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

• Published in: Plant physiology (Bethesda) 2012-12, Vol.160 (4), p.2239-2250
• Main Authors: Kopečná, Jana, Komenda, Josef, Bučinská, Lenka, Sobotka, Roman
• Format: Article
• Language: English
• Subjects: Acclimatization; Acclimatization - radiation effects; Bacterial Proteins - metabolism; BIOENERGETICS AND PHOTOSYNTHESIS; Biological and medical sciences; Biosynthesis; Biosynthetic Pathways - radiation effects; Carbon Isotopes; Cell growth; Chlorophyll - biosynthesis; Chlorophylls; Cyanobacteria; Fundamental and applied biological sciences. Psychology; Light; Luminous intensity; Photosystem I Protein Complex - metabolism; Photosystem II Protein Complex - metabolism; Plant physiology and development; Plants; Spectrum Analysis; Stoichiometry; Synechocystis - cytology; Synechocystis - physiology; Synechocystis - radiation effects; Synechocystis - ultrastructure; Tetrapyrroles; Time Factors; Trimers; Up-Regulation - genetics; Up-Regulation - radiation effects
• ISSN: 0032-0889; 1532-2548
• DOI: 10.1104/pp.112.207274

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⁻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 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.