ABSTRACT
Atrazine-resistant weeds are well known, and the resistance is primarily caused by a point mutation in the psbA chloroplast gene encoding the photosystem II D1 protein. Heteroplasmy, the presence of different types of chloroplasts in an individual plant, is also very common. Thus, atrazine-resistant weeds may also partly possess the atrazine-binding sequence and vice versa. The region of the psbA gene containing the mutation was sequenced from atrazine-resistant and atrazine-sensitive Chenopodium album and Senecio vulgaris plants. In atrazine-sensitive C. album plants, the expected AGT triplet was found. The atrazine-resistant plants contained the expected base substitution (AGT to GGT); however, in addition the AGT triplet was found. The atrazine-resistant S. vulgaris plants contained the expected GGT sequence, whereas the atrazine-sensitive plants contained both the AGT and GGT sequences. This clearly indicates that in addition to Gly264 also Ser264 is present in atrazine-resistant plants, and vice versa in atrazine-sensitive plants, indicating heteroplasmy in these weeds.
