Higher concentration of QB-nonreducing photosystem II centers in triazine-resistant Chenopodium album plants as revealed by analysis of chlorophyll fluorescence kinetics

Plants resistant to triazine-type herbicides are known to be altered in their photosystem II reaction center. Serine at site 264 in D1 protein is replaced by glycine. The measurements of chlorophyll a fluorescence excitations with a variable number of saturating flashes in Chenopodium album plants show characteristic differences between the resistant and the wild-type plants. These differences appear in response to the first flash as well as in the rise pattern of subsequent flashes of a 12.5 Hz flash train. The differences indicate a higher concentration of QB-nonreducing reaction centers in the resistant biotype, and confirm earlier results on a slower rate of electron transport between the primary and secondary electron acceptors.