A proper spatial distribution of photosynthetic pigment-protein complexes - PPCs (photosystems,
light-harvesting antennas) is crucial for photosynthesis. In plants, photosystems
(PSI and PSII) are heterogeneously distributed between granal and stromal thylakoids.
Here we have described similar heterogeneity in the PSI, PSII, and Phycobilisomes
(PBS) distribution in cyanobacteria thylakoids into microdomains by applying a new
image processing method suitable for the Synechocystis sp. PCC6803 strain with YFP-tagged
PSI. The new image processing method is able to analyze fluorescence ratios of PPCs
on 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 x-y 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. Further, during a 6 hour 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 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. This article is protected by copyright.
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