Abstract
When the excitation energy balance between photosystem I (PSI) and photosystem II (PSII) is disturbed due to the changing light environment, light-harvesting complex II (LHCII) is thought to adjust the energy balance by a mechanism called state transition. Recently, we successfully isolated the protein supercomplexes, so-called PSII-LHCII supercomplex and PSI-LHCI/II supercomplex, from Chlamydomonas reinhardtii and revealed the structural changes and reversible phosphorylated proteins during state transitions. However, direct evidence for such dynamic changes of photosystem protein complexes are still remained to be proved. Therefore, to visualize state transitions in vivo, we applied fluorescence lifetime imaging microscopy technique. First, we established a method to induce state transitions in living C. reinhardtii cells under a microscope and then optimized the imaging parameters for live imaging. By comparing the lifetime data between wild type and several mutant cells, we visualized the spatio-temporal dynamics of chlorophyll fluorescence lifetime reflecting state transitions.
