The photodamage process of pigments and proteins of PSI complexes fromSpinacia Oleracea L.

Purified PSI complexes fromSpinacia Oleracea L. were exposed to the strong light (PFD=2300 μmol m⁻²s⁻¹) for various period. Along with the illumination the photo-damage process of pigments and proteins of PSI complexes was investigated using absorption, fluorescence, circular dichroism (CD) spectroscopy and SDS-PAGE. It was found from the optical absorption spectra that the maximal absorbance of PSI complexes decreased and maximal peaks blue-shifted during the illumination, and the forth derivative spectra demonstrated that the absorbance decreasing at red region mainly resulted from the aborbance decreasing of the long wavelength Chla, implying that the long-wavelength Chla was readily to be bleached. The CD signals contributed by LHCI decreased more rapidly than other CD signals contributed by Chla and Carotenoid, indicating that the LHCI was more sensitive to light than core complexes. It was observed by SDS-PAGE that some small polypeptides of PSI complexes were damaged earlier than reaction center proteins PsaA and PsaB. Lhca3, Lhca2 and PsaD were the early degraded proteins during illumination. In addition, it is also observed that the insoluble-cohesive-denatured proteins appeared after prolonged illumination.