Inhibition of Photosystem II by Ioxynil in Wild Type and Resistant Mutant of Synechocystis 6714

Abstract

Abstract A Synechocystis 6714 mutant resistant to the phenol-type herbicide ioxynil was isolated and characterized. Ioxynil was shown to inhibit both the donor and the acceptor sides of photosystem II, but at different concentrations. The mutation found in the psbA gene (encoding the D, protein) at codon 266 (asparagine to threonine) [G. Ajlani, I. Meyer, C. Vernotte, and C. Astier, FEBS Lett. 246, 207-210 (1989)] gives a ten-fold resistance of the acceptor side to ioxynil without any modification of the sensitivity of the donor side. Electron transfer between the primary and the secondary acceptor of photosystem II was identical in the mutant and the wild type. The mutant remains sensitive to atrazine and is even more sensitive to DCMU than the wild type.