Heat- and light-induced detachment of the light harvesting complex from isolated photosystem I supercomplexes

Our absorption and circular dichroism spectroscopy and immuno blotting data show that the dissociation of LHCI from PSI-LHCI supercomplex starts above 50 °C. Also, the low temperature fluorescence emission spectra depicts decrease of maximum fluorescence emission at 730 nm and an increase of the intensity at 685 nm, and about 10 nm blue-shifts, from 730 to 720 nm and from 685 to 676 nm, respectively, indicating the heat (50 °C) induced detachment of LHCI from PSI core complexes. The reaction centre proteins are highly stable even at high temperatures. Lhca2 is more heat stable than the other light harvesting protein complexes of PSI, whereas Lhca4 and Lhca3 are rather labile. Combined heat and light treatments significantly enhances the disorganization of PSI-LHCI supercomplexes, indicating a thermo-optic mechanism, which might have significant role under combined heat and light stress conditions.