Abstract:Strong light (800μmol photons/m2 per s)-induced bleaching of the pigment in the isolated photosystem II reaction center (PSII RC) under aerobic conditions (in the absence of electron donors or acceptors) was studied using high-pressure liquid chromatography (HPLC), absorption spectra, 77K fluorescence spectra and resonance Raman spectra. Changes in pigment composition of the PSII RC as determined by HPLC after light treatment were as follows: with increasing illumination time chlorophyll (Chl) a and β-carotene (β-car) content decreased. However, decreases in pheophytin (Pheo) could not be observed because of the mixture of the Pheo formed by degraded chlorophyll possibly. On the basis of absorption spectra, it was determined that, with a short time of illumination, the initial bleaching occurred maximally at 680 nm but that with increasing illumination time there was a blue shift to 678 nm. It was suggested that P680 was destroyed initially, followed by the accessory chlorophyll. The activity of P680 was almost lost after 10 min light treatment. Moreover, the bleaching of Pheo and β-car was observed at the beginning of illumination. After illumination, the fluorescence emission intensity changed and the fluorescence maximum blue shifted, showing that energy transfer was disturbed. Resonance Raman spectra of the PSII RC excited at 488.0 and 514.5 nm showed four main bands, peaking at 1 527 cm–1 (υ1), 1 159 cm–1 (υ2), 1 006 cm–1 (υ3), 966 cm–1 (υ4) for 488.0 nm excitation and 1 525 cm–1 (υ1), 1 159 cm–1 (υ2), 1 007 cm–1 (υ3), 968 cm–1 (υ4) for 514.5 nm excitation. It was confirmed that two spectroscopically different β-car molecules exist in the PSII RC. After light treatment for 20 min, band positions and bandwidths were unchanged. This indicates that carotenoid configuration is not the parameter that regulates photoprotection in the PSII RC.(Author for correspondence.Tel (Fax): +86 (0)10 8259 4106; E-mail: kuangty@ibcas.ac.cn)