Herbicide binding in various mutants of the photosystem II D1 protein of Chlamydomonas reinhardtii

Various mutants of the D1 protein of photosystem II were generated by transforming a Chlamydomonas reinhardtii strain specifically engineered to lack a 0.4 kb fragment in the psbA gene. This mutant is unable to grow photosynthetically. The following mutants were obtained: Asp170Glu, Gly178Ser, Leu218Ser or Thr, Arg238Val, Thr245Ala or Ser and Ser264Lys or Ile. In these mutants, the following herbicides were assayed for their inhibitory activity: triazines, triazinones, ureas, biscarbamates, and phenols. The results indicate that besides Leu218 and Ser264 also Gly178 influences herbicide binding, probably via long-range effects. The herbicide resistances of Ser264 mutants have been recognized since a long time. However, substitution of Ser264 specifically by Lys exhibit extreme resistance to triazines and triazinones, but no or slight resistance to ureas.