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

Abstract

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: Asp 170Glu, Gly 178Ser, Leu 218Ser or Thr, Arg 238Val, Thr 245Ala or Ser and Ser 264Lys 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 Leu 218 and Ser 264 also Gly 178 influences herbicide binding, probably via long-range effects. The herbicide resistances of Ser 264 mutants have been recognized since a long time. However, substitution of Ser 264 specifically by Lys exhibit extreme resistance to triazines and triazinones, but no or slight resistance to ureas.