"MSMT LO 1416" Dotaz Zobrazit nápovědu
A proper spatial distribution of photosynthetic pigment-protein complexes - PPCs (photosystems, light-harvesting antennas) is crucial for photosynthesis. In plants, photosystems I and II (PSI and PSII) are heterogeneously distributed between granal and stromal thylakoids. Here we have described similar heterogeneity in the PSI, PSII and phycobilisomes (PBSs) distribution in cyanobacteria thylakoids into microdomains by applying a new image processing method suitable for the Synechocystis sp. PCC6803 strain with yellow fluorescent protein-tagged PSI. The new image processing method is able to analyze the fluorescence ratios of PPCs on a single-cell level, pixel per pixel. Each cell pixel is plotted in CIE1931 color space by forming a pixel-color distribution of the cell. The most common position in CIE1931 is then defined as protein arrangement (PA) factor with xy coordinates. The PA-factor represents the most abundant fluorescence ratio of PSI/PSII/PBS, the 'mode color' of studied cell. We proved that a shift of the PA-factor from the center of the cell-pixel distribution (the 'median' cell color) is an indicator of the presence of special subcellular microdomain(s) with a unique PSI/PSII/PBS fluorescence ratio in comparison to other parts of the cell. Furthermore, during a 6-h high-light (HL) treatment, 'median' and 'mode' color (PA-factor) of the cell changed similarly on the population level, indicating that such microdomains with unique PSI/PSII/PBS fluorescence were not formed during HL (i.e. fluorescence changed equally in the whole cell). However, the PA-factor was very sensitive in characterizing the fluorescence ratios of PSI/PSII/PBS in cyanobacterial cells during HL by depicting a 4-phase acclimation to HL, and their physiological interpretation has been discussed.
We explored photoprotective strategies in a cryptophyte alga Rhodomonas salina. This cryptophytic alga represents phototrophs where chlorophyll a/c antennas in thylakoids are combined with additional light-harvesting system formed by phycobiliproteins in the chloroplast lumen. The fastest response to excessive irradiation is induction of non-photochemical quenching (NPQ). The maximal NPQ appears already after 20 s of excessive irradiation. This initial phase of NPQ is sensitive to Ca2+ channel inhibitor (diltiazem) and disappears, also, in the presence of non-actin, an ionophore for monovalent cations. The prolonged exposure to high light of R. salina cells causes photoinhibition of photosystem II (PSII) that can be further enhanced when Ca2+ fluxes are inhibited by diltiazem. The light-induced reduction in PSII photochemical activity is smaller when compared with immotile diatom Phaeodactylum tricornutum. We explain this as a result of their different photoprotective strategies. Besides the protective role of NPQ, the motile R. salina also minimizes high light exposure by increased cell velocity by almost 25% percent (25% from 82 to 104 μm/s). We suggest that motility of algal cells might have a photoprotective role at high light because algal cell rotation around longitudinal axes changes continual irradiation to periodically fluctuating light.
In the present paper, we report an improved method combining sucrose density gradient with ion-exchange chromatography for the isolation of pure chlorophyll a/c antenna proteins from the model cryptophytic alga Rhodomonas salina. Antennas were used for in vitro quenching experiments in the absence of xanthophylls, showing that protein aggregation is a plausible mechanism behind non-photochemical quenching in R. salina. From sucrose gradient, it was also possible to purify a functional photosystem I supercomplex, which was in turn characterized by steady-state and time-resolved fluorescence spectroscopy. R. salina photosystem I showed a remarkably fast photochemical trapping rate, similar to what recently reported for other red clade algae such as Chromera velia and Phaeodactylum tricornutum. The method reported therefore may also be suitable for other still partially unexplored algae, such as cryptophytes.
