Herbicide resistance and supersensitivity in photosystem II

Resistance to triazine herbicides in higher plants was first observed in 19 70. A mutation in the photosystem II reaction center D1 protein at position Ser(264) --> Gly is responsible for this resistance. So far, 37 single mut ants, 16 double mutants, 5 triple mutants and 5 deletion/insertion mutants in the D1 protein have been obtained by randomly induced and site-directed mutagenesis in cyanobacteria and algae. The influence of these mutations on the binding affinities of different classes of herbicides will be discusse d. Because a sufficiently high resolution X-ray structure of photosystem II does not yet exist, the reaction center of purple photosynthetic bacteria, which is homologeous to photosystem II, served as a model. In the bacteria l reaction center a total of 25 single and 3 double herbicide-resistant mut ants have been generated.