Biophysical Society Thematic Meeting | Tutzing 2026

Single-Molecule FRET: The Next 30 Years

Poster Abstracts

11-POS Board 5 NON-LOCAL MICRON-SCALE FLUORESCENCE LIFETIME EFFECTS DUE TO LOCAL PHOTOBLEACHING OF PHOTOSYNTHETIC PIGMENTS IN RED ALGAE Shira Brand 1,2 ; Debjit Roy 1 ; Eitan Lerner 1 ; Nir Keren 2 ; 1 The Alexander Silberman Institute of Life Science at The Hebrew University of Jerusalem, Department of Biological Chemistry, Jerusalem, Israel 2 The Alexander Silberman Institute of Life Science at The Hebrew University of Jerusalem, Plant and Environmental Sciences, Jerusalem, Israel Photosynthetic organisms are nature's light harvesting (LH) and energy conversion systems. Sunlight is absorbed by LH complexes (LHCs) containing thousands of pigments, and the excitation energy transfers (EET) to special chlorophyll-containing reaction centers (RCs), where it is harnessed to drive photochemical reactions. Traditionally, EET in photosynthesis has been mostly viewed as transfer from LHCs, vertically towards the RCs. However, the tightly packed organization of LHCs atop thylakoid membranes may allow EET laterally between pigments of neighboring LHCs. Notably, although LHC arrays can extend to long distances, long-range spatial analysis of EET in photosynthetic cells has not been studied in vivo. Moreover, while it was indicated in vitro, possible mechanisms of spatial biological reactions and EET across the thylakoid membrane are largely unexplored. Recently, we studied the EET in phycobilisomes (PBSs), LHCs found in red algae, in vivo. Using fluorescence lifetime imaging microscopy (FLIM) to measure autofluorescence of the photosynthetic pigments, we study both the vertical EET from PBSs to RCs, and spatial effects of different conditions on EET. Using high intensity laser, we locally photobleach different PBS pigments in both living and fixed red algae cells and observe differences in fluorescence lifetimes away from the photobleached region. In live cells, 64 ms of local photobleaching results in a non-local gradient of fluorescence lifetime changes across PBSs that spans microns away from the photobleached region. Importantly, this non-local effect was not observed in fixed cells, indicating an underlying biological mechanism that could support changes in lateral EET. Our results open the possibility that PBS-containing photosynthetic cells are capable of dynamically maintaining excitation energy over long distances in the chloroplast for efficient energy distribution under low and intermediate light intensities.

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