EPR measurements on the effects of bicarbonate and triazine resistance on the acceptor side of Photosystem II

Abstract

CO* depletion leads to an approximately IO-fold increase in the light-induced EPR signal at g = 1.82, attributed to the Qi. Fe*+ complex, in Photosystem II-enriched thylakoid membrane fragments. Upon reconstitution with HCO;the signal decreases to the size in control samples. The split pheophytin-signal is broader in control or reconstituted than in CO,-depleted samples. It is concluded that HCO; strongly influences the localization and conformation of the Q;. Fez+ complex. The QA * Fe*+ and split pheophytin-EPR signals from triazine-resistant Brassica napus were virtually identical to those from triazine-susceptible samples, indicating that the change in the 32-kDa azidoatrazine-binding protein does not lead to a conformational change of the Qi. Fe*+ complex. Semiquinone-iron complexPhotosystem II Bicarbonate effect Triazine resistance Photosynthesis Herbicide

Evidence for two tightly bound iron‐quinones in the electron acceptor complex of photosystem II

“…Illumination of the titration samples at 200 K results in the reduction of the pheophytin and appearance of the split radical signal due to interaction between the pheophytin and iron semiquinone. As reported by Vermaas and Rutherford [13] the signal is narrower than in untreated preparations, although we have found considerable variation between preparations. This may reflect varying success in depleting COZ.…”

“…Vermaas and Rutherford [13] have recently shown that the EPR signal of the iron-quinone complex, which is normally very small, can be readily observed in higher plant preparations which have been formate-washed to remove CO2. We have now used pea PS II preparations treated in this way to redetermine the redox properties of the iron-quinone acceptors of PS II.…”

The nature of the Fe(III) EPR signal from the acceptor‐side iron in photosystem II

“…The involvement of tyrosines is interesting because model studies have shown that coordinating phenolates lower the reduction potential [25]. Bicarbonate strongly influences both the Fe2+QT~ EPR signal [26] and the pH obtained after successive light flashes [27] and has been suggested as an iron ligand [28]. An interesting comparison can be made with the transferrins in which bicarbonate (or carbonate) is very likely directly coordinated [29] to the strongly bound ferric iron.…”

The psbC start codon in Synechocystis sp. PCC 6803

“…PCC 6803 lacking the psbD-I/C operon as well as psbD-II, in order to introduce the mutated psbD-I/C operon into Synechocystis and obtain psbC expression solely from the mutated gene has also been described in [18]. Herbicide binding experiments, Western blotting, and immunodetection (using BCIP (5bromo-4-chloro-3-indolyl phosphate, p-toluidine salt)/NBT @-nitro blue tetrazolium chloride) staining to detect alkaline phosphatase linked to the secondary antibody) were done according to previously published procedures [19,20].…”