Low resistance against novel 2-benzylamino-1,3,5-triazine herbicides in atrazine-resistant Chenopodium album plants

The effects of nine novel 2-benzylamino-1,3,5-triazines on photosynthetic r eactions were measured in thylakoids isolated from wild-type and atrazine-r esistant plants of Chenopodium album. The resistant plants have a mutation of serine for glycine at position 264 of the D1 protein. The measurement of oxygen evolution and chlorophyll a fluorescence induction indicated a 2-4- fold stronger inhibition by the 6-trifluoromethyl analogues of Photosystem II-dependent electron flow than atrazine. Analogues having a 6-methyl-, 6-m onofluoromethyl or 6-difluoromethyl substitution were weak inhibitors, indi cating that the 6-trifluoro group is very important for strong inhibition. All the nine novel 2-benzylamino-1,3,5-triazines were almost as active in w ild-type as in atrazine-resistant thylakoids, indicating that the benzylami no substitution may be important for the lack of resistance in the atrazine -resistant plants.