Imaging state-transitions visualized energy-dissipative light-harvesting complexes in photosynthesis

Masakazu Iwai1, Makio Yokono1, Noriko Inada2, and Jun Minagawa1

1) Inst. of Low Temp. Sci., Hokkaido Univ., Sapporo 060-0819, Japan 2) Grad. Sch. of Biol. Sci., Nara Inst. of Sci. and Tech., Ikoma 630-0192, Japan.

Plants and green algae maintain efficient photosynthesis under changing light environments by adjusting their light-harvesting capacity (1,2). It has been suggested that energy redistribution is brought about by shuttling the light-harvesting antenna complex II (LHCII) between photosystem II (PSII) and photosystem I (PSI) (state transitions), but such molecular remodeling has never been demonstrated in vivo. In this study, using chlorophyll Fluorescence Lifetime Imaging Microscopy (FLIM), we visualized phospho-LHCII dissociation from PSII in live cells of the green alga Chlamydomonas reinhardtii. Induction of energy redistribution upon illumination of the cells by blue light led to an increase in, and spreading of, a 250-ps lifetime chlorophyll fluorescence component, which was not observed in the stt7 mutant incapable of state transitions. The 250-ps component was also the dominant component in a mutant containing the light-harvesting antenna complexes but no photosystems. The appearance of the 250-ps component was accompanied by activation of LHCII phosphorylation, supporting the visualization of phospho-LHCII dissociation. The dissociated phospho-LHCII spread through the cell during State 2 transitions and forms several large aggregated areas. The extremely short lifetime of fluorescence (250-ps) from aggregation of the dissociated LHCII suggested an energy dissipation mechanism in photosynthesis (3). 1) Iwai, Takahashi, and Minagawa (2008) Plant Cell 20:2177-2189 2) Tokutsu, Iwai, and Minagawa (2009) J. Biol. Chem. 284:7777-7782 3) Iwai, Yokono, Inada, and Minagawa (2010) Proc. Natl Acad. Sci. U. S. A. 107:2337-2342.

e-mail address of presenting author: minagawa@lowtem.hokudai.ac.jp