| Article ID | Journal | Published Year | Pages | File Type |
|---|---|---|---|---|
| 1942685 | Biochimica et Biophysica Acta (BBA) - Bioenergetics | 2011 | 7 Pages |
The photodamage process of photosystem II by strong illumination was investigated by examining the herbicide effects on the photoinactivation of redox cofactors. O2-evolving photosystem II membranes from spinach in the absence of herbicide and in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) and bromoxynil were subjected to strong white-light illumination at 298 K, and the illumination-time dependence of the activities of QA, the Mn cluster, and P680 were monitored using light-induced Fourier transform infrared (FTIR) difference spectroscopy. The decrease in the QA activity was suppressed and accelerated by DCMU and bromoxynil, respectively, in comparison with the sample without herbicide. The intensity change in the S2/S1 FTIR signal of the Mn cluster exhibited a time course virtually identical to that in the QA signal in all the three samples, suggesting that the loss of the S1 → S2 transition was ascribed to the QA inactivation and hence the Mn cluster was inactivated not faster than QA. The decrease in the P680 signal was always slower than that of QA keeping the tendency of the herbicide effect. Degradation of the D1 protein occurred after the P680 inactivation. These observations are consistent with the acceptor-side mechanism, in which double reduction of QA triggers the formation of 1O2* to promote further damage to other cofactors and the D1 protein, rather than the recently proposed mechanism that inactivation of the Mn cluster initiates the photodamage. Thus, the results of the present study support the view that the acceptor-side mechanism dominantly occurs in the photodamage to PSII by strong white-light illumination.
Research highlights► The photodamage process of PSII was investigated using FTIR spectroscopy. ► The damage to QA was suppressed by DCMU and accelerated by bromoxynil. ► The Mn cluster was inactivated not faster than QA. ► The decrease in the P680 signal was always slower than QA. ► The results support the acceptor-side mechanism in the PSII photodamage.
