Light plays an essential role in photosynthesis; however, its excess can cause damage to cellular components. Photosynthetic organisms thus developed a set of photoprotective mechanisms (e.g., non-photochemical quenching, photoinhibition) that can be studied by a classic biochemical and biophysical methods in cell suspension. Here, we combined these bulk methods with single-cell identification of microdomains in thylakoid membrane during high-light (HL) stress. We used Synechocystis sp. PCC 6803 cells with YFP tagged photosystem I. The single-cell data pointed to a three-phase response of cells to acute HL stress. We defined: (1) fast response phase (0-30 min), (2) intermediate phase (30-120 min), and (3) slow acclimation phase (120-360 min). During the first phase, cyanobacterial cells activated photoprotective mechanisms such as photoinhibition and non-photochemical quenching. Later on (during the second phase), we temporarily observed functional decoupling of phycobilisomes and sustained monomerization of photosystem II dimer. Simultaneously, cells also initiated accumulation of carotenoids, especially ɣ-carotene, the main precursor of all carotenoids. In the last phase, in addition to ɣ-carotene, we also observed accumulation of myxoxanthophyll and more even spatial distribution of photosystems and phycobilisomes between microdomains. We suggest that the overall carotenoid increase during HL stress could be involved either in the direct photoprotection (e.g., in ROS scavenging) and/or could play an additional role in maintaining optimal distribution of photosystems in thylakoid membrane to attain efficient photoprotection.

• Klíčová slova
• Synechocystis, carotenoids, high light, microdomains, non-photochemical quenching, photoinhibition, photoprotection, photosystems, thylakoid membrane,
• MeSH
• bakteriální proteiny genetika   metabolismus   MeSH
• fotosystém I (proteinový komplex) genetika   metabolismus   MeSH
• fotosystém II (proteinový komplex) genetika   metabolismus   MeSH
• karotenoidy metabolismus   MeSH
• světlo * MeSH
• Synechocystis metabolismus   účinky záření   MeSH
• tylakoidy metabolismus   účinky záření   MeSH
• velikost buňky účinky záření   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• bakteriální proteiny MeSH
• fotosystém I (proteinový komplex) MeSH
• fotosystém II (proteinový komplex) MeSH
• karotenoidy MeSH

Photosynthetic light reactions proceed in thylakoid membranes (TMs) due to the activity of pigment-protein complexes. These complexes are heterogeneously organized into granal/stromal thylakoids (in plants) or into recently identified cyanobacterial microdomains (MDs). MDs are characterized by specific ratios of photosystem I (PSI), photosystem II (PSII), and phycobilisomes (PBS) and they are visible as sub-micrometer sized areas with different fluorescence ratios. In this report, the process of long-term plasticity in cyanobacterial thylakoid MDs has been explored under variable growth light conditions using Synechocystis sp. PCC6803 expressing YFP tagged PSI. TM organization into MDs has been observed for all categorized shapes of cells independently of their stage in cell cycle. The heterogeneous PSI, PSII, and PBS thylakoid areas were also identified under two types of growth conditions: at continuous light (CL) and at light-dark (L-D) cycle. The acclimation from CL to L-D cycle changed spatial distribution of photosystems, in particular PSI became more evenly distributed in thylakoids under L-D cycle. The process of the spatial PSI (and partially also PSII) redistribution required 1 week and was accompanied by temporal appearance of PBS decoupling probably caused by the re-organization of photosystems. The overall acclimation we observed was defined as TM plasticity as it resembles higher plants grana/stroma reorganization at variable growth light conditions. In addition, we observed large cell to cell variability in the actual MDs organization. It leads us to suggest that the plasticity, and cell to cell variability in MDs could be a manifestation of phenotypic heterogeneity, a recently broadly discussed phenomenon for prokaryotes.

• Klíčová slova
• cyanobacteria, membrane organization, microdomains and rafts, phenotypic heterogeneity, photosynthesis, photosystems, phycobilisomes decoupling, thylakoid membrane,
• Publikační typ
• časopisecké články MeSH

The slow kinetic phases of the chlorophyll a fluorescence transient (induction) are valuable tools in studying dynamic regulation of light harvesting, light energy distribution between photosystems, and heat dissipation in photosynthetic organisms. However, the origin of these phases are not yet fully understood. This is especially true in the case of prokaryotic oxygenic photoautotrophs, the cyanobacteria. To understand the origin of the slowest (tens of minutes) kinetic phase, the M-T fluorescence decline, in the context of light acclimation of these globally important microorganisms, we have compared spectrally resolved fluorescence induction data from the wild type Synechocystis sp. PCC 6803 cells, using orange (λ = 593 nm) actinic light, with those of mutants, ΔapcD and ΔOCP, that are unable to perform either state transition or fluorescence quenching by orange carotenoid protein (OCP), respectively. Our results suggest a multiple origin of the M-T decline and reveal a complex interplay of various known regulatory processes in maintaining the redox homeostasis of a cyanobacterial cell. In addition, they lead us to suggest that a new type of regulatory process, operating on the timescale of minutes to hours, is involved in dissipating excess light energy in cyanobacteria.

• Klíčová slova
• Fluorescence quenching, Interplay of regulatory processes, Kautsky effect, Photoprotection, Synechocystis, The M–T phase,
• MeSH
• bakteriální proteiny genetika   metabolismus   MeSH
• chlorofyl a MeSH
• chlorofyl chemie   genetika   metabolismus   MeSH
• diuron chemie   MeSH
• fluorescence MeSH
• fluorescenční spektrometrie MeSH
• fykobilizomy genetika   metabolismus   MeSH
• kyanid draselný chemie   MeSH
• luminiscenční měření MeSH
• světlo MeSH
• Synechocystis chemie   genetika   metabolismus   MeSH
• teplota MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• bakteriální proteiny MeSH
• chlorofyl a MeSH
• chlorofyl MeSH
• diuron MeSH
• fykobilizomy MeSH
• kyanid draselný MeSH
• orange carotenoid protein, Synechocystis MeSH Prohlížeč