015854:Up-Regulation / Q000235:genetics / Q000528:radiation effects
chemical_list: D001426:Bacterial Proteins; D002247:Carbon Isotopes; D045331:Photosystem I Protein Complex; D045332:Photosystem II Protein Complex; D002734:Chlorophyll